Columns from Manufacturers

Rt-TCEP Rtx-440 Stx-500 l,2,3-Tris(cyanoeth-oxy)propane Restek Exclusive Phenylpoly- carbo-rane-siloxane TCEP 

Integra-Guard Built-in guard column DuraGuard  

Source Data from the Restek Corporation. See Table 2.8. 

Rtx-CLPesticides, Rtx-CLPesticides2, Stx-CLPesticides, Stx-CLPesticides2 Rtx-OPPesticides, Rtx-OPPesticides2 Rtx-5, Rtx-35, Rtx-50, Rtx-1701 

Rtx-BAC, BAC2 esters (FAMEs) Blood alcohol DB-ALCl, 

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TABLE 3.20 Cross-reference of Columns From Manufacturers... 

For capillary columns fused siHca is the material of choice for the column container. It has virtually no impurities (<1 ppm metal oxides) and tends to be quite inert. In addition, fused siHca is relatively easily processed and manufacture of columns from this material is reproducible. In trace analysis, inertness of tubing is an important consideration to prevent all of the tiny amounts of sample from becoming lost through interaction with the wall during an analysis. 

Reactive distillation is a technique for combining a number of process operations in a single device. One company has developed a reactive distillation process for the manufacture of methyl acetate that reduces the number of distillation columns from eight to three, also eliminating an extraction column and a separate reactor (Agreda et al., 1990 Doherty and Buzad, 1992 Siirola, 1995). Inventory is reduced... 

In order to maintain good column performance the separation efficiency of SEC columns should be checked regularly. Because some column manufacturers do not test columns individually prior to shipping, a new column should always be tested before first use. All PSS SEC columns are tested individually before they are shipped. PSS delivers all columns in the solvent the user wants to run it in and tests the column using these conditions. This guarantees maximum certainty for the user to receive exactly what they pay for. Additionally, the risk of reconditioning columns from one to another solvent is taken over by PSS as the manufacturer. 

Two linear columns from Showa Denko, Shodex SB-806M and Shodex SB-806MHQ, and two linear columns from TosoHaas, TSK GM-PWxl and TSK GM-PW, were evaluated. Prior to the evaluation, the number of theoretical plates for Shodex SB-806MHQ, SB-806M, PWxl, and PW was determined to be 15,100, 15,700, 11,390, and 4710, respectively, as per manufacturer inspection. The lower plate count of the TSK PW column is due to the larger particle size of this column. Two mobile phases, water with 0.1 M LiNOi and 50 50 methanol/water (v/v) with 0.1 M LiNOi, were used for each of the four columns. These four columns were new and only PEO and PVP were analyzed with these columns in this study. Waters Ultrahydrogel columns have also been used in this laboratory. However, Ultrahydrogel columns are exactly the same as the TSK GM-PWxl columns based on the calibrations curves supplied by the manufacturers and by the pyrolysis GC data discussed later. 

With the first part of the project having been completed, two more challenges remained. We first had to decide how we would ensure that the quality of data from each column set remained high. This meant setting up a quality control procedure for each GPC. The second challenge was determining what to do when we ran out of columns from a particular hatch of gel from the manufacturer. 

The final step in the process of standardizing our columns was to try and maintain the high quality of columns from batch to batch of gel from the manufacturer. This was done by following the basic procedures outlined earlier for the initial column evaluation with two exceptions. First, we did not continue to use the valley-to-peak ratios or the peak separation parameters. We decided that the D20 values told us enough information. The second modification that we made was to address the issue of discontinuities in the gel pore sizes (18,19). To do this, we selected six different polyethylenes made via five different production processes. These samples are run every time we do an evaluation to look for breaks or discontinuities that might indicate the presence of a gel mismatch. Because the resins were made by several different processes, the presence of a discontinuity in several of these samples would be a strong indication of a problem. Table 21.5 shows the results for several column evaluations that have been performed on different batches of gel over a 10-year period. Table 21.5 shows how the columns made by Polymer Laboratories have improved continuously over this time period. Figure 21.2 shows an example of a discontinuity that was identified in one particular evaluation. These were not accepted and the manufacturer quickly fixed the problem. 

FIG. 24 Manufacture of p-toluenesulfonic acid. R, reactor S, separator E, extraction column D, distillation column (From Ref. 162.)... 

Periodic system disassembly allows more extensive CDS procedures to be undertaken. Most columns are manufactured from glass, or more usually, tough plastic or stainless steel. After a thorough cleaning of all disassembled components, sterilization by autoclaving is usually undertaken prior to re-assembly. Most chromatographic media likewise can be autoclaved before column re-pouring. 

Level two requires a verification of the effect of more severe changes in conditions, such as the use of chromatographic columns from different manufacturers or the substitution of different equipment, and should be performed in a different laboratory . This second level can be considered as being equivalent to the US Pharmacopeia (USP) definition. 

Preparation of the Columns. Columns were manufactured from 3l6 SS steel tubes l/U" x U mm diam. Swagelok 1/8" x 1/U" 3l6 SS... 

Automatic headspace samplers are available from manufacturers of gas chromatographs. These devices are based on the technique of sampling an amount of vapor above the sample itself. Samples are sealed, neat or in a suitable solvent, in containers, and hold at a preset temperature in a thermostatted liquid bath. The headspace vapor results as a partition equilibrium is established between the liquid or solid and the gaseous phase of the volatiles. As each sample is presented to the analyzer, the vessel is punctured and a portion of the headspace gas is withdrawn by a pneumatic injection technique and forced into the column. The main application for those samplers is in the routine analysis of low-boiling fractions in samples containing nonvolatile solids or high-boiling components. Some of the more popular applications today are ... 

Column ovens vary considerably in dimensions and geometry from manufacturer to manufacturer. Many types of columns have to be accommodated in gas chromatograph column ovens, from short capillary columns to the larger diameter preparative columns. The "best" oven really depends on the application which dictates the type of chromatograph. In the past, three configurations have been common ... 

The importance of the amount of carbon load on the column, which varies widely between columns from different manufacturers, has been discussed for a long time. The differences in chromatographic retention and selectivity are a result of the utilization of different silica materials as supports and a variety of reagents and procedures to produce the bonded phases. Several studies have shown that the capacity factor, k, generally increases with increasing carbon content (12). However, sometimes the results show that k values are not always correlated with the differences in carbon content. This may be explained, as Unger (13) illustrates, by the fact that the carbon content alone is often misleading in the comparison of columns because of differences... 

Remove the column from the magnet, place over a new tube, and flush the column content with 1 mL of PBS buffer using plunger supplied by the manufacturer. The eluted cell suspension is enriched in the CD56+ cells, and is designated as the positive cell fraction. 

Purification of the biotinylated sample To remove uncoupled biotin and side products, use desalting columns (e.g., PD-10 columns from Amersham) and follow the instructions of the manufacturer. Elute the sample with PBS, pH 7.4. After the purification, calculate the resulting protein concentration. 

The results of such tests are most useful for determining differences in stability among columns from various manufacturers (ie., they are good relative tests). However, these tests should not be considered absolute measures of column stability since their relationship to real-life use conditions is not known. 

In most cases, absolute retention times are used for the identification. Modem GCs have high precision and accuracy of retention times within 0.05 %, or better can be obtained in subsequent runs during the same day. When the analysis is repeated by another instrument, the deviation may be of several percent. The reproducibility of absolute retention times is strongly dependent on the proper adjustment of all chromatographic parameters. In addition, the column properties are not exactly the same even when similar columns from the same manufacturer are used. On the other hand, absolute retention times are the most useful identification parameters if a few chemicals are to be monitored and the background is low. This method requires frequent calibration because even small changes in chromatographic conditions will influence the absolute retention times. 

The first item to remember when using modern LC columns is that all columns of the same name can be different. For a given compound a C 8 (sometimes called ODS or octadecyl) column from one manufacturer will often behave differently compared to a C,8 column from another manufacturer. If they behave similarly, thank your lucky stars, since this is the exception and not the rule. Even from the same manufacturer, a Brand Name A C 8 column and a Brand Name B C 8 column may behave differently for the same sample compounds. 

Pore size was also found to be the main factor affecting separation selectivity of C18 columns from different manufacturers, compared to evaluate the applicability of sequence-specific retention calculator peptide retention prediction algorithms. Differences in end capping chemistry did not play a major role while the introduction of embedded polar groups to the C18 functionality enhanced the retention of peptides containing hydrophobic amino acid residues with polar groups [6]. 

Alkyl-Type Phases (C1-C18, C30). Probably 90% of all reversed-phase columns are alkyl-type bonded phases. An enormous amount of publications are devoted to the classiflcation, standardization, and comparison of these phases. In their book Practical HPLC Method Development, Snyder and Kirkland [57] indicate that reversed-phase retention for nonpolar and nonionic compounds generally follows the retention pattern Cl < C4 < C8 = Cl 8. At the same time, they refer to the comparison of Cl 8-type columns from different manufacturers and find dramatic variation in the retention of both polar and nonpolar compounds at the same conditions on different columns. 

In this case study, two different Cl 8 columns from different manufacturers were used. Alternatively, other stationary phase types could also be used such as a polar embedded phase and a Cl 8 phase. Some systems come also equipped with a six-column switcher and in that case, two different types of polar embedded phases, phenyl phase, pentafluorophenyl phases, two different Cl 8 phases (of different bonding density) and an alternate C8 phase could be used. 

The most popular reversed-phase columns are manufactured from silica-based bonded phases, and, among those, the Cig-type bonded phase is most frequently used. These bonded phases are prepared by reacting silica with a reactive silane that carries the hydrophobic ligand after which the phase is named. However, the poor stability of silica at extreme pH values, along with the presence of underivatized silanol groups that most frequently cause secondary interactions, limits the application of silica-based supports in liquid chromatography. 

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