Analysis for transaminases in serum with an amperometric glutamate electrode

We determined transaminases in human blood serum with an amperometric glutamate biosensor. The probe was a hydrogen peroxide sensor assembled with appropriate selective membranes to enhance the probe specificity and lifetime. Calibration curves of glutamate were linear in the range 1-1000 mumol/L, with a response time of < 1 min. This probe was subsequently applied to the measurement of activities of aspartate and alanine aminotransferases in human sera. Analytical recovery studies demonstrated the suitability of the glutamate sensor by measuring 91-99% of added glutamate, 92-106% of added aspartate aminotransferase, and 101-105% of added alanine aminotransferase. Transaminase activity measured in 80 sera correlated well with results obtained with a spectrophotometric procedure.

Improving lactate analysis with the YSI 2300 GL: hemolyzing blood samples makes results comparable with those for deproteinized whole blood

To obviate the well-documented problem of hematocrit dependency of the Yellow Springs Instruments (YSI) whole-blood lactate analyzer, we modified the dilution buffer by including a lysing reagent. This makes the results comparable with those of methods performed with deproteinized whole-blood samples. No centrifugation step is needed, thus preserving the convenience of the YSI instrument for stat and field use. The modification works equally well on plasma samples. Lactate concentrations measured in nonhemolyzed whole blood are not comparable with results for hemolyzed whole blood or protein-precipitated whole blood. We therefore recommend to all users of YSI equipment to lyse the erythrocytes before lactate determinations.

A biocompatible needle-type glucose sensor based on platinum-electroplated carbon electrode

A biocompatible needle-type glucose sensor with a 3-electrode configuration was constructed. A platinum-electroplated carbon stick was used as the working electrode, Ag/AgCl as the reference electrode, and a disposable hypodermic needle made of stainless steel as the counter electrode. A Nafion membrane, an immobilized glucose oxidase (GOD) membrane, and a biocompatible membrane with diffusion-limiting effect were coated successively onto the working electrode. The sensor showed a rapid response (< 120 s in batch operation), good reproducibility (RE < 3%), good stability (over 36 h in control serum), a wide dynamic range (5-600 mg/dL glucose), and superior biocompatibility. It was used to determine glucose in serum. The data obtained from the sensor showed good agreement with that from a clinical autoanalyzer (R > 0.95).

Whole blood electrolyte assay using ChemPro 500. A comparison of assay performance with standard laboratory instruments

The ChemPro 500 'near-the-patient' analyser, with ChemPro 'Ion Profile' sensor cards, was evaluated for the assay of pH, Ca2+, K+ and Na+ in whole blood samples from patients in the intensive care unit or during surgery for heart or major blood vessel disease, or for liver transplantation. Imprecisions estimated from replicate whole blood measurements were much greater for all four ions than even the least stringent of the generally accepted analytical goals, and much greater than those estimated using quality assurance materials. Comparisons of assayed values with those obtained using standard laboratory instruments showed significant constant and proportional biases. The performance of the ChemPro 500 with the Ion Profile cards gave us no confidence in recommending their use to anaesthetists and intensivists.

A differential paramagnetic sensor for breath-by-breath oximetry

The operating principles of a fast paramagnetic oxygen sensor are described in detail. Some historical background of the paramagnetic effect in oxygen measurement is given as well. This sensor measures the difference between oxygen partial pressures in two gases as an alternating pressure signal being generated by the interaction of oxygen molecules with a switched magnetic field. Factors affecting the ideal performance of the sensor are analyzed. The main sources of interference are external pressure and vibration, and asymmetry in the transfer of the pressure signal to the microphone. Finally, the advantages of clinical breath-by-breath oximetry are briefly discussed.