Thiocyanate method

Hydroperoxide (OOH) groups can be determined colorimetrically with thiocyanate [NH SCN—FeS04(NH4)2S04 6H20] reagent [26,1406,1713, 1714, 1996, 2327]  

The application of colorimetric methods for the analysis of hydroperoxides in polymers requires the sample to be dissolved, or at least swollen, in a solvent (the reactants have to diffuse into the amorphous regions in the polymer matrix). The polymer sample should be in contact with the reagent for a minimum of 30 min (in the dark). A mixture of benzene-methane (95 4 or 92 8) can be used as a solvent for polyolefins or poly(vinyl chloride). The colorimetric measurements are carried out at A = 512.5 nm (A, of the ferric thiocyanate complex). The concentration of hydroperoxide in the polymer sample is calculated according to the expression  

A = absorbance of a sample in a 1 cm cell, as measured against the blank solution (thiocyanate reagent in pure benzene) e = stoichiometric coefficient of hydroperoxide interaction with the reagent 

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A. Thiocyanate method Discussion. Iron(III) reacts with thiocyanate to give a series of intensely red-coloured compounds, which remain in true solution iron(II) does not react. Depending upon the thiocyanate concentration, a series of complexes can be obtained these complexes are red and can be formulated... 

Mercury(II) thiocyanate method Discussion. This second procedure for the determination of trace amounts of chloride ion depends upon the displacement of thiocyanate ion from mercury(II) thiocyanate by chloride ion in the presence of iron(III) ion a highly coloured iron(III) thiocyanate complex is formed, and the intensity of its colour is proportional to the original chloride ion concentration ... 

Figure 14 also demonstrates the principle that sometimes extraction into an organic solvent increases the intensity of the color. This is true, for example, for ferric thiocyanate, where extraction into an organic solvent will increase the sensitivity of iron determination to that obtainable with the phenanthrolines. The advantage of the iron ferric thiocyanate method in organic solvents is the fact that it is insensitive to pH changes, which is not true for the phenanthroline procedures (19). 

Parent acrylonitrile molecule and its metabolites have been measured in blood and urine, but, except for measurement of thiocyanate, methods have not been developed for routine monitoring of exposed humans. 

The thiocyanate method involves measurement of the peroxide value using linoleic acid as substrate and has also been widely used to measure the antioxidant activity in plant-based foods such as ginger extracts (Kikuzaki and Nakatani 1993), fruit peels (Larrauri and others 1996 1997), extracts from vegetable by-products (Larrosa and others 2002 Llorach and others 2003 Abas and others 2006 Peschel and others 2006), blueberry juice, wines, and vinegars (Su and Chien 2007). 

The pH, EC and Fe3+ were used as control parameters. The first two were measured with an Orion probe combined pH/ATC electrode Triode and a conductivity cell DuraProbe ref. 0133030. Fe3+ was determined by molecular absorption (thiocyanate method). Mineralogical composition of the precipitates was determined by X-ray powder diffraction (XRD). Scanning electron microscopy, combined with an energy dispersive system (SEM-EDS), allowed the observation of morphological and compositional aspects of the precipitates. 

Give the theory and procedure for the determination of Mo(VI) by the thiocyanate method. 

Iwaski, I., S. Utsumi, K. Hagino, and T. Ozawa, A New Spectropho-tometric Method for the Determination of Small Amounts of Chloride Using the Mercuiy Thiocyanate Method, Bull. Chem. Soc. Jpn., 29, 860-864 (1956). 

Loftus Hills, G. and Thiel, C. C. 1946. The ferric thiocyanate method of estimating peroxide in fat or butter, milk and dried milk. J. Dairy Res. 14, 340-353. 

Won, Ck. H. Sensitive Spectrophotometric Determination of Submicrogram Amounts of Orthophosphate in Natural Water by a Modified Molybdenum(V)-thiocyanate Method. J. Chem. Soc. Japan, Pure Chem. Sect. 85, 859 (1964). 

Figure 7.7. Agarose gel electrophoresis of total RNA. Total RNA from mouse skin (panel a, lane 2) and two human cadaver skin samples (panel b, lanes 1 and 2) were isolated by guanidine thiocyanate method and size fractionated on denaturing formaldehyde containing 1% agarose gel and stained with 0.5 pg/mL ethidium bromide. Note that in case of mouse skin RNA, two distinct ribosomal RNA bands (upper 28S and lower 18S bands) are clearly visible. In contrast, in case of human skin samples, which were collected several hours postmortem, there is partial RNA degradation as is evident by fuzzy 28S and 18S ribosomal RNA bands. RNA degradation is more pronounced in one of the samples than the other (panel b, compare lane 1 and lane 2). Ribosomal RNA bands are indicated by arrowheads. RNA size markers (Invitrogen, Carlsbad, CA) in the range 0.24 to 9.5 kb are in lane 1 (panel a) and lane 3 (panel b).

Aryl thiocyanates, ArSCN, are formed by direct thiocyanation of the aromatic nucleus or by treating diazonium salts with metallic thiocyanates. Methods for the thiocyanation of organic compounds have been reviewed. ... 

In addition to the DCP determinations, other analytical techniques were employed as necessary. One of these was the colorimetric determination of ferric ion by the thiocyanate method (2). This was used to calculate the ferrous iron content which is the difference between the total iron, determined by DCP, and the trivalent iron obtained by the thiocyanate reaction. 

A change of valence of some ions effectively prevents their reaction with certain reagents. As an example, Nb can be determined by the thiocyanate method in presence of Fe if this had been reduced to Fe(ri). 

Thiocyanate methods vary widely in sensitivity. The methods for determining Te, Fe(IlI), and Nb are highly sensitive, whereas those for U and Co are less sensitive. 

In the indirect thiocyanate method (not very sensitive, e 5 10 ) the determination of chloride [20-28] has been based on the displacement of SCN ion from the mercury(II) thiocyanate complex by chloride ions, to give a stable mercury chloride complex. After addition of Fe(III) in excess, the red Fe(SCN) complex is formed, and the absorbance is measured at 480 nm. In the FIA method the UV detection has been applied in the absence of Fe(III) ions [29]. 

The indirect thiocyanate method has been applied for determining chloride in blood serum [27], water [2,55,56], plants [57,58], industrial waste waters [24], geological materials [59], organic substances [60,61], barium sulphate [28], silicate minerals [62], and catalysts [63]. The FIA technique was used in determination of chlorine in ethanol [64]. 

The thiocyanate method is suitable for the determination of relatively large amounts of cobalt. Methods with nitroso-naphthols or nitroso-R salt are specific but not very sensitive. An example of a really sensitive method is that using the azo reagent, 5-Br-PADAP. 

The thiocyanate method has been used for determining cobalt in vitamin B12 [94], steel [24,94], and nickel [25]. Cobalt present in considerable amounts in alloys with aluminium, nickel, chromium, manganese, copper, and iron was determined by the differential spectrophotometric analysis [95]. 

Iron can be determined by the thiocyanate method in aqueous and aqueous-acetone media, or after extraction of the coloured complex with a suitable organic solvent. 

Extraction increases the sensitivity of the thiocyanate method. The molar absorptivity of the Fe(III) thiocyanate complex solution in MIBK (see procedure below) is 2.4-10 (a = 0.43) at A.max = 495 nm. The position of the absorption maximum for the complex varies between 470 and 530 nm, depending on the medium. 

The thiocyanate method has been used for determining iron in waters [139,140], in organic materials [141], nickel and its salts [142], non-ferrous metals [143], titanium tetrachloride [144], and alkalis [8]. 

Trace amounts of molybdenum have been separated from natural waters by retention of the anionic Mo-thiocyanate complex on the anion-exchanger Dowex 1. Mixtures of 2 A/ HCIO4 and 1 M HCl are used for the elution [24]. The Mo-thiocyanate complex has also been concentrated on the anion exchanger Amberlite XAD [25,26], with the use of acetone as the eluent [25]. Molybdenum has been retained on anion-exchange columns from an HCl medium prior to being determined by the thiocyanate method [27-30]. Mo has been sorbed selectively (pH 3.5) on the anion exchanger Sephadex G-25, from which it can be eluted withEDTA [31]. 

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