Analytical chemistry is based not only on the proper preparation of test substances, but also on a statistical analysis of the results. However, there are substances which preparation for the research can be problematic. We are talking about highly hygroscopic substances.
PREPARATION OF SAMPLES IN CONTROLLED CONDITIONS
Hygroscopic substances start very quickly absorption of water contained in air that can be observed during weighing, when in short time there is increasing of measured value on the balance, even though there is no more substance added. In some cases absorption of water contained in air by substances can effect on their weight or viscosity, but also on other physical properties.
For example, anhydrous sulfates absorb moisture until their natural, hydrated form is reached. We can include many organic compounds to hygroscopic substances. Among them is e.g. biphenyl, which is used as pesticide, and its content in food samples is controlled.But it’s also worth noting that the rate of water absorption and its quantity is changing depending on season or time of the day – because this is depending on moisture in the air.
Absorption of water by hygroscopic substances causes the appearance of mistakes during weighting, which are impossible to statistical evaluation.Because of variability of water contained in air, we are not able it DETERMINE precisely, how much water will be absorbed by substance and how it will effect on actual quantity of substance. This, in turn, causes that we can’t consider these mistakes during formulate quantitative results of chemical analyzes and also during the certification of the standard material. It is apparent that it is impossible precise weighing of hygroscopic substances without previously preparation of controlled environment.
CONTROLLED ENVIRONMENT – ACCURACY OF MEASUREMENT
Controlled conditions can be achieved by placing a balance with sealed and weighted substance (previously subjected to drying process in the appropriate conditions) in so called glove-box also know as dry box or itsequivalent insulating the contained objects from the surrounding atmosphere.
After placing the balance with weighted substance in box the air with moisture must be removed by a pump and replaced by dry inert gas e. g. nitrogen. Process of emptying and filing the box should be performed at least twice to minimize the content of water in gas. This will make weighing reference hygroscopic substance much more accurate and implicate smaller mistake. The final result of the analysis of the sample will be more precise and more reliable.
ACCURACY OF OUR STANDARDS
Such weighing of reference substance in protective atmosphere allows you toachieve high repeatability. It is worth mentioning that removing of weighted portion from box does not affect the final concentration of reference substance. Even thoughsubstance can absorb moisture from the atmosphere.
All hygroscopic substances, weighed in our laboratories, are prepared in controlled conditions by the above-mentioned glove box. We care about accuracy and certainty of outcome and reliability of our certificates.