VOCs via Static Headspace/GC/MS is not old hat - new DIN 38407-43

Introduction

Clean water is a valuable asset to mankind. Every government therefore has its own regulation on water quality. For the territory of the European Union the “EU Water Framework Directive” gives the governmental frame for water quality monitoring.  The chemical composition of surface water and ground water is described in terms of Priority Substances, which are in fact a mixture of substances and substance classes. A good portion of them can be observed via GC techniques, especially the Volatile Organic Compounds (VOC).

Due to the installed base of instruments, static headspace is generally the first choice in measuring VOCs in Germany as well as in the rest of Europe. Mass spectroscopy has become the most popular detection system in this analytical field during the last 10 years. Using the requirements of the European Water Framework Directive and the most popular instrumentation, a new DIN Standard method was created and validated in a qualified round robin under leadership of chairwomen Ute Brüll-Pehl from the governmental lab from LANUV (Regional Authority for Nature, Environment and Customer Care) in Düsseldorf. The resulting DIN 38407-43 is available as a draft.

To show the capability of this DIN method a data set of 53 VOCs was chosen as base for the validation round robin, discussed and approved by the responsible DIN working group (Tab. 1).

Reference Material

As different compounds show different relative response factors in the mass spectrometer due to varying ionization efficiencies and different headspace distribution equilibrations, the calibration and the validation of a multi parameter method requires multiple calibration runs at a wide range of concentrations.  This is needed to create an acceptable calibration curve for each compound. To minimize this work, Restek introduced a multi component mix with three different concentration levels for the different compounds, based on an extensive study of distribution equilibria and detection responses for defined qualifier ions. This complex study, done by the LANUV lab under leadership of Mrs. Brüll-Pehl, led to a reference standard mix with comparable peak areas per compound at each dilution, which makes it easy to run a calibration with only one dilution series. This interesting concept leads to a new and powerful strategy in setting up Mega Mixes or Multi-Component Mixes.

GC Column

The Restek RXI-624Sil MS column, a modified 624 phase with Silarylene backbone, is the ideal column for this method because it shows an optimized separation, especially for the earliest eluting compounds.

The following measurements show the use of both Restek reference standards as well as GC column technology to fulfill all requirements of the new DIN 38407-43 draft and the European Water Framework Directive.

Measurements

Shown measurements were performed by Axel Semrau GmbH, Germany, using a DANI Master SHS Gas chromatograph with Static Headspace Autosampler, combined with a Thermo Fisher Trace DSQ II mass spectrometer.

Reference standards from Restek were used for calibration (VOA Standard Kit #1-3 + Vinylchloride, cat. No. # 567783, #567784, #567785, #567787)

A 60 m x 0.25 mm x 1.4 μm Restek Rxi-624Sil MS was chosen as GC-Column (cat. No. # 13869)

Headspace Sampler settings

Oven temp.:                         80°C Manifold temp.:                    120°C Transferline temp.:               200°C Incubation time:                   30 min Aux pressure:                       1 bar Nitrogen Pressure equilibration:          0.2 min Injection time:                      30 s Injection mode:                    Standard Vial Venting:                        Ja (yes?) Injection volume:                 1 mL Sample volume:                   10 mL Vial volume:                         20 mL

GC Settings

Oven program: 40 °C (1 min) -> 4 °C/min -> 120 °C (5 min) -> 4 °C/min -> 140 °C (4 min) -> 25 °C/min -> 280 °C (4.4 min) Injector temp.:                     200 °C Carrier gas flow:                  1.2 mL/min Helium Split ratio:                            1:10

Mass Spec. settings

Ionisation mode:                  EI Ion source temp.:                 200 °C Transferline temp.:               250 °C Data sampling rate:       5 spectra/sec, full scan

Compounds and Target Ions as discussed in the DIN Group (Tab. 1)

Compound	target ion	qualifier 1	qualifier 2
Dichloromethane	84	86	49
Trichloromethane	83	85	47
1,1,1-Trichloroethane	97	99	117
Tetrachloromethane	117	119	121
Trichloroethene	130	95	132
1,1,2-Trichloroethane	97	83	99
Tetrachloroethene	166	129	164
1,1-Dichlorethane	63	83	65
1,1-Dichloroethene	61	96	63
1,2-Dichloroethane	62	64	98
1,2-Dichloropropane	63	62	76
2,3-Dichloropropene	75	110	77
Hexachloroethane	117	201	119
1,1,2-Trichlorotrifluoroethane	101	151	103
Chloroprene	53	88
Hexachlorobutadiene	225	260	227
1,2-Dibromomethane	107	109
1,2-Dichlorobenzene	146	111	148
1,3-Dichlorobenzene	146	111	148
1,4-Dichlorobenzene	146	111	148
1,2,3-Trichlorobenzene	180	145	182
1,2,4-Trichlorobenzene	180	145	182
1,3,5-Trichlorobenzene	#	#	#
Vinylchloride	62	64	56
Allylchloride	#	#	#
cis-1,2-Dichloroethene	96	61	98
trans-1,2-Dichloroethene	96	61	98
cis-1,3-Dichloropropene	75	110	77
trans-1,3-Dichloropropene	75	110	77
Benzene	78	77	50
Toluene	91	92	65
Ethylbenzene	91	106
o-Xylene	91	106
m/p-Xylene	91	106
Styrene	78	104
Chlorobenzene	112	77	114
2-Chlorotoluene	91	126
3-Chlorotoluene	91	126
4-Chlorotoluene	91	126
Cumol	105	120
n-Propylbenzene	91	120
MTBE	73	57	61
ETBE	59	87	57
1,1,1,2-Tetrachloroethane	131	117	133
1,2,4-Trimethylbenzene	105	120
1,3,5-Trimethylbenzene	105	120
Bromodichloromethane	83	85	129
Tribromochloromethane	173	175	171
Dibromochloromethane	129	127	131
Naphthaline	128	102
Dichlorodiisopropylether	45	121
Biphenyl	154	153	76
TAME	55	73
Internal Standards
Toluene-D8	98	100
1,2-Dichloroethane-D4	65	67	102
4-Bromofluorobenzene	175	176	95

First part of the TIC Chromatogram of the new Restek Reference Standard Kit

Second part of the TIC Chromatogram of the new Restek Reference Standard Kit

TIC chromatogram of a doped wastewater sample

TIC Chromatogram of a doped surface water sample

 

The complete measurements, performed by Axel Semrau GmbH, can be found here:

http://www.axel-semrau.de/en/Downloads.html

A complete analysis of the described round robin will be part of the validation documents of the DIN 38407-43, possibly in final form at the end of this year.

Restek Corp. wants to thank Mrs. Brüll-Pehl and her laboratory staff for the intensive and successful collaboration and Dr. Rüdiger Kohl, Axel Semrau GmbH, for performing the shown measurements.