Nanogram level quantification of molybdenum(vi) by novel hyphenated SDME/DRS-FTIR in human biological fluid

Abstract

A novel hyphenated single-drop micro-extraction (SDME) diffuse-reflectance Fourier-transform infrared spectroscopy (DRS-FTIR) technique was employed for the quantification of hexavalent molybdenum, i.e., Mo(VI) in human blood serum and urine. Mo(VI) was extracted as the Mo(VI) : HDPBA complex into a single-drop of dichloroethane solution of N¹-hydroxy-N¹,N²-diphenylbenzamidine (HDPBA). Mo(VI) formed a 1 : 2 complex in the organic phase with HDPBA in acidic medium, which was further analyzed by diffuse-reflectance Fourier-transform infrared spectroscopy (DRS-FTIR). The factors affecting the SDME process, such as extraction solvent, size of the acceptor drop volume, pH, reagent concentration, extraction time and stirring rate, were optimized for better extraction efficiency. The extracted micro-drop was analyzed using DRS-FTIR, the most steady and the strongest vibrational IR peak at 911 ± 2 cm⁻¹ (υ₁) corresponding to the asymmetric stretching mode of MoO₄²⁻ was selected for the quantification of Mo(VI). The limit of detection (LOD) and limit of quantification (LOQ) of the method were 8.0 ng mL⁻¹ and 26.4 ng mL⁻¹, respectively. The absorbance and peak area were determined by the SDME/DRS-FTIR method, which showed excellent linearity with a correlation coefficient value of 0.99 for the concentration range of 1–100 ng mL⁻¹. The standard deviation (SD) and relative standard deviation (RSD) for 10 replicate measurements were found to be 0.13 ng mL⁻¹ and 1.3%, respectively, at a level of 10 ng mL⁻¹ Mo(VI) in the aqueous phase.