What Is GPC Analysis?
Gel permeation chromatography (size exclusion chromatography) is based on dissolved polymer chains passing through a porous packing at different speeds according to their hydrodynamic volume. Large chains cannot enter the pores and leave the column first.
Purpose of GPC Analysis
The purpose is to determine a polymer's average molecular weight and molecular weight distribution. A polymer's processability, mechanical strength and ageing behaviour largely depend on this distribution.
Which Products Is GPC Analysis Applied To?
- Thermoplastic raw material and granules
- Adhesive and coating resins
- Recycled polymers
- Biodegradable polymers
- Rubber and elastomer compounds
In Which Sectors Is GPC Analysis Used?
Standards Related to GPC Analysis
- ISO 16014 series (plastics — determination of average molecular mass by size exclusion chromatography)
- ASTM D6474 (molecular weight distribution in polyolefins)
GPC Analysis Conditions
- Solvent and temperature
- According to polymer; Polyolefins are worked at high temperatures
- Calibration
- Relative calibration with narrowly dispersed reference polymers
- detector
- Refractive index; also light scattering and viscometry can be used
- Result type
- In relative calibration the values are relative to the reference polymer
Equipment for GPC Analysis
- GPC/SEC system and pump
- Size exclusion columns
- Column oven (for high-temperature applications)
- Refractive index, light scattering and viscometry detectors
- Polymer dissolution unit
Sample Requirements for GPC Analysis
- The sample must fully dissolve in a suitable solvent
- Insoluble gel and filler materials must be removed by filtration
- A few hundred milligrams of sample is generally sufficient
- The polymer type must be stated — solvent and column selection depend on it
- Cross-linked polymers cannot be analysed by this method as they do not dissolve
Duration of GPC Analysis
A run is generally 30–60 minutes. The dissolution stage can take hours for polyolefins requiring high temperature.
GPC Analysis Procedure
- 1The sample is dissolved in a suitable solvent and filtered.
- 2A curve is built with calibration reference polymers.
- 3The sample is injected onto the column.
- 4The detector signal is recorded against retention volume.
- 5The chromatogram is converted to molecular weight using the calibration curve.
- 6Number- and weight-average molecular weights and the distribution width are calculated.
GPC Analysis Acceptance Criteria
The acceptance range for molecular weight and distribution comes from the raw material specification or customer specification.
Evaluation of Results
Values obtained with relative calibration are relative to the reference polymer used and cannot be directly compared with results measured against a different reference. A light scattering detector is required for absolute molecular weight. The report must clearly state the calibration type.
GPC Analysis Report
- Sample description, receipt date and laboratory number
- Method applied and reference standard, if any
- Instrument and measurement conditions
- Sample preparation steps
- Measurement results and units
- Measurement uncertainty (if requested)
- A statement that the results relate only to the sample submitted for testing
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- Assessments under EU 10/2011 for food-contact plastics
- Raw material procurement specifications
Pages Where This Method Is Used
Analytical Methods — What Does This Group of Methods Do?
The section below describes the field that the GPC Analysis test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Analytical method pages are pages about a MEASUREMENT TECHNIQUE rather than about a test. The difference matters: "salt spray testing" is a test and answers one question; "ICP-MS" is a technique and is used in dozens of different tests. Sometimes the user is looking not for the test but for the technique — because the method name is what appears in their specification.
This distinction becomes decisive in choosing a laboratory. When a customer asks for "heavy metal analysis", the real question is by which technique it will be done: XRF is fast and non-destructive but does not distinguish compounds; AAS is economical for a single element; ICP-OES screens multiple elements; ICP-MS sees trace levels. The same sample gives results with different detection limits and different uncertainties across the four techniques.
Method selection is made against three criteria. DETECTION LIMIT: is the concentration sought within the range the method can see? MATRIX COMPATIBILITY: is the sample matrix (plastic, food, soil, metal) one the method can handle, and is pre-treatment required? SPECIFICATION LINK: does the product standard or legislation mandate a particular method? The third often overrides the first two — the specification binds the method.
Method pages build a CHAIN. A technique is linked to the test pages where it is used, to the standards those tests rest on, to the legislation those standards are tied to and ultimately to market access regimes. The example chain in the source document works like this: XRF → metal analysis → RoHS compliance → heavy metal restriction → coating pages. Whichever link the user enters from, they reach the others.
Sample preparation is the invisible half of the result in this family and is a greater source of error than the technique itself. The digestion method, degree of grinding, extraction solvent and dilution ratio change the result markedly. The same sample on the same instrument gives a different result with different preparation; the definition of the method therefore covers preparation too.
Calibration and verification are the third determining component. An instrument is calibrated with certified reference material, the calibration curve is verified periodically and a control sample is run in each batch. Without these steps, a number produced is not traceable even if the instrument is working correctly.
Method groups in this field
Elemental analysis
ICP-OES, ICP-MS, AAS and XRF. They differ in detection limit, matrix tolerance and multi-element capacity.
Chromatography
GC, GC-MS, HPLC, LC-MS/MS and ion chromatography. It separates a mixture into its components and measures each separately.
Spectroscopy
FTIR, Raman, UV-Vis and optical emission. For material identity, functional group identification and alloy composition.
Thermal analysis
DSC, TGA, DMA and dilatometry. Transition temperatures, composition, decomposition and dimensional behaviour.
Microscopy and imaging
Optical microscopy, SEM-EDS, radiography and tomography. Structure, defects and elemental distribution.
Classical (wet) chemistry
Titration, gravimetry and colorimetry. Used as a reference method and in confirming instrumental results.
Commonly confused in this field
- XRF is a screening tool; it sees elements and does not distinguish compounds. A decision on a restricted compound requires confirmation by wet chemistry.
- The phrase "not detected" is not proof of absence; it is read together with the detection limit of the method.
- The specification binds the method. A technically better method is not accepted if the specification calls for another.
- Sample preparation is part of the result; a report that does not state the preparation is not reproducible.
- Results obtained by different techniques cannot be compared directly; their detection limits and uncertainties differ.
- A method page is not a test page; which method applies to which test comes from the product standard.
Which decisions these results support
- Matching the method written in the specification to the laboratory's scope
- Method selection according to detection limit and matrix compatibility
- Confirming an instrumental result with a reference method
- Eliminating deviations arising from sample preparation
Related Tests
Frequently Asked Questions About GPC Analysis
Why are results given as 'polystyrene equivalent'?
In relative calibration, the column is calibrated according to the hydrodynamic volume of the reference polymer. A polymer of different structure can have a different molecular weight at the same volume; the result is therefore expressed relative to the reference.
Can a thermoset material be analysed?
No. GPC cannot be applied because cross-linked structures do not dissolve; thermomechanical methods such as DMA or TMA are used for these materials.