Spectrophotometric analysis ultraviolet/visible

Although considered a basic technique, ultraviolet-visible (UV-vis) is perhaps the most widely used spectrophotometric technique for the quantitative analysis of pure chemical substances such as APIs in pharmaceutical analysis. For pharmaceutical dosage forms that do not present significant matrix interference, quantitative UV-vis measurements may also be made directly.114,115 It is estimated that UV-vis-based methods account for 10% of pharmacopoeia assays of drug substances and formulated products.116... 

A few more papers should be mentioned as regards electronic spectra of aromatic nitro compounds nitrobenzene, dinitrobenzene and trinitrobenzene [20] and the work of Barth [21 ] who subjected mono-, di- and tri-nitrobenzenes and toluenes to detailed spectrophotometric ultraviolet-visible studies and developed a quantitative analysis of TNT in the presence of cyclonite, octogene and waxes. 

This chapter deals with the origin, nature, and measurement of the spectra of molecules arising from the absorption of near-ultraviolet and visible radiation and the dependence of the spectra on molecular structure, reactivity, and interactions with the environment. In addition, the instrumentation employed to obtain the spectra and the techniques used in absorption spectrophotometric analysis are discussed. 

P. W. Alexander and A. Thalib, Nonsegmented Rapid-Flow Analysis with Ultraviolet/Visible Spectrophotometric Determination for Short Sampling Times. AnaL Chem., 55 (1983) 497. 

Products were characterized by Fourier transform infrared spectrophotometry-attenuated total reflectance (FTIR-ATR), ultraviolet visible (UV-Vis) spectrophotometry, scanning electron microscopy (SEM), and broadband dielectric/impedance spectroscopy (BDS). New absorption bands were observed corresponding to the conjugated pol5mieric units by FTIR-ATR and UV-Vis spectrophotometric analysis. The influence of concentration of PEDOT-PSS and PEDOT on the composite electrospun nanofibers was studied by EIS. Morphologies of electrospun nanofibers were also investigated by SEM. 

Generally, methods are based on solvent extraction of the additive followed by analysis for the extracted additive by a suitable physical technique such as visible spectrophotometry of the coupled antioxidant, redox spectrophotometric methods, ultraviolet spectroscopy, infrared spectroscopy, gas chromatography, thin-layer chromatography or column chromatography. In general, direct chemical methods of analysis have not foimd favour. These include potentiometric titration with standard sodium isopropoxide in pyridine medium or reaction of the antioxidant with excess standard potassium bromide-potassium bromate (ie. free bromine) and estimation of the unused bromine by addition of potassium iodide and determination of the iodine produced by titration with sodium thiosulphate to the starch end-point. ... 

Absorption spectroscopy based on ultraviolet and visible radiation is one of the most useful tools available to the chemist for quantitative analysis. The important characteristics of spectrophotometric and photometric methods are... 

Nowadays, spectrophotometry is regarded as an instrumental technique, based on the measurement of the absorption of electromagnetic radiation in the ultraviolet (UV, 200-380 nm), visible (VIS, 380-780 nm), and near infrared region. Inorganic analysis uses UV-VIS spectrophotometry. The UV region is used mostly in the analysis of organic compounds. Irrespective of their usefulness in quantitative analysis, spectrophotometric methods have also been utilized in fundamental studies. They are applied, for example, in the determination of the composition of chemical compounds, dissociation constants of acids and bases, or stability constants of complex compounds. 

The steps involved in spectrophotometric measurement in the ultraviolet and visible range include irradiation of a sample at a specific wavelength, detection (commonly using a photomultiplier tube or a photodiode array), and transduction into an electronic signal. Specifications and sample analysis procedures are listed in the USP General Chapter <851 >. 

Table 1. Possibilities of application of visible and ultraviolet spectrophotometric determinations for analysis of P-lactam antibiotics in the period of time 1994-2011.

Absorption spectroscopy based on ultraviolet and visible radiation is one of the most useful tools available to the scientist for quantitative analysis. Important characteristics of spectrophotometric and photometric methods include (1) wide applicability to both organic and inorganic systems, (2) typical detection limits of 10" to 10 M (in some cases, certain modifications can lead to lower limits of detection), (3) moderate to high selectivity, (4) good accuracy (typically, relative uncertainties are 1% to 3%, although with special precautions, errors can be reduced to a few tenths of a percent), and (5) ease and convenience of data acquisition. 

The remaining methods of analysis addressed in this chapter are instrumental methods of analysis. The first group of these to be addressed are spectrophotometric methods based on the absorption and anission of photons of electromagnetic radiation including visible light, ultraviolet radiation, and infrared radiation. 

For routine HPLC analysis, the detection of flavins is carried out either spectro-photometrically, using variable- or fixed-wavelength HPLC detectors in the ultraviolet (e.g., 254 nm) or visible (e.g., 405 nm) region, or fluorimetrically. For riboflavin, the excitation wavelength for fluorimetric detection is usually 440 to 450 nm, and the emission wavelength 530 nm. The detection limit for fluorescence detectors is >1 pmol (0.38 ng) riboflavin, whereas <30 pmol (11 ng) can be detected spectrophotometrically at 254 nm. Photodiode array detectors are significantly less sensitive than normal HPLC spectrophotometers (38). 

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