Thiocyanate is the end product of detoxification of cyanide compounds and excreted in urine, saliva and serum. The determination of SCN− is particularly important in saliva, urine, and blood serum because it is considered to be a biomarker in distinguishing smokers from non-smokers. Saliva of non-smokers contains thiocyanate concentrations between 0.5 and 2 mM while in smokers concentrations as high as 6 mM can be found. Human plasma levels are 2–3 mg/L in non-smokers and 9–12 mg/L in smokers [2]. Chronically elevated levels of thiocyanate in body fluids are known to be toxic and its relation to local goiter, vertigo, or unconsciousness has been pointed out [3]. Another important sample where the determination of the thiocyanate anion is of interest is in water, especially wastewaters. At low pH values, thiocyanate present in waste water converts into cyanide ion in the presence of oxidants and thereby causes profound damage to aquatic life. Thiocyanate is administered as drug in the treatment of thyroid conditions [4] and to achieve an optimal antibacterial effect of the lactoperoxidase system in milk [5]. Therefore, the determination of thiocyanate in food, wastewater, and biological samples is of important practical significance. Therefore, precise knowledge of the thiocyanate content in biological fluids and environmental samples is mandatory.