Coated Columns

Zhou and colleagues determined the %w/w H2O in methanol by GG, using a capillary column coated with a nonpolar stationary phase and a thermal conductivity detector. A series of calibration standards gave the following results. 

Stainless steel column coated with y -bis(y -phenoxyphenoxy)benzene. 

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. 

Naphthalenedisulfonate-acetonitrile as the only mobile phase with a silica column coated with a crosslinked aminofluorocarbon polymer has proven to be an effective combination for the separation of aliphatic anionic surfactants. Indirect conductivity and photometric detection modes are used to monitor these analytes. The retention of these surfactants is found to depend on both the ionic strength and the organic solvent content of the mobile phase. The mechanism of retention is considered to be a combination of both reverse phase and ion exchange processes. Selective separation of both alkanesulfonates and... 

The signal was recorded on a Hewlett Packard Integrator Model 3393A Integrator. Samples were injected onto a 30 m megabore column coated with 1.5 micron DB-5 purchased from J W Scientific. The flow of nitrogen carrier gas was maintained at 30 cc/min. The column was equilibrated at 150°C. On injection of the sample, this temperature was maintained for five minutes followed by a programmed increase at a rate of 8°C/min. to a maximum of 300°C, which was maintained for 30 minutes. 

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. 

Oxyfluorfen column, fused-silica capillary column coated with cross-linked methyl silicone (25 m x 0.3-mm i.d., 0.52- am film thickness) temperature, column 200 °C (1 min), 10°Cmin to 250 °C (5 min), inlet and detector 250 and 300 °C, respectively gas flow rates, N2 carrier gas 30mLmin , N2 makeup gas 30mLmin H2 3.5mLmin" air llOmLmin injection volume, 2 p.L. ... 

In practice, it is more difficult to optimize resolution as a function of the relative retentlvity than to optimize retention. Thus, unless the mixture is very complex or contains components that are particularly difficult to separate it may be possible to optimize a particular separation using the linear equation (1.72) as demonstrated by Bttre [177]. Figure 1.13 illustrates the relative change in peak position for a polarity test mixture with two identical, serially coupled open tubular columns, coated with a poly(dimethylslloxane) and Carbowax 20 M stationary phases, as a function of their relative retentlvity on the second column. The linear relationship predicted by equation (1.72) effectively predicts the relative peak positions and indicates that a nearly... 

Figure 8.41 Separation of the enantiomers of the common protein amino acids (N-perfluoropropionylamide isopropyl esters) on a 20 m X 0.25 mm I.D. open tubular column coated with Chirasil-Val. (Reproduced with permission from ref. 764. Copyright Elsevier Scientific Publishing Co.)...

Figure 2.3 Coluon efficiency test for a 1.5 m x 2 ra i.D. packed column coated with 10% (w/w) OV-101 on chromosorb P-AH (100-120 mesh) at 100 C with a nitrogen carrier gas flow rate of 30 Bl/nin. The test sample is a mixture of n-alkanes.

Figura 2.9 Dse of th Grob test Mixture to compare tbe activity of various glass surfaces coated with ov-ioi. Surface types A > Untreated pyrex glass, B pyrex glass deactivated by thermal degradation of Ceurbowax 20M, C < SCOT column, prepared with Silanox 101, D pyrex glass column coated with a layer of barium carbonate and deactivated as in (B), and E - untreated fused silica. Components are identified in Table 2.7 with ac - 2-ethylhexanoic acid. (Reproduced with permission from ref. 152. Copyright Elsevier Scientific Publishing Co.)...

Figure 2.15 Separation of a mixture of saturated and unsaturated hydrocarbons on a 50 m x 0.32 mm fused silica porous-layer open tubular column coated with alumina modified wl potassium chloride. The separation was performed by temperature programming from 70 to 200°C at 3 C/mln. (Reproduced with permission fr

Figure 8.19 Two-diaenslonal separation of the components of a coal derived gasoline fraction using live switching. Column A was 121 n open tubular column coated with poly(ethelene glycol) and column B a 64 m poly(dimethylsiloxane) thick film column. Both columns were temperature programmed independently taking advantage of the two oven configuration. Peak identification 1 acetone, 2 2-butanone, 3 > benzene, 4 isopropylmethylketone, 5 isoprop-anol, 6 ethanol, 7 toluene, 8 => propionitrile, 9 acetonitrile, 10 isobutanol, 11 — 1-propanol, and 12 = 1-butanol. (Reproduced with permission from Siemens AG).

Figure 8.43 Separation of enantiomers using complexation chromatography. A, Separation of alkyloxiranes on a 42 m x 0.2S mm I.O. open tubular column coated with 0.06 M Mn(II) bis-3-(pentafluoro-propionyl)-IR-camphorate in OV-ioi at 40 C. B, Separation of D,L-amino acids by reversed-phase liquid chromatography using a mobile phase containing 0.005 M L-histidine methyl ester and 0.0025 M copper sulfate in an ammonium acetate buffer at pH 5.5. A stepwise gradient using increasing amounts of acetonitrile was used for this separation.

A number of developments have increased the importance of capillary electrophoretic methods relative to pumped column methods in analysis. Interactions of analytes with the capillary wall are better understood, inspiring the development of means to minimize wall effects. Capillary electrophoresis (CE) has been standardized to the point of being useful as a routine technique. Incremental improvements in column coating techniques, buffer preparation, and injection techniques, combined with substantive advances in miniaturization and detection have potentiated rugged operation and high capacity massive parallelism in analysis. 

The extracted fractions were esterified with either BF3-MeOH reagent or diazomethane and analyzed by GLC. Gas liquid chromatography (GLC) was conducted with a Perkin-Elmer Sigma 3 equipped with flame ionization detector. Separations were obtained on a Hewlett Packard 12 m x 0.2 mm i.d. capillary column coated with methyl silicon fluid (OV-101). The temperature was maintained at 80°C for 2 min then programmed from 80 to 220°C at 8°C/min. The injector temperature was 250°C. Mass spectra were obtained on a Hewlett Packard model 5995 GC-MS mass spectrometer, equipped with a 15 m fused silica capillary column coated with 5% phenyl methyl silicone fluid. Spectra were obtained for major peaks in the sample and compared with a library of spectra of authentic compounds. 

Different column coatings of different polarities can be used to achieve the separation of a wide variety of stabilisers. Irganox 1010 (MW 1178) can be gas chromatographed, but cannot be routinely quantified because of the on-column fouling that takes place. 

Analysis Techniques. The contents of the major breakdown products of xetralin (naphthalene and 1-methyl indan) present in the distillate were determined by gas-liquid chromatography using a Hewlett Packard Series 5750 Research Chromatograph with a 62m x 0.5mm diameter glass capillary SCOT column coated with nonpolar SE 30 liquid phase (see Reference (4 ) for details). 

Ito et al. [175] used this technique employing octadecyl silane reverse phase columns coated with cetyltrimethyl ammonium chloride for the determination of nitrite and nitrate in seawater. 

Organosilicon and organogermanium compounds were separated at 330-350 K on a Cromaton column coated with squalene. Improved quantitative determination was achieved by accumulation of preliminary decomposition products of the organometallic compounds in a graphite atomizer, followed by ETAAS32. 

Thiocyanate Human urine, saliva Dilution with water then filtration (0.45 pm) Ion chromatography utilizing ODS column coated with cetyl-dimethylamine and with UV absorbance (210 nm) detection 20 ng/mL 95-101 Michigami et al. 1992... 

Fig. 15. Electrochromatograms obtained in columns coated with sol-gel composites (A) TEOS and (B) C8-TEOS/TEOS. (Reprinted with permission from [80]. Copyright 1999 American Chemical Society). Separation conditions fused silica capillary, 12 pm i.d., 60 cm total length, 40 cm active length, mobile phase 60/40 methanol/1 mmol/1 phosphate buffer, voltage 30 kV, electrokinetic injection 5 s at 6 kV, UV detection at 214 nm. Peaks toluene (1), naphthalene (2), and biphenyl (3)...

Extensive comparisons between GC and SFC have been reported in chiral separation [63-66]. Zoltan investigated the performance of SFC and GC using the same chiral capillary columns coated with cyclodextrin-based stationary phases. It was observed that chiral selectivity was higher in GC than in SFC using the same open tubular column at the identical temperature (e.g., >100°C). However, the selectivity in SFC was significantly increased at low temperatures, especially for polar compounds [67]. 

Amino acids (serine, proline, leucine), atenolol, norephedrine, homocysteine thiolactone RP-HPLC column coated with chiral Schiff base 1 mM CUSO4 in water 213... 

Chromatographic Conditions. GC/MS-MS analyses were performed on a Varian 3800 gas chromatograph (Varian Chromatography Systems, Walnut Creek, CA) equipped with a 1079 split/splitless injector and a ion trap spectrometer (Varian Saturn 2000, Varian Chromatography Systems) with a waveboard for MS-MS analysis. The system was operated by Saturn GC/MS Workstation v5.4 software. The MS-MS detection method was adapted from reference. PCBs were separated on a 25 m length x 0.32 mm i.d., CPSil-8 column coated with a 0.25-pm film. The GC oven temperature program was as follows 90 °C hold 2 min, ramp 30 °C/min to 170 °C, hold for 10 min, rate 3 °C/ min to 250 °C, rate 20 °C/min to a final temperature of 280 °C, and hold for 5 min. Helium was employed as the carrier gas, with a constant column flow of 1.0 mL/min. 

After elution from the SPE cartridges, the eluents will be evaporated slowly under nitrogen gas. The concentrated samples containing metolachlor will be analyzed by GC/MS while the fractions containing the polar metabolites will be analyzed by HPLC. Both the GC and HPLC will be equipped with chiral columns. For GC/MS, a fused silica column coated with tert-butyldimethylsilyl-P-cyclodextrin will be used. This column has been shown to partially separate metolachlor isomers (13). 

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