Array, photodiode

Photodiode arrays (PDAs) are used especially in single-beam spectrophotometer mode, as the spectra are acquired very quicMy. The diode is a solid-state semiconductor device that exhibits a nonlinear current voltage characteristic. PDAs, which were first introduced in 1979, incorporate an integrated circuit with an 

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Listed below is a two-part series on the application of photodiode arrays in UV/Vis spectroscopy. 

Spectroscopy Partl, AnaZ. Chem. 1985, 57, 1057A-1073A. Jones, D. G. Photodiode Array Detectors in UV-Vis... 

Remcho, V. T. McNair, H. M. Rasmussen, H. T. HPLC Method Development with the Photodiode Array Detector, /. Chem. Educ. 1992, 69, A117-A119. 

A mixture of methyl paraben, ethyl paraben, propyl paraben, diethyl phthalate, and butyl paraben is separated by HPLC. This experiment emphasizes the development of a mobile-phase composition capable of separating the mixture. A photodiode array detector demonstrates the coelution of the two compounds. 

No collector sHt is fitted, and the full width of the ion beam falls onto microchaimel plates which emit electrons. The emitted electrons strike a phosphor coating on the end of a fiber-optic cable (see Fiber optics). The phosphor emits photons which travel along the cable to the photodiode array. 

Hplc techniques are used to routinely separate and quantify less volatile compounds. The hplc columns used to affect this separation are selected based on the constituents of interest. They are typically reverse phase or anion exchange in nature. The constituents routinely assayed in this type of analysis are those high in molecular weight or low in volatility. Specific compounds of interest include wood sugars, vanillin, and tannin complexes. The most common types of hplc detectors employed in the analysis of distilled spirits are the refractive index detector and the ultraviolet detector. Additionally, the recent introduction of the photodiode array detector is making a significant impact in the analysis of distilled spirits. 

An optical detector with appropriate electronics and readout. Photomultiplier tubes supply good sensitivity for wavelengths in the visible range, and Ge, Si, or other photodiodes can be used in the near infrared range. Multichannel detectors like CCD or photodiode arrays can reduce measurement times, and a streak camera or nonlinear optical techniques can be used to record ps or sub-ps transients. 

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.)... 

A method which uses supercritical fluid/solid phase extraction/supercritical fluid chromatography (SE/SPE/SEC) has been developed for the analysis of trace constituents in complex matrices (67). By using this technique, extraction and clean-up are accomplished in one step using unmodified SC CO2. This step is monitored by a photodiode-array detector which allows fractionation. Eigure 10.14 shows a schematic representation of the SE/SPE/SEC set-up. This system allowed selective retention of the sample matrices while eluting and depositing the analytes of interest in the cryogenic trap. Application to the analysis of pesticides from lipid sample matrices have been reported. In this case, the lipids were completely separated from the pesticides. 

Figure 15.3 Separation of tricyclic antidepressants by using multidimensional LC-LC. Peak identification is as follows DOX, doxepin DES, desipramine NOR, noitryptylene IMI, imipramine AMI, amiti yptyline. Adapted from Journal of Chromatography, 507, J. V. Posluszny et al., Optimization of multidimensional high-performance liquid cliromatography for the deterTnination of drugs in plasma by direct injection, micellar cleanup and photodiode array detection , pp. 267 - 276, copyright 1990, with permission from Elsevier Science.

Photodiode array (LED) Photodiode chips can be arrayed monolithically or non-monolithically to any element... 

Watmough, N.J.. Turnbull, D.M., Sherratt. H.S.A. Bartlett. K. (1989). Measurement of the acyl-CoA intermediates of p-oxidation by hplc with on-line radiochemical and photodiode-array detection. Application to the study of [U- C]hexadecanoate by intact rat liver mitochondria. Biochem. J. 262,261-269. 

BAILY R G, MCDOWELL L and NURSTEN H E (1990) Use of an HPLC photodiode array detector in a study of the nature of black tea liquor , J Sci Food Agric, 52, 509-25. 

Hong, V. and Wrolstad, R.E., Use of HPLC separation/photodiode array detection for characterization of anthocyanins, J. Agric. Food Chem., 38, 708, 1990. Osmianski, J. and Lee, C.Y., Isolation and HPLC determination of phenolic compounds in red grapes. Am. J. Enol. Vitic., 41, 204, 1990. 

Muller, H., Determination of the carotenoid content in selected vegetables and fruit by HPLC and photodiode array detection, Z. Lebensm. Enters. Forsch. A, 204, 88, 1997. 

D2O = deutered water. HPLC = high performance liquid chromatography. IS = internal standard. MeOH = methanol. MS = mass spectrometry. NMR = nuclear magnetic resonance. PDA = photodiode array detector. TEA = triethylamine. MTBE = methyl tert-butyl ether. 

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