Peak wavelength, spectrophotometric measurements

Stabilisers are usually determined by a time-consuming extraction from the polymer, followed by an IR or UV spectrophotometric measurement on the extract. Most stabilisers are complex aromatic compounds which exhibit intense UV absorption and therefore should show luminescence in many cases. The fluorescence emission spectra of Irgafos 168 and its phosphate degradation product, recorded in hexane at an excitation wavelength of 270 nm, are not spectrally distinct. However, the fluorescence quantum yield of the phosphate greatly exceeds that of the phosphite and this difference may enable quantitation of the phosphate concentration [150]. The application of emission spectroscopy to additive analysis was illustrated for Nonox Cl (/V./V -di-/i-naphthyl-p-phcnylene-diamine) [149] with fluorescence ex/em peaks at 392/490 nm and phosphorescence ex/em at 382/516 nm. Parker and Barnes [151] have reported the use of fluorescence for the determination of V-phenyl-l-naphthylamine and N-phenyl-2-naphthylamine in extracted vulcanised rubber. While pine tar and other additives in the rubber seriously interfered with the absorption spectrophotometric method this was not the case with the fluoromet-ric method. 

Incident sunlight is partially absorbed by minerals on an asteroid s surface, and the fraction of light that is reflected can vary as a function of wavelength. Spectrophotometric studies of asteroids have been carried out for decades. Asteroid reflectance spectra have been compared to the spectra of meteorites measured in the laboratory (Fig. 11.3), providing a way to link some kinds of meteorites to possible parent bodies. Most measurements are made at visible wavelengths ranging from 0.4 to 1.0 pm, because the illuminating solar flux peaks... 

Spectrophotometric measurement of apparent absorbance was carried out at wavelength of 290 nm for the duration of the reaction. After it had been determined to be the most reliable peak for monitoring the absorbance due to silica formation (unpublished, results). Measurement of turbidity at this wavelength was performed in order to rapidly determine and compare the relative growth kinetics of the three peptides of interest. All reactions were... 

Spectrophotometric noise tests include measuring spectra of high- and low-reflectance (or transmittance) reference materials. Peak-to-peak noise and root-mean-square (RMS) noise levels are acceptable parameters for evaluation. The preferable measurement involves tabulating the RMS noise in successive 100-nm spectral segments. Instrument noise is usually evaluated as a function of wavelength by using a reference standard as the sample and the background reference. 

Another type of method is based on the spectrophotometric properties of Cr (VI), sometimes used as standard solution [38]. Moreover, the spectrophotometric determination of Cr (VI) is well known in the field of water examination, as it can be used for COD alternative measurement [39] (see Chapter 4). Two other UV-visible spectrophotometric methods have been proposed. The first one [40], designed for natural water, uses the peak height measurement at 372 nm, for a basified sample (pH > 9). The peak height is calculated from the absorbance values at three wavelengths (310, 372 and 480 nm), taking into account a very simple third-degree-polynomial interference signal. 

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