Clean-up of sample

Classical vs. High Performance LC. Most workers are familiar with classical LC, a tool that has been predominantly used for preparative scale clean-up of samples. In order to appreciate more fully HPLC, Table I compares some of the column characteristics of classical vs. HPLC. 

Florisil is a form of magnesium silicate with acidic properties. It is used for clean up of sample extracts containing the following types of analytes orga-... 

Human adipose tissue (CDDs) Clean-up of sample on potassium silicate/silica gel column, elution with cyclohexane/CH2CI2 clean-up on carbon column, elution with toluene clean-up sequentially on potassium silicate column in tandem with alumina column, elution with hexane followed by CH2CI2 in hexane HRGC/HRMS (EI/MIM) No data No data Nygren et al. 1988... 

Fig. 13.9 The benefits of strong cation exchange (SCX), solid phase extraction (SPE) clean-up of samples. The reversed phase HPLC-ESI-MS base ion (m/z 200-500) chromatograms of a reduced (zinc/sulfuric acid) extract of Senecio ovatus. (a) Methanolic solubles of the reduced extract and, (b) the SCX SPE of the methanolic solubles of the reduced extract.

Instrument-based extraction techniques such as supercritical fluid extraction (SEE) and pressurized liquid extraction (PEE) offer advantages because of their potential for automation, more selective isolation of residues through tuning of parameters, and on-line clean-up of samples. Their applications have been slowed by the limited number of commercially available instruments, additional extraction costs, and instrumental downtime. Although several applications have been developed using SEE and PEE, these techniques are not widely used in routine laboratories. 

While the chemiluminescence detectors have considerable selectivity for nitrosamines it must also be recognized that the possibility exists that any compound that can produce NO during pyrolysis will produce a signal (20). For example, TEA responses have been observed from organic nitrites, C-nitro and C-nitroso compounds (17,28) and nitramines (29). In the routine analysis of N-nitroso compounds, possible TEA analyzer responses to compounds other than N-nitroso derivatives normally do not represent a problem since the the identity of a compound can be readily established by co-elution with known standards on GC-TEA and/or HPLC-TEA systems (30-34). Additional confirmation could be provided when the sample can be chromatographed on both GC-TEA and HPLC-TEA (30,33). The technique accepted as the most reliable for the confirmation of N-nitrosamines is based on mass spectrometry (22, 35,36). Low-resolution mass spectrometry is satisfactory for the analysis of relatively simple mixtures and in those instances in which extensive clean-up of samples has been performed. However, complex samples require more sophisticated GC and MS procedures (e.g., high resolution-MS). 

The most effective method of preconcentration and clean-up of samples in determination of MC is lAP however, sorbents with immobilized antibodies have limited repetitive use and they are expensive for routine monitoring. In some cases they can be replaced by SPE sorbents, but especially promising seems to be the use of imprinted polymers developed for selective binding of MC molecules. With a comparable selectivity to antibodies they should exhibit longer life-time for repetitive use. 

Active Donnan dialysis is employed most commonly with ion chromatography and is useful for clean-up of sample solutions at extreme pHs. Electrodialysis can be used with ion chromatography for the off-hne analysis of strongly alkaline samples containing trace amounts of common inorganic anions. ... 

Great care has to be exercised in the preparation of materials for sample extraction and concentration/clean-up of sample extracts so as to detect any source of contamination and to reduce it to an acceptably low level. All work should be carried out in clean-room laboratories, in clean benches or under pure gas protection. 

Microwave extraction realized at 120 °C for 30 min with Hexane -Acetone (3 2 V/V) as the extraction solvent was identified as the most effective extraction procedure for isolation of TPH from biotic matrices. The aim of this research is to develop a silica gel and alumina fractionation procedure for plant sample extraction. Column chromatography with two solvents (chloroform and hexane dichloromethane) as a mobile phase were used for clean-up of extract. In this research the efficiency of recovery received from chloroform as a mobile phase. 

There has for some years been a considerable backlog in the development of practicable prechromatographic methods [5]. It is becoming more and more recognized that the future direction to be taken by trace analysts is to make improvements in the extraction, enrichment and clean-up of the sample and in the optimization of derivatization. It is only in this way that it is possible to employ the sensitive chromatographic techniques optimally for the solution of practically relevant problems. 

In addition, information must be provided concerning the enrichment and clean up of the sample. If possible the sample solution prepared should be adjusted to a particular concentration, so that the application of the chosen volume gives a preliminary idea of the amounts in the chromatogram produced. 

The application of automated GPC for the clean-up of various matrices has been demonstrated by other authors (58, 59). As well as organophosphorus pesticides, conventional methods for the analysis of organochlorine pesticides (OPCs) in fatty samples may involve various clean-up methods, such as LC or GPC. The main... 

Transfer the sample extract (from Section 6.1) into a 200-mL separatory funnel, add 30 mL of water and extract the sample extract three times with 30 mL of n-hexane. Collect and dry the n-hexane layer with anhydrous sodium sulfate in a funnel in a similar manner as described for the juice, pulp and rind, and evaporate the solvent under reduced pressure. Dissolve the residue in 3 mL of benzene and clean up the sample by silica gel column chromatography in a similar manner as described for juice, pulp and rind. 

The sample volume initially introduced onto the sorbent, the choice of sorbent and solvent system and careful control of the amount of solvent used are of paramount importance for effective pre-concentration and/or clean-up of the analyte in the sample. The number of theoretical plates in an SPE column is low (/V = 10-25). SPE is a multistage separation method and as such requires only a reasonable difference in extractability to separate two solutes. In SPE concentration factors of 1000 or more are possible, as compared to up to 100 for LLE with vortex mixing. 

Fig. 3.4f shows an exclusion chromatogram on unmodified silica. The sample is an epoxy resin with an average Mr of 900. Fig. 3.4g shows the determination of pesticide residues in a sample of chicken fat, and is an example of how exclusion can be used to clean up complex samples. First, a pesticide-free sample of the fat is run as a blank, then the blank is spiked with the pesticides to determine their retention volumes. When the sample is injected, the eluent containing the pesticides is collected. The solvent is evaporated, the residue dissolved in acetonitrile and the pesticides are then separated on a reverse phase column. 

The next section describes the utilization of //PLC for different applications of interest in the pharmaceutical industry. The part discusses the instrumentation employed for these applications, followed by the results of detailed characterization studies. The next part focuses on particular applications, highlighting results from the high-throughput characterization of ADMET and physicochemical properties (e.g., solubility, purity, log P, drug release, etc.), separation-based assays (assay development and optimization, real-time enzyme kinetics, evaluation of substrate specificity, etc.), and sample preparation (e.g., high-throughput clean-up of complex samples prior to MS (FIA) analysis). 

Online SPE after conditioning of the SPE cartridge, the sample solution is flushed into the cartridge by the washing solvent after a positional switch of the injection valve. A large volume of washing solvent is used to clean up the sample. 

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