Spectrophotometric method with methylene

Other detection methods are based on optical transmittance [228-231], Alcohol sulfates have been determined by spectrophotometric titration with barium chloride in aqueous acetone at pH 3 and an indicator [232] or by titration with Septonex (carbethoxypentadecyltrimethylammonium bromide) and neutral red as indicator at pH 8.2-8.4 and 540 nm [233]. In a modified two-phase back-titration method, the anionic surfactant solution is treated with hyamine solution, methylene blue, and chloroform and then titrated with standard sodium dodecyl sulfate. The chloroform passing through a porous PTFE membrane is circulated through a spectrometer and the surfactant is analyzed by determining the absorbance at 655 nm [234]. The use of a stirred titration vessel combined with spectrophotometric measurement has also been suggested [235]. Alternative endpoint detections are based on physical methods, such as stalag-mometry [236] and nonfaradaic potentiometry [237]. 

The methods most commonly used to detect hydrogen sulfide in environmental samples include GC/FPD, gas chromatography with electrochemical detection (GC/ECD), iodometric methods, the methylene blue colorimetric or spectrophotometric method, the spot method using paper or tiles impregnated with lead acetate or mercuric chloride, ion chromatography with conductivity, and potentiometric titration with a sulfide ion-selective electrode. Details of commonly used analytical methods for several types of environmental samples are presented in Table 6-2. 

The spectophotometric methylene blue method for anionic surfactants has been applied to seawater. In one version, the surfactants are collected in ethyl acetate. The solvent is then evaporated, the surfactants put back in solution in water, and the standard spectrophotometric methylene blue method is applied to this solution. In this manner, the salt error introduced by seawater is eliminated [195]. A similar method, with the methylene blue-surfactant complex extracted into chloroform, and measured directly was proposed by Hagihara [192]. 

Spectrophotometric methods have been used to determine water soluble boron in soils. In one method [1] the soil is extracted with boiling water then converted to fluoroborate which is evaluated spectrophotometrically as the methylene blue complex. 

A further spectrophotometric method [3, 4] for water soluble boron in soil, boron is extracted from soil with boiling water. Borate in the extract is converted to fluoroborate by the action of orthophosphoric acid and sodium fluoride. The concentration of fluoroborate is measured spectrophotometrically as the blue complex formed with methylene blue and which is extracted into 1, 2-dichloroethane. Nitrates and nitrites interfere they are removed by reduction with zinc powder and orthophosphoric acid. 

The very sensitive curcumin method is often used for determining trace amounts of boron. The carmine-acid method is much less sensitive. Extraction-spectrophotometric methods based on ion-associates of BF4 with Methylene Blue and other basic dyes are of importance in the determination of boron. 

Besides the Methylene Blue, other spectrophotometric methods, based on ion-associates of anionic boron complexes with basic dyes are used. Extractable associates with BF4 are obtained with Nile Blue A (formula 4.32) [7,36,37], Capri Blue (formula 4.31) [38], Malachite Green (formula 4.26, with Me instead of Et), Chrompyrazole II (CHCI3, e = 6.7-10 at 595 nm) [40], etc. 

A large group of extraction-spectrophotometric methods, similar to the Rhodamine B method, is based on extraction of ion associates of AuCU with various basic dyes, such as Brilliant Green (toluene) [47 9], Methylene Blue (chloroform) [50-53], Nile Blue A [54], Chrompyrazole I (an antipyrine dye, formula 23.1) (toluene, e = 6.5-10 at 580 nm) [55]. 

Extraction-spectrophotometric methods have also been based on other anionic complexes of Au, such as AuBr4 with Chrompyrazole I [56], Au(CN)2 with Methylene Blue (1,2-dichloroethane, e = 1.1-10 ) [57], azide complex with Methylene Blue (chloroform) [39]. 

In a sensitive flotation-spectrophotometric method (e = 3.4-10 ), a compound [(MB )(Hgl3)]-3[(MB )(l3)] (MB = Methylene Blue) is separated by flotation with cyclohexane from a 0.4 M HCl medium, containing T and MB then it is washed with water and dissolved in methanol [55]. Mercury has also been determined spectrophotometrically after separation (by flotation with cyclohexane) from solutions containing the iodide complex and Brilliant Green (e = 5.96-10 ) [56]. 

A sensitive spectrophotometric method is based on the extraction of the Ni complex with pyridine-2-aldehyde-2-quinolylhydrazone (e = 6.7-10 at 515 nm) [48-50]. The following similar reagents have also been recommended 5-methylfurfural-l-phthalazine-hydrazone [51], 2-pyridinecarbaldehyde-2-(5-nitro)pyridylhydrazone (e = 1.0-10 ) [52], 2-pyridinecarbaldehyde-3,5-dinitro-2-pyridylhydrazone [53], and 1,5-bis(di-2-pyridyl-methylene)thiocarbonylhydrazide [54]. 

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. 

Some sensitive spectrophotometric methods for determining nitrate utilize extractable ion-associates of the nitrate ion with the basic dyes Crystal Violet (chlorobenzene, pH 6) [97], Nile Blue A [98], and Methylene Blue (1,2-dichloroethane) [99]. Nitrogen has been determined also by the FIA technique with the use of Malachite Green [ 100]. 

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... 

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]. 

Attaway and co-workers [34] discuss in some detail the application of the optical density and spectrophotometric methods discussed previously to the determination of esters by TLC. They used glass plates coated with Silica Gel G. Chromatoplates were developed by the ascending technique, using benzene or trifluorotrichloroethane methylene chloride (60 40) as developing solvents. 

The interaction between three thiazine dyes, namely Azure B, Methylene blue, and Toluidine blue with an anionic polyelectrolyte, and Sodium Carrageenate has been investigated by spectrophotometric method. The polymers induced metachromasy in the dye resulting in the shift of the absorption maximum towards shorter wavelengths. The stoichiometiy and stability of the complexes formed between Thiazine dyes and the polymers are found to be dependent on the stracture of the polymers. The stability of the complexes followed the order AB-NaCar>MB-NaCar>TB-Na-Car. This iirference was further confirmed by reversal of metachromasy by alcohols, urea, surfactants, and electrolytes. The thermodynamic parameters of interaction revealed that binding between Thiazine dyes and the polymers was found to involve both electrostatic and hydrophobic forces. 

In general, any of the visible spectrophotometric methods described in Chapter 12 can be converted to a qualitative test by replacing the instrumental measurement of color intensity with a visual inspection. A typical procedure is use of a mixture of methylene blue (a blue, cationic dye) and pyrocatechol violet (a yellow, anionic dye) to provide a general test for surfactants (29). The aqneons sample (pH 5-6), mixed indicator, and petroleum ether are mixed. Test results are as follows ... 

A more efficient method of isolating anionic surfactants is extraction as part of an ion pair (33). An inorganic salt is added to decrease the solubility of the ion pair in the aqueous phase. Sometimes, the methylene blue spectrophotometric method described in Chapter 12 is used as the cleanup step. This permits the analyst to estimate the amount of surfactant isolated before proceeding with more definitive analytical techniques. Methylene blue may be removed from the surfactant extract by passage through a cation exchange column (56). If concentration is performed by liquid-liquid extraction of the ion pair with an alkyl quaternary compound, the UV spectrum of the ion pair is identical to that of LAS alone (55). 

A second method is the adsorption of a dye from a solution, e.g. methylene blue, fuchsine, methyl violet and malachite green. A certain grain fraction of a dried clay is stirred for a certain time in a dye solution with a specific concentration. The reduction of the solution s colour intensity is a measure for the adsorbed amount of dye and it is measured spectrophotometrically. The dye molecules are much larger than nitrogen molecules and so they are only adsorbed and will not enter the pores. 

Spectrophotometric detection based on the methylene blue (MB) method is the approach most commonly adopted for online derivatization and determination of sulfide in water due to its inherent selectivity. The so-called Fischer s reaction involves oxidative coupling of A, iV-dimethyl-p-phenylenediamine (DMPD) with sulfide ions in the presence of an oxidizing reagent (namely, Fe(III)) in acidic medium, thus rendering a heterocyclic thiazine dye, the MB. Different flow techniques described in the literature, such as FIA, SIA [11,12], and multisyringe flow injection analysis (MSFIA) [13-17] have exploited this reaction, covering a broad spectrum of possibilities with respect to analytical features. 

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. 

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