Microcolumns microbore

L. Mondello, G. Dugo and K. D. Baitle, On-line microbore high perfoimance liquid cliiomatography-capillaiy gas cliiomatography foi food and water analyses a review , J. Microcolumn Sep. 8 275-310 (1996). 

The low flow rate in the microbore column ensures sample volumes compatible with the secondary conventional column and permits the injection of a small volume onto the secondary column, making the transfer of incompatible solvents possible without peak shape deterioration or resolution losses [63], The possible disadvantage could be the lower sample capacity of microbore LC columns. However, in LCxLC, a sensitivity enhancement can be obtained if the formation of compressed solute bands at the head of the secondary column is achieved during the transfer from the first to the second dimension. Moreover, a larger volume can be injected into the first-dimension microcolumn, used as a highly efficient pre-separation step, and a limited decrease in efficiency due to a large injection volume can be tolerated. 

Further improvements of HPLC separations can be expected through the use of newly developed columns (e.g., microcolumn) and stationary phases (e.g., microbore material), which lower the required sample volume and the consumption of solvents. Online characterization and identification of eluted pigments will be improved through the employment of more sophisticated de-... 

Figure 8.1 Different types of microcolumns (a) open tubular capillary column (1-50 fim I.D.), (b) dry packed capillary column ( 200 jim I.D.), and (c) microbore column (0.5-1 mm I.D.), narrow-bore column (1-2 mm I.D.), and slurry packed capillary column ( 500 /xm I.D.). (Adapted from Ref. 2 with permission.)...

MondeUo, L. Dugo, G. Bartle, K.D. On-line microbore high performance Uquid chromatography capillary gas chromatography for food and water analyses. A review. J. Microcolumn September 1996, 8, 275-310. 

Microbore columns 953, 955 Microcolumn chromatography 963 reversed phase 953... 

This technique has increased rapidly in popularity over the past several years. In certain situations an electrochemical detector can offer picogram limits of detection. Furthermore, it is one of the few detectors that is easily adaptable for use with microcolumns. White et al. have shown the feasibility of using a single carbon fiber as the working electrode inserted into the end of a 15-p.m-i.d. capillary column (62,63). Slais has reviewed the use of electrochemical detectors with low-dispersion (microbore) columns (64). 

Four main categories of microcolumn types can be distinguished [110] open tubular [111] packed open tubular [112] microbore and narrow microbore [113]. The principal features of these column types are outlined in Table 6.11. 

Despite the numerous advantages the instrumental demands of microcolumn LC are considerable, and these demands are further accentuated as the requirements vary from one column type to another. A consequence of the reduced flow rates is that the detector flow-cell volume should be reduced to <10nl for OTCs, 0.1 pi for packed microcapillaries and 1 pi for microbore columns. An additional demand of the detector is that it should have a rapid response, <0.5 s. Development of suitable detectors is paramount if the potential of micro-LC is to be realised. Study of detector systems has focused in two areas firstly, the miniaturisation of ultraviolet, fluorescence and electrochemical systems, using in the former two systems LASERS as excitation sources and ultraviolet fibre optic and on-line cells to reduce band broadening and increase sensitivity [123,124] secondly, the direct interfacing with systems which previously required transport and/or concentration of the eluant. Interfacing of HPLC with mass spectroscopy has been undertaken by Barefoot et al. [125] and Lisek et al. [126] and flame systems (FPD and TSD) have been reviewed by Kientz et al. [127]. Jinno has reviewed the interfacing of micro-LC with ICP [128]. 

Mondello L, Dugo G, and Battle K (1996) On-line microbore HPLC-capillary GC for food and water analysis. A review. Journal of Microcolumn Separations 8 275-310. 

In the 1980s microcolumns became available with inside diameters of 1 to 4.6 mm and lengths of 3 to 7.5 cm. These columns, which are packed with 3- or 5-pm particles, achieve as many as 100,000 plates/m and have the advantage of speed and minimal solvent consumption. This latter property is of considerable importance because the high-purity solvents required for LC are expensive to purchase and to dispose of after use. Figure 28-7 illustrates the speed with which a separation can be performed on a microbore column. In this example, eight diverse components are separated in about IS s. The column was 4 cm long and had an inside diameter of 4 mm it was packed with 3-pm particles. 

Lee, E. D. Henion, J. D. Covey, T. R. Microbore high performance liquid chromatography-ion spray mass spectrometry for the determination of peptides. J. Microcolumn Sep. 1989, 1, 14—18. 

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