Determining Volatile Organic Compounds in Industrial Discharges with Gas Chromatography Combined with Mass Spectrometry

method 624

Method 624 is used for determining volatile organic compounds in liquid environmental samples, including industrial discharges, by gas chromatography in combined with mass spectrometry (GC/MS). Inter-laboratory studies performed more than 29 years ago were used to develop and validate this method. The purge and trap parameters were restricted to purging the sample at ambient temperature at 40 ml/minute for 11 minutes and then desorbing it for 4 minutes.

In addition, the Method 624 has a relatively limited list of analytes. Method 624.1 is a performance-based method. Latest technologies such as more sensitive GC/MS instruments, optimized instrument parameters, better purge and traps, and capillary columns will allow laboratories to achieve better precision and % Relative Standard Deviation (%RSD) for calibrations when compared to the prescribed 35% in Method 624 and 624.1. Enabling such high RSD values on majority of compounds usually indicates that the analytical system is uncontrollable and the associated data is likely to be suspect. The analyte list for 624.1 has been expanded and includes many compounds that can also be run by 8260.

4100, 4760, and GC/MS

Figure 1. 4100, 4760, and GC/MS

Now, Internal Standards as well as Surrogate Standards can be varied by concentration and compound to match 8260.  Since, laboratories are allowed to use more stringent acceptance criteria than the prescribed method which means the samples for Method 624.1 and 8260 could also be analyzed simultaneously. Method 624.1 involves running a matrix spike and matrix spike duplicate on 5% of samples from each discharge type sample or every site, which can make it difficult for the laboratory. It also helps to improve the procedure for Method Detection Limit (MDL) studies using 40 CFR Part 136  which many labs are already implementing for Method 8260.

The aim of this article is to use Method criteria from 8260 and 624.1 in such a way that it will most effectively and efficiently enable laboratories to run 8260 and 624 in the same batch.

Experiment

For sample concentration, the instrumentation used was an OI Analytical 4760 Purge and Trap with a #10 trap containing silica gel, Tenax, and carbonized molecular sieve together with a 4100 Sample Processor. For chromatographic separation and detection, an Agilent 7890A/5975C GC/MS was employed. Instrument parameters are shown in Table 1.

Table 1. Instrument Parameters

Purge-and-Trap Eclipse 4760 P&T Sample Concentrator
Trap #10 trap; Tenax® / Silica gel / CMS
Purge Gas Zero grade Helium at 40 mL/min
Purge Time 11 min
Sparge Mount Temperature 45 °C
Sample Temperature (purge) 45 °C
Sample Temperature (bake) 55 °C
Desorb Time 0.5 min
Bake Time 3 min
OI #10 Trap Temperature Ambient during purge
180 °C during desorb pre-heat
190 °C during desorb
210 °C during bake
Water Management 120 °C during purge
Ambient during desorb
240 °C during bake
Transfer Line Temperature 140 °C
Six-port Valve Temperature 140 °C

Gas Chromatograph Agilent 7890A
Column Restek Rtx – VMS
30 meter, 0.25 mm ID, 1.4 µm
Carrier Gas Zero grade helium
Inlet Temperature 240 °C
Inlet Liner Agilent Ultra Inert, 1 mm straight taper
Column Flow Rate 0.8 mL/min
Split Ratio 125:1
Oven Program Hold at 40 °C for 2 min
16 °C/minute to 180 °C
40 °C/minute to 220 °C
Hold at 220 °C for 2.5 min
Total GC Run is 14.25 min

Mass Spectrometer Agilenet 5975C
Mode Scan 35-300 amu
Scans/Second 5.19
Solvent Delay 1.60 min
Transfer Line Temperature 250 °C
Source Temperature 300 °C
Quadrupole Temperature 200 °C
Draw Out Plate 6 mm

50 ng of Bromofluorobenzene (BFB) was injected on all days that the instrument was run for this study.. This was followed by analyzing an eight point calibration, which included all compounds listed as Priority Pollutants in Method 624.1 Table 1; extra purgeables from Method 624.1 Table 2; and many more compounds from the Method 8260 scope of work. The selected list was based on compounds which are representative of volatiles analysis by Method 8260, appropriateness of the method, and availability of standards. Purge and trap may be an inappropriate or complicated method for a number of compounds listed in both methods. For most compounds, the calibration range was 2 ppb to 200 ppb with higher concentrations run for the poor performers such as 1,4-Dioxane, nitriles, alcohols, and ketones.

Both Internal Standards and Surrogate Standards were selected based upon what is readily available in commercial mixes for Method 8260. Next, an initial demonstration of capability (IDOC) was run at 50 ppb for a good number of compounds with the above-mentioned compounds at higher concentrations. A method detection limit study was carried out over a period of three days at different concentrations.

Results

BFB criteria listed in Table 3 of 8260C, Table 4 of 8260B, and Table 4 of Method 624.1 were met on all the three days the instrument was run. The calibration was able to meet the 624.1 RSD criteria of 35% easily. It also met the 15% RSD criteria for Method 8260B and Calibration Check Compound (CCC) criteria and System Performance Check Compound (SPCC) criteria. Method 8260C needs a 20% RSD, so meeting the Method 8260B criteria means all three methods can be used for data reporting. Laboratories will have to check with reporting authorities for this allowance.

Each calibration point was re-quantited using average response factor and linear regression was also weighted with the inverse of concentration (1/C). This provided readback for each calibration level, making sure that all levels had excellent calculated recovery. Using % Relative Standard Deviation (%RSD) and % Relative Standard Error (%RSE), the results obtained for this re-quantitation were assessed.

It is the RSE that indicates whether any point has a high deviation from the curve. It was observed that the %RSE and %RSD were quite similar for quantitation using linear and average response. The MDLs and IDOCs were processed using average response since the %RSD criteria were met for both Method 624.1 and 8260B/C. The DOC recovery and RPD limits were met for the compounds listed in Table 6 of Method 624.1, while for the remainder of the compounds the interim criteria of 30% RPD and 60-140% recovery were easily met. The MDLs also met 40 CFR Part 136 rules for acceptance. The MDL spike level was found to be greater than the quantified MDL, and the ratio of spiked amount to the quantified MDL was observed to be less than 10. Refer Table 2 for results.

50 ppb Calibration Standard

Figure 2. 50 ppb Calibration Standard

Compound Quant
Ion
RL
(ppb)
Avg
RF
% RSD % RSE
(Avg RF Calc.)
% RSE
(Linear 1/C Calc.)
MDL
(ppb)
IDOC
Precision (% RPD)
IDOC Accuracy
(% REC)
Pentafluorobenzene (IS) 168 N/A N/A N/A N/A N/A N/A N/A N/A
Dichlorodifluoromethane 85 2 0.18 4.08 4.07 5.59 0.28 4.97 96.1
*Chloromethane(S) 50 2 0.54 7.01 7.01 11.0 0.17 1.29 101
*Vinyl chloride(C) 62 2 0.42 7.48 7.48 10.7 0.17 1.08 99.9
*Bromomethane 94 2 0.23 6.06 6.06 8.01 0.35 8.22 103
*Chloroethane 64 2 0.23 3.63 3.63 2.95 0.28 1.29 99.6
Trichlorofluoromethane 101 2 0.54 4.82 4.81 7.91 0.30 1.62 101
Ethyl ether 74 2 0.21 4.14 4.19 4.44 0.37 1.41 106
Ethanol 45 100 0.01 6.75 10.3 3.17 26.3 19.8 90.0
*1,1-Dichloroethene(C) 96 2 0.34 5.63 5.66 5.27 0.22 1.18 99.1
Carbon disulfide 76 2 0.94 5.35 5.34 5.90 0.36 1.32 102
1,1,2-Trichloro-1,2,2-trifluoroethane 101 2 0.36 3.56 3.55 4.96 0.22 1.86 101
Methyl iodide 142 2 0.64 3.30 3.32 4.00 0.13 0.84 101
*Acrolein 56 4 0.10 5.10 5.11 3.57 0.75 4.95 107
Allyl chloride 76 2 0.21 1.90 1.94 1.24 0.27 1.94 102
Isopropanol 45 20 0.07 9.21 9.20 10.1 7.15 19.8 99.0
*Methylene chloride 84 2 0.37 3.98 4.01 6.09 0.16 1.06 103
Acetone 58 10 0.08 5.34 5.33 7.90 2.10 8.85 105
*trans-1,2-Dicholroethene 96 2 0.48 9.05 9.12 2.38 0.43 1.26 97.3
Methyl tert-butyl ether 73 2 1.99 4.66 4.60 1.45 0.08 1.27 105
2-Methyl-2-propanol 59 10 0.11 5.59 5.59 5.54 3.98 13.8 106
Acetonitrile 41 20 0.07 4.27 4.26 3.02 1.27 13.9 106
Chloroprene 53 2 1.14 3.50 3.54 2.28 0.11 1.43 104
Diisopropyl ether 45 2 2.07 5.00 4.95 3.81 0.06 1.15 103
*1,1-Dichloroethane(S) 63 2 1.07 1.97 1.98 1.92 0.14 1.34 103
*Acrylonitrile 53 2 0.33 5.72 5.69 5.25 0.26 7.00 112
Vinyl acetate 43 2 1.96 5.73 5.66 1.93 0.24 1.68 106
Ethyl-tert-butyl ether 59 2 1.72 2.76 2.77 2.70 0.12 1.04 103
cis-1,2-Dichloroethene 96 2 0.51 2.19 2.21 2.56 0.20 1.23 102
2,2-Dichloropropane 77 2 0.40 9.19 9.17 12.9 0.34 1.49 102
Bromochloromethane 128 2 0.28 3.53 3.46 3.56 0.15 0.94 104
*Chloroform(C) 83 2 0.84 1.86 1.89 2.65 0.16 1.29 104
Methyl acrylate 55 2 1.02 5.90 5.90 5.13 0.13 2.05 107
*Carbon tetrachloride 117 2 0.71 3.64 3.66 5.45 0.14 2.43 102
Tetrahydrofuran 42 2 0.35 4.15 4.38 2.86 0.35 3.67 108
Dibromofluoromethane (SS) 113 N/A 0.46 1.08 1.09 1.17 N/A 1.58 101
*1,1,1-Trichloroethane 97 2 0.69 3.41 3.41 5.59 0.13 0.48 102
2-Butanone 72 10 0.08 6.01 6.01 5.52 1.99 3.98 106
1,1-Dichloropropene 75 2 0.62 1.98 1.97 2.36 0.20 1.36 104
1,4-Difluorobenzene (IS) 114 N/A N/A N/A N/A N/A N/A N/A N/A
*Benzene 78 2 1.24 2.09 2.10 3.46 0.08 1.33 103
Propionitrile 54 2 0.22 6.89 6.88 3.59 1.28 9.00 99.5
Methacrylonitrile 41 2 0.58 6.08 6.14 3.60 0.41 1.85 106
tert-Amyl methyl ether 73 2 0.69 4.29 4.23 5.26 0.22 1.65 101
1,2-Dichloroethane-d4 (SS) 102 N/A 0.05 1.67 1.67 1.81 N/A 2.11 103
Isobutanol 43 20 0.04 4.39 5.06 4.36 3.10 7.25 99.8
*1,2-Dichloroethane 62 2 0.61 2.46 2.47 4.28 0.14 1.43 104
*Trichloroethene 130 2 0.40 3.05 3.09 4.30 0.16 1.00 102
tert-Amyl ethyl ether 59 2 0.96 2.91 2.89 1.37 0.09 0.67 101
Dibromomethane 93 2 0.27 2.77 2.78 4.88 0.12 2.13 105
*1,2-Dichloropropane(C) 63 2 0.49 2.47 2.46 3.40 0.19 0.66 102
*Bromodichloromethane 83 2 0.48 3.23 3.22 5.41 0.07 0.99 104
Methyl methacrylate 69 2 0.30 4.97 4.97 4.37 0.12 5.17 108
1,4-Dioxane 88 50 0.003 9.28 4.42 4.03 10.7 21.1 96.0
*2-Chloroethyl-vinyl-ether 63 2 0.35 5.83 5.85 3.23 0.18 0.91 105
*cis-1,3-Dichloropropene 75 2 0.54 1.83 1.80 2.60 0.10 0.90 104
Chlorobenzene-d5 (IS) 117 N/A N/A N/A N/A N/A N/A N/A N/A

Compound Quant
Ion
RL
(ppb)
Avg
RF
% RSD % RSE
(Avg RF Calc.)
% RSE
(Linear 1/C Calc.)
MDL
(ppb)
IDOC
Precision (% RPD)
IDOC Accuracy
(% REC)
Toluene-d8(SS) 98 N/A 1.27 0.77 0.76 0.83 N/A 0.66 99.9
*Toluene(C) 92 2 0.96 1.87 1.89 2.04 0.12 1.02 102
2-Nitropropane 43 2 0.29 1.97 1.97 2.16 0.28 2.65 102
4-Methyl-2-pentanone 100 10 0.06 5.93 5.92 2.08 0.87 1.37 104
*Tetrachloroethene 164 2 0.38 2.58 2.59 4.60 0.13 0.89 102
*trans-1,3-Dichloropropene 75 2 0.60 3.00 3.01 2.78 0.10 1.17 104
Ethyl methacrylate 69 2 0.49 7.38 7.33 5.15 0.16 1.47 106
*1,1,2-Trichloroethane 83 2 0.36 2.19 2.16 2.83 0.19 0.96 102
*Chlorodibromomethane 129 2 0.56 1.91 1.91 2.73 0.07 1.45 103
1,3-Dichloropropane 76 2 0.56 2.05 2.08 2.38 0.08 0.87 103
1,2-Dibromoethane 107 2 0.48 3.00 3.00 4.26 0.09 1.28 102
2-Hexanone 43 10 0.72 8.40 8.40 5.88 0.30 1.63 107
*Chlorobenzene(S) 112 2 1.18 2.31 2.31 4.04 0.08 0.94 103
*Ethylbenzene(C) 91 2 1.82 1.77 1.77 2.55 0.12 0.80 103
1,1,1,2-Tetrachloroethane 131 2 0.39 2.43 2.44 4.09 0.17 1.32 102
m,p-Xylenes 106 4 0.69 2.98 2.98 2.03 0.13 0.58 105
o-Xylene 106 2 0.63 1.90 1.89 2.04 0.11 0.31 103
Styrene 104 2 1.10 4.01 3.98 1.63 0.17 0.85 105
*Bromoform(S) 173 2 0.43 2.14 2.13 3.14 0.19 1.19 103
Isopropylbenzene 105 2 1.62 2.80 2.78 3.00 0.08 0.89 104
cis-1,4-Dichloro-2-butene 75 2 0.21 4.99 4.98 4.67 0.20 1.75 104
1,4-Dichlorobenzene-d4 (IS) 152 N/A N/A N/A N/A N/A N/A N/A N/A
4-Bromofluorobenzene (SS) 95 N/A 0.94 1.35 1.36 1.46 N/A 1.05 99.7
n-Propylbenzene 91 2 4.43 3.79 3.84 3.19 0.06 1.45 104
Bromobenzene 156 2 1.14 3.21 3.23 3.92 0.12 1.34 102
*1,1,2,2-Tetrachloroethane(S) 83 2 1.28 3.34 3.33 4.61 0.16 1.39 101
2-Chlorotoluene 91 2 2.85 2.41 2.41 3.10 0.06 0.91 103
1,3,5-Trimethylbenzene 105 2 2.96 3.75 3.73 2.88 0.09 0.86 103
1,2,3-Trichloropropane 75 2 1.51 2.65 2.80 2.68 0.27 1.72 103
trans-1,4-Dichloro-2-butene 53 2 0.68 2.62 2.62 2.87 0.21 1.07 103
4-Chlorotoluene 91 2 2.65 2.69 2.67 2.87 0.12 1.08 103
tert-Butylbenzene 119 2 2.42 3.00 2.95 3.03 0.10 0.97 101
1,2,4-Trimethylbenzene 105 2 2.98 3.88 3.88 2.83 0.08 1.37 104
sec-Butylbenzene 105 2 3.71 2.94 3.00 3.40 0.09 1.48 102
p-Isopropytoluene 119 2 3.04 3.92 3.87 2.25 0.10 1.27 103
*1,3-Dichlorobenzene 146 2 1.92 2.89 2.90 4.54 0.14 1.08 100
*1,4-Dichlorobenzene 146 2 1.92 2.21 2.20 3.58 0.12 0.77 101
n-Butylbenzene 91 2 2.91 3.10 3.14 2.20 0.06 1.12 102
*1,2-Dichlorobenzene 146 2 1.77 2.00 2.00 3.42 0.11 1.29 99.6
1,2-Dibromo-3-chloropropane 75 2 0.26 4.72 4.75 4.84 0.56 4.26 97.7
Hexachlorobutadiene 225 2 0.55 3.61 3.60 3.51 0.17 1.50 97.6
1,2,4-Trichlorobenzene 180 2 1.04 3.56 3.57 3.82 0.13 1.23 98.7
Naphthalene 128 2 3.26 5.18 5.14 4.24 0.16 2.40 99.7
1,2,3-Trichlorobenzene 180 2 1.00 4.07 4.08 5.49 0.14 1.75 99.0

*Priority Pollutant (40 CFR 423, Appendix A)
IS - Internal Standard
SS – Surrogate Standard
S – 8260B System Performance Check Compound (SPCC)
C – 8260B Calibration Check Compound (CCC)

Conclusions

Method performance is considerably enhanced with the allowance of better purge and trap parameters, such as the considerable instrument enhancements which have been made over the past 29 years as well as the 0.5 minute desorb and heating sample during purge. For these reasons, method performance is better than Method 624.1, enabling the laboratories to integrate QC criteria with Method 8260 and thus boost sample capacity and productivity.

References

  1. USEPA Method 624.1: Purgeables by GC/MS, December 2014.
  2. USEPA EPA Method 8260B: Volatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC/MS), Revision 2, December 1996.
  3. USEPA EPA Method 8260C: Volatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC/MS), Revision 3, August 2006.
  4. USEPA 40 CFR Part 136, Appendix B. Definition and Procedure for the Determination of the Method Detection Limit.
  5. Parr, Jerry L. 2017. Proposed Changes to the Clean Water Act, Methods 608, 624, and 625. Catalyst Information Resources Presentation.
  6. Parr, Jerry L. 2017. 2016 Chemistry Standard. Volume 1, Module 4. NELAC Institute Presentation.
  7. Burrows, Richard. 2017. Why We Need a Standard on Calibration. NELAC Institute Environmental Measurement Methods Expert Committee Presentation.

This information has been sourced, reviewed and adapted from materials provided by OI Analytical.

For more information on this source, please visit OI Analytical.

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