Reagent Arsenazo

Leary NO, Pembroke A, Duggan PF. Single stable reagent (Arsenazo III) for optically robust measurement of calcium in serum and plasma. Clin Chem 1992 38 904-8. 

Fig. 3 Separation of lanthanides using gradient elution. Experimental conditions column, reverse phase Cig mobile phase, camphor-10-sulfonic acid (0.05 M) a-HIBA varied from 0.07 to 0.3 M, pH 3.8 flow rate 2 ml/min. Postcolunm reagent Arsenazo III (l.SxlO Af) flow rate 1.5 ml/min detection 655 nm.

Fig. 5 Separation of lanthanides using HDEHP coated column. Experimental conditions reverse phase Cjg column coated with HDEHP (0.27 mil/) mobile phase, a-HIBA varied from 0.07 to 0.3 Af pH 3.5 flow rate, 1.5 ml/min postcolumn reagent, Arsenazo IB flow rate, 2 ml/min detection, 655 nm lanthanide, 5 p-g/ml, 100 1x1 injected.

Distribution ratios (chloroform-water) have also been reported for curium complexes with 8-hydroxyquinoline (oxineX cupferron, and JV-benzoyl-phenylhydroxylamine (NBPHA) [136]. Only 1 3 complexes with Cm(iii) and Am(iii) were reported, and extraction into the organic phase appears to be very high at pH values above 5. Solution interaction of Cm(iii) with bis(salicylidene)ethylenediimine (SALEN) and derivatives has also been studied [137], With the reagent arsenazo(iii), both Cm(iii) and Am(iii) form 1 1 and 1 2 complexes [138]. 

Azo dyes contain an azo link between two aromatic rings possessing a orthohydroxy group. The most important reagents include PAN, PAR, and Arsenazo III and generally they offer high sensitivity for the majority of transition metals. 

Thorium coprecipitated from acidified sample with Fe(OH)3, clean-up Th by selective solvent extraction, coprecipitated with Al(OH)3 and develop color by Arsenazo III reagent. After color development, coprecipitate Th with LaF3. 

Table 6 merely lists reagents such as xylenol orange (44) and arsenazo(III) (45) which are often used absorptiometrically, and morin (46) used also in fluorimetric procedures, together with other reagents for the commoner metals. It would be pointless to give practical details of procedures which can be found in standard text books3-7,22,30,33 or specialist publications.76,77 IUPAC have... 

Until Arsenazo I and related reagents were introduced into spectrophotometric analysis, there were no sensitive reagents for such elements as Th, Zr, Hf, U, and rare earths. 

In strongly acid solutions (1-10 M HCl) Arsenazo III reacts only with Th, Zr, Hf and U(rV). The molar absorptivities, e, of the complexes with these metals are about 10. At pH 1-4 Arsenazo III reacts with U(VI), Sc, Fe(ni), Bi, and rare earths. The sensitivity of the colour reactions is lower in this case ( -510 ). The use of Arsenazo III in strongly acid medium overcomes difficulties connected with the hydrolysis of some multivalent metals (c.g., Zr, Th, U). In the determination of these metals the high acidity enhances the selectivity of the reagent. 

The absorbance of free Arsenazo III ( max 520-530 nm) at the absorption maxima of the metal complexes (k 655-665 nm) is very slight. The large difference (AX) between the wavelengths of the absorption maximums of the complexes and the free reagent is important. In the case of Th and U the spectrophotometric method with Arsenazo HI is specific owing to the use of masking agents (oxalic acid, HF) and an appropriate acidity of the medium. 

Savvin S.B., Organic Reagents of Arsenazo III Group, Atomizdat, Moscow, 1971. 

Cadion (p-nitrobenzenediazoaminobenzene-p-azobenzene) (formula 13.1) [48,49] is the basis of a very sensitive method for cadmium. In the presence of the non-ionic surfactant, Triton X-100, the absorptivity is 1.2-10 at 477 nm. Other azo reagents used are bromobenzothiazo (extraction into toluene, e = 5.8-10 ) [50] and Arsenazo III [51]. 

Numerous methods for determining fluoride are based on compounds of thorium with organic reagents, such as Alizarin S [55], Xylenol Orange [48], Arsenazo I [4], and chloranilic acid [56]. An exceptionally sensitive method is based on the ternary system Th-Chrome Azurol S-CTA (e= 1.0-10 at 635 nm) [57]. 

Direct spectrophotometric methods proposed for fluoride (similar to the Alizarin Complexone method) involve use of Arsenazo lE-Zr reagent [62,63], Sulphochlorophenol S-Zr reagent (e = 3.0-10 ) [64], Xylenol Orange-Al (extraction of ternary fluoride-containing complex into CHCI3 in the presence of TOA, e = 4.MO" ) [65], and Xylenol Orange-Zr reagent (e = 3.4-10 ) [66]. 

Some other azo reagents, apart from PAR described above, have been proposed for the determination of lead, namely PAN [52] and its derivatives [53], 5-BrPADAP (e = 4.9-lO at 575 nm) [54], TAR [55], Arsenazo III [56] (the formulae of these reagents have been given in Chapter 4), Sulpharsazen (e = 4.5-10 at 520 nm) [57]. 

In weakly acidic media the lanthanides and yttrium react with Arsenazo III (formula 4.10) to form coloured complexes which are the basis of the sensitive method for determining the total of REE or any element from this group [48-51]. In weakly acidic solution, the reagent is violet, and its complexes with the rare-earth elements are green. The maximum absorbance for Ce(III) is obtained at pH 2.3-2.7. The optimum pH values for the various REE differ slightly. 

The reagent does not absorb at the wavelength of the absorption maximum of the complex (650 nm). The molar absorptivity of the Arsenazo III complex with cerium is 5.6T0 (specific absorptivity 0.40). The other REE complexes have similar molar... 

In addition to Arsenazo HI, the following azo dyes containing the arsonic or phosphonic acid group have also been recommended as spectrophotometric reagents for either individual lanthanides or the total REE Arsenazo I [58,59], p-Acetylarsenazo [60], Carboxyarsenazo (e = 5.210 for La) [61], Dicarboxyarsenazo III [62], Chlorophosphonazo III [63,64], Chlorophosphonazo [65], Chlorophosphonazo DAL [66], p-Acetylchlorophosphonazo... 

The related reagents such as Chlorophosphonazo III [39], Sulphonazo III [40], Carboxy-nitrazo [41], and Arsenazo III (e = 4.010 at 650 nm) [42] have also been used for the determination of strontium. 

The following bisazo derivatives of chromotropic acid have been proposed as related reagents for barium Nitchromazo [38], Chlorophosphonazo DI [47], Carboxyarsenazo (in 50% ethanol, pH 5.6, e = 4.1-10 at 640 nm) [48], and Arsenazo III [42]. 

Determination of Th. Place the sulphate-free acid sample solution, containing not more than 30 pg of Th, in a 25-ml standard flask. Add 6 ml of cone. HCl and 3 ml of 8% oxalic acid solution, and mix well. Add 2 ml of the Arsenazo IE solution, dilute to the mark with water, mix well, and measure the absorbance at 655 nm against a reagent blank solution. 

From among azo reagents containing the arsonic acid group, Arsenazo I (Neothoron) [67], Arsenazo DAL [68], and p-Dimethylarsenazo III (8 = 1.3-10 5 M HCl) [69] have been applied for determining thorium. Reagents with phosphonic groups, such as Chlorophosphonazo III (e = 1.2-10 at 620 nm) [70-72] and m-Carboxychlorophosphonazo (e = 1.0-10 at 676 nm [73,74] have been proposed... 

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