Methylthymol blue

Sulphate in Waters, Effluents and Solids (2nd Edition) [including Sulphate in Waters, Effluents and Some Solids by Barium Sulphate Gravimetry, Sulphate in waters and effluents by direct Barium Titrimetry, Sulphate in waters by Inductively Coupled Plasma Emission Spectrometry, Sulphate in waters and effluents by a Continuous Elow Indirect Spectrophotometric Method Using 2-Aminoperimidine, Sulphate in waters by Elow Injection Analysis Using a Turbidimetric Method, Sulphate in waters by Ion Chromatography, Sulphate in waters by Air-Segmented Continuous Elow Colorimetry using Methylthymol Blue], 1988... 

BPR = bromopyrogallol red FSB = fast sulphone black F M = murexide MTB = methylthymol blue SB = solochrome black TPX = thymolphthalexone VB = variamine blue XO = xylenol orange. 

With methylthymol blue, lead may be titrated at a pH of 6 without interference by calcium the calcium is subsequently titrated at pH 12. 

Procedure. Pipette 25 mL of the test solution (which may contain both calcium and lead at concentrations of up to 0.01 M) into a 250 mL conical flask and dilute to 100 mL with de-ionised water. Add about 50 mg of methylthymol blue/potassium nitrate mixture followed by dilute nitric acid until the solution is yellow, and then add powdered hexamine until the solution has an intense blue colour (pH ca 6). Titrate with standard (0.01 M) EDTA solution until the colour turns to yellow this gives the titration value for lead. 

Xylenol orange and methylthymol blue as chromogenic reagents. B. Budesinsky, Chelates Anal. Chem., 1967,1,15-47 (124). 

Methylthymol blue and methylxylenol blue, prepared by the Mannich reaction from thymol-sulfonphthalein and p- xylenol blue respectively, have been intensively studied and resemble xylenol orange in many respects. If only one chelating group is introduced into cresol red, semi-xylenol orange results which is a common contaminant in XO and proves to be a more sensitive reagent for zirconium. 

Ping et al. have fabricated an integrated microsensor array on a silicon wafer for pH imaging [89]. Six different pH-sensitive colorimetric dyes (methyl violet 6B, phenolic red, alizarin complexone, 5-carboxy-fluorescein, alizarin red and methylthymol blue) were used to cover the whole pH range. The dyes were adsorbed on microbeads and placed in etched microwells on the silicon wafer. The indicator array was also used as a cation sensor chip (see Sect. 2.4). 

Hydroxyanthraquinone derivatives, especially alizarine red S (fig. 67), also form 1 1 complexes with Ybm ions (Korovin et al., 1988). The observed lifetimes are very short, around 0.3 ps, but comparable to those listed in table 15 for the complexes with triphenylmethane dyes. The relative luminescence intensities of Ybm complexes with several different dyes are summarized in fig. 68. The intensities are given relative to the more luminescent complex, with phthalexon S. It is noteworthy that all these complexes have absorption maxima at wavelengths longer than 500 nm, between 505 nm for thorin I and 590 nm for methylthymol blue H475d, and can thus be excited by the 546 nm-emission line of a mercury lamp. 

Nazarenko, V. A., and Nevskaya, E. M. Chemistry of the reactions between the ions of multivalent elements and organic reagents. XVII. Interaction of aluminum and gallium ions with methylthymol blue. J. Anal Chim. USSR 24(6), 670-673 (1969). 

Sulphates. Modifications to the automated photometric method for the determination of sulphate, which is based on decreasing the blue colour of the Ba-methylthymol blue complex by the precipitation of barium sulphate, have permitted150 determinations of 0—1.0 mg of SOT 1 with a 1.7% relative error. A flow cell was used with a high flow rate, produced by adding MeOH to the sample stream. A flow apparatus has also been used151... 

Methylthymol blue (see Figure 49-9) forms a blue complex with magnesium, which is measured around 600 nm. EGTA is added to reduce interference by calcium. 

Xylenol Orange (formula 4.19) [48,49] and its relative Methylthymol Blue [48,50] are characterized by the presence of the iminodiacetic acid groups, which occur in complexones such as EDTA. 

Other indirect methods involve reactions with the mercury(II) complexes of diphenylcarbazone [20] or Methylthymol Blue [21], or the displacement of thiocyanate ion from AgSCN or Hg(SCN)2 by bromide, followed by the spectrophotometric determination of thiocyanate with ferric ions [22,23]. 

Several indirect methods for determination of cyanide involve the displacement by cyanide of metals from their complexes with organic reagents, with subsequent change in colour of the solutions, such as the methods using Hg(II) complexes with diphenylcarbazone [21] and Methylthymol Blue [22]. 

In another indirect method for determining chloride use is made of the fact that HgCl2 is more stable than the violet Hg(II) diphenylcarbazone complex [30,31]. The violet colour of the solution is a function of the chloride concentration. In other indirect methods chloride displaces Methylthymol Blue [32] or Xylenol Orange [33] from their complexes with mercury(II). 

In indirect methods for determination of fluoride, aluminium complexes with Eriochrome Cyanine R (ECR) [58] and Xylenol Orange [59] have been applied. The sensitivity of the ECR method increases considerably in the presence of CP [60]. The complexes of scandium with Methylthymol Blue (e = 1.07-10 at 590 nm) and Pyrocateehol Violet [61] have also been recommended. 

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]. 

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]. 

The following triphenylmethane dyes have been employed for determination of Sc similarly to Xylenol Orange Methylthymol Blue [33], Chrome Azurol S [34,35], Chromal Blue G [36], and Eriochrome Brilliant Violet B [37]. Much higher sensitivities have been obtained in the presence of some cationic surfactants [38 0]. In the method with Chrome Azurol S and Zephiramine, the e value is 1.5-10 at 610 nm, and in the method with Eriochrome Cyanine R and CP, e = 9.2-10" at 600 nm [40]. When o-hydroxy-quinonephthalein and CP are used, the molar absorptivity is 1.1-10 at 555 nm [41], Scandium has been determined with the use of Nile Blue in a poly(vinyl alcohol) medium [42]. 

Many complexes of various organic reagents with Ba have been used as reagents for indirect determination of sulphate, such as Chlorophosphonazo III [35-37], Dimethylsulphonazo III [11,38 0], Sulphonazo III [40], Nitchromazo [41], Orthanilic K [42], Thoron I [43], Methylthymol Blue [44,45]. 

Calcium and Mg in mineral water were simultaneously determined with Methylthymol Blue by both batch and flow-injection techniques [3], FIA method using murexide as a colour agent was employed to the determination of Ca in ores and Ca-containing pharmaceutical formulations [4]. 

---