Method For Determination Of Thiocyanate Research Articles

Determination of thiocyanate in exhaled breath condensate

Thiocyanate is a heme peroxidase substrate that scavenges oxidants produced during inflammation and regulates host defense. In cystic fibrosis (CF) patients, increased airway thiocyanate levels are associated with improved lung function. Research on airway thiocyanate is limited, however, because convenient non-invasive airway sampling methods, such as exhaled breath condensate (EBC), yield low concentrations that are difficult to detect with available assays. In the present study, we developed a method for the determination of thiocyanate in dilute samples using isotope dilution headspace gas chromatography-coupled high-resolution, accurate-mass mass spectrometry (GC-HRMS). The method reliably quantified as little as 4 pmol thiocyanate in EBC and could detect even lower amounts. We successfully measured thiocyanate in EBC from seven healthy donors, with a mean ± SD of 27 ± 16 nM and a median inter-assay coefficient of variation of 10.4% over six months. The method was applied to other biological fluids (plasma from the same visit as EBC donation; bronchoalveolar lavage fluid [BALF] from infants with CF; and healthy adult mouse BALF), giving reliable quantification of samples ranging from 10 nM to 100 µM. Thiocyanate concentrations in fluids besides EBC were (from lowest to highest): 0.73 ± 0.39 µM in BALF of healthy adult mice (n = 6); 1.4 ± 1.4 µM in BALF from infants with CF (n = 24); 46 ± 22 µM in the plasma of adult volunteers (n = 7). These results demonstrate the utility of this new method for clinical determination of thiocyanate in EBC and other biological fluids.

Kinetic spectrophotometric method for trace determination of thiocyanate based on its inhibitory effect

A kinetic spectrophotometric method for the determination of thiocyanate, based on its inhibitory effect on silver(I) catalyzed substitution of cyanide ion, by phenylhydrazine in hexacyanoferrate(II) is described. Thiocyanate ions form strong complexes with silver(I) catalyst which is used as the basis for its determination at trace level. The progress of reaction was monitored, spectrophotometrically, at 488 nm ( λ max of [Fe(CN) 5PhNHNH 2] 3−, complex) under the optimum reaction conditions at: 2.5 × 10 −3 M [Fe(CN) 6] 4−, 1.0 × 10 −3 M [PhNHNH 2], 8.0 × 10 −7 M [Ag +], pH 2.8 ± 0.02, ionic strength ( μ) 0.02 M (KNO 3) and temperature 30 ± 0.1 °C. A linear relationship obtained between absorbance (measured at 488 nm at different times) and inhibitor concentration, under specified conditions, has been used for the determination of [thiocyanate] in the range of 0.8–8.0 × 10 −8 M with a detection limit of 2 × 10 −9 M. The standard deviation and percentage error have been calculated and reported with each datum. A most plausible mechanistic scheme has been proposed for the reaction. The values of equilibrium constants for complex formation between catalyst–inhibitor ( K CI), catalyst–substrate ( K s) and Michaelis–Menten constant ( K m) have been computed from the kinetic data. The influence of possible interference by major cations and anions on the determination of thiocyanate and their limits has been investigated.

English

The cyanide overload of 40 cassava (gari) processing workers, 25 frequent consumers of cassava foods and 20 cigarette smokers (all Nigerians) were assessed using a new simple kit method for determination of thiocyanate (cyanide metabolite) in urine. The mean thiocyanate measured in the urine of three groups of cassava processing workers were 9.48±2.8, 8.70±2.23, and 7.46±2.57 ppm. The mean thiocyanate measured in the urine of frequent cassava consumers and cigarette smokers were 3.57±0.6 and 13.99±13.81 ppm, respectively. The urine samples of 15% of the processing workers measured ³10 ppm SCN (172µmol/L), while two urine samples from the smokers measured 30, and 44 ppm SCN. The cyanide contents of some cassava based foods commonly consumed among Nigerians were determined and ranged from 0.68± 0.31 to 0.88±0.21 for total cyanide and 0.14±0.03 to 0.52±01 mgCN - 100g -1 DM for free cyanide. The toxicological implications of these findings are discussed. Keywords: Cyanide overload, thiocyanate, simple kit method, cassava foods. African Journal of Biotechnology Vol.3(7) 2004: 358-361

Indirect determination of thiocyanate with ammonium sulfate and ethanol by extraction-flotation of copper.

A new method for the indirect determination of thiocyanate with ammonium sulfate and ethanol by extraction-flotation of copper in the presence of ascorbic acid is described. A small amount of Cu(II) is reduced to Cu(I) by ascorbic acid, then Cu(I) is precipitated with SCN-. In the course of phase separation of ethanol from water, the precipitated CuSCN stays in the interface of ethanol and water. A good linear relationship is observed between the flotation yield of Cu(II) and the amount of SCN-. Using 1.0 ml of 1 x 10(-3) M ascorbic acid solution, 50 micrograms of Cu(II), 3.5 g of (NH4)2SO4 and 3.0 ml of ethanol with a total volume of 10 ml, the concentration of thiocyanate could then be determined by determining the flotation yield of Cu(II). The detection limit for thiocyanate is 5 x 10(-5) M. Every parameter was optimized and the reaction mechanism was studied. The method is simple and rapid and it was successfully applied to the determination of thiocyanate in urine and saliva of smokers and non-smokers and in venous blood of patients infused with sodium nitroprusside.

Simple Method for Determination of Thiocyanate in Urine

It would be useful to develop a simple kit method for determination of thiocyanate in urine, which could be used to monitor cyanide overload in cassava-consuming populations. The method was based on the quantitative oxidation of thiocyanate in acid permanganate at room temperature in a closed vial with liberation of HCN, which reacted with a picrate paper. For semiquantitative analysis in the field, the colored picrate paper was matched with a color chart prepared using known amounts of KSCN. In the laboratory, a more accurate result was obtained by elution of the colored complex in water and measurement of the absorbance at 510 nm. Over the range 0-100 mg/L, there was a linear relationship given by the equation: thiocyanate content (mg/L) = 78 x absorbance. The picrate thiocyanate method gave no interference with urine samples containing protein at less than 7 g/L, 21 amino acids, histamine, glucose, NaCl, urea, blood, and linamarin. For 53 urine samples analyzed by an accurate column method and the thiocyanate picrate method, a regression line gave very good agreement (r(2) = 1. 000). Quantitative recoveries of thiocyanate added to urine samples were obtained with the picrate method. A simple picrate kit for determination of thiocyanate in urine was developed and is available free of charge for workers in developing countries.

Determination of thiocyanate by carbonyl sulphide (OCS) generation and gas-phase molecular absorption spectrometry

A method for determination of thiocyanate by gas-phase molecular absorption spectrometry is described. The proposed method is based on the continuous generation of carbonyl sulphide and preconcentration in a liquid nitrogen trap. Later, the product is volatilised and the absorbance at 224 nm is measured. Under the optimised conditions, the calibration graph was linear for 2–80 μg ml −1, with a detection limit of 1 μg ml −1. No metal ions interfered. The method was tested with saliva samples from non-smokers and smokers; the results show that it is possible to distinguish between these two categories of individuals.

An improved method for determination of thiocyanate in plasma and urine.

An improved spectrophotometric method is described for the determination of thiocyanate in plasma and urine. Thiocyanate is adsorbed on a weak anion-exchange resin with strong affinity for chaotropic ions, and eluted with perchlorate. Thiocyanate is then chlorinated by hypochlorite and quantified according to the König (J Prakt Chem 1904; 69:105-37) reaction by use of isonicotinic acid and 1,3-dimethyl-barbituric acid. The method affords a simple, rapid and sensitive assay for thiocyanate and has a detection limit of 0.93 mumol/l. At thiocyanate concentrations of 107.1 and 167.4 mumol/l in plasma and urine the within-day CVs were 0.69% and 1.1% respectively, and the total imprecision measured for a period of 65 days was 0.98%. Analytical recoveries were quantitative both with urine and plasma samples.

A simple method for determination of plasma thiocyanate.

We describe a method for the determination of thiocyanate in plasma from blood collected under field conditions in heparinised glass capillary tubes. After deproteinisation of plasma with perchloric acid, thiocyanate is directly determined colorimetrically by the König reaction with sodium hypochlorite as the chlorinating reagent and barbituric acid as the coupling agent. This simple method cannot be applied to urine as the latter contains interfering compounds.

Spectrophotometric determination of thiocyanate via coprecipitation and thermal decomposition of copper(I) thiocyanate

A method for determination of thiocyanate (6–100 μg described. It is based on the coprecipitation of copper(I) thiocyanate with copper(I) iodide, followed by decomposition of copper(I) thiocyanate in air at 450°C. The decomposition products are CuS, CuO, SO 2, CO 2 and N 2. Released sulphur dioxide is absorbed in sodium tetrachloromercurate(II) solution, and determined spectrophotometrically with bleached p-rosaniline. The method is unaffected by the presence of halides, sulphide, sulphite and thiosulphate.