Cyanide spectrophotometric methods

Agrawal V, Cherian L, Gupta VK. 1991. Extraction spectrophotometric method for the determination of hydrogen cyanide in environmental samples using 4-aminosalicylic acid. Intern J Environ Anal Chem 45 235-244. 

Drikas M, Routley BI. 1988. Spectrophotometric method for the determination of total cyanide in wastewater samples. Analyst 113 1273-1276. 

Harris et al. [8] has described methods for the determination of cyanide in these materials based on either spectrophotometry using p-phenylene diamine pyridine or gas chromatographically following conversion of cyanide to cyanogen bromide. Cyanide is extracted from the sample by digestion with phosphoric acid. Recoveries were in the range 96-99% (spectrophotometric method) and 90-96% (gas chromatographic method). 

Many of the UV-VIS spectrophotometric methods (shown in Tables 12.3 and 12.6) have been automated by using flow analyzers. Thus, nitrite and nitrate,50,82 ammonium,50,83 orthophosphate,50,84,85 silicates,50,86 chloride,50,87 cyanide,50,88 and sulfate50,89 are measured by CFA and FIA. Oxygen is measured by iodometric titration51,90 and electrochemical methods91 (Table 12.7). Other dissolved gasses (Table 12.2) are measured by ISE-based gas sensors. 

A spectrophotometric method was developed for the quantitative evaluation of cyanide ions in the concentration range of 25 ppb by using a silica-supported Fe(acac)3 column. The concentration of CN was calculated from the absorbance at 295 nm. VO(acac)2 and luminol (55) show a chemiluminescent reaction which served to devise a micelle-mediated method for determination of V(IV) . ... 

Cruz-Landeria A, Lopez-Rivadulla M, Concheiro-Carro L, Ferndndez-Gomez P, Tabernero-Duque MJ. A new spectrophotometric method for the toxicological diagnosis of cyanide poisoning. J Anal Toxicol 2000 24 266-70. 

Selectivity in spectrophotometric methods for determining metals with dithizone is attained by controlling the acidity of the medium and using masking agents such as cyanide, EDTA, thiosulphate, or iodide. 

The most important spectrophotometric methods for determining cyanide are based on the formation of polymethine dyes. These methods are highly sensitive and specific. The benzidine-pyridine method is often used. Lower colour stability is a drawback of the pyrazolone method. The barbituric acid method can also be recommended. 

In an extractive spectrophotometric method for determining cyanide, a coloured ion-pair formed between cyanide complex of Fe(II) and bathophenanthroline is extracted into chloroform [20]. 

Cyanide enhances the redox potential of copper(II). Spectrophotometric methods for determining cyanide based on this property involve oxidation of phenolphthalein [27]. Phenolphthalein has been used in determining cyanide by the flow injection technique [27]. 

Sensitive extraction-spectrophotometric methods are based on the extractable (into CHCI3, 1,2-diehloroethane, benzene, or toluene) ion-associates of basic dyes and anionic Ag complexes with cyanide [35,36], iodide [37,38], and bromide [39]. In these methods, use has been made of such dyes as Crystal Violet [35,39], Brilliant Green [38,39], Malachite Green [39], Methylene Blue [36], and Nile Blue A [37]. In some of these methods the molar absorptivities are elose to MO [36,39]. A flotation method has been proposed, based on the addition compound [R6G ][Ag(SCN )2] [R6G ][SCN ] which is formed by silver ions (at pH 2-5) in the presence of thiocyanate and Rhodamine 6G (flotation with DIPE, the precipitated compound is washed and dissolved in acetone, e = 1.5-10 ) [40]. The complex Ag(CN)2 , associated with Crystal Violet, has been utilized in another flotation-spectrophotometric method of determining silver [41]. Silver has been determined also in a system comprising thiocyanate and Rhodamine B, as an aqueous pseudo-solution, in the presence of poly(vinyl alcohol) [42]. 

In conclusion, there are a number of techniques that will give reliable results for lead analysis. The spectrophotometric method, while probably the most popular, suffers from lack of specificity, and great care must be taken to ensure that a positive test is due to lead. In addition, the technique is quite tedious, requiring several extractions and pH adjustments, and the use of cyanide solutions always poses a danger in the laboratory. The use of sulfuric acid for digestion in the procedure recommended by Rice et al. for blood and urine should be used with caution. 

The advantage of discrete analyzers is that sample crossover in the system itself is the lowest possible. Volumes of 75 pi of reagent and sample volumes as large as 100 pi are sufficient. In an automated system with a throughput of 200 determinations per hour in the same sample 6 to 10 components (such as ammonium, alkalinity, aluminum, boron, bromide, calcium, chloride, chromium(VI), cyanide, fluoride, iron, magnesium, nitrate, nitrite, phosphate, etc.) can be determined. In discrete analyzers normally conventional spectrophotometric methods are used. These methods are prone to interference of the matrix of the sample. As a good concept for interference studies still is not available, interferences are as yet not sufficiently studied systematically even for routine analyses. 

A good correlation was found between the results of the electrochemical method and those of the spectrophotometric cyanidation analysis method, which is used in clinical practice as a standardized protocol. 

S.SM. Hassan, M.S.A. Hamza, A.E.A. Kelany, A novel spectrophotometric method for batch and flow injection determination of cyanide in electroplating wastewater, Talanta 71 (2007) 1088-1095. 

One of the reviews cited earlier enumerates spectrophotometric methods for the determination of cyanide up to 1962 [8]. Also, instrumental methods such as colorimetric and spectrophotometric methods, electroanalytical methods, catalytic methods, gas chromatography methods, radiochemical methods, and miscellaneous methods for determination of cyanide up to 1977 have been summarized by Williams [7]. The instrumental methods developed since 1977 are considered here. 

A simple spectrophotometric method involving 2,2-dihydroxy-l,3-indanedione (Ninhy-drin) in an alkaline medium has been used in trace determination of cyanide in environmental samples [22-24]. Beer s law is obeyed in the range of cyanide concentration of 0.04—0.24 jLg cm , the molar absorptivity at 590 nm is 2.20 x 10 dm mol cm , and SandelTs sensitivity of the product is 0.000118 pg cm [22]. This method is described in the following paragraphs. 

A spectrophotometric method has been used for the determination of free cyanide in Prussian blue [30]. Trace amoimts of free cyanide in Prussian blue are hydrolyzed into hydrocyanic acid. The latter is captured by a lithium picrate solution contained in a test tube, which is placed in the reaction vessel. The color change due to the resulting lithium isopurpurate is measured spectrophotometrically at 500 nm. This method can detect cyanide down to a level of 2.5 pg in 100 mg of Prussian blue. 

An indirect spectrophotometric method for determination of cyanide is based on complexation of Pd + with cyanide inhibits the extraction of the palladium complex of 5-phenylazo-8-aminoquinoline [32]. This effect is used for the indirect spectrophotometric determination of cyanide at the xg level. Cyanide in industrial wastewater and in seawater is determined after distillation as HCN from the sample and collection in sodium hydroxide solution. 

Chance, using the spectrophotometric method, found cyanide to inhibit the oxidatic reaction just as well as the peroxidatic reaction. He observed a small cyanide insensitive activity in presence of maganese but does not mention the effect of cyanide on autoxidation in the absence of enzyme described by Swedin and Theorell. 

Spectrophotometric deterrnination at 550 nm is relatively insensitive and is useful for the deterrnination of vitamin B 2 in high potency products such as premixes. Thin-layer chromatography and open-column chromatography have been appHed to both the direct assay of cobalamins and to the fractionation and removal of interfering substances from sample extracts prior to microbiological or radioassay. Atomic absorption spectrophotometry of cobalt has been proposed for the deterrnination of vitamin B 2 in dry feeds. Chemical methods based on the estimation of cyanide or the presence of 5,6-dimethylben2irnida2ole in the vitamin B 2 molecule have not been widely used. 

A determination of dimethyl sulphoxide by Dizdar and Idjakovic" is based on the fact that it can cause changes in the visible absorption spectra of some metal compounds, especially transition metals, in aqueous solution. In these solutions water and sulphoxide evidently compete for places in the coordination sphere of the metal ions. The authors found the effect to be largest with ammonium ferric sulphate, (NH4)2S04 Fe2(S04)3T2H20, in dilute acid and related the observed increase in absorption at 410 nm with the concentration of dimethyl sulphoxide. Neither sulphide nor sulphone interfered. Toma and coworkers described a method, which may bear a relation to this group displacement in a sphere of coordination. They reacted sulphoxides (also cyanides and carbon monoxide) with excess sodium aquapentacyanoferrate" (the corresponding amminopentacyanoferrate complex was used) with which a 1 1 complex is formed. In the sulphoxide determination they then titrated spectrophotometrically with methylpyrazinium iodide, the cation of which reacts with the unused ferrate" complex to give a deep blue ion combination product (absorption maximum at 658 nm). 

Continuous monitoring methods based on amperometric (Nikolic et al. 1992) or spectrophotometric (Kuban 1992 Ma and Liu 1992) techniques for the quantification of free cyanide are also available. Ion chromatography with amperometric determination provides good sensitivity (2 ppb) and selectivity for free cyanide and the weak complexes of cadmium and zinc (Rocklin and Johnson 1983). Postcolumn derivatization and fluorescence detection provides low detection limits as well (0.1 ppb) (Gamoh and Imamichi 1991). 

Fonong T. 1987. Enzyme method for the spectrophotometric determination of micro-amounts of cyanide. Analyst 112 1033-1035. 

Stopped flow and continuous flow methods [11] have been used to follow proton transfer reactions with half-lives in the millisecond range. The stopped flow method which is more popular is essentially a device for mixing the reactants rapidly (typically in one millisecond) together with some means of observing the fast reaction which follows. Proton transfer from p-nitrobenzyl cyanide to ethoxide ion in ethanol/ether mixtures at —77 °C was studied in this way [12]. The reaction was followed spectrophotometrically. The most rapid reaction occurred with ti/2 ca. 2 x 10 2 sec although the equipment was suitable for following reactions with f1/2 ca. 2 x 10 3 sec. A similar method has been used to measure rates of proton transfer between weak carbon acids (for example, triphenylmethane) and bases (for example, alkoxide ions) in dimethyl sulphoxide [13], A continuous flow apparatus with spectrophotometric detection was used [14] to measure rates of ionization for substituted azulenes in aqueous solution (4), reactions for which half-lives between 2 and 70 msec were observed. 

Studies of proton transfers from carbon with f1/2 less than one microsecond are quite rare. The ionization of hydrogen cyanide in aqueous alkaline solution has been studied [20] using the ultrasonic stationary method which is applicable to reactions with tl/2 in the range 10 5 to 10 9 sec. Several reactions of benzyl carbanion having f 1/2 in the range 10-6—5 x 10-8 sec have been studied in tetrahydrofuran. The carbanion was generated by pulse radiolysis of solutions of dibenzyl mercury and its subsequent reaction with water and alcohols was followed spectrophotometrically [21]. 

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