Resolution packed columns

ASTM Test Method D2163 is quite old. It utilizes lower resolution packed columns, a less sensitive detector, and manual peak area measurement. Thus, it is technically out of date, and Committee D02.0D is currently in the process of developing a revision for the determination of hydrocarbons in LP gases and lower-purity mixtures of Cj and C4 hydrocarbons. The revision will still be performance based, but the recommended column will be the AljOj/KCl PLOT colunm, as used in the recently standardized ASTM Test Method D6159,... 

This method uses a short, packed column that generally produces a poor resolution of chromatographic peaks. The liquid-liquid extraction used to extract the trihalomethanes is nonselective. Besides the trihalomethanes, a wide range of nonpolar and polar organic constituents, such as benzene and... 

Contaminant by-products depend upon process routes to the product, so maximum impurity specifications may vary, eg, for CHA produced by aniline hydrogenation versus that made by cyclohexanol amination. Capillary column chromatography has improved resolution and quantitation of contaminants beyond the more fliUy described packed column methods (61) used historically to define specification standards. Wet chemical titrimetry for water by Kad Eisher or amine number by acid titration have changed Httle except for thein automation. Colorimetric methods remain based on APHA standards. 

The packed columns of Shodex OHpak SB-800HQ series are packed with polyhydroxymethacrylate gels and are designed for use with high-resolution, high-speed aqueous size exclusion chromatography. The packed columns are best suited for the analysis of water-soluble polymers and proteins (Table 6.8). 

All packing materials produced at PSS are tested for all relevant properties. This includes physical tests (e.g., pressure stability, temperature stability, permeability, particle size distribution, porosity) as well as chromatographic tests using packed columns (plate count, resolution, peak symmetry, calibration curves). PSS uses inverse SEC methodology (26,27) to determine chromatographic-active sorbent properties such as surface area, pore volume, average pore size, and pore size distribution. Table 9.10 shows details on inverse SEC tests on PSS SDV sorbent as an example. Pig. 9.10 shows the dependence... 

Mourier s report was quickly followed by successful enantiomeric resolutions on stationary phases bearing other types of chiral selectors, including native and deriva-tized cyclodextrins and derivatized polysaccharides. Many chiral compounds of pharmaceutical interest have now been resolved by packed column SFC, including antimalarials, (3-blockers, and antivirals. A summary is provided in Table 12-2. Most of the applications have utilized modified CO, as the eluent. 

The difference in resolution between LC and SFC can be significant enough to turn a marginal LC separation into a viable chromatographic method in SFC. String-ham et al. reported that packed column SFC yielded satisfactory chiral analysis... 

Packed column SFC has also been applied to preparative-scale separations [42], In comparison to preparative LC, SFC offers reduced solvent consumption and easier product recovery [43]. Whatley [44] described the preparative-scale resolution of potassium channel blockers. Increased resolution in SFC improved peak symmetry and allowed higher sample throughput when compared to LC. The enhanced resolution obtained in SFC also increases the enantiomeric purity of the fractions collected. Currently, the major obstacle to widespread use of preparative SFC has been the cost and complexity of the instrumentation. 

This paper will be limited to a discussion of our packed column studies in which we have addressed attention to questions regarding, (a) the role of ionic strength and surfactant effects on both HDC and porous packed column behavior, (b) the effects of pore size and pore size distribution on resolution, and (c) the effects of the light scattering characteristics of polystyrene on signal resolution and particle size distribution determination. 

The porous glass packed columns did not yield high resolution separations, but the major species present in a latex were adequately separated. Figure 1. Insoluble polymer, when present, was excluded from the pores and eluted at interstitial volume. Elution order of remaining species was soluble polymer, unreacted monomers, and water. In both types of resins studied, no separation of the two unreacted monomers was achieved. A single chromatographic peak, that included both monomers, was obtained. 

Early work relied on the use of packed columns, but all modern GC analyses are accomplished using capillary columns with their higher theoretical plate counts and resolution and improved sensitivity. Although a variety of analytical columns have been employed for the GC of triazine compounds, the columns most often used are fused-silica capillary columns coated with 5% phenyl-95% methylpolysiloxane. These nonpolar columns in conjunction with the appropriate temperature and pressure programming and pressure pulse spiking techniques provide excellent separation and sensitivity for the triazine compounds. Typically, columns of 30 m x 0.25-mm i.d. and 0.25-qm film thickness are used of which numerous versions are commercially available (e.g., DB-5, HP-5, SP-5, CP-Sil 8 CB, etc.). Of course, the column selected must be considered in conjunction with the overall design and goals of the particular study. 

The most common and diverse approach to cleanup (and extraction of water samples) in pesticide residue analysis is SPE. Over the last 20 years, improvements and diversifications in SPE formats, sorbent types, and apparatus have made SPE a widely used approach for a variety of applications, including the analysis of pesticide residues. SPE cartridges or disks can be likened to low-resolution HPLC columns in that similar stationary and mobile phases are used. A typical particle size in SPE is 40 pm, and the plastic cartridges are generally packed with 0.1-1 g of sorbent in plastic tubes. The choice of reversed-phase, normal-phase, and ion-exchange media in SPE is very diverse, and Table 2 lists some of the more popular SPE applications for the cleanup of pesticides. 

The problems associated with coupling packed columns to a mass spectrometer are s re severe than those encountered with capillary columns. Conventional pacdced columns are operated at much higher flow rates, 20 to 60 al/ain, and although this diminishes the influence of dead volumes in the interface on sample resolution, it poses a problem due to the pressure and volume flow rate restrictions of the mass spectrometer. The interface must provide a pressure drop between column and mass spectrometer source on the order of 10 to 10, it must reduce the volumetric flow of gas into the mass spectrometer without diminishing the mass flow of sample by the same amount, and it must retain the integrity of the sample eluting from the column in terms of the separation obtained and its chemical constitution [3,25,26]. To meet the above requirements the interface must function as a molecular separator. 

SFC-NMR is available from 200 to 800 MHz, and is suitable for all common NMR-detected nuclei. SFC/SFE-NMR requires dedicated probe-heads for high pressure (up to 350 bar) and elevated temperature (up to 100 °C). SFC-NMR is carried out with conventional packed columns, using modifier, pressure and temperature gradients. The resolution of 1H NMR spectra obtained in SFE-NMR and SFC-NMR coupling under continuous-flow conditions approaches that of conventionally recorded NMR spectra. However, due to the supercritical measuring conditions, the 111 spin-lattice relaxation times 7) are doubled. 

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