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GPC-IR® Frequently Asked Questions

We are aware that acquiring a lab instrument is an important decision, furthermore if Polyolefins’ research is related with your core business.

Although you can ask directly to our consultants whenever you want, you may prefer to know first the answers to the most typical questions about our instruments. Here are packed the most relevant questions about GPC-IR.


Questions


Answers

Which is the purpose of the GPC analysis?
The purpose of a GPC (or SEC) instrument is the analysis of the Molar Mass Distribution, which has been always considered a demanding task due to the requirement of high temperature operation for dissolution of polyolefins and multi-detection methods.

How many samples can be run at a time and how long will it take?
Up to 42 vials can be handled by the GPC-IR autosampler, and they can be dissolved and analyzed and no supervision is required. Total time will depend on the number of columns and number of injections per vial. Each injection of each vial will last the programmed analysis time (typically 40 min for a 3 columns set), so total time should be NxA, being N the total number of injections, and A the Analysis time. Only the dissolution time of the first sample should be added to this total time, as the dissolution of the injection “i” will be carried out while the sample “i-1” is being analyzed.

How many grams of sample do I need for a GPC analysis?
16mg are used as standard for preparing a 2mg/mL solution in the autosampler vial.

Which solvents can be used?
1.2.4-Trichlorobenzene (TCB) and Orto-Dichlorobenzene (oDCB) are the most used solvents. Perchloroethylene could be used too. To use other solvents please consult Polymer Char first.

Is it for high or for room temperature?
GPC-IR instrument is focused on high temperature applications (column oven maximum temperature: 250ºC, solvent and columns dependant) but it can be used at room temperature as well.

What kind of sample preparation is required by the user?
No samples preparation is required by the user but weighing the dry samples and putting them inside of the disposable glass vials. The rest of the steps are performed by the instrument automatically: solvent filling into the vials, dissolution, filtration, injection, etc.

Can I use different dissolution times for each vial within the same run?
Different dissolution times can be selected from the GPC-IR Software for each vial in the run-queue within the same run; therefore, samples with different preparation requirements can be analyzed at once.

Do I need to handle solvents?
Solvents don’t need to be handled at any time; the whole process is fully automated and the instrument performs all the needed steps: vials filling, dissolution, filtration, injection, etc.; under software control.

Do I need to prefilter the samples out of the instrument?
When using a GPC-IR instrument, no pre-filtration step is required thanks to an in-line filter integrated in the instrument, connected in the high temperature zone before the injection valve. After each sample, this filter is automatically cleaned in backflush to become ready and clean again for the next injection.

Do I need to transfer vials?
There is no solvents handling or vials transfer at any moment. Vials used throughout the whole process are the same: glass disposable 10 ml vials. Therefore there is no solvents handling or vials transfer at any moment.

Which kind of samples can be analyzed?
GPC-IR is specially designed for the difficult task of Polyolefin analysis at high temperature with chlorinated solvents. The instrument with the standard IR detector can be used to analyze all polymers soluble in chlorinated solvents (TCB, o-DCB, perchloroethylene) which have C-H bonds in the backbone. When adapting an external Refractive Index or an ELSD detector it can be used with all type of synthetic polymers.

Which detector is used for the concentration measurement?
Concentration in Polymer Char Instruments is measured by an Infrared Detector integrated. For GPC-IR instrument, both IR4 and also IR5 MCT can be used, measuring not only concentration, but also composition.

Can I couple additional detectors to GPC-IR?
Additional detectors can be easily connected to GPC-IR instrument, like a capillary viscometer, a Light Scattering (DAWN® HELEOS™ II 8 or 18 angles of Wyatt Technology), external Refractive Index or ELSD detectors.

Can I perform multiple injections per vial?
GPC-IR injection system has been designed in an innovative way allowing up to 3 injections per vial with no dilution of the sample concentration. Therefore, the reproducibility among the injections is outstanding.

Where are the columns located?
Columns are isolated into a dedicated and high precision oven, to better protect them from suffering any temperature changes during maintenance tasks.

Do I need to cool down the columns if I want to perform any maintenance task in the instrument?
The columns can be kept at high temperature continuously even when performing maintenance tasks in the detectors, filters or injection loop since they are located in a dedicated oven, where temperature can be operated independently from the detectors/injector oven.

How can I access and review my results?
After each injection, data can already be accessed and processed through the GPC-IR Software database. Polymer Char’s GPC One is currently the most comprehensive GPC Calculations Software package, developed in collaboration with the leaders in the industry, as it integrates all detectors signals and has the possibility of being customized to include in-house data-processing procedures. A reporting tool has also been developed, generating reports in Excel adapted to each user needs.

Can I get SCB and LCB results?
Yes, GPC-IR is equipped as standard with an IR4 infrared detector having a methyl group sensitive sensor for short chain branching quantification across the molar mass distribution. Optionally the high sensitivity IR5 MCT detector can be coupled when low levels of SCB need to be detected.

LCB results can be obtained by just using the standard capillary viscometer by comparison of the branched sample intrinsic viscosity with that of a linear reference at every molar mass slice. Nevertheless, more accurate results are produced when using both light scattering and viscometer detectors. SCB information is very useful to correct LCB calculations.

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