Meaning
Chemical compounds added to the liquid carrier in gel permeation chromatography prevent polymer molecules from sticking to the column packaging. In the analysis of engineering resins like polyamides, mobile phase additives such as salts or acids are used to suppress unwanted ionic interactions and ensure separation is based solely on molecular size. This separation is necessary to measure the true molecular weight distribution of the polymer.
If these additives are omitted, the measured values will be skewed, causing the factory to use resin with incorrect flow properties. The additives must be of high purity to prevent baseline noise during analysis.
Chemical Interaction
Retention behavior of polar polymers on the stationary phase of the column is modified by the presence of salts. Utilizing mobile phase additives reduces the adsorption of polymer chains, which otherwise would delay the elution of the molecules. This modification is critical when analyzing regrind materials where degradation products can alter chemical behavior.
Precise control of additive concentration ensures reproducible chromatography runs.
Separation Accuracy
Correct molecular weight determination depends on pure size-exclusion mechanism without secondary interactions. When mobile phase additives are adjusted correctly, the resulting polymer chromatograms show symmetric peaks and stable baselines. This baseline stability allows accurate calculation of polydispersity, which governs the processing window during injection moulding.
The accurate measurement prevents processing failures.
System Maintenance
Long-term exposure to corrosive salts can accelerate the wear of chromatography pumps and columns. Regular flushing of the system with clean solvent prevents salt crystallization and corrosion of stainless steel parts. This maintenance schedule extends the life of the analytical equipment.
