Direct Compound-Specific Stable Chlorine Isotope Analysis of Organic Compounds with Quadrupole GC/MS Using Standard Isotope Bracketing

Abstract

A method has been developed for the direct determination of the stable chlorine isotope composition (delta(37)Cl) of organochlorines that eliminates sample preparation, achieves precision comparable to earlier techniques while improving the sensitivity, and makes use of benchtop gas chromatography-quadrupole mass spectrometry instruments (GCqMS). The method is based on the use of multiple injections (n = 8-10) of the sample, bracketed by a molecularly identical isotopic standard with known delta(37)Cl, determined using off-line thermal ionization mass spectrometry (TIMS). Mass traces of two isotopologues differing by one chlorine isotope were used to calculate delta(37)Cl values. Optimization of mass spectrometry and peak integration parameters as well as method validation was achieved using tetrachloroethene (PCE), p,p'-dichlorodiphenyltrichloroethane (DDT), and pentachlorophenol (PCP), spanning a delta(37)Cl range of -5.5 to +3.2 per thousand vs SMOC. Injecting 1.6-1100 pmol resulted in standard deviations (1sigma) of 0.6-1.3 per thousand, and the delta(37)Cl results agreed with values independently measured with TIMS. The method was tested by determining the Rayleigh fractionation during evaporation of pure liquid PCE, resulting in a chlorine isotopic enrichment factor of epsilon(Cl) = -1.1 +/- 0.4 per thousand. Furthermore, position-specific delta(37)Cl analysis based on analysis of DDT mass fragments was evaluated. The GCqMS-delta(37)Cl method offers a simplified yet sensitive approach for compound-specific chlorine isotope analysis.

Compound-specific bromine isotope compositions of one natural and six industrially synthesised organobromine substances

“…A similar range in the d 37 Cl of compounds with various properties (i.e. chlorophenols and chlorinated ethenes) was found by Aeppli et al [29] In the bromine industry, the bromine comes from bromide-rich brine wells and from the Dead Sea waters (up to 50 000 ppm Br). The brines are treated through flushing with chlorine gas admixed with air.…”

Identification of abiotic and biotic reductive dechlorination in a chlorinated ethene plume after thermal source remediation by means of isotopic and molecular biology tools

“…A DB-5 column (30 m, 0.25 mm, 0.25 μm, Agilent) with a constant helium flow of 1.2 mL·min −1 was used to perform chromatographic separation. Molecular ions were targeted and calculations were carried out according to the method developed by Aeppli et al, 2010. Calibration with two external standards (δ 37 Cl EIL1 = +0.3 ‰ and δ 37 Cl EIL2 = −2.5‰ for PCE and δ 37 Cl EIL1 = +3.05‰ and δ 37 Cl EIL2 = −2.70‰ for TCE) which were formerly characterized by the Holt method (Holt et al, 1997) Molecular biology analysis: DNA extraction for the 454 pyrotag analysis was carried out at SiREM (Guelph, ON, Canada) as follows: Sterivex™ filters were opened and the filter membrane with attached biomass was removed and placed into the Bead Solution of a PowerMag DNA Isolation Kit (MoBio, Carlsbad, CA, USA) and pulverized using a sterile pipet tip.…”

Carbon and chlorine isotopologue fractionation of chlorinated hydrocarbons during diffusion in water and low permeability sediments

“…All four chlorine isotopologues intensities of TCE (mass 130, 132, 134, 136) were quantified using the GC-qMS. Thus raw chlorine isotopic ratios were calculated with the method developed by SakaguchiSoder et al (2007) and further improved by Aeppli et al (2010), which takes all chlorine isotopologue of TCE (130, 132, 134 and 136) into account. The raw chlorine isotopic ratios of TCE were then calculated using the following equation:…”