Calcium oxalate permanganate titration

Newbrun (N2) reported the determination of calcium in saliva by atomic absorption. When samples were diluted with water only, results were obviously too low, but with strontium, lanthanum, or EDTA the values agreed with those obtained by oxalate permanganate titration. Calcium was higher in the excretion from the submaxillary glands than in that from the parotid. Depletion of saliva calcium content was not seen after 15-minute. stimulation. 

Quantitative Analysis. OxaUc acid is precipitated as calcium oxalate from a solution containing oxaUc acid, and the calcium oxalate obtained is then weighed. If there are no organic substances other than oxaUc acid present, oxaUc acid can be titrated quantitatively with potassium permanganate. 

These direct titrations form the basis of more complicated analytical procedures. Many analytical procedures are indirect and involve additional preliminary reactions of the sample before the titration can be carried out. For example, a soluble calcium salt will not take part in a redox reaction with potassium permanganate. But adding ammonium oxalate to the solution containing Ca causes the quantitative precipitation of calcium oxalate ... 

For example, we showed in earlier chapters that the calcium ion concentration of an aqueous solution is readily determined by titration with a standard EDTA solution or by potential measurements with a specific-ion electrode. Alternatively, the calcium content of a solution can be determined either from atomic absorption or atomic emission measurements or by the precipitation of calcium oxalate followed by weighing or titrating with a standard solution of potassium permanganate. 

The solubility of CaSe04-2H20(cr) in water was determined between 270.6 and 375.4 K. The calcium concentration was found by the oxalate-permanganate method and by a complexometric titration. As the solubility data are not readily available they are reproduced in Table A-16. 

The only common redox titration applied in the clinical laboratory is for the analysis of calcium in biological fluids. Calcium oxalate is precipitated and filtered, the precipitate is dissolved in acid, and the oxalate, which is equivalent to the calcium present, is titrated with standard potassium permanganate solution. This method is largely replaced now by more convenient techniques such as complex-ometric titration with EDTA (Chapter 9) or measurement by atomic absorption spectrophotometry (Chapter 17). 

The calcium in an unknown hard-water sample is precipitated as calcium oxalate in ammonia solution, and the precipitate is quantitatively filtered and washed, and is then dissolved in dilute sulfuric acid. The oxalic acid is titrated with standardized potassium permanganate solution. 

Titrimetric methods have also commonly been proposed for the determination of fixed and total acids in wines. After treating the wine with a cation-exchange resin, oxalic acid can be precipitated as its calcium salt and titrated with potassium permanganate. For determination of tartaric acid in wine the acid can be precipitated as calcium tartrate or potassium hydrogentartrate. 

With regard to the determination of oxalic acid, see the standardization of potassium permanganate, above.) An interesting extension of the oxidization reaction of oxalic acid is the determination of calcium ions. The latter are precipitated as calcium oxalate in hot acetic acid (solubility product = 10 ). The precipitate is separated out from the solution, washed, and dissolved into a 2 mol/L sulfuric acid solution. After heating, the liberated oxalic acid is titrated with permanganate. In fact, oxalic acid is simply liberated by displacement of the precipitation equilibrium ... 

M EDTA 0-01712 g can be assayed for their calcium content either by precipitation as oxalate and titration with permanganate or by EDTx titration, both described above. 

Calcium aminosalicylate, Ci4Hi206N2Ca,JH20, Mol. Wt. 353 4, or Ci4Hi206N2Ca, 3H2O, Mol. Wt. 398 4, may be determined by the method given for the sodium salt. Calcium can be assayed either by permanganate titration after precipitation as oxalate, or by EDTA. 

When the precipitated calcium oxalate is dissolved in hot dilute sulphuric acid, the oxalic acid liberated can be titrated against standardised permanganate. 

Elemental composition Ca 40.04%, C 12.00%, O 47.96%. CaCOs dissolves in water in the presence of a few drops of HCl. The solution is analyzed for calcium by AA or ICP spectroscopy or by treatment with ammonium oxalate followed by titration with potassium permanganate. 

The classical method for calcium is by gravimetric determination as oxalate. A hot solution of calcium salt in hydrochloric acid is treated with ammonium oxalate or oxalic acid and neutralised with ammonia the precipitate is washed with dilute ammonium oxalate solution and is then ignited to calcium carbonate or oxide, or is converted to calcium sulphate by treatment with sulphuric acid. An alternative volumetric finish is to dissolve the precipitated oxalate in sulphuric acid and titrate with potassium permanganate. 

---