Multiwavelength detection

Thormartn, W., Meier, R, Marcolli, C., and Binder, F., Analysis of barbiturates in human serum and urine by high-performance capillary electrophoresis-micellar electrokinetic capillary chromatography with on-column multiwavelength detection, /. Chromatogr., 545, 445, 1991. 

In this work we describe a method based on modern LC which avoids an extraction step. This technique is rapid and selective and gives, with multiwavelength detection, good qualitative and quantitative information. 

Identification is considerably improved by the use of multiwavelength detection and absorbance ratioing. It was possible to analyse some commercial hair dyes with the method described here. However, several substances were found that could not be identified with the present standard substances. Recent results in this laboratory make a possible improvement of the chromatography probable. Future work will consider this aspect and an increased number of standard substances (17) will be examined. 

Liquid chromatography has been hindered by the lack of a universal detector-and as yet no equivalent for the GC/MS system has been described. For several years it has been evident that UV/VIS spectroscopy could provide a viable detector if multiwavelength detection principles were employed. 

The classical potentiometric approach (Sirius, GLpKa) can be coupled with multiwavelength detection, thus gaining enhanced sensitivity with decreased sample consumption. 

Since multi-wavelength detection has now been mentioned and will feature quite prominently in other apphcations, it is worthwhile discussing the reasons for this and why forensic laboratories have been keen to use and develop new multiwavelength detection techniques. Traditionally, solute characterisation in HPLC is based upon the measurement of retention time. However, for the purpose of sample identification or discrimination retention time is a very poor parameter because of the possibility of this being similar or identical to other compounds. 

F Lazaro, A. Rios, M.D. Luque de Castro, M. Valcarcel, Simultaneous multiwavelength detection in flow injection analysis, Anal. Chim. Acta 179 (1986) 279. 

The pulse-probe technique can be extended to multiwavelength detection by using the ultrafast laser pulse to generate a white-light continuum probe, which can be dispersed with a spectrograph across a diode array or CCD detector after traversing the sample. Due to lower probe intensity, Cerenkov emission from the sample would be expected to be more of a complication in this case, but the correction methods developed for stroboscopic Cerenkov detection would also work here. 

Fig. 5.23 Multiwavelength detection system with dichroic heamsplitters...

The efficiency of the measurement can be increased by multiwavelength detection. The monochromator is replaced with a polychromator, and a multianode PMT with routing electronics is used to detect the full spectrum. However, despite its obvious benefits, no application of multiwavelength TCSPC to sonoluminescence has yet been published. 

Evolving Factor Analysis (EVA) This method is a further development of FA, where intrinsically ordered data can be investigated. Multiwavelength detection of the elution of compounds in a chromatogram in dependence on time is a typical example, and the spectroscopic investigation of simultaneous equilibria in dependence on the pH value can also be carried out by evolving factor analysis (EVA). 

S.-K. Hsiung, C.-H. Lin, G.-B. Lee, "A microfabricated capillary electrophoresis chip with multiple buried optical fibers and microfocusing lens for multiwavelength detection," Electrophoresis, vol. 26, pp. 1122-1129, 2005. 

AL Sowell, DL Huff, PR Yeager, SP Caudill, EW Gunter. Retinol, a-tocopherol, lutein/zeaxanthin, P-cryptoxanthin, lycopene, a-carotene, frawi -P-carotene, and four retinyl esters in serum determined simultaneously by reversed-phase HPLC with multiwavelength detection. Clin Chem 40 411-416, 1994. 

Jacobsen, P.B. High performance liquid chromatography with multiwavelength detection a technique for identification of iodinated x-ray contrast agents in human body fiuids and brain tissue, Am.J.NeuroradioL, 1992, 13, 1521—1525. 

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