DERIVATIVESPECTROSCOPY

MADE BY:

MOHAMMED ABDULWAHHAB HASSENI

Under supervision of Dr. Mahmood Ali

14-JUNE-2015 SEMESTER

BACKGROUND INFORMATION:

In Chemistry, Analytical methods based on measurements of UV or visible light absorption belong to the most popular and most often used in laboratory practices.Its Commercially available apparatuses are cheap and easy for operation. Spectroscopy procedures usually are not time and labor-consuming. The economical aspects of UV-Vis techniques is worth emphasizing as it is easily accessible and is a basic equipment available in all laboratories.The main disadvantage and limitation of the spectroscopy is its low selectivity.

BACKGROUND INFORMATION CONT.:

One of the simplest method for increasing a selectivity is derivitisation of spectra. this operation allows us to remove spectral interferences and as a consequence, leads to the increase selectivity of assay.

Derivatisation of sets of digital data is a well known method of separation, using signals from noised data.

historically, the beginning of derivative spectroscopy is dated on 1953 when the first analogue spectroscopy was build by Singleton and Cooler.But the fast development of this technique started in 70-s of twentieth century, when new generation of spectroscopy controlled by computers were constructed.

So what is Derivative Spectroscopy?...

DERIVATIVE SPECTROSCOPY: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 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 is a plot of Δ2A/ Δλ2 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

TYPES OF DERIVATIVE SPECTRA

So how can we deduce the amount of each derivative?

DERIVATIVE SPECTROSCOPY:To find the quantitative estimation of binary mixtures using the derivative spectroscopy, we first need to find out the Zero Crossing Points (ZCP) for both the components (A and B). After that we must select the ZCP for A and B so that particular ZCP of other component show as remarkable absorbance. Then, we must prepare the calibration curve of A at the ZCP of B and of B at the ZCP of A.

In doing this we can find out the unknown concentration using this calibration curves.

DERIVATIVE SPECTROSCOPY:

Derivative spectroscopy is excellent for determination of multi components in a sample, if they can be resolved.

DERIVATIVE SPECTROSCOPY:

So how does the mechanics inside the Derivative Spectrum work?

OBTAINING A DERIVATIVE SPECTRUM:

The mechanics of Derivative spectra can either be recorded on time or by manipulation of data obtained in an absorbance/wavelength spectrum. The latter is easy and can be made by simple electronic or mathematic operations; by taking A for a fixed (few nm) and plotting the data versus wavelength. However, the most common instrumental recording of derivative spectra involves the use of a dual wavelength instrument with two monochromator operated at the same speed but with a lag of few nm from each other. A chopper will sequentially pass the beams from both monochromators and thus their difference divided by the constant nm lag value is recorded versus the average wavelength.

This is how it works…

The Mechanics of the Derivative Spectroscopy:

So what are the applications for use?

APPLICATIONS OF DERIVATIVE SPECTRA:

The applications for the derivative spectra include: Better qualitative analysis and identification of the

number of absorbing species in a sample

Accurate determination of max

Obtaining spectra in solutions with high scattering is possible using dual wavelength instruments

And gaining Spectral resolution of multi component systems by the measurement of two wavelengths; where the interferent has identical molar absorbtivity while the analyte does not, meaning that there are no interferencesLets put this application into practice…

To better understand the importance of this mathematic method lets see an example of a Bi-component dye solution

The Derivative Spectroscopy mechanism in action;

QUANTITATIVE ANALYSIS OF BICOMPONENT DYE SOLUTIONS BY DERIVATIVE SPECTROSCOPY :

For example the absorbance (zero-order) spectra of single and binary solutions of the red, scarlet, yellow, blue, and navy blue dyes are shown in Figures 1-4.

In the case of binary mixtures of (blue-navy blue) and (redscarlet),due to spectral overlap of zero-order spectra (Figures 1 and 4), simultaneous determination of both colorants is not accurate by direct absorption measurements. Some possibilities that may be chosen to solve this problem are derivative spectroscopy methods such as zerocrossing or ratio spectra derivative techniques In these examples the last method was applied to avoid this problem.Take a look at these four figures…

Figure 1 Absorbance Spectra Of 0.025 G/L Scarlet, 0.025 G/L Red And Their Binary Mixture

Figure 2 Absorbance spectra of 0.025 g/l scarlet, 0.025 g/l yellow and their binary mixture

Figure 3 Absorbance spectra of 0.05 g/l yellow, 0.05 g/l red and their binary mixture

Figure 4 Absorbance spectra of 0.01 g/l blue, 0.01 g/l navy blue and their binary mixture

THE IMPORTANCE OF THE DERIVATIVE SPECTROSCOPY APPLICATION

In Figures 1 to 4 the application of the normal method in samples prepared by binary mixtures as seen in these dyes have absorbance peaks that are not well separated in terms of wavelength. Therefore, simultaneous determination of both dyes by normal method was not done with sufficient precision.However, the obtained results show that in case of strong overlapping spectra the accuracy of the derivative method is higher and it can be easily applicable for the analysis of the dye contents.Figures 5-12 show the first-order ratio derivative spectra of different concentrations of red, scarlet and yellow, blue and navy blue dyes in their binary mixtures.

Figure 5 Ratio first order derivative spectra of different concentrations of scarlet (0.0025, 0.01, 0.025, and 0.05 g/l) using 0.025 g/l red as divisor ( At 435 nm )

Figure 6 Ratio first order derivative spectra of different concentrations of red (0.0025, 0.01, 0.025, and 0.05 g/l) using 0.025 g/l scarlet as divisor ( At 540 nm )

Figure 7 Ratio first order derivative spectra of different concentrations of scarlet (0.0025, 0.01, 0.025, and 0.05 g/l) using 0.05 g/l yellow as divisor ( At 500 and 550 nm )

Figure 8 Ratio first order derivative spectra of different concentrations of yellow (0.025, 0.05, 0.1, and 0.125 g/l) using 0.05 g/l scarlet as divisor ( At 450 nm )

Figure 9 Ratio first order derivative spectra of different concentrations of red (0.0025, 0.01, 0.025, and 0.05 g/l) using 0.05 g/l yellow as divisor ( At 506 and 570 nm )

Figure 10 Ratio first order derivative spectra of different concentrations of yellow (0.025, 0.05, 0.1, and 0.125 g/l) using 0.05 g/l red as divisor ( At 449 nm )

Figure 11 Ratio first order derivative spectra of different concentrations of navy blue (0.0025, 0.005, 0.01, and 0.025 g/l) using 0.01 g/l blue as divisor ( At 575 and 600 nm )

Figure 12 Ratio first order derivative spectra of different concentrations of blue (0.0025, 0.005, 0.01, and 0.025 g/l) using 0.01 g/l navy blue as divisor ( At 562 and 587 nm )

The proposed derivative technique was found to be easily applicable for the quantitative analysis of dyes with both overlapping and non-overlapping spectra in their binary mixtures.

Practical implications – The developed method can be a simple and practical solution to obtain the quantitative analysis of bicomponent dye solutions with overlapping spectra.

CONCLUSION:

The Derivative spectroscopy is a simple method used during the analysis based on how we can solve the problem of interferances between two components inside binary solutions that gives two maximum wavelengths overlapping one another. By using this method we can increase the selectivity and accuracy of binary mixtures.