Journal of Basic and Applied Research International 13(4): , 2016 ISSN: (P), ISSN: (O)

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1 Journal of Basic and Applied Research International 13(4): , 2016 ISSN: (P), ISSN: (O) International Knowledge Press TEMPERATURE EFFECT ON THERMAL CONDUCTIVITY DETECTOR IN GASES (CARBON DIOXIDE, PROPANE AND CARBON MONOXIDE) ANALYSIS: A GAS CHROMATOGRAPHY EXPERIMENTAL STUDY OMAN ZUAS 1*, HARRY BUDIMAN 1 AND MUHAMMAD RIZKY MULYANA 1 1 Research Center for Chemistry, Indonesian Institute of Sciences, Puspiptek Serpong, Tangerang 15314, Indonesia. AUTHORS CONTRIBUTIONS This work was carried out in collaboration between all authors. Author OZ designed the study, wrote the protocol, interpreted the data and produced the initial draft. Author HB anchored the field study, gathered the initial data and performed preliminary data analysis. Author MRM managed the literature searches. All authors read and approved the final manuscript. Received: 29 th August 2015 Accepted: 29 th September 2015 Published: 31 st October 2015 Original Research Article *Corresponding author: oman.zuas@lipi.go.id; ABSTRACT Vehicle exhaust gas component analysis, such as carbon dioxide (CO 2 ), propane (C 3 H 8 ), and carbon monoxide (CO) is of great importance to support controlling program for the atmospheric gases below the allowable levels. Among all the available methods, the gas chromatography with thermal conductivity detector (GC-TCD) was used to achieve the study purpose. However, in the real application, the operational parameter of the GC- TCD have to be firstly well optimized. In this study, the effect of detector temperature on the GC-TCD parameters including, retention times, sensitivity, selectivity, precision, limit of detection (LoD), and limit of quantitation (LoQ) were evaluated, while other operational parameters of GC-TCD were kept the same. The result shows that most of the investigated parameters such as retention times and selectivity were unaffected by detector temperature changes. On the other hands, the GC-TCD sensitivity, precision, LoD, and LoQ were significantly affected by changes in the detector temperature. In general, findings of this study indicated that the optimum detector temperature of GC-TCD for the analysis of CO 2, CO, and C 3 H 8 was found to be 150 C by keeping constant for other operational parameters. Keywords: GC; TCD; carbon dioxide; propane; carbon monoxide. 1. INTRODUCTION Atmospheric pollution by gaseous pollutants has currently become worldwide concern for most of scientists. This fact is marked by increasing the concentration level of the gas pollutant in the atmospheric air. One of the biggest contributor to such pollution phenomena is the gaseous pollutant emitted from vehicle s during operational [1]. In the last decade, increasing of vehicle gases type in global atmospheric air from time to time has devised the more stringent of regulations with the purpose to keep the concentration at allowable levels. Although the more stringent discharge regulated limit of pollutant

2 has improved for meeting the air quality standards; however, adequate evaluation of such regulation by controlling via regulatory monitoring programs and its enforcement are also important [2]. In this regards, providing the gaseous pollutant data that are obtained by using analytical instrument operated under optimum operational conditions is extremely required. There are numbers of accessible analytical method have been used for analyzing of vehicle gases pollutant including gas chromatography [3], fluorometry [4], and fourier transform infrared spectroscopy [5]. Among others, the gas chromatography-based technique (GC) is one of the most preferred techniques over the last century due to its inexpensive of operational cost. Besides, the GC is easily available worldwide to both government and private sector including university, research institute and industry [6]. In spite of the progress that has been made on the GC application, there is still effort remaining that can be directed toward a specific purpose, where optimizing the operational parameters of the GC equipped with thermal conductivity detector (TCD) can be taken as a specific example. Historically, the TCD has been utilized since the beginning of gas chromatography development. The TCD has no interaction neither with carrier gases nor with gas target alone but instead respond to changes in a bulk physical property, namely, the thermal conductivity of carrier gas compared with the conductivity of the gas target in the carrier-gas target mixtures. Practically, during the detection process, the thermal conductivity difference resulted and yielded in the form of voltage unit as the output signal [7]. In this study, the effect of detector temperature on the measurement parameter of the GC-TCD was investigated. Such GC-TCD measurement parameters includes retention times, sensitivity, selectivity, precision, limit of detection (LoD), and limit of quantitation (LoQ). To achieve the objective of this study, three common vehicle emission gases were used as the models including carbon dioxide (CO 2 ), propane (C 3 H 8 ) and carbon monoxide (CO). 2. METHODOLOGY 2.1 Materials Certified standard gas mixtures (SGM in short) having composition as listed in Table 1 were utilized in all experiment runs. The concentration values of gas components in the certified SGM are traceable to National Institute of Standards and Technology (NIST), USA. Table 1. Composition of gas components in the mixture of certified and working SGMs Gas components Concentration (% mol/mol) CO CO 3.18 C 3 H N 2 (gas balance) Relative Uncertainty ±2% from reported concentration 2.2 GC Instrumentation System and Operating Conditions The GC instrumentation used was Agilent Model 6890 series (Agilent, CA, USA) equipped with a single stage dual-packed column for separating the target gas component (CO 2, C 3 H 8, and CO) from their mixture. In such dual-packed column, a packed J&W porapack Q column (6 feet x 1/8 inch o.d. x 2 mm, mesh particle size) was connected in series to a packed J&W molsieve 5A column (9 feet x 1/8 inch o.d. x 2 mm, mesh particle size). The detection was performed by using a TCD and the output signal was monitored using OpenLAB CDS Chemstation version A , which is installed on a HP personal computer (HP Pavilion Slimline 400 PC series). For introducing the gas sample into the GC system, a Brooks 5890E mass flow controller (Brooks Instrument, Hatfield, USA) was used to ensure a consistent sample flow in addition to as an auto sampler. The mass flow controller (MFC) was installed just before the injection system consisted of a stainless steel tubing having 1/16 inch in diameters up to the loop inlet, a 2 ml stainless steel loop (Agilent, CA, USA). 2.3 Sample Analyses Analyses of the gas components in the sample were conducted in details as follows: a certain amount of gas sample from aluminum SGM sample cylinder was introduced to the column in the GC system through an MFC at flow rate of 100 ml/min. The injector and detector temperatures are 200 C and 250 C, respectively. The elution of the studied gas mixture was achieved with following temperature program: 40 C for 10 min, 40 to 160 C at 60 C/min, and 160 C was held for 2 min. The data was estimated by automated integration of the area under the resolved chromatographic profile, using the HP computer (Hawlet Packard Pavilion Slimline 400 PC series ) of OpenLAB CDS Chemstation version A In addition, the concentrations of all components in the gas sample were determined by inserting the peak 233

3 Table 2. Data indicating linearity of the GC-TCD method Gas components Slope Intercept Linearity range n (number of injection) R 2 (% mol/mol) CO C 3 H CO area of corresponding gas component into their calibration curve with linearity properties as shown above in Table 2. The following detector temperatures were investigated including: 125, 150, 175, 200, 225, 250, 275, 300, and 325 C. 3. RESULTS AND DISCUSSION 3.1 Typical Chromatogram Fig. 1 displays a typical chromatogram of gas component in the SGM. It was found that the CO 2, C 3 H 8, and CO were well separated from their mixture and detected at retention time (R t ) of 2.99, 13.32, and min, respectively. No other interfering peaks at or nearby the retention times of CO 2, C 3 H 8 and CO were observed, demonstrating that a good separation of the target analytes has been well-achieved [8]. This good component separation establishes that the response identity of target component was identified clearly and the component response in the form of signal produced is only due to the analyte and not from the presence of other components as interferences [9]. 3.2 Retention Time Fig. 2 shows the effect of detector temperature on the Rt of target component. As can be seen in Fig. 2, the detector temperature did not significantly affect the Rt of the target component, indicating that the detector temperature change had independent effect on the Rt of the target components. Theoretically, the Rt for any GC analysis (reported in minutes) is the time needed for a compound to travel from the injection port to the detector. While the detector detects a signal for any eluted compound from the column. Thus, under any normal circumstances, retention time should be unaffected by the detector temperature. On the other hand, the Rt in the GC may highly depends on the several factors including volatility and polarity of analyte, column temperature, column packing polarity, flow rate of the gas through the column, and length of the column [10]. 3.3 Sensitivity The GC sensitivity or response factor of the target component was determined by dividing the peak area with its corresponding concentration [11] and the Fig. 1. A typical chromatogram of gas component under this study at TCD temperature of 150 o C, showing the separation of CO 2, C 3 H 8 and CO (For interpretation of the references to color in the figure the reader is referred to the web version of the article) 234

4 Retention time (min) CO C3H CO Fig. 2. Effect of detector temperature on the Rt results are depicted in Fig. 3. It can be seen in Fig. 3 that the sensitivity of the detector was found to slightly increase from 125 C to 150 C and then gradually decreased for further increase of detector temperature. The detector is found to be less sensitive at higher detector temperature because the component may possibly condense inside the detector, lowering the detector sensitivity [7]. 3.4 Selectivity Generally, selectivity is an important factor to be evaluated in any GC measurement to ensure by which the target component being analyzed is not interfered by other non-target components [9]. The evaluation results for the effect of detector temperature on the selectivity are shows in Fig. 4. From Fig. 4, it can be seen that no detector temperature dependency of the selectivity can be observed. The selectivity is the relative retention of two adjacent peaks, meaning that selectivity is highly dependent on the change of the Rt values of the two corresponding analytes. As discussed above (Fig. 2), no significant effect of detector temperature on the Rt; thus, the selectivity tends to unchanged as well. In addition, the method used had a good selectivity which is indicated by the factor value larger than 1.0 [12]. 3.5 Precision The method precision was evaluated in term of repeatability precision to observe the closeness between measured values of a number of measurements under the same analytical condition during a short period of time [9]. In this study, no information of precision from reference methods are available for a comparison with the precision parameter, therefore, the repeatability precision comparison was made by using the prediction of relative standard deviation (%RSD) of precision that is theoretically calculated using Hortwitz function (Eq. 1) [13]. CV Hortwitz % = log c (1) where c is the concentration of gas component stated in decimal fraction. The requirement of %RSD for repeatability precision is between half and two-third times of a theoretical values determined by Hortwitz function [14]. From the calculation result, the % of CV- Hortwitz was found to be 3.59, 3.60, and 3.36 for CO 2, C 3 H 8 and CO, respectively. Moreover, the repeatability of the method is categorized acceptable when the %RSD is less than 0.67 of the % CV- Hortwitz (0.67CV-Hortwitz). For examining the %RSD, at least seven replications of injection measurement of sample were conducted and the results are presented in Table 3. From the Table 3, it can be seen that the repeatability precision of all target components at different detector temperature ranges were found to be less than their corresponding 0.67CV- Hortwitz, indicating that the precision of the method used is sufficient. However, the lowest %RSD for CO 2 (0.05), C 3 H 8 (0.07); and CO (0.09) were achieved at detector temperature of 150, 250, and C, respectively, as shown in Table LoD and LoQ A LoD is defined as the lowest amount of analyte that can be detected which is not necessarily quantified as 235

5 an exact value. Meanwhile, LoQ is the lowest concentration of an analyte that can be quantitatively determined with appropriate precision [15]. The LoD (Table 4) and LoQ (Table 5) for the target components were determined based on signal to noise ratio which are 3:1 and 10:1, respectively [16]. According to the Table 4, the lowest LoD for the target component were found at detector temperature of 125 C, except for CO 2 whose the lowest LoD at 175 C. Moreover, the LoQ values were found to be , 7.433, and ppm for CO 2, C 3 H 8, and CO, respectively. In addition, from the LoD (Table 4) and LoQ (Table 5), it can be observed that change in the detector temperature caused vary in both LoD and LoQ obtained, indicating that the detector temperature affects the LoD and LoQ values. In a GC measurement, both LoD and LoQ are important. Because for any quantification produces a measurement values that are below the LoD and LoQ level, it could make the quite high uncertainty which associated with the measurement. Consequently, the unreliable measurement would occur. 750 Sensitivity C3H8 CO2 CO Selectivity factor Fig. 3. Sensitivity dependence on detector temperature C3H8 to CO CO toc3h Fig. 4. Effect of detector temperature on selectivity 236

6 Table 3. %RSD and Horwitz s %RSD calculation %RSD CO 2 CV-hortwitz (0.67 x CVhortwitz) C 3 H 8 CV-hortwitz (0.67 x CVhortwitz) CO CV-hortwitz (0.67 x CVhortwitz) (2.405) (2.412) (2.251) Table 4. LoD values Detector LoD (ppm) temperature ( C) CO 2 C 3 H 8 CO Table 5. LoQ values Detector LoQ (ppm) temperature ( C) CO 2 C 3 H 8 CO CONCLUSIONS From the evaluation above, it can be concluded that the GC-TCD temperature had no effect on the retention times and selectivity of the GC-TCD for the measurement of CO 2, C 3 H 8 and CO, but the sensitivity, precision and LoD/LoQ were found to be affected. The highest sensitivity of the TCD on all target gas components was found at the detector temperature of 150 C. Interestingly, it was found that both precision and LoD/LoQ were likely dependent on the detector temperature. For the precision, the highest level for CO 2, C 3 H 8, and CO were achieved at detector temperature of 150, 250, and 200 C, respectively. In term of LoD/LoQ values, the lowest LoD/LoQ for the all target gas components were found at detector temperature of 125 C, except for CO 2 whose the lowest LoD/LoQ at 175 C. ACKNOWLEDGEMENTS The authors gratefully acknowledge the Indonesian Government for the financially support this study under Project No. SP.DIPA COMPETING INTERESTS Authors have declared that no competing interests exist. REFERENCES 1. Dubey A. Studies on the air pollution around cement and lime factories. Journal of Environmental Earth Science. 2013;3: Budiman H, Zuas O. Validation of analytical method for the determination of high level carbon dixode (CO 2 ) in nitrogen gas (N 2 ) matrix using gas chromatography thermal conductivity detector. Periodico Tche Quimica. 2015;12: Berezkin VG, Drugov YS. Gas chromatography in air pollution analysis. Elsevier Science, Amsterdam. 1991; Chang W, et al. A simple fluorometric method for the determination of sulfur dioxide in ambient air with a passive sampler. Environmental Science. 2006;13: Orphal J, et al. Monitoring tropospheric pollution using infrared spectroscopy from 237

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