The Pharmaceutics and Compounding Laboratory
Accuracy in Measurements

Liquid Measurement

The pharmacist is concerned with liquid measurement from two perspectives. First, he/she should be concerned with the ability to accurately measure the components of a prescription preparation. Secondly, he/she must be concerned with how the patient will measure and deliver an accurate dose of a liquid medication.

The techniques used to measure liquids are probably the simplest of the operations related to prescription compounding. At the same time, they are also the most susceptible to errant selection and unprofessional execution leading to inaccuracies. In this section, we will consider factors which influence selection of liquid measurement devices.

Precision volumetric glassware is used to measure and/or deliver exact volumetric quantities of liquid substances. The capacity of the vessel (1 ml, 50 ml, 1000 ml, etc.) is inscribed on the vessel, and some types of devices will have calibration marks for measuring multiple volumes. The inscriptions TD or TC mean, respectively, "to delivery" and "to contain". A moment's reflection should indicate the significance of these designations as they apply to the function of the glassware. Calibrated pipets, burets, syringes and droppers are T.D. glassware; volumetric flasks and cylindrical or conical graduates are T.C. glassware although in practice, graduates are used as T.D. vessels for volumes of 1 ml or more.

Erlenmeyer flasks, beakers, and prescription bottles, regardless of markings, are NOT volumetric glassware, but are simply containers for storing and mixing liquids. The designated volume(s) express the approximate capacity of the vessel.

Erlenmeyer Flasks
Beakers
Prescription Bottles

Erlenmeyer flasks

Beakers

Prescription Bottles