Derivative spectroscopy

types of derivative spectroscopy and Area under curve spectroscopy

1. Derivative spectroscopy and area under curve UV spectroscopy Presented by: A.Padma M.pharmacy Department of pharmaceutical analysis oil technological and pharmaceutical research institute- JNTU A Ananthapuramu, A.P

2. What Is Derivative spectroscopy? I t is a simplest method for an increasing a selectivity is derivatisation of spectra. This operation allows to remove spectral interferences and as a consequence leads to increase selectivity of assay. Derivative spectroscopy involves the conversion of a normal spectra to its first, second or higher derivative spectra. The normal spectrum is known as fundamental, zero order or D spectra. The normal absorption spectrum is reffered to as the fundamental zero order or D spectrum.

3. The first derivative spectrum (D 1 ) is a plot of the rate of change of absorbance with wavelength against wavelength, i.e. plot of ΔA/Δλ vs. λ. The second derivative spectrum(D 2 ) is a plot of Δ 2 A/ Δλ 2 vs. λ. Not only can the first and second derivative of the absorbance spectrum be obtained, but up to the fourth derivative is possible. However, as the differentiation order increases, the noise increases as well, and if a lower derivative is fine, going to higher derivatives is a waste of time and effort. The next slide will show how mathematically the derivatives are graphed

4. Zero order First order Second order Zero, first and Second-order UV derivative spectrum

5. First derivative spectrum of an absorption band is characterised by a maximum, a minimum and cross over point at the λ max of the absorption band. Positive maxima Negative minima

6. Advantages of First derivative spectroscopy: (1) Precise determination of the λ max can be obtained from the zero crossing of the first derivative. (2) Improved spectral resolution (3) Discrimination of broad bands Resolution enhancement in derivative spectroscopy

7. Second derivative spectrum is characterised by two satelite maxima and an inverted band of which the minimum corresponds to the λ max of the fundamental band. Satelite maxima's Second derivative spectrum eliminates the broad band absorption.

8. Instrumentation Derivative spectra may be generated by three techniques. 1.Modification of the optical system Spectrophotometers with dual monochromators , photo detectors used G enerates a signal with an amplitude proportional to the slope of the spectrum over the wavelength interval. Disadvantage: Expensive ,Restricted to the recording of first derivative spectra only.

9. 2.To generate derivative spectra is electronic differentiation of the spectrophotometer analog signal. Resistance capacitance (RC) modules are highly dependent on instumental parameters, the scan speed and the time constant. Standard solution of analyte is employ to calibrate the measured value under the instrumental condition selected 3.Based upon microcomputers differentiation Micro computers incorporated in to or interfaced with spectrophotometer may be programmed To provide Derivative spectra during or after scan To measure derivative amplitudes between specified wavelengths To calculate concentrations and associated statistics from the measured amplitudes

10. Applications of derivative spectroscopy Multicomponent analysis Derivative spectrophotometry (DS) has been mainly used in pharmaceutical analysis for assaying of a main ingredient in a presence of others components or its degradation product. Calculation of some physico-chemical constants, e.g. reaction, complexation or binding constants. Disadvantage The main disadvantage of derivative spectrophotometry is its poor reproducibility.

11. Area under curve spectroscopy (AUC) The AUC method is applicable where there is no sharp peak or when broad peak is obtained. It involves the calculation of integrated value of absorbance with respect to wavelengths λ 1 and λ 2 . Area calculation processing item calculates area bound by the curve and the horizontal axis. The horizontal axis is selected by entering the wavelength range over the which area had to be calculated. Graphically represented by area under curve

12. Spectra of AUC Method

13. References 1) Mark , H. and Workman, J. Derivatives in spectroscopy. Spectroscopy. 2003 ,18 (4): 32-37. 2) Beckett AH and Stenlake JB. Practical pharmaceutical chemistry; 4 th edition, the athlone press. 2007, 269-299.