Optimization of compound-specific chlorine stable isotope analysis of chloroform using Taguchi design of experiments.

Rationale Chloroform, a probable human carcinogen, is commonly detected in various concentration levels in many surface water and groundwater sources. Compound-specific chlorine stable isotope analysis (Cl-CSIA) is significant in investigating the fate of chlorinated contaminants in the environment. Analytical conditions should, however, be thoroughly examined for any isotopic fractionation. In this study, we simultaneously optimize three analytical parameters for a robust online Cl-CSIA of chloroform using Taguchi design of experiments. METHODS For Cl-CSIA, a purge and trap autosampler coupled to a gas chromatograph in tandem with a quadrupole mass spectrometer, with electron ionization in SIM mode was used. Using the Taguchi method, the dominant parameter affecting the results of Cl-CSIA for chloroform was identified through concurrent investigation of the signal to noise ratios of three parameters, each at three levels; purging time (5, 10, 15 minutes), transfer time (80, 120, 160 seconds) and dwell time (20, 60, 100 milliseconds). Moreover, the optimum combination of the levels was identified. RESULTS The purging time, with a maximum signal to noise ratio, resulted in highest influence on the isotope ratios determined. It was further refined through additional experiments to sufficiently extract chloroform from the aqueous phase. Accordingly, 8 minutes of purging time, 120 sec transfer time and 100 ms dwell time were the optimum conditions for Cl-CSIA of chloroform. Post optimization, a precision of ± 0.28 ‰ was achieved for 8.4 nmol of chloroform (equivalent to 0.89 μg or app. 25 nmol Cl-mass on column). CONCLUSIONS A simple online method for Cl-CSIA of chloroform was optimized with Taguchi design of experiments. Taguchi method was very useful for the optimization of the analytical conditions. However, the purging conditions should be fine-tuned and selected so that sufficient extraction of a target compound is confirmed to acquire a stable and higher precision of the method.