Dichloromethane-Enhanced Negative Ion Chemical Ionization for the Determination of Polychlorinated n-Alkanes

Abstract

The use of dichloromethane/methane reagent gas mixtures is described as an alternative to conventional electron capture negative ionization for the determination of polychlorinated n-alkanes (PCAs). A nearly exclusive formation of [M + Cl]- adduct ions was observed suppressing the generation of other fragment ions. The resulting enhanced selectivity and sensitivity lowered quantification limits to 3 ng for a technical PCA mixture and 10.5-13.5 pg for single congeners. Response factors for congeners of different degrees of chlorination varied by not more than a factor of 2. Interferences from other polychlorinated compounds present in environmental samples such as toxaphene or chlordanes were suppressed by a factor of 5 or more. The technique was applied for the determination of the composition of technical PCA mixtures as well as for the analysis of PCAs in North Sea dab liver.

Limitations of low resolution mass spectrometry in the electron capture negative ionization mode for the analysis of short- and medium-chain chlorinated paraffins

“…For quantification, a selection of a retention time window for the main elution range of a congener group would allow us to improve selectivity somewhat, although at the risk of introducing a systematic error due to the cut-off of minor humps. [12] and later Zencak et al [13] showed that the relative abundance of the adduct ion is much higher for lower chlorinated congeners (4-5 chlorine atoms) than for higher chlorinated ones. The [M+Cl] -ion was the base ion for the investigated single tetrachlorodecanes, but it decreased to about 60% for the pentachlorodecane and 10% for the hexachlorodecane [13].…”

“…[12] and later Zencak et al [13] showed that the relative abundance of the adduct ion is much higher for lower chlorinated congeners (4-5 chlorine atoms) than for higher chlorinated ones. The [M+Cl] -ion was the base ion for the investigated single tetrachlorodecanes, but it decreased to about 60% for the pentachlorodecane and 10% for the hexachlorodecane [13]. As can be seen from Table 4, the [M+Cl] -ions from SCCP congeners with 4-6 chlorine atoms can also cause mass overlap.…”

An analytical method for chlorinated paraffins and their determination in soil samples

“…Using electron capture negative ion high/low-resolution mass spectrometry, the number of carbon and chlorine atoms in the molecules are determined by monitoring [M-Cl] -ions of specific m/z value corresponding to formula groups [3][4][5]. Reth et al [6] changed the ionization mode of CPs using ECNI with CH 4 /CH 2 Cl 2 as carrier gas and achieved precise quantitative results of chlorinated CP congeners, which also occurs using metastable atom bombardment (MAB) coupled with HRMS [7]. Based on electron ionization tandem mass spectrometry (EI-MS 2 ), Zencak et al [8] selected m/z 91, 102 as common fragment ions for all CPs and determined the total CP amount with CIDs (collision-induced dissociation) by detecting m/z 91 → 53, 102 → 65.…”

Presence of Chlorinated Paraffins in Sediments from the North and Baltic Seas

“…The mass spectrometer was tuned to optimal performance using perfluorotributylamine at m/z 283, 414, and 452. CH 2 Cl 2 (Scharlau, Barcelona, Spain) was introduced through a modified transfer line by adding a T-piece and a small glass bulb of 6 ml volume filled with dichloromethane (Zencak et al 2003b). A needle valve was used to meter the dichloromethane pressure, CH 4 / CH 2 Cl 2 -NICI was performed at a total reagent gas pressure of 2.0 mbar (1.5 Torr) measured at the transfer line inlet and a CH 4 /CH 2 Cl 2 ratio of 4:1.…”

“…CPs were detected in the selected ion monitoring (SIM) mode using the most abundant isotope ion [M+C1] ) of each CP compound (dwell time 75 ms per ion) and m/z 419.8 for the internal standard 13 C 10 -trans-chlordane. Further details are described elsewhere (Zencak et al 2003b).…”