Determination of Thiocyanates

Cyanogen iodide and sulfate ions are formed. It is a back- titration. The excess iodine is titrated with a thiosulfate solution in hydrogen carbonate medium. When the medium is acidified before the titration of the excess iodine, the reaction follows a different course. It becomes 

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Chattaraj S, Das AK. 1992. Indirect determination of thiocyanate in biological fluids using atomic absorption spectrometry. Spectrochica Acta 47(5) 675-680. 

Liu X, Yun Z. 1993. High-performance liquid chromatographic determination of thiocyanate anions by derivatization with pentafluorobenzyl bromide. J Chromatogr A 653 348-353. 

Miura Y, Koh T. 1991. Determination of thiocyanate in human urine samples by supressed ion chromatography. Anal Sci 7(Suppl Proc Int Congr Anal Sci, 1991, Pt 1) 167-170. 

Pettigrew AR, Fell GS. 1972. Simplified colorimetric determination of thiocyanate in biological fluid and its application of investigation of toxic amblyopias. Clin Chem 18 996-1000. 

Tominaga MY, Midio AF. 1991. Modified method forthe determination of thiocyanate in urine by ion-exchange chromatography and spectrophotometry. Rev Farm Bioquim Univ Sao Paulo 27(1) ... 

Han, K. and Boulange, M. 1963. Determination of thiocyanate in milk by a technique of immuno-diffusion. Clin. Chim. Acta 8, 779-785. 

The method is based on the partitions of the anions to a cationic micelle phase and shows different selectivity from ion exchange chromatography In a kinetic method [13] for the determination of thiocyanate, sulphite and sulphide the anions are reacted with 5,5 dithiobis (2-nitrobenzoic acid) in aqueous cetyltrimethyl/ammonium bromide micelles. 

Details of X-ray structure determinations of thiocyanate complexes of these metals are given in Table XXII. Not included are the incomplete results which indicated sulfur bonding in K3Cr(SCN)e-4H20 (793) —these findings have been superseded by the recent results on the hexa-N-thiocyanatochromate salt of a complex lanthanide cation (427). 

Granda Valdes, M., Diaz-Garcia, M.E. Determination of thiocyanate within physiological fluids and environmental samples. Current practice and future trends Crit. Rev. Anal. Chem., 2004, 34,1-13... 

An important example of an uncatalyzed method is the fixed-time method for the determination of thiocyanate ion based on spectrophotometric measurements of the red iron(III) thiocyanate complex. The reaction in this application is... 

Other indirect methods involve reactions with the mercury(II) complexes of diphenylcarbazone [20] or Methylthymol Blue [21], or the displacement of thiocyanate ion from AgSCN or Hg(SCN)2 by bromide, followed by the spectrophotometric determination of thiocyanate with ferric ions [22,23]. 

Thiocyanate is separated from cyanide by distilling off HCN from a weakly acid medium. With bromine and chloramine-T, thiocyanate is converted into cyanogen bromide and cyanogen chloride, respectively, and determined as a polymethine dye by the benzidine-pyridine method or pyridine—barbituric acid method [38—40]. The latter method has been applied for continuous determination of thiocyanate in blood plasma and in urine [40]. 

A. Tanaka, M. Miyazaki, and T. Deguchi, New Simultaneous Catalytic Determination of Thiocyanate and Iodide by Flow Injection Analysis. Anal. Lett., 18 (1985) 695. 

No studies of humans have demonstrated inhibition of iodide transport into breast milk of mothers from thiocyanate in diet. In many countries the most important determinant of thiocyanate levels in blood is tobacco smoking, as discussed above, and smoking is associated with similar increases in thiocyanate in blood as may be found from diets with high cyanide content. We therefore investigated the effect of maternal smoking on iodine transfer to the breast-fed neonate. 

Ensafi, A.A., Khayamian, T., Tabaraki, R. Simultaneous kinetic determination of thiocyanate and sulfide using eigenvalue ranking and correlation ranking in principal component-wavelet nenral network. Talanta 71, 2021-2028 (2007)... 

The oxidation of thiocyanate is also well-known to cause electrode passivation. Although it is usually attributed to accumulation of electrolysis products, it may be just deactivation of the surface by consumption of the oxide. The latter occurs, for example, with the oxidation of As(III) at a Pt (oxide-coated) electrode.We have found that with an electrode modified with the ruthenium-containing inorganic film, mvRu, the problem is alleviated. The general characteristics of flow injection determinations of thiocyanate with an amperometric detector based on the mvRu electrode are summarized in Table 1. The sample throughput was calculated as described above. 

Table 1. Flow injection amperometric determination of thiocyanate at a glassy carbon electrode modified with a Ruthenium-containing inorganic film.

Amini, M.K., S. Shahrokhian, and S. Tangestaninejad (1999). PVC-based cobalt and manganese phthalocyanine coated graphite electrodes for determination of thiocyanate. Anal. Lett. 32(14), 2737-2750. 

Y. Yamamoto and K. Ueda, Determination of thiocyanate in human serum by ion chromatography. Analyst (London), 113, 389, 1988. 

The publications of these chemists are so significant that it is worthwhile to reconstruct an example of their thinking, as described by Swift (10) "These workers were interested in the determination of thiocyanate. They either knew or learned that the anodic oxidation of thiocyanate to cyanide and sulfate with 100% current efficiency is difficult if not impossible of attainment. However, it was known that thiocyanate could be quantitatively, stoi-chiometrically, and rapidly oxidized by bromine in acid solutions with 100% current efficiency. Therefore they added a relatively high concentration of a soluble bromide to an acid solution containing the thiocyanate, anodically produced bromine, and allowed this bromine to diffuse into the solution and to oxidize the thiocyanate. By working with relatively large samples of thiocyanate, and by measuring the quantity of electricity involved by means of a chemical coulometer, they demonstrated that an accuracy within 1 ppt could be attained."... 

An SIA system has been proposed for the spectrophotometric determination of thiocyanate as Fe(SCN)2 The system, shown in Figure 7.19, is fully computerized and able to monitor thiocyanate in... 

Schematic depiction of an SiA anaiyzer used for the determination of thiocyanate with Fe(iii). Detector spectrophotometer (Xmax = 480 nm) HC hoiding coii RC reaction coii SV seiection vaive.

J.F. van Staden, A. Botha, Spectrophotometric determination of thiocyanate by sequential injection analysis. Anal. Chim. Acta 403 (2000) 279-286. 

Michigami Y, Fuji K, Ueda K, Yamamoto Y (1992) Determination of thiocyanate in human saliva and urine by ion chromatography. Analyst 117 1855-1858... 

Cox JA, Gray T, Kulkami KR (1988) Stable modified electrodes for flow-injection amperometry application to the determination of thiocyanate. Anal Chem 60 1710-1713... 

It has been known for a long time that thiosulfate is present in normal human urine, but reliable methods for the determination of fairly low concentrations have not been available. A method based on the precipitation of the nickel-ethylenediamine complex of thiosulfate followed by iodometric determination was reported many years ago, but gives according to our experience unreliable results. We have earlier described a simple colorimetric method for determination of thiosulfate, based on the cyanolysis of thiosulfate to thiocyanate by the action of cyanide and cupric ions followed by determination of thiocyanate as its ferric ion complex. Unfortunately, this method is not sensitive enough for direct application to urine and, furthermore, other urinary compounds interfere in the cyanolysis reaction. It may, however, be used for assay of the very... 

We have recently developed a simple and specific method " for determination of thiocyanate, based on our finding that the ion-exchange resin Lewatit MPTO80 has a high affinity for thiocyanate. 

IT. G. E. Boxer and J.C. Richards, Determination of thiocyanate in body fluids. Arch. Biochem. 39 292 (1952). l8. P. Lundquist, J. Martensson, B. Sorbo and S. Ohman, Method for determining thiocyanate in serum and urine, Clin. Chem. 

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