Fourier transform infrared spectroscopy combined with single-drop micro-extraction for quantitative analysis of tungstate in biological samples

This work demonstrates a simple, rapid and convenient method based on Fourier transform infrared (FTIR) spectroscopy combined with single-drop micro-extraction (SDME) and chemometrics for the analysis of tungstate. Nanogram quantities of tungstate using N1-hydroxy-N1, N2-diphenylbenzamidine (HDPBA), were quantitatively extracted into chloroform at 4.0-6.0 M sulphuric acid medium by the SDME method. The method is fairly selective and almost all common ions including Mo(VI), Cr(VI) etc. do not interfere in the extraction. The tungstate formed an orange-red colored, 1:2 complex with HDPBA in chloroform. This complex was characterized by FTIR spectroscopy, and tungstate in it was determined. The factors affecting SDME were optimized for better extraction efficiency. The most steady and strongest asymmetric vibrational (υ3) band at 840 ± 2 cm−1 was selected for the quantitative analysis of the tungstate-HDPBA complex. The calibration curves for the concentration range of 1.0-100.0 ng mL−1 were prepared with the help of the chemometric software TQ analyst using partial least squares (PLS) regression models. The limit of detection and limit of quantification of the method were found to be 3.0 ng mL−1 and 10.0 ng mL−1, respectively. The standard deviation and relative standard deviation for the concentration 10 ng mL−1 for 10 replicate measurements were found to be 0.14 ng mL−1 and 1.3%, respectively. The method was applied to human blood and urine samples for quantification of tungstate.