Deactivation capillary columns

As described in above, all the official methods for the determination of phenolic compounds in water are based on GC. The GC methods are normally more sensitive than the HPLC methods, but because of the high polarity and low-vapor pressure of the phenols, a derivatization step is normally necessary before the final GC analysis. GC separation of underivatized phenols using capillary columns with conventional phases is difficult, for phenols (in particular, nitrophenols) exhibit severe tailing. Highly deactivated capillary columns have been used for the direct separation of phenols [81,82], but in most cases the phenols are derivatized in order to improve their chromatographic performance. Several different derivatization agents have been used, for example, pentafluorobenzyl bromide [83,84], pentafluorobenzyl chloride [85], acetic anhydride [86,87], and heptafluorobutyric anhydride [88]. 

Continuous LLE with ethyl acetate in combination with direct GC separation using highly deactivated capillary columns has been used for the determination of nitrophenols in groundwater [82]. When GC-MS was used for identification of nitrophenols and with a nitrogen-phosphorus detection, limits of detection in the trg/L range were found. 

Many forms of chromatography have been used to separate mixtures of quinoline and isoquinoline homologues. For example, alumina saturated with cobalt chloride, reversed-phase Hquid chromatography, and capillary gas chromatography (gc) with deactivated glass columns have all been employed (38,39). 

Capillary column A narrow bore tube (0.25-1 mm ID) typically 30-100 m long (usually of deactivated fused silica), whose walls are coated with a liquid stationary phase to produce high-efficiency separations (N > 100,000). 

FIGURE 4.5 Chromatograms of a-phenylethanol enantiomers nsing (a) SFC and (b) open tubular column GC. Conditions (a) 12 cmx250 p.m ID capillary packed with 5-p.m porous (300 A) silica particles encapsulated with fS-CD polymethylsiloxane (10% w/w) and end-capped with HMDS, 30°C, 140 atm, CO2, FID, 10 cmxl2 p.m ID restrictor, (b) 25 mx250 p.m ID cyano-deactivated capillary cross-linked with fi-CD polymethylsiloxane (0.25 xm df) 130°C He FID. (Reprinted from Wu, N. et al. 2000. J. Microcol. Sep. 12 454-461. With permission.)... 

The surrogate compounds were mono-, tetra-, octa-, deca- C-PCBs, dg-naphthalene, C-PCP and C-phenol. The soil samples were dried with Na2S04 (60 g) and then Soxhlet extracted with hexane acetone (9 1) for 16 h. The extract was dried with sodium sulfate, concentrated, and split. While one portion was held for other analyses, the other portion was placed on a 3% deactivated silica gel column and eluted with increasing solvent polarity systems [hexane, followed by methylene chloride hexane (1 1), and then methylene chloride acetone (95 5)]. The extracts were combined and reduced to 1 mL, split and two internal standards added (tetrafluorobiphenyl and di2 Chrysene). The extracts were chromatographed on a 15-m DB-5 fused silica capillary column and detected with flame ionization (FID). Sludge samples were extracted according to the EPA sludge protocol (2) developed at Midwest Research Institute. 

Packed columns are conventional stainless steel columns that contain small deactivated particles to which the stationary phases adheres. Capillary columns are open tubular columns of narrow internal diameter made of fused silica, with... 

A siliceous support material (Cab-O-Sil) is deactivated with benzyltriphenyl phosphonium chloride and deposited on the inside wall of a glass capillary column. After additional coating with OV-225, a number of anticonvulsant drugs were run. 

Both capillary and packed columns are available for use. Much of recent interest in SFC is based on the stability and high efficiencies capillary columns. Because these columns are deactivated, the elution analytes with unmodified carbon dioxide is possible. Some of the comm stationary phases available as capillary columns are as follows ... 

Capillary columns coated with aluminum oxide and molecular sieves can be described as absorption phases [22]. These columns are also known as porous-layer open tubular (PLOT) columns. Aluminum oxide PLOT columns deactivated with potassium chloride have been very effective at the separation of C,.,0 hydrocarbons. 

For the preparation of capillary columns for gas chromatography, the fused silica column wall is deactivated using polysiloxanes, and modified with a suitable stationary phase. Hetem19 discussed the use of polymethylhydrosiloxanes (PMHS) for deactivation and subsequent coating with a polymerized C18-type silane for stationary phase formation. Stationary phases used in packed GC are analogous to HPLC. 

One of the first steps in modifying the performance of capillary electrophoresis was the deactivation of silica groups of the capillary column by physically coating the capillary wall with methylcellulose (58,59), as well as via silane derivatization (10,44,60). Presently, many other changes have been carried out either to the capillary surface or addition of chemical agents to the separation buffer (see Table II), including manipulation of... 

Grob, K., Crob, G., and Grob, K., Jr. (1979). Deactivation of glass capillary columns by silylation. /. High Resolut. Chromatogr. Chromatogr. Commun. 2, 31-35. 

Apparatus Gas chromatograph with flame ionization detector (Flewlett-Packard 5890 Series n, or equivalent) equipped with a 5- xL syringe for 0.32-mm (id) columns. Automatic sampler (HP 7673, or equivalent). Chromatographic data system or integrator (HP 3365 Series II software, or equivalent). Retention gap, deactivated fused silica, 1-mm x 0.32-mm (id) with capillary column connectors. DB 5-HT,... 

Procedure Use a gas chromatograph equipped with a flame-ionization detector, a cold-on-column injector, a suitable deactivated precolumn, and a 10-m x 0.32-mm (id) capillary column coated with an apolar stationary phase 0.12-p.L film thickness. Program the column to heat to 60°, hold for 1 min, heat to 300° at 20°/min, and hold for 3 min. Set the flame-ionization detector to 320°. Chromatograph five injections of the Standard Preparation. Measure the responses. The relative standard deviation for each peak should be below 2%. The peaks for brassicasterol and campesterol should be baseline resolved (Rs > 1.0) and show no tailing. Measure the response of the Internal Standard Solution and all the individual sterols eluting in the relative retention window of 0.98 to 1.13. 

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