# A Method for the Colorimetric Quantification of Sodium Lauryl Sulphate in Tablets: A Proof of Concept

## TL;DR

This paper introduces a simple and cost-effective method to measure sodium lauryl sulphate in metformin tablets using a colorimetric technique.

## Contribution

A new extraction and colorimetric method for quantifying SLS in tablets, resistant to interference from metformin.

## Key findings

- The method achieved a precision of 3.3% and accuracy of 5% for SLS quantification.
- The method is linear (R2 = 0.99990) and works within a range of 0.38 µg/mL to 10 µg/mL of SLS.
- The method is suitable for deformulation and total SLS determination in tablets.

## Abstract

The deformulation stage of original drug products, which includes the quantification of critical excipients, is crucial for the successful development of generic drug products of solid dosage form. Sodium lauryl sulphate (SLS) belongs to the group of critical excipients due to its influence on the bioavailability of drugs, such as metformin. The purpose of this work is to carry out a feasibility study in order to develop a simple, economical, and robust analytical method for the quantification of SLS in metformin-containing tablets after their dissolution in water. Firstly, SLS is extracted with chloroform in acidic conditions, followed by the addition of methylene blue (MB) in order to form a SLS-MB ion pair, which is then measured photometrically at a wavelength of 651 nm. Additionally, interference from matrix components (excipients and APIs) was assessed, and it was found that metformin also forms a blue complex; therefore, this specific extraction method was developed. Other matrix components did not interfere with SLS determination. This method shows a well-estimated precision of 3.3% and accuracy of 5%, a calibration linearity of R2 = 0.99990, and a working range of 0.38 µg/mL to 10 µg/mL of SLS in water. The midpoint of the calibration graph corresponds to the concentration of SLS obtained by dissolving a single tablet in 1 L of water. This method seems appropriate for total SLS determination in tablets and can be applicable for deformulation.