IR4 is a dual-wavelength Infrared (IR) detector, which uses the principle of infrared absorption spectroscopy to measure the concentration and chemical composition in Polyolefins.
IR4 is the workhorse detector in most Polymer Char analytical instruments and was designed to determine the concentration and chemical composition as GPC detector or when coupled to other separation techniques (CRYSTAF, TREF/CEF, …). After its introduction in the 90’s it was shown to be the most appropriate detector for high-temperature analysis of Polyolefins, given its high baseline stability and short stabilization time.
When adding a methyl or a carbonyl group sensor, other useful information can be obtained in addition to the concentration. It can be used for high-temperature GPC analysis of ethylene-propylene copolymers to determine the ethylene content and its variation along with the molar mass distribution, short-chain branching analysis in linear low-density polyethylene (LLDPE) as well as for determination of vinyl acetate content and distribution in EVA copolymers, among other applications.
Other Infrared detectors available are IR5 and IR6. Each detector has been developed with a specific application in mind: comparison of Infrared detectors (IR4, IR5, and IR6)
Robust and reliable detection in high-temperature solution techniques for polyolefin characterization: CRYSTAF, TREF/CEF, CRYSTEX, QC instruments: CRYSTEX QC, CRYSTEX 42, IVA, GPC QC.
Short stablization time after flow rate change or oven temperaure variation and outstanding baseline stability ideal for GPC application
Spurious injection peaks usually seen in DRI,
do not appear in IR. The baseline is very clean before and after the sample peak which helps in a more precise definition of baseline and integration range. Therefore, consistent values of Mw and Mn are obtained.
A methyl sensitive detection head (installed as default option in GPC-IR instruments) allows detection of short chain branching in LLDPE. Determination of average SCB or comonomer content as well as SCB variation along MMD.
IR4 is a dual-wavelength infrared detector, which uses the principle of infrared absorption spectroscopy to measure the concentration and composition in polyolefins. Thus, sensors inside are specifically designed in fixed wavelengths optimized for polyolefin analysis.
Any solvent which is transparent in the band of interest and compatible with the detector cell materials: stainless steel, sapphire, and Teflon, etc.
1,2,4-Trichlorobenzene (TCB), or ortho-dichlorobenzene are typically used, the former not being compatible with the carbonyl group detection.
Concentration and composition measurement in separation techniques like GPC, TREF, CRYSTAF or HPLC.
IR4 is the optoelectronic standard detector for most applications. It is provided with two measuring elements. The IR4 is a very robust detector for concentration measurement in GPC, TREF, CRYSTAF, etc. It also provides the possibility of measuring composition (methyls per 1000 carbons or level carbonyls, acetate, acrylate…) in copolymers.
The IR5 is the most sensitive detector by using a specially designed MCT thermoelectrically cooled sensing element. It can incorporate up to 5 wavelengths measurement and it provides superior stability and sensitivity in the GPC analysis of Polyolefins. It is being used in most demanding applications such as the analysis of very low levels of branching (methyls) in HDPE pipe resins; as well as main detector in 2-dimensional separation techniques (CFC, SGIC 2D).
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