Capillary column manufacturers

Fig. 11 Typical chromatograms showing injection volume (I.V.) optimization for pooled serum spiked with 100 pg/mL of l,25(OH)2VitD3 and extracted by selective SPE. The I.V. was (a) 0.2 pL (b) 0.6 pL (c) 3 pL and (d) 9.5 pL. A 15 cm x 0.5 mm I.D. capillary column (manufacturer suggestion I.V. was 0.2-0.4 pL) was used for separation. Using the selective SPE and a sample focusing approach before the separation, a large I.V. was enabled without compromising chromatographic performance and with substantially increased sensitivity (Reproduced with permission from American Chemical Society)...

Chromatographers can expect to see continued splendid efforts by capillary column manufacturers to produce columns that have lower residual activity and are... 

WCOT Methyl Silicone Column—It is suggested that this column be purchased directly from a suitable capillary column manufacturer (see 6.3.2.1). 

For capillary columns fused siHca is the material of choice for the column container. It has virtually no impurities (<1 ppm metal oxides) and tends to be quite inert. In addition, fused siHca is relatively easily processed and manufacture of columns from this material is reproducible. In trace analysis, inertness of tubing is an important consideration to prevent all of the tiny amounts of sample from becoming lost through interaction with the wall during an analysis. 

Numerous types of GC injectors have been manufactured over the past four decades. The most commonly used injection techniques have been reviewed and described by Grob, who correctly states that analysts must fully understand the techniques before they can make the most appropriate choice for their particular application(s). For most GC capillary column applications, the split/splitless, programmed-temperature vaporization (PTV) and on-column injectors remain the most popular. However, over the last few years, technology has progressed rapidly to provide injectors that allow more of the sample extract on to the GC column without overloading it. 

The main bottleneck in the further development of CEC is related with the state of the art of the column manufacturing processes and the robustness of the columns/instrumentation. Moreover, evidence to demonstrate reproducibility of separations from column to column still has to be established. The formation of bubbles in the capillaries due to the Joule heating and variations in EOF velocity on passing from the stationary phase through the frit and into the open tube is still very challenging in packed column CEC. A way to overcome this problem is to use monolithic columns or apply open tubular CEC [108]. Currently, many efforts are placed in improving column technology and in the development of chip-CEC [115] as an attractive option for lab-on-a-chip separations. 

Several manufacturers of gas chromatographs now offer all glass splitters for use with glass capillary columns. Figure 6.13 is one design available. Splitters are generally used for solventless samples and also in petroleum and petro-chemistry a and for the analysis of essential oils. 

Column ovens vary considerably in dimensions and geometry from manufacturer to manufacturer. Many types of columns have to be accommodated in gas chromatograph column ovens, from short capillary columns to the larger diameter preparative columns. The "best" oven really depends on the application which dictates the type of chromatograph. In the past, three configurations have been common ... 

Liquid chromatography is now a mature technique. Instruments are reliable and increasingly computer assisted. Column-to-column reproducibility is ensured by most manufacturers. The quest for the universal detector is about to end with the advent of a sophisticated and miniaturized MS detector. Development of a method can be achieved in a rather short period with available software. The emphasis is on validation more than on how to handle it. Capillary columns are sure to improve, and the trend will be toward many parallel analyses. 

Several packed and capillary columns have been reported in the U.S. EPA methods, research literature, and manufacturers product catalogs. Some common columns are described below. 

The use of hydrothermally formed retaining frits in capillary columns packed with stationary phase particles is an accepted limitation in CEC. The introduction of the frit to hold the packed bed is vital, yet introduces problems such as EOF and flow non-uniformities, compromised frit permeability [87], capillary fragility, increased likelihood of bubble formation [88] and a thermally induced modified frit surface chemistry which can detrimentally alter the chromatography [23]. Practical aspects to be considered include the appreciable effort and skill of the analyst who is required to repeatably manufacture capillaries of a particular phase and redevelop the fritting and packing methodology for each different stationary phase type. 

CEC is often presented as a hybrid method that combines the capillary column format and electroosmotic flow typical of capillary electrophoresis (CE) with the use of a solid stationary phase and a separation mechanism characteristic of HPLC based on specific interactions of solutes with a stationary phase. Therefore CEC is most commonly implemented by means typical of both HPLC (packed columns) and CE (use of electrophoretic instrumentation). As described in another chapter of this book, both commercial columns and instrumentation manufactured specifically for CEC remain scarce. 

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