Optical errors in a liquid chromatography absorbance cell

Abstract

The shadowgraph method is used to visualize mobile phase flow through a liquid chromatography absorbance cell with "Z" flow geometry. It is shown that mixing is incomplete in the cell. Composition gradients persist throughout the elution of any sample. The gradients systematically change as the sample flows through the cell. Additionally, window wedge angles are measured in several cells. The implications for low noise absorbance detectors are discussed.

Flow dependence and sensitivity of the refractive index gradient measurement with the Z-configuration flow cell at low Reynolds number

“…They observed a nonuniform absorbance as a function of radial position in the flow cell due to incomplete mixing. The flow pattern was not particularly ordered either (Figure 3 in ref 25). This result is not in contradiction to our results, and this can be explained in terms of the flow dynamics going into, and in, the flow cell.…”

“…The results of the experiments presented in Figures 3-5 suggest that the flow is well behaved in the flow cell leading to a sensitive means of detecting the RIG. This conclusion must be put into context with other work in the field (11,25). Peck and Morris examined the RI aberration associated with the absorbance measurement by using a commercially available wedge-shaped Z-configuration flow cell, nominally 1 mm i.d.…”

“…Peck and Morris examined the RI aberration associated with the absorbance measurement by using a commercially available wedge-shaped Z-configuration flow cell, nominally 1 mm i.d. by 1 mm path length, although R was not constant along L (25). Water was delivered at 2 mL/min, and the uniformity of the absorbance for an injected dye was examined by shadowgraph images.…”

Advances in Ultrahigh-Pressure Liquid Chromatography Technology and System Design

“…The minimum detectable change in absorbance is set by the baseline noise on the absorbance output, which depends on the selected wavelength and the detector design. Under these conditions the noise characteristics of the photodetectors and electronics predominate and so-called “shot noise” (essentially thermally generated rather than photogenerated electrons) is observed . A well-designed UV absorbance detector can detect a minimum change in absorbance below 10 μAU.…”

“…Under these conditions the noise characteristics of the photodetectors and electronics predominate and so-called "shot noise" (essentially thermally generated rather than photogenerated electrons) is observed. 133 A welldesigned UV absorbance detector can detect a minimum change in absorbance below 10 μAU. At high absorbance, the limitation is typically stray light and inadequate spectral resolution.…”