Simple and rapid screening of the thiocyanate level in saliva for the identification of smokers and non-smokers by capillary electrophoresis with contactless conductivity detection†
A simple and rapid capillary electrophoresis method with contactless conductivity detection for direct determination of thiocyanate in saliva to differentiate between smokers and non-smokers is proposed. Simple saliva preparation was performed by centrifugation and the dilute and shoot method (1 : 1, v/v) with a running buffer prior to hydrodynamic injection. The running buffer was 20.0 mM His/MES at pH 6.00 containing 0.1 mM CTAB as the electroosmotic flow modifier. Maleate anions were employed as the internal standard for the precision of the response factor of electrophoresis separation which was carried out at −8.0 kV (266 V cm−1) with a total analysis time of 3.5 min per sample. A linear calibration curve for thiocyanate in the concentration range 0.2–4.0 mM was obtained (r2 > 0.999). The limit of quantification was 0.12 mM which is sufficient for the quantitative determination of thiocyanate in saliva for the purpose of identification of smokers and non-smokers. Intra-day and inter-day precisions were 0.7–1.7% RSD and 2.4–6.4% RSD, respectively. Accuracy based on the percentage recovery of spiked saliva samples was in the range of 72–141% (n = 18). The measured thiocyanate levels were significantly different to classify non-smokers from smokers; a cut-off value of 1.0 mM is proposed to separate the two groups. This method is convenient and rapid, suitable for screening of a large number of subjects, such as in clinical work or health-care surveys.