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

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

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 wastewater sample

TIC Chromatogram of a doped surface water 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.

 

 

 

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