Use Of Derivative Spectroscopy Research Articles

Sensitive detection of weak absorption signals in photoacoustic spectroscopy by using derivative spectroscopy and wavelet transform

This report presents a practical analytical method of photoacoustic (PA) spectroscopy that is based on wavelet transform (WT) and the first-derivative PA spectrum. An experimental setup is specially designed to obtain the first-derivative spectrum, which aims to identify some unnoticeable absorption peaks in the normal PA spectrum. To enhance the detectability of overlapping spectral bands, the WT is used to decompose the PA spectrum signals into a series of localized contributions (details and approximation) on the basis of the frequency. For the decomposed contributions do not change the absorption peak position of PA spectrum, one can retrieve the weak absorption signals by the decomposed result of WT. Because of the use of derivative spectroscopy and WT, three unnoticeable absorption peaks that are hidden in the PA spectrum of carbon absorption are precisely retrieved, the wavelengths of which are 699.7, 752.7, and 775.5nm, respectively. This analytical method, which has the virtue of using a physical method and using a computer software method, can achieve great sensitivity and accuracy for PA spectral analysis.

Improved quality control in gas chromatography interfaced to stable isotope ratio mass spectrometry by application of derivative chromatography

Compound-specific isotope analysis using gas chromatography interfaced to isotope ratio mass spectrometry (GC-IRMS) is a versatile technique for applications ranging from source appointment and the elucidation of biochemical pathways. When δ 13C values are going to be determined, the sample is combusted to CO 2 and the resulting gas is analyzed relative to a standard with known stable carbon isotope ratio. With the combustion step any information on the identity of a peak is lost. Co-eluting compounds can no more be identified which can lead to significant alterations of the δ 13C value of the analyte. For improvement of the QA/QC protocols in GC-IRMS, we used first, second, and third order derivative chromatography. The suitability of the technique was studied using mixtures of 2,3,3′,4,4′,5,5′-heptachloro-1′-methyl-1,2′-bipyrrole (Q1) and 2,2′,4,5,5′-pentachlorobiphenyl (PCB 101). By application of different GC oven programs four scenarios ranging from baseline separation to full co-elution were obtained. Derivative chromatography enabled identification of the interference of Q1 with PCB 101 even when both peaks fully co-eluted. Although the δ 13C values could not be determined from interfered scenarios, the use of derivative spectroscopy will help to prevent acceptance of incorrect data due to co-elutions. Derivative chromatography was finally used to study the peak purity of 2,2′,3,4,4′-pentabromodiphenyl ether (BDE 85) in technical pentabromo diphenyl ether (DE-71). Already the first order derivative demonstrated that this key-BDE congener was interfered by a compound identified as 2,2′,4,4′,6,6′-hexabromodiphenyl ether (BDE 155).

Simultaneous determination of polythiazide and prazosin in tablets by second-order derivative UV spectroscopy

A second-derivative spectroscopic method for the simultaneous determination of polythiazide and prazosin in tablets was developed. Solutions of these tablets in 0.2 N methanolic hydrochloric acid were analyzed by measurement of the amplitudes of the positive peak at 356 nm with respect to the negative peak at 346 nm ( 2D 346,356) for prazosin, and the amplitude of the positive peak at 236 nm with respect to the baseline ( 2D 236) for polythiazide. Confirmation of the technique was established using HPLC. The use of derivative spectroscopy in this manner provides a specific, rapid and accurate determination of the binary mixture in the tested concentration range of 1–10 μg/ml for polythiazide and 1–20 μg/ml prazosin.

Standard Normal Variate Transformation and De-Trending of Near-Infrared Diffuse Reflectance Spectra

Particle size, scatter, and multi-collinearity are long-standing problems encountered in diffuse reflectance spectrometry. Multiplicative combinations of these effects are the major factor inhibiting the interpretation of near-infrared diffuse reflectance spectra. Sample particle size accounts for the majority of the variance, while variance due to chemical composition is small. Procedures are presented whereby physical and chemical variance can be separated. Mathematical transformations—standard normal variate (SNV) and de-trending (DT)—applicable to individual NIR diffuse reflectance spectra are presented. The standard normal variate approach effectively removes the multiplicative interferences of scatter and particle size. De-trending accounts for the variation in baseline shift and curvilinearity, generally found in the reflectance spectra of powdered or densely packed samples, with the use of a second-degree polynomial regression. NIR diffuse reflectance spectra transposed by these methods are free from multi-collinearity and are not confused by the complexity of shape encountered with the use of derivative spectroscopy.

The use of second-order derivative UV spectroscopy to monitor the percutaneous absorption of naphazoline and oxprenolol

Derivative spectroscopy was used to measure the transfer of the cationic drugs, oxprenolol and naphazoline, across full-thickness human skin in vitro. Flow-through diffusion cells were employed. These allowed the receptor fluid to be pumped through a microprocessor-controlled UV spectrophotometer. Spectra were then recorded at preprogrammed intervals. From the second-order derivative curves it was possible to evaluate the concentration of each diffusant within the receptor phase. Confirmation of the technique was established using HPLC. The steady-state fluxes of both drugs were measured. The diffusion of naphazoline and to a lesser extent oxprenolol were enhanced in the presence of lauric acid. The use of derivative spectroscopy in this manner provides a rapid, labour-saving technique for the continuous monitoring of the absorption of various drugs across excised skin.

Spectrophotometric determination of the critical micellar concentration of bile salts using bilirubin monoglucuronide as a micellar probe. Utility of derivative spectroscopy.

We have developed a simple biologically non-invasive method for determining the critical micellar concentration (CMC) of bile salts using pure naturally occurring bilirubin IX alpha monoglucuronide (BMG), an important bile pigment present in virtually all mammalian biles. This methodology employs visible absorbance spectroscopy of BMG in bile salts over a range of bile salt concentrations that include the reported CMC. Using 100 microM-BMG in 0.4 M-imidazole buffer at pH 7.8, we calculated that the CMC for sodium taurochenodeoxycholate is between 2.5 and 3.0 mM based on: (1) an abrupt change in lambda max. in this concentration range, (2) a precipitous decrease in the amplitude of the absorbance shoulder at 450 nm, (3) a sudden decrease in the second derivative absorbance of BMG at 400 nm and an increase in absorbance at 470 nm, (4) a sharp change in the 4th derivative absorbance at 375 and 395 nm. In contrast, sodium taurocholate, a bile salt that reportedly does not have a CMC but continuously self-associates over a wide concentration range, exhibited none of these changes. The use of derivative spectroscopy enhances the ability to detect the CMC changes and also indicates the number of BMG species in solution and their relative energy states.

Remote Sensing Fiber Optic Probe NIR Spectroscopy Coupled with Chemometric Data Treatment

A near-infrared fiber optic probe remote sensing spectroscopic system has been developed for online multicomponent composition analysis. The Guided Wave Model 200 UV-VIS-NIR spectrophotometer has been evaluated as the base of this system. Multiple linear regression (MLR) software has been combined with data transfer, graphics, and online monitoring programs. The system has been evaluated in plant trials to monitor the composition of mixed alcohol purification streams, mixed solvent distillate, and a fatty acid derivative. The combined use of derivative spectroscopy and MLR data treatment provided good prediction equations for the real-time (20 s) monitoring of the concentrations of several components in moving streams.

The use of derivative techniques in astronomical spectroscopy

Some remarks on the use of derivative spectroscopy in astronomy are considered. The advantages and the problems which arise with this technique are outlined.

Determination of phenolic antioxidants in polypropylene by derivative ultraviolet spectroscopy

A method has been developed for the determination of two phenolic antioxidants exhibiting virtually identical ultraviolet absorption spectra (2,6-di-tert-butyl-4-methylphenol and 4-substituted 2,6-xylenol, denoted by AO-4K and Chemantox AO-49, respectively). The absorption coefficient of AO-4K is an order of magnitude higher than that of Chemantox AO-49. The anti-oxidants can be distinguished in alkaline medium, where the latter forms phenolate readily, thus allowing the utilisation of the bathochromic shift for its determination. The use of derivative spectroscopy reduces light scattering and matrix interferences when extracts from polypropylene samples are measured.

Comment on Gor'kov and Eliashberg's theory for far-infrared absorption by small metallic particles

Numerous errors exist in Gor'kov and Eliashberg's expressions for the electric susceptibility $\ensuremath{\chi}(\ensuremath{\omega})$ of a small metallic particle. We have reevaluated the integral for $\ensuremath{\chi}(\ensuremath{\omega})$ for Dyson's circular ensembles and use the results to examine the dependence of the far-infrared absorption coefficient $\ensuremath{\alpha}(\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\nu}})$ and its derivative $\frac{d\ensuremath{\alpha}}{d\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\nu}}}$ on particle size and the geometric standard deviation $\ensuremath{\sigma}$ of a log-normal distribution of sizes. We conclude that experimental observation of the oscillations characteristic of quantum-size effects by far-infrared absorption requires use of derivative spectroscopy and a distribution of particles with $\ensuremath{\sigma}\ensuremath{\lesssim}1.05$ for the symplectic ensemble, which is the most favorable case. Thus, experimental verification of the applicability of the Gor'kov-Eliashberg theory is unlikely with currently available methods of sample preparation.

The use of derivative spectroscopy for determining methyl groups in polythene

The second derivative of the infra-red absorption spectrum of polythene in the region of 1378 cm −1 has been used for the estimation of the number of methyl groups per hundred carbon atoms in the range 2.0–0.05. It has been shown that in the second derivative there is no overlap between the 1378 cm −1 methyl band and adjacent methylene absorptions when measurements are made at 1378 cm −1. The principles which enable this conclusion to be reached from experimental data have been explained and illustrated. Calibration has been made using polythenes of known methyl content, and checked with butylbranched polymethylenes of known methyl content. In the appendix, the electrical circuits used are described and circuit diagrams given.