Derivative spectroscopy

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DERIVATIVE SPECTROSCOPY:

DERIVATIVE SPECTROSCOPY UNDER GUIDENCE OF Mr. B.THANGABALAN sir H.O.D Dept. of PHARMACEUTICALANALYSIS PRESENTED BY AVINASH KOYA, I/II M.Pharm, Dept. of Pharmaceutical analysis, SIMS COLLEGE OF PHARMACY, GUNTUR.

WHAT IS DERIVATIVIVE SPECTROSCOPY?:

19-Jan-12 AVINASH KOYA 2 WHAT IS DERIVATIVIVE SPECTROSCOPY? In spectroscopy, the differentiation of spectra is a widely used technique, particularly in infra-red, u.v.-visible absorption, fluorescence, and reflectance spectrophotometry, referred to as derivative spectroscopy. 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.

INVENTION:

19-Jan-12 AVINASH KOYA 3 INVENTION This technique was first described by Hammond and Price in 1953, followed by the work of Morrison and French et al. Theoretical aspects have been discussed by several authors and a number of reviews concerning these aspects and the performance of the technique have been published.

INSTRUMENT:

19-Jan-12 AVINASH KOYA 4 INSTRUMENT 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 spectra, chromatography or densitometry.

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19-Jan-12 AVINASH KOYA 5 Derivative spectroscopy uses first or higher derivatives of absorbance with respect to wavelength for qualitative analysis and for quantitative analysis . However, the technique received little attention primarily because of the complexity of generating derivative spectra using early UV-Visible spectrophotometers. The introduction of microcomputers in the late 1970s made it generally practicable to use mathematical methods to generate derivative spectra quickly, easily and reproducibly. In derivative spectroscopy the ability to detect and measure minor spectral features is considerably enhanced. This enhancement of characteristic spectral detail can distinguish very similar spectra and follow subtile changes in spectrum..

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19-Jan-12 AVINASH KOYA 6 A first-order derivative is the rate of change of absorbance with respect to wavelength. A firstorder derivative starts and finishes at zero. It also passes through zero at the some wavelength as max of the absorbance band. Either side of this point are positive and negative bands with maximum and minimum at the some wavelengths as the inflection points in the absorbance band. This bipolar function is characteristic of all odd-order derivatives.

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19-Jan-12 AVINASH KOYA 7 The most characteristic feature of a second-order derivative is a negative band with minimum at the same wavelength as the maximum on the zero-order band. It also shows two additional positive satellite bands either side of the main band. A fourth-order derivative shows a positive band. A strong negative or positive band with minimum or maximum at the same wavelength as max of the absorbance band is characteristic of the even-order derivatives. Note that the number of bands observed is equal to the derivative order plus one.

OBTAINING DERIVATIVE SPECTRA:

19-Jan-12 AVINASH KOYA 8 OBTAINING DERIVATIVE SPECTRA Derivative spectra can be obtained by optical, electronic, or mathematical methods. Optical and electronic techniques were used on early UV-Visible spectrophotometers but have largely been superseded by mathematical techniques. The advantages of the mathematical techniques are that derivative spectra may be easily calculated and recalculated with different parameters, and smoothing techniques may be used to improve the signal-to-noise ratio.

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19-Jan-12 AVINASH KOYA 9 OPTICAL AND ELECTRONIC TECHNIQUES The main optical technique is wavelength modulation,where the wavelength of incident light is rapidly modulated over a narrow wavelength range by an electromechanical device. The first and second derivatives may be generated using this technique The electronic method suffers from the disadvantage that the amplitude and wavelength shift of the derivatives varies with scan speed, slit width, and resistance-capacitance gain factor.

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19-Jan-12 AVINASH KOYA 10 MATHEMATICAL TECHNIQUES To use mathematical techniques the spectrum is first digitized with a sampling interval of wavelenth. The size depends on the natural bandwidth (NBW) of the bands being processed and bandwidth of the instrument used to generate the data. Typically, for UV-Visible spectra, the NBW is in the range 10 to 50 nm. Firstderivative spectra may be calculated simply by taking the difference in absorbance between two closely spaced wavelengths for all wavelengths

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19-Jan-12 AVINASH KOYA 11 Where the derivative amplitude, D , is calculated for a wavelength intermediate between the two absorbance wavelengths. For the second-derivative determination three closely-spaced wavelength values are used Savitzky and Golay developed a very efficient method to perform the calculations and this is the basis of the derivatization algorithm in most commercial instruments. Other techniques for calculating derivatives, for example, using Fourier Transforms, are available but not commercially popular.

QUANTIFICATION:

19-Jan-12 AVINASH KOYA 12 QUANTIFICATION If we assume that the zero-order spectrum obeys Beer’s law, there is a similar linear relationship between concentration and amplitude for all orders of derivative For single component quantification the selection of wavelengths for derivative spectra is not as simple as for absorbance spectra because there are both positive and negative peaks. For the evenorder derivatives there is a peak maximum or minimum at the same wavelenth as the absorbance spectrum but for the odd-order derivatives this wavelength is a zero crossing point.

FACTORS AFFECTING:

19-Jan-12 AVINASH KOYA 13 FACTORS AFFECTING Background elimination is a common, unwanted effect in spectroscopy is baseline shift. This may arise either from instrument (lamp or detector instabilities) or sample handling (cuvette repositioning) effects. Discrimination is the most important effect of the derivative process is that broad bands are suppressed relative to sharp bands and this suppression increases with increasing derivative order. Matrix suppression is the analytical problem is often not simply scattering, baseline shift, or unwanted broad absorbing components. It is a combination of two or more of these that results in a broad absorbing background matrix.

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19-Jan-12 AVINASH KOYA 14 Spectral Discrimination as a qualitative fingerprinting technique to accentuate small structural differences between nearly identical spectra Spectral resolution enhancement as a technique for increasing the apparent resolution of overlapping spectral bands in order to more easily determine the number of bands and their wavelengths Quantitative Analysis as a technique for the correction for irrelevant background absorption and as a way to facilitate multicomponent analysis. USES

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19-Jan-12 AVINASH KOYA 15 ADVANTAGES An effective enhancement of resolution, which can be useful to separate two or more components with overlapping spectra. A discrimination in favour of the sharpest features of a spectrum, used to eliminate interferences by broad band constituents.

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19-Jan-12 AVINASH KOYA 16 NOW THE HALL IS OPEN FOR ANY QUERIES

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19-Jan-12 AVINASH KOYA 17