IJERD – International Journal of Environmental and Rural Development (2014) 5-2

Research articleerd

Gas Chromatography with Vacuum-Assisted Sampling
System in the Analysis of Hydrogen-Balanced Nitrogen Gas
SOMPORN PLEANJAI*Rajamangala University of Technology Thanyaburi, Pathumthani, Thailand
Email: spleanjai@gmail.com

YONGYUTH SEANSUPHANAir Liquide (Thailand) Company Limited, Nongkhae, Saraburi, Thailand

SINGTO SAKULKHAEMARUETHAI
Rajamangala University of Technology Thanyaburi, Pathumthani, Thailand

WANNASIRI SREVARIT
Rajamangala University of Technology Thanyaburi, Pathumthani, Thailand

CHAWISA PINSUWAN
Rajamangala University of Technology Thanyaburi, Pathumthani, Thailand

THIDARUT LAOCHAI
Rajamangala University of Technology Thanyaburi, Pathumthani, Thailand
Received 30 December 2013

Accepted 1 April 2014(*Corresponding Author)

Abstract A vacuum-assisted (VA) sampling system in gas chromatography (GC) with athermal conductivity detector has been developed to analyze low-pressure hydrogenbalanced nitrogen gas (H2/N2) sample. The objective is to determine hydrogen-balanced
nitrogen gas by GC assembled with the vacuum-assisted (VA) gas sampling systemcomparison to the conventional system, pressure reduced to zero (PRZ) gas samplingsystem. The results show that both systems were not significantly different at the 95%
confidence level. The developed sampling system was applied to analyses the quality of
the low-pressure-volume gas.
Keywords vacuum-assisted sampling system, pressure reduced to zero sampling system,
gas chromatography

INTRODUCTION
Nitrogen is a colorless, odorless and tasteless substance. It present in the atmosphere at aconcentration of 78.1%. It is used widely in commercial and technical applications. As liquid
nitrogen, it is used for cooling in many industrial processes and in the food industry. As gaseous
nitrogen, it is used to form an inert blanket over substances that would otherwise be oxidized by theair. It can be distributed as a cryogenic liquid or as a gas in cylinders (Greenwood, and Earnshaw,
1997, Kaganer et al.1967).
Gas chromatographic methods have been utilized for determination of many compounds
present in air and gaseous mixtures (Slemer et al. 2004, Taverniers et al. 2004). In the conventional
method, the GC with the pressure reduced to zero (PRZ) gas sampling system (or pressure flowsampling system) is used. This system allows the compressed gas in cylinders or containers flow
into the analysis system of GC as shown in Fig. 1. Unfortunately, this method is available for thegas sample with appropriate volume and pressure. In this work, the vacuum-assisted (VA) gas
sampling system in GC, as shown in Fig. 2, was developed for the analysis of low-pressure gas.
Therefore, the gaseous sample was easily collected by using a gas bag and conveniently transported
to the laboratory.
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IJERD – International Journal of Environmental and Rural Development (2014) 5-2

The present work describes a developed VA sampling system of GC for determination of low
pressure - volume hydrogen-balanced nitrogen (H2/N2) gas. The result obtained through the use ofthis newly developed sampling system was statistically compared to the conventional samplingsystem of GC.
Flow controller

Sampling system

Column oven

ColumnSample in
Detector

Gas Chromatograph

RecorderSample vent

SampleCarrier gas

Fig. 1 Schematic diagram of the GC equipped with pressure reduced
to zero gas sampling system

Flow controller Sampling system

Column oven

Sample in
Detector
Gas Chromatograph
Sample bag Sample vent

RecorderVacurm pumpCarrier gas

Fig. 2 Schematic diagram of the GC equipped with vacuum-assisted sampling system
OBJECTIVES
Followings are the objectives of this study.
1. To developed the vacuum-assisted sampling system in gas chromatography
2. To analyze the hydrogen-balanced nitrogen gas sample by gas chromatography equipped withthe developed sampling system
METHODOLOGY
The gas chromatograph (GC) with a thermal conductivity detector (TCD) (Agilent, CA, USA) wasused for quantitative analyses of the H2/N2 gas. Ultra high purity argon (Ar) gas cylinder with apurity of 99.99% as the carrier gas was connected to the GC. Separation was carried out in an HPPLOT Molesieve (5Å zeolite molecular sieve, porous layer open tubular) column (30 m  0.25 mmi.d., and film thickness 0.25 m). The oven temperature was isothermal at 30 C. The detector
temperature was maintained at 250 C.
The standard gas was 49.66% mol H2/N2 gas certificate reference material (CRM).
The working standard H2/N2 gases with different concentrations were individually prepared.
Then the calibration gas mixture was introduced and a chromatogram was recorded. The values ofpeak area (y) were plotted against the concentration (x) of H 2/N2 to obtain a calibration curve.
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IJERD – International Journal of Environmental and Rural Development (2014) 5-2

Regression analysis for a calibration line, y = ax + b, was carried out by Deming’s least square
method (International Organization for Standardization, ISO6143:2001, 2001).
Analysis of H2/N2 was conducted with a GC- TCD. A vacuum-assisted gas sampling system
and a pressure drop to zero gas sampling system were tested. The results obtained from the analysisof both sampling systems were compared.
RESULTS AND DISCUSSION
The response linearity of the gas analysis by GC equipped with the developed sampling system andthe conventional sampling system were determined by analyzing different concentrations of themixed standard gas containing 10-50% mol of N2. The response factor of the standard solutions
was calculated.
For the GC equipped with VA sampling system, the peak area of N2 gas response was plottedagainst the concentration of standard gas to obtain the calibration curve (Fig. 3(a)) and was foundto be linear over the concentration range of 1-50% mol and the values of correlation coefficient (r2)0.9984. Linear regression least squares fit data are given in Table 2. Mean recovery was estimatedto be 98.45%. The limit of detection (LOD), evaluated as three times the signal-to-noise ratio, wasestimated to be 3.4 mol/mol. The limit of quantification (LOQ) of the method, as theconcentration that produced a signal 10 times the baseline noise, was calculated as 4.2 mol/mol.
The results of precision as relative standard deviation (RSD) of the proposed sampling system aresummarized in Table 2.
For the GC equipped with PRZ sampling system, the obtained calibration curve (Fig. 3(b) was
found to be linear over the concentration range studied with the values of correlation coefficient(r2) 0.9997. Linear regression least squares fit data are given in Table 1. The LOD was estimatedto be 3.2 mol/mol. The LOQ of the method was calculated as 5.3 mol/mol. The results ofrelative standard deviation (RSD) of the PRZ sampling system are summarized in Table 2. Theresults indicating that there was no significant difference at 95% confidence level between thedeveloped sampling system and conventional sampling system.
The optimum experimental conditions were used to assess applicability of GC equipped with
developed and conventional sampling systems for quantitative determination of H2/N2 gas sample
analysis. The average analytical concentrations and %recovery of the nitrogen gas samples weredetermined by GC. The results, as shown in Table 3, showed that the values of average analyticalconcentration of N2 gas samples (n=3) for GC(VA) and GC(PRZ) were 9.62%mol and 9.70%mol,respectively. The percentage recovery of gas analysis determined by GC(VA) and GC(PRZ) givevalues in the acceptable range, 100±2% (AOAC Peer-Verified Methods. Nov. 1993). The analysisof the test system and vacuum sampling system is created that can use analyzing. The analysis iscorrect and is in an acceptable range.

Fig. 3 Calibration curves for the standard gases with different concentrations analyzed by
GC equipped with (a) vacuum-assisted (VA) and (b) pressure reduced to zero (PRZ)
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Table 1 Equations, correlation coefficients, and recovery percentage of the N2 in the mixtures
standard
Sampling
system of GC

Calibration curveequation

VA
PRZ

y = 460,571x + 291,050
y = 491,451x + 11,154

Correlation
coefficient(r2)
0.99840.9997

Mean
recovery
(%)
98.45
97.27

LOD
(mol/mol)

LOQ(mol/mol)

3.4
3.2

4.2
5.3

Table 2 Standard deviation, t-value, and percentage standard deviation of the N2 in themixtures standardSDtcaltcrit%RSD%RSDr

VA
0.0058-0.1632
4.3
0.05951.1880PDZ0.0200-0.28454.3
0.10501.1880

Table 3 Analytical concentrations and %recovery of the H2/N2 gas sample analyzed byGC(VA) and GC(PRZ)
Sampling system of GC
GC (VA)
GC (PRZ)

Analytical concentration (%mol)
9.62
9.70

% Recovery
99.95
99.15

Note: VA = vacuum-assisted sampling system and PRZ = pressure reduced to zero sampling system.

CONCLUSION
In this study, the vacuum-assisted sampling system for GC was developed. It was considered as anefficient sampling system for the determination of H2/N2 gas. The GC equipped with vacuumassisted sampling system compared to the GC equipped with pressure reduced to zero samplingsystem were not significantly difference with a statistical type F-test and t-test at confidence levelof 95%.
ACKNOWLEDGEMENTS
This project was conducted under the Cooperative Education Program-Rajamangala University ofTechnology Thanyaburi (RMUTT) and the Air Liquide (Thailand) Co., Ltd., Nong Khae, Saraburi.
The authors wish to thanks the Air Liquide (Thailand) Co., Ltd., for the provision of all chemicalstandards and GC instrument for this work.
REFERENCES
Greenwood, N.N. and Earnshaw, A. 1997. Chemistry of the elements, Second ed. Butterworth-Heimann, U.K.
Kaganer, M.G., Kozheurov, V. and Levina, Zh. L. 1967. Vessel for the storage and transport of liquid oxygenand nitrogen. Chemical and Petroleum Engineering, 3 (12), 918-922.
Slemer, J., Slemer, F., D’Souza, H. and Partridge, R. 2004. Study of the relative response factors of various
gas chromatograph-flame ionization detector systems for measurement of C2-C9 hydrocarbons in air.
Journal of Chromatography A, 1061, 75-84.
Taverniers, I., De Loose, M. and Van Bockstaele, E. 2004. Trends in quality in the analytical laboratory. II.
Analytical method validation and quality assurance. Trends in Analytical Chemistry, 23, 535-552.
International Organization for Standardization, ISO6143:2001. 2001. Gas analysis comparison methods fordetermining and checking the composition of calibration gas mixtures. International Organization forStandardization, Geneva.

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