Array detectors modes

To give increased sensitivity when the analysis is not limited by chemical noise, eg, in the ms/ms mode, array detectors (15) have been developed. 

Microcoulometric titration is used as the detection mode in some commercial sulfur-specific analysers. Sulfur in PP and waxes (range from 0.6 to 6 ppm S) were determined by means of an oxidative coulometric procedure [537]. The coulometric electrochemical array detector was used for determining a variety of synthetic phenolic antioxidants (PG, THBP, TBHQ, NDGA, BHA, OG, Ionox 100, BHT, DG) in food and oils [538],... 

There is a recent trend towards simultaneous CE separations of several classes of food additives. This has so far been applied to soft drinks and preserved fruits, but could also be used for other food products. An MEKC method was published (Lin et al., 2000) for simultaneous separation of intense sweeteners (dulcin, aspartame, saccharin and acesulfame K) and some preservatives (sorbic and benzoic acids, sodium dehydroacetate, methyl-, ethyl-, propyl- and isopropyl- p-hydroxybenzoates) in preserved fruits. Ion pair extraction and SPE cleanup were used prior to CE analysis. The average recovery of these various additives was 90% with good within-laboratory reproducibility of results. Another procedure was described by Frazier et al. (2000b) for separation of intense sweeteners, preservatives and colours as well as caffeine and caramel in soft drinks. Using the MEKC mode, separation was obtained in 15 min. The aqueous phase was 20 mM carbonate buffer at pH 9.5 and the micellar phase was 62 mM sodium dodecyl sulphate. A diode array detector was used for quantification in the range 190-600 nm, and limits of quantification of 0.01 mg/1 per analyte were reported. The authors observed that their procedure requires further validation for quantitative analysis. 

HPLC - Beckman 125 binary gradient pumps, 168 diode-array detector, 507 autosampler MS - Ion-trap mass spectrometer Finnigan LCQ equipped by APCI (atmospheric pressure chemical ionization), data analyzed in negative mode, spectra confirming found compounds were obtained from tandem mass spectromectry (MS/MS). 

For the rapid pKa measurement with daily throughput of 96 compounds using a pressure-assisted mode with a photodiode array detector, the following modifications were required. 

It is also possible to monitor a broad range of wavelengths without interrupting the flow in the column. This results in the full UV spectrum of the eluting mobile phase and provides a good means of identification of the analytes (Fig. 3.14). Such diode-array detectors (DAD) can be used in the gradient elution mode. Actually, they are frequently used in automated routine analysis. 

ESI-Mass spectra were obtained using JEOL HX/HX110A mass spectrometer equipped with ESI source (Analytica of Branford, Branford, Cl) and channel array detector, calibrated in the FAB mode with alkali metal iodides. Sample solutions were diluted 2000- fold with 50% aqueous methanol (v/v) containing 0.1% acetic acid. 

It is important to correctly identify the provitamin A peak(s) of interest in the chromatogram. A tentative identification can be made by a combination of retention time and spectral characteristics, using a photodiode array detector. Identification is aided by comparisons with authentic carotenoid standards in more than one chromatographic mode. Because of the ease of cis-trans isomerization when solutions of carotenoids are exposed to heat, light, oxygen, etc., it is difficult to ascertain whether a cis isomer occurs in nature or whether it is formed during its isolation. 

Many published articles on HPLC-ECD refer to the use of one of three voltammetric detectors (amperometric, coulometric, or polarographic). More detailed information on principles and techniques of various electrochemical detection modes can be obtained from the recent book, Coulometric Electrode Array Detectors for HPLC (34). There are also two electrode array detectors, the coulometric electrode array system and the CoulArray detector, currently available. Both detectors offer the qualitative data of PDA and the extreme sensitivity of ECD (34). The... 

Although most of the radiation sources for AAS are LSs, the great advances in detector technology, especially the development of solid-state array detectors and charge-coupled devices (CCDs), have led to the successful application of continuous sources (CSs) for AAS. A modern CS is based on a conventional xenon short-arc lamp that has been optimized to run in the so-called hot-spot mode.9 This discharge mode requires the appearance of a small plasma spot close to the cathode... 

Crude extract was also separated and collected on another Waters system, which consisted of a 600 pump, a 2996 Photodiode Array Detector, and a 2767 fraction collector. The detection wavelength was set in the ultraviolet (UV) between 190 and 400 nm. The column used was a 150 x 21 mm long ACE AQ with 10-mm particles (Advanced Chromatography Technologies, Aberdeen, UK). The system was operated at room temperature. The injection volume was 1500 pL. The mobile phase consisted of 1 3 acetonitrile water with 0.01% trifluoroacetic acid, which was flowing at a rate of 10 mL/min. The system was operated in the isocratic mode. Fractions of 1.25 mL were collected every 7.5 s. 

Figure 6 Block diagram of the two-color optical parametric amplifier (OPA) and IR-Raman apparatus. CPA = Chirped pulse amplification system Fs OSC = femtosecond Ti sapphire oscillator Stretch = pulse stretcher Regen = regenerative pulse amplifier SHGYAG = intracavity frequency-doubled Q-switched Nd YAG laser YAG = diode-pumped, single longitudinal mode, Q-switched Nd YAG laser KTA = potassium titanyl arsenate crystals BBO = /J-barium borate crystal PMT = photomultiplier tube HNF = holographic notch filter IF = narrow-band interference filter CCD = charge-coupled device optical array detector. (From Ref. 96.)...

The main components of an LC-MS are the HPLC apparatus, an optional UV or photodiode array detector, the interface, the mass spectrometer and a computer system for data management and evaluation. The interface is the key component of the LC-MS system. All other components must be adapted to the particular interface that is used. Most commercially available systems work with thermospray, electrospray, or particle beam interfaces. Each interface has a distinct mode of action and its own operational parameters. 

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