Liquid chromatography bulk property detectors

To many analysts the major limitation of electrochemical detection for liquid chromatography (LCEC) is its limited applicability to gradient elution techniques. Amperometric electrochemical detectors exhibit both the best and the worst characteristics of solute property and bulk property detectors. While the Faradaic current arises only from the solute, the non-Faradaic current arises from... 

Hyphenation refers to the online combination of a separation technique and a spectroscopic detection method that provides structural information on the analytes concerned. Liquid chromatography (LC), mass spectrometry (MS), and gas chromatography (GC) are the most popular hyphenated techniques in use today. The choice of detection is important to the overall scheme of LC make up and is contingent upon criteria such as the noise, sensitivity, and linearity. Of the two basic categories of detectors, viz., solute and bulk property detectors, UV detection belongs to the former category. 

One of the first on-line liquid chromatography detectors to be developed in the early forties was, in fact, a bulk property detector, the refractive index detector (1). Bulk property detectors continuously monitor some physical property of the column eluent and by the use of a suitable transducer provide a voltage - time output that is either proportional to the physical property being measured, or made proportional to the concentrations of the solute eluted. The properties of the mobile pheuse that are most commonly monitored in commercially available bulk property detectors are refractive index, electrical conductivity, and dielectric constant, the dielectric constant detector being the least popular of the three. 

When entering the field of liquid chromatography, the scientist is always faced with the problem of detector selection. The subject of detector choice will be dealt with later in this book but at this point, it should again be emphasized, that there is no ideal LC detector. Consequently, the practicing liquid chromatographer needs to have at least two, if not more, different types of detector available, or the full versatility of the technique will not be realized. It is therefore recommended that one of the detectors available should be a bulk property detector, which should probably be the refractive index detector. This would be a particularly appropriate detector if preparative or semi-preparative chromatography is likely to be required. If the separation and quantitative analysis of ionic materials are contemplated, then the refractive index detector might be replaced... 

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