Use of optional gas and collision cell for enhanced sensitivity of the organophosphorus pesticides by GC-ICP-MS

Abstract

Organophosphorus pesticides (OP) are used widely in agricultural and residential applications as insecticides, herbicides and fungicides. This family of chemicals is one that replaced the organochlorine pesticides banned for use in the United States in the 1970s. In this work, inductively coupled plasma mass spectrometry (ICP-MS) is explored as an option for the detection of OPs, monitoring the phosphorus present in the compounds previously separated by GC. Historically, phosphorus has been recognized as one of the elements that is difficult to analyze in an argon plasma. This is due to its relatively high ionization potential (10.5 eV) as well as the inherent presence of the polyatomic interferences ¹⁴N¹⁶O¹H⁺ and ¹⁵N¹⁶O⁺, overlapping its only isotope at m/z = 31. In this work, the use of a commercially available GC-ICP-MS interface, in conjunction with the addition of small amounts of optional gases, has been investigated to obtain enhanced sensitivity and it is found that nitrogen yields an increase in sensitivity of over one order of magnitude. Accompanying this increase in sensitivity is an observed increase in the background due to the above detailed interferences formed in the gas phase. A collision cell is employed to reduce this background without affecting analyte signal using He as collision gas. Instrument detection limits in the high ng L⁻¹ range are reported and the developed methodology is applied to the analysis of tap water samples from the City of Cincinnati.