PDA detector

FIGURE 13.22 Sur ctants on the 6 column set, using a photodiode array (PDA) detector. The Span and Tween 80 can be distinguished from each other very nicely in a mix. THF was the solvent used at 50°C. (A restrictor after the detector minimizes bubbles.)... 

FIGURE 13.23 Using the PDA detector and THF at SO C. a comparison of soybean cooking oils provides good separations of the glycerides. 

Solvent — The transition energy responsible for the main absorption band is dependent on the refractive index of the solvent, the transition energy being lower as the refractive index of the solvent increases. In other words, the values are similar in petroleum ether, hexane, and diethyl ether and much higher in benzene, toluene, and chlorinated solvents. Therefore, for comparison of the UV-Vis spectrum features, the same solvent should be used to obtain all carotenoid data. In addition, because of this solvent effect, special care should be taken when information about a chromophore is taken from a UV-Vis spectrum measured online by a PDA detector during HPLC analysis. 

NOTE HPLC detection of test drugs at 200 nm UV. Peak are named for the drugs they represent. Peak identity was discerned by analyzing each dmg individually and observing its retention time and UV spectrum by photodiode array detection between 190 and 360 nm using a Waters Model 990 PDA detector. Retention times are listed in the text. 

HPLC coupled to MS was used for the determination of dimethyl xanthine metabolites in plasma.82 There have also been a number of methods published on the use of HPLC with a PDA detector. In 1996, Mei published a method for the determination of adenosine, inosine, hypoxanthine, xanthine, and uric acid in microdialysis samples using microbore column HPLC with a PDA detector.63 In this method, samples were directly injected onto the HPLC without the need for any additional sample treatment. 

A PDA detector provides UV spectra of eluting peaks in addition to monitoring the absorbance of the HPLC eluent like the UVA is absorbance detector. It is the preferred detector for testing impurities and for method development. PDA facilitates peak identification during methods development and peak purity evaluation during method validation. Detector sensitivity was an issue in earlier models but has improved significantly (more than ten-fold) in recent years. ... 

FIGURE 16 The chromatogram of an injection of a caffeine solution without the column showing the instrumental bandwidth of a Waters Alliance HPLC system with a 966 PDA detector with a standard flow cell. 

With a modern variable-wavelength or PDA detector, it is safe to use a maximum absorbance of up to 1.0-1.5 absorbance units (AU). A typical UV detector today should have a baseline noise in the order of 10 micro absorbance units (10 AU). Therefore, modern UV detectors should have a dynamic range of 4-5 orders of magnitude. The sample concentration and injection volume can be adjusted to make it possible to quantify the major component and impurities at the 0.05% level in the same chromatographic run without changing detection wavelength, sample concentration, or injection volume. 

Identification (ID) tests in Category IV require only specificity for their validation. Identification by HPLC usually involves comparison of the retention time (%) or relative retention time (RRT) of a sample and standard injection. The increasing use of photodiode array (PDA) detectors in HPLC methods also allows identification by comparison of UV spectra for standards and samples, in addition to retention characteristics. The information required for either ID test by HPLC can be gathered while performing any other HPLC method for a given sample. Identification tests are often incorporated into the assay method and the satisfactory completion of specificity for the assay will meet the requirements for ID as well. 

The following guidelines are recommended for UV/Vis absorbance or photodiode array (PDA) detectors ... 

FIGURE 2 Spectrum of anthracene solution (l(lg/mL in acetonitrile) from Waters 996 PDA detector showing the annotations of The inset shows an expanded view of the 340-nm band. 

A system is typically comprised of multiple instrument components. Therefore, there is usually an individual IQ for each of these instruments and for any corresponding instrument control/data-handling software. The typical instrument components making up an HPLC system include a binary or quaternary HPLC pump, an autosampler supporting multiple vials or microtiter plates (autosamplers often include cooled Peltier trays for sample stability), a column oven, and a UV-Vis or photodiode array (PDA) detector. 

On a PDA detector, using the spectral energy output from the deuterium lamp, one can also use the sharp calibration lines at 486 and 656nm (Balmer line). 

For TRP-2 analysis, a reversed phase gradient method already developed (13) was slightly modified for our purpose. We used a Waters Alliance 2695 separations module equipped with a Waters 996 PDA detector and a CC125/3 Lichrospher 100-5 RP-18 column (Macherey und Nagel, Diiren, Germany) at 30°C and a flow rate of 0.5 mL/min. 

Two types of detectors were evaluated UV/PDA and LIF detector. The use of the UV/ PDA detector is relatively simple, as no sample pre-labeling derivatization with fluorophore is... 

In the US market, there are two major brands of commercially available CE instruments Agilent (HP ° CE System) and Beckman (PA 800). Agilent uses a PDA detector, while the Beckman instrument uses a UV, PDA, or LIF detector. For CE-SDS, we have compared CE... 

The emergence of sensitive and affordable array detectors in 1980s and 1990s has also improved measurement capability in the UV-vis. Commercially available UV-vis instrumentation with photodiode-array (PDA) detectors appeared in the mid-1980s. This made it possible to produce a UV-vis spectrophotometer... 

Figure 4 presents an example of rapid pKa measurement using a pressure-assisted system in combination with a photodiode array (PDA) detector. The migration time of DMSO (EOF marker) was measured at 220 nm, whereas the migration time of the analyte, naphazoline, was measured at 270 nm. The CE run time as well as data analysis time was drastically reduced. Consequently, this system allows the analysis of more than 96 compounds in one day. The limitation of this method is the application to drugs without UV chromophore at more than 250 nm. In some cases, it was effective to remove DMSO by evaporation under vacuum followed by the addition of methanol or acetonitrile as a neutral marker. 

Capillary electrophoresis is one of the powerful tools for pA(, measurement, especially when the pressure-assisted CE system with PDA detector is employed. It allows one to measure pA(, values of more than 96 candidate drugs... 

PDA detectors can be operated at rapid data acquisition rates (up to 40 Hz) and are the most common used. Quadrupole MS systems are capable of supplying sufficient spectra for peak. For reliable component assignment, of course, TOF-MS systems possessing higher scan speed can be used. 

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