Spectrophotometric determination with rhodamine

2 Spectrophotometric determination with rhodamine B General remarks 

In hydrochloric solution antimony (V) together with rhodamine B forms a red-purple complex insoluble in water. 

The complex is extracted with CCl /chlorobenzene (1 4) and determined spectrophotometrically at 365 nm (8 555 = 70 000). Due to the low antimony content in natural waters it is necessary to concentrate the element by coprecipitation with manganese dioxide hydrate. The addition of ethanol to the KMnOz solution improves the adsorption characteristics of the carrier. 

Sb is isolated from manganese, iron and interfering elements by extraction with MIBK from 3 m H2SOz with 0.01 m iodide. After back-extraction with 0.4 m hydrochloric acid, excess iodide is removed by oxidation with H2O2 and extraction of the liberated iodine with chloroform. Any H2O2 still 

Antimony concentrations up to about 0.1 pg/1 can be determined using this 

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Analysis. Colorimetric analysis of Ga permits detection of 20 ppb. Ga or a Ga compound in the flame gives a violet (lilac) color. This is due to its emission of 414.0 nm photons. This photon line allows for the spectrophotometric determination of Ga by AAS, which is sensitive to about 10 ppm. ETAAS increases this sensitivity to 5 ppb, and ICPAES to about 1 ppb, with ICPMS going as low as 0.1 ppb. Rhodamine B is a reagent which facilitates the spottest detection at a level of 10 ppm or above. 

A method for determination of sodium isoascorbate (see 2) in boiler feed water, where it is used for deoxygenation, consists of following the reaction kinetics of Rhodamine B (13) in the presence of KBrOs, measuring at 555 nm. A linear correlation exists between the catalytic effect of the analyte on the reaction rate and its concentration Fe(III), Ca(II) and Mg(II) in the 5-200 ppm range interfere with the analysis . The effects of solvents, pH, surfactants, metal ions and other food additives on the absorbance were studied for the micelle-enhanced UV spectrophotometric determination of the food preservative sodium D-isoascorbate. The optimal conditions were using water at pH 7-8 as solvent and polyvinyl alcohol as surfactant, which causes an up to 3-fold increase of the UV absorbance. ... 

Rhodamine 6G [53] and Rhodamine B [54] have been used for spectrophotometric determination of mercury(II) in the aqueous phase. The systems can be stabilized with gelatine or poly(vinyl alcohol). 

Besides Rhodamine 6G (see above). Malachite Green and Crystal Violet form ion-associates with the anionic iridium chloride-SnCl j complexes and these ean also be used for flotation-spectrophotometric determination of iridium. The molar absorptivity e with Malachite Green is 1.55-10 [77,78]. 

Thallium(III), in the form of the TICU or TlBr4" complex ions, reacts in acid media (1-2 M HCl) with the basic xanthene dye, Rhodamine B (formula 4.29), to form a red-violet, slightly fluorescent ion-associate complex, which is soluble in benzene, DIPE, and isoamyl alcohol. These extracts have been used for the spectrophotometric determination of thallium [8]. A mixture of CeHe and CCI4 (2+1) is a convenient extractant since it is denser than water. 

Other organic spectrophotometric reagents, recommended for determination of thorium are Bromopyrogallol Red [85], morin (e = 3.3-10 at 422 nm), quercetin [86,87], phenylfluorone [87], and 8-hydroxyquinoline [88], The anionic complex of 5,7-dibromo-oxine with Th forms an ion-associate with Rhodamine B which can be extracted into benzene (e = 8.8-10 at 552 nm) [89],... 

High sensitivity characterizes the methods based on ion-associates formed by anionic complexes of V(V) with basic dyes. The Brilliant Green method has been described above [33]. The vanadium complex with PAR associated with Crystal Violet is extracted into a mixture of benzene with MIBK (3-f2) (e = l.l lO ) [51]. In a proposed flotation-spectrophotometric method, the V complex with 3,5-dinitropyrocatechol, associated with Rhodamine B, is separated by shaking the solution with cyclohexane the separated compound is washed and dissolved in acetone (e = 2.1-10 at 555 nm) [52], A similar sensitivity is achieved in the method using 5,7-dichloro-oxine and Rhodamine 6G [53]. Another flotation-spectrophotometric method for determining V has been based on 3,5-dinitrosalicylic acid and Rhodamine B [54]. 

It has been reported that y3-CD could improve the selectivity of the color reactions of various metal ions with triphenylmethane, xanthene acid dyes and some other coloring reagents. The effect of fi-CD on the association compound system of metal (Mo, Zn, Co)-thiocyanate basic dyes such as malachite green, crystal violet, rhodamine B, rhodamine 6G and butyhhodamine B, has been investigated and the result shows that /3-CD could contribute to a more sensitive and stable system which improve the solubility of the basic dyes and produce a favorable microenviromnent for the color reactions [63]. /3-CD could be employed to solubilize the 1,2-amino anthraquinone in water due to the formation of inclusion complex which acts as a ligand for metal ions could be used for the determination of palladium at trace levels by spectrophotometry. In the spectrophotometric determination of microamounts of Zn based on the Zn-dithizone color reaction, -CD could increase the apparent molar absorptivity at 538 nm by 8.37 times. In the presence of cr-CD, the determination sensitivity of copper in leaves based on the color reaction of Cu(II) and mesotetrakis (4-methoxy-3-sulfophenyl) porphyrin was enhanced by 50% in the spectrophotometric analysis [64,65]. 

Phosphomolybdate forms strong ion association complexes with basic dyes at low pH. For example, the sensitivity of a method based on spectrophotometric determination of the 12-MPA-malachite Green complex [84,85] was approximately 30 times that of a reduced phosphomolybdate determination. Other dyes used for this purpose include Saffranin, brilliant green, Fuchsine red, methylene blue, methyl violet, and Rhodamine B [5]. Surfactants such as polyvinyl alcohol are frequently used to avoid precipitation of the ion association complex. 

Kamaya, M., Hikita, Y., Nagashima, K., and Namiki, H., Spectrophotometric determination of silica in highly purified water after collection of ion associate of molybdosilicate with Rhodamin... 

Spectrophotometric determination of the metal-ligand complex Fluorimetric determination of thallium (in silicate rocks) with rhodamine B after separation by adsorption on a crown ether polymer... 

Drozd, A. V., B. G. Klimov, Extraction-spectrophotometric determination of anionic surfactants with Rhodamine 6G, J. Anal. Chem., 1998,55, 711-713. 

To the filtered seawater (500 ml about 1.5 xg U) is added 0.05 M ferric chloride (3 ml), the pH is adjusted to 6.7 0.1 and the uranium present as (U02(C03)3)4- is adsorbed on the colloidal ferric hydroxide which is floated to the surface as a stable froth by the addition of 0.05% ethanolic sodium dodecyl sulfate (2 ml) with an air-flow (about 10 ml min-1) through the mixture for 5 min. The froth is removed and dissolved in 12 M hydrochloric acid-16 M nitric acid (4 1) and the uranium is salted out with a solution of calcium nitrate containing EDTA, and determined spectrophotometrically at 555 nm by a modification of a Rhodamine B method. The average recovery of uranium is 82% co-adsorbed WO4- and M0O4- do not interfere. 

Many other basic dyes besides Methyl Violet have been used in sensitive extraction-spectrophotometric methods for the determination of Ta as the anionic complex TaFe [92]. Mention may be made of Crystal Violet (formula 4.27) (e = 8.5-10" ) [91-93], Brilliant Green (e = 1.2-10 ) [94,95], Malachite Green [96,97], Methyl Green (e = 1.2-10 ) [98], Rhodamine 6G and butylrhodamine B [99], Methylene Blue (e = 9.1-10" ) [98], Nile Blue A [100], Capri Blue (e = I.TIO ) [101], and Victoria Blue B [102]. Ion-associates with these dyes are extractable from acid solutions into benzene, toluene, CHClj, xylene, or dichloroethane. 

Methods for Pd determination based on ion-associates with basic dyes are often very sensitive. In extraction-spectrophotometric methods, thiocyanate [84-89], chloride, and bromide [84] anionic complexes of palladium are associated with Brilliant Green [84], Malachite Green [85,88], Rhodamine B (e = 9.0-10 ) (86), Rhodamine 6G [89], and Methylene Blue [87]. In flotation-spectrophotometric methods, ion-associates formed by the... 

Rhodamine B, and the anionic complexes of REE with oxine [112], salicylic acid derivatives [113,114], and 3,5-dinitrocatechol [115] have been the basis for sensitive methods of determining REE (e = 9-10 at 550 nm). Praseodymium has been determined by a sensitive flotation-spectrophotometric method (e = 1.8-10 ) with the use of 5,7-dichloro-oxine and Rhodamine 6G [116]. 

The most sensitive spectrophotometric methods for the determination of Re involve the extraction of ion-associates formed by Re04" with basic dyes. From among the triaryl methane dyes, use has been made of Methyl Green (benzene, e = 1.2-10 at 640 nm) [37], fuchsine (formula 27.1) [1] Brilliant Green (benzene, e = 1.010 ) [38], Crystal Violet [39], Victoria Blue 4R (formula 4.28) [40], Rhodamine B [41], Safranine T [42], Nile Blue... 

In hydrochloric acid medium, iridium reacts with SnCb ions to form an anionic complex which reacts with the basic dye, Rhodamine 6G (R6G), yielding a sparingly soluble ion-associate. The compound precipitates at the phase boundary when the solution is shaken (for about 1 min) with DIPE. The precipitate is readily soluble in acetone. This solution has been used as a basis for a very sensitive flotation-spectrophotometric method for determining Ir [6]. 

The method based on the ion-associate with Capri Blue has already been presented. The thiocyanate-Ru complex has also been associated with Crystal Violet and Rhodamine 6G (in the presence of gelatine) (e = 1.4-10 ) [15,51]. The ion-associate of the Ru complex with SnCff and Crystal Violet is a basis of a flotation-spectrophotometric method of Ru determination (e = 2.110 at 600 nm) [52]. More sensitive methods are based on flotation of... 

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]. 

An important consideration in the determination of antimony in aqueous matrices is the fact that antimony can be present in the (III), (IV), or (V) valence state. To avoid analytical problems, it is desirable that the antimony be present in a specific valence state. This is particularly important if a spectrophotometric method is to be used because the reagents employed usually react only with a particular oxidation state. Maren observed in a study of the use of rhodamine B that Sb(IV) could not be easily oxidized to the required Sb(V) (3). In work on the determination of antimony using 3,4,7-trihydroxyflavone, a reagent which reacts only with Sb(III), Fider demonstrated that Sb(IV) and Sb(V) could be reduced to Sb(III) by hydroxylamine sulfate (13). 

An ozone analyser operates with a high degree of the selectivity, based on a chemiluminescent reaction [15, 30]. Rhodamine B, adsorbed on sihca gel is applied onto a disc, which is then exposed to air containing ozone. Radiation emitted is detected by a photomultiplier. Ozone can be determined on the basis of the ozonolysis of 4-4 -dimethylstilbene to yield anisaJdehyde, which is determined by a spectrophotometric measurement at 510 nm [31]. 

Another modification of the catalytic kinetic spectrophotometric method has been established for the determination of iodine using the principle that potassium periodate oxidize rhodamine B (RhB) to discolor and 1 has a catalytic effect on the reaction. The absorbance difference (AA) is linearly related with the concentration of iodine in the range of 0 - 2.6 pg/mL and fits the equation AA = 0.1578 C(C pg/mL) + 0.0052, with a regression coefficient of 0.9965. The detection limit of the method is 7.10 ng/mL. The method was used to determine iodine in kelp, potato, tap water, and rain water samples. The relative standard deviation of 13 replicate determinations was 1.81-2.10%. The recovery of the standard addition of the method was 96.2-99.2% (Zhaiet al., 2010). 

Ternary complexes. Traces of proteins have been determined spectrophotometrically by formation of colored ternary ion-association complexes with pyrogallol red and molybdenum(VI) or pyrocatechol violet and molybdenmn(VI). Compounds containing the sulfydryl group were determined spectrophotometrically based on the extraction of their ternary ion-association complexes of rhodamine 6G and as-traphloxine cations with hexachloroantimonate(III) from buffered aqueous solutions into toluene. 

Extraction and spec A = 510 nm of gallium with 4-(2-pyridylazo)resorcinol Comparison of the determination of gallium by a rhodamine B spectrophotometric method and by an AA method based on preliminary solvent... 

It is possible to perform the paired-ion determination without using a water-immiscible solvent. The ion pair formed by an anionic surfactant with many cationic dyes, including methylene blue and rhodamine 6G, is water-insoluble and, with shaking, will adsorb to the walls of the vessel. After discarding the aqueous solution, the ion pair can be washed from the walls with ethanol or methyl cellosolve and measured spectrophotometri-cally. Best results are obtained with a poly(tetrafluoroethylene) vessel (52). In a similar vein, the ion pair can be filtered out, then dissolved and measured spectrophotometrically. This was demonstrated using a cationic iron complex with a nitrocellulose membrane filter which was soluble in the 2-methoxyethanol used for the spectrophotometric measurement (53). 

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