Sensitivity gravimetric, comparison

The gravimetric sensitivity, S , of each of our four main sensors can be expressed in a simple form that permits easy comparison of device sensitivity. The key is to focus on the dimensions of the active region of each device where wave energy is present. 

The preparation of standards for the analysis of VOCs does present difficulties for many laboratories. Firstly, the common use of many solvents in laboratories means that contamination and high blanks are real problems. The analytical techniques used are highly sensitive, standard solutions are usually prepared in methanol, and therefore absorption of atmospheric contaminants readily occurs. Secondly, the volatile nature of the components may make quantitative transfer susceptible to losses. For these reasons, and because of the large number of components involved, many laboratories prefer to buy in solutions of standard mixtures, which are usually prepared gravimetrically under clean conditions. However, laboratories need to check the accuracy of such solutions, usually by comparison to solutions from other suppliers and by means of proficiency schemes, and take care to minimise evaporative losses over the time-scale of use. 

After lyophilization, the dry material is assayed for radioactivity using liquid scintillation counting and the water content is calculated. A comparison was made between the tritium method and the gravimetric method. The sensitivity of the tritium method was stated to be 1 pg of water it measures the water content of 1 mg of dry material with an accuracy of 0.1%. It was noted that small amounts of tritium were found in the nontest ampoules after lyophilization. In addition, tritium oxide was used to measure the exchange of water molecules between stopper and material. Kassai and Sikos stated that the product distributed into the vial takes up water from the stopper until a state of equilibrium ensues. ... 

Table 10. Comparison of sensitivities and other characteristics of acoustic gravimetric sensors [228], 255], [256) international symbols (short form) have been used to denote specific cuts of the various materials...

---