Sample matrix whole water

The same considerations apply for metals. Heavy metals have a strong tendency to be adsorbed onto the surface of solids and for this reason the template requires the determination of the concentration of SPM in the sample for all measurements on whole water samples. However, it should be taken into account that the principal matrix... 

Since the analyte is often present in quite a complex matrix comprising other elements or substances that may or may not interfere with any projected method of determination, and may indeed be quite a minor constituent of the whole sample, these considerations will effectively dominate the working details of any analytical procedure. There can therefore be no case for prescribing a single definitive method for (say) nickel that would be universally applicable to its determination in alloys see Alloys), organometallic compounds see Organometallic Complexes), inorganic salts see Ionic Bonds), or coordination compounds see Coordination Complexes), to its presence as a trace constituent see Trace Element) in maize or other plant products, or in natural waters or effluents. 

Two examples of modern clean-up methods that use columns that have been prepared commercially are the Extube (Analytichem International) and the Sep-Pak (Waters). The Extube was designed to isolate drugs from a complex biological sample by the principle of liquid-liquid extraction. Samples to be analyzed, such as urine, whole blood or bile, are introduced into a disposable Extube, which is packed with an inert fibrous matrix of large surface area. When a suitable solvent is poured into the Extube, it interphases film-on-film with the sample. The compound of interest is extracted by a solvent that passes freely through the matrix, whereas impurities such as water, pigment, particulate matter and other polar components are retained by the matrix. The Extube has been used to extract and purify cortisol from plasma by liquid-liquid partition with methylene chloride [40]. The Sep-Pak... 

The use of low-resolution TD-NMR for oil, fat, and moisture is often easier and more accurate than the use of near IR (NIR) (Chapter 4) because it is less dependent on the product matrix, so it is possible to calibrate an oil determination against 100% oil. In addition, NMR acquires the signal from the whole sample, not the surface. In some cases, if water is <10%, oil and moisture may be able to be determined simultaneously. Other applications of TD-NMR can be found on the websites of Oxford Instruments and Bruker and include oils in snack foods, chocolate and cocoa, milk powder, and so on. 

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