https://doi.org/10.21577/0103-5053.20210015
“Chromatographic conditions
Chromatographic analyses were performed by using a gas chromatographer (GC) (Shimadzu GC-2014, Kyoto, Japan) equipped with TCD and FID detectors, respectively, which were operated in series. Data were processed using the GC-Solution software. A Carboxen 1010 PLOT column (0.53 mm internal diameter ? 30 m long ? 30 µm thick) was used as stationary phase.
Helium (12.9 mL min-1) was used as carrier gas. Synthetic air and hydrogen were combined to generate the FID flame. Inorganic gases (H2, N2, O2, CO and CO2) and hydrocarbons (CH4, C2H2, C2H6, C2H4, C3H6, C3H8, C3H4 (propadiene and propyne), iso-C4H10 and n-C4H10) were detected by TCD and FID, respectively.
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Analytical curves and linearity
Method linearity was evaluated by developing calibration curves with data obtained from the injection of 5-10 different concentrations (ranged from 0.0916 to 274 ppm, and prepared in triplicate) of each analyte.10–13
Tedlar bags of polyprolyene (1 L, CEL Scientific Corporation, Cerritos, USA) were used to transfer the sample of each isolated analyte from the cylinders to the atmospheric pressure. Dilution of gases was performed by adding argon gas to each analyte directly by using a suitable microsyringe (fixed needle, Teflon tip and capacity of 1000 µL) for collecting gas samples (Hamilton Gastight 1001, Nevada, USA).
The concentration of each analyte was calculated considering the volume of gas in the temperature of 0 °C to facilitate the comparison with the results obtained with ASTM D3612-02 (methods A and C).6
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Precision
Both intra-day and inter-day precision were assessed for the mixture of different concentrations of analytes prepared in triplicates in three different concentrations. Three separate bags were prepared with the mixture for the three evaluated concentrations (low, medium and high), and the linear range obtained for each compound was checked as shown in Table S1 (Supplementary Information (SI) section). Subsequently, the mixture of each bag was injected only once for each concentration under analysis.
For the evaluation of intra-day precision (repeatability), samples were injected in the GC/TCD/FID four times within intervals of 2 h (1, 3, 5 and 7 h). Inter-day precision (reproducibility) was evaluated by injecting sample in over 5 different days (1, 3, 7, 15 and 30 days). The relative standard deviations (RSD, in percentage) were determined as according to data obtained during these runs.
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Table 2 Chromatographic conditions tested and established for the GC/TCD/FID method developed for the quantification of inorganic gases and light hydrocarbons
| Parameter | Evaluated range | Established values |
|---|---|---|
| Detector temperature (FID and TCD) / °C | 200 and 250 | 250 |
| Oven temperature | 35 ºC (10 min), rates of 12, 24, 48 and 60 ºC min-1 up to 240 ºC |
35 ºC (10 min), rate of 48 ºC min-1 up to 240 ºC |
| Injector temperature / °C | 200 | 200 |
| Injection mode | split and splitless | split |
| Splitratio | 1:10 to 1:20 | 1:15 |
| Carrier gas | He or Ar | He |
| Flow control mode | linear velocity or pressure 16 kPa (10 min), rates of 12, 24, 48 and 60 ºC min-1 up to 240 ºC |
linear velocity |
Figure 1
(a) TCD chromatograms and (b) FID obtained from the mixture of inorganic gases and light hydrocarbons under the best chromatographic conditions.