Water Determination in Gentamicin Sulfate

According to the Ph. Eur., gentamicin sulfate is a mixture of sulfates of antimicrobial substances. Its maximum water content is listed as 15%; 0.3 g sample is to be titrated in methanol.

Appendix 1 shows how water content is determined with this method. The sample does not dissolve; 10.90% and 10.58% water are found for titrations of 12-15 minutes in duration. The retrieval rate of added water is too high because water was still being extracted from the sample in these titrations.

It is advisable to add formamide as a solubilizer. The trial then takes only 2 minutes; we found 11.56% and 11.60% water. The added water was retrieved again with a high degree of accuracy, see Appendix 2.

Procedure for volumetric one-component titration:

Add 20 mL Hydranal-Methanol dry (or Hydranal-Methanol Rapid) and 20 mL Hydranal-Formamide dry to the titration vessel and titrate to dryness with Hydranal-Composite 5. Precisely weigh-in approx. 0.3 g sample using differential weighing and titrate the water content with Hydranal-Composite 5.

Note: A Suitability test including protocol according to Ph. Eur. is available on request (hydranal@honeywell.com).