Thiocyanate levels in human saliva: quantitation by Fourier transform infrared spectroscopy

A new quantitative method, based on Fourier transform infrared spectroscopy, was developed to evaluate the thiocyanate concentration in human saliva. Saliva samples were collected following a typical protocol and infrared spectra obtained from very small volumes (5 microl) deposited on a barium fluoride substrate. Exogenous potassium thiocyanate was used for calibration of the endogenous thiocyanate. This methodology does not require separation or extraction procedures. Human saliva spectra contain a characteristic marker band, due to thiocyanate, at 2058 cm-1. The integrated area of this band can be used for linear regression analysis and provides a good correlation between band area and thiocyanate concentration. Recovery of thiocyanate added to saliva was 100%. Centrifugation and dialysis experiments demonstrated that thiocyanate in saliva exists as a free or loosely bound ion. Saliva collected in the afternoon from 25 different subjects had a thiocyanate concentration of 0.83 +/- 0.42 (mean +/- SD) mmol/liter. In 4 subjects whose circadian pattern was investigated there was evidence of a higher thiocyanate concentration in saliva samples collected in the morning hours.