Derivative spectroscopy involves converting a normal absorption spectrum into its first or second derivative spectrum. This allows for more precise determination of the wavelength of maximum absorption and improved spectral resolution. The first derivative spectrum plots the rate of change of absorbance versus wavelength and shows a maximum, minimum and zero crossing at the absorption band's wavelength. The second derivative shows two satellite maxima with an inverted band minimum at the wavelength of maximum absorption. Area under curve spectroscopy calculates the integrated absorbance value over a specified wavelength range, graphically representing the area under the absorption curve. Both techniques have applications in pharmaceutical analysis for multicomponent assays and determination of physical constants.

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?
 It 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 D0 spectra.
 The normal absorption spectrum is reffered to as the fundamental zero
order or D0 spectrum.

3. The first derivative spectrum (D1) 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(D2) is a plot of Δ2A/ Δλ2vs. 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 λmax of the absorption
band.
Positive maxima
Negative minima

6. Advantages of First derivative spectroscopy:
(1) Precise determination of the λmax 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 λmax 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
 Generates 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 λ1 and λ2. 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; 4th
edition, the athlone press. 2007, 269-299.