Universal detection for capillary electrophoresis-using micro-interferometric backscatter detection

✍ Scribed by Kelly A. Swinney; Darryl J. Bornhop

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 161 KB
• Volume: 11
• Category: Article
• ISSN: 1040-7685
• DOI: 10.1002/(sici)1520-667x(1999)11:8<596::aid-mcs5>3.0.co;2-w

✦ Synopsis

We describe a method for determining subpicomole quantities of analyte in capillary electrophoresis by probing fluid bulk properties with laser interferometric backscatter. In micro-interferometric backscatter detection Ž . MIBD , an unfocused beam from a He-Ne laser impinges onto unmodified fused silica capillary tube and subsequent backscattered laser light is analyzed. Positional Ž . changes of interference pattern extrema backscattered light are directly related to Ž . refractive index RI , n, of fluid in the tube, and allow for determination of ⌬ n at the 10 y7 level. MIBD was interfaced to commercial CE instrument allowing for simultaneous RIr UV-Vis detection. Utility of MIBD detector for capillary electrophoresis was shown by detecting caffeine in beverages. Analysis was performed in 100-m capillary, and direct comparison of RI detector's performance with Ž . UV-Vis absorbance detector 211 nm was possible. In system without active Ž .

y6 thermal control, RI detection limit 3 for caffeine was 2.33)10 M, whereas detection limit of the commercial UV-Vis detector was 1.16)10 y6 M. At detection limit of 2.33 M, MIBD is capable of performing universal detection on just 2.02)10 y14 or 20 fmole of solute in probe volume of 4.7 nL. It is shown that a Ž . solute like caffeine, which has large molar absorptivity at probe wavelength, MIBD has comparable sensitivity. Therefore, it is useful in other CE applications, particularly those involving solutes with low values.