Columns analytical

Alltech Alltima C18 (or equivalent) analytical column 15 cmx2.1 mmx5 pm. 

Dg-Alprazolam Internal Stock Standard Working Solution 1 pg/mL. To a 100 mL volumetric flask add 1.0 mL of Dg-Alprazolam Stock Standard (100 pg/mL) and dilute to the mark with deionized water. Store refiigerated in glass. 

Benzodiazepine Multi-Component Mixture-8 Stock Standard 250 pg/mL of alprazolam, clonazepam, diazepam, flunitrazepam, lorazepam, nitrazepam, oxazepam, temazepam (Cerilliant Corp, Round Rock, TX). 

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In this case, a preliminary separation will have taken place either in the plant by stabilization, or by the chromatograph which will have had a prefractionating column. This column will isolate the components having boiling points higher than pentane, allowing only the noncondensable hydrocarbons and a fraction of the pentanes to pass through to the analytical column. 

An HPLC typically includes two columns an analytical column responsible for the separation and a guard column. The guard column is placed before the analytical column, protecting it from contamination. 

Analytical Columns The most commonly used columns for HPLC are constructed from stainless steel with internal diameters between 2.1 mm and 4.6 mm, and... 

An inexpensive column used to protect a more expensive analytical column. 

To minimize the mobile phase s contribution to conductivity, an ion-suppressor column is placed between the analytical column and the detector. This column selectively removes mobile-phase electrolyte ions without removing solute ions, for example, in cation ion-exchange chromatography using a dilute solution of HCl as... 

The cells of the monitoring devices are very small (ca 5 pi) and the detection is very good. The volumes of the analytical columns are quite small (ca 2mL for a 1 metre column) hence the result of an analysis is achieved very quickly. Larger columns have been used for preparative work and can be used with the same equipment. Most... 

Proteoglycans (from cultured human muscle cells). Separated by ion-exchange HPLC using a Biogel TSK-DEAE 5-PW analytical column. [Harper et al. Anal Biochem 159 150 1986.]... 

Preparative chromatography involves the collection of individual solutes as they are eluted from the column for further use, but does not necessarily entail the separation of large samples. Special columns can be designed and fabricated for preparative use, but for small samples the analytical column can often be overloaded for preparative purposes. Columns can be either volume overloaded or mass overloaded. Volume overload causes the peak to broaden, but the retention time of the front of the peak... 

Elow rate determines the separation time and can significantly affect resolution and efficiency. The effect of flow rate on HETP for TSK-GEL SW and TSK-GEL SWxi analytical columns is shown in Fig. 4.6. Resolution is typically higher at slower flow rates, although results shown in Fig. 5B indicate that, with increasing sample load, the faster flow rates can give higher resolution. 

The recommended flow rates of 0.5 to 1.0 ml/min for stainless steel and 0.4 to 0.8 ml/min for glass analytical columns will provide adequate resolution of most protein mixtures. 

Plow rate has a tremendous effect on resolution with aqueous GFC as shown in Fig. 4.20. Lower flow rates will decrease HETPs (up to a point) and increase resolution. In general, a flow rate range of 0.5-0.8 ml/minute is recommended for TSK-GEL PW analytical columns. 

All H type analytical columns are supplied containing tetrahydrofuran, with the exception of GMH-HT columns, which are only shipped in o-dichlorobenzene. Semipreparative and preparative columns contain chloroform... 

Table 6.7 shows the available preparative columns and corresponding analytical columns. Preparative columns are also available in larger diameters of up to 50 mm. 

Column type Column size (mm) Theoretical plate number Particle size (pm) Pore size (A) Maximum flow rate (ml/min) Maximum pressure (kgf/cm ) Maximum temperature (°C) Exclusion limit Analytical column... 

Column type Column size (mm) Theoretical plate number Range Flow rate (ml/min) Max Analytical column... 

However, for quantities substantially less than this level, 7- to 10-mm i.d. analytical columns can often be used in a semipreparative mode. By repeatedly injecting 300 to 500 ju,l of up to 1% polymer, reasonable quantities of polymer can be isolated. An autosampler and automated fraction collector can be setup to perform such injections around the clock. Although the larger injections and higher concentrations will lead to a loss of resolution, in some situations the result is quite acceptable, with a considerable savings in time being realized over other means of trying to make the same fractionation. 

These effects refer to the reconcentration obtained with an uncoated inlet. In fact, the term retention gap means a column inlet of a retention power lower than that of the analytical column. This retention gap is placed in front of the analytical column, thus allowing different reconcentration mechanisms to occur. 

Phase ratio focusing is based on the higher migration speed of components through the retention gap compared to that through the analytical column. Reconcentration depends on the ratio between the retention power in the pre- and in... 

Figure 2.12 Schematic representation of an on-line SPE-GC system consisting of three switching valves (VI-V3), two pumps (a solvent-delivery unit (SDU) pump and a syringe pump) and a GC system equipped with a solvent-vapour exit (SVE), an MS instrument detector, a retention gap, a retaining precolumn and an analytical column. Reprinted from Journal of Chromatography, AIIS, A. J. H. Eouter et al, Analysis of microcontaminants in aqueous samples hy fully automated on-line solid-phase extraction-gas chromatography-mass selective detection , pp. 67-83, copyright 1996, with permission from Elsevier Science.

Step 2) Introduce heart-cut to the analytical column and detector. At the predetermined time interval, which was previously calculated by eluting analyte standards without the analytical column, i.e. the onset of the heart-cut, valve B is closed to divert the precolumn effluent to the analytical column. 

Step 3) Bypass the precolumn and detection of the analyte of interest. When all of the analytes of interest have been eluted from the precolumn, valve A is opened so that the eluent stream is diverted to valve B, which is immediately opened to allow eluent from valve A to flow into the analytical column, thus bypassing the precolumn. 

Step 4) Precolumn clean-up not shown in Figure 5.4. After the heart-cut analytes have been transferred to the analytical column, a step-gradient programme is used to flush the precolumn of the more strongly retained compounds. An additional pump configuration makes precolumn clean-up possible while the analysis is running. 

GC using chiral columns coated with derivatized cyclodextrin is the analytical technique most frequently employed for the determination of the enantiomeric ratio of volatile compounds. Food products, as well as flavours and fragrances, are usually very complex matrices, so direct GC analysis of the enantiomeric ratio of certain components is usually difficult. Often, the components of interest are present in trace amounts and problems of peak overlap may occur. The literature reports many examples of the use of multidimensional gas chromatography with a combination of a non-chiral pre-column and a chiral analytical column for this type of analysis. 

Another way to improve the analysis of complex matrices can be the combination of a multidimensional system with information-rich spectral detection (31). The analysis of eucalyptus and cascarilla bark essential oils has been carried out with an MDGC instrument, coupling a fast second chromatograph with a matrix isolation infrared spectrometer. Eluents from the first column were heart-cut and transferred to a cryogenically cooled trap. The trap is then heated to re-inject the components into an analytical column of different selectivity for separation and subsequent detection. The problem of the mismatch between the speed of fast separation and the... 

Considering the numerous applications, heart-cut LC-LC has convincingly proven its value. Nevertheless, in LC-LC specific method development is generally needed for each analyte. Moreover, heart-cut procedures require accurate timing and, therefore, the performance of the first analytical column in particular should be highly stable to thus yield reproducible retention times. This often means that in LC-LC some kind of sample preparation remains necessary (see Table 11.1) in order to protect the first column from proteins and particulate matter, and to guarantee its lifetime. 

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