Methylthymol blue indicator

Lime plus magnesia. Titrimetrically with EDTA in triethanolamine and ammonia using methylthymol blue indicator. For chrome-bearing samples, a cleanup through an ion-exchange resin is required first followed by EDTA titrimetry with an Eriochrome Black T indicator. 

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). 

This test is based upon formation of barium sulfate in the presence of excess barium, followed by chelation of the remaining barium with methylthymol blue, a metallochrome indicator recently developed for complexometric titrations (13, 14, 15, 16, 17). The reagent is a solution containing equimolar amounts of barium chloride and methylthymol blue at a concentration equivalent to the largest amount of sulfate ion anticipated in the test solution 18). 

Subsequent addition of O.IN sodium hydroxide to an apparent pH of 12.8 causes methylthymol blue to become either blue in the presence of barium, or grey in its uncomplexed form. The maximum absorption of the uncomplexed form is at 465 m/x, and the reaction stream is conducted through the colorimeter equipped with filters transmitting at this wavelength. Since the indicator reagent is initially equimolar in barium ion and methylthymol blue, the amount of uncomplexed indicator remaining is directly related to the concentration of sulfate ion in the original sample. 

Sulfate is still determined in CE systems with barium and a metallochromic indicator such as dimethylsulfonazo(III) (DMSA(III)) or methylthymol blue. As DMSA(in) is a metallochromic indicator, interfering cations should be removed prior to the determination step. Such pretreatment can be done in the flow-through system. The method suffers interference only from high concentrations of potassium, phosphate, hydrogen ion, chloride, and nitrate. As a consequence the method performs favorably when applied to groundwater, wastewater, or percolation water from tipped refuse. 

Methylthymol Blue (3,3 -bis-(N,N-dicarboxymethyl)aminomethylsulfo-naphthalene), a metallochromic indicator, shows a yellow color and forms a deep blue chelate with scandium in acid conditions. At pH 1.5, this color reaction is selective. ... 

Procedure. One drop of the test solution is mixed with one drop of a pH 1.5 buffer solution and then with one drop of a 0.02 % aqueous solution of Methylthymol Blue on a spot plate or in a micro test tube. A blue color indicates the presence of scandium. 

Prepare 0.01 M solution of purest barium chloride or nitrate. Pipette 25.0 cm into a conical flask, add 75 cm water and a few cm of M NaOH to give a pH 12 0.5 (use a pH meter to check) and dissolve in the solution 50 mg methylthymol blue/potassium nitrate mixture (containing 1% w/w indicator). Titrate with standardised 0.1 M EDTA solution until the colour changes from blue to grey. Similarly, Mg, or Sr can be titrated. 

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