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Potentiometric measurements of hydrogen and cyanide ions in buffered media

1990; Elsevier BV; Volume: 187; Issue: 2 Linguagem: Inglês

10.1016/0003-2697(90)90460-q

1096-0309

Frank J. Lebeda, Sharad S. Deshpande,

Cassava research and cyanide

Potentiometric measurements of hydrogen and cyanide levels were studied in different buffered media that are used in biological experiments. The addition of 1–10 mm NaCN increased the pH (from 7.2–7.5 up to 9.5) of either bicarbonate/phosphate-buffered (artificial cerebrospinal fluid (ACSF), sera, and whole blood) or Hepes-buffered solutions in a concentration-dependent manner. While in aerated ACSF this increase was transient (half-relaxation time < 4 min), the increase in pH was sustained in Hepes buffer. A mathematical model that predicts the maximum cyanide-induced increases in pH was derived. When NaCN was added to either ACSF or Hepes-buffered solutions, a Nernst relation was obtained, but deviations from Nornstian responses resulted when NaCN was added to sera or whole blood. These responses, however, differed substantially from the theoretical results that were based on the relative amounts of ionized cyanide present in the various pH environments. In addition, attempts were made to indirectly examine the formation and escape of HCN by calculating the time constants of decay (τd) of the cyanide-induced potentiometric responses. With progressively higher NaCN concentrations in ACSF, the values of τd did not decrease, but were constant. As predicted, however, the values of τd were larger when solutions were covered or had higher initial pH values. These results suggest that in the solutions tested, the cyanide electrode used in the present study measured the total amount rather than the ionized portion of dissolved cyanide and that the values of τd do not correspond to formation/escape rates of HCN.