Introduction
Infrared spectroscopy can be used as an analytical measurement technique to identify the molecular constituents (chemical groups) of an extremely wide range of solid, liquid and gaseous sample types.
Certain plastics and polymer type samples in a raw, bead or pellet shaped form can be classified as irregular shaped, hard solid samples. Due to their physical nature small quantities of these sample types cannot be ground with KBr powder to form a homogenous mix of the sample suspended in the KBr matrix for infra red spectral analysis using a transmission technique. Traditionally a plastic or polymer sample type can be melted and then compressed into the formation of a uniform thickness of film (circa 50 microns in depth) that allows for infra red spectral collection via transmission spectroscopy. However, a plastic or polymer sample type can be analysed “as is” using the ATR spectroscopic technique for collection of a representative IR spectrum. This obviates the need for a timely sample preparation method for a thin film production for a transmission spectral measurement, if the reflection technique for qualitative and quantitative analysis of the sample is sufficient.
Application
ATR measurement of an irregular shaped, hard solid sample in order to try and obtain as wide a spectral transmission range of light frequency collection for the sample as possible.
Equipment and Method
For the ATR measurement of a plastic or polymer bead material to obtain a full spectral range for the sample between 4000cm-1 and 400cm-1, the Quest ATR Accessory P/N GS10801-B was used with the single reflection diamond extended range ATR crystal puck option on the black surface coloured optical unit. Both the stainless steel flat and pellet anvil options from the anvil arm assembly were used for an appropriate sample type to cover over the sample when in contact with ATR crystal for correct and consistent positioning. The spectra were collected on a Thermo Nicolet iS5 instrument using the standard room temperature detector system set at a resolution of 4cm-1 for 16 scans.The following plastic and polymer bead samples studied were:-
PET (Polyethylene Terephthalate) 100% as small, hard, short rod type fragments.
Blue Coloured Plastic Pen Cap (Polypropylene) as small, hard, shards of material.
Grey Plastic Construction Brick (Acrylonitrile Butadiene Styrene) as small, hardish fragments.
PVA (Polyvinylacetate) as softish beads.
PolyB (Polyethylene) as hard beads. For preparation of each sample for the ATR spectral measurement, a particular example of the sample was taken “as is” and placed over the diamond ATR crystal of the Quest ATR puck option. A new example of the same sample was repeated for a couple of further spectral collections to check for consistency of result. A set load from either the flat or pellet anvil option from the anvil arm assembly was used to cover over the sample when in contact with the ATR crystal for correct positioning of the sample and application of a constant and reproducible force to obtain an acceptable IR ATR spectrum.
The sample was then ready for spectral data collection.
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