Zone electrophoresis in open-tubular glass capillaries

Chromium occurrence in the environment and methods of its speciation.

Inner filter effect-based fluorescent sensing systems: A review.

Seventy-eight metal species are examined for fluorescence properties of their chelates with 8-hydroxyquinoline-5-sutfonic acid (HQS); 42 of these fluoresce, many intensely. The optimum pH, determined by ligand ionization vs. hydroxo compiex formation, iles between 5 and 8. Cadmlum forms the most fluorescent complex In a purely aqueous solution. Fluorescence Is enhanced for many metals in surfactant (hexadecyltrlmethyiammonlum ion, HTA') containing media and in a water:dimethytformamide solvent. A number of metal ions quench the fluorescence of other metal-HQS chelates, Fe(II1) being by far the most effective, and such quenching is accentuated in media contalnlng HTA'. The fluorescence propertles can be exploited by introducing the ligand through a postcolumn reactor or by Incorporating it in the eluent in a chromatographic system. Subpicomole detection limits are attainable for Cd, Mg, and Zn.

Fluorescence Properties of Metal Complexes of 8-Hydroxyquinoline-5-sulfonic Acid and Chromatographic Applications

Recorded fluorescence intensity is in general not proportional to sample concentration owing to absorption of the incident and emitted light passing through the sample to and from the point inside the cell where the emission is detected. This well known inner-filter effect depends on sample absorption and on instrument geometry, and is usually significant even in samples with rather low absorption (the error is about 8% at an absorbance of 0.06 in a 1 cm square cell). In this work we show that a particular experimental set-up can be calibrated for the inner-filter effect from the absorption and fluorescence excitation spectra of a suitable standard. The calibration takes only a few minutes and provides correction with sufficient accuracy for most practical situations.

Experimental correction for the inner-filter effect in fluorescence spectra

Fluorescence (FL) and absorbance (ABS) data are acquired simultaneously with a multiple detector spectrometer. The measured ABS is utilized in mathematical equations for automatic correction of fluorescence signals for attenuation (inner-filter effects) caused by significant absorption of the excitation or emission radiation by the fluorophore or other species. Correction equations are presented which apply to situations in which the excitation or emission beam cannot be considered monochromatic, for collection geometries involving optical fibers, and for chemiluminescence measurements. The correction scheme was tested with quinine sulfate (QS) as the analyte in the absence and presence of other chromophores (gentisic acid and methyl red). Even when conditions are such that the FL signal is attenuated by a factor of 5, the correction scheme is accurate to 2% or better. These corrections extend the linear range of the QS calibration curve by a factor of over 100, and they can improve the accuracy up to a factor of ten in cases for which polychromatic effects are important.

J.D. Ingle

Papers

Correction of Polychromatic Luminescence Signals for Inner-Filter Effects

Determination of the speciation of chromium with an automated two-column ion-exchange system

Problems with sub-p.p.b. mercury determinations: preservation of standards and prevention of water mist interferences

Precision of flame atomic absorption measurements of copper

A chemiluminescence photometer for trace chromium(III) determinations