Diode array detectors, variable wavelength

Series 10 chromatography LC-95 variable wavelength UV/visible detector, LC-90 variable wavelength UV detector, LC-135 and L-235 diode array detectors, LC 1-100 computing integrator, 1SS-100 intelligent amjj in s stjm, Series 410 LC pump... 

High-Performance Liquid Chromatography. A Varian 5060 delivery system was used for this work with detection by UV absorption. Either a Varian UV-50 variable wavelength detector or a Hewlett Packard 1040A scanning diode array detector was used. All HPLC columns were packed in our laboratory (10) with 5-/um particle size Spherisorb-ODS, Spherisorb-CN (Phase Separations), or 8-pm particle size Zorbax-CN (Dupont Ltd). HPLC columns (20 or 25 cm X 4.6 mm i.d.) were coupled via short lengths of stainless steel capillary tubing (5 cm X 0.25 mm i.d.). Separation conditions were as follows ... 

NOTE While a variable wavelength UV-Vis detector is sufficient for the protocols in this unit, a UV-Vis diode array detector, which collects spectra for individual peaks, greatly enhances the methods. 

Figure 5.10. Schematic diagram of a variable wavelength dual beam absorption detector (A) and a diode array detector employing reverse optics (B).

Diode array detector. The diode array detector records in about 10 msec the complete spectrum from 190 to 600 nm using an array of over 200 photodiodes. The advantage of this is that the complete spectrum at any point on a peak can be obtained and compared with that at any other point. This gives confidence (or not) as to peak homogeneity and also as to peak identity. However, it is less sensitive than the variable wavelength detector. 

In the vast majority of straight forward analytical applications the performance of the fixed wavelength detector will be found to be perfectly adequate and its suitability should always be carefully examined before the purchase of more complex UV detectors is considered. If a variable wavelength detector is deemed necessary then either the dispersion instrument or the diode array detector could be the possible choice. In the remote case where UV spectra are required on the fly then the diode array detector should be considered. However, the chromatographer should avoid choosing expensive detectors which provides many facilities that might be required but, in fact, in practice will never be used. 

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