Analytes apolar

Preferred for polar analytes (apolar analytes better analyzed via GC-MS)... 

This technique is used to extract effectively analytes that are polar in nature and strongly bound to soil. Typically, a solvent mixture containing a water-miscible solvent and an apolar solvent (e.g. methanol-dichloromethane) is used. A small aliquot of soil (10-30 g) is dried by mixing with sodium sulfate and refluxed for 8-16h to extract the residues. 

SPE is a useful device for working up of polymer additive dissolutions the apolar polymer is retained on the Cj 8 sorbent, while analytes may be eluted. In the fractionation of dissolutions it is advantageous to make use of the differences in polarity and affinity of the components with the sorbent. SPE of applied samples may be done with cartridges or disks, either off- or on-line. A flow-chart for the use of SPE has been published [3], Applications of SPE have been described in several monographs [511,512]. 

A simple TLC method has been developed for the separation and identification of flavons and flavon glycosides in the extract of Phillyrea latifolia L. The leaves (100 g) were defatted in 11 of chloroform for 24 h and then extracted with 2 X 11 of ethanol-water (80 20, v/v). The collected extracts were concentrated and extracted again with n-hexane to remove chlorophylls and other apolar constituents. Analytes were extracted with ethyl acetate. Both normal phase and RP-TLC have been used for the separation of flavonoids. The results are compiled in Table 2.36. It was concluded from the data that TLC can be successfully applied for the quality control of plant extracts containing various flavone derivatives [124],... 

If the size of the literature is a reliable indicator, the analysis of compo-uents fotmd In nvironmfntnl samples has not been developed t the same extent as clinical applications of re versed-phase chromatography. More attention has been paid to the analysis of volatile species by gas phase chromatography. This is due in part to the difficulty in identifying large molecular weight complex molecules which are present in water at trace levels. However, determination of a variety of analytes in water, soil, or other matrices has been reported and the wider use of RPC in the evaluation of water quality especially can be expected. The apolar phases used in RPC may be a boon in the determination of dilute analytes. Frei (4M) has discussed how relatively unpolar compounds dissolved in water can be concentrated at the top of a reversed-phase column and then eluted as a narrow band with an appropriate solvent. This technique can be used for the analysis of environmental samples in which the analyte of interest is in exceedingly low concentration. 

In recent years, the wide diffusion of precolumn derivation agents able to increase analyte hydro-phobicity and hence its retention on an apolar phase allowed a gradual replacement of dedicated amino acid analyzer with more versatile and less expensive RP-HPLC systems. 

The use of commercially available SPE cartridges is an attractive technique, because the volume of elution solvent is reduced and the cartridges can be used in different cleanup methods. C 8 retains OPPs because of its apolar characteristics, and it allows polar analytes to pass. This method has been used to clean up extracts from beef tissues (60,61,63). The opposite is true of polar stationary phases such as Florisil, which has been used to clean up extracts from marine mammal tissues (62). 

Another emerging technology is supercritical fluid chromatography (SFC) that uses supercritical carbon dioxide as the apolar eluent [46]. The main advantage of SFC, which can be applied both in the analytical and in the purification area, is the higher resolution than the traditional HPLC, allowing time reduction and more efficient separations. Also this technique can be advantageously coupled with a MS detector, to further improve the full analytical process. 

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