tailieunhanh - Ebook Essentials of pharmaceutical chemistry (3rd edition): Part 2
(BQ) Part 2 book "Essentials of pharmaceutical chemistry" has contents: Volumetric analysis of drugs, analytical spectroscopy, stability of drugs and medicines, kinetics of drug stabilityb, licensing of drugs and the British Pharmacopoeia, answers to problems. | 6 Volumetric analysis of drugs This chapter will deal with volumetric analysis, that is analysis carried out by the accurate measurement of volumes. To measure volumes accurately, use must be made of volumetric glassware. There are three pieces of volumetric glassware that are fundamental to successful volumetric analysis. These are the volumetric flask, the pipette and the burette, and each will be described below (see Figure ). It should be stated, however, that no amount of reading about these pieces of apparatus (no matter how eloquently written!) is sufficient to educate a student. Analytical pharmaceutical chemistry is first and foremost a practical subject, and the laboratory is the best place to get to grips with the techniques required for consistent, reproducible analysis. Volumetric flask Pipette Burette Figure A volumetric flask, a pipette and a burette. 134 Essentials of pharmaceutical chemistry Volumetric flask A volumetric flask is used to prepare accurate volumes of solution. These flasks are pear-shaped with long, thin necks that allow the operator to dilute accurately to the mark with solvent. Volumetric flasks are available in all sizes from 1 mL up to 10 litres, but the most common sizes are 20, 50 and 100 mL. When selecting which size of flask to use, a compromise should be reached between the desire to use a small-volume flask and so save on expensive reagent, and the desire to use a large-volume flask to minimise dilution errors. The usual procedure is to pipette in a known volume of concentrated solution, add solvent until just short of the mark, shake or invert the flask to mix the contents and then make up to the mark, as accurately as possible, with a Pasteur pipette. Volumetric flasks should be used for all accurate dilutions. Use of measuring cylinders or (even worse) beakers to dilute solutions should be avoided. Pipette Pipettes are used to transfer accurate volumes of solution from a container (usually a beaker) to a reaction flask
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