Abstract
Abstract Soft-glass, Pasteur-type pipets are widely used as disposable transfer pipets, especially in clinical and biochemical laboratories. These pipets possess an alkaline surface contamination that can affect the accuracy of chemical analyses if proper precautions are not taken. Microtitrations of aqueous rinsings from these pipets have consistently yielded values of 0.1 to 0.2 µmol of hydroxide equivalent per pipet. A possible detrimental effect of this residue was demonstrated, using chloroform solutions of bilirubin. Absorbance was diminished by as much as 5% when unwashed, soft-glass pipets were used to transfer these solutions to spectrophotometric cells. Absorption and fluorescence characteristics of other unidentified surface contaminants are also described. The effect of multiple rinsings is discussed and several ways are suggested for cleaning these pipets. Oven drying must be avoided, however, since it enhances alkali release.
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