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Biomedical subjects

R T Fowler

Publications and source records attributed to R T Fowler.

10 recordsLinked to original sources
PubMed1992

Colorimetric measurement of iron in plasma samples anticoagulated with EDTA.

AIMS: To determine if the iron in EDTA anticoagulated plasma samples can be measured by colorimetric assays using Ferrozine. METHODS: Paired samples of serum and EDTA plasma were obtained from 24 patients and analysed by three commercial iron methods. The EDTA plasmas were also analysed using methods modified by the addition of zinc sulphate or with different concentrations of Ferrozine. The iron contamination of EDTA sample tubes was measured by atomic absorption spectroscopy. RESULTS: Two commercial colorimetric iron methods gave results of zero for EDTA plasma samples. A third commercial reagent gave plasma results that were about 30% lower than their corresponding serum samples. Addition of 7 mmol/l zinc sulphate to this reagent system and extending the sample preincubation time to 300 seconds yielded comparable results from paired serum and EDTA plasma samples. Linear regression analysis gave a slope of 0.97 with an intercept of 0.60 mumol/l and R2 = 0.9943. Measurements by atomic absorption spectroscopy showed that this positive intercept was due to contamination of the blood collection tubes with about 90 ng of iron. CONCLUSIONS: Modification of commercial colorimetric iron methods permits the biochemical assessment of iron status and a full blood count from a single EDTA anticoagulated blood sample.

Anticoagulants↗
PubMed1983

Microsampling on the Technicon SMAC system.

The sample volume needed for a Technicon SMAC continuous-flow analyzer has been reduced for routine operation. Two options are available: 141 microL for a 17-test profile, or 224 microL, which allows the direct-sampling assays for creatinine and iron to be included. The sample decrease is achieved by the sequential dialysis of creatinine and iron, an increased sample dilution from sixfold to ninefold, the strict minimization of diluted sample stream wastage, and development of more sensitive methods for glucose and alkaline phosphatase to allow greater use of the diluted sample stream. A glycine-containing diluent increases the sensitivity of the iron method by 25% and prevents the protein precipitation that plagues the continuous-flow analysis for iron in plasma. No deterioration in performance of the analyzer has been detected during nine months of routine operation at the reduced sample size. Added advantages are the decreased consumption of calibration materials and an increased ability to do repeat tests.

Alkaline Phosphatase↗
PubMed1982

Micellar improvement of the calmagite compleximetric measurement of magnesium in plasma.

Magnesium in plasma is determined by diluting a 50-microL sample with 5.0 mL of stable calmagite reagent containing the amphoteric detergent Empigen BB, and buffered with 2-amino-2-methyl-1-propanol at pH 11.5. The calcium response is masked with strontium-buffered [ethylene-bis(oxyethylenenitrilo)]tetraacetate (EGTA), while iron is masked with triethanolamine. The detergent causes an increased separation of the test and blank spectral absorbance bands. The test absorbance peaks, which may be measured immediately, are at 520 nm, while the blank peak shifts from 610 to 655 nm on addition of detergent. The blank absorbance at 520 nm is relatively decreased by the detergent. This allows the use of a more concentrated calmagite reagent, which in turn extends the linear relation of absorbance to magnesium concentration to 5 mmol/L in plasma. This method (y) has been compared with atomic absorption procedure (x) of McDonald and Watson (Clin, Chim. Acta 14: 233, 1966) and gives favorable regression statistics (y = 1.001X + 0.057 mmol/L).

Azo Compounds↗
PubMed1982

Measurement of magnesium by continuous-flow colorimetry.

We describe the application to the Technicon SMAC system of a micellar-improved calmagite method for the measurement of magnesium. In this continuous-flow method a dialyzer is not needed, because protein interference is negligible. Sample interaction was estimated to be 3%. The increased sensitivity of the method allows for a small sample volume (37 microL/min). Results obtained agreed well with those by an atomic absorption procedure (x): SMAC magnesium - 0.971 x + 0.030 mmol/L (n = 58). The estimated total error for the SMAC procedure was less than 50 mumol/L at two analyte concentrations: 0.50 and 1.50 mmol/L. The inclusion of magnesium estimation on SMAC should extend the screening function of this analyzer.

Colorimetry↗
PubMed1980

Kober reaction kinetics and their influence on the design of assays for oestrogens in urine during pregnancy.

Rates of reaction of different oestrogens in Kober reagent vary greatly. Rate constants were measured between 100 degrees C and 150 degrees C. Oestradiol, oestrone, 16-oxo-oestradiol, 16 alpha hydroxyoestrone, 16-epioestriol and urine pool show two sequential first order reactions at 100 degrees C; oestriol and its conjugates give a single reaction (slower than the other oestrogens except for the very slow oestretrol). Above 120 degrees C differences decrease, all oestrogens having one rate for Kober product formation: the decay reaction, which is also first order, becomes significant. Oestriol and its conjugates have relatively high apparent activation energies in the Kober reaction (120-138 kJmol-1) compared to other oestrogens studied (105-124 kJmol-1). The apparent activation energy for the decay reaction is the same within experimental error (115 +/- 3 kJmol-1). This is consistent with a common product formed from oestrogen reacting with Kober reagent. Analytical methods must respond similarly to major urinary oestrogens. Appropriate conditions include 100 degrees C for at least 20 min or 135 degrees C for 3 to 4 minutes.

Autoanalysis↗
PubMed1979

Factors in the choice of detergent in automated oestriol estimation.

Detergent must be added to the strongly acidic Kober reagent to obtain reproducible and well separated peaks in continuous flow analytical methods for oestriol in pregnancy urine. Brij 35 and other polyether detergents are not satisfactory because they or their impurities interfere in the reaction causing high blank response in colorimetric reactions and diminished fluorescence responses. In a single phase fluorometric method these detergents also caused turbidity or phase separation in the solution which passed through the fluorometer. Some anionic sulphate and sulphonate detergents were also unsatisfactory being immiscible with Kober reagent. Selected cationic and betaine detergents are shown to be possible alternatives, although one which is satisfactory in the kober reagent may be unsuitable for a dilution reagent. The betaine Empigen BB was found to be suitable for inclusion in both of these reagents.

Autoanalysis↗
PubMed1978

Some pitfalls in the quality control of alkaline phosphatase activity.

A study of the pH optimum of alkaline phosphatase activity in calibration and control serum preparations reveals a wide variation in pH optima. It is shown that as small an error of +/- 0.05 pH units in preparation of the buffered substrate results in an error in the order of +/- 5% in the response between the calibrating serum and patient specimens. It is recommended that a calibration serum should closely parallel the pH optimum of alkaline phosphatase in human sera and that a quality control serum containing alkaline phosphatase of alternative source to that present in the calibration serum be included with patient samples as a sensitive means of monitoring pH changes in the buffered substrate.

Alkaline Phosphatase↗