title: Ammonium chloride salting out extraction/cleanup for trace-level quantitative analysis in food and biological matrices by flow injection tandem mass spectrometry.
abstract: A sample extraction and purification procedure that uses ammonium-salt-induced acetonitrile/water phase separation was developed and demonstrated to be compatible with the recently reported method for pesticide residue analysis based on fast extraction and dilution flow injection mass spectrometry (FED-FI-MS). The ammonium salts evaluated were chloride, acetate, formate, carbonate, and sulfate. A mixture of NaCl and MgSO4, salts used in the well-known QuEChERS method, was also tested for comparison. With thermal decomposition/evaporation temperature of <350°C, ammonium salts resulted in negligible ion source residual under typical electrospray conditions, leading to consistent method performance and less instrument cleaning. Although all ammonium salts tested induced acetonitrile/water phase separation, NH4Cl yielded the best performance, thus it was the preferred salting out agent. The NH4Cl salting out method was successfully coupled with FI/MS/MS and tested for fourteen pesticide active ingredients: chlorantraniliprole, cyantraniliprole, chlorimuron ethyl, oxamyl, methomyl, sulfometuron methyl, chlorsulfuron, triflusulfuron methyl, azimsulfuron, flupyrsulfuron methyl, aminocyclopyrachlor, aminocyclopyrachlor methyl, diuron and hexazinone. A validation study was conducted with nine complex matrices: sorghum, rice, grapefruit, canola, milk, eggs, beef, urine and blood plasma. The method is applicable to all analytes, except aminocyclopyrachlor. The method was deemed appropriate for quantitative analysis in 114 out of 126 analyte/matrix cases tested (applicability rate=0.90). The NH4Cl salting out extraction/cleanup allowed expansion of FI/MS/MS for analysis in food of plant and animal origin, and body fluids with increased ruggedness and sensitivity, while maintaining high-throughput (run time=30s/sample). Limits of quantitation (LOQs) of 0.01mgkg(-1) (ppm), the 'well-accepted standard' in pesticide residue analysis, were achieved in >80% of cases tested; while limits of detection (LODs) were typically in the range of 0.001-0.01mgkg(-1) (ppm). A comparison to a well-established HPLC/MS/MS method was also conducted, yielding comparable results, thus confirming the suitability of NH4Cl salting out FI/MS/MS for pesticide residue analysis.
authors.affiliation: DuPont Crop Protection, Stine-Haskell Research Center, Newark, DE 19714, USA. sergio.c.nanita@dupont.com
authors.forename: Sergio C
authors.initials: SC
authors.lastname: Nanita
authors.forename: Nilusha L T
authors.initials: NL
authors.lastname: Padivitage
mesh_terms: D000643:Ammonium Chloride / Q000737:chemistry*; D000818:Animals; D001826:Body Fluids / Q000737:chemistry; D005504:Food Analysis; D006540:Herbicides / Q000032:analysis; D007306:Insecticides / Q000032:analysis; D010573:Pesticide Residues / Q000032:analysis* / Q000302:isolation & purification / Q000652:urine; D051381:Rats; D053719:Tandem Mass Spectrometry; D013696:Temperature
chemical_list: D006540:Herbicides; D007306:Insecticides; D010573:Pesticide Residues; D000643:Ammonium Chloride