Simultaneous quantitation of tobramycin and colistin sulphate by HPLC with evaporative light scattering detection.

A rapid and simple method for the simultaneous determination of tobramycin and colistin sulphate in a pharmaceutical formulation by reversed phase HPLC and evaporative light scattering detection is described. Chromatographic separation was carried out in gradient mode using a Zorbax SB C18 column (150mmx4mm, 3.5microm) with mobile phases of acetonitrile and water containing trifluoroacetic at 1ml/min. The method was validated using methodology described by the International Conference of Harmonization. The method was shown to be specific, precise, accurate and linear. Real samples were analyzed to demonstrate the applicability of the chromatographic method in a routine use.

Interlaboratory study of a liquid chromatography method for erythromycin: determination of uncertainty.

Erythromycin is a mixture of macrolide antibiotics produced by Saccharopolyspora erythreas during fermentation. A new method for the analysis of erythromycin by liquid chromatography has previously been developed. It makes use of an Astec C18 polymeric column. After validation in one laboratory, the method was now validated in an interlaboratory study. Validation studies are commonly used to test the fitness of the analytical method prior to its use for routine quality testing. The data derived in the interlaboratory study can be used to make an uncertainty statement as well. The relationship between validation and uncertainty statement is not clear for many analysts and there is a need to show how the existing data, derived during validation, can be used in practice. Eight laboratories participated in this interlaboratory study. The set-up allowed the determination of the repeatability variance, s(2)r and the between-laboratory variance, s(2)L. Combination of s(2)r and s(2)L results in the reproducibility variance s(2)R. It has been shown how these data can be used in future by a single laboratory that wants to make an uncertainty statement concerning the same analysis.

Optimised immunofluorescence procedure for enumeration of Cryptosporidium parvum oocyst suspensions.

The aim of this study was to evaluate an optimised immunofluorescence assay in terms of the variability of sets of counts for Cryptosporidium parvum oocyst suspensions and data recovery and the reliability of the procedure. A coefficient of variation (CV) of 10% was determined to be the maximum value acceptable for count variability. It was found that the optimised IFA tested provided a high precision for the sets of enumerations for suspensions containing 800-20,000 oocysts/mL. The procedure was found to be robust and providing high recovery level (96.3%). In terms of counting precision, the technique described here approaches the performance of flow cytometry and surpasses other manual techniques with a CV of 10% for a concentration close to 800 oocysts/mL. The procedure described is particularly suitable for the production of seed doses and for other applications requiring the titration of oocyst suspensions with a high degree of precision and accuracy.

Experimental investigations and numerical modelling of Cryptosporidium parvum transport behaviour in aquifers.

The purpose of this study was to improve understanding of the potential for transfer of the protozoan pathogen Cryptosporidium parvum through aquifers to drinking water wells. Therefore, the factors characterising this transport were experimentally determined. We have developed a continuously recirculating column assay. The latter allows small amounts of C. parvum oocysts to be manipulated providing as much protection as possible from the risks of contamination. As the analysis of oocyst samples is time consuming, a numerical model, simulating the transport phenomena of oocysts under the experimental conditions of assays, was developed to establish the whole experimental curve of results using a small number of experimental points. The comparisons drawn between analytic solutions, experimental results with tracer (NaCl solution) and numerical simulation were in good agreement. A continuously recirculating column assay was performed using oocysts in suspension (flow rate = 1.43 mL/min). Treated sand was used as previous experiments had shown that no adsorption occurs. We observed almost total filtration (99.85%). To check this result, an assay with an open column was carried out under the same conditions. We observed a filtration value of 97%. Consequently, we may say that the continuously recirculating column assay provides satisfactory results.