A multi-centre evaluation of the measurement of high density lipoprotein cholesterol by the Reflotron assay.

A multi-centre study was undertaken to evaluate the performance of the Reflotron high density lipoprotein cholesterol method in twelve different clinical chemistry hospital laboratories. Results were compared with phosphotungistic acid/Mg2+ and polyethylene glycol/dextran sulphate/Mg2+ precipitation methods, routinely performed in these laboratories. Precision was found to be excellent, for both the day-to-day results (SD = 0.03 mmol/l) and for the overall between-laboratory precision (SD = 0.02 mmol/l), measured with control sera. HDL cholesterol concentrations measured with the Reflotron system were about 10% lower than those obtained with the two routine precipitation methods, using different instruments with different cholesterol standardization procedures.

Direct potentiometric determination of sodium ion in blood. III. Influence of (bi)carbonate.

We measured the emf of a sodium ion-selective electrode in NaCl-NaHCO3 solutions (160 mmol of Na+, 160-120 mmol of Cl-, and 0-40 mmol HCO3- per liter) with a home-built cell in steady-state after 10 min and with two commercial direct potentiometric analyzers about 20 s after the sample was introduced. Substitution of HCO3- for Cl- resulted in a small decrease in emf. We calculated the effect of chloride ion replacement by bicarbonate ion on the liquid-junction potential and found that this accounted only for one-third of the emf decrease. The exact composition of bicarbonate solutions is closely related to the pH. To control the formation of carbonate, we performed measurements with the home-built cell at two pH values (7.0 and 8.2), controlled by tonometry with carbon dioxide. From the differences in the slope of the emf vs the amount of bicarbonate added at the two pHs we calculated the thermodynamic association constants of the sodium bicarbonate and sodium carbonate complexes (KNaHCO3(0) = 0.53 and KNaCO3- = 24). We conclude that, for the direct potentiometric measurement of sodium ion, only fresh serum should be used, to avoid pH changes. Replacement of sodium chloride by sodium bicarbonate caused different results when emf was measured with commercial analyzers, owing to their short measuring time of about 20 s.

Nephrotoxicity of 1,1-diaminomethylcyclohexane sulphato platinum II (spiroplatin; TNO-6).

1,1-Diaminomethylcyclohexane sulphato platinum II (spiroplatin; TNO-6) is a new platinum-containing analog used as an antitumor agent. Renal function studies were performed in eight patients treated with this drug (30 mg/m2). During and after the first spiroplatin infusion there was a decrease in effective renal plasma flow (ERPF:P less than 0.05) and an increase in filtration fraction (P less than 0.01) without changes in glomerular filtration rate (GFR), suggesting changes in renal hemodynamics. During the same period there was an increase in relative N-acetyl-beta-D-glucosaminidase excretion (P less than 0.01), pointing to tubular cell damage. Also, an increase in relative beta 2-microglobulin excretion was established during and after spiroplatin infusion. On day 21 a decrease in GFR was found (median 7.4%), together with a decrease in ERPF (median 11.8%).

Direct potentiometric determination of sodium ion in blood. II. Influence of cations.

We measured the emf of NaCl solutions (120-160 mmol/L), with and without the addition of KCl (5-20 mmol/L), CaCl2 (2-8 mmol/L), or MgCl2 (1-4 mmol/L). Measurements were made with a home-built cell in steady-state and with two commercial direct potentiometric analyzers about 20 s after the sample was introduced. We calculated the sodium ion activity in the mixed NaCl-KCl solutions according to different thermodynamic theories and found almost the same results. We conclude that the influence on the emf of physiological concentrations of these cations was negligible when emf measurements were made in steady-state with the home-built cell. Of the three added cations, K+ caused the greatest increase in apparent sodium ion activity (up to about 4%) when emf measurements were made with commercial analyzers, owing to low salt-bridge concentration and the short measuring time of about 20 s.

Direct potentiometric determination of sodium ion in blood. I. Potentiometric response in simple sodium chloride solutions.

We measured the emf of NaCl solutions (120-160 mmol/L) with a home-built cell in steady-state and with some commercial direct potentiometric analyzers about 20 s after the sample is introduced into the instrument. We compared the results with the theoretical sodium ion activity calculated according to different thermodynamic theories. The slope of the calibration graph was calculated with and without correction for the influence of NaCl concentration on the liquid junction potential of the calomel reference electrode. We conclude that different theories used to calculate the sodium ion activity in the concentration range investigated give almost the same results; furthermore, introduction of the liquid junction potential leads to a more nernstian-like slope of the calibration graph. Measurement of identical NaCl solutions with various commercial analyzers showed different displayed concentrations, presumably because of differences in junction structure, measuring time, and concentration of calibration solutions.

Influence of erythrocytes on direct potentiometric determination of sodium and potassium.

We have shown that the sodium concentration in whole blood measured by direct potentiometry is higher than in plasma. The 'erythrocyte-effect', already described by Siggaard Andersen, is most pronounced for instruments equipped with a reference electrode with an open static liquid junction and is thus a general phenomenon. Instruments with a modified liquid junction show less interference. The same phenomenon appears for the determination of the potassium concentration, although the difference between whole blood and plasma, when measured with instruments equipped with a modified liquid junction, can be neglected in practice.

On the standardisation of the direct spectrophotometric bilirubin determination. Influence of the albumin source and the molar bilirubin: albumin ratio.

The influence of different albumin solutions and of the molar bilirubin/albumin ratio on the bilirubin concentration determined by the method for Hertz et al. was studied. There is good agreement between the true-bilirubin concentrations and those obtained by the Hertz method for bilirubin-HSA and bilirubin-serum solutions. Moreover the observed concentration is scarcely influenced by the molar ratio. Bilirubin standards in HSA-solutions can thus be used to standardise this method. Errors are introduced by preparing standards in BSA-solutions as the absorption spectrum of bilirubin-BSA is different from that of bilirubin-HSA.

Gelatin derivatives in blood: interference with the determination of inorganic phosphate in serum.

The method of Goldenberg and Fernandez (1966) Clin. Chem. 12, 871--882) for the determination of inorganic phosphate in serum is significantly influenced by turbidity after intravenous application of gelatin derivatives, even at low quantities. This turbidity can be eliminated by the addition of sodium dodecyl sulphate to the reaction solution.

Determination of amitriptyline and some of its metabolites in blood by high-pressure liquid chromatography.

Conditions for the determination of amitriptyline and some of its metabolites in serum on a reversed-phase material (C-8) by high-pressure liquid chromatography with UV detection at 254 nm were systematically investigated. The separation of tricyclic antidepressants is best carried out on a phase system consisting of C-8 bonded-phase material as the stationary phase and water--methanol--dichloromethane--propylamine as the mobile phase. The precision and detection limit of the method and the extraction efficiency were established. A chromatogram of a serum extract from a patient treated with amitriptyline is shown. Serum levels of amitriptyline and its four main metabolites (nortriptyline, desmethylnortriptyline, trans-10-hydroxy-amitriptyline and trans-10-hydroxy-nortriptyline) in a patient receiving 150 mg of amitriptyline daily, are reported.