Patton and Reeder’s indicator

Patton and Reeder s indicator. The indicator is 2-hydroxy-l-(2-hydroxy-4-sulpho-l-naphthylazo)-3-naphthoic acid the name may be abbreviated to HHSNNA. Its main use is in the direct titration of calcium, particularly in the presence of magnesium. A sharp colour change from wine red to pure blue is obtained when calcium ions are titrated with EDTA at pH values between 12... 

The titration with EDTA, using solochrome black as indicator, will yield the calcium content of the sample (if no magnesium is present) or the total calcium and magnesium content if both metals are present. To determine the individual elements, calcium may be evaluated by titration using a suitable indicator, e.g., Patton and Reeder s indicator or calcon — see Sections 10.48 and 10.60, or by titration with EGTA using zincon as indicator — see Section 10.61. The difference between the two titrations is a measure of the magnesium content. 

Discussion. Patton and Reeder s indicator (HHSNNA), see Section 10.48, makes it possible to determine calcium in the presence of magnesium, and is... 

The calcium content may then be determined by titration wth EDTA using either Patton and Reeder s indicator or calcon (Section 10.60), or alternatively by titration with EGTA (see Section 10.61). 

Palladium, D. of as dimethylglyoximate. (g) 463 as nioximate, (g) 474 by EDTA, (ti) 329 Paper chromatography 229 see Thin layer chromatography Parallax errors due to, 85 Parallel determinations 132 Partial ionic equations 850, (T) 851 Partition chromatography 13. 217 Partition coefficient 162 Patton and Reeder s indicator 317, 328 Peptisation 419. 421... 

The titration with EDTA, using Solochrome Black (Eriochrome Black T) as indicator gives the total calcium plus magnesium content. To determine the individual elements, calcium may be estimated by titration using Patton and Reeder s indicator. The difference between the two gives the estimate of magnesium. 

There are other dyestuffs, named eriochrome black A, B, and R, whose structures are very close to that of black T. Another indicator of the same chemical family is Patton and Reeder s indicator, whose structure is as follows ... 

A first methodology consists of carrying out two successive titrations, one in the presence of Patton and Reeder s indicator, the other in the presence of eriochrome black T. The former allows us to determine Ca + alone, the latter both globally. The global content in both ions is the total hardness. The difference between the added volumes at the two endpoints determines Mg +. 

A variation of this methodology consists of replacing Patton and Reeder s indicator by calcon as the indicator in the first titration and then in operating as in the above-mentioned conditions. 

For most work in pharmaceutical analysis classical methods have now been superseded by complexometric titration. Determination of calcium by itself presents little difficulty and two basic procedures are applicable, (i) titration at pH 10 in ammonia buffer using solochrome black as indicator and (ii) titration at pH 12 to 13, either in diethylamine using alizarin black (diadem chrome black) or in potassium hydroxide solution using Patton and Reeder s indicator. Provided a small quantity of complexed magnesium is included for titration (i) sharp and satisfactory end-points are obtained by these methods and there is no significant difference in the results obtained at the two pH values if a pure calcium compound is titrated. Difference in the two results would be expected if the calcium salts were contaminated with magnesium, when the titration at pH 10 would include both ions and that at the higher value the calcium only. 

Dissolve a suitable quantity of calcium salt, to contain about 0 05 g Ca, in about 150 ml of water. Add 4 ml of 8N potassium hydroxide and about 0-2 g of Patton and Reeder s indicator (containing ascorbic acid— see Appendix ID. Titrate with 0 05M EDTA to a pure blue end-point. 

Patton and Reeder s Indicator (containing ascorbic acid)... 

---