Experimental design modeling of carryover to optimize air-segmented continuous flow analysis Original Research Article

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 R2 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 (2 s) water segments are inserted. Under this condition, carryover is essentially zero and total loading time is 22 s. 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.