18 Environmental Laboratory
Table 3. Calculated recoveries (%) for n = 5 tap water samples spiked with diluted raw gasoline and fortified with standard solution at a concentration of 1000 and 10,000 µg/L (ppb). Average concentrations are calculated subtracting the raw gasoline matrix.
Gasoline Range Organics Average Blank Matrix Conc. (µg/L, n = 5)
Methyl tert-butyl ether (MTBE)
Benzene Toluene
Ethylbenzene
m-Xylene, p-Xylene o-Xylene
1,3,5-Trimethylbenzene 1,2,4-Trimethylbenzene Naphthalene Average
7 4
142 25 54 54 8
31 7
Spiked
Conc. 1 (µg/L)
1000
1000 1000 1000 1000 1000 1000 1000 1000
Average
Measured Conc.
(µg/L, n = 5) 1,130
890 990 890 900 920 910 920
1,160 970
Average Recovery (%, n = 5)
113
89 99 89 90 92 91 92
116 97
Spiked Conc. 2 (µg/L) 10,000
10,000 10,000 10,000 10,000 10,000 10,000 10,000 10,000
Average
Measured Conc.
(µg/mL, n = 5) 10,300
9,300 9,300 9,400 9,300 9,300 9,400 9,200
10,500 9,600
Average Recovery (%, n = 5)
103
93 93 94 93 93 94 92
105 96
window ranged from MTBE (RT = 2.92 min) to naphthalene (RT = 11.96 min) according to the Wisconsin method and from 2-methylpentane (RT = 2.62 min) to 1,2,4-trimethylbenzene (RT = 9.25 min) according to EPA 8015 C method. The “baseline to baseline” integration did not include the solvent peak. Calculated correlation coefficient (R2
) were 1.000 and the residual values
(measured as % RSD of average response factors) were ~4% for both retention time windows confirming an excellent linearity. MDL, LOQ, and recovery were calculated for the total peak area calibration curves applying Equations 1, 2, and 3. Calibration curves and calculated MDL, LOQ, and percent recovery (total area integration applied) are shown in Figure 3. As an example, a chromatogram of a tap water sample (5 mL) spiked with raw gasoline solution (5%) (single component and EPA 8015 C total area integration) as well as the quantitation results obtained for the analyzed samples (single components and total area quantitation) are reported in Figure 4. A series of blank water vials (n = 5) was run after completing the sample sequence. No compound carry-over was detected in the blanks as demonstrated in Figure 5.
Table 4. Peak area %RSDs obtained from n = 10 consecutive injections of tap water spiked with the standard solution at 50 µg/L (ppb) and n = 10 consecutive injections of tap water spiked with diluted raw gasoline. Average peak area %RSDs are 0.91 and 1.1 respectively.
Peak area %RSD Gasoline Range Organics
Methyl tert-butyl ether (MTBE) Benzene Toluene
Ethylbenzene
m-Xylene, p-Xylene o-Xylene
1,3,5-Trimethylbenzene 1,2,4-Trimethylbenzene Naphthalene Average
Tap Water Spiked with Stock Solution (n = 10) 1.0
0.93 0.87 0.78 0.85 0.92 0.98 0.99 0.82 0.91
Tap Water Spiked with
Raw Gasoline (n = 10) 1.0 1.2 1.1 0.8 1.5 1.2 1.2 1.1 1.2 1.1
Conclusions The results presented here demonstrate the suitability of the
TriPlus 500 HS autosampler in combination with the Trace 1310 GC-FID for GRO analysis in environmental samples.
• Excellent linearity with correlation coefficient R2 = 1.000 was
obtained for all analytes. The Instant Connect Flame Ionization Detector (FID) allows sensitive detection of organic compounds as demonstrated by the calculated MDL and LOQ (average MDL = 1.4 µg/L (ppb) and average LOQ = 4.6 µg/L (ppb)).
• The advanced Quick Spin Shaking (QSS) feature of vials and direct column connection to the valve manifold ensure efficient analyte extraction. In the experiments performed here, the average compound recovery for matrix spiked samples was >96%.
• The low bleed and superior inertness of the TraceGOLD column allowed for highly reliable results. The high column efficiency allowed for a fast GC oven ramp supporting short analysis time (all analytes elute in <13 min) and high sample throughput to easily meet the needs of routine laboratories. Moreover, up to 240 sample vials can be accommodated into the trays for unattended 24-hour operations.
• The pneumatic control and the sample path inertness of the TriPlus 500 HS autosampler ensure reliable and reproducible analyte injection and transfer. Average peak area RSDs (n = 10 consecutive injections) were 0.91% for tap water samples spiked with the standard solution at 50 µg/L (ppb) and 1.1% for tap water spiked with diluted raw gasoline.
• The efficient purging of the pneumatic circuit of the TriPlus 500 HS autosampler eliminated potential for carry-over; no matrix components or gasoline organics were detected in the blank vials after a sequence of real samples contaminated with GRO chemicals.
Gasoline Range Organics
Total Total
Spiked Conc. (µg/L)
12.5 12.5 Average
Measured Conc. (µg/L, n = 7)
Calculated MDL (µg/L)
1.9 2.2
Calculated LOQ (µg/L)
Total Area Integration (Wisconsin method) 11.4
Total Area Integration (EPA 8015 C method) 13.0
6.1 7.0
Average Recovery (%, n = 7)
91 105
Figure 3. Calibration curves were obtained integrating the total area within the gasoline range at each calibration level for Wisconsin (A) and EPA 8015 C (B). R2
, response factor relative standard deviations (% RSD) as well as calculated MDL, LOQ, and percent recovery (C) are shown.
assessments are reported in Table 4. Excellent repeatability was obtained for both standard and matrix spiked samples with an average %RSD of 0.91 and 1.1, respectively.
Quantitation of GRO
in real water samples Tap water samples (5 mL, n = 10) were spiked with 1 µL of raw gasoline solution (5%) and analyzed. According to Wisconsin
and EPA method 8015 C,4 GRO quantitation is based on a direct
comparison of the total area within a defined retention time window to the total peak areas of the gasoline component standard. Therefore, the calibration curves previously plotted using the single component peak integration were calculated integrating the total peak area and used to quantitate the spiked water samples. The total area was obtained integrating all the chromatographic peaks within the retention time
References
1. Thermo Fisher Scientific, Chromeleon CDS Enterprise – Compliance, Connectivity, Confidence, BR72617-EN0718S.
2. EPA 821-R-16-006 Definition and Procedure for the determination of the Method Detection Limit, Revision 2, December 2016.
3. Wisconsin DNR, Modified GRO, Method for Determining Gasoline Range Organics, PUBL-SW-140, September 1995.
4. EPA Method 8015 C, Nonhalogenated organics by gas- chromatography, Revision 3, February 2007.
• Quantitation of spiked samples is simplified with the Chromeleon CDS advanced reprocessing features allowing for easy single component and total peak area integration and compound quantitation.
Overall, the data shows that the TriPlus 500 gas chromatography static headspace autosampler provides a reliable analytical tool allowing environmental laboratories to produce consistent results with outstanding analytical performance for GRO quantitative analysis in water samples.
AET October / November 2019
www.envirotech-online.com
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