Trace Nitrogen Determination in Adipic Acid by Catalyst-Free High-Temperature Combustion and Chemiluminescence Detection Application Note · multi EA 5100

Introduction

Adipic resp. hexanedioic acid is a versatilely used organic compound. Besides its application as a food additive (acidifier), for pH-stabilization in flue gas desulfurization plants, or plasticizer for PVC, the most important application is as a precursor for polymer production. Adipic acid and hexamethylenediamine (hexane-1,6-diamine) are the two monomers used to produce Nylon-66 (Polyamide-66). The polymerization reaction forms an amide link between both monomers by reacting a carboxylic group of the diacid with an amine group of the diamine. Production of high molecular weight Nylon greatly relies on the purity of both monomers. A contamination of adipic acid with amines or other nitrogencontaining compounds is particularly critical because it can lead to termination of the polymerization, unwanted side chains or unspecific building blocks incorporated into the polymer, and thereby impairing product quality.

Nitrogen contamination (TN) in adipic acid may be introduced during its production, which includes oxidation of precursor molecules with nitric acid, and therefore needs to be strictly monitored as a quality parameter. The most sensitive method available today for determination of total nitrogen contents is the combustion-based elemental analysis with TN detection by means of chemiluminescence. Due to its high selectivity and sensitivity even lowest nitrogen quantities in the sub-nanogram range can be detected. But there are still challenges for the analysis technique including contamination from the laboratory atmosphere, poor reproducibility, accuracy and precision due to incomplete sample combustion, formation of not detectable nitrogen compounds, and detectability of trace amounts of nitrogen.

The multi EA 5100 with its flame sensor technology facilitates quantitative combustion of all components without splattering during melting, fuming off during pyrolysis, explosive ignition or soot formation. This avoids outliers or TN results that are too low as well as a contamination of the analysis system. This smart sensor ensures not only matrix-optimized digestion, but also a remarkable increase in processing speed and thereby sample throughput while reducing downtime and maintenance to a minimum.