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A simple potentiometric determination of the total calcium concentration in human blood serum using a liquid membrane electrode is described. The bound calcium Is displaced from its complexes through acidification of the serum sample with an acetate buffer to pH 3.5. A novel neutral carrier based Ca2+-seiective electrode showing a much higher rejection of H+ ions in comparison to previously described carrier membranes as well as classical ion-exchanger membranes permits the Ca2+ determination at such a low pH value. A correlation of the total calcium concentrations determined by ion-selective electrodes with those obtained by atomic absorption spectrometry gives a residual standard deviation of f 0.04 mM over the 1.48-3.00 mM CaZ+ range.Through the introduction of Ca2+-selective electrodes especially by Ross (1, 2) the determination of ionized Ca2+ in blood serum became possible. Today improved electrodes based on organic phosphates ( 3 , 4 ) and on neutral carriers (5, 6 ) are used in several routine instruments (7-10). Although the activity of the ionized Ca2+ is claimed to be physiologically more relevant (11)(12)(13), the determination of the total calcium concentration remains a useful diagnostic parameter (14)(15)(16). For the assessment of total calcium, e.g., the sum of the concentrations of the ionized Ca2+ and the calcium bound to proteins and various other complexing agents, atomic absorption spectrometry (AAS) and colorimetry predominate in daily use (see ref 13 and 14). AAS is rather complex for clinical environments and colorimetry necessitates an extended and involved sample treatment (1 7-21). Several components interfere with the colorimetric detection (13, 14, 20, 21). Potentiometric sensors would offer an attractive alternative if it became possible to displace the bound calcium by a simple procedure. It has been shown that calcium can be displaced by hydrogen ions (13,14,(22)(23)(24)(25). This requires ion-selective electrodes with sufficient preference of Ca2+ over H 3 0 ' .Neutral carrier based Ca2+-selective electrodes are unique in this respect (5). Here we report on the use of a newly developed membrane for the measurement of total Ca2+ in diluted, acidified human blood serum. EXPERIMENTAL SECTIONMacroelectrode Systems. Cells of the type Hg,Hg&&;KCl (satd.)l3 M KCllsample solution(lmembrane)lO.OOl M CaC1,; AgC1,Ag were used for macroelectrodes. The external macroreference electrode was a double junction calomel electrode Philips R 44/2 SD-1. Two different membranes were examined, one consisted of 1.0 wt % ligand ETH 1001, 0.7 wt % potassium tetrakisb-chloropheny1)borate (KTpClPB), 65.3 wt % o-nitrophenyl n-octyl ether (o-NPOE), and 33.0 wt % poly(viny1 chloride) (PVC) and the other of 3.4 wt % ligand ETH 1001, 2.0 wt % potassium tetrakisb-chlorophenyl)borate, 62.9 wt % bis(2-ethylhexyl) sebacate (DOS), and 31.7 w t % poly(viny1 chloride). Both membranes were prepared by dissolving the four membrane 'Permanent address: Medico-chemical Central Laboratory, University Hospital, CH-8091 Zurich...

Lipophilic neutral carriers were synthesized which show Li+/Na+ selectivities of up to ca. 80 in highly lipophilic liquid membranes. The sensor membranes exhibit improved response times and increased lifetimes as compared to systems described earlier. They allow reliable measurements of Li+ in blood serum within the clinical concentration range. A 1 :I Li+/ionophore complex of one representative (N,N,N,N'-tetracyclohexyl-5,5-dimethyl-3,7-dioxaazelaamide) has been prepared, and its structure was elucidated by X-ray analysis.Introduction. -Among the different neutral carrier-based membranes recommended for Li+-selective electrodes [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], only few show acceptable Li+/Na+ selectivities for the potentiometric assay of Li' in blood serum during therapy of manic depressive psychosis

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1:1‐Complexes between nonactin and monactin, and sodium, potassium, and ammonium thiocyanate are described.