Fused-silica capillary columns tubing

Samples of both fulvic and humic acids were suspended in methanol and methylated with diazomethane. Both H and spectra of the free acids were obtained, at 299.94 MHz and 75.42 MHz respectively, on a Varian XL-300 spectrometer having a Nicolet TT-100 PET accessory. Spectra were obtained in D2O, in a 12-mm tube, with deuterated TSP (sodium 3-(trimethylsilyl)propionate-, , 3,3- 4) added as internal reference. GC/MS of methylated acids was conducted on a Hewlett-Packard Model No 5995 GC/MS/DA system equipped with a fused silica capillary column (12 m x. 020 mm ID, Hewlett Packard) internally coated with crosslinked methylene silicone. Infrared spectra were obtained with solid samples dispersed in KBr pellets, by using a Beckman IR-33 spectrophotometer. The various absorption peaks in IR and NMR were interpreted conventionally (9-10). 

One can find 1-mm glass-lined stainless steel columns or fused silica capillary columns. Fused silica is available with 75-yU.m, 100-/xm, or 320-/xm internal diameter by 20-cm, 25-cm, or 30-cm length. Fused silica is a glass tubing with an outside polyimide coating to prevent breakage. 

On-line analysis of the effluent gases was conducted using a gas chromatograph (Hewlett Packard model 5890 Series H), equipped with FID and TCD detectors. A DB-624 fused silica capillary column was used for the hydrocarbon separation. The carbon monoxide and carbon dioxide were separated using molecular sieves (5A) and Hayesep R columns. Tlie effluent gases were analyzed for the unconverted VOCs, partial oxidation products such as chloroform and 1,1,2-trichlorocthanc, and total oxidation products (CO and COj). The HO and Clj analysis was performed using Drager tubes. The total conversion is based on total cartoon atoms in the feed. 

Most SPME applications involve GC. Following extraction, the analytes are thermally desorbed in the chromatograph injector. More recently, the scope of apphcation has been extended to nonvolatile and thermally unstable compounds by coupling SPME to LC. Desorption is performed at an appropriate interface consisting of a standard six-way HPLC injector with a special fiber-desorption chamber used instead of the sample loop. A different approach to SPME-LC called in-tube SPME has also been developed, it uses an open tubular fused-silica capillary column instead of the typical SPME fiber. This latter method has been used for the determination of carbamate pesticides in water with relative standard deviations of... 

Formaldehyde can be analyzed by several instrumental techniques, such as GC, colorimetry, polarography, and GC/MS. The GC method involves the passage of air through a solid sorbent tube containing 2-(benzylamino)ethanol on Chro-mosorb 102 or XAD-2. The derivative, 2-benzyloxazolidine, is desorbed with isooctane and injected into GC equipped with an FID (NIOSH 1984, Method 2502). Car-bowax 20M or a fused-silica capillary column is suitable. 2-Benzyloxazolidine peak is sometimes masked under the peaks, due to the derivatizing agent or its decomposition and/or polymeric products. The isooctane... 

Analysis of dimethyl- and diethylamine in air may be performed in accordance to NIOSH Method 2010 (NIOSH 1984, Suppl. 1989). About 3-30 L of air at a fiow rate of 10-1000 mL/min is passed through a silica gel (20/40 mesh, 150 mg front and 75 mg back) sorbent tube. The analytes are desorbed with dilute sulfuric acid in 10% aqueous methanol (3-h ultasonication) and injected into a GC equipped with a FID. A packed column, 4% Carbowax M over 0.8% KOH on Carbosieve B (60/80 mesh) was used in the NIOSH laboratory. A nitrogen-specific detector may be used for amine analysis instead of an FID, using a DB-5 fused-silica capillary column. This method may be applied for the analyses of other aliphatic amines in air and also for certain ethanolamines (NIOSH 1984, Suppl. 1989, Method 2007). Alternatively, ethanolamines may be analyzed by NIOSH Method 3509 (NIOSH 1984, Suppl. 1989). These compounds present in air (5-300 L of air) are... 

Analysis. Aqueous solutions were extracted with 2 (iL of toluene In tubes used for Irradiation. Pesticide concentrations in the toluene extracts were determined directly by GLC using a 1 electron capture detector and a 15 meter X 0.53 mm (ID) bonded silicone phase (1.5 micron film thickness, 95% dlmethyl-5% diphe-nylpolyslloxane, 06-5 equivalent to SE-S) fused silica capillary column mounted in a conventional packed port. The Instrument operating conditions weret Inlet, 250 °C detector, 300 helium carrier gas flow rate, 7 nL/tnln. With a column temperature of 180 °C the dinitroanilines were completely resolved and exhibited the following retention tlmest fluchloralln (4.71 min) profluralln (4.29 min) isopropalln (11.27 min) trlfluralln (185 OC, 2.4 min). Details of the analysis of DOE, methoxychlor, methyl parathlon and -nltroanlsole are provided elsewhere (7). 

Figure 1.2 Various columns and materials employed for capillary gas chromatography (a) left 25 m x in. o.d. stainless steel capillary column in a pancake format, center 30 m X 0.25 mm i.d. aluminum-clad fused-silica column, right blank or uncoated stainless steel capillary tubing o.d. (b) 60 m x 0.75 mm i.d. borosilicate glass capillary column for EPA method 502.2 (c) 30 m x 0.25 mm i.d. fused-silica capillary column also pictured is a typical cage used to confine and mount a fused-silica column.

Capillary electrophoretic separations are performed in small diameter tubes, made of Teflon, polyethylene, and other materials. The most frequently used material is fused silica. Fused silica capillaries are relatively inexpensive and are available in different internal and external diameters. An important advantage of a fused silica capillary is that the inner surface can be modified easily by either chemical or physical means. The chemistry of the silica surface is well established due to the popularity of silica surfaces in gas chromatography (GC) and liquid chromatography (LC). In capillary electrophoresis, the silica surface is responsible for the EOF. Using surface modification techniques, the zeta potential and correspondingly the EOF can be varied or eliminated. Column fabrication has been done on microchips.13... 

FIGURE 7.1 Scanning electron micrographs of a polystyrene-divinylbenzene monolithic column prepared in a 20-pm fused silica capillary tube (reproduced from the reference, Ivanov et al. (2003), with permission from American Chemical Society). 

FIGURE 7.3 Scanning electron micrographs of monolithic silica prepared from sol-gel methods, (a) monolithic silica prepared from TMOS in a test tube, and monolithic silica columns prepared from a mixture of TMOS and MTMS, (b) in a 50-pm fused silica capillary, (c) in a lOO-pm fused silica capillary, and (d) in a 200-pm fused silica capillary tube (reproduced from the reference, Motokawa et al. (2002), with permission from Elsevier). 

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