Derivative spectrophotometers

Synchroton radiation has been employed as a spectral source for a study of the absorption of HCN and DCN in the wavelength range 80—120nm. A vacuum-u.v. spectrophotometer for absorptions in the region 105—200 nm has been described. Solid-, liquid-, and gas-phase samples could be analysed at temperatures from —200 to 100 °C and at pressures between 0 and 150 atmospheres. The absorption spectrum of tra j-di-imide in the vacuum-u.v. has been measured. First-derivative u.v. spectroscopy has been employed in the analysis of Watts nickel plating solutions for trace amounts of saccharin. Impurity levels of 0.1 p.p.m. have been recorded. A wavelength modulated derivative spectrophotometer with a multi-pass absorption cell has been developed for the automatic analysis of atmospheric pollutants. Traces of SOj, NO, and NO2 were detected with limits of 15, 13, and Sp.p.b., respectively. A double-beam single-detector absorption spectrometer has been constructed. Independence... 

This method sank into oblivion until 1953, when Singleton and Collier [2, 3] took advantage of developments in electronics and built the earliest derivative spectrophotometer. They modified an IR spectrophotometer by an analog device to generate second-order spectra and took out a patent for this concept [2]. At the same time, Hammond and Price [4] proposed the wavelength modulation principle (cf. Section 3.3.1), and Giese and French [5] adapted it to study first-order derivative visible spectra of photosynthetic systems. 

Kinetic experiments were performed on a Perkin Elmer 12, 15, or 12 spectrophotometer following methods described in Chapter 2. Values for k. , given in Tables 3.1 and 3.2 were calculated using equation A8, derived in Appendix 2.1 in Chapter 2. 

In the case of 2- and 6-hydroxypteridine and their derivatives, the anhydrous species in neutral solutions (produced by rapid addition of equilibrated alkaline solutions to neutral buffers) change sufficiently slowly into the hydrated species that serial scans on a recording spectrophotometer can be used to demonstrate the process. The results shown in Fig. 1 for 6-hydroxy-2-methylpteridine are typical. 

For this determination a spectrophotometer which is equipped to produce derivative curves is essential. 

Amotf was the first to develop a set of equations for acetone to simultaneously calculate chlorophyll a and chlorophyll b in 1949. Several authors later proposed different new equations based on more adjusted and accurate extinction coefficients due to the development of higher resolution spectrophotometers adapted to each special condition. Moreover, besides 80% acetone, coefficients for diethyl ether and ethanol were also established and their respective equations developed, as reviewed by Schwartz and Lorenzo and Eder. Solvents chosen should be those for which specific absorbance coefficients have been published to derive equations and updates should be carefully tracked for new values. 

The homopolymers of styrene and acrylonitrile were not soluble In the acetonitrile mobile phase. Calibration factors thus had to be derived from a combination of literature data and experimental measurements. To calibrate the UV detector for polystyrene, 254 nm absorbance of both monomer and polymer was measured with a conventional spectrophotometer, using chloroform... 

A colorimetric procedure is described for the determination of small amounts of Compound 118 (1,2,3,4,10,10-hexa-chloro - 1,4,4a,5,8,8a - hexahydro - 1,4,.5,8 - dimethano-naphthalene). Reaction with phenyl azide to form a di-hydrotriazole derivative and subsequent treatment with diazotized dinitroaniline in strongly acid medium produce an intense red color. Amounts of the insect toxicant of 10 to 40 micrograms in the final 10-ml. aliquot are readily determined with a spectrophotometer. Commonly used insect toxicants do not interfere. 

Determination of organolead metabolites of tetraalkyllead in urine can be carried out after solid-phase enrichment and end analysis using reversed-phase HPLC with chemical reaction detector and by LC-MS (thermospray127). The chemical derivation consists of conversion to the dialky Head form, as shown in reaction 1, followed by complex formation with 4-(2-pyridylazo)resorcinol (11) and spectrophotometic measurement at 515 nm128. 

Even with the knowledge of the reactive moieties that are suspected to trigger M BI, there are numerous potential pathways for the chemistry to lead to protein inactivation [174,196]. Differentiating these mechanisms can facilitate the generation of alternate and safer chemical scaffolds. The UV-Vis spectrophotometer has been a key instrument in activity and functional characterization for CYPs for the past 40 years, as indicated by the derivation of its name, pigment 45 0 being the signature UV band present when reduced in the presence of CO [5,197]. This technique has been... 

The colorimetric methods depend on a chemical reaction or interaction between the protein and the colorimetric reagent. The resulting generation of a chro-mophore, whose intensity is protein-concentration dependent, can be quantified using a spectrophotometer. Beer s Law is employed to derive the protein concentration from a standard curve of absorbances. Direct interaction of the protein with a chromogenic molecule (dye) or protein-mediated oxidation of the reporter molecule generates a new chromophore that can be readily measured in the presence of excess reagent dye. 

Peak purity tests are used to demonstrate that an observed chromatographic peak is attributable to a single component. Mass spectrometry is the most sensitive and accurate technique to use for peak purity evaluation because of the specific information derived from the analysis. However, a good number of HPLC methods use mobile phase conditions that are incompatible with mass spectrometry detection. In this case, PDA spectrophotometers using peak purity algorithms may be used to support the specificity of the method. Almost all commercially available diode array detectors are equipped with proprietary software that will perform these calculations. Although this technique is more universal in application to HPLC methods, the data provided is neither particularly... 

An ultraviolet-visible light spectrophotometer (Lambda 10, Perkin Elmer, Norwalk, CT) was used to measure the characteristic absorbance of the samples taken from the receptor half-cell. Using a calibration curve derived from known concentrations of the model dmgs, the concentration of each sample taken from the receptor half-cell could be determined. 

Figure 2. 13C NMR solid state difference spectra of (a) L. leucocephala and (b) T. aestivum (24) root tissue previously administered [1-13C] ferulic acid 5a. Fig. 2c shows the difference spectrum of a DHP polymer, derived from [1-13C] coniferyl alcohol 2a (29). CP/MAS spectra were obtained at 50 MHz on a Varian XL-200 Spectrophotometer equipped with a Doty Scientific MAS Probe. SSB = spinning side band.

Selenite in aqueous solution can be measured by colorimetric or fluoromet-ric methods. Selenite reacts with 2, 3-diaminonaphthalene to form a brightly colored fluorescent derivative that is extracted with hexane. The absorbance can be measured by a spectrophotometer at 480 nm, or the fluorescence may be measured by a fluorometer at 525 nm. 

There are also nonthematic methods that allow the formation of acylenzymes under conditions where they are stable, so that they can be stored in a syringe in a stopped-flow spectrophotometer. For example, it is possible to synthesize certain nonspecific acylenzymes and store them at low pH.9 12 When they are restored to high pH, they are found to deacylate at the rate expected from the steady state kinetics. This approach has been extended to cover specific acylenzymes. When acyl-L-tryptophan derivatives are incubated with chymotrypsin at pH 3 to 4, the acylenzyme accumulates. The solution may then be pH-jumped by mixing it with a concentrated high-pH buffer in the stopped-flow spectrophotometer.1314 The deacylation rate has been measured by the proflavin displacement method and by using furylacrylolyl compounds. 

The acetyl bromide procedure was developed by Johnson et al. (1961) to determine lignin content in small samples from woody species. This method uses acetyl bromide (4.10) to acetylate unbound hydroxyl groups in the lignin (4.11), while the hydroxyl group on the a-carbon is substituted with a bromine group. The substituted lignin derivative (4.12) is soluble under acidic conditions, and its concentration can be measured with a spectrophotometer at 280 nm. 

The infrared absorption spectrum of atorvastatin calcium, Form-I, was obtained using a Nicolet FT-IR Impact 410 spectrophotometer equipped with deuterated triglycine sulfate detector, and using Omnic 5.1 a software. The sample was contained in a pressed KBr pellet, with each spectrum being derived from 16 single scans over the range of 4000-400 cm-1 at a... 

Alternatively, air drawn through a PTFE membrane followed by sodium bisulfite solution in impingers impinger solution treated with chromotropic acid and H2S04 color developed due to formation of a derivative of formaldehyde absorbance measured by a spectrophotometer at 580 nm a standard calibration curve prepared from formaldehyde standard solutions for quantitation (NIOSH Method 3500,1989) recommended air flow 500 mL/min sample volume 50 L. 

Air drawn through an impinger containing 4,4 -nitrobenzyl pyridine in diethyl phthalate phosgene forms a colored derivative absorbance measured by a spectrophotometer. 

The radial concentration scans obtained from the UV spectrophotometer of the analytical ultracentrifuge can be either converted to a radial derivative of the concentrations at a given instant of time (dc/dr)t or to the time derivative of the concentrations at fixed radial position (dc/dt)r (Stafford, 1992). The dcf dt method, as the name implies, uses the temporal derivative which results in elimination of time independent (random) sources of noise in the data, thereby greatly increasing the precision of sedimentation boundary analysis (Stafford, 1992). Numerically, this process is implemented by subtracting pairs of radial concentration scans obtained at uniformly and closely spaced time intervals c2 — G)/( 2 — h)]. The values are then plotted as a function of radius to obtain (dc/dt) f versus r curves (Stafford, 1994). It can be shown that the apparent sedimentation coefficient s ... 

The samples of free lipase, pure silica (PS), silanized and activated silica, and immobilized derivatives were submitted to the Fourier Transform Infrared Spectroscopy (FTIR) analysis (Spectrophotometer FTIR BOMEM MB-100). The spectra were obtained in the wavelength range of 400-4000 cm-1 for evaluation of the immobilization procedures. 

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