UV Method Development Using Multicomponent Analysis

1.1       Analytical Chemistry

Analytical chemistry is a scientific discipline that develops methods, instruments, and strategies to obtain information on the composition and nature of matter. Unlike other major sub-disciplines of chemistry such as inorganic and organic chemistry, analytical chemistry is not restricted to any particular type of chemical compound or reaction. An analytical method is a specific application of technique to solve an analytical problem.The use of instrumentation is an exciting and fascinating part of chemical analysis that interacts with all areas of chemistry and with many other areas of pure and applied science. Analytical instruments play an important role in production and evaluation of new products and in the protection of consumers and the environment. Pharmaceutical analysis deals with qualitative and quantitative analysis of drugs in bulk, dosage forms, and in biological samples.

1.2       Classification of Analytical Methods

Common techniques indispensable to analytical chemistry are categorised as follows:

2.         UV-VISIBLE SPECTROSCOPY

Ultraviolet–Visible (UV–Visible) Spectroscopy is one of the most powerful, widely used, and fundamental analytical techniques in modern chemistry and related scientific fields. It is based on the measurement of the absorption of ultraviolet (200–400 nm) and visible (400–800 nm) electromagnetic radiation by molecules or ions. When a molecule absorbs light in this region, it undergoes electronic excitation, where electrons are promoted from a lower-energy orbital to a higher-energy orbital.These transitions provide valuable information about the electronic structure of the molecule, the presence of chromophores, and the molecular environment. Because of its ability to generate rapid, reliable, and non-destructive analytical data, UV–Visible spectroscopy has become an essential tool in both research and industrial laboratories.

2.1       Principle

The principle of UV–Visible spectroscopy is dependent on absorption of polychromatic light or visible light by a sample which gives spectra. When the sample absorbs radiation, the sample molecule moves from the ground state to the singlet excited state. There are three possible categories of ground state orbital involved:

•           sigma (σ) bonding molecular orbital

•           pi (π) bonding molecular orbital

•           n (non-bonding) atomic orbital

In addition, two classes of antibonding orbitals may be involved in the transition process: σ* (sigma star) orbital and π* (pi star) orbital. Electronic transitions can take place by absorbing ultraviolet and visible light.

2.2       Electronic Transitions

When a beam of light moves through a material, some wavelengths are absorbed because the substance takes in part of the light. This occurs when electrons inside the molecules gain energy from the incoming photons, causing them to jump from their ground states to higher-energy levels.

Key transition types include:

π → π* Transitions: Often seen in conjugated organic molecules, where electrons in a π-bond system absorb energy and move into a π* (anti-bonding) orbital.

n → π* Transitions: Involves non-bonding electrons getting excited into a π* anti-bonding orbital.

σ → σ* Transitions: High-energy transitions in sigma bonds, typically occurring below 200 nm.

2.3       Beer–Lambert Law

The Beer–Lambert Law is one of the fundamental foundations of UV–Visible spectroscopy. It clarifies how the quantity of light absorbed by a solution is related to the concentration of the absorbing species and the path length.

A = log??(I?/I) = ε · c · l

2.4       Advantages and Disadvantages of UV–Visible Spectroscopy

3.         MULTICOMPONENT ANALYSIS

Multicomponent analysis refers to the simultaneous quantitative determination of two or more analytes in a mixture using a single set of measurements. In UV spectrophotometry, this exploits the additive nature of absorbance (Beer–Lambert Law applies to each component independently), enabling the resolution of overlapping spectra.

3.1       Vierordt’s Simultaneous Equation Method

The simultaneous equation method (also known as Vierordt’s method) is applied for multicomponent samples containing two absorbing drugs (X and Y), each of which absorbs at the other’s maximum wavelength. Using this method, the concentration of both drugs can be determined simultaneously.

For a binary mixture of drugs X and Y, measurements are made at two wavelengths λ? (λmax of X) and λ? (λmax of Y). Two simultaneous equations are constructed based on the additive nature of absorbance:

A? = ax?·b·Cx + ay?·b·Cy A? = ax?·b·Cx + ay?·b·Cy

Solving these simultaneous equations:

Cx = (A?·ay? – A?·ay?) / (ax?·ay? – ax?·ay?) Cy = (A?·ax? – A?·ax?) / (ax?·ay? – ax?·ay?)

3.2       Isobestic Point Method

The isobestic point is the wavelength at which the molar absorptivity is the same for two interconvertible substances (or for two components of a mixture). At the isobestic point, the total absorbance is proportional only to the total concentration of both components combined, independent of their individual ratios.

This property makes the isobestic point particularly valuable for eliminating the interference of impurities or one component when estimating the other. The concentration of each component is derived using Q-value (absorbance ratio) equations:

Cx = [(Qm – Qy) / (Qx – Qy)] × (A? / ax?)

Cy = [(Qm – Qx) / (Qy – Qx)] × (A? / ax?)

4.         DRUG PROFILES

4.1       Paracetamol (PCM)

Paracetamol (acetaminophen; N-(4-hydroxyphenyl)acetamide) is a widely used analgesic and antipyretic agent. It acts centrally by inhibiting prostaglandin synthesis within the central nervous system, particularly through modulation of the prostaglandin H? synthase (PGHS/COX) enzyme complex at its peroxidase site.

Paracetamol’s analgesic mechanism is multimodal: it suppresses central prostaglandin E? (PGE?) synthesis, enhances descending serotonergic inhibitory pathways from the brainstem, and produces the active metabolite AM404 (N-arachidonoylphenolamine) which modulates endocannabinoid and

TRPV1 systems. Unlike NSAIDs, it has minimal peripheral anti-inflammatory activity due to the high peroxide tone at inflammation sites.

4.2       Ibuprofen (IBU)

Ibuprofen [(2RS)-2-[4-(2-methylpropyl)phenyl]propanoic acid] is a non-steroidal anti-inflammatory drug (NSAID) that reversibly inhibits cyclooxygenase enzymes COX-1 and COX-2, thereby reducing prostaglandin and thromboxane synthesis. This leads to analgesic, anti-inflammatory, and antipyretic effects.

5.         AIM AND OBJECTIVES

5.1       Aim

To develop a UV spectroscopic method for the simultaneous estimation using Vierordt’s simultaneous equation method and Isobestic point method for Paracetamol and Ibuprofen in Combiflam tablet dosage form.

5.2       Objectives

•      To develop a UV spectroscopic method for simultaneous estimation of Paracetamol and Ibuprofen.

•      To determine the wavelength of maximum absorbance (λmax) of both drugs by spectral scanning in the range 200–400 nm.

•      To apply Vierordt’s simultaneous equation method and Isobestic point method for quantitative estimation.

•      To ensure accuracy and precision of the developed analytical method.

•      To use the method for routine quality control of Combiflam tablet dosage forms.

6.         METHODOLOGY

6.1       Instrumentation

A double-beam UV–Visible spectrophotometer (Shimadzu UV-1900I, S/N: A12536385522) equipped with quartz cuvettes of 1 cm path length was used for all absorbance measurements (Software:

LabSolutions UV-Vis, Version 1.15). An analytical balance was employed for weighing standards and samples. An ultrasonic bath was utilized to aid in dissolution.

6.2       Selection of Solvent

Ethanol was selected as the common solvent for developing spectral characteristics and preparing standard and sample solutions, based on solubility studies demonstrating complete dissolution of both PCM and IBU.

6.3       Preparation of Standard Solutions

6.3.1    Paracetamol Stock Solution

Paracetamol powder (10 mg) was weighed accurately and transferred into a 100 mL volumetric flask. It was dissolved in 50 mL of ethanol and the volume was made up to 100 mL with ethanol to obtain a stock solution of 100 μg/mL. A working stock solution of 10 μg/mL was prepared from this stock. The working solutions were scanned in the UV range (200–400 nm) to determine the λmax. The wavelength of maximum absorbance was found at 245 nm.

6.3.2    Ibuprofen Stock Solution

Ibuprofen powder (10 mg) was weighed accurately and transferred into a 100 mL volumetric flask. It was dissolved in 50 mL of ethanol and the volume was made up to 100 mL with ethanol to obtain a stock solution of 100 μg/mL. A working standard stock solution of 10 μg/mL was prepared from this stock. These working solutions were scanned in the UV range (200–400 nm) to determine the λmax. The wavelength found for analysis was 220 nm.

6.4       Preparation of Sample Solution

Ten tablets of Combiflam were weighed and ground to a fine powder. An accurately weighed powder equivalent to 1 tablet (325 mg PCM + 400 mg IBU) was transferred to a 100 mL volumetric flask containing ethanol and ultrasonicated for 15 minutes. The volume was made up to the mark with ethanol. The solution was filtered through Whatman filter paper No. 41. Appropriate aliquots were subjected to analysis.

7.         RESULTS

7.1       Determination of λmax

Spectral scanning of individual standard solutions (10 μg/mL) of both drugs in ethanol across the range 200–400 nm confirmed the following wavelengths of maximum absorbance:

7.2       Results by Vierordt’s Simultaneous Equation Method

Using the absorbance values of the sample mixture at 245 nm and 220 nm, the following calculations were performed to determine the concentration of each drug:

Cx = (A?·ay? – A?·ay?) / (ax?·ay? – ax?·ay?) = 331.64 / 325 × 100 = 102.04% w/v Cy = (A?·ax? – A?·ax?) / (ax?·ay? – ax?·ay?) = 441.31 / 400 × 100 = 110.3% w/v

7.3       Results by Isobestic Point Method

Using Q-value ratios at the isobestic point (268 nm) alongside λmax readings:

Qm = 0.821/2.575 = 0.318 | Qx = –6.503 | Qy = 6.974

Cx (PCM) = 305.6 / 325 × 100 = 94.03% w/v

Cy (IBU) = 396.8 / 400 × 100 = 99.2% w/v

7.4       Summary of Results