Homogenising steps

For example, if the purpose of the experiment is to study the speciation of an element in a specific cell type in a given tissue it is essential that all the extracellular fluid is removed from the tissue before the homogenisation step. This step could be followed by ultracentrifugation of the homogenate in order to separate the cell under study from others that may be present in the medium. An estimate of the degree of purity of the end product should be given. The harvested cells may then be further processed. 

Method of manufacture, although there is often a lack of important detail (e.g. clear protocols for the homogenisation step in the preparation of suspensions) impairing their reproducibility Special mention (if any) regarding its use... 

To eliminate bubbles and chemical inhomogeneities, a fining and homogenisation step has to be followed. These process steps are described in the following section considering the problems that may occur if a microstructured glass device shall be produced. 

Preparation of AIR and extraction of pectic fractions For the preparation of the alcohol-insoluble residue (AIR) the apples were peeled, cut into small pieces and boiled in 96% ethanol for lOmin. After this enzyme inactivation step, the sample material was blended, homogenised and filtered through a G3 sintered glass niter funnel. The residue was washed with 96% ethanol, followed by acetone and diethyl-ether, dried overnight at 40°C under vacuum and stored at -20°C in the dark. Portions of about lOg of AIR were fractionated according to the method of Selvendran et al. [10] as shown in figure 1. 

For the selection and reproduction step the idea of elitism plays a role in so far as individuals of high quality should not become extinct. On the other hand, a larger number of elitists produces untimely a homogenisation of the population. 

Fish. Solid biota samples, mainly fish, should be quickly killed by liquid N2 [28] or cervical dislocation [32] and kept at low temperatures (— 20°C). Some authors preferred desiccation of the sample at high temperature (70°C) [33,34] or lyophylisation [28]. The extraction and isolation steps would be combined when using lyophylisation and homogenisation, followed by a Soxhlet extraction, usually with MeOH, and a subsequent solid-phase extraction (SPE) clean-up, prior to the quantification. 

The HbHnl is obtained from the leaves of the rubber tree plant and a crude extract is easily prepared by homogenisation of the frozen leaves, followed by centrifugation [38-40]. A 5-step purification procedure of this crude extract (with over a 100-fold purification factor) to yield a homogenous HbHnl has... 

Figure 5.1.2 Matrix solid-phase dispersion (MSPD) extraction as a micro-preparative extraction technique for an on-flow LC-NMR-MS screening. Since the latter requires only sample amounts in the 0.5-2 mg range, the sample preparation can be achieved by fast small-scale extraction procedures, such as MSPD. This is a sample preparation technique that combines both sample homogenisation and extraction of compounds of interest in one single step starting from the intact sample material. Thus, it simplifies the extraction and clean-up steps, reduces the sample manipulation and is much faster than conventional techniques. It is therefore very well suited for a rough separation of extracts into classes of compounds of similar polarities, which can then be submitted to LC-NMR-MS analysis...

Sediment obtained from several sites in Lake Flumendosa, Italy, was collected, homogenised and, following a certification campaign, became available as BCR CRM 601 lake sediment certified for its extractable trace metal contents -sequential extraction (Quevauviller et d., 1997). In sediment CRM 601, concentrations of extractable Cd, Cr, Ni, Pb and Zn are certified in Step 1, but only Cd, Ni and Zn in Step 2, and Cd, Ni and Pb in Step 3. Indicative values are also given for extractable Cu in Step 1 and Pb in Step 2 (European Commission, 1997). The long-term stability of the extractable trace metal content of the reference material was recently demonstrated in a European intercomparison exercise (Lopez-Sanchez, 1998). 

Determine the extractable contents of the analytes using the procedure described below. Carry out all extractions on air-dried sediment. Before subsampling, ensure the sample is suitably homogenised. Take the sample using a suitable (see Apparatus) plastic spatula. For each batch of extractions, dry a separate 1 g sample of the sediment in a layer of about 1 mm depth in an oven (105 2°C) to constant mass. From this, a correction to dry mass is obtained, which should be applied to all analytical values reported (i.e. results should be quoted as amount of metal per gram of dry sediment). Perform the extractions by shaking in a mechanical, end-over-end, shaker at a speed of 30 10 rpm and a room temperature of 22 5°C. Perform the sequential extraction according to the steps described below. 

Most soft materials such as tomatoes, grapes or bananas are homogenised and then solvent extracted before further sample processing is carried out. However, material such as potatoes or apples have to be chopped first and the initial step can be Soxhlet extraction or homogenisation. Some materials (for example oranges or potatoes) may have to be peeled depending on whether the aim is to analyse the peel, the inner part of the food or the whole sample. 

The first step in the analysis is that loose foods must be representative and reduced down by multiple squaring to a suitably representative sample size for analysis. The wide array of foodstuffs would require different methods to achieve homogenisation. One must be applied that is practical and fits with the available resources and does not contaminate... 

VALIDATION FIGURES OF VARIOUS STEPS OF THE DETERMINATION OF CB IN FRESH HOMOGENISED MUSSEL TISSUE... 

As mentioned on the chapter on homogenisation, for each batch or set of material processed (e.g. one bottle on a batch of 50 bottles filled between two mixing steps), one is set aside. This approach is to be preferred to random sampling of vials. In the latter case it will not be possible to detect trends in the procedure. 

A quantity (1650 L) of cooled (4°C) cow milk was transported to NIZO in Ede (The Netherlands). The milk was heated to 74°C for 10 seconds, homogenised at 55°C under 200 bar and further cooled to 5°C. The homogenised product was concentrated to 46 M> (mass fraction) dry matter in four temperature steps from 74°C to 46°C. The concentrate was spray-dried at a temperature of 72°C to give a final water content of about 2%... 

An alternate sample pre-extraction preparation was to blend the composite sample without the addition of water. Then, the analytical sample was weighed, ethyl alcohol was added, the sample was homogenised again, diatomaceous earth was added, and finally the pre-treated, chopped sample was placed in the thimble. At this point, the sample should not be dried in an oven due to the fire hazard with ethyl alcohol. The ethyl alcohol wiU be extracted away in the first few minutes of the dynamic extraction. It may be preferable to carry out the alcohol drying step of the SFE at a low density (lower than 0.40 g/mL) and a temperature of perhaps 80 C. The pre-treated sample - enveloped in the filter paper - was input to the SFE where extraction and reconstitution proceeded. 

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