Enrichment method

Job enlargement and job enrichment methods may also be employed. The multiskilling approach used in Zimbabwe is one such strategy. The MCAZ streamlines its procedures and uses teamwork in the performance of dmg regulatory functions. Staff are trained to handle multiple functions. 

Verification of the proper choice of the enrichment method can be done through recovery studies under varying conditions of the most important parameters, such as amount and quality of the enrichment material, pH of the sample, as well as the amount and quality of analyte and matrix to be enriched. These parameters not only differ based on the chemical behaviour of the analyte, but are also strongly dependent on the matrix to be analysed. 

An excellent review of modern sorptive sampling techniques that could be considered for the enrichment of volatiles from mammalian secretions appeared recently [10]. To be on the safe side, more than one sample preparation and sample enrichment method should be used to analyze mammalian secretions. If GC and GC-MS analyses are employed, the results obtained with split/split-less, on-column, SPME and solventless (solid) sample introduction methods [11,12] should be compared. 

Camel, V., and M. Caude, Trace Enrichment Methods for the Determination of Organic Pollutants in Ambient Air, J. Chro-matogr. A, 710, 3-19 (1995). 

Liquid chromatography cleanup on a LiChrosorb Diol column has been further proposed for the offline purification of chloramphenicol residues from bovine muscle and eggs (32). An online approach based on reversed-phase principles has also been described for isolation of chloramphenicol residues from swine kidney by an automated column switching system (63). Use of a protein exclusion column (Hisep) has been also suggested in an online trace-enrichment method for the determination of chloramphenicol in animal tissues (52). By employing a column-switching system, all chloramphenicol that eluted from the protein exclusion column was trapped at the entry of a 5 m Supelcosil LC-18 preconcentration column, to be subsequently back-flashed into the analytical column. 

Data in Table 6 show accumulation of the trans isomers of 4-alky Icy clohexanols (47, 48 and 49) in the crystalline complexes.The same tendency in combination with partial resolution of trans-50 and trans-51 can be observed at 2-alkylcyclohexanols. [39] Furthermore, cis isomer content of the solid complexes remained racemic, consequently DBTA is selective resolving agent of trans-50 and trans-51. Efficiency of this isomer enrichment method is moderate, but it gives a very simple route to break up cis-trans and racemic compositions of the products obtained by nonselective synthesis. 

European Standard. 1998. Water quality. Determination of mercury. Enrichment methods by amalgamation. EN 12338. European Committee for Standardization, Brussels, Belgium. 

Schonmann and Kern [33] have used on-line enrichment for microgram per litre analysis of PAHs in water by high performance liquid chromatography. The trace enrichment method is based on the affinity of non polar pollutants for reversed phase chromatography supports. 

They used a Varian Model 5500 liquid chromatograph with three reservoir capability for on-line enrichment methods one reservoir can be used to quantitatively transfer large sample volumes into the column and a binary gradient can then be introduced from the remaining reservoirs. 

Figure 9 Formation of native contacts during a multiple copy MD simulation with and without ensemble enriching after an initial 100 ps multiple copy MD simulation see text for details. Ensembles that each consist of 10 barnase and 10 barstar copies are simulated, giving rise to 100 putative complexes. The thick lines show the mean and standard deviations, along with the best/worst values for the ensemble enriching method. The superposed thin lines show the corresponding data for the plain multicopy MD simulations without ensemble enriching.

Bass S, Greene R, Wells JA, Hormone phage An enrichment method for variant proteins with altered binding properties, Proteins, 8 309-314, 1990. 

Several methods have been proposed to produce polyunsaturated fatty acid (PUFA) concentrates particularly high in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Most PUFA enrichment methods are based upon a combination of techniques such as saponification, solvent extraction, urea fractionation, molecular distillation, fractionation distillation, liquid chromatography, and super critical carbondioxide extraction. Current evidence suggests that the physiological effects of omega-3 fatty acids are such that the annual world supply of fish oils will be grossly inadequate as a source of these materials, and alternative sources will be needed (Belarbi et al, 2000). 

Membrane Techniques The interest in membrane techniques for sample preparation arose in the 1980s. Extraction selectivity makes membrane techniques an alternative to the typical sample enrichment methods of the 1990s. Different membrane systems were designed and introduced into analytical practice some more prominent examples are polymeric membrane extraction (PME), microporous membrane liquid-liquid extraction (MMLLE), and supported liquid membrane extraction (SEME) [106, 107]. Membrane-assisted solvent extraction (MASE) coupled with GC-MS is another example of a system that allows analysis of organic pollutants in environmental samples [108-111] ... 

The H has been the traditional nucleus for biological studies in the past decade and researchers have successfully utilized multidimensional NMR methods to assign spectra for proteins up to 30 kDa. Other nuclei such as C, N, and P have been used but their lower gyromagnetic ratios and/or natural abundances reduce sensitivity unless expensive isotopic enrichment methods are employed. An alternative nucleus for studies of biological materials is F. F NMR is a powerful technique due to several unique... 

The concentration depends only on that of the leading ion it is independent of the initial concentration in the sample. Therefore, ITP can act as an enrichment method, analogous to displacement chromatography and in contrast to zone electrophoresis and elution chromatography. The concentration in the steady state is adjusted to the value given in Eq. (2). If the concentration of the analyte species is lower in the initial sample, the higher steady-state concentration is established. This concentration is independent of the migration distance there is no dilution with a BGE as there is in capillary zone electrophoresis (CZE). 

Differences in retention times in the chromatograms are due to the different oven temperature program used. Some remarkable differences in the profiles evidence the different enrichment obtained by the two methods. Data reported in Table 5.2 and Figure 5.3 show evidence of generally good linear correlations between XAD-2 extraction and HS-SPME enrichment methods. In the conditions used for SPME/GC-FID analysis, some compounds such as octanoic and decanoic acids partially overlap ethyl myristate and ethyl palmitate, respectively. 

Another area in which SLMs have interesting prospects is sample preparation in analytical chemistry. Unlike in other fields where a high active area is required, the new trends are toward miniaturization, which in the case of SLM is represented by the hquid-phase microextraction (LPME) method based on porous hollow fibers [231]. The other issues being addressed are to improve automation and high throughput of the analytical methods, in which the SLM system is used as an analyte enrichment method [167, 232-234]. Additionally, the improvement of selectivity of SLM extraction is one of the main areas of interest see the immuno-SLM method example described earher. Several improvements in this methodology have recently been reported [35, 36, 235-237]. 

In order to valuate the effects of the treatments, each inoculated sample was diluted in peptoned water and 0.1 of the dilution was plated in Palcam agar according to the ISO 11290-2 method. The enrichment method (ISO II290-I) was used in order to assess the presence of L. monocytogenes in a 25 g sample. 

---