Detection photo diode array

JUSTESEN u, KNUTHSEN p and LETH T (1998) Quantitative analysis of flavonols, flavones, and flavanones in fruits, vegetables and beverages by high-performance liquid chromatography with photo-diode array and mass specfrometric detection, /C/u matogr A, 799, 101-10. 

Liquid chromatography was developed to analyze carbonyl (2,4-dinitro-phenyl) hydrazones with detection by diode array ultraviolet spectroscopy (DA-UV) and by atmospheric pressure negative chemical ionization (APNCI) mass spectrometry [716]. In addition, LC can be combined with electrospray ionization coupled on-line with a photolysis reactor for better detection and confirmation of photo degradation products [717]. 

Fig. 1.14 LC-MS analysis of a mixture of daidzein and acetophenone with a ESC source (A) ESI, (B) APCI, (C) photo diode array detection.

The variety of detection modes available for HPLC analysis that provide additional information about the eluent as it exits the column greatly facilitates unknown characterization. The majority of analytical methods for phenolic compounds includes HPLC with spectrophotometric-based detection techniques (UV absorption, fluorescence, photo diode array—PDA) as well as HPLC with electrochemical detection. 

Amakura Y, Okada M, Tsuji S, Tonagai Y. 2000. High performance liquid chromatographic determination with photo diode array detection of ellagic acid in fresh and processed fruits. J Chromatogr A 896 87-93. 

Csillag K, Vereczkey L, Gachalyi B (1989) Simple high-performance liquid chromatographic method for the determination of tolbutamide and its metabolites in human plasma and urine using photo-diode array detection. J Chromatogr 490 355-363... 

Zgorka, G. Dawka, S. 2001. Application of conventional LW, photo-diode array (PDA) and fluorescence (FL) detection to analysis of phenolic acids in plant material and pharmaceutical preparations. J. Pham. Biomed. Anal. 24 1065-1072. 

Welkera (2002) developed an HPLC method to analyze enviromnental samples for their content of cylindrospermopsin (CYL) based on HPLC with photo diode array detection as an alternative to costly LC-MS approaches. A gradient from 0% to 50% aqueous methanol(+0.05% trifluoroacetic acid) in 20 minntes proved to be highly reproducible with respect to peak height, peak area, and retention time of pnrified CYL. Good linearity of peak area response was found for 1-300 ng CYL on colnmn. For a good performance, the duration of equilibration prior to individual runs was crucial. Extraction from cell material (culture and bloom) was efficiently done with pure water in one extraction step, and CYL contents determined matched well with results previously obtained by LC-MS. 

The selection of an appropriate mobile phase is another aspect of concern. Most often the commonly used LC mobile phase is not compatible with thermospray LC/MS, for instance owing to the use of non-volatile buffers can be left out or replaced by volatile ones. In other cases the buffers are present for retention time reproducibility, which mostly is not very important for identification. In other applications however a correspondence between UV or fluorescence peaks and MS identification is obligatory, which makes mobile phase changes unattractive. In this respect it is often overlooked that LC-UV and LC/MS give different responses as a result of different detection principles. For not too complex samples a UV photo-diode array detector can be used to link up the chromatographic peaks obtained under different mobile phase conditions. To cut short, despite many successes also many potential problems are met in LC/MS to which tailor-made creative solutions are needed. 

Quantitation of 1,4BD by high-performance liquid chromatography (HPLC) with photo-diode-array detection was described by Duer et al. (2001). The 1,4BD was extracted from the biological matrix with acetonitrile and derivatized with 3.5-dinitrobenzoyl chloride. This method has a linear range from 3 to 250 rng L with a limit of quantitation of 10 rng L . Also, as was mentioned previously, the United Chemical Technologies GHB SPE column method has been modified to include 1,4BD analysis (Kraner et al., 2000). 

UV is the most popular detector but has limited usage and is not universal as not all compounds absorb in that range. Current instruments can be set at specific wavelengths but care must be exercised in the choice of solvent to be used since some solvents are not transparent to UV. The new photo-diode array instruments are very useful because they can acquire a full spectrum and data manipulation can be performed to aid in the detection of unresolved peaks at one specific wavelength. 

The cleaned up sample extract still contains many impurities thus, these impurities have to be separated from the analyte before it is determined. The detection and determination of OPs is usually with GC coupled with selective detectors, such as electron capture detector, NPD, FPD, and mass spcc-trometric detector (MSD or MS). Large varieties of packed as well as megabore and capillary columns are used with these detectors. CMs are determined with GC coupled to NPD or FPD (in S mode). CMs are effectively determined with HPLC/photo diode array or HPLC/fluoresccncc, For a trace amount, it is essential to do a postcolumn dcrivaiization (All, 1989). 

Z-isomers con tribute up to about 50% of total plasma lycopene content [16, 20]. Schierle et al. [8] and others [26] found the 5-Z-isomer to be the next most abundant form after all-E-lycopene (Fig. 3). It should be noted that some analytical methods are unable to resolve the 5-Z- and all-E-lycopene isomers because of congruency in the UV/ Vis spectra (e.g., from photo-diode array detection) used for identification (Fig. 3, insert). 13-Z-, 15-Z-, and 9-Z-Lycopene isomers are also detectable in human plasma at low concentrations, typically less than 5% of the all-E compound. 

Figure 3 Pattern of lycopene isomers in a human blood sample. (Insert) Photo-diode array detection spectra of all-E-lycopene and 5-Z-lycopene. (From Ref. 8.)...

In another configuration of instmmentation, irradiation of white light onto the electrode surface and detection of reflected light by the use of a multi-channel detector (such as CCD or photo-diode array) through a grating monochromator makes multi-channel measurement possible [21]. 

Anthocyanins are separated under acidic conditions (formic acid, trifimo-acetic acid) with methanol and/or acetonitrile as organic modifier [18, 65, 67, 123-125, 130, 139-145]. Nowadays photo-diode array (PDA) detection is used to collect on-line UV-absorption spectra for the individual anthocyanins. The shape of the spectra together with the piuity checks of the peaks supports the interpretation of the analytical results. 

Xiong, X. Lim, B.A. Lat-Luna, M. Chew, P. Tan, D. Quantitation of mitomycin C in human ocular tissues by high-performance liquid chromatography-photo-diode array detection, J.Chromatogr.B, 2001, 755, 65-72. 

Biacs, P.A. and Daood, H.G., High-performance liquid chromatography with photo-diode-array detection of carotenoids and carotenoid esters in flnits and vegetables, /. Plant. Physiol, 143, 520, 1994. 

Photo-diodes are semiconductor devices whose electrical resistance is reduced when exposed to light. This can be detected by suitable electronics. Modern fabrication methods allow construction of arrays of such diodes (in one or two dimensions), each of which may be interrogated separately. This allows simultaneous measurement of light intensity over the array area. 

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