Abstract: A cell separator design is presented for rapid, efficient separation of analytical quality plasma samples from whole blood for use in a continuous segmented flow point-of-care testing system. Sedimentation theory for multiple species suspensions, modified to account for continuity and rouleau formation, is used to model the separation process and optimize the separation chamber geometry. Model predictions, relating the sample separation time to a chamber taper angle, indicate respective separation times of 37-28 s for a chamber with a taper angle ranging from 16 to 20 degrees, while maintaining sample volumes in the 1-1.5 mL range. Experimental observations of separation time agree to within 25% of theoretical predictions resulting in complete separation in 40 s, showing the ability to separate small 1-1.5 mL samples in less than 1 min. Results of characterization experiments conducted using the separator indicate indiscernible hemolysis when compared with hemoglobin levels measured from samples prepared in a bench-top centrifuge. Results show that cellular carryover is reduced in seven clean-in-place wash steps to 0.00063% of the original cellular content, and theory based on these results predicts no carryover in 11 steps.

Abstract: Multiple blood chemistry assays were performed in an air-segmented continuous flow analysis system with plasma/reagent pairs separated from each other by air bubbles and water segments. Carryover of one reaction pair to subsequent ones was investigated in this study where red dye simulates the original. reaction pair and water segments simulate the target reaction pair. Several factors were tested for their effects on the carryover coefficient by using two three-factorial experimental designs. The carryover coefficient in each design was regressed as a function of three parameters by fitting to a second-order model. The significance probabilities for individual parameters revealed that the size of air bubbles and of the initial slug do not have significant effects, so these were excluded from the two designs and two-parameter models re-fit to the data. The statistical analysis for each case confirms that the two-parameter model for the second design gives the best fit with an F-value of 147.44 and R-2 of 0.955. The average absolute difference between the model and data is 2.3%. An objective function, that balances carryover with total processing time, shows optimal loading when six bubbles and five 5.3 µl (2s) water segments are inserted. Under this condition, carryover is essentially zero and total loading time is 22s. This scheme will allow processing of three chemistries in 3 min. Larger numbers of chemistries can be processed in the same time by re-configuring the system to allow smaller sub-second samples.

Abstract: The clinical applications of the sequential flow technique are emphasized in this study by considering glucose determinations in a standard blood chemical analysis. The sequential flow configuration is modeled to predict experimental behavior. A rigorous theoretical formulation of the model is presented incorporating temperature relationships for the hydrodynamic and kinetic parameters. A comparisons of model predictions with experiments show agreement satisfactory for determining optimal design strategies. To perform this analysis, factorial design results of model predictions are used to locate regions where a full set of model predictions should be made. Also, experimental results and theoretical predictions are used to determine the best temperature for glucose determinations