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H L Pardue

Publications and source records attributed to H L Pardue.

At least 19 recordsLinked to original sources
PubMed1992

Data-processing method to reduce error coefficients for membrane-based analytical systems. 1. Amperometric-based sensor evaluated for quantification of oxygen.

This paper describes the use of a predictive, curve-fitting method to reduce the effects of experimental variables on results obtained with membrane-based devices. Multipoint data from the transient regions of responses are used with suitable models and curve-fitting methods to predict the signal that would be measured for the system at equilibrium. The resulting equilibrium response usually is much less dependent on experimental variables than the transient responses used to predict it. The approach is evaluated for the membrane-based amperometric electrode for oxygen. Current vs time data are used to predict the equilibrium current expected when oxygen concentrations are the same on both sides of the membrane. Predicted equilibrium currents vary linearly with oxygen concentration. Relative to the more common steady-state method, the sensitivity of the predictive method is about 5-fold higher, the measurement time is about 17-fold shorter and the dependencies on membrane thickness and stirring rate are 125- and 8-fold lower, respectively. Pooled standard deviations (n = 40) correspond to uncertainties in oxygen concentration of about 0.009 mmol L-1.

Chemistry Techniques, Analytical↗
PubMed1992

Evaluation of transient responses of ammonia-selective potentiometric electrodes for quantitative applications.

An error-compensating, predictive kinetic method is adapted and evaluated for quantitative applications based on transient responses from an ammonia-selective electrode. Transient data collected during the early part of the electrode response are used with a curve-fitting method and appropriate mathematical models to predict the signal that would be measured if the response were monitored to equilibrium. Several different theoretical and empirical models were evaluated, and all but one of the models tested permitted reliable prediction of equilibrium potentials for most responses. Predicted values of equilibrium signal were close to measured values and exhibited the expected logarithmic dependence on ammonia concentration in the range from 0.1 to 100 mmol/L. Slopes of calibration plots E infinity vs log C, varied from about 50.5 to 65.0 mV per decade with an average value of 56.9 +/- 4.2 mV per decade. Quantitative data are used to rank the different models in terms of their utility for kinetic-based determinations of ammonia by using the ammonia-selective electrode.

Ammonia↗
PubMed1992

Instrumentation for the breath-by-breath determination of oxygen and carbon dioxide based on nondispersive absorption measurements.

This paper describes the development and evaluation of instrumentation for the breath-by-breath determination of oxygen and carbon dioxide in respiratory gases. The method is based on nondispersive absorption and uses the 145-nm absorption band for detection of oxygen and the 4.3-micron band for detection of carbon dioxide. A xenon discharge lamp with a sharp band at 147 nm was chosen as the source for the determination of oxygen, and a carbon dioxide discharge lamp with a sharp band at 4.3 micron was chosen for determination of carbon dioxide. A vacuum photodiode was used as the detector for oxygen, and a photoconductive cell with a built-in interference filter was used for detection of carbon dioxide. Plots of absorbance (A) vs concentration (C, %) were linear for oxygen and were nonlinear for carbon dioxide. Typical least-squares calibration equations were A = 0.020C + 0.02 for oxygen (0-100%) and A = 0.0012C2 + 0.050C + 0.008 for carbon dioxide (0-8%). Comparisons of computed (y) vs prepared (x) values for the concentrations given above were linear for both gases, yielding y = (1.00 +/- 0.01)x - 0.13 +/- 0.73 for oxygen and y = (1.07 +/- 0.02)x - 0.04 +/- 0.06 for carbon dioxide. The standard deviations were 1.2% at 50% oxygen and 1.5% at 4% carbon dioxide. Records are presented to illustrate breath-by-breath monitoring of these gases in a healthy subject.

Absorption↗
PubMed1992

Simultaneous determinations of liver- and bone-type alkaline phosphatase by curve-fitting of inhibition kinetic data. I. Development and evaluation of an absorbance-based method.

We describe an approach for the simultaneous determination of isoenzymes of alkaline phosphatase (EC 3.1.3.1) based on the kinetic behavior of inhibition reactions. Data for absorbance vs time, collected while enzymes are being inhibited, are fitted with suitable models to obtain results related to activities of the individual isoenzymes. The primary focus is on two-component mixtures of the bone and liver isoenzymes of alkaline phosphatase, but some results are reported for three- and four-component mixtures. Factors studied include choices of inhibitors, buffers, pH, ionic strength, substrate concentration, kinetic models, data ranges, data densities, and data-processing approaches and programs. Criteria used to select optimal conditions include measurement times, detection limits, useful range, and agreement between expected and computed results for mixtures of isoenzymes. For two-component mixtures, a linear least-squares fit of isoenzyme content computed with the curve-fitting method (y) v a comparison method (x) gave y = 0.96 (+/- 0.05)x + 3.8 (+/- 3)% with r = 0.97 and standard error of the estimate of 9.4% for a range from 15 to 300 U/L. The pooled relative standard deviation (CV) for results was about 5%. Results were degraded for three- and four-component samples.

Alkaline Phosphatase↗
PubMed1992

Simultaneous determinations of liver- and bone-type alkaline phosphatase by curve-fitting of inhibition kinetic data. II. Development and evaluation of a fluorescence-based method.

We describe a kinetic method for the determination of alkaline phosphatase (ALP) isoenzymes, based on fluorescence detection of 4-methylumbelliferone. Several different buffer-inhibitor combinations and substrate concentrations were evaluated. Best results were obtained for inhibition with 2.9 mol/L urea in amino-2-methyl-1-propanol buffer. With this combination, normal concentrations of bone- and liver-type ALP could be determined from kinetic data during an 8-min measurement period. We computed initial velocities from parameters for first-order fits during 1.2 half-lives of the response for liver-type ALP. A linear least-squares fit of initial velocities (y) determined in this way vs results obtained with a comparison procedure (x) gave good correlations. We also estimated total signal changes, delta S, from first-order fits during four half-lives. Isoenzyme content correlated well with parameters computed from the first-order fits. Values for standard errors of the estimates represent 5% and 3% of median responses for activities and isoenzyme content, respectively. When compared with an absorbance-based method described previously, this method had threefold shorter measurement times, but imprecisions were 1.6- to 1.8-fold larger.

Alkaline Phosphatase↗
PubMed1991

International Federation of Clinical Chemistry. The expanding role of robotics in the clinical laboratory.

Increasing numbers of robots are going to be employed industrial chemical laboratories. Most of these will be used to reduce the monotonous tasks of sample preparation, to minimize human exposure to dangerous environments or to carry out huge numbers of repetitive experimental procedures. For example, looking for the most effective condition or combination in chemical synthesis or the best microorganism in a large number of cultures. In the clinical laboratory the situation is slightly different and robotics is not so widely applied in clinical laboratories, but there is a definite trend to employ robots or robotic systems both to reduce labor volume and exposure of employees to possible biohazards and to help get more precise and correct results. These needs will be hard to fulfill via the usual automated devices and especially when adequate devices are not available. Specially designed machines will have to be produced to satisfy these demands and robotics will play a part. Finally we need to evaluate the effectivity of introduction of robotics in terms of economy, strategy, biosafety and other aspects. Typical examples of implementation of robotics in the clinical laboratory are transportation of specimens, front-end automation of sample preparation, separation and aliquotting as well as selected processes in a large scale automation systems. As described previously, robots that are commercially available now, are not intelligent enough to be easily handled by personnel who are not trained for robotics. There is a need for personnel dedicated to robotics who join the project from the very beginning of the plan and who can maintain the system properly.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemistry, Clinical↗
PubMed1991

Predictive, error-compensating kinetic method for enzymatic quantification of creatinine in serum.

Here we describe an error-compensating kinetic-based method for the enzymatic quantification of creatinine in serum. The method, which has a large linear range and very low dependency on experimental variables that influence enzyme activity, is based on the use of creatinine amidohydrolase in a four-step coupled reaction sequence to generate a product that is monitored photometrically. We collected data for absorbance vs time during two to four half-lives of each reaction and fit a first-order model to the data to compute the total absorbance change that would be measured if the reaction were monitored to completion. Computed values of absorbance change agreed well with measured values and varied linearly with creatinine concentration in the sample throughout the range examined: 44 to 1326 mumol/L. A twofold change in enzyme activity in the final reaction mixture (3.3 to 6.6 kU/L) produced changes of only 12% and 4% for creatinine concentrations of 44 and 353 mumol/L, respectively. Results (y) for 39 serum samples that contained creatinine concentrations between 20 and 1800 mumol/L agreed well with liquid-chromatographic results (x), yielding linear least-squares statistics of y = (1.03 +/- 0.01) x + (5 +/- 5) mumol/L (r = 0.995, Sy.x = 37 mumol/L). We conclude that the predictive kinetic approach is a robust method for the quantification of creatinine in serum.

Chromatography, High Pressure Liquid↗
PubMed1990

Continuum-source atomic absorption spectroscopy with an echelle spectrometer adapted to a charge injection device.

An instrumental system for continuum-source atomic absorption spectroscopy has been developed for simultaneous multielement determinations. The system consists of an electrothermal atomizer and a charge injection device adapted to an echelle spectrometer to achieve multiplex detection. A continuous 40-nm spectral range in the two-dimensional echelle spectrum was acquired simultaneously through the capability of the charge injection device to integrate signals in its MOS capacitors. Novel methods were developed to compute absorbances by "scanning" through all orders in the entire echelle spectrum or selecting absorption lines randomly. In the range 300-430 nm, characteristic concentrations (1% absorption) were 1.6, 2.6, 2.9, and 3.8 ng mL-1 respectively for Cu, Mn, and two Cr lines; these values are similar to those (1.3, 2.2, 1.2, and 3.6 ng mL-1) obtained for single-element detection with an image-dissector system.

Elements↗
PubMed1989

Characteristics of methods for the simultaneous determination of catalysts by first-order inhibition kinetics.

Factors that affect the simultaneous kinetic determination of catalysts based on differences in rates of inhibition by a common inhibitor are investigated by computer simulation. Both derivative and integral models for the kinetic responses are studied. Nonlinear regression is used to fit data with a fixed level of noise for the combined responses due to the first-order inhibition of two catalysts. Effects of rate constants, ratios of rate constants, fitting ranges, data density, and number of replicate determinations on reliability, useful activity range, sensitivity, scatter, limits of detection, and measurement/data-processing times are considered. It is found that values for rate constants, ratios of rate constants, and fitting ranges which provide results with desired reliability are restricted. Small ratios of rate constants and short fitting ranges were observed to produce the largest useful activity ranges and shortest measurement times but also gave the worst accuracy and most dependence on initial estimates of fitting parameters. Values of the coefficients of correlation between the individual first-order responses can aid in the selection of the smallest ratio of rate constants and fitting range which will yield suitable results.

Catalysis↗
PubMed1989

Linearized model for error-compensated kinetic determinations without prior knowledge of reaction order or rate constant.

This paper describes a new algorithm for calculation of reaction orders, rate constants, and initial and final values of detector signal from several signal vs time data points. The algorithm utilizes a linearized version of the rate equation and is intended primarily to provide initial estimates of these kinetic parameters for other curve-fitting methods. However, under some circumstances, the linearized model can provide sufficiently reliable results that subsequent processing by other methods is not needed. Simulated data with different levels of superimposed noise, data densities, reaction orders, rate constants, and signal change are used to evaluate the algorithm both for its primary purpose of providing initial estimates for other curve-fitting methods and as an independent method. Results are compared with those obtained with a nonlinear least-squares method and two initial-rate methods. The new algorithm provides less reliable results than those obtained by the nonlinear curve-fitting method for some situations (e.g. reaction orders greater than two, low data densities) but has the advantage that it is applicable to reaction orders at and near unity where the nonlinear method to which it is compared fails.

Kinetics↗
PubMed1989

Kinetic study of the Jaffé reaction for quantifying creatinine in serum: 2. Evaluation of buffered reagent and comparison of different data-processing options.

Here we describe the evaluation of several data-processing options for the kinetic determination of creatinine by use of the Jaffé reaction. Data-processing options evaluated include initial-rate, two-point fixed-time, rate at t = k-1, and multipoint curve-fitting predictive methods. We evaluated these options for a buffered formulation of the Jaffé reagent and studied the effects of potential interferents, including glucose, acetoacetate, bilirubin, and albumin, on each option. To reduce effects of bilirubin, we evaluated the inclusion of a preoxidation step with ferricyanide. All the data-processing options gave good precision and linearity between the measurement objective and creatinine concentration. However, differences between slopes of calibration plots in aqueous and serum matrices ranged from a high of +60% for the two-point, fixed-time method to a low of -11% for the curve-fitting, predictive method. Standard additions of creatinine to sera were quantified reliably (yielding 96% to 102% of target values) by the predictive method and less reliably (62% to 102%) by the other methods. We conclude that the predictive method has the potential to yield the most reliable results for creatinine.

Acetoacetates↗
PubMed1988

Effects of reaction variables on nephelometric and turbidimetric responses for the immunochemical reaction of immunoglobulin G.

Here we report a kinetic study of the immunoprecipitin reaction involving immunoglobulins G, A, and M. We used stopped-flow mixing adapted for simultaneous monitoring of nephelometric and turbidimetric signals for some studies and centrifugal mixing for others. The variables having the most significant effects on the kinetic responses in the regions of excess antibody and excess antigen are polyethylene glycol concentration, ionic strength, and the ratio of antigen to antibody. We document effects of these variables on maximum velocities and signal changes over a fixed-time interval for both monitoring modes and on the maximum signal change for nephelometry. We use response-surface methodology to help identify interactive effects among these variables (polyethylene glycol, NaCl, and antibody concentrations) and to select the best combination to use to quantify antigen in all regions of the immunoprecipitin curve. We also observe that turbidimetric responses are more reproducible and much simpler than are nephelometric responses. Implications of these results for quantification of the immunoglobulins are discussed.

Antigens↗
PubMed1988

Kinetic turbidimetric method for the immunochemical quantification of immunoglobulins, including samples with excess antigen.

Here we describe a kinetic approach for quantification of the immunoglobulins (IgG, IgA, IgM) in all regions of the immunoprecipitin curve. We use centrifugal mixing and report results for maximum-velocity, two-point, and multipoint curve-fitting methods as well as the use of rate coefficients obtained from the curve-fitting process to differentiate among regions of excess antibody, equivalence, and excess antigen. We show that it is possible to quantify each immunoglobulin over a concentration range from a large excess of antibody to moderate excesses of antigen with a single set of measurements made on a single dilution of each sample. Results for standard additions of the immunoglobulins to pooled sera have relative standard deviations (coefficients of variation) in the range of 1% to 3%, with analytical recoveries in the range of 95% to 106%. Correlations among determined and reported values in individual sera are quite good, with slopes ranging from 0.86 to 1.03 and no intercepts differing from zero by more than two standard deviation units. Concentrations quantified in 14 pathological sera by the proposed method correlated well with concentrations quantified by a fluorescence immunoassay method.

Antigens↗
PubMed1987

Kinetic immunochemical method for the simultaneous quantification of creatine kinase isoenzymes.

We describe the development and evaluation of a kinetic immunochemical method for the simultaneous quantification of isoenzymes. Specifically, we use the inhibition of the M subunit of creatine kinase (CK; EC 2.7.3.2) by antibodies to quantify isoenzymes CK-MM and CK-MB in serum matrices. Nonlinear least-squares data-processing is used to compute the enzyme activities from the time-dependent response of absorbance vs time. Variables affecting the method, namely temperature, substrate concentration, and antibody concentration as well as their interactions, are evaluated by using response-surface methodology. For several concentrations of CK-MM and CK-MB in the range of diagnostic significance, least-squares fits of computed (y) vs expected (x) values yielded equations of y = 0.98x + (2.0 X 10(-5)) s-1 for CK-MM and y = 1.04x - (4.6 X 10(-5)) s-1 for CK-MB for rates between 0 and 3.5 X 10(-3) s-1 (CK-MM) and 0.5 X 10(-3) s-1 (CK-MB). The equations for comparison of kinetic results (y) with results by a kit method (x) were y = 0.97x + (6.5 X 10(-5)) s-1 for CK-MM and y = 1.02x + (4.3 X 10(-5)) s-1 for CK-MB. Pooled day-to-day relative standard deviations (CVs) for the kinetic method were 4.1% and 2.8% for CK-MM and CK-MB, respectively.

Antibodies↗
PubMed1987

Kinetic study of the Jaffé reaction for quantifying creatinine in serum: 1. Alkalinity controlled with NaOH.

We studied the kinetic behavior of the reaction of alkaline picrate and creatinine and evaluated a nonlinear curve-fitting method for quantifying creatinine in serum. Using a 3 X 3 factorial experimental design, we evaluated interactive effects among temperature and concentrations of creatinine, picrate, and NaOH. We found no evidence of interference by glucose or unconjugated bilirubin; the effects of the acetoacetate reaction, which is fast, are easily compensated by the curve-fitting method. The reaction with human serum albumin is very complex, but its effects are compensated by the curve-fitting method and by preparing standards containing 50 g of albumin per liter. Calibration plots are linear under a wide variety of conditions for both aqueous standards and standard additions of creatinine to pooled serum. Reproducibility studies with standards containing creatinine at 2, 10, and 20 mg/L yielded relative standard deviations (RSD) of 8.2, 2.5, and 1.3%, corresponding to absolute variations of 0.16, 0.25, and 0.26 mg/L. The average SD for 17 sera containing creatinine at 15-50 mg/L was 0.7 mg/L. The averages of ratios (as percent) of determined vs expected concentrations in 17 sera with added creatinine (7.27 mg/L) were 97.8% for aqueous standards, 99.9% for standards with added albumin.

Acetoacetates↗
PubMed1987

Fast kinetic method for methemoglobin developed and adapted for quantification of hemoglobin in whole blood.

We studied the kinetics of the reaction of cyanide with methemoglobin (mHb), used the information to develop a fast kinetic method for quantifying methemoglobin, then used that method to quantify hemoglobin (Hb) in whole blood based on the reaction with ferricyanide to produce mHb. Reaction conditions for mHb and cyanide are adjusted to give pseudo-first-order behavior with an apparent rate constant that increases linearly with cyanide concentration, decreases linearly with pH, and follows an Arrhenius-type relationship with temperature. Absorbance change, computed from kinetic data with a curve-fitting method, varies linearly with mHb concentration. Although the reactions are monitored most reliably with stopped-flow mixing, cyanide concentration was used to decrease reaction velocities to be compatible with centrifugal mixing. Kinetic results (y) for Hb in blood by both mixing methods correlate well with equilibrium results (x): y = 1.000x + 0.02 mmol/L, Syx = 0.06 mmol/L with stopped-flow mixing; y = 1.03x + 0.12 mmol/L, Syx = 0.07 mmol/L with centrifugal mixing; r = 0.96 and n = 21 in each case.

Ferricyanides↗