It is necessary to maintain appropriate standards for the preparation of measurement solutions in chemical analytics. There is no doubt that the correct preparation of a certified reference material is one of the major factors affecting its quality.
A lot of certified reference materials occur as solution in volatile solvents. The process of weighting this solvents is very difficult – hence process of preparation of certified reference materials needs to be optimized to minimize mistakes that accumulate during the subsequent stages. The first step is weighting a required quantity of substance on the analytical balance in controlled conditions. Then the substance needs to be transferred into measuring vessel A class (certified) and the vessel filled with solvent to specified volume.In our laboratories we have volumetric flask with accuracy of ±6 µl at 20°C.On the other hand, our analytical balances have repeatability of 0.1 mg and linearity of ± 0.2 mg. During weighting of substances you must remember about controlled environmental conditions. Not only the vibrations of the surface influence on the accuracy of measurement but also the temperature and air movement which causes the additional non-uniform pressure on pan and evaporation of volatile materials. Also moisture content in the air, especially in the case of highly hygroscopic substance can impact on the accuracy of measurement (you can read about process of preparation of samples of hygroscopic substance here).
PRECISION OF SYRINGE
During the preparation of following dilutions of solution is necessary to keep high accuracy. For preparation of solution we use in our laboratories an automated analytical syringe eVol®. Connecting a 500 µl syringe to the electronic control module allows to uptaking a solvent with the accuracy of ± 0.5% for uncalibrated syringe at entire range from 1 to 500 µl. After calibration of syringe on specific solvent the accuracy is 0.2% at entire range and precision of device is 0.3%. So precise device allows for significant reduction of error caused by preparation of subsequent solutions.