Gas Chromatography

Polyhedron – Chromatography
Polyhedron Laboratories offers a complete array of chromatography services, including Gas Chromatography, Gas Chromatography – Mass Spectrometry, Liquid Chromatography, and Thin Layer Chromatography.

Chromatography is a family of analytical chemistry procedures for the division of mixtures. Chromatography consists of passing the specimen (sample), a mixture that includes the analyte, in what is termed the “mobile phase”, frequently in a solvent stream, through what is known as the “stationary phase.” The stationary phase slows down the transit of the components of the specimen. As component parts travel through the system at various speeds the parts become separated in terms of time, like runners in a long-distance race. Every component has a unique (or characteristic) time of travel through the system, often referred to as the “retention time.” Chromatographic separation is attained when the retention time of the analyte is different from other sample components.

Polyhedron offers liquid chromatography, specifically High Performance Liquid Chromatography (HPLC) with photo diode array detection. HPLC is a form of column chromatography used in analytical chemistry and biochemistry. Basically, an analyte is forced through a stationary phase column in a liquid (the mobile phase) at high pressure, resulting in a decrease in the time the separated parts remain on the stationary phase. The result is narrower peaks in the chromatogram, leading to better sensitivity (taller, narrower peaks are easily distinguishable from noise than broader, shorter peaks) and better resolution (again, one peak is easy to distinguish from another). Polyhedron Laboratories also provides determination of antioxidants and slip additives by ASTM D5815.

ASTM D5815-95e1 - Standard Test Method for Determination of Phenolic Antioxidants and Erucamide Slip Additives in Linear Low-Density Polyethylene Using Liquid Chromatograph (LC) - This test procedure outlines a liquid-chromatographic routine for the separation of some additives currently used in linear low-density polyethylene. These additives are extracted with either isopropanol or isobutanol prior to liquid-chromatographic separation. The ultraviolet absorbance of the compound is calculated; quantitation is done using an internal standard method.

Gas Chromatography utilizes a carrier gas, such as helium or nitrogen and a pressurized gas cylinder to carry the sample through the column. The two most common detectors used in Gas Chromatography are flame ionization and thermal conductivity detectors. Using Gas Chromatography, Polyhedron handles solvents, monomers and additives, and utilizes Head space (analysis) Gas Chromatography for residual monomers or solvents.

Gas Chromatography – Mass Spectrometry (GC-MS) is a type of chromatography that combines the features of gas chromatography and mass spectrometry to distinguish and identify various components in a test sample. GC-MS is comprised of two systems – the mass spectrometer and the gas chromatograph. The two combined components, when used together, deliver a substantially finer degree of sample (substance) identification than using each component separately. Another result of combining the two systems (and processes) is that it is highly improbable that two different particles will behave in the same manner in both a mass spectrometer and a gas chromograph. Polyhedron Laboratories performs GC-MS analysis using the AMDIS and the NIST02 mass spectra database. In addition, Polyhedron performs Pyrolysis GC-MS, Head Space GC-MS, target compound analysis, and semi-quantitative analysis by forward library searching.

In Thin Layer Chromatography (TLC), the stationary phase is comprised of a thin layer of adsorbent such as cellulose, alumina, or silica gel on a flat carrier, typically a plastic sheet, thick aluminum foil, or a glass plate. Some of the advantages of TLC include a choice of different adsorbents, better separations, and faster runs. TLC is frequently used for the qualitative analysis of reaction components and monitoring chemical reactions due to its speed and simplicity. Polyhedron Laboratories offers Adsorption and reversed phase TLC, as well as Quantitative (Iotroscan).