S.R. Crouch

Simultaneous kinetic determinations with the kalman filter

Abstract The linear Kalman filter is successfully applied to the processing of data for simultaneous kinetic determinations. The Kalman filter offrs all of the advantages of linear least squares over traditional methods of data processing, but is simpler and more efficient than batch-mode least squares. The viability of the Kalman filter is demonstrated with synthetic data and it is then applied to the analysis of amino acid mixtures by their reaction with trinitrobenzenesulfonic acid. Mixtures of glycine and asparagine are successfully analyzed even though their pseudeo-first-order rate constants differ by a factor of only 2.5. The potential of the Kalman filter for real-time application is discussed.

Experimental comparison of flow-injection analysis and air-segmented continuous flow analysis

Abstract A miniature continuous flow analyzer that can be configured for either air-segmented continuous flow analysis (c.f.a.) or flow-injection analysis (f.i.a.) was used to compare the performance of the two techniques in terms of sampling rates, samples and reagent consumption factors and analtical precision. Details of simply dye dispersion experiments and spectrophotometric chloride determinations are presented. Chloride determinations at rates of up to 360 determinations per hour could be achieved with either technique; sample and reagent consumption was less for the air-segmented flow system than for flow-injection systems equipped with either coiled open tubular reactors (0.05 cm i.d.) or single-bead-string reactors. The advantages of single-bead-string reactors for determinations by merging-zones f.i.a. are demonstrated. The c.f.a. and f.i.a. techniques are shown to be complementary, and the relative merits of each for various applications are discussed.

Evaluation of classical and three-way multivariate calibration procedures in kinetic-spectrophotometric analysis

The bidimensional multivariate regression procedures: multiple linear regression (MLR), principal component regression (PCR), partial least squares regression (PLS) and continuum regression (CR), and several N-way methods such as N-way PLS (nPLS) and parallel factor analysis (PARAFAC) are tested as calibration methods for the kinetic-spectrophotometric determination of ternary mixtures in a pseudo first-order kinetic system. The different calibration procedures were first applied to computer simulated kinetic-spectrophotometric data where the effect of spectral overlap and the differences in the kinetic constants were evaluated at a low level of experimental noise. Later they were applied to the stopped-flow kinetic-spectrophotometric simultaneous resolution of Co(II), Ni(II) and Ga(III) using 4-(2-pyridylazo)resorcinol (PAR) as a chromogenic reagent. Accurate estimations of concentrations with relative standard errors of prediction of about 8% were obtained even though a high degree of spectral overlap and similar rate constants were present. The study of the influence of experimental noise on the 3-component system justifies the difference between the simulations and the experimental results for the different calibration procedures. PARAFAC and MLR did not allow the resolution of the proposed 3-component system. CR provided slightly better results than those obtained by PLS, PCR and nPLS.

Investigation of a Chemiluminescent System for the Determination of Ammonia by Flow-Injection Analysis

Abstract A novel system for the determination of ammonia based on the chemiluminescent reaction between hypochlorite and luminol is presented. The technique of flow injection analysis was employed to automate the system. Ammonia reacts with hypochlorite to form monochloramine in basic solution which decreases the observed chemiluminescence intensity. Several interferents are identified, and the reasons why they interfere are discussed. The effects of interferents are Minimized through the use of a double-tube dialyzer where the ammonia is diffused across the dialyzer membrane into a recipient stream of hydrochloric acid.

Computer-assisted optimization of an immobilized-enzyme flow-injection system for the determination of glucose

Abstract A flow-injection system utilizing the Trinder reaction for the determination of glucose is designed and optimized. Glucose is converted to gluconic acid by passing it through a single-bead-string reactor (SBSR) onto which glucose oxidase enzyme has been immobilized. As it flows through a second SBSR, the gluconic acid reacts with a reagent stream of horseradish peroxidase, 4-aminoantipyrine and 3,5-dichloro-2-hydroxyphenyl sulfonate. The absorbance of the quinoneimine dye produced is then monitored at 510 nm in a flow-through cell. Optimum operating conditions were sought by using both univariate and Composite Modified Simplex procedures. Seven variables were considered. The performance of the system was improved by a factor of 22.5 relative to the starting conditions. A calibration curve obtainedat the optimum conditions was linear for 0–3.3 mM glucose and usable for 0–5.5 mM glucose. The optimization procedures revealed some interesting aspects of the Trinder reaction. scatter diagrams generated from the simplex data showed definite trends for each of the seven variables. These are discussed.

Design and optimization of a flow-injection system for enzymatic determination of galactose

Abstract A flow-injection system for the determination of galactose has been designed and optimized. Galactose is oxidized in the flow-injection manifold via immobilized galactose oxidase to produce hydrogen peroxide. The hydrogen peroxide formed subsequently reacts with a leucomalachite green/ peroxidase reagent, and the malachite green product is monitored spectrophotometrically at 620 nm. Optimal system conditions were investigated for both enzyme kinetics and reactor configurations. A Composite Modified Simplex routine was employed for multivariate optimization of five rate-dependent parameters. System factors considered in the Simplex optimization were sensitivity, precision, and sample throughput. The performance of the system was improved by a factor of 5.1 relative to initial conditions. Four immobilized enzyme reactor configurations were also investigated for their substrate conversion efficiencies and dispersion characteristics. Optimal system performance is attained by combining the results from the reactor design evaluations and the Simplex optimization. The galactose determination working range was 80 μM to approximately 2 mM for a 30-μl sample volume with an optimal sample throughput of 41 samples per hour. The relative standard deviation ranged from 0.02 to 2.450 over the galactose working curve.

Critical study of temperature effects in stopped-flow mixing systems

Abstract A comparative study of temperature effects in three different stopped-flow mixing systems is reported. Special emphasis was placed on the determination of the signs and magnitudes of the temperature changes which occur before and during mixing when the modules are maintained at 20–30°C. Temperature changes were found to occur under almost all experimental conditions, but two of the stopped-flow modules exhibited reproducible temperature changes, provided that thermal equilibrium was reached between pushes. Based on the results of the experiments that are presented, guidelines are suggested for minimizing the effects of the temperature changes which occur during mixing, particularly when the modules are utilized routinely in reaction-rate methods of analysis.

Experimental studies on the effect of temperature on dispersion in a flow-injection system

Abstract The effect of temperature on dispersion in a flow-injection system is described. Systems both with and without chemical reaction were investigated. The reaction studied was that of p -nitrophenol with sodium hydroxide. The results indicate that temperature does indeed have a significant and predictable effect on the dispersion of a sample plug. Findings agree with the random walk model for flow-injection systems.

Air-segmented flow injection : a hybrid technique for automated, low dispersion determinations

Abstract A novel approach to the design and use of an air-segmented flow injection (ASFI) system is described. The ASFI system possesses features of both classical flow injection (FI) and air-segmented continuous flow (ASCF) methods. The entire air-segmented sample zone is injected through a simple 6-way valve into the carrier stream. Preliminary studies of dye dispersion and spectrophotometric glucose determinations in wine and serum samples are presented. These results indicate that the proposed system has advantages for most determinations in sensitivity, sampling rate and solution consumption when compared to the other flow analysis techniques. Analytical results are also compared with those obtained by kinetic-based determinations.

Stopped-flow, air-segmented continuous flow: kinetic determinations of glucose and phosphate in wine and serum samples

Abstract The feasibility of using the stopped-flow technique with an air-segmented continuous-flow analysis system has been investigated. Kinetic determination of glucose and phosphate are used to evaluate the potential of this approach. The effects of such instrument characteristics as delay time and flow-rate on the observed reaction rates are discussed. The results of determining glucose and phosphate in wine and serum samples are reported.