Derivative Spectroscopy Applied to the Determination of Alpha- And Beta-Acids in Hops

Abstract

Derivative spectroscopy is applied for the first time to the determination of alpha-and beta-acids in hops. The second derivative of the absorption spectrum provides adequate resolution for the simul taneous analysis of these compounds without any previous separation technique. The method is simple and rapid since the measurements are performed in a single scan. The results are comparable to those obtained by the ASBC photometric method and correlate well with the HPLC method (EBC).Key Words: Derivative spectroscopy, analysis method, hop products, spectrophotometry. IntroductionDerivative technique is becoming increasingly popular in analytical spectrophotometry as a resolution enhancement technique4 and as a background correction one31. It offers a convenient solution to a number of well defined analytical problems, such as resolution of multicornponent systems, sample turbidity or matrix background and enhancement of spectral details. This technique was first described by Hammond andPrice" in 1953, followed by the work of Morrison23 and French et al." Theoretical aspects have been discussed by several authors12-19-26-27 and a number of reviews concerning these aspects and the performance of the technique have been published7-24-25. Its usefulness has been demonstrated in biochemical3-14-15-31, pharmaceutical7, toxicological"' and inorganic analysis21- 22.3OAlthough UV-VIS spectrophotometry offers a very wide field of application for derivative spectroscopy, the derivative technique is perfectly general and can be applied to any other areas such as infrared spectra2", chromatography*-9 or densitometry28.In essence, derivative spectroscopy involves plotting the first, second or higher order derivatives of a spectrum with respect to wavelength. Usually this is obtained by an elec tronic RC or microcomputer device connected in series with the spectrophotometer, which computes the derivative with respect to time as the spectrum is scanned at constant speed (dMd)The "true" wavelength derivative is linearly related to the time derivative recorded, the magnitude of which is directly affected by scanning speed and spectral band width.The derivative process provides two general advantages: first, an effective enhancement of resolution, which can be useful to separate two or more components with overlapping spectra; second, a discrimination in favour of the sharpest features of a spectrum, used to eliminate interferences by broad band constituents. However, this process results in a decrease in the signal to noise ratio.Both advantages and disadvantages increase with the derivative order. Generally, the second derivative is more useful than the first ones.In this report, derivative spectrophotometry is applied for the first time to the analysis of alpha-and beta-acids in hops. The method developed allows the simultaneous determi nation of these compounds without the need for any separ ation technique and avoids the background absorption which is corrected in the ASBC method2 by means of a ternary spectrophotometric analy...

Effect of Controlled Humidity and Tissue Hydration on Colon Cancer Diagnostic via FTIR Spectroscopic Imaging

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“…Second derivative spectra have the advantage that they are free from the baseline shift, as well as enhancing resolution by deconvoluting overlapping peaks from multiple components. 36 As the surrounding humidity changes, it is apparent that the second derivative spectra vary, reflecting a change in the conformation or arrangement of biomolecular components of the tissue. A critical finding from this experiment is the consistent peak shift, perceptibly from 1230 to 1238 cm −1 across all tissues, regardless of their malignancy states, as the humidity gradually rises.…”

Photoacoustic Spectrometric Evaluation of Soil Heavy Metal Contaminants

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Derivative UV/Vis spectroelectrochemistry in a thin-layer regime: deconvolution and simultaneous quantification of ascorbic acid, dopamine and uric acid

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