Pesticide residue is of concern as an environmental pollutant when present at medium to high concentrations. Such residue was quantified in both vegetable and soil samples by an enzyme inhibition technique. The multistep reactions were integrated into centrifugal microfluidic devices allowing automated simultaneous analysis of several samples or of replicates. The small sample size inherent to microfluidic devices allowed for less reagent to be used including less of the expensive enzyme which is key to this method. Liquid-solid magnetically actuated extraction, filtration, sedimentation, and detection were all integrated on the same device. Several parameters were optimized including the concentration of enzyme, substrate, chromatic agent, and reaction time. In this environmental application of centrifugal microfluidics, the percent inhibition of enzyme activity is logarithmically proportional to the demonstration pesticide concentration (in this case carbofuran). This meant that as the pesticide concentration increased in the samples, the reaction was more inhibited and the final product absorbed less light at 525 nm. Two versions of the centrifugal microfluidic devices were made. One version was designed for the analysis of vegetable samples (cabbage) and the other for the analysis of soil samples. Each version provided results that were statistically similar to the conventional benchtop method with a carbofuran limit of detection of 0.1 ppm or 0.1 μg g(-1) (5 ng absolute limit of detection).

A prototype for solid sample preparation on centrifugal microfluidic devices has been designed and characterized. The system uses NdFeB magnets in both the centrifugal device and a fixed base. As the centrifugal device rotates, the magnets move and spin in their chambers creating a pulverizing mechanical motion. This technique was successfully applied to the dissolution of potassium ferricyanide (K(3)[Fe(CN)(6)]), a hard colored crystal. A 0.10 g sample was completely dissolved in 3 s in 1.0 mL of water while rotating at 1000 rpm. This is a 300-fold improvement over static dissolution.

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An online standard additions calibration method for transient signals in ICPMS is demonstrated in which a small volume of standard is injected as a spike into the sample/carrier stream, overlaying the analyte peak. This technique provides the advantages of conventional standard additions but requires only a single sample run. The method corrects for matrix effects and is suitable for transient signals in which the severity of the matrix effect changes over the analyte peak. The method uses a peak-fitting program to determine the area of the underlying peak and is shown to be effective for the determination of trace metal concentrations in both a high ionic strength matrix and in a biological matrix (urine). Eight analytes with concentrations in the range of 0.82-233.2 mug L-1 in urine were simultaneously determined using a standard spiking solution of 75 mug L-1 injected through a 100-muL loop. The measured concentrations for analytes free of spectral interferences agreed with the certified values, and the precision achieved was comparable to that achieved by the certifying agency. Using a conventional cross-flow nebulizer and Scott-type spray chamber, the accuracy obtained for online standard additions calibration was within 2%, and the precision was within 5%.