Calcium/ions/salts determination

Comparison of results for the first and last entries in Table 7 (AOS 2024 and IOS 2024) was for samples for which the hydrophobe linearity, hydrophobe carbon number, and relative disulfonate content were held nearly constant. The major differences in these surfactants were possible differences in the relative locations of the double bond and the sulfonate group in the alkenesulfonate and in the relative locations of the hydroxy group and the sulfonate group in the hydroxyalkanesulfonate. Analyses to determine these are quite difficult. At calcium ion concentrations below 100-250 ppm, AOS 2024 appeared to be more salt-tolerant than linear IOS 2024. At higher calcium concentrations, the calcium ion tolerance of the two surfactants was similar. 

The stabilizing effect of buffers that have multiple charged species in solution should also be investigated to determine the potential reaction between excipients and API. For example, buffers that use carbonates, citrate, tartrate, and various phosphate salts may precipitate with calcium ions by forming sparingly soluble salts. However, this precipitation is dependent upon the solution pH. Because phosphate can exist in mono-, di-, and tribasic forms, each calcium salt has its own solubility product, and precipitation will only occur when one of the solubility product is exceeded. Calcium ions may also interact or chelate with various amino acids, and other excipients, which may also lower the effective concentration of calcium that is capable of interacting with phosphate ions. Finally, the activity of phosphate ions may be lowered due to interactions with other solution components. 

As a consequence of the precipitation of calcium ions inside the vesicles, the product of the ion activities of calcium and the respective anions in the internal vesicular space is fixed by the solubility product of the precipitating salts (L). Since in the external solution changes of the ion activities of calcium (Ca0) and of the precipitating anions (A ) can be followed experimentally, the energy requirement for calcium uptake can be determined at every moment. The energy requirement is given by the expression ... 

Wenner, V. R. 1958. Rapid determination of milk salts and ions. I. Determination of sodium, potassium, magnesium and calcium by flame spectrophotometry. J. Dairy Sci. 41, 761-768. 

Other physical phenomena that may be associated, at least partially, with complex formation are the effect of a salt on the viscosity of aqueous solutions of a sugar and the effect of carbohydrates on the electrical conductivity of aqueous solutions of electrolytes. Measurements have been made of the increase in viscosity of aqueous sucrose solutions caused by the presence of potassium acetate, potassium chloride, potassium oxalate, and the potassium and calcium salt of 5-oxo-2-pyrrolidinecarboxylic acid.81 Potassium acetate has a greater effect than potassium chloride, and calcium ion is more effective than potassium ion. Conductivities of 0.01-0.05 N aqueous solutions of potassium chloride, sodium chloride, potassium sulfate, sodium sulfate, sodium carbonate, potassium bicarbonate, potassium hydroxide, and sodium hydroxide, ammonium hydroxide, and calcium sulfate, in both the presence and absence of sucrose, have been determined by Selix.88 At a sucrose concentration of 15° Brix (15.9 g. of sucrose/100 ml. of solution), an increase of 1° Brix in sucrose causes a 4% decrease in conductivity. Landt and Bodea88 studied dilute aqueous solutions of potassium chloride, sodium chloride, barium chloride, and tetra-... 

Electrodes suitable for the potentiometric determination of surfactants are either specially designed liquid or solid membrane electrodes or ion-selective electrodes that in addition to being selective to a particular ion, also quantitatively respond to surfactants. For example, a nitrate ion-selective electrode responds to anionic surfactants, a calcium ion-selective electrode is sensitive to quaternary ammonium salts, and a barium ion-selective electrode can be used for assaying polyethoxylates [43], In some cases it is possible for one to perform potentiometric determination of a counter-ion, e.g. one can titrate alkylpyridinium chloride or bromide salts with silver nitrate solution using silver wire as an indicator electrode [38]. 

Figure 5.14 Change in ratio of calcium ions to sodium ions in the membrane phase during electrodialysis (KNaCa) with polymerization time of aniline. After a 1 1 mixed salt solution of 0.250N calcium chloride and 0.250N sodium chloride (concentration of chloride ions 0.500N) had been electrodialyzed for 1.0 h at 10 mA cm 2 using a membrane with polyaniline layers, the membrane was immediately removed from the cell during electrodialysis and the ratio of calcium ions to sodium ions in the membrane phase was determined (starting membrane NEOSEPTA CM-1).

UV-visible spectrophotometry, and potentiometry. The last is primarily used for the measurement of ionized (free) calcium ions in the (extracellular) water phase of blood or serum. The other techniques are used for the determination of total calcium in serum and urine. Urine must be acidified (pFI 1) to release calcium ions from stable salts in the sediment. 

Alginate is present as the salt of different metals, usually sodium and calcium. Calcium ions are important in determination of gel strength. 

Carboxy groups present in polyvinyl alcohol are transformed into calcium salts and isolated. After hydrolysis, the calcium ions can be determined by using the zinc ethylenediaminetetraacetate complex. The current of the liberated zinc ions is then measured. 

The calcium ion concentration was determined by chromatic comparison of the red-violet complex produced by the reaction with Merck Calcospectral in an aequeous medium with a maximum error of 1.5 mg/1 and titrimetrically utilizing the disodium salt of ethylene-dinitrilotetraacetic acid to chelate the calcium and calconcarboxylic acid as the calcium specific indicator. The titrimetric method was preferred. 

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