Inkjet Metrology: High-Accuracy Mass Measurements of Microdroplets Produced by a Drop-on-Demand Dispenser

We describe gravimetric methods for measuring the mass of droplets generated by a drop-on-demand (DOD) microdispenser. Droplets are deposited, either continuously at a known frequency or as a burst of known number, into a cylinder positioned on a submicrogram balance. Mass measurements are acquired precisely by computer, and results are corrected for evaporation. Capabilities are demonstrated using isobutyl alcohol droplets. For ejection rates greater than 100 Hz, the repeatability of droplet mass measurements was 0.2%, while the combined relative standard uncertainty (uc) was 0.9%. When bursts of droplets were dispensed, the limit of quantitation was 72 μg (1490 droplets) with uc = 1.0%. Individual droplet size in a burst was evaluated by high-speed videography. Diameters were consistent from the tenth droplet onward, and the mass of an individual droplet was best estimated by the average droplet mass with a combined uncertainty of about 1%. Diameters of the first several droplets were anomalous, but their contribution was accounted for when dispensing bursts. Above the limits of quantitation, the gravimetric methods provided statistically equivalent results and permit detailed study of operational factors that influence droplet mass during dispensing, including the development of reliable microassays and standard materials using DOD technologies

α-Aminoadipate pool concentration and penicillin biosynthesis in strains of <i>Penicillium chrysogenum</i>

Intracellular amino acid pools in four Penicillium chrysogenum strains, which differed in their ability to produce penicillin, were determined under conditions supporting growth without penicillin production and under conditions supporting penicillin production. A significant correlation between the rate of pencillin production and the intracellular concentration of α-aminoadipate was observed, which was not shown with any other amino acid in the pool. In replacement cultivation, penicillin production was stimulated by α-aminoadipate, but not by valine or cysteine. Exogenously added α-aminoadipate (2 or 3 mM) maximally stimulated penicillin synthesis in two strains of different productivity. Under these conditions intracellular concentrations of α-aminoadipate were comparable in the two strains in spite of the higher rate of penicillin production in the more productive strain. Results suggest that the lower penicillin titre of strain Q 176 is due to at least two factors: (i) the intracellular concentration of α-aminoadipate is insufficient to allow saturation of any enzyme which is rate limiting in the conversion of α-aminoadipate to penicillin and (ii) the level of an enzyme, which is rate limiting in the conversion of α-aminoadipate to penicillin, is lower in Q 176 (relative to strain D6/1014/A). Results suggest that the intracellular concentration of α-aminoadipate in strain D6/1014/A is sufficiently high to allow saturation of the rate-limiting penicillin biosynthetic enzyme in that strain. The basis of further correlation of intracellular α-aminoadipate concentration and penicillin titre among strains D6/1014/A, P2, and 389/3, the three highest penicillin producers studied here, remains to be established. Preliminary studies which attempted to explain the differences in intracellular α-aminoadipate concentrations in strains Q 176, D6/1014/A, and P2 in terms of differences in activities or kinetics of two enzymes of lysine biosynthesis (homocitrate synthase and saccharopine dehydrogenase) did not reveal differences in those enzymes among the three strains. </jats:p

Évaluation intégrée de la qualité d’un milieu récepteur basée sur des données en continue validées et la modélisation de la qualité

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