Tham khảo tài liệu 'photodiodes communications bio sensings measurements and high energy part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Photodiode Array Detection in Clinical Applications Quantitative Analyte Assay Advantages Limitations and Disadvantages 171 measured simultaneously on the array of fixed photodiodes. The speed of scanning the spectrum is thus determined by the speed of data acquisition. In modern diode-array UV detectors equipped with powerful computers the time necessary to take the full spectrum from 190 to 600 nm can be reduced to as short as about 10 msec. This speed is more than sufficient in the overwhelming majority of cases in pharmaceutical analysis when the halfband width of peaks separated by HPLC is usually in the order of 1 min and it is only very rarely in the order of 1-10 sec in fast HPLC systems and especially in capillary electrophoresis where the peaks are in general narrower. The quality of the UV spectrum of the separated impurities obtained by the diode-array detector is influenced by several of photodiodes. For example the number of diodes in a DAD of the HPLC instrument is only 205 while in the other it is 1024. If the spectrum has fine structure better quality spectra are obtainable with the latter. In addition to this the quality of the spectra of especially the low level impurities greatly depends on the baseline noise. This can be reduced by using a light source with high intensity by selecting a suitable reference wavelength which is as close to the cut-off wavelength of the separated analyte as possible and a suitable slit width. Generally speaking the sensitivity of the new generation of diode-array detectors is much higher than that of the older ones. There are three main areas within drug impurity profiling where the advantages of diodearray detectors can contribute to the success of the HPLC CE analysis see Figures 5-7 . a Peak purity determination. The determination of peak homogeneity is an integral part of the protocol in the validation of any kind of HPLC and CE analysis of pharmaceuticals. In the course of impurity profiling studies it is .
