An on-line high-pressure liquid chromatography (HPLC) system capable of measuring amino acids and carbohydrates was used to study metabolism in mammalian cell culture systems. The HPLC method utilized anion-exchange chromatography followed by integrated pulsed amperometric detection. The method is capable of measuring 19 amino acids plus glucose with a complete method time of 65 min. In actual cell cultures, the method was shown to be useful for monitoring 17 amino acids plus glucose. The two amino acids that were not accurately monitored were arginine and lysine, possibly due to their elution near the void volume of the column. The HPLC system was used to study variability in metabolism across different cell culture processes, as well as the effect of glucose and glutamine limitation on a single cell culture process. Chemometric analysis was used to draw statistically meaningful conclusions from the highly correlated, multivariate data set that resulted from these experiments. Using chemometrics, variation between processes was linked to differences in uptake rates of seven amino acids. Similarly, lactate concentration, cell density, and aspartate uptake rate were linked to glucose and glutamine limitation. The effect of nutrient limitation on glutamate, alanine, and ammonium was also considered.

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Abstact The forcing test used in the brewing industry is shortened from a few weeks to a few days using a new protocol employing impedimetry. The generation times of four different brewing yeasts growing in brewery wort were calculated from measurements obtained using impedimetry.

CORRESPONDENCE 73tested under different conditions. Problems were encoun tered with mixed keg populations comprising aluminium kegs, high-grade steel kegs and other containers. The out come of these studies has contributed to better hygienic standards and lower cost of cleaning (Stillman et at., GB).