Sampling and filtration

Water for the analysis of suspended particles may be collected with any clean water sampler used for oceanographic work, e.g., Niskin bottles, Go-Flo bottles, Nansen bottles. Hydrobios water samplers (see also Chapter 1). The sample volume will depend on the expected concentration of POM. In nearshore and/or biologically productive water, 0.5-2 L usually is an adequate sample volume. Ten litres may be required in particle-poor open ocean waters such as the Sargasso Sea. For sampling large volumes of water, 30 L Niskin bottles are recommended. Even larger volumes may be sampled with in situ pumps. (See Chapters 1,2 and 13). 

Immediately after recovery of a sampler a suitable volumetric flask is rinsed twice with about 50-100 mL of sample seawater. The flask is then filled to the mark to subsample a precisely known water volume. Volumetric flasks or Stohmann bottles with ground glass stoppers were found to be fairly handy for the purpose. 

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Precleaning of material, sampling, and filtration in the field are not very different from the procedures used for the other trace metals described above, except that for Hg borosilicate glass bottles can also be used, and that samples collected for volatile, metallic mercury Hg(0) and dimethylmer-cury (DMHg) species are not filtered. When filtration cannot be carried out in the field, samples should be kept unpreserved, cold, and in the dark. More specific information about our techniques can be found in Baeyens80 and Leermakers et al.47,84... 

Solid samples such as soil and sediments are air dried and extracted using Soxhlet/Dean-Stark apparatus. Aqueous samples are separated into solids and filtrates by filters. Solids are Soxhlet extracted similar to biological samples and filtrates are liquid-liquid extracted. These extracts are then cleaned up and injected into HRGC-HRMS, similar to biological samples. 

In the recycle process, the increase in the reaction yield is a direct result of increasing the Iso/7-chloro ratio from 1.5 1 to 3 1, which effectively increases the ratio of Iso/Mono and crystallization of Mono during the reaction. It should be pointed out that due to the difficulty of sampling and filtration of slurry at the reaction temperature, the solid phase cannot be easily assayed to quantify the percentage of Mono present. 

Although the desalting and concentration steps are time-consuming, and therefore only a limited number of samples may be processed, efforts should be taken to perform these steps soon after sampling and filtration to ensure that sample composition and concentrations of constituents reflects those in situ. Until a direct method of determination in real time is available, the effects of sample filtration, preservation and storage will be difficult to assess. It is also difficult to judge whether the pattern of free monosaccharides reported reflects the actual in situ distribution. 

The AOAC and Codex recommended methods for determination of potassium and sodium are by flame atomic emission spectrometry. These methods have the advantage of quick and simple sample preparation, aqueous dilution of sample and filtration, with rapid, reasonably accurate detection. The samples can be aspirated directly into the flame and the readings quantified by comparison with a range of known standards. Atomic absorption spectrometry can also be used, giving increased accuracy and low-level sensitivity and a far wider range of detectable... 

The sampling of solution for activity measurement is carried out by filtration with 0.22 pm Millex filter (Millipore Co.) which is encapsuled and attached to a syringe for handy operation. The randomly selected filtrates are further passed through Amicon Centriflo membrane filter (CF-25) of 2 nm pore size. The activities measured for the filtrates from the two different pore sizes are observed to be identical within experimental error. Activities are measured by a liquid scintillation counter. For each sample solution, triplicate samplings and activity measurements are undertaken and the average of three values is used for calculation. Absorption spectra of experimental solutions are measured using a Beckman UV 5260 spectrophotometer for the analysis of oxidation states of dissolved Pu ions. 

A 10-g sample of the homogenized dry sample is soaked in 20 mL of distilled water for 2 h. After adding 100 mL of acetone to the soaked sample and shaking vigorously on a mechanical shaker for 30 min, the extract is filtered. After the addition of a further 100 mL of acetone, the sample homogenate is shaken as before and the acetone extract is filtered. The filtrates are combined and acetone is removed with a rotary evaporator. " ... 

For example, the metabolite of clomeprop is determined by the following procedures. Water (20 mL) is added to 10 g of sample and then the mixture is allowed to stand at room temperature for 2h. To the mixture, 4mL of IN hydrochloric acid and 100 mL of acetone are added and shaken for 30 min. The filtrate is extracted twice with 50 mL of dichloromethane after 50 mL of water and 5 g of sodium chloride have been added. The combined dichloromethane extract is concentrated, the final residue is dissolved in 50 mL of dichloromethane, then the dichloromethane layer is rinsed with alkaline and acid and extracted twice with 50 mL of 1 % sodium bicarbonate-5% sodium chloride (1 1, v/v) for 5 min. To the combined aqueous layer, 6 N hydrochloric acid is added and extracted twice with 50 mL of dichloromethane for 5 min. The organic extract is concentrated after drying with anhydrous sodium... 

Weigh 20 g (fresh weight) of chopped and homogenized plant samples into a 300-mL Erlenmeyer flask. Add 80 mL of acetone and shake the flask vigorously for 30 min with a shaker. In the case of brown rice and pea, add 20 mL of water to 10 g of sample and allow to stand for 2 h before adding 80 mL of acetone. Filter the extraction mixture by suction through a glass filter and re-extract the residue on the filter with 50 mL of acetone, then filter the mixture by suction. Concentrate the combined filtrate in the 300-mL of round-bottom flask to remove acetone at below 30 °C after addition of a 25% aqueous solution of potassium carbonate (0.2 mL). 

Comparison between the inventories in the collected fractions (the colloidal and ultrafiltered fractions) and in the starting sample often indicate that there are losses of nuclides on to the ultrafiltration cartridge. These are largely recovered by subsequent acid rinses of the ultrafilters and filtration system. It is not clear whether the recovered abundances should be considered part of the colloids retained by the filter, or solutes that have adsorbed in the system (Gustafsson et al. 1996 Andersson et al. 2001), even though test experiments with colloidally-bound " Th showed significant losses in the ultrafiltration system (Baskaran et al. 1992.)... 

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