Large-volume injection rapid

Figure 13.10 LC-LC chromatogram of a surface water sample spiked at 2 p.g 1 with ati azine, and its metabolites (registered at 220 nm). Conditions volume of sample injected, 2 ml clean-up time, 2.60 min ti ansfer time, 4.2 min The blank was subtracted. Peak identification is as follows 1, DIA 2, HA 3, DEA 4, atrazine. Reprinted from Journal of Chromatography, A 778, F. Hernandez et al, New method for the rapid detemiination of triazine herbicides and some of thek main metabolites in water by using coupled-column liquid cliromatography and large volume injection , pp. 171-181, copyright 1997, with permission from Elsevier Science.

P. Hernandez, C. Hidalgo, J. V. Sancho and P. J. Lopez, New method for the rapid determination of triazine herbicides and some of their main metabolites in water by using coupled-column liquid cliromatography and large volume injection , 7. Chromatogr. 171-181 (1997). 

There are basically three methods of liquid sampling in GC direct sampling, solid-phase extraction and liquid extraction. The traditional method of treating liquid samples prior to GC injection is liquid-liquid extraction (LLE), but several alternative methods, which reduce or eliminate the use of solvents, are preferred nowadays, such as static and dynamic headspace (DHS) for volatile compounds and supercritical fluid extraction (SFE) and solid-phase extraction (SPE) for semivolatiles. The method chosen depends on concentration and nature of the substances of interest that are present in the liquid. Direct sampling is used when the substances to be assayed are major components of the liquid. The other two extraction procedures are used when the pertinent solutes are present in very low concentration. Modem automated on-line SPE-GC-MS is configured either for at-column conditions or rapid large-volume injection (RLVI). 

PSE Pressurised solvent extraction RLVI Rapid large-volume injection... 

The need for maximum sample throughput and minimal human interaction within analytical procedures has provided considerable impetus to the development of integrated systems. SPE-LC in-tube SPME followed by ultraviolet (UV) or MS detection and membrane introduction mass spectrometry (MIMS) have both been used to this end. Submersible MIMS systems capable of extended underwater deployment down to 200 m and with a mass range of up to 200 amu have recently come onto the market. Elow injection coupled with MIMS allows fast, near-real-time determination of, for example, phenols in water. Derivatization of the phenols with acetic anhydride can be used to enhance both the selectivity and sensitivity of this method. Other online derivatization procedures are under development with a view to increasing the scope for rapid determination of highly polar compounds that have previously proved difficult to analyze. Large volume injection techniques and developments in enzyme-linked immunosorbent assay (ELISA) technologies... 

On-column large-volume injection has wide applications in terms of volatility and thermostability of the analytes. " If the solvent exit valve is operated carefully, compounds with boiling points only slightly above that of the solvent can be recovered quantitatively. However, the technique is generally not very suitable for dirty samples. Frequent analysis of samples with high contents of matrix compounds can rapidly decrease the column performance. ... 

A selective, direct and relatively rapid method has been developed for the determination of thiodiglycol (TDG) in aqueous samples by using microcolumn liquid chromatography coupled on-line with sulfur flame photometric detection using large-volume injections and peak compression [32]. Figure 4.7 reports the separation improvement with the addition of -propanol to a TDG sample. The combined effect of peak compression by displacement with -propanol... 

Fosphenytoin Fosphenytoin is a water-soluble, phospho-ester prodrug of phenytoin that is rapidly converted to phenytoin in the body. It is compatible with most IV solutions and is well tolerated as an IM injection, even with the large volumes associated with loading doses (20 to 30 mL).19 It is dosed in phenytoin equivalents (PE), and it can be infused three times as fast as phenytoin, up to 150 mg PE/minute. The loading dose for patients not taking phenytoin is 15 to 20 mg PE/kg. It can be an advantage to use IM fosphenytoin when IV access cannot be obtained immediately and in patients with poor venous access. Although it has fewer cardiovascular side... 

Injection ports for packed columns are aligned so that the sample can be deposited on a heated surface just before the column or directly on the end of the column. In the first instance, the injection port is heated above the boiling point of the sample in order to get rapid volatilization, but for on-column use, the injection port is kept at column temperature. On-column injection is usually preferred because there is less chance of decomposition and the sample is not exposed to a high injection port temperature. Remember also that a typical GC analyte will have a retention ratio of 0.25 or much less. This means that 75% or more of it is sorbed in the stationary phase, and that is where the on-column technique puts it—in the stationary phase. It is probably for this reason that on-column injection is so efficient. The use of large volumes of solvents will wash... 

This method avoids the need for large volumes of solutions by focusing attention on the mixing chambers. The device is shown in Fig. 7.5. The two solutions are mixed very rapidly by injecting the material into a cavity. The cavity is fitted with a plunger that moves back... 

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