Nanolitre-scale cell based on L-shaped silica capillary and optical fibre for absorption photometric detection in capillary liquid chromatography

Abstract

Miniaturised photometric detection cell based on the 150 μm I. D. L-shaped fused silica capillary (L-cell) and silica optical fibre is discussed in this paper. Light enters the cell via right angle bend and transmitted light is collected by silica optical fibre inserted into the capillary outlet. Ray trace analysis reveals that L-cell geometry works as a waveguide and effectively eliminates parasitic light, which is guided by the wall of any fused silica capillary cell. Low total level of stray light is further documented by measurement of absorbance of acetone-water mixture at 266 nm with the observed upper limit of dynamic range 2.2 AU. 3-mm L-cell has a volume of 53 nL and exhibits effective optical path 2.7 mm. Cell variance determined in the flow rate range 1-10 μL min^-1 indicates, that 3-mm L-cell is optimal for use with 200-300 μm I. D. capillary columns. Furthermore, isocratic separation of alkylbenzenes mixture at 0.5 μL min^-1 demonstrates effective use of 0.5-mm L-cell (8.8 nL) and possible performance of longer L-cells with high efficiency 100 μm I. D. capillary column.

Keywords: Absorption photometry; Capillary liquid chromatography; Millimetre-scale optical path; Miniaturised detection cell; Optical fibre; Stray light.