title: Near-field thermal lens detection at 257 nm as an alternative to absorption spectrometric detection in combination with electromigrative separation techniques.
abstract: A device is presented that permits detection of analytes absorbing electromagnetic radiation at lambda = 257 nm (in fused-silica capillaries with 75-microm i.d.) via the near-field thermal lens effect. The detector was realized by using a frequency-doubled argon ion laser as pump laser and a laser diode (emission wavelength, 633 nm) coupled into a monomode optical fiber as probe laser. Comparing the performance of this detector to the performance of a commercial absorption spectrometric detector working at lambda = 257 nm equipped with a unit for on-column detection in fused-silica capillaries showed a substantial improvement in detection limits (up to 30-fold improvement) for the near-field thermal lens detector (NF-TLD). The feasibility of the NF-TLD for sensitive detection of nonfluorescent analytes in real samples after separation by micellar electrokinetic chromatography was shown taking the determination of nitroaromatic compounds in contaminated water from a former ammunition plant as an example. Dependence of the thermal lens signal on pump laser power, velocity of the mobile phase, and chopper frequency was investigated. A linear calibration range over 2 orders of magnitude was obtained.
authors.affiliation: Department of Chemistry, Philipps University Marburg, Germany.
authors.forename: Natalia
authors.initials: N
authors.lastname: Ragozina
authors.forename: Stefan
authors.initials: S
authors.lastname: Heissler
authors.forename: Werner
authors.initials: W
authors.lastname: Faubel
authors.forename: Ute
authors.initials: U
authors.lastname: Pyell