Arsenazo III method

The Arsenazo III method presented below can be used to determine either the total REE or the individual lanthanides and yttrium. The 8-hydroxyquinoline method gives a possibility of determining cerium as Ce(IV) in the presence of all the remaining REE. 

The Arsenazo III method has been utilized for determining Sc in minerals [51]. Scandium in mixtures with rare earth elements was determined by derivative spectrophotometry with the use of Chlorophosphonazo-p-Cl [27]. p-Acetyl-chlorophosphonazo with Ce(III) has been used for determining Sc in copper, aluminium, manganese, and magnesium alloys [28]. Traces of scandium in silicate rocks and sediments were determined with the use of Bromopyrogallol Red [43]. 

The Arsenazo III method for determining thorium is highly selective. In the presence of oxalic acid as a masking agent, thorium can be determined in 2.5-3.5 M HCl in the presence of Zr, Hf, and Nb. Iron(III), which interferes, is reduced to Fe(II) by ascorbic acid, and U(IV) is oxidized to U(VI) by adding some KMn04 (followed by ascorbic acid to decolorize the solution). At high concentrations of chloride (HCl -1- LiCl) Th can be determined in the presence of a 100-fold amount of uranium(Vl). The effect of Ti on the determination of Th has been discussed [55,56],... 

The Arsenazo III method has been applied for determination of zirconium (and hafnium) in silicate rocks [2,97], titanium dioxide [98], phosphate rocks [99], cast iron and steel... 

The use of silk fibroin for separating Th from aqueous solutions was studied [2]. Arsenazo III method was employed to determine Th in the filtrate. 

One manifestation of the arsenazo-III method was deployed for the determination of the uranium concentration in various process streams in a uranium extraction plant in India (Murty et al. 1997). The uranyl-arsenazo-III complex in 4 M HCl was used for determining low uranium concentrations while the complex in dilute phosphoric acid was used for high concentrations. 

Jauberty, L., Droget, N., Decossas, J.L. et al. (2013). Optimization of the arsenazo-III method for the determination of uranium in water and plant samples, Talanta 115, 751-754. 

Only slightly less accurate ( 0.3—0.5%) and more versatile in scale are other titration techniques. Plutonium maybe oxidized in aqueous solution to PuO " 2 using AgO, and then reduced to Pu" " by a known excess of Fe", which is back-titrated with Ce" ". Pu" " may be titrated complexometricaHy with EDTA and a colorimetric indicator such as Arsenazo(I), even in the presence of a large excess of UO " 2- Solution spectrophotometry (Figs. 4 and 5) can be utilized if the plutonium oxidation state is known or controlled. The spectrophotometric method is very sensitive if a colored complex such as Arsenazo(III) is used. Analytically usehil absorption maxima and molar absorption coefficients ( s) are given in Table 10. Laser photoacoustic spectroscopy has been developed for both elemental analysis and speciation (oxidation state) at concentrations of lO " — 10 M (118). Chemical extraction can also be used to enhance this technique. 

The results of the complexation study of Cu(II), Pb(II), Zn(II), Fe(III), Hg(II), Cd(II), Sn(IV), Zr(IV), Ti(IV) with arsenazo III, sulfonazo III, SPADNS, Eriochrome T, Acid Chrome Dai k Blue, Xylenol Orange, Methyl Thymol Blue, Pyrocatechol Violet, Chrome Azurol S, Eriochrome Cyanin R, Basic Blue K, Methyl Violet, Brilliant Green, Rhodamine C and Astraphoxin in solid phase. The obtained data ai e used for the working out of a new method of metal determination. 

Arsenazo (III) to produce a colored complex, which can be determined with standard colorimetric methods. Arsenic compounds are highly toxic. 

Finally it should be noted that while classical methods for analysis tend to be little used, there are certain colorimetric methods for calcium which are of value. Thus, determinations with arsenazo III involve a detection limit of 10-7 mol dm 3. Calcium may also be determined using the photoproteins aequorin and obelin, which emit light on interaction with Ca2+ and have detection limits around 5 x 10-8 mol dm-3. These methods have had some interesting in vivo applications. 

Total calcium is most frequently measured by spectrophotometry using metaUochromic indicators or dyes. Of the metaUochromic indicators that change color on selectively binding calcium, o-cresolphthalein complexone (CPC) (3, 3"-bis [ [bis-(carboxymethyl)amino] -methyl] -5", 5"-dimethylphenolphthalein) (Figure 49-3) and arsenazo III are most widely used. These methods, although less accurate and reproducible than atomic absorption spectrophotometry, have been easier to automate on chemistry analyzers. 

Arsenazo ill Method. Arsenazo III (1,8-dihydroxynaph-thaiene- 3,6-disulfonic acid- 2,7-bis [azo- 2 ] -phenylarsonic... 

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. 

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]. 

The methods described in detail in Section 36.2, or only mentioned, have been used as follows for spectrophotometric determination of palladium the thio-Michler s ketone — in silver, copper, and anodic slime [32], in catalysts [31] with thiosemicarbazide derivatives — in water [44] and alloys [46] with palladium-carbon powder — with a-benzilmonoxime [48] with PAR — in catalysts and ores [58] with thiazolylazo derivatives — in Ni-Al catalysts [63] with 5-Br-PADAP — in titanium alloys with pyridylazo derivatives - in nickel alloys [68] with sulphonitrophenol - in silver alloys [70] with Arsenazo III — in iron and meteorites and with Palladiazo — in catalysts, minerals, silica gel, and calcium carbonate [78]. 

Numerous indirect amplification methods have been devised for the determination of phosphate. The molybdenum in an extract of molybdophosphoric acid (Mo P = 12 1) has been determined with thiocyanate [63], phenylfluorone [64], dithiol (e = 1.7-10 ), Sulphonitrophenol S (e = 4.610 ) [65], or 2,2 -diquinoxalyl [66]. The indirect method that involves the Fe(ll)-ferrozine complex [67] is unusually sensitive (e = 9.7-10 ). In another method involving the complex of Ce(III) and Arsenazo III, the phosphate gives a sparingly soluble CeP04 and liberates an equivalent quantity of Arsenazo III [68]. 

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. 

Arsenazo III (formula 4.10) reacts with thorium in strongly acidic solution to give a grey-green water-soluble complex, which has been used for the determination of thorium [50-54]. The method is very sensitive, and the absorbance varies only slightly with change in HCl concentration between 1 and 10 M. The maximum absorbance is obtained in 8 Af HCl. 

Thorium-Arsenazo 111 complex can be extracted with butanol from 1 M HCl (e = 6.41 O at 670 nm) [57]. Thorium has been determined in the organic phase after extraction with HDEHP in cyclohexane and addition of aqueous Arsenazo 111 and isopropyl alcohol (e = 8.8-10 at 660 nm) [41]. In another method Arsenazo III was added to the xylene extract of the ion-associate of the nitrate complex of thorium with Aliquat 336 [34]. Thorium has been determined after froth flotation separation of the ternary compound of Th with Arsenazo III and surfactants [58,59]. 

Arsenazo III (formula 4.10) reacts with uranium(IV) in strongly acidic medium, to give (as with Th and Zr ions) a green-blue complex. The method based on this reaction is far superior in sensitivity and selectivity to the other spectrophotometric methods for... 

Arsenazo III gives with U(VI) a coloured complex which is also used for determination of uranium [65,68,69]. The colour reaction is usually carried out either in slightly acidic (pH 2-3) or strongly acidic (5-6 M HNO3, HCl or HCIO4) medium. In the latter case, a considerable excess of Arsenazo III is needed. The method based on this reaction is convenient, since it eliminates the reduction step, but its sensitivity is much lower. The molar absorptivity is 6.0-10 (specific absorptivity 0.25) at 655 nm. 

The anionic uranium(VI)-Arsenazo III complex has been extracted from aqueous solution (pH 1-3) with CHCI3 in the presence of Zephiramine [72]. In another method U(VI) is extracted with triphenylarsine oxide in CHCI3, back-extracted with 5.5 M HCIO4 containing oxalic acid, and converted into the Arsenazo III complex (e = 7.3-10 ) [8]. 

The old Alizarin S method of low sensitivity is still of use. High sensitivity methods are those based on Xylenol Orange and Arsenazo III. The latter is also highly selective. 

The sensitivity of the method depends very much on the acidity of the medium [55-57]. The maximum colour intensity can be obtained in 9-10 M HCl (with an excess of Arsenazo III). As the HCl concentration is reduced, the colour intensity diminishes, in 2-A M HCl being only 1/3 to 1/2 of that obtained in 8-10 M HCl. In the media of higher HCl or HCIO4 concentration both Zr and Hf give the complexes of a metal reagent ratio of 1 2. 

A chemometric method for simultaneous determination of calcium and magnesium in natural waters using Arsenazo III and FIA system was described [5], The concentrations of the analytes were calculated by the H-point standard addition method for ternary mixtures. 

The special criteria of validation for an analytical method are directly related to the characteristics of the analytical method. For UV/Vis spectrometry, the reaction between the analyte and reagent must be fast, reproducible, and quantitative. The solution of the product resulting from the reaction must have at least 10,000 times the value of molar absorbtivity. In this regard, higher values can be obtained by using a polyfunctional reagent (e.g., Arsenazo III). For atomic absorption spectrometry and ICP, reproducibility of the flame and plasma, respectively, are essential for the quality and reliability of the analytical information, as well as for the validation criteria of the method. 

Ultrafiltration and ion exchange techniques were used to study characteristics of the formation path of Ln(III) binding to humic acid. A competitive ligand exchange technique was employed to study the complex dissociation. In the latter, arsenazo III (Ars) was used as the competitive ligand. Eu(III) was used in the methods requiring radioactivity while Sm(III) was used in the other studies however, the chemistry of Sm(III) and Eu(III) can be considered identical within the uncertainties of these methods. 

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