Specific and robust ion chromatographic determination of hypothiocyanite in saliva samples

The enzymatic system in saliva, consisting of salivary peroxidase (SPO), hydrogen peroxide (H₂O₂), and thiocyanate (SCN^-), produces hypothiocyanite (OSCN^-) as a high effective antibacterial compound. OSCN^- is of great importance for the natural non-specific antibacterial resistance in the oral cavity. However, no analytical method currently exists to selectively quantify OSCN^- in saliva samples. A robust and specific analytical method for the determination of OSCN^- was developed based on ion chromatography with combined UV and electrochemical detection. Calibration was achieved by calculating a derived calibration factor based on the known ratio of molar extinction coefficients of SCN^- and OSCN^-. Thus, the specific quantification of OSCN^- in saliva samples is possible, as demonstrated here. The median value of 200 saliva samples was determined to be 0.56 mg L^-1 (median), with a maximum of 3.9 mg L^-1; the minimum value was below the detection limit (< 0.09 mg L^-1). The recovery rate in individual saliva samples was 95 ± 8%.