Stationary phases[ edit ] In the s, most liquid chromatography was performed using a solid support stationary phase also called a column containing unmodified silica or alumina resins.
Thin-layer Chromatography High-performance liquid chromatography HPLC also know as high-pressure liquid chromatography is an instrumental system based on chromatography that is widely used in forensic science.
HPLC is used in drug analysis, toxicology, explosives analysis, ink analysis, fibers, and plastics to name a few forensic applications. Like all chromatography, HPLC is based on selective partitioning of the molecules of interest between two different phases. Here, the mobile phase is a solvent or solvent mix that flows under high pressure over beads coated with the solid stationary phase.
While traveling through the column, molecules in the sample partition selectively between the mobile phase and the stationary phase. Those that interact more with the stationary phase will 5 05 chromatography behind those molecules that partition preferentially with the mobile phase.
As a result, the sample introduced at the front of the column will emerge in separate bands called peakswith the bands emerging first being the components that interacted least with the stationary phase and as a result moved quicker 5 05 chromatography the column.
The components that emerge last will be the ones that interacted most with the stationary phase and thus moved the slowest through the column.
A detector is placed at the end of the column to identify the components that elute.
Occasionally, the eluting solvent is collected at specific times correlating to specific components. This provides a pure or nearly pure sample of the component of interest. This technique is sometimes referred to as preparative chromatography. Many different types of detectors are available for HPLC.
The simplest and least expensive is the refractive index detector RI. Although this detector is a universal detector, meaning it will respond to any compound that elutes, it does not respond well to very low concentrations and as a result is not widely used.
In many ways, the ideal detector for HPLC is a mass spectrometer MSwhich provides both quantitative information and in most cases a definitive identification of each component qualitative information. Other detectors that are sometimes used include fluorescence detectors which are very sensitive and electrochemical detectors.
Unlike in gas chromatography GC in which the mobile phase is an inert gas, the mobile phase in HPLC can be one of many different solvents or combinations of solvents. Because the sample does not have to be converted to the gas phase, compounds such as explosives that break down at high temperatures are much more amenable to HPLC than GC.
For HPLC, all that is required is that the sample be soluble in the solvents selected for the analysis.
In addition, there are several types of HPLC defined by the type of mobile phase and stationary phase that is used. Water, methanol methyl alcoholethanol ethyl alcoholand acetone are examples of polar solvents. The stationary phase in reverse phase HPLC is a nonpolar material such as a long chain hydrocarbon molecule.
In this type of HPLC, components in the sample will partition and separate based on their degree of interaction with the stationary phase relative to the mobile phase. In other words, the separation is based primarily on the relative polarity of the sample molecules.
Normal phase HPLC uses a polar stationary phase and a nonpolar mobile phase, but this is not widely used in forensic applications. Size exclusion chromatography SEC is more common and separates compounds based on relative sizes.
The stationary phase in SEC is composed of a gel with different sizes of microscopic pores through it. The larger the molecule, the longer it takes for it to navigate through the pores and reach the detector.
SEC is useful for the analysis of large molecules that come in a range of sizes such as plastic polymers, proteins, and nitrocellulose, a component of GSR. Chiral chromatography, a relatively recent development, is making inroads into forensic science since it is capable of separating enantiomers, molecules that are mirror images of each other.
This capability is particularly valuable in forensic toxicology and drug analysis. Finally, ion exchange chromatography is available for detection species such as nitrate NO,3- and other ions.Phenomenex Zebron™ GC columns and consumables offer performance nothing short of extraordinary, with exceptional inertness, long lifetimes, and versatile selectivities.
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Background Information and Research: 1 - Ink Chromatography introduction. Paper chromatography type of method that is used to separate mixtures of substances from a solution. 2. There are many uses for paper chromatography, especially concerning the fields of chemistry and biology. One use is to allow scientists to detect any sort of . Page 1 of 2. Lab Title Background Information and Research 1. Give a simple explanation, in your own words, of what paper chromatography is and. 1) Paper chromatography is a technique that is used to determine and separate parts of a mixture in order for identification. Paper chromatography is used to identify chemicals such as inks and dyes. Mixtures and solutions.
Find MSDS or SDS, a COA, data sheets and more information. Reversed-phase chromatography (also called RPC, reverse-phase chromatography, or hydrophobic chromatography) includes any chromatographic method that uses a hydrophobic stationary phase.
RPC refers to liquid (rather than gas) chromatography.