Efficiency and Speed

Electrodriven techniques are useful as components in multidimensional separation systems due to their unique mechanisms of separation, high efficiency and speed. The work carried out by Jorgenson and co-workers has demonstrated the high efficiencies and peak capacities that are possible with comprehensive multidimensional electrodriven separations. The speed and efficiency of CZE makes it possibly the best technique to use for the final dimension in a liquid phase multidimensional separation. It can be envisaged that multidimensional electrodriven techniques will eventually be applied to the analysis of complex mixtures of all types. The peak capacities that can result from these techniques make them extraordinarily powerful tools. When the limitations of one-dimensional separations are finally realized, and the simplicity of multidimensional methods is enhanced, the use of multidimensional electrodriven separations may become more widespread. 

A new brush-type CSP, the Whelk-0 1, was used by Blum et al. for the analytical and preparative-scale separations of racemic pharmaceutical compounds, including verapamil and ketoprofen. A comparison of LC and SFC revealed the superiority of SFC in terms of efficiency and speed of method development [50]. The Whelk-0 1 selector and its homologues have also been incorporated into polysiloxanes. The resulting polymers were coated on silica and thermally immobilized. Higher efficiencies were observed when these CSPs were used with sub- and supercritical fluids as eluents, and a greater number of compounds were resolved in SFC compared to LC. Compounds such as flurbiprofen, warfarin, and benzoin were enantioresolved with a modified CO, eluent [37]. 

The particle size of a solid support is critical in striking a compromise between column efficiency and speed of separation. Both the multiple path term A and the mass transfer term (CSl of equation (4.46) (p. 89)) are reduced by reducing particle size thus leading to increased efficiency. However, as particle size is reduced, the pressure drop across the column must be increased if a reasonable flow rate is to be maintained. The optimum particle sizes for 1/8 in columns are 80/100 or 100/120 mesh and for 1/4 in columns 40/60 or 60/80 mesh. 

The speed of response of the photodiode depends on the diffusion of carriers, the capacitance of the depletion layer, and the thickness of the depletion layer. The forward bias itself increases the width of the depletion layer thus reducing the capacitance. Nevertheless, some design compromises are always required between quantum efficiency and speed of response. The quantum efficiency of a photodiode is determined largely by the absorption coefficient of the absorbing semiconductor layer. Ideally all absorption should occur in the depletion region. This can be achieved by increasing the thickness of the depletion layer, but then the response time increases accordingly. 

Dne to their inherent simplicity, small size, efficiency and speed, the CE and CEC techniques are well suited for adoption as miniaturized process monitoring tools. Efforts have been made for such applications, conpled with continuous sampling from reaction mixtures. The CE lab on a chip has been shown to be a viable tool for real-time quantitation of a reacting system. 

The analysis time for chiral HPLC separations will probably remain relatively long until CSPs with higher efficiency than the present ones become available. But monolithic columns, columns with a smaller particle size (i.e., UPLC ), and miniaturized systems would increase the efficiency and speed up the enantioseparation of existing types of CSPs. 

The penetration depth of electrons into substrate decreases at lower energy. Consequently, the surface dose increases and thin coatings and inks can be cured with higher efficiency and speed. The higher surface dose produces a higher concentration of radicals, which in turn reduces the oxygen inhibition. 

The choice of carrier gas depends on the detector and the desired separation efficiency and speed. 

The current varies somewhat with changes in temperature and concentration and must be adjusted occasionally. If very efficient cooling can be had, currents as high as 0.07 ampere per square centimeter may be used. The current efficiency and speed of reduction are decreased with currents below 0.06 ampere per square centimeter. A current of 13.5 amperes was satisfactory for the cell described. 

Fig. 9.5. Efficiency and speed of sorting are affected by the flow rate of cells. At high flow rates, more desired cells are lost, but the speed of collecting these desired cells increases until the loss of efficiency becomes greater than the increase in speed. Highspeed sorting, with more drops per second, increases the efficiency and decreases the time required to obtain the desired number of cells. The model from which these graphs were generated was derived by Robert Hoffman for these data, a three-drop sort envelope was used, 1% of the cells were sorted, and the electronic dead time was set at 6 ps. If one drop is sorted with each sort decision (instead of three), the theoretical efficiency of the sorting improves considerably (as does the rate of collecting the sorted cells).

The column is the heart of the chromatograph, providing the means for separating a mixture into components. The length, diameter, and construction material of the column affect the lifetime, efficiency, and speed of separation. The size and nature of the packing material affect resolution. 

Carter, G.T. 1998. LC/MS and MS/MS procedures to facilitate dereplication and structure determination of natural products. In Natural Products Drug Discovery II New Technologies to Increase Efficiency and Speed. Sapienza, D.M. and Savage, L.M., Eds. Southborough, MA IBC Communications, pp. 3-19. 

The particle size of a solid support is critical in striking a compromise hetween column efficiency and speed of separation. Both the multiple path term A and the mass transfer term (Cu of equation (4.45) (p. 83)) are reduced... 

---