Verification of the chemical composition and specifications of haemodialysis membranes by NMR and GPC-FTIR-coupled spectroscopy

Abstract

The chemical composition of a dialysis membrane is decisive towards determining its physical and biochemical properties—two fundamental determinants of the success of therapy offered to patients suffering from chronic renal failure. From the vast variety of synthetic polymers available, only a few are suitable for the manufacture of dialysis membranes that have to conform to the diverse demands of modern haemodialysis and related therapies. Recently, a membrane labelled as polyamide (Polyamide S™) has caused some confusion to end-users in that the product specification for the membrane is given as ‘polyarylethersulfone’ or simply as Polyamide S membrane. As the chemical and physical properties of these two polymer types are distinctly different, it is unclear whether the functional characteristics of Polyamide S™ are to be attributed to polyamide, polyarylethersulfone, or, to both polymers. We therefore undertook investigations to ascertain the exact chemical nature of the Polyamide S™ membrane using a series of chemical analytical tools and an appropriate polyamide reference. The analytical techniques were conventional gel permeation chromatography (GPC), GPC-FTIR coupled spectroscopy using dimethyl acetamide and hexafluoroisopropanol as solvents and nuclear magnetic resonance spectroscopy. Glass transition temperature measurements and quantitative elemental analysis were also carried out. None of the analytical techniques used showed any traces of polyamide in Polyamide S™; no aliphatic or aromatic polyamide chemical entities were detected in any of the samples tested. The Polyamide S™ dialysis membrane thus comprises, solely, of polyarylethersulfone, which is also known as polyethersulfone.