Liquid Chromatographic-Electro-Chemical Technique for Determination of Ethylenethiourea Residues

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Abstract
A high performance liquid chromatographic-electrochemical (HPLC-EC) technique was developed to selectively determine ethylenethiourea (ETU) at residue levels without derivatization. ETU was eluted from a C-8 column with water, a phosphoric acid electrolyte solution was added to the column eluate, and then ETU was detected with an electrochemical detector containing a Au/Hg working electrode. The HPLC-EC system produced a sharp chromatographic peak for ETU that was detected by the Au/Hg electrode at an applied potential of +0.36 V. With detector sensitivity adjusted so that 10 ng ETU produced a 50% full scale deflection peak (1% baseline noise), the detector's response was linear from 2 to 400 ng ETU. No peaks were observed in potato and spinach controls, and only small apparent ETU peaks of 7 and 3 ppb, respectively, were found in apple and grape controls. Detector response was equivalent to 90% of actual ETU added (0.1 ppm) to purified spinach extracts. Crop coextractives from apples, grapes and potatoes did not affect detector response to ETU at the 0.1 ppm fortification level.