Pyrocatechol violet reagent

Dipping solution Dissolve 100 mg pyrocatechol violet (pyrocatecholsulfophtha-lein) in 100 ml ethanol. 

Storage The reagent should always be freshly made up. 

Pyrocatechol violet forms colored complexes with a variety of metal ions, the complexes are stable in differing pH ranges. 

The chromatogram is freed from mobile phase, dipped for 1 s in the reagent solution or sprayed evenly with it until the plate begins to be transparent and dried in a stream of cold air. 

Colored zones are formed (tin violet-red to blue) on a yellow ochre background 

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Pyrimidines la 266,438,439 lb 32,430 Pyrimidine nucleoside derivatives lb 290 Pyrocatechol lb 170,172,185 -, 4-rerr-butyl- lb 201 Pyrocatechol derivatives lb 119 Pyrocatechol violet reagent la 398 Pyrogallol lb 383,399,400 Pyrogallol derivatives lb 312 Pyrolysis of organic substances la 92,96 a-Pyrone derivatives la 288 lb 387,388 Pyrrole lb 268,270 Pyrrole alkaloids la 66 lb 279 Pyrrole derivatives la 266.269,270 lb 63 Pyrrolidine derivatives lb 290 Pynolizidine alkaloids lb 243,246,291... 

Pyridoxal 157,158,253 Pyridoxamine 253 Pyridoxine 253 Pyrimidines 266,438, 439 Pyrocatechol see 1,2-Dihydroxybenzene I ocatecholsulfophthalein 398 I ocatechol violet reagent 398 Pyrolysis of organic compounds 92, 96 a,y-Pyrone derivatives 288 Pyrrole alkaloids 66 Pyrrole derivatives 266, 269, 270 Pyruvic acid 426... 

Fig. 14 a. Schematic arrangement for Flow Injection Analysis for a simple spectrophotometric determination, b A typical experimental output from such a system, showing lack of carry over even with large samples. (Metal ion Bismuth Reagent Pyrocatechol violet, 5 x 10 3 M pH 2-4 Sample size 200 pi Analysis rate 80 hr-1)... 

Pyrocatechol Violet (formula 4.16) is a frequently used chelating reagent, readily soluble in water and in aqueous ethanol. An aqueous solution of the reagent is yellow (pH 1-8), and the colour of the solution changes to violet with increasing pH as a result of proton dissociation from the hydroxyl groups. Pyrocatechol Violet forms coloured (most often blue) chelates with many metals (e.g., Be, Al, Bi, Co, Cu, Fe, Ga, In, Mn, Pb, V, Zn) in weakly acidic and weakly basic solutions. 

Pyrocatechol Violet (formula 4.16) is a popular reagent for determining aluminium [11,31,33-36]. The value of 8 is 6.3-10 at 580 nm (pH 6.5-7.2) [35]. A relatively small increase in sensitivity is observed in ternary systems with CTA, CP, or poly(vinylbenzyltriphenylphosphonium) chloride [37-39]. The ternary complex with Zephiramine can be extracted into CHCI3 or 1,2-dichloroethane (e 9-10 at 590 nm) [40]. The extractive (xylene) method with the use of tridodecylethylammonium bromide is of very high sensitivity (e = 1.7-10 at 613 nm [41]. Aluminium was also determined by the FIA technique using Pyrocatechol Violet [42]. 

The anionic complex formed by bismuth(III) and Alizarin S gives floatable sparingly soluble ion-associates with some basic dyes. The best results have been obtained with Brilliant Green (flotation with CCU-toluene mixture, dissolution of the separated compound in ethanol, e = 2.2-10 ) [55]. Other organic reagents used for spectrophotometric determination of Bi, include Bromopyrogallol Red [56], Pyrogallol Red [57], 3-nitrophenylfluorone (e = 5.0-10 ) [58], and Pyrocatechol Violet [59]. 

Gallium ions form coloured complexes with a number of triphenylmethane chelating reagents besides Eriochrome Cyanine R. Pyrocatechol Violet (PV) gives with Ga and diphenylguanidine a ternary complex, extractable into n-butanol-CHCh (1-fl) mixture (e=1.08-10 ) [32]. In another extractive spectrophotometric method with PV,... 

Some authors recommend Pyrocatechol Violet (PV) as a reagent for germanium... 

Besides Eriochrome Cyanine R, which has been discussed above, some other triphenylmethane chelating reagents have been proposed for determination of indium. Like ECR, Chrome Azurol S allows a sensitive determination of indium with the use of cationic surfactants, such as CTA (e = 1.2310 ) [31], or CP [30]. Indium has been determined with Pyrocatechol Violet (PV) in a binary system [32], and in a ternary one with tridodecylammonium bromide (e = 8.2-10 ) [33]. A considerable increase of sensitivity is obtained in the presence of surfactants, such as CTA, CP, or Zephiramine [29]. Xylenol Orange has been recommended for determination of In [34]. Methylthymol Blue has also been studied as a reagent for determination of indium [35]. 

Other triphenylmethane reagents, besides the Eriochrome Cyanine R and Chrome Azurol S discussed above, have been applied for determination of Fe(III). A large increase in sensitivity and significant bathochromic shifts are observed when the reactions are performed in the presence of cationic surfactants, CTA, CP, Zephiramine, or dimethyllaurylbenzylammonium ions [70]. Systems of Fe(III) with Pyrocatechol Violet and CTA [71], Chromal Blue G and CTA [72], and Sulphochrome and CP [73] have been applied. The molar absorptivities of these systems are within 1.3-10 -1.7-10. The methods based on Pyrogallol Red alone or with the use of surfactants are less sensitive (e within 5.2-10 -7.5-10 ) [74-76]. 

Fig. 27.1. Absorption spectra of Pyrocatechol Violet (PV) vs. water (1), Pb-PV complex vs. the reagent solution (2), and Pb-PV-CP complex vs. the reagent solution (3)...

Pyrocatechol Violet (PV) is an interesting triphenylmethane reagent for determination of tungsten [146,147]. No better results were obtained in experiments with its analogues, such as ECR, CAS, or Xylenol Orange [146]. 

Xylenol Orange has been applied for determination of REE [91-95]. High sensitivity is obtained in the presence of CP (e = 9.2-10 at 625 nm for La) [96-99]. Other triphenylmethane reagents proposed are Methylthymol Blue [100], Chrome Azurol S [101-103], and Pyrocatechol Violet [104]. The sensitivity of these methods increases in the presence of CP [105-107]. 

Besides Xylenol Orange (discussed above), other triphenylmethane reagents have been proposed for determining Zr (Hf), such as Pyrocatechol Violet [71,72], Methylthymol... 

Storage Substances The reagent should always be freshly made up. Pyrocatechol violet Mobile phase Methyl isobutyl ketone — pyridine — glacial acetic add (97.5 + 1.5 + 1). 

Postcolumn reagents PAR - 4-(2-pyridylazo)resordnol o-CPC - o-cresolphthalein complexone CAS - chrome azurol S PCV - pyrocatechol violet HQS - 8-hydroxyquinoline-5-sulfonic acid. 

Chemists in Korea demonstrated a clever, rational approach to designing a reagent for the spectrophotometric analysis of phosphate. A ligand containing six N atoms and one O atom that could bind two ions was selected. The distance between ions is just right for the metal ion indicator pyrocatechol violet to bind, as shown at the left below. Pyrocatechol violet is blue when bound to metal and yellow when free. 

A number of valuable metallochromic reagents are based on the triphenylmethane structure. A typical example is Pyrocatechol violet which is an acid-base indicator, as well as forming coloured (usually blue) chelates with a wide range of metal ions. Compounds such as Xylenol orange are also based on this structure, with the addition of two iminodiacetic acid groups. 

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