Desorption corona beam ionization coupled with a poly(dimethylsiloxane) substrate: broadening the application of ambient ionization for water samples.

Current direct analysis methods in mass spectrometry (MS) are predominantly focused on desorbing and ionizing samples in the solid phase. Some sampling difficulties are associated with liquid (solution) or gas samples. The present study has expanded direct MS analysis to solution samples by using the desorption corona beam ionization (DCBI) technique in combination with poly(dimethylsiloxane) (PDMS) substrate sampling. Typically, the PDMS substrate is dipped in water for microextraction of pesticide compounds and then is transferred to an MS ion source for desorption and ionization. This approach improves the detection limit for DCBI and allows more organic compounds in complex mixtures to be identified within seconds. The practical application of this device is demonstrated by identifying five pesticides (acephate, isoprocarb, dimethoate, dichlorvos, and dicofol) in water. The obtained detection limits of pesticides are 1 μg/L, the measured dynamic ranges are 3 orders of magnitude, the calculated correlation coefficients are between 0.939 and 0.979 at concentration levels of 5-5000 μg/L, and the repeatabilities defined as a relative standard deviation of five successive injections are in the range of 13-17%. The results indicate that the DCBI technique coupled with PDMS sampling is an excellent method for the analysis of organic pesticides in solution, and it also opens up a new avenue for direct MS studies of solution samples with general importance.