Meaning
Quantitative errors in gas chromatography arise when different compounds do not transfer from a heated injection port to the column in the same proportions as they existed in the sample. This phenomenon of splitless injection discrimination leads to the under-reporting of high-boiling polymer additives, such as heavy plasticizers and light stabilizers. It occurs because the slow vaporization of heavy molecules allows them to remain on the syringe needle or in the inlet liner while lighter components enter the column.
The discrimination is confined to hot vaporizing injectors and can be bypassed using cold injection techniques, which provide a more representative sample introduction for high-molecular-weight analytes.
Thermal Effect
Inlet vaporizers must be kept at high temperatures to ensure the rapid volatilization of the injected polymer extracts. When splitless injection discrimination occurs, the heat of the injector is insufficient to vaporize the high-molecular-weight components within the brief splitless hold time. This results in the loss of heavy additives, which condense on the cooler parts of the injection system.
It leads to inaccurate chromatograms that do not reflect the true composition of the molded plastic.
Quantitative Deviation
Material specifications for food-contact plastics require the precise measurement of migrating additives to ensure regulatory compliance. If splitless injection discrimination is not corrected, the reported values for heavy plasticizers will be falsely low. This analytical error can lead to the false approval of a polymer batch that actually exceeds the migration limits.
It creates a major financial and legal risk for the moulding company.
Resin Sourcing
Quality control laboratories must evaluate the additive packages of incoming resin batches to ensure consistent moulding performance. Using calibration methods that correct for splitless injection discrimination prevents the mischaracterization of virgin polymers and recycled feedstocks. This correction ensures that the melt flow and thermal stability of the resin match the values on the manufacturer’s datasheet.
It helps moulders make informed purchasing decisions and maintain stable extrusion runs.
