Conductivity Detector



High Pressure Liquid Chromatography (HPLC) can use a variety of detectors, including the variable wavelength, ultra violet (UV), visible spectrum (Vis), fluorescence, refractive index, evaporative light scattering, and the conductivity detector. Note that ultra violet and visible spectrum are often combined into one detector that is termed UV/Vis. However, it was a long journey from the early observations that led to HPLC as a standard tool in the analytical laboratory.



The process of separating compounds by mechanical and chemical forces as a dissolved solute is passed through a column of particles was actually first observed in the early part of the 18th century (1903 to be exact) by Russian botanist Mikhail Tswett, who separated leaf pigments by passing them through columns of calcium carbonate or alumina. His observation heralded a new area in sample preparation and later work would revolutionize chemistry and its practical application in the isolation and purification of compounds based on particle charges, particle size, and hydrophobicity.

Tswett's work was expounded upon and gel liquid chromatography which separated compounds based on particle size, as well as hydrophbicity LC, which separated them by attraction and repulsion to water, apparently were not in uncommon use by the 1950s. In 1975, Small, Stevens and Bauman introduced ion chromatography as a new method. Detectors to accurately assess the concentration of solvated components as they were eluted through the column were improved to provide greater sensitivity, and were applied to the ion methods of Small, etal.

While measuring the adsorbtion of light in the UV and visible spectrum became one of the more common techniques for analyte detection, detectors that measure light adsorbtion are are generally not as suitable for measuring analytes when dealing with ion-exchange chromatography. In this particular type of separation, one usually uses the reverse-phase process (about 70% of the time), the column media is conditioned with an acid or base just prior to passing the the solute though. Once the media has been conditioned, the solute can be passed through, retaining the compound of interest (as anions or cations), which is then recovered by eluting with a solvent that will alter the ionization and free the compound.

The company "Waters" makes a line of extraction products called OASIS SPE (solid phase extraction), with various polymeric reverse-phase sorbents, according to characteristics of the compound that needs to be separated. These cartridges, which look similar to a thick plastic syringe, include a prefilter that keeps larger containment particles out of the sorbent media. The cartridges are available with a variety of sorbates offered under different product lines, according to the characteristics of the analyte of interest; OASIS HLB, OASIS MCX, OASIS MAX, OASIS WCX, and OASIS WAX.