Resolution spectrophotometry

Lebofsky et al., 1981 [196] pursued these studies of Ceres by high-resolution Fourier spectra (1.7-3.5 microns) and medium-resolution spectrophotometry (2.7-4.2 microns). The 3-micron feature is compared with the 3-micron bands due to water of hydration in clays and salts and they conclude that the spectrum of Ceres shows a strong absorption at 2.7-2.8 microns due to structural OH groups in clay minerals. The dominant minerals on the surface of Ceres are therefore hydrated clay minerals structurally similar to terrestrial montmorillonites. There is also a narrow absorption feature at 3.1 microns which is attributable to a very small amount of water ice on Ceres. 

The identification of synthetic colorants (pure or mixtures) in foods is usually carried out using spectrophotometry but the resolution of complex mixtures in food requires a previous separation of extract components by SPE and chromatographic techifiques. Dual wavelength, solid phase, and derivative spectrophotometric methods combined with chemometric approaches have been used. ... 

All these methods give similar results but their sensitivities and resolutions are different. For example, UV-Vis spectrophotometry gives good results if a single colorant or mixture of colorants (with different absorption spectra) were previously separated by SPE, ion pair formation, and a good previous extraction. Due to their added-value capability, HPLC and CE became the ideal techniques for the analysis of multicomponent mixtures of natural and synthetic colorants found in drinks. To make correct evaluations in complex dye mixtures, a chemometric multicomponent analysis (PLS, nonlinear regression) is necessary to discriminate colorant contributions from other food constituents (sugars, phenolics, etc.). 

Their increased application in light food and drink products has given a new impetus to develop fast and accurate method for their determination. Among computer-controlled instruments multivariate calibration methods and derivative techniques are playing very important role in the multicomponent analysis of mixtures by UV-VIS molecular absorption spectrophotometry [2]. Both approaches ate useful in the resolution of overlapping band in quantitative analysis [3, 4]. 

As might be expected, the problem of obtaining spectra of a reacting system increases as the time resolution involved decreases. The spectral changes associated with a reaction may be constructed by wavelength point-by-point measurements. The method, although tedious and costly on materials, is still used. However rapid-scan spectrophotometry, linked to stopped-flow, is now more readily available and reliable. Two systems are used, shown schematically in (3.29) and (3.30). An example of its use is shown in Fig. 3.9. Rapid scan... 

Because infrared spectrophotometry is detector noise limited, a profitable trade-off is possible between signal-to-noise ratio and resolution. Such a trade-off may be useful when deconvolution is used to recover resolution lost by opening monochromator slits to increase acquisition rates. In any system where degrading the resolution improves the signal-to-noise ratio nonlinearly, a potentially useful trade-off is possible. 

The pulse radiolysis method has been described in detail in some of the early papers (22, 22), in a brief review of the subject (23), and in a current comprehensive review (14). It is, in brief, a fast reaction method in which the external perturbation applied to the system is a microsecond pulse of electrons. The current is sufficiently high to produce an instantaneous concentration of transient species high enough to be observed by fast measurement of the optical absorption. Spectra may be recorded either photographically or spectrophotometrically. The kinetics are studied by fast spectrophotometry. Since a perturbing pulse as short as 0.4 /xsec. has been used, the time resolution has approached 10-7 sec. The flash photolysis method used in some of the other studies (27, 15) has been reviewed in detail (24). 

Nemutlu et al. [22,23] reported the determination of lornoxicam in pharmaceutical preparations by using spectrophotometric and chromatographic methods. Derivative UV spectrum of lornoxicam was used to resolve overlapping bands at 258 and 288 nm and to increase the linearity range of calibration curve. A good resolution and sensitivity for lornoxicam was observed with the first-order derivative spectrophotometry. 

Johnson, K. S., and Coletti, L. J. (2002). In situ ultraviolet spectrophotometry for high resolution and long-term monitoring of nitrate, bromide and bisulfide in the ocean. Deep Sea Res. Part I Oceanogr. Res. Papers 49(7), 1291—1305. 

UVV spectrophotometry is one of the simplest and fastest methods for determination of aromatic amines and may serve also for identification purpose with the aid of diode array detectors. A study was carried out on the performance of direct phase (silica gel) and RP (Cis) columns, using a MeOH-O.l M NaC104 mobile phase, for the HPLC-UVD (at 256 nm) analysis of five aromatic amines aniline (la), 1- (8a) and 2-napththylamine (9a), di- (DPA) and triphenylamine (TPA). Good resolutions and separation factors were observed with the RP column for la vs. the other analytes and for 8a or 9a vs. DPA or TPA however, separation of the 8a-9a or DPA-TPA pairs was poor210. 

Ruiz-Medina, A., Fernandez-de Cordova, M. L., and Molina-Diaz, A. A very simple resolution of the mixture paracetamol and salicylamide hy flow injection-solid phase spectrophotometry. Anal. Chim. Acta 394(2-3) 149-158, 1999. 

Just as in ultraviolet-visible spectrophotometry, derivative techniques have also been applied to the analysis of fluorescent substances in multicomponent preparations. The advantages here are reported to be the enhanced spectral resolution and amplification of signal that manifests with substances exhibiting narrower spectral bands. Derivative spectrofluorimetric techniques have been applied, for example, to the determination of chlorpromazine sulfoxide in chlorpromazine hydrochloride preparations. 

---