Sampling stored material

Inner tube split into separate containers 

Outer tube case of thief sampling device 

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Sample Preservation Without preservation, many solid samples are subject to changes in chemical composition due to the loss of volatile material, biodegradation, and chemical reactivity (particularly redox reactions). Samples stored at reduced temperatures are less prone to biodegradation and the loss of volatile material, but fracturing and phase separations may present problems. The loss of volatile material is minimized by ensuring that the sample completely fills its container without leaving a headspace where gases can collect. Samples collected from materials that have not been exposed to O2 are particularly susceptible to oxidation reactions. For example, the contact of air with anaerobic sediments must be prevented. 

Stored Free-Flowing Material. It is practicahy impossible to representatively sample stationary free-flowing powder because of the severe segregation that has almost certainly occurred. If there is no alternative but to sample this material, several samples should be taken and analyzed separately, so that an estimate can be made of the rehabhity of the measured parameter. For free-flowing materials stored in small hoppers, dmms, cans, boxes, and... 

Sperling [133] has reported extensively on the determination of cadmium in seawater, as well as in other biological samples and materials. He added ammonium persulfate, which permitted charring seawater at 430 °C without loss of cadmium. For workbelow 2 pg/1 cadmium in seawater he recommended extraction of the cadmium to separate it from the matrix [126,134,135]. He found no change in the measured levels over many months when the seawater was stored in high-density polyethylene or polypropylene. 

Another step of the production process, equally important to the homogeneity measurement, is the stability measurement. The measurement method requirements are the same as those for the measurement of homogeneity for the same reasons. At this stage there are two additional requirements. The measurements are performed on samples stored at different temperatures, in order to determine the appropriate storage temperature and at different times, in order to determine the lifetime of the certified reference material. 

Each stream sediment sample comprises material taken from 5-10 points over a stream stretch of250 -500 m. Prior to stream water and stream sediment collection, it is important to identify the 250 - 500 m stream stretch where obvious signs of contamination can be avoided and suitable sediment can be collected from 5-10 different locations. Sites should be located at least 100 m upstream of roads and settlements. Stream sediment sampling should start from the water sampling point and the other sub-samples should be collected up stream. A composite sample should not be made from samples taken from beds of different nature (ISO 5667-12 1995). From one small catchment basin of a duplicate cell (one in each country) minimum 0.5 kg (dry weight) + 0.5 kg (duplicate sample) of <0.150 mm material is required. From all other small catchment basins a minimum of 0.5 kg (dry weight) <0.150 mm material is required. Larger sample quantities can be taken and stored separately in each country. 

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. 

Different materials became contaminated to different extents when stored with a tritium emanator such as active concrete (Figure 3). The absorbers used, silica gel, zeolite and Drierite (CaS04), were contaminated to a greater extent than were metal and plastic, especially in an open scintillation vial. Zeolite and Drierite (CaS04) were more contaminated in the fridge (Figure 3). Plastic and metal, however, were relatively little contaminated which implies physical and compositional controls on the extent of contamination [5, 9]. All samples stored in closed vials showed very low contamination. 

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