Method Verification of the Modified Lowry Assay for Determination of Protein in Medical Gloves

Protein Determination Based on Modified Lowry Method

Abstract

         Thailand is a leader in manufacturing and export of medical gloves made from natural rubber. Unfortunately, the protein content of natural rubber latex products can cause allergies in some latex-sensitive individuals. Thus, American Society for Testing and Materials prescribes a method for detecting residual protein in finished gloves, which recommended a maximum limit of 200 μg/dm². The objective of this work is to study and verify the modified Lowry methods for protein analysis in accordance with the ASTM D5712-15 and EN 455-3 standards, which aimed not only to protect customer safety but also to encourage the rubber glove export industry. The measurements relied on a colorimetric analysis as a consequence of the reactivity of proteins with Cu²⁺ and Folin reagent in an alkaline condition, producing blue-colored products that can be measured using 750 nm spectrophotometer. Protein binding capacity of the materials used throughout the work, the precipitation processes, and analytical performance characteristics of the methods were sequentially investigated. The verified ASTM results demonstrated linearity from 5–60 μg/mL with a LOD and a LOQ of 1.8 and 5.0 μg/mL, respectively. Meanwhile, the linear range of 5–100 μg/mL with the LOD of 2.0 and the LOQ of 5.0 μg/mL were received according to the EN standard. Furthermore, the precision and trueness of these two methods were assessed. The HORRAT values were less than 2.0 and the recovery percentages were found as 101–104% and 86–99% for ASTM and EN standards, respectively. In conclusion, the standard testing is appropriately verified and can be applied to detect the protein content in medical gloves, leading to further expanding the scope of services to promote the medical rubber gloves in the country.