Ultraviolet-visible detector, chromatography

Ultramicroelectrode Synonymous with microelectrode. Ultraviolet/visible detector, HPLC Detector for high-performance liquid chromatography that uses ultraviolet/visible absorption to monitor eluted species as they exit a chromatographic column. 

PBLG molecular weights were verified by gel permeation chromatography (GPC). Instrumentation (Waters Associates, Inc.) included a dual pump Multi-Solvent Delivery system (Waters 600/600E), 712 WISP Autosampler, a Waters 486 tunable ultraviolet/visible detector, and a Waters 410 differential refractometer detector. Data collection and analysis are facilitated by a Maxima 825 software program. 

Reversed-phase high-performance liquid chromatography (RP-HPLC) is the usual method of choice for the separation of anthocyanins combined with an ultraviolet-visible (UV-Vis) or diode-array detector (DAD)(Hebrero et al., 1988 Hong et ah, 1990). With reversed-phase columns the elution pattern of anthocyanins is mainly dependent on the partition coefficients between the mobile phase and the Cjg stationary phase, and on the polarity of the analytes. The mobile phase consists normally of an aqueous solvent (water/carboxylic acid) and an organic solvent (methanol or acetonitrile/carboxylic acid). Typically the amount of carboxylic acid has been up to 10%, but with the addition of a mass spectrometer as a detector, the amount of acid has been decreased to as low as 1 % with a shift from trifluoroacetic acid to formic acid to prevent quenching of the ionization process that may occur with trifluoroacetic acid. The acidic media allows for the complete displacement of the equilibrium to the fiavylium cation, resulting in better resolution and a characteristic absorbance between 515 and 540 nm. HPLC separation methods, combined with electrochemical or DAD, are effective tools for anthocyanin analysis. The weakness of these detection methods is a lack of structural information and some nonspecificity leading to misattribution of peaks, particularly with electrochemical... 

Analysis is an integral part of research, clinical, and industrial laboratory methodology. The determination of the components of a substance or the sample in question can be qualitative, quantitative, or both. Techniques that are available to the analyst for such determinations are abundant. In absorption spectroscopy, the molecular absorption properties of the analyte are measured with laboratory instruments that function as detectors. Those that provide absorbance readings over the ultraviolet-visible (UV-vis) light spectrum are commonly used in high-performance liquid chromatography (HPLC). The above method is sufficiently sensitive for quantitative analysis and it has a broader application than other modes of detection. 

Ion-exchange chromatography is generally used for the separation of the transplutonium elements (americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, lawren-cium). Determinations are usually made directly by a-spectrometry with solid-state detectors. Some elements (americium, curium, berkelium, californium) also have long-lived isotopes and can be determined by chemical methods such ultraviolet-visible spectrophotometry. 

The fundamental components of any modern-day HPLC system are a solvent delivery system, a sample injector, a column, a detector, and a computer with the appropriate data acquisition and processing software. There are numerous HPLC methods described in the literature for isoflavones [13-25] and for the common anthocyanins, each method invokes different combinations of solvent systems, columns, and detectors. HPLC has been interfaced with a variety of detection methods such as ultraviolet/visible (UV/vis) spectrocopy and hquid chromatography-mass spectrometry (LC-MS) [21,22]. In this chapter, however, discussion is restricted to the most commonly used pairing in flavonoid analysis, that of a reverse-phase (RP-18) column and a UV/visible detector. 

Some High-Performance Liquid Chromatography (HPLC) Procedures for the Determination of Multiple Classes of Flavonoids in Foods with Ultraviolet-Visible (UV-Vis) Detector... 

Initially, simple methods such as ultraviolet-visible (UV-Vis), fluorescence or infrared (IR) spectroscopy were proposed in order to estimate the total amount of antioxidants in various food samples. However, coupled methods such as gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography with ultraviolet-visible (HPLC-UV-Vis) or nuclear magnetic resonance detector (HPLC-NMR) and liquid chromatography-mass spectrometry (LC-MS) are employed more to quantify individual tocols or carotens from various corn-based food samples. In this chapter all these methods of analysis will be briefly described. 

Key abbreviation (in alphabetical order) AAS atomic absorption spectrometry ECD electron capture detector FID flame ionization detector GC gas chromatography LC liquid chromatography TLC in layer chromatography UVA ultraviolet/visible spectrometry. Symbol means coupling between techniques. 

A method based on ultraviolet/visible spectrometry (UVA IS) is proposed for the determination of oxyquinoline and its sulphate. On the other hand, liquid chromatography (LC) with UVA IS detector is used for the determination of quinine and its salts. 

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