How to Weigh Viscous Samples?

Viscous Liquid

Viscous samples constitute a major segment in studies on pharmaceuticals, foods, cosmetics and petroleum products. Some examples of such samples are:

• Pharmaceuticals – syrups, ointments, gels
• Foods – syrups, jellies, jams, yoghurt, honey
• Cosmetics – facial creams, lotions, shaving creams, toothpastes, gels
• Petroleum products – oils and grease

Volumetric measurement, weighing and quantitative transfer of viscous samples has posed a challenge to the analytical chemists. However, accurate weighing of samples is essential for generation of reliable results. Initial weighing and transfer of samples needs careful attention as errors start creeping into the analysis from this stage itself.

A lot of documentation is available on correct weighing practices for liquids, solids and powders and high levels of accuracy and precision are achievable for such samples. However, there is not much documentation on recommended procedures for weighing of viscous samples

A simple procedure being adopted in our laboratories is suggested. This procedure overcomes the problems associated with handling and weighing of viscous samples.

A disposable syringe is partially filled with the viscous sample and weighed. Next adequate quantity is transferred to the receptacle and after transfer the syringe is reweighed. The difference of readings is the amount of sample transferred to the receptacle.

The advantages of the technique are:

• Quantitative weight transfer of the sample
• Sample does not come in contact with the sample transfer device such as a spatula
• Risk of contamination during sample transfer due to contact with the spatula is eliminated
• Elimination of incomplete transfer of weighed sample due to adherence to the sample transfer spatula

After transfer the next important stage is to dissolve the sample using a suitable solvent so that a homogeneous solution is prepared for subsequent analysis.

Hope you find the method suitable for your applications. Please do offer your suggestions and comments.