Capillary column technology fused-silica

Capillary electrophoresis has also been used to examine the enantiomeric purity of brinzolamide. The system consisted of a Polymicro Technologies fused silica capillary column (50 cm x 50 pm), UV detection at 255 nm, pH 2.4 buffer (28 mM heptakis-(2,6-di-o-methyl)-P-cyclodextrinand 30 mM TRIS-(hydroxylmethylaminomethane),adjusted to pH with 85% H3PO4) and an applied voltage of 20 kV. Injection of a 200 pg/mL sample was accomplished with 50 mm gravity for 10 seconds. 

Column Technology. Increased sensitivity and component resolution have resulted from advances in solid-state electronics and column and detector technologies. In the field of column technology, the capillary column has revolutionized toxicant detection in complex samples. This column generally is made of fused silica 5 to 60 m in length with a very narrow inner diameter (0.23-0.75 mm) to which a thin layer (e.g., 1.0 11 in) of polymer is bonded. The polymer acts as the immobile or stationary phase. The carrier gas flows through the column at flow rates of 1 to 2 ml/min. 

A Beckman P/ACE 5000 (Schaumberg, IL) was used for all CE separations. The background electrolyte (BGE) was CH3CN/H2O/HCOOH (50 45 5). Washing solution was 1% NH4OH. All untreated fused-silica capillaries were obtained from Polymicro Technologies (Phoenix, AZ). Column... 

Triazine herbicides represent another class of herbicides that are found widely in groundwater and surface water. This method uses the automated analysis of 10-mL water samples by SPE followed by analysis directly by GC/MS (Brinkman, 1995). The method uses innovative technology to interface the SDU of the PROSPEKT with a precolumn in the GC. The GC is modified such that the sample may be injected onto a precolumn, which is essentially a retention gap column of uncoated deactivated fused-silica capillary that is several meters in length, with the analytical column off-line (see Fig. 10.20). Then the GC may be turned on and analyze the sample automatically. Because the retention-gap column is uncoated, there is refocusing of the analyte on the retaining precolumn, even with large injection volumes of up to 100 pL. 

Monolithic technology first originated as an alternate technique to fabricate capillary columns. It is a radical departure from packed-column technology and uses in situ polymerization to form a continuous bed of porous silica24 inside the fused silica capillaries. Because end frits are problematic in packed capillaries, this new approach eliminates this problem since no end frits are required for monoliths. For years, capillary monoliths remained a scientific tool for academic research. 

Solid-phase micro-extraction (SPME) first became available to analytical researchers in 1989. The technique consists of two steps first, a fused-silica fiber coated with a polymeric stationary phase is exposed to the sample matrix where the analyte partitions between the matrix, and the polymeric phase. In the second step, there is thermal desorption of analytes from the fiber into the carrier gas stream of a heated GC injector, then separation and detection. Headspace (HS) and direct insertion (DI) SPME are the two fiber extraction modes, whereas the GC capillary column mode is referred to as in-tube SPME. The thermal desorption in the GC injector facilitates the use of the SPME technology for thermally stable compounds. Otherwise, the thermally labile analytes can be determined by SPME/LC or SPME/GC (e.g., if an in situ derivatization step in the aqueous medium is performed prior to extraction). Different types of commercially-avarlable fibers are now being used for the more selective determination of different classes of compounds 100 /rm polydimethylsiloxane (PDMS), 30 /rm PDMS, 7 /rm PDMS, 65 /rm carbowax-divinylbenzene (CW-DVB), 85 /rm polyacylate (PA), 65 /rm PDMS-DVB, and 75 /rm carboxen-polydimethyl-siloxane (CX-PDMS). PDMS, which is relatively nonpolar, is used most frequently. Since SPME is an equilibrium extraction rather than an exhaustive extraction technique, it is not possible to obtain 100% recoveries of analytes in samples, nor can it be assessed against total extraction. Method validation may thus include a comparison of the results with those obtained using a reference extraction technique on the same analytes in a similar matrix. 

Capillary Columns for SFC-MS. At present, the major limitation to broad application of capillary SFC technology is related to the availability of columns compatible with supercritical fluid mobile phases. The fused silica capillary columns used in this work were deactivated and coated with crosslinked and surface-bonded stationary phases using techniques similar to those reported by Lee and coworkers (40,41). Columns from less than 1 m to more than 20 m in length and with inner diameters of 10 to 200 ym have been examined. Colvimn deactivation was achieved by purging with a dry nitrogen flow at 350 C for several hours followed by silylation with a polymethylhydrosiloxane. Any unreacted groups on the hydro-siloxane were capped by treatment with chlorotrimethylsilane at 250 C. After deactivation, the columns were coated with approximately a 0.15-.25 ym film of SE-54 (5Z phenyl polymethylphenyl-siloxane) or other polysiloxane stationary phases. The coated stationary phases were crosslinked and bonded to the deactivation layer by extensive crosslinking with azo-t-butane (41). The importance of deactivation procedures for elution of more polar compounds, such as the trichothecenes, has been demonstrated elsewhere (42). 

Fused silica is made by the reaction of SiCU and water vapor in a flame. The product, pure Si02, contains about 0.1% hydroxyl or silanol groups on the surface and less than 1 ppm of impurities (Na, K, Ca, etc.). The high purity of fused silica is responsible for its very inert chemical nature. A working temperature of about 1800°C is required to soften and draw fused silica into capillary dimensions. Fused silica columns are drawn on expensive sophisticated machinery using advanced fiber optics technology. 

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