Meeting NJ Low Level TO-15 Air Testing Method Requirements

Abstract

The following study evaluated the efficacy of pairing a Markes Unity with CIA Advantage preconcentrator with a 30 m Rtx-VMS column to meet the criteria outlined for time-integrated, whole-air, canister samples in the New Jersey (NJ) Department of Environmental Protection (DEP) Site Remediation Program (SRP) Low Level (LL) U.S. EPA TO-15 Method. The majority of the method criteria closely follow the U.S. Environmental Protection Agency’s (EPA) Compendium Method TO-15 for toxic organic compounds (Determination of Volatile Organic Compounds [VOCs] in Air Collected in Specially-Prepared Canisters and Analyzed by Gas Chromatography–Mass Spectrometry [GC-MS]). Results demonstrate satisfactory chromatography, calibration relative response factors (RRFs) with an average relative standard deviation (RSD) of 14.8%, average scan method detection limits (MDLs) of 0.101 ppbv, average replicate precisions of 13.3% RSD, average audit accuracies of 7.6%, and acceptable carryover levels for all 75 target analytes evaluated. These performance levels met all NJ LL TO-15 Method guidelines and were achieved using a 30 m Rtx-VMS column.

Introduction

The Clean Air Act Amendments of 1990 require the U.S. Environmental Protection Agency (EPA) to control 189 hazardous air pollutants (HAPs). In accordance, the U.S. EPA has published a Compendium of Methods for the Determination of Toxic Organic (TO) Compounds in Ambient Air, Second Edition (EPA/625/R-96/010b, January 1999). More specifically, Compendium Method TO-15 (Determination of Volatile Organic Compounds [VOCs] in Air Collected in Specially-Prepared Canisters and Analyzed by Gas Chromatography–Mass Spectrometry [GC-MS]) has been developed for the sampling and analytical procedures for the measurement of a subset of 97 VOCs included in the 189 HAPs [1].

A comprehensive application note on how end users may utilize Restek products to meet the criteria outlined in Method TO-15 is available [2]. However, the state of New Jersey determined that Method TO-15 was insufficient to meet the demands of the Site Remediation Program (SRP). Therefore, the New Jersey (NJ) Department of Environmental Protection (DEP) published their own variant of Method TO-15, which is the New Jersey (NJ) Department of Environmental Protection (DEP) Site Remediation Program (SRP) Low Level (LL) U.S. EPA TO-15 Method [3]. For the most part, the NJ Low Level TO-15 air testing method follows the requirements of U.S. EPA Method TO-15 with the incorporation of the NJ DEP modifications listed below. The main goal of the NJ Low Level TO-15 method is to “provide for a lower reporting limit and additional quality control requirements.” The following is a list, as identified in the method, of what modifications have been made to the U.S. EPA TO-15 in the NJ Low Level TO-15 method.

• Holding times
• Canister types and regulators
• Method detection limits
• Reporting limits
• Clean canister certification levels
• GC-MS tuning and instrument performance check requirements
• GC-MS techniques
• Standard type and concentrations
• Initial and continuing calibration standards
• Laboratory control samples
• Limitation regarding the source of make-up air

Some of the aforementioned changes are straightforward/self-explanatory; therefore, they are outside the scope of this application note. Rather, this application note focuses on the analytical side of the method and the issues commonly reported by laboratories struggling to meet the NJ low level TO-15 air testing method requirements (e.g., calibrating from 0.2 ppbv to 40 ppbv).

Experimental

Analytical System

For all of the experiments, the following analytical system was utilized: a Markes Unity with CIA Advantage preconcentrator paired with an Agilent 7890B gas chromatograph (GC) coupled with an Agilent 5977A mass selective (MS) detector. The preconcentrator and GC-MS parameters may be found in Table I. The Markes Unity with canister interface accessory (CIA) Advantage utilizes one multi-sorbent trap, which is heated and cooled by a thermoelectric (i.e., Peltier) system. This arrangement allows for near instantaneous cooling and heating from -30 °C to 425 °C and, more important, does not require the use of liquid nitrogen. Similar to the well-known purge-and-trap systems, a split is utilized to remove water vapor, nitrogen, oxygen, and carbon dioxide prior to sample delivery to the GC-MS system. All samples were analyzed by preconcentrating 250 mL of sample with the addition of 5 mL of the TO-14A internal standard/tuning mix (cat.# 34408) (bromochloromethane, 1,4-difluorobenzene, chlorobenzene-d5, and 4-bromofluorobenzene) prepared at 500 ppbv concentrations.

Table I: Markes Unity with CIA Advantage and Agilent 7890B-5977A GC-MS Parameters (Default Preconcentration Volume = 250 mL)

Canister Cleaning/Blanks

NJ Low Level TO-15 air testing method blank requirements are identical to U.S. EPA TO-15 blank requirements (i.e., all target analytes less than 0.20 ppbv). Therefore, all canisters were cleaned and blanks were generated as detailed in application note EVAN1725B-UNV, which demonstrated acceptable blank cleaning practices [2].

Calibration Curve

A six-point calibration curve was generated by analyzing a series of canisters (Table II). The default preconcentration volume was 250 mL. Each canister standard was prepared from a 1.0 ppmv stock standard of 75-component TO-15 + NJ mix (cat.# 34396). More specifically, each working standard was generated by using a gas-tight syringe (e.g., cat.# 21275) to inject the volume listed in Table II into an evacuated six-liter SilcoCan air monitoring canister (cat.# 27411) and pressurizing the canister to 34 psig. All canister pressures were verified with an Ashcroft digital test gauge (cat.# 24268). All canisters were pressurized with 50% RH air, which was generated by bubbling the air through a humidification chamber (cat.# 24282). The standard was allowed to age for at least 24 hours, but was no older than 30 days at the time of use.

Table II: Calibration Curve

Method Detection Limits

Method detection limits (MDLs) were determined as prescribed in the Code of Federal Regulations (40 CFR 136, Appendix B). Specifically, MDLs were determined from seven replicate measurements of a low-level standard containing each compound of interest at concentrations near (within a factor of five) the expected detection limits. MDLs were calculated as the standard deviation of the seven replicate measurements multiplied by 3.14 (i.e., the Student's t-value for 99 percent confidence for seven values). MDLs were determined for the analytical system in full scan mode using a 0.20 ppbv standard.

Precision

Precision determinations were made from seven replicate measurements of a 0.20 ppbv standard. Precision for each analyte was calculated as the standard deviation of the seven replicate measurements divided by the average value of the seven replicate measurements and expressed as a percentage as follows:

σ = The standard deviation of an array
μ = The average of an array

Analytical Accuracy

Analytical accuracy for each compound was determined from the analysis of an audit standard prepared at 10.0 ppbv and 50% RH, which was representative of a continuing calibration verification (CCV) standard. Analytical accuracy was calculated as the difference between the nominal concentration of the audit standard and the measured value divided by the nominal concentration of the audit standard, expressed as a percentage as follows:

Carryover

Carryover was evaluated by analyzing a series of blanks and relatively high concentration samples. The following two carryover experiments were conducted to evaluate the carryover effect of a moderately high sample (experiment 1) and an inordinately high sample (experiment 2).

Experiment 1: Blank – 200 ppbv – Blank – 200 ppbv – Blank – 200 ppbv – Blank
Experiment 2: Blank – 1,000 ppbv – Blank – 1,000 ppbv – Blank – 1,000 ppbv – Blank

Carryover was calculated as the concentration in the subsequent blank divided by the concentration in the preceding sample, expressed as a percentage as follows:

Results and Discussion

Results from the calibration, MDL, precision, and accuracy experiments are shown in Table III and discussed relative to the specific method requirements below. It is important to note that the NJ LL TO-15 Method requires 61 compounds; however, the current study evaluated 75. Overall, excellent performance was obtained by the combination of the Markes Unity with CIA Advantage and the 30 m Rtx-VMS column.

Chromatography

U.S. EPA Method TO-15 is applicable to 97 VOCs that are a subset of the 189 HAPs that are included in Title III of the Clean Air Act Amendments; however, only a few laboratories are analyzing all 97 components. Most laboratories are evaluating a standard suite of 65 VOCs for TO-15 (cat.# 34436). Some researchers add or remove a compound or two from the standard 65, but again the majority of laboratories are assessing approximately the same 65 analytes. The NJ Low Level TO-15 method clearly specifies 63 compounds (denoted in Table III), which means the following 10 extra VOCs (cat.# 34398) must be analyzed in addition to the standard 65: n-butane, tert-butyl alcohol, 3-chloroprene, 2-chlorotoluene, cumene, n-nonane, n-pentane, n-propylbenzene, 2,2,4-trimethylpentane, and vinyl bromide. However, it is important to note that Table 2 (pages 34–37) of the NJ Low Level TO-15 air testing method indicates, “ethanol and isopropyl alcohol are listed only because labs report data for these compounds, but dilutions are not required. If looking for these compounds, other methods may be required.” Based on the aforementioned, one may interpret that the NJ Low Level TO-15 method does not require ethanol and isopropyl alcohol and, therefore, is only applicable to 61 VOCs. Regardless, in order to keep things simple and cover all the analytes of interest, the following study evaluated 75 VOCs (cat.# 34396). Although separation of the standard suite of 65 VOCs has already been demonstrated in application note EVAN1725B-UNV [2], the additional 10 compounds (75 total) could pose a chromatographic challenge; however, by utilizing the parameters outlined in Table I, satisfactory separations are achieved (Figure 1).

	Peaks	tR (min)
1.	Propylene	1.21
2.	Dichlorodifluoromethane (Freon 12)	1.25
3.	1,2-Dichlorotetrafluoroethane (Freon 114)	1.37
4.	Chloromethane	1.43
5.	n-Butane	1.45
6.	Vinyl chloride	1.49
7.	1,3-Butadiene	1.51
8.	Bromomethane	1.82
9.	Chloroethane	1.94
10.	Vinyl bromide	2.06
11.	n-Pentane	2.08
12.	Trichlorofluoromethane (Freon 11)	2.09
13.	Carbon disulfide	2.64
14.	1,1-Dichloroethene	2.64
15.	1,1,2-Trichlorotrifluoroethane (Freon 113)	2.68
16.	Ethanol	2.68
17.	Acrolein	3.09
18.	Allyl chloride	3.25
19.	Methylene chloride	3.40
20.	Isopropyl alcohol	3.45
21.	Acetone	3.51
22.	trans-1,2-Dichloroethene	3.62
23.	Hexane	3.75
24.	Methyl tert-butyl ether (MTBE)	3.82
25.	Tertiary butanol	4.13
26.	1,1-Dichloroethane	4.58

	Peaks	tR (min)
27.	Vinyl acetate	5.16
28.	cis-1,2-Dichloroethene	5.56
29.	Cyclohexane	5.83
30.	Bromochloromethane (IS)	5.90
31.	Chloroform	6.12
32.	Carbon tetrachloride	6.22
33.	Tetrahydrofuran	6.36
34.	1,1,1-Trichloroethane	6.37
35.	Ethyl acetate	6.46
36.	2-Butanone (MEK)	6.70
37.	2,2,4-Trimethylpentane	6.84
38.	Benzene	7.03
39.	Heptane	7.07
40.	1,2-Dichloroethane	7.40
41.	Trichloroethylene	8.05
42.	1,4-Difluorobenzene (IS)	8.18
43.	1,2-Dichloropropane	8.90
44.	Bromodichloromethane	9.07
45.	1,4-Dioxane	9.44
46.	Methyl methacrylate	9.45
47.	cis-1,3-Dichloropropene	10.11
48.	Toluene	10.46
49.	Tetrachloroethene	11.05
50.	4-Methyl-2-pentanone (MIBK)	11.19
51.	trans-1,3-Dichloropropene	11.21
52.	1,1,2-Trichloroethane	11.45

	Peaks	tR (min)
53.	Dibromochloromethane	11.70
54.	1,2-Dibromoethane	12.01
55.	2-Hexanone (MBK)	12.58
56.	Chlorobenzene-d5 (IS)	12.89
57.	Chlorobenzene	12.91
58.	n-Nonane	12.99
59.	Ethylbenzene	13.02
60.	m-Xylene	13.27
61.	p-Xylene	13.27
62.	o-Xylene	13.97
63.	Bromoform	14.05
64.	Styrene	14.07
65.	Cumene	14.53
66.	4-Bromofluorobenzene*	14.96
67.	n-Propylbenzene	15.24
68.	1,1,2,2-Tetrachloroethane	15.42
69.	2-Chlorotoluene	15.44
70.	4-Ethyltoluene	15.45
71.	1,3,5-Trimethylbenzene	15.62
72.	1,2,4-Trimethylbenzene	16.28
73.	1,3-Dichlorobenzene	16.74
74.	1,4-Dichlorobenzene	16.92
75.	Benzyl chloride	17.41
76.	1,2-Dichlorobenzene	17.64
77.	1,2,4-Trichlorobenzene	20.28
78.	Hexachlorobutadiene	20.29
79.	Naphthalene	20.72

*Tuning standard

Column	Rtx-VMS, 30 m, 0.25 mm ID, 1.40 µm (cat.# 19915)
	with MXT low-dead-volume connector kit (cat.# 20536)
Standard/Sample	TO-14A internal standard/tuning mix (cat.# 34408)
	75 comp TO15 + NJ mix (cat.# 34396)
Diluent:	Nitrogen
Conc.:	10.0 ppbv 250 mL injection
Injection	on-column
Oven
Oven Temp.:	32 °C (hold 5 min) to 150 °C at 8 °C/min to 230 °C at 33 °C/min
Carrier Gas	He, constant flow
Flow Rate:	2.0 mL/min
Linear Velocity:	51.15 cm/sec @ 35 °C

Detector	MS
Mode:	Scan
Scan Program:
Group Start Time (min) Scan Range (amu) Scan Rate (scans/sec) 1 0.00 35.0 - 226.00 3.8
Transfer Line Temp.:	250 °C
Analyzer Type:	Quadrupole
Source Type:	Extractor
Extractor Lens:	6 mm ID
Source Temp.:	230 °C
Quad Temp.:	150 °C
Electron Energy:	70.0 eV
Tune Type:	BFB
Ionization Mode:	EI
Instrument	Agilent 7890B GC & 5977A MSD

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As shown in the Figure 1 total ion chromatogram (TIC), the 79 VOCs (i.e., 75 target analytes and four internal standards) were separated well in a 22-minute GC analysis. Only one critical coelution was found: chloromethane and n-butane. Chloromethane’s quantitation ion (50 m/z) is a minor ion for butane. Analysts can watch for this coelution during real-world sample analyses by monitoring for butane’s quantitation ion (43 m/z). In addition, in an effort to quantify the bias butane contributes to chloromethane, a calibration curve was prepared as outlined in the Experimental section (Table II). Both chloromethane and butane were present in the calibration standards. Then, a 10-ppbv audit sample that did not contain butane was analyzed over seven replicate injections. The average chloromethane concentration was 8.01 ppbv, which is ~20% different from the audit concentration (note that this was a separate experiment from the accuracy results presented in Table III), but well within the accuracy requirements of ±30% for the NJ Low Level TO-15 method.

The focus of this study was evaluating the efficacy of the Markes Unity with CIA Advantage paired with a 30 m Rtx-VMS column in meeting the requirements of the NJ Low Level TO-15 air testing method; therefore, optimizing the chromatography was not a priority. Consequently, the GC oven program was based on speed-optimized flow (SOF) and optimal heating rate (OHR) [4]. Despite the simple oven program leaving plenty of room for optimization, the chromatography provided by the Markes Unity with CIA Advantage and the 30 m Rtx-VMS column (cat.# 19915) is still very good. For example, ethanol and isopropyl alcohol (IPA) are polar compounds, which often present chromatographic challenges for preconcentrators and GC columns. However, as shown in the extracted ion chromatogram (EIC) in Figure 2, excellent peak shape with no sign of tailing was obtained for both ethanol and IPA.

	Peaks	tR (min)
1.	Ethanol	2.68
2.	Isopropyl alcohol	3.45

Column	Rtx-VMS, 30 m, 0.25 mm ID, 1.40 µm (cat.# 19915)
	with MXT low-dead-volume connector kit (cat.# 20536)
Standard/Sample	TO-14A internal standard/tuning mix (cat.# 34408)
	75 comp TO15 + NJ mix (cat.# 34396)
Diluent:	Nitrogen
Conc.:	10.0 ppbv 250 mL injection
Injection	on-column
Oven
Oven Temp.:	32 °C (hold 5 min) to 150 °C at 8 °C/min to 230 °C at 33 °C/min
Carrier Gas	He, constant flow
Flow Rate:	2.0 mL/min
Linear Velocity:	51.15 cm/sec @ 35 °C

Detector	MS
Mode:	Scan
Scan Program:
Group Start Time (min) Scan Range (amu) Scan Rate (scans/sec) 1 0.00 35.0 - 226.00 3.8
Transfer Line Temp.:	250 °C
Analyzer Type:	Quadrupole
Source Type:	Extractor
Extractor Lens:	6 mm ID
Source Temp.:	230 °C
Quad Temp.:	150 °C
Electron Energy:	70.0 eV
Tune Type:	BFB
Ionization Mode:	EI
Instrument	Agilent 7890B GC & 5977A MSD

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