Diode array detector commercial availability

A variety of commercial diode array detectors are available which cover the wavelength range from 200 to over 1000 nm (see Table I for representative examples). However, for work in the red and in particular the near-infrared spectral range, the number of available dedicated detec-... 

Peak purity tests are used to demonstrate that an observed chromatographic peak is attributable to a single component. Mass spectrometry is the most sensitive and accurate technique to use for peak purity evaluation because of the specific information derived from the analysis. However, a good number of HPLC methods use mobile phase conditions that are incompatible with mass spectrometry detection. In this case, PDA spectrophotometers using peak purity algorithms may be used to support the specificity of the method. Almost all commercially available diode array detectors are equipped with proprietary software that will perform these calculations. Although this technique is more universal in application to HPLC methods, the data provided is neither particularly... 

With diode array detectors or scanning detectors, the spectral peak homogeneity can be investigated. However, such an approach requires a difference in both the spectra and in the retention time of the coeluting substances. If this is fulfilled, detection of inhomogeneities with commercially available software is easy, if the concentration difference is not too large (Fig. 3B). However, impurities below 1% are difficult to recognize (Fig. 3C). 

The limited availability of affordable commercial RSSF instruments has been an important factor that has prevented the widespread application of RSSF spectroscopy to the study of biological systems. However, in the past year, a significant change in the availability of commercial instrumentation hats come about. There currently are at least five manufacturers of computerized rapid-scanning detector systems. The choices in commercial instrumentation range from a mechanically scanned system with a single photomultiplier detector to photodiode array detector systems. This review includes descriptions of the currently available commercial systems. Because the authors experience in the field of RSSF spectroscopy is limited to the use of diode array detector systems and because most of the commercial instruments have appeared on the market just within the past 12 months, it has not been possible to make detailed performance evaluations and comparisons of the new commercial systems. 

UV diode array and fast scanning detectors not only enable the generation and use of libranes of known natural product standards, but can also enhance chromatographic resolution. This enhancement is due to peak punty assessment, which allows the researcher automatically to compare UV spectra at different time points across a peak of interest and thus detect the presence or absence of multiple poorly resolved components. This feature is generally included in the standard software of most commercially available diode array detectors. 

Commercial CH systems are available with diode array detectors that allow spectra to be collected over the UV-visibIc range in less than 1 s. 

Photometric detectors are the most popular in CE instruments including diode array detectors. Laser-induced fluorescence (LIE) detection and electric conductivity detectors are also popular. LIE is particularly sensitive and powerful for detecting low concentration analytes. However, most analytes are not natively fluorescent and some derivatizations are necessary. Conductivity detector is useful for the detection of non-ultraviolet (non-UV) absorbing analytes such as inorganic ions or fatty acids. Both LIE detection and conductivity detectors are commercially available and easy to interface with conventional CE instruments. Electrochemical detectors are also useful for selective high-sensitivity detection. Several techniques have been developed to circumvent the problem of strong effects of electrophoretic field on electrochemical detection, but despite this, commercial electrochemical detectors are not used extensively. 

Stopped-flow apparatuses are commercially available from Applied Photophysics Ltd. (in the U.K.) or Hi-Tech Sci-entiflc (also in the U.K., this company also commercializes a setup for work rmder high pressure), and Bio-logic (Prance), to name a few. The mixing time can vary between 0.5 and 10 ms. Modern stopped-flow apparatuses are equipped with a diode array detector, which permits the acquisition of the full absorption spectnim of the system in a very short time. Thus the kinetics can be followed simrdtaneously at several wavelengths where different reactants or products absorb hght. 

In contrast, diode array based instruments, popular as relatively low cost spectrometers, have a reverse arrangement by having the dispersion of wavelengths post-sample by a dispersive optic (e.g. a diffraction grating) which irradiates the diode array detector with the spectrum across its elements. Whilst commercially available diode array instruments are invariably of lower optical quality than the best scanning instruments, and are limited by their spectral resolution through the number of elements in their array, they do offer the advantage of rapid spectral acquisition as the complete... 

An automated log P workstation using a shake-flask method and robotic liquid handling in 96-well plate format is commercially available [30]. The system is equipped with a diode-array spectrophotometer and equimolar nitrogen detector. 

There are two basic types of chiral detectors for LC, those that measure optical rotation and those that measure circular dichroism. At the time of writing this book, the only commercially available chiral detectors are those that measure optical rotation. Nevertheless, a detector that measures circular dichroism and utilizes a diode array sensor system is thought to be in the design stage and will be briefly described later. 

The use of a commercially available diode array multichannel detector is also described. The advantage of using such a detector is the ability to immediately record a complete spectrum from near UV to IR with one measurement. The detector is a linear photodiode array consisting of 1024 diodes. It takes 25 ms to record the full spectrum, making the apparatus suitable for applications which start in the millisecond time domain. The experiment, i.e. the arbitrary recording of the spectra as well as the irradiation of the sample, is controlled by a computer program according to a timetable which is preset individually. 

A molecular absorption spectrophotometer based on diode array detection has been available for many years. Although some commercial molecular fluorescence spectrometers have provision for attaching a multichannel detector, it is... 

---