O-Cresolphthalein

Polymeric pH indicators, phenolphthalein-formaldehyde (PPF) and o-cresolphthalein-formaldehyde (CPF) were synthesized with phenolphthalein and o-cresolphthalein reacted by formaldehyde under alkaline conditions, respectively. They can be immobilized in hydrolyzed cellulose diacetate membranes (HCDA) mainly due to macromolecular entrapment, and can be covalently bound to poly(vinyl alcohol) (PVA) via the considerable newly produced hydroxylmethyl groups [168,169], Phenol red (phenolsulfonphthalein) and its derivatives are commonly used for pH determination. 

Analysis. Ca gives a brick-red flame coloration, indicating that various optical spectroscopies will be effective in its determination. Ca is quantitatively determined by colorimetry down to 100 ppb using murexide or o-cresolphthalein, by atomic absorption spectroscopy (AAS) to 20 ppb, to 1 ppb by electrothermal absorption spectroscopy (ETAS), to 0.01 ppb by inductively-coupled plasma emission spectroscopy (ICPES), and to 10 ppb by inductively-coupled plasma mass spectroscopy (ICPMS). A spot test for Ca which extends to 3 ppm is provided by glyoxal bis(2-hydroxyanil). 

Usually, phenolphthalein-derived polymers are polymerized through the hydroxyl groups, thus destroying their well-known indicator properties. There is one example in which phenolphthalein and o-cresolphthalein 284 have been polymerized with formaldehyde to form phenol/formaldehyde type polymers, for example, 285. These polymers retain the indicating properties of the monomers with potential application in pFl test strips and optical pH sensors <2005PSA1019>. 

A series of novel polyimides were prepared from diaminophthalide 288 and four anhydrides 289 for the investigation of water-permeable membranes. Of the polymer products 290, the best permeability was associated with bulky groups (trifluoromethyls) on the polyimide chains <2005JAPS2047>. There are other variants of diaminophthalide 288 used to prepare polyimides and polyamides. A fluorinated variation 291 has been used for polyimide synthesis <2004MI979> as has 292, derived from o-cresolphthalein 284 <1999PSA455>. 

Kang HP, Scott MG, Joe BN, Narra V, Heiken J, Parvin CA Model for predicting the impact of gadolinium on plasma calcium measured by the o-cresolphthalein method. Clin Chem 50 741 -746,2004. 

The procedures given in sections (D), (E), (F), and (G) are intended to illustrate the preparation of a number of useful indicators. Phenolphthalein is not selected because it is available at a very low price. o-Cresolphthalein has about the same range (pH 8.2-9.8) as phenolphthalein, while th3unolphthalein is useful at pH 9.4-10.6. Both are formed by essentially the same method as phenolphthalein. 

Indicator for titrations. Phenolphthalein, methyl red, and o-cresolphthalein are dissolved in 90 per cent methanol. The useful concentration is 0.5 to 1.0 g per liter. 

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. 

A number of other phthaleins such as o-cresolphthalein, pyro-gallolphthalein, etc., as well as halogen substitution products of certain of the above-mentioned compounds have been prepared and partially investigated. In general, however, these additional indicators offer few advantages over the compounds described in detail. 

The transformation interval of o-cresolphthalein is between 8.2 and 9.8 (colorless to red). The colors of the pyrogallolphthalein in alkaline media are not very stable. 

Various organic reagents are used for direct determination of calcium, such as murexide (ammonium purpurate) (e = 1.4-10 at 500 nm) [2,49], Metalphthalein [50], Calcein [51,52], Chrome Azurol S (in the presence of 1,10-phenanthroline) [53], Alizarin S [54], 8-hydroxyquinoline (extraction into CHCI3 in the presence of n-butylamine or butoxyethanol) [55], and Emodine (l,3,8-trihydroxy-6-methylanthraquinone) [56]. Calcium has been determined as a complex with Emodine, in the presence of Be and Mg, by the derivative spectrophotometry technique. The anionic complexes of calcium with bromo-oxine [57] or HTTA [58] have been extracted into benzene as ion associates with Rhodamine B. Calcium was also determined as a complex with o-cresolphthalein [59-63], or thymolphthalein [64]. 

Calcium has been determined with o-cresolphthalein in proteins [59], waters [60-62], and soil extracts [62]. The flow-injection technique has been applied [60,62]. Thymolphthalein has been used for determining Ca in blood semm [64]. Calcium has been determined with metalphthalein in water, urea, and pharmaceutical samples [50]. 

Some other organic reagents have been also proposed for determination of Mg, e.g., Eriochrome Cyanine R [45], Alizarin S [46], o-cresolphthalein [47] and its derivatives [48], 1,2,7-trihydroxyanthraquinone [49], 1,8-dihydroxyanthraquinone (e = 1.2-10 at 510 nm) [50], and leuco-quinizarin [51]. Mg has been determined also with the use of emodin... 

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