842. The interaction of calcium ions with some phosphate and citrate buffers

Abstract

The p H of phosphate and citrate buffers is markedly reduced by the Dissociation constants in water a t 25' are reported for the species addition of calcium ions, owing to the formation of association products.CaH,PO,+, CaHPO,, CaH,Cit+, and CaHCit (Cit = citrate).IT is to be expected by analogy with other multivalent electrolytes that fairly extensive ion-pair formation will occur when calcium ions are introduced into buffer solutions containing multivalent anions (Davies, Endeavour, 1945, 4, 15). We have confirmed this by pH measurements. The pHs of Sorensen's hydrogen phosphate buffers are appreciably lowered by saturating them with the sparingly soluble calcium iodate; and with acid citrate buffers the effect is so great that the pH may be reduced by more than a unit. This increase in the hydrogen-ion concentration is due to the preferential association of the calcium ion with the most highly charged anions, leading to the displacement of equilibrium by reactions such as : Ca2+ + H,Cit-+ CaHCit + H+. A further effect of the interaction is the enhancement of the solubility of the calcium salt, and we have studied the interaction quantitatively by means of solubility measurements. EXPERIMENTALCalcium iodate was prepared, and its solubility measured, according t o the methods usedThe buffer solutions were made up from " AnalaR " p H measurements were made colonmetrically by in our previous work ( J . , 1951, 233). reagents and carbon dioxide-free water.

Solubility of CaHPO4 2H2O and formation of ion pairs in the system Ca(OH)2 - H3PO4 - H2O at 37.5 C

“…Davies and Hoyle [20] reporten dissociation constants at 25°C for systems containing sodium and potassium phosphate buffers and calcium iodate. Allowing for experimental differences , the constants obtained by Davies [CaHP04]0; these varied from 1.01 to 9.55 X 10-3 • As in previous reports by the same author [23,24], ionic concentrations were used instead of activities.…”

“…For each selected pair of values for XO and Y~, eq (20) was solved by successive approximations starting with unitary activity coefficients analogously to the procedure outlined above.…”

Chromatography as the Major Tool in the Identification and the Structure-Function Relationship Study of Amylolytic Enzymes from Saccharomycopsis Fibuligera R64

“…Further, AMY demonstrated lower activity in phosphate-citrate buffer. This phenomenon may arise from the citrate, which is reported to interact with calcium ion (37). The activity of AMY decreased concomitantly with the increase of the citrate buffer concentration but was fully recovered upon back-titration with calcium chloride (data not shown).…”

Néhány, hiperalkalikus körülmények között képződő Ca(II)-komplex oldategyensúlyainak és szerkezetének jellemzése

“…Az ezt követő munkákban nagyszámú adat található a CaOH + (aq) képződési állandójára különféle analitikai módszerekkel (oldhatósági- [3,15,64,[66][67][68], potenciometriás- [69,70], valamint kinetikai mérésekkel [2,71]) meghatározva.…”