Ultraviolet absorption spectrometry

Tittarelli et al. [48] have identified some 20 organic and inorganic pigments (used for coloration of polymers, polymer films and coatings) directly without dissolution by means of vapour-phase UV absorption spectrometry. The influence of a polymeric matrix on TUV profiles was not specified. Each pigment has a characteristic thermal UV profile at a particular temperature. Alpha and beta forms of copper phthalocyanine (Pigment Blues 15 and 15.4) produce different TUV profiles. The heating rate plays 

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Di Corcia and Marchetti [160] determined chlorinated phenoxy acid and ester type herbicides in amounts down to lmg kg-1 or lower in soil by liquid chromatography combined with particle beam mass spectrometry and ultraviolet absorption spectrometry. 

Kim et al. [161] used particle beam mass spectrometry and ultraviolet absorption spectrometry as detectors in a method for the determination of down to lppm of chlorinated phenoxy and ester herbicides in soil. 

Quantitative analysis of the peroxy group of macroinitiators is performed by iodometry [38] and that of the azo group is done by ultraviolet (UV) spectrometry. Recently, type II MAI composed of PU was determined of its azo concentration by UV [20]. When the UV absorption spectral peak of the azo group overlaps other peaks, DSC is available by determining the azo group from the exothermal peak area [1IJ. 

J A Howell and L Harges, Ultraviolet and light absorption spectrometry, Anal. Chem., 1982, 54, 171R... 

Measurement techniques that can be employed for the determination of trace metals include atomic absorption spectrometry, anodic stripping voltammetry, differential pulse cathodic stripping voltammetry, inductively coupled plasma atomic emission spectrometry, liquid chromatography of the metal chelates with ultraviolet-visible absorption and, more recently, inductively coupled plasma mass spectrometry. 

Millward and Bihan [59] studied the effect of humic material on the determination of mercury by flameless atomic absorption spectrometry. In both fresh and seawater, association between inorganic and organic entities takes place within 90 min at pH values of 7 or above, and the organically bound mercury was not detected by an analytical method designed for inorganic mercury. The amount of detectable mercury was related to the amount of humic material added to the solutions. However, total mercury could be measured after exposure to ultraviolet radiation under strongly acid conditions. 

The basic instrumentation used for spectrometric measurements has already been described in Chapter 7 (p. 277). The natures of sources, monochromators, detectors, and sample cells required for molecular absorption techniques are summarized in Table 9.1. The principal difference between instrumentation for atomic emission and molecular absorption spectrometry is in the need for a separate source of radiation for the latter. In the infrared, visible and ultraviolet regions, white sources are used, i.e. the energy or frequency range of the source covers most or all of the relevant portion of the spectrum. In contrast, nuclear magnetic resonance spectrometers employ a narrow waveband radio-frequency transmitter, a tuned detector and no monochromator. 

Capillary column gas chromatography is an even quicker and equally accurate alternative. Mass spectrometry (ASTM D1137) is also suitable for the analysis of petroleum gases. Of the other spectroscopic techniques, infrared and ultraviolet absorption may be applied to petroleum gas analysis for some specialized applications. Gas chromatography has also largely supplanted chemical absorption... 

GC = gas chromatography EC = electrochemical (detector ECD = electron capture (detector HCD = Hall conductivity detector HFBA = heptafluorobutyric anhydride HPLC = high performance liquid chromatography NCI-MS = mass spectrometry in the negative chemical ionization mode NPD = nitrogen-phosphorus detector ppb = parts per billion UV = ultraviolet absorption SPE = solid phase extraction wt wt = weight weight... 

GFAAS = graphite furnace (flameless) atomic absorption spectroscopy TLC = thin layer chromatography HFP-AES = high frequency plasma-atomic emission spectroscopy NAA = neutron atomic analysis ICP-AES = inductively coupled plasma-atomic emission spectroscopy AAS = atomic absorption spectrometry GSE = graphite spectroscopic electrode UV = ultraviolet spectrophotometry PD = photodensitometer and (3,5-diBr-PADAP) = 2(-3,-5-dibromo-2-pyridylazo)-5- diethyl-ami nophenol. 

Ultraviolet-visible (UV-Vis) spectrophotometric detectors are used to monitor chromatographic separations. However, this type of detection offers very little specificity. Element specific detectors are much more useful and important. Atomic absorption spectrometry (AAS), inductively coupled plasma-atomic emission spectroscopy (ICPAES) and inductively coupled plasma-mass spectrometry (ICP-MS) are often used in current studies. The highest sensitivity is achieved by graphite furnace-AAS and ICP-MS. The former is used off-line while the latter is coupled to the chromatographic column and is used on-line . 

Knowles, A. Burgess, C., Ed. Practical absorption spectrometry. In Techniques in Visible and Ultraviolet Spectrometry Chapman Hall London, 1984 3. 

The analyses of colors in foods have been mainly achieved by thin-layer chromatography (TLC), because TLC is a simple and effective technique for the separation of components in a mixture. However, the only useful information obtained from a TLC plate to identify a component is the Rf value the identification of the separated components is difficult unless an appropriate spectrometiic method, such as ultraviolet-visible absorption spectrometry, is used. A stepwise operation, including individual component separation by TLC and measurement of the spectrum, is laborious and time-consuming, because it requires extra steps such as extraction of the desired compound from the TLC plate and elimination of adsorbents. 

The spectrophotometric methods to be discussed (methods of molecular absorption spectrometry) are based on the measurement of absorption of radiation, in the visible and near ultraviolet regions, owing to coloured compounds formed, before the determination, by the elements to be determined. Only seldom is use made of the intrinsic colour of the element itself, in its ionic form. In cases where an element neither forms coloured compounds nor occurs in a coloured form, indirect spectrophotometric methods are applied. 

LOD, limit of detection NR, not reported MDC. mircodiffusion cell TCA, trichloroacetic acid AAS. atomic absorption spectrometry UV, ultraviolet absorbance detection ECD, electron capture detection NPD, nitrogen phosphorus detection GC-MSD, gas chromatography-mass selective detection GC, gas chromatography ATC, 2-amino-1hiazoline-4-carboxylic acid. 

Spectrophotometers came into widespread use beginning around 1940, and this led to wide application in petroleum analysis. Ultraviolet absorption spectroscopy, infrared spectroscopy, mass spectrometry, emission spectroscopy, and nuclear magnetic resonance spectroscopy continue to make major contributions to petroleum analysis. 

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