Spotlight on Analytical Applications Complete e-Zine - Volume 3

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VOLUME 3

INTRODUCTION
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CONTENTS

Energy
• Determination of Methanol in Crude Oils According to ASTM D7059-04 Using the
Clarus 680 GC with S-Swafer Micro-Channel Flow Technology
• Determination of Low-Level Oxygenated Compounds in Gasoline Using the Clarus 680 GC
with S-Swafer Micro-Channel Flow Technology
• Fatty Acid Methyl Ester Contamination of Aviation Fuel by GC/MS
• Curing Determination of EVA for Solar Panel Application by DSC

Environmental
• Determination of Mercury in Wastewater by Inductively Coupled Plasma-Mass Spectrometry
• Qualitative Analysis of Evolved Gases in Thermogravimetry by Gas Chromatography/Mass
Spectrometry

Food & Beverage
• The Determination of Metals in Dietary Supplements
• Solid Phase Extraction and GC/MS Analysis of Melamine Adulteration in Dairy Products

Pharmaceuticals & Nutraceuticals
• Fast Analysis of Fat-Soluble Vitamins Using Flexar FX-10 UHPLC and Chromera CDS
• Assuring Safety of Traditional Chinese Herbal Medicines by Monitoring Inorganic Impurities
using ICP-MS
• Polymorphism in Acetaminophen Studied by Simultaneous DSC and Raman Spectroscopy
• Pressure-Balanced Headspace for the Determination of Class I, II and III Residual Solvents in
Pharmaceuticals by USP Chapter <467> Methodology

PerkinElmer

a p p l i c at i o n n o t e

Gas Chromatography

Author
Andrew Tipler
PerkinElmer, Inc.
Shelton, CT 06484 USA

Determination of Introduction
The gas chromatographic (GC) analysis of crude oil
Methanol in Crude Oils is a challenging undertaking. Samples are viscous,
making them difficult to handle, and they contain
According to ASTM hundreds of different compounds with carbon
numbers up to or even above C120, making a complete
D7059-04 Using the chromatographic separation effectively impossible.

Clarus 680 GC with ASTM® D7059-04 is an established method that has
been well validated for the determination of methanol
S-Swafer Micro- in crude oils. The method lists five variants of the instru-
mentation that have demonstrated compliance with
Channel Flow this method. The method also allows for alternative

Technology configurations that will meet the required performance
criteria.

In this application note, a method based on a
PerkinElmer® Clarus® 680 GC with an S-Swafer™
micro-channel flow splitting device is described;
the data presented here will demonstrate that this
method complies with the requirements of ASTM®
D7059-04.

Experimental will enter the first column, leaving the heavier crude-oil
The Clarus 680 GC used in this application note is described compounds in the liner. The two alcohols enter the first
in Figure 1 with a diagram, and Figure 2 with a photograph non-polar column and elute early in the chromatography.
of the S-Swafer micro-channel flow splitting device used to A chromatogram of a standard mixture is shown in Figure 3.
perform this analysis. This two-column backflushing configura-
tion (designated as S6 in the Swafer documentation) enables
the first column to be backflushed while the analytes are still
being chromatographed on the second column. A restrictor
tube is also connected to one of the S-Swafer outlets to enable
the carrier-gas flow rate to be increased and to allow the
chromatography to be monitored on the first column by
connecting the restrictor outlet to the FID. Nitrogen is used
as the carrier gas throughout this application – it is well
suited for use with 0.530 mm i.d. columns. Nitrogen, when
compared to helium, is less expensive, more available, and
not in limited supply. The use of nitrogen is consistent with
PerkinElmer initiatives to reduce the use of the declining
global stocks of helium.
Figure 3. Chromatogram of standard mixture on first column with the
The crude-oil sample is diluted 50:50 with clean toluene restrictor tube connected to the FID.
solvent containing 1-propanol internal standard to produce
a final concentration of 500 ppm. 1.0 µL of the diluted
sample is injected into the programmable split/splitless (PSS) From Figure 3, it can be seen that the last peak of interest,
injector which has the liner temperature set to 125 °C. the 1-propanol internal standard, elutes at about 3.2 minutes.
At this temperature, only the volatile fraction of the sample Anything that elutes later than this time is of no analytical
interest and backflushing should commence soon after
elution of the 1-propanol peak – in this case 3.3 minutes.

The backflushing process occurs when the pressure at the
column inlet is less than that at the column outlet. This
can be achieved by reducing the first-column inlet pressure
at the PSS injector, increasing the (midpoint) pressure at
the S-Swafer or doing both. In this analysis, we want to
continue chromatography on the second column while we
backflush the first column so the only option is to reduce
the pressure at the injector. To enable a large backpressure
to be used, the second column has an inline restrictor
Figure 1. The S-Swafer system used to determine methanol in crude oil. connected between it and the S-Swafer. This enables the
midpoint pressure to be increased, yet still allows reasonable
flow rates to be applied to the second column. The reduction
in the inlet pressure is affected through the use of a simple
GC timed event.

When the backflushing commences after a crude-oil sample
has been injected, the heavier fraction of the sample will still
reside within the injector liner which has been held at 125 °C.
At this point, the PSS liner is temperature programmed to
a high temperature to vaporize this less-volatile material.
Because the column is being backflushed, none of this vapor
will enter the column, but will be flushed out of the system
through the split vent. In this way, removal of the heavy
compounds is very efficient and doesn’t expose the columns
to this material, thus prolonging the column life.
Figure 2. Photograph of installed system showing the S-Swafer connections.

2

Figure 4 shows a chromatogram of a standard solution on the backflushed until the oven reaches its initial programmed
first column with backflushing applied at 3.3 minutes. The temperature. The initial split-flow rate is set to 100 mL/min
chromatography is now very clean beyond the 1-propanol peak. to ensure that the pre-run pressure change equilibrates
quickly. The split flow is reset to 10 mL/min by a pre-run
event at -0.50 minutes, which occurs once the pressure has
stabilized. These split-flow changes serve only to save time.

Table 1. Analytical Conditions for the Determination of
Methanol in Crude Oil.
Gas Chromatograph PerkinElmer Clarus 680 GC
Oven Temperature 125 °C for 1 minute, then 25 °C/min to
250 °C
Injector Programmable Split/Splitless (PSS)
Injector Temperature 125 °C for 3.3 minutes, then 200 °C/min
to 400 °C and hold until the end of the run
Carrier Gas Nitrogen
Figure 4. Chromatogram of standard mixture on first column with backflushing Initial Injector Pressure
at 3.3 minutes with the restrictor tube connected to the FID. Setpoint 2 psig (see text)
Initial Injector Split
Figure 5 shows chromatograms from the CP-Lowox column ® Flow Rate 100 mL/min (see text)
of three calibration mixtures that cover the calibration range Detector Flame Ionization (FID)
of this method. Again, the chromatography looks very clean. Detector Temperature 325 °C
Detector Combustion
Gases Air: 450 mL/min, Hydrogen: 45 mL/min
Detector Range x1
Detector Attenuation x4
Backflush System S-Swafer configured in S6 mode
Precolumn 30 m x 0.530 mm x 5 µm PerkinElmer
Elite™ 1 with 25 cm x 0.250 mm
deactivated fused silica restrictor
connected between S-Swafer and column
Analytical Column 10 m x 0.530 mm x 10 µm Varian®
CP-Lowox® with in-line 25 cm x 0.100 µm
connected between S-Swafer and column
Restrictor Tubing
Figure 5. Chromatography of three methanol standard solutions containing between S-Swafer
~500 ppm w/w 1-propanol internal standard. and Detector 30 cm x 0.100 µm deactivated fused silica
(Midpoint) Pressure
The full method for this analysis is given in Table 1. The use at S-Swafer 20 psig
of timed events in this method needs explanation. The GC Timed Events (see text) PSS pressure set to 24 psig at -1.00 min
oven needs to be programmed up to 250 °C in order to PSS split flow set to 10 mL/min at -0.50 min
elute the analytes from the CP-Lowox® column. At this PSS pressure set to 2 psig at 3.30 min
temperature, there is some slight stationary-phase bleed from
PSS split flow set to 100 mL/min at 3.31 min
the thick-film methyl silicone precolumn. The precolumn
remains in the backflush mode during cooling to prevent any Sample Preparation 5 g of crude-oil sample mixed with 5 g of
toluene containing 1-propanol internal
of the bleed from the precolumn at the onset of cooling from
standard to deliver a final concentration
entering the CP-Lowox® column. The initial injector pressure of 500 ppm w/w
of 2 psig and the pre-run timed event to set the pressure
Sample Injection Normal injection of 1.0 µL of prepared
to 24 psig at -1.00 minutes ensures that the pre-column is
sample using an autosampler

3

Discussion What should also be noted is that the total chromatography
The calibration plot obtained for the mixtures of methanol time is just six minutes. For most of this time, the injector
and 1-propanol in toluene are shown in Figure 6. This plot liner is being heated at a high temperature and the precolumn
demonstrates good linearity which is in compliance with is being backflushed at a very high flow rate, while the oven
ASTM® D7059. is being temperature programmed. This means that, at the
end of the run, all of the less-volatile sample compounds
have been flushed from the system. All that is then necessary is
to cool the oven, reset the inlet pressure and inject the next
sample. The Clarus 680 GC used for this analysis has rapid
oven cooling and starts to load the autosampler with sample
prior to the GC coming ready and so sample throughput
exceeds six samples per hour.

Table 2 shows the quantitative precision obtained from ten
replicate injections of a high-level and a low-level check
standard. Considering the complexity of the sample matrix,
these results demonstrate the efficacy of the Swafer tech-
nology for this type of application. These results greatly
exceed the requirements of ASTM® D7059.
Figure 6. Calibration plot showing response ratio vs. amount ratio for
methanol:1-propanol internal standard.
Table 2. Quantitative precision of low-level and high-level
check standards prepared using a sample of light crude oil.
Figure 7 shows a chromatogram of a low-level check standard
Run Results for Results for
prepared from a sample of light crude oil. The hydrocarbons Check Standard A Check Standard B
that elute with the alcohols into the second column before 28.2 ppm w/w 1096 ppm w/w
backflushing is initiated are lightly retained on the CP-Lowox® 1 33.2 1063
column and so quickly elute in the chromatography. The
2 32.2 1063
alcohols are much more strongly retained and require an
extended temperature program to elute and are well separated 3 32.7 1065
from the light hydrocarbons in the crude oil. Note the clean 4 32.6 1059
baseline around the alcohols, which facilitates precise quan- 5 32.9 1059
tification.
6 35.6 1062
7 33.4 1065
8 33.9 1068
9 33.6 1061
10 33.8 1064
Relative Std Dev % 2.88 0.26

The analytical system was validated using a set of 20 ‘round-
robin’ samples prepared by Spectrum Analytical Standards,
Sugarland, Texas. These are shown in Figure 8. These sam-
ples were prepared five years ago to validate the published
ASTM® D7059-04 method. It is believed that these samples
are stable and would provide a good basis for validating this
Figure 7. Chromatogram of 25 ppm w/w check standard prepared in a sample Swafer system for compliance with the ASTM® method.
of light crude oil.

4

One of the concerns regarding the GC analysis of crude oil
is that non-volatile sample residue will accumulate in the
system giving rise to adsorption, thermolysis or carryover
effects. This method uses a combination of low injection
temperature and column backflushing to keep heavier
sample compounds out of the columns. Figure 9 shows the
chromatography of crude-oil samples soon after a new liner
and septum have been installed compared against the chro-
matography after over 150 crude-oil injections have been
made into the same liner and septum. Clearly, sample residue
will accumulate as the number of injections increases (particu-
larly with heavy crude oils) and eventually the liner and the
septum will need to be changed. Figure 9 shows that after
150 injections, this method continues to perform.

Figure 8. ASTM® D7059 round-robin validation samples.

Table 3 summarizes the results from the round-robin sample
set. All are within the ASTM® D7059 limits except the result
for Sample 19, which is just outside the accepted range.
Given the age of these samples, these results are considered
acceptable, and the method does tolerate one result deviation
out of twenty.

Table 3. Results obtained for ASTM® D7059 round-robin
validation samples.
Sample Experimental Expected
1 2.0 2.7
Figure 9. Chromatograms of the same crude-oil sample spiked with 400 ppm
2 4.3 5.8 w/w methanol produced using a single injector liner showing no significant
degradation in chromatography after over 150 runs.
3 7.4 11.7
4 11.4 14.9
5 7.8 12.9
6 29.8 35.1
7 23.8 27.6
8 31.2 35.7
9 58.1 66.3
10 60.4 67.0
11 69.5 74.5
12 105.5 113.4
13 113.4 133.2
14 265.3 285.2
15 393.8 404.7
16 542.8 592.9
17 596.3 524.2
18 873.2 912.2
19 739.8 826.5
20 709.9 734.7

5

Conclusion
This method, based on the S-Swafer technology, fully
complies with the requirements of ASTM® D7059-04 and
offers the user a number of unique benefits:

• The method presented here will provide very high throughput
and fast delivery of results; with a complete analysis cycle
time less than ten minutes per sample (more than six
samples/hour throughput)

• Reduced instrument maintenance as a result of temperature-
programmed injection which prevents heavy sample
compounds from entering and degrading columns

• Additional protection of the analytical columns and reduction
of run time with the use of backflushing

• Single-detector configuration simplifies and reduces the cost
of the system

• Splitting restrictor enables precolumn chromatography to be
monitored, facilitating the setup of backflush timing

• Nitrogen carrier gas reduces costs associated with carrier
gas and serves to help preserve helium stocks

• Quantitative performance exceeding the method specification
delivers results that will meet laboratory quality-control
specifications.

PerkinElmer, Inc.
940 Winter Street
Waltham, MA 02451 USA
P: (800) 762-4000 or
(+1) 203-925-4602
www.perkinelmer.com

For a complete listing of our global offices, visit www.perkinelmer.com/ContactUs

Copyright ©2010, PerkinElmer, Inc. All rights reserved. PerkinElmer® is a registered trademark of PerkinElmer, Inc. All other trademarks are the property of their respective owners.

009027A_01


Gas Chromatography

Author
Andrew Tipler
PerkinElmer, Inc.

Determination of Introduction
The existing ASTM® D4815 method is designed to monitor
Low-Level Oxygenated oxygenated compounds in gasoline at percentage concen-
trations. The method described in this application note is
Compounds in Gasoline intended to enable these analytes to be monitored down to

Using the Clarus 680 GC low-ppm concentrations.

There is an increased need to monitor the level of oxygen-
with S-Swafer Micro- ates in reformulated gasoline because of the increased risk
of contamination from more abundantly available biofuels.
Channel Flow Technology Gasoline contamination with oxygenated compounds can
lead to more toxic carbonyl emissions into the atmosphere
from engines running the fuel.

Contamination of feedstocks with oxygenated compounds
can cause degradation of expensive catalysts and impact the
refining process.

The analytes targeted in this method are those specified in
ASTM® D4815 and are given in Table 1.

Table 1. Targeted Oxygenated Compounds.
Methanol
Ethanol
Isopropanol
tert-Butanol
n-Propanol
Methyl tert-butyl ether (MTBE)
sec-Butanol Figure 1. Diagram of the S-Swafer micro-channel flow technology used to
determine trace-level oxygenated compounds in gasoline.
Diisopropyl ether (DIPE)
Isobutanol
Ethyl tert-butyl ether (ETBE) to one of the S-Swafer outlets to enable the carrier-gas flow
tert-Pentanol rate to be increased and to allow the chromatography to be
1,2-Dimethoxyethane monitored on the first column by connecting the restrictor
outlet to the FID. Note the use of nitrogen as the carrier gas.
n-Butanol
This carrier gas is well suited to 0.530 mm i.d. columns and
tert-Amyl methyl ether (TAME) is consistent with initiatives to reduce the use of the declining
global stocks of helium.

Experimental The experimental details for this analysis are given in Table 2.
Figure 1 shows a diagram of the S-Swafer™ micro-channel The sample of gasoline is injected and chromatographed on
flow splitting device used to perform this analysis. This two- the non-polar precolumn. The polar oxygenated compounds
column backflushing configuration (designated as S6 in the are quick to elute into the second CP-Lowox® column and
Swafer documentation) enables the first column to be back- will precede the bulk of the gasoline hydrocarbons. Once
flushed while the analytes are still being chromatographed the oxygenated compounds are in the second column, the
on the second column. A restrictor tube is also connected first column is backflushed to remove the hydrocarbons

Table 2. Analytical Conditions for the Determination of Trace-Level Oxygenated Compounds in Gasoline.
Gas Chromatograph PerkinElmer® Clarus® 680 GC Analytical Column 10 m x 0.530 mm x 10 µm Varian® CP-Lowox®
Oven Temperature 80 °C for 1 minute then 5 °C/min with in-line 25 cm x 0.100 µm deactivated
to 125 °C then 10 °C/min to 230 °C fused silica restrictor connected between
S-Swafer and column
Injector Heated split/splitless
Restrictor Tubing 30 cm x 0.100 µm deactivated fused silica
Injector Temperature 250 °C between S-Swafer
Carrier Gas Nitrogen and Detector
Initial Injector Pressure 2.0 psig (see text) (Midpoint) Pressure 35 psig
at S-Swafer
Injector Split-Flow Rate 15 mL/min
Timed Events Carrier gas pressure set to 45 psig at -1.00 min
Detector Flame Ionization (FID)
(see text) Carrier gas pressure set to 2 psig at 1.52 min
Detector Temperature 325 °C
Sample Preparation a) AccuStandard® 4815-RT-PAK diluted
Detector Combustion Gases Air: 450 mL/min, ~1:1500 in washed gasoline to give 27.4
Hydrogen: 45 mL/min to 50 ppm w/w
Detector Range x1 b) AccuStandard® 4815-RT-PAK diluted
Detector Attenuation x4 ~1:7500 in washed gasoline to give 5.5
to 10 ppm w/w
Backflush System S-Swafer configured in S6 mode
Sample Injection Fast injection of 1.0 µL of prepared sample
Precolumn 15 m x 0.530 mm x 1 µm PerkinElmer using an autosampler
Elite™-1 with 25 cm x 0.250 mm
connected between S-Swafer and
column

2

from the GC system. While the backflushing is in progress,
the oxygenated compounds are chromatographed on the
highly polar CP-Lowox® column which easily separates them
from any hydrocarbons that also enter the second column.

Precolumn backflushing is initiated by a timed event at
1.52 minutes that reduces the pressure inside the injector
to 2.0 psig so that carrier gas flows backwards. The inlet
pressure is set to 2.0 psig to maintain the backflushing of
the precolumn during oven cooling. A pre-run timed event
sets the inlet pressure to 45 psig so that forward flow is
restored prior to injection of the sample.

Figure 2 shows a chromatogram of gasoline on the pre-
column with no backflushing. The oxygenated compounds
would elute within the first one or two minutes of this
Figure 3. Precolumn chromatogram of a mixture of oxygenated compounds
chromatogram and would be totally obscured by the early-
at 4% to 7.3% w/w concentration indicating the proposed backflush point.
eluting hydrocarbons in the gasoline. The later-eluting peaks Injector split flow increased to 100 mL/min.
are not needed in this analysis so they will be the target of
the backflushing step.
Figure 4 shows the same sample run under the same conditions
as those for Figure 3 but with the detector connected to
the end of the analytical column. Good peak shapes and
separations of the oxygenated compounds are seen within a
20.5-minute run time. On this column, some of the alcohol
isomers are not separated. The total cycle time was about
25 minutes, which included oven cooldown and equilibration
and autosampler loading.

Figure 2. Chromatogram of 87-octane gasoline on the precolumn.

Figure 3 shows a chromatogram of a mixture of the oxygenated
compounds (no solvent) on the precolumn and it can be
seen that all the peaks of interest have eluted from this
column in just less than 1.50 minutes. From this trace, the
backflush point was chosen to be 1.52 minutes.

Figure 4. Analytical column chromatogram of a mixture of oxygenated
compounds at 4% to 7.3% w/w concentration with precolumn backflushing
at 1.52 minutes. Injector split flow increased to 100 mL/min.

3

To test the system on samples of gasoline containing known The standard mixture of oxygenated compounds was diluted
levels of oxygenated compounds, a quantity of gasoline was with the washed gasoline to produce low-level mixtures.
‘washed’ with water. 5 mL of 87-octane gasoline obtained These were chromatographed using the newly developed
from a local filling station were shaken with 10 mL of deionized method and the chromatogram is shown in Figure 6.
water for two minutes and then centrifuged at 5000 rpm for
ten minutes. The aqueous layer was discarded and the
process was repeated. 0.5 g of anhydrous sodium sulfate
was added to the cleaned gasoline and shaken to remove
any traces of water.

Figure 5 shows chromatography of the gasoline before
and after washing. Even though the gasoline contained up
to 10% ethanol, this and all other polar compounds were
effectively removed by the washing procedure.
Figure 6. Chromatogram of washed gasoline spiked with low levels of
oxygenated compounds.

The 27.4 – 50 ppm w/w mixture was injected repeatedly to
measure the area and retention-time precisions. These are
summarized in Table 3.

The area precision is around 1% relative standard deviation
which is an excellent result – especially for polar compounds
at low levels in a highly complex sample matrix like gasoline.
The retention-time precision, which ranges from 0.013%
to 0.039% relative standard deviation, is again an excellent
result, considering the nature of this analysis.

Figure 5. Efficacy of gasoline washing procedure for preparation of standard
mixtures.

Table 3. Area and Retention-Time Precision of a Standard Mixture of Oxygenated Compounds (n=9).
Compound Conc. (ppm w/w) Mean Area RSD% Area Mean R.T (min) RSD% R.T.
Ethyl tert-Butylether (ETBE) 27.4 64807 0.69 9.580 0.028
Methyl tert-Butylether (MTBE) 27.4 58557 0.64 9.827 0.021
Diisopropylether (DIPE) 27.4 53993 0.80 10.044 0.039
tert-Amylmethylether (TAME) 50.0 101209 0.65 11.503 0.039
Methanol 50.0 31028 1.11 13.642 0.023
Ethanol 50.0 60104 0.96 15.663 0.015
n & i-Propanol 50.0/50.0 142362 1.10 17.109 0.016
i, s & t-Butanol 50.0/50.0/50.0 273656 0.72 18.233 0.009
n-Butanol 50.0 89299 0.76 18.740 0.013
tert-Pentanol 50.0 103335 0.63 19.287 0.013
1,2-Dimethoxyethane 41.1 64233 1.26 19.982 0.016

4

Conclusion
This method, based on the S-Swafer technology, is able to
separate and quantify the ASTM® D4815 target analytes at
low-ppm levels and offers the following user benefits:

• High-throughput analysis, with a complete analysis cycle
time of 25 minutes

• A robust system – the analytical column is protected from
most of the gasoline compounds by backflushing

• In-line restrictor with secondary column allows the primary
column to be backflushed during chromatography, reducing
analysis time

• Splitting restrictor enables precolumn chromatography to be
monitored – facilitating system setup

• Use of nitrogen carrier gas to help preserve helium stocks
and reduce operating costs

• Excellent quantitative precision.

PerkinElmer, Inc.
940 Winter Street
P: (800) 762-4000 or
(+1) 203-925-4602
www.perkinelmer.com



009033_01


Gas Chromatography/
Mass Spectrometry

Author
Greg Johnson
PerkinElmer, Inc.

Fatty Acid Methyl Introduction
The contamination of aviation fuel with fatty acid
Ester Contamination of methyl esters (FAMEs) can arise due to the use of
multi-product pipelines for fuel supply and distribution.
Aviation Fuel by GC/MS In some countries, the widespread, mandatory intro-
duction of automotive fuels with a bio-material content
means that these pipelines are exposed to both auto-
motive biodiesel with a 5% FAME (BD 5) content as
well as to aviation fuel. FAMEs can adsorb onto the
surface of the pipeline and later desorb, contaminating
whatever fuel that follows, including aviation fuel.

FAMEs alter the physical properties of the fuel. While presence of FAMEs in aviation fuel is
of global concern, the United Kingdom is at the forefront of the analysis. The specification
of aviation fuel in the UK is defined in the Ministry of Defence (MoD) Defence Standard
91-91. Technical authority for this standard is controlled by the MoD Defence Fuels Group
with the agreement of the UK Civil Aviation Authority (CAA). This specification has recently
been amended to formalize the acceptance of FAMEs in aviation fuel up to a maximum of
5 mg/Kg (ppm) combined total. To measure this specification, the Energy Institute has issued
a method entitled IP PM DY: Determination of fatty acid methyl esters (FAME) derived from
biodiesel fuel, in aviation turbine fuel – GC/MS with selective ion monitoring/scan detection
method. The US specification of aviation fuel is covered by ASTM® D1655; in August of
2009, in a special airworthiness bulletin (NE-09-25R1), the Federal Aviation Administration
(FAA) stated its intent to include a similar regulation in its specifications.

Current methods for determining FAME in aviation fuel use Table 1. Detailed instrument parameters for the GC/MS
a polar ‘wax’ type GC column with mass spectrometry (MS) analysis of FAMEs.
for detection. The polar column will be more retentive for
GC Conditions
FAME compounds relative to the less polar hydrocarbon
Column 25 m x 0.32 mm id x 0.25 μm BPX70
compounds of the fuel. The MS will identify FAMEs based
on unique spectral data, further distinguishing FAMEs from Injector Split/splitless @ 280 ˚C with glass wool packed
hydrocarbon aviation fuel. The limitation of current methods liner
is that the wax column has a relatively low maximum- Carrier Gas Helium @ 15 psig at injector and 3 psig at Swafer
temperature limit and high column bleed as it approaches Injection 1.0 μL splitless for 0.75 minutes then 50 mL/min
this limit. Oven 150 ˚C for 2 minutes then 10 ˚C/min to 220 ˚C
and hold for 6 minutes
MS Conditions
Mode Electron Ionization (70 eV)
Source 180 ˚C
Transfer Line 300 ˚C
Photomultiplier 550 V

Table 2. Calibration summary for FAMEs with GC/MS.

Figure 1. 0.1 ppm (wt/wt) individual FAME compounds in n-dodecane. FAME Concentration Range Coefficient of
Determination (r2)
C16:0 0.5 to 10.0 ppm 0.999929
In this application note, a different type of polar capillary
C18:0 0.5 to 10.0 ppm 0.999872
column is used. This column reduces the temperature necessary
to elute all compounds, while also providing a higher maxi- C18:1 0.5 to 10.0 ppm 0.999744
mum temperature. This will reduce both the wear on the C18:2 0.5 to 10.0 ppm 0.999577
column and the amount of signal in the chromatogram C18:3 0.5 to 10.0 ppm 0.999092
associated with column bleed. Additionally, this method will
increase sample throughput. The specification of 5 mg/Kg is
a total for all FAME compounds present and therefore the Calibration
limit of detection for individual FAME compounds needs to A commercially available standard (Supelco®) containing
be significantly lower than 5 mg/Kg. Figure 1 demonstrates equal masses of pure C16:0, C18:0, C18:1, C18:2 and
that 0.1 mg/Kg is possible using this experimental setup. C18:3 was diluted by weight to 2000 mg/Kg with n-dodecane
solvent, as recommended in Institute of Petroleum method
Experimental PM-DY/09. Calibration standards were prepared at 0.5, 1.0,
This application was performed on a PerkinElmer® Clarus® 2.5, 5.0 and 10.0 mg/Kg and spiked with 2.0 µL of C21:0 in
680 GC/MS with a capillary split/splitless injector. A 1.0 µL n-dodecane solution used as an internal standard.
splitless injection was used to introduce the standards and
samples into an unpacked, 2 mm i.d., quartz liner. The chro-
matographic separation was achieved on a 25 m x 0.32 mm
i.d. x 0.25 µm BPX70 column (SGE, Australia). The MS was
used in single-ion-recording mode (SIR) to provide maximum
sensitivity and specificity. Complete instrument parameters
are presented in Table 1.

Figure 2. The calibration result from TurboMass™ GC/MS software
demonstrating the linear response of FAME C16:0 across a range of
0.5-10.0 mg/Kg.

2

The calibration standards were analyzed in triplicate. All data
points were used without exception. The response across the Table 5. The precision results from the analysis of a rapeseed
oil mixture (n=10).
calibration range was very linear (r2 > 0.9991) for all FAME
compounds; complete calibration data is presented in Table 2. RSD%
Additionally, Figure 3 demonstrates the calibration output RSD% Int’l Std.
Conc. (%) in Conc. Absolute Response
from the PerkinElmer TurboMass software.
FAME original mix (ppm) final Area Ratio
Immediately following the instrument calibration, a 5 mg/Kg C14:0 1.0 0.50 2.02 0.86
standard was analyzed to provide additional precision data. C16:0 4.0 2.00 1.66 1.18
The results of this precision study are reported in Table 3. C18:0 3.0 1.50 2.08 0.63
C18:1 60.0 30.00 1.52 0.54
Table 3. System precision evaluation, replicate injections
C18:2 12.0 6.00 1.84 0.19
(n=15) of the 5.0 mg/Kg calibration mixture.
C18:3 5.0 2.50 2.34 0.89
FAME Concentration RSD% Absolute RSD% IS
Peak Area Resp. Ratio C20:0 3.0 1.50 2.08 0.33
C16:0 5.0 ppm 1.34 0.78 C20:1 1.0 0.50 3.41 1.71
C18:0 5.0 ppm 1.34 0.50 C22:0 3.0 1.50 2.83 1.10
C18:1 5.0 ppm 1.40 0.62 C22:1 5.0 2.50 3.04 1.53
C18:2 5.0 ppm 1.22 0.86 C24:0 3.0 1.50 3.66 1.86
C18:3 5.0 ppm 1.55 0.86 Internal Standard = C21:0

The ability of the method to determine a wide range of
FAMEs at various concentrations was verified by analyzing a
commercially available rapeseed oil standard (Supelco®). The
standard was diluted 100 fold (100 mg to 10 g) by weight
in n-dodecane, with a further 200:1 dilution resulting in a
mixture with the composition in Table 4.

Table 4. Composition of fame mixture used to verify the
method identification of a mixture of FAMEs.
FAME Initial Concentration Final Concentration
C14:0 1.0 % 0.5 ppm
C16:0 4.0% 0.8 ppm
C18:0 3.0% 0.6 ppm
Figure 3. Chromatography of the rapeseed oil reference mixture using SIR.
C18:1 60.0% 30.0 ppm
C18:2 12.0% 6.0 ppm
The final verification of this method was to analyze an
C18:3 5.0% 2.5 ppm
aviation-fuel sample spiked with a known amount of FAME.
C20:0 3.0% 1.5 ppm Figure 4 presents the resultant chromatogram from the
C20:1 1.0% 0.5 ppm analysis of an aviation-fuel sample spiked with between
C22:0 3.0% 1.5 ppm 0.5 and 30 ppm FAME.
C22:1 5.0% 2.5 ppm
C24:0 3.0% 1.5 ppm

The rapeseed oil was analyzed in ten replicates to verify the
precision of the method when the FAME materials span a
wide concentration range (Table 5). An example chromatogram
from this analysis is shown in Figure 3.

3

Figure 4. The resultant chromatogram of the analysis of aviation fuel spiked
with FAME.

As you can see in Figure 4, the GC conditions provide
adequate resolution of C16:0 FAME from the hydrocarbon
envelope of the aviation fuel, as well as low-level detection
capabilities independent of matrix.

Conclusions
This application note demonstrated the use of the Clarus
680 GC/MS to identify and determine the concentration of
low-level FAMEs. A polar column was used in conjunction
with a short GC run to provide a fast and robust method.
The MS was operated in SIR mode to achieve the highest
levels of sensitivity and specificity.

Also demonstrated in this note is compliance with the newly
released methods set forth by regulatory agencies such as
the Institute of Petroleum. In addition, preliminary results
indicate that the current method used for the analysis of
FAME contamination in aviation fuel can be speeded up very
significantly without sacrificing either sensitivity or precision.

PerkinElmer, Inc.
940 Winter Street
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009031_01


Differential Scanning
Calorimetry

Authors
Ji-Tao Liu
Tiffany Kang
Peng Ye
PerkinElmer, Inc.

Curing Determination Introduction
Renewable energy has attracted a lot of
of EVA for Solar Panel interest due to the limited supply of coal
and oil and the environmental concern
Application by DSC of carbon dioxide (CO2) emission. There
are many different forms of renewable
(green) energy including: solar, wind,
geothermal, biomass, and so on. Among
them, solar energy is the fastest-growing
segment. Increasing manufacturing capacity and decreasing product costs have
led to significant growth in the solar industry over the past several years. For
instance, solar photovoltaic (PV) production has been increasing by an average
of 48% each year since 2002. By the end of 2008, the cumulative PV installation
reached more than 15 giga-watts globally.

A solar cell is a device that can convert sunlight directly into electricity. Different
solar-cell technologies including crystalline silicon, organic photovoltaics, and
dye-sensitized solar cells have been developed for various solar-cell applications.
Currently, the most widely commercially available solar cell is based on crystalline-
silicon technology. This technology is mature compared with the other solar-cell
technologies and its energy-conversion efficiency is high.

A photovoltaic module or system consists of many jointly Experimental
connected solar cells. The solar cells are packaged between The instrument used here is the PerkinElmer® double-furnace
a backsheet on the bottom and a tempered-glass window DSC 8000. It features power-controlled design for direct and
on the top. The cells are encapsulated by a polymer encapsulant accurate heat-flow measurements to and from the sample
(Figure 1). The polymer encapsulant serves many functions – material. The cooling accessory is an Intracooler 2P mechanical
it provides mechanical support, electrical isolation, and refrigerator. Nitrogen is used as the sample purge gas at
protection against outdoor environmental elements of 20 mL/min. The instrument was calibrated with two metal
moisture, UV radiation and temperature stress. Many different reference materials: indium and zinc were used for temperature
materials can be used for encapsulation, but one commonly calibration, and indium was used for heat of fusion for
used encapsulant for this purpose is EVA (ethylene-vinyl-acetate). heat-flow calibration. The EVA samples are from a solar PV
manufacturer. They were cured at a high temperature and
EVA, a thermal-set material, is a copolymer elastomer supplied
pressure for some time. Each EVA sample weighed approxi-
in sheet form for use in the encapsulation of PV modules.
mately 10 mg. Each EVA sample cured at different times
It has many desirable properties which make it the material
was encapsulated in the standard aluminum pans. The DSC
of choice for this application.
program started from -50 ˚C and heated to 220 ˚C at 10 ˚C/min.
• It is not adhesive at room temperature for easy handling.
Results
• It makes a permanent and adhesive tight seal in the
The raw EVA material exhibits several transitions during
solar-cell system through crosslinking and enhanced
heating, as shown in Figure 2 (Page 3). It was heated in the
bonding when the film is heated and pressed.
DSC from -50 ˚C to 220 ˚C at 10 ˚C/min, and after that it
• After crosslinking, the EVA has high optical transmittance, was cooled to the starting temperature quickly at 100 ˚C/min.
good adhesion to the different module materials – it It was heated for the second time at the same heating rate.
provides good dielectric properties and great moisture- The first heating curve shows an endothermic melting peak
barrier properties with adequate mechanical compliance (26 J/g) followed by the exothermic curing peak with the
to accommodate system thermal stresses due to the curing enthalphy of 16.6 J/g. The second heating curve
different thermal-expansion coefficiencies. shows a glass transition (Tg) at -35.6 ˚C; the melting peak is
smaller (12 J/g vs. 26 J/g) and there is no detectable curing
During the PV-package process, the EVA sheet is placed exothermal peak. So by comparing the first heating curve
between the solar cells and the backsheet/glass. It is heated, with the second heating curve, it is clear that the EVA raw
pressed into place, and cured at a certain high temperature material is cured completely after first heating it up to 220 ˚C.
for some time. Since the final cured material’s properties are
largely dependent on the curing degree, it is important to For a partially cured EVA sample, the residual curing peak
know the degree of curing of the EVA so that the encapsu- during the first heating will be between the curing enthalpy
lation process is optimized. Differential scanning calorimetry of raw EVA material and zero for completely curing EVA. So
(DSC) has been traditionally used for curing studies of thermoset the residual curing enthalpy can be used as an indicator of
resins. DSC can study the degree of cure and curing kinetics. the curing degree of EVA material. A series of EVA samples
In this note, different EVA materials with different curing with different curing time are studied by DSC and the results
times were investigated with PerkinElmer‘s high-end DSC 8000. are shown in Figure 3 (Page 3). The calculated residual curing
enthalpy is tabulated in Table 1 and fitted to a straight line
in Figure 4 (Page 3). As can be seen, the residual curing
enthalpy can be correlated to the curing time very nicely
(R2 = 0.9893).

Table 1. Residual curing enthalpy of eight different EVA
samples with different curing times.
EVA Curing Time ΔH (residual curing
samples (min) enthalpy J/g)
EVA-1 1 11.3572
EVA-2 2 10.7635
EVA-3 3 9.6878
EVA-4 4 7.9689
Figure 1. Scheme of a crystalline solar panel. EVA-5 5 7.5885
EVA-6 6 6.7448
EVA-7 8 4.9335
EVA-8 9 3.9811

2

Figure 2. The first (red) and second (blue) heating curve of raw EVA material.

Figure 3. Partially cured EVA samples with different curing times.

Conclusion
This study shows that DSC can be used to study the curing
degree of the EVA resin by measuring the residual curing
enthalpy. The data show that the residual curing enthalpy can
be correlated to the curing time in a linear way. The DSC test
is quick and easy. The double-furnace PerkinElmer DSC 8000
delivers accurate heat-flow data with great reproducibility.
The power-controlled design ensures great accuracy and
true isothermal measure so that it can be used for both
scanning-curing and isothermal-curing studies of EVA resin.

Figure 4. The relationship between residual-curing enthalpy and the curing
time of the eight different EVA samples.

PerkinElmer, Inc.
940 Winter Street
P: (800) 762-4000 or
(+1) 203-925-4602
www.perkinelmer.com



009038_01


ICP-Mass Spectrometry

Authors
Jianmin Chen
PerkinElmer, Inc.

Determination of Mercury is ubiquitous in nature, and the human health
consequences of mercury exposure were recognized from

Mercury in Wastewater prehistory to the present. The first emperor of unified China
who came to power in 221 B.C., Qin Shi Huang, reportedly

by Inductively Coupled died of ingesting mercury pills that were intended to give
him eternal life. The severity of mercury's toxic effects
Plasma-Mass Spectrometry depends on the form and concentration of mercury and
the route of exposure. Although its potential for toxicity in
highly contaminated areas such as Minamata Bay in Japan
is well documented, research has shown that mercury can
be a threat to the health of people and wildlife in many
environments that are not obviously polluted. There is no
safe level of mercury for humans. The main toxic effects
of mercury are known to negatively affect the neurological,
renal, cardiovascular and immunological systems.

Mercury exists in three chemical forms: elemental or metallic,
organic or methylmercury, and inorganic complexes. Table 1. ELAN ICP-MS Instrumental Conditions and
Experimental Parameters.
Mercury has thousands of industrial applications. Some
common uses for mercury include conducting electricity, RF power 1100 W
measuring temperature and pressure, acting as a biocide, Plasma gas flow 15 L/min
preservative, and disinfectant, as well as being a catalyst for Auxiliary gas flow 1.2 L/min
reactions. Unlike most other pollutants, mercury is highly
Nebulizer gas flow 0.96 L/min
mobile, non-biodegradable, and bio-accumulative; as a
result, it must be closely monitored to ensure its harmful Nebulizer MEINHARD® Concentric Type A3
effects on local populations are minimized.1 Thus, measurement Spray chamber Baffled Quartz Cyclonic
of mercury in environmental samples, and in particular waste- Scanning mode Peak Hopping
water, is of great importance as a major tool to protect Dwell time 50 ms
the environment from mercury released through emissions
Replicates 3
from manufacturing, use, or disposal activities. Currently,
the prominent methods typically utilized by the environmental Integration time 1 sec/mass
community for the determination of mercury generally
require detection limits as low as 0.5 ng/L (ppt, parts-
per-trillion).2 Sample Preparation
The stability of mercury-containing solutions has been
Traditionally, mercury is analyzed using Cold Vapor Atomic
a topic of concern for all trace analysts performing Hg
Absorption Spectroscopy (CVAAS) or Cold Vapor Atomic
determinations. It is reported that a trace amount of gold
Fluorescence Spectroscopy (CVAFS). Both of these techniques
salt added to HNO3 preserved all forms of mercury. The
are relatively straightforward to use and can accomplish
gold ion acts as a strong oxidizing agent that converts or
the analytical requirements of detection limits in the low
maintains mercury as mercuric ion which remains in solution.3
ppt range. However, they are generally specific for mercury
Thus, a solution of 2% (v/v) HNO3 containing 200 ug/L Au
analysis only.
was used for preparation of all samples and standards.
In recent years, Inductively Coupled Plasma Mass Spectrometry Two simulated wastewater certified reference materials
(ICP-MS) has become one of the most powerful analytical (Trace Metals Solutions, CWW-TM-A and CWW-TM-C,
techniques for trace element analysis because of its high High-Purity Standards, Charleston, SC, USA) were prepared
sensitivity, wide linear dynamic range, and simultaneous according the manufacturer’s description using the same
multi-element detection capability. As a result, ICP-MS has diluent in this study.
been increasingly adopted in environmental and biomonitoring
laboratories for the simultaneous measurement of mercury Calibration
with other toxic metals since this technique can offer the External calibration standards of mercury were at the level
same analytical performance as CVAAS or CVAFS. This of 10, 20, 50, 100, 200, 500, 1000 ng/L. Figure 1 shows
application note describes the application of ELAN® ICP-MS the calibration curve of 202Hg. The correlation coefficient is
to the determination of mercury in wastewater. 0.999973, which allowed the accurate quantitative analysis
of mercury at the low ppt levels.
Instrumentation
For this study, the PerkinElmer® ELAN DRC™ II ICP-MS
was used for the analysis of wastewater samples under
standard mode. The ELAN ICP-MS instrument conditions
and general method parameters are shown in Table 1.

Figure 1. External calibration curve of 202Hg. Standard solutions were prepared
in 2% HNO3 containing 200 ug/L Au with concentrations ranging from 10 to
1000 ng/L.

2

Spike recovery
The spike recovery test was performed using two simulated
wastewater certified reference materials (HPS CWW-TM-A
and CWW-TM-C). The results are presented in Table 2.

Table 2. Spike recovery test results from two simulated
wastewater certified reference materials (HPS CWW-TM-A
and CWW-TM-C).
Wastewater Found Spike Measured Recovery
Sample (ng/L) Level (ng/L) %
(ng/L)
CWW-TM-A 49 200 238 95
CWW-TM-C 375 1000 1370 99

Memory effect
It is generally viewed that routine determination of mercury
by ICP-MS is affected by a pronounced memory effect in the Figure 2. Uptake and wash out profile for Hg at 1000 ng/L level. The signal of
sample introduction system. This results in long washout times four mercury isotopes returns to the background level in around 60 seconds,
for the analyte, which affects the accuracy and reliability of which is equivalent to the typical rinse time used for many other analytes.
the analytical procedure. To minimize the memory effect, the
system was washed using 2% (v/v) HNO3 containing 200 ug/L
Au between samples. Figure 2 shows the uptake and wash out Conclusion
profile of Hg. The signal of four mercury isotopes returns to The ELAN ICP-MS combines high sensitivities and superior
the background level in around 60 seconds, which is equivalent detection limits with ease of use and high sample throughput.
to the typical rinse time used for many other analytes. Thus, This allows it to be an excellent tool for trace mercury
the results indicated application of gold salt is effective in determination in wastewater samples. Mercury can be detected
preventing mercury sorption and vapor buildup within the simultaneously with the other trace elements of interest within
sample introduction system. a single sample run.

References
1. J.O. Nriagu, Global inventory of natural and anthropogenic
emissions of trace metals to the atmosphere, Nature 279
(1979) 409–411.

2. EPA Method 1631. Mercury in Water by Oxidation,
Purge and Trap, and Cold Vapor Atomic Fluorescence
Spectrometry.

3. www.epa.gov/nerlesd1/factsheets/mpt.pdf. Mercury
Preservation Techniques.

PerkinElmer, Inc.
940 Winter Street
P: (800) 762-4000 or
(+1) 203-925-4602
www.perkinelmer.com


Copyright ©2009-2011, PerkinElmer, Inc. All rights reserved. PerkinElmer® is a registered trademark of PerkinElmer, Inc. All other trademarks are the property of their respective owners.

008973A_01


Thermogravimetric Analysis –
GC Mass Spectrometry

Author
Greg Johnson
PerkinElmer, Inc.

Qualitative Analysis Introduction
Thermogravimetric analysis (TGA)
of Evolved Gases in measures the change in the weight of
a sample as a function of temperature.
Thermogravimetry by A limitation of TGA is that it cannot identify

Gas Chromatography/ what material is lost at a specific tempera-
ture. The analysis of gases evolved during

Mass Spectrometry a TGA experiment by gas chromatography
mass spectrometry (GC/MS) provides
laboratories with a way to identify the
compound or groups of compounds
evolved during a specific weight-loss
event in a TGA analysis.

This application note discusses the utility of TG-GC/MS with an example
application – the identification of specific organic acids evolved during TGA
analysis of switchgrass.

Figure 3 describes in greater detail the pneumatic supply
to the S-Swafer device and assists in explaining why this
approach is so well suited to interfacing the Pyris 1 TGA
to the Clarus 600 GC/MS.

Figure 1. Clarus 600 GC/MS interfaced to the Pyris 1 TGA.

Switchgrass (Panicum Irgatum) is a perennial warm-season
grass native to the northern states of the USA; it is easily
grown in difficult soils. Switchgrass is potentially useful in Figure 3. Schematic showing carrier-gas supply to the S-Swafer device.
the production of biofuels, specifically cellulosic ethanol
and bio-oil.

The instrumentation used in this study was a PerkinElmer® The S-Swafer configuration is optimal because it will ensure
Pyris™ 1 TGA interfaced to the PerkinElmer Clarus® 600 GC/ a very rapid adjustment of carrier gas to the Swafer device,
MS with the S-Swafer™ micro-channel flow splitting device allowing for a rapid switch between backflush of the transfer
(S4 configuration). The preferred mode of operation of the line and sampling from the TGA. The samples of evolved gas
TGA maintains the atmosphere around the sample at ambi- are collected by setting a simple parameter in the GC method;
ent atmospheric pressure. The sample is collected from the multiple samples can be collected during a TGA analysis.
TGA by allowing the high vacuum of the MS to create a Additionally, backflush of the transfer line will isolate the
pressure drop across the GC column, causing a flow of gas GC/MS and enable purge gas at the TGA to be switched
from the TGA through the transfer line and the analytical from an inert gas (during analysis) to an air supply for
column to the MS. During the analysis, there are times when cleaning of the TGA pan prior to the next sample.
the TGA inlet will be surrounded by air, rather than an inert
atmosphere. This would cause air to flow into the GC/MS; this Oven subambient cooling will be extremely useful in this
is undesirable as it will cause oxidation to a number of dif- application, allowing protracted sampling periods to be
ferent areas of the system. The S-Swafer device (shown in refocused into a narrow band of analytes on the column.
Figure 2) is used to switch between backflushing of the
TGA transfer line during non-sampling time and sampling Experimental
of the TGA environment during analysis. The deactivated fused-silica transfer line used here was
1.6 m x 0.32 mm i.d. A few centimeters of the deactivated
fused silica protrudes into the sample weighing area of the
TGA. Approximately 30 cm of fused silica passes through
the injector into the oven environment and is connected to
the S-Swafer using specialized SilTite™ nuts and ferrules to
ensure a leak-free connection that will not shrink and leak
during normal or even extended thermal cycling of the main
oven.

In all cases, a 30 m x 0.32 mm analytical column was
employed as this allows a carrier flow of approximately
1 mL/min with the fixed 1.00 atmosphere pressure drop
from ambient at the TGA to vacuum at the MS. Data was
Figure 2. Schematic showing the pneumatic interfacing of the TG-GC/MS acquired using an Elite™ WAX stationary phase.
using the S-Swafer.

2

A small quantity of dried and ground switchgrass was timed events that will be used to sample the evolved gases
placed on the TGA pan and weighed using Pyris software. onto the GC/MS column. Note that the TGA is held iso-
A rapid TGA analysis based on heating the sample from thermal for the first 5.0 min at which point heating begins.
30 ˚C to 1000 ˚C at 100 ˚C/min in a nitrogen atmosphere Simultaneously, the GC/MS analysis is started.
was performed to determine which regions of the weight-
loss curve were to be further studied using the TG-GC/MS Figure 5 illustrates the TG-GC/MS analysis of the switch-
technique. grass based on timed events that collect the evolved gases
from the main transition shown in Figure 4. The smaller
The primary reason for using such rapid heating, which earlier transition, also seen in the same figure, was also sampled
reduces the resolution of the weight-loss curve produced onto the GC/MS but preliminary findings indicate that this
by the TGA, is to transfer the evolved gas quickly into the is simply evolved water. The major transition produced large
GC column. A quick transfer will improve GC peak shape, numbers of oxygenated volatile organic compounds (VOCs),
sensitivity and resolution. including some very polar species. Earlier work using a non-
polar capillary column had generated extremely smeared-out
After the sample was loaded onto the TGA and the furnace early-eluting peaks. The chromatogram below was generated
raised, the analysis was started immediately. The first step in using a thick-film polar Elite WAX column.
the TGA heating program maintained the low initial furnace
temperature for 5 to 10 min. During this time, the furnace
environment is being purged with helium (or nitrogen/argon),
and the carrier-gas pressure of 7.0 psig maintained at Aux 1
(Figures 2 and 3) ensures that no sample can enter the ana-
lytical column. After this initial hold period, the TGA furnace
begins to heat the sample, and simultaneously, the GC/MS
run is started using an external start command.
Figure 5. TG-GC/MS analysis of the switchgrass sample on a 30 m x 0.32 mm
Based on previous TGA runs on the same sample, timed
x 1 μm Elite WAX column.
events within the GC method switch off the carrier gas
supplied by the Aux 1 PPC module and then close the
solenoid valve (SV3) shown in Figure 2 (Page 2). This begins The three peaks labeled with asterisks in Figure 5 are identified
the sampling and this procedure is reversed to bring the sam- as a homologous series of free fatty acids (Figure 6 – Page 4),
pling period to an end. After the sampling is complete, both based on a library search of their MS spectra (NIST® 2008).
the GC oven-temperature program and MS data acquisition Usually in GC, a homologous series tends to elute in carbon-
begins. The TGA can now be programmed to switch purge number order but here, the elution order appears to be
gases to clean the system using oxidation at elevated acetic, followed by formic, followed by propanonic acid. As
temperature, prior to the next analysis. this retention behavior is not typical and in the absence of a
literature reference or a similar chromatogram in the public
A typical TGA weight-loss curve for the switchgrass is shown
domain, it seemed prudent to analyze a simple retention-
in Figure 4 and reveals a typical weight % loss curve for the
time standard to confirm this tentative result. Figure 7 (Page 4)
sample of switchgrass that was tested. In addition, super-
shows the same analysis again but with the retention-time
imposed on the weight-loss curve is the derivative of this
standard shown in parallel. This standard was a simple
curve which greatly assists the analyst in setting up the GC
mixture diluted in water with a small (5 μL) aliquot of this
aqueous solution deposited by syringe onto the TGA pan
for analysis.

Figure 4. Typical result for the TGA analysis of switchgrass.

3

Conclusions
In this application note, we describe the technique of TG-
GC/MS through the analysis of switchgrass. TG-GC/MS is
demonstrated to be a valuable technique in the separation
and identification of complex mixtures of gas evolved during
a TGA analysis. The S-Swafer device is demonstrated as a
means to interface a TGA to GC/MS. The main benefits are
its simplicity and the inertness of the entire sample path.

Figure 6. Mass spectra extracted from the total ion chromatogram of the
switchgrass sample. The spectral data matches that of acetic, formic and
propionic acid respectively available in the 2008 NIST® mass spectral library.

Figure 7. TG-GC/MS analysis of the switchgrass sample (bottom) on a 30 m
x 0.32 mm x 1 μm Elite WAX column and the analysis of a simple retention
time mix (top) under the same TGA and GC conditions.

PerkinElmer, Inc.
940 Winter Street
P: (800) 762-4000 or
(+1) 203-925-4602
www.perkinelmer.com



009030_01


ICP-Mass Spectrometry

Authors
Lee Davidowski, Ph.D.

Zoe Grosser, Ph.D.

Laura Thompson

PerkinElmer, Inc.
710 Bridgeport Avenue
Shelton, CT USA

The Determination Introduction
Dietary supplements are regulated by the FDA under the general umbrella of foods,
of Metals in Dietary but with different regulations than conventional foods. Dietary supplements have been
defined by Congress as materials taken by mouth that include ingredients intended to
Supplements provide dietary supplementation. They can be found in various forms, including tablets,
powders, and liquids. They may consist of vitamins, minerals, herbs or other botanicals,
amino acids, and substances such as enzymes, organ tissues, glandulars, and metabolites.
Under the Dietary Supplement Health and Education Act of 1994 (DSHEA), the dietary
supplement manufacturer is responsible for ensuring that a dietary supplement is safe
before it is marketed. FDA is responsible for taking action against any unsafe dietary
supplement product after it reaches the market.1

One facet of ensuring a safe product is analysis of the final product before distribution. Although organic components often
form the majority of a supplement, metals may be found due to their inclusion in vitamin structures such as vitamin B-12
(cobalt) and minerals, such as selenium. They may also be added as a contaminant through natural products or in the manu-
facturing process. The measurement of toxic metals or metals intended to be present for quality and labeling confirmation
may be required. Analysis challenges include measurement at low concentrations in a variety of matrices. In this note we
will use inductively coupled plasma mass spectrometry (ICP-MS) to measure a variety of elements generally considered to
be hazardous to human health at low to medium concentrations. The four elements generally considered to be hazardous
and not necessary for nutrition are Pb, Cd, As, and Hg. The elements Se and Cr are often added at low concentrations for
nutritional purposes and were also included.

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