Sampling and Storage of Samples

The first stage of the analytical procedure involves representative sampling of material. This stage is of key importance for the quality of results and must be performed in a manner ensuring minimum loss of the assayed element and maximum protection from contamination, including impurities that could upset the delicate equilibria existing between active forms. 

A major role in speciation analysis is played by appropriate selection of laboratory ware (material, color) used for sampling, storing samples, and maintaining their purity. The problem of contamination or loss of assayed elements at this stage depends for the most part on the susceptibility of analyzed compounds to ultraviolet (UV) radiation and oxidation through contact with air. Other factors that need to be considered include the possibility of evaporation of the element, its transformation into a different form, and absorption/adsorption on the vessel wall. All vessels should be thoroughly washed with deionized or distilled water or, if the nature of the sample allows, with 10 % nitric acid. 

Gaseous samples are typically taken by means of isolation techniques (using gas pipettes, ampoules, plastic bags, or canisters with walls lined with an inactive polymer) or aspiration techniques (absorption on solid sorbents or in appropriate 

Liquid samples should be taken and stored in containers made of materials whose components do not migrate into the analyzed solution. For assays of metal forms, polycarbonate vessels are recommended however, when mercury compounds are analyzed, glass is a more appropriate material [35]. 

Summing up, samples must be stored in a manner that does not affect their representativeness. The rule applies not only to freshly collected samples but also to extracts obtained at every stage of concentration or purification. It is also important to note that there are no universal methods. Therefore, methods should be optimally adjusted to the compounds being assayed. This demanding task is addressed next using the example of arsenic compounds. 

---

CEN/ISO EN/ISO 16000-11 Indoor Air-Part 11 Procedure for sampling and storage of samples and preparation of test specimens Will supercede 13419-3... 

Aqueous samples such as drinking water, surface water, and waste water but also beverages and urine samples, should always be acidified with mineral acids for stabilization purposes immediately after collection. This is especially true for the prevention of desorption processes during sampling and storage of samples in the course of trace metal analysis. Acidification reduces the tendency for ions to be adsorbed onto active sites at the surface of the containment vessel, and it also inhibits bacterial growth [9]). Glacial acetic acid and... 

---