Polarography detectors

Polarographic detectors find application in monitoring the effluent from chromatography columns, including those used in HPLC. Applications of polarography are discussed in Refs 46-48 (Section 16.38). 

Specifications for modem detectors in HPLC are given by Hanai [538] and comprise spectroscopic detectors (UV, F, FUR, Raman, RID, ICP, AAS, AES), electrochemical detectors (polarography, coulometry, (pulsed) amperometry, conductivity), mass spectromet-ric and other devices (FID, ECD, ELSD, ESR, NMR). None of these detectors meets all the requirement criteria of Table 4.40. The four most commonly used HPLC detectors are UV (80%), electrochemical, fluorescence and refractive index detectors. As these detectors are several orders of magnitude less sensitive than their GC counterparts, sensor contamination is not so severe, and... 

A thorough discussion of electroanalytical techniques, including polarography, voltammetry, and amper-ometry, is given in Chapter 14. An understanding of these would be useful for understanding the amperometric HPLC detector. 

Detection was effected with a conductivity detector. The method was used to determine procaine in mass-produced suppositories and ointments, and in locally prepared pharmaceutical solutions. The results were found to agree with those obtained using either spectrophotometry or polarography. 

Contrary to potentiometric methods that operate under null current conditions, other electrochemical methods impose an external energy source on the sample to induce chemical reactions that would not otherwise spontaneously occur. It is thus possible to measure all sorts of ions and organic compounds that can either be reduced or oxidised electrochemically. Polarography, the best known of voltammetric methods, is still a competitive technique for certain determinations, even though it is outclassed in its present form. It is sometimes an alternative to atomic absorption methods. A second group of methods, such as coulometry, is based on constant current. Electrochemical sensors and their use as chromatographic detectors open new areas of application for this arsenal of techniques. 

Phosphorescence, 191, 223 Photoacoustic detector, 177 Photoelectric effect, 238 Photoelectron, 238 Photovoltaic, 176 Plasam, 274 Plate, 10 Polarogram, 361 Polarographic wave, 361 Polyethylene glycols, 32 Polysiloxanes, 31 POPOP, 333 PPO, 333 Precession, 129 Precision, 386 Pulse polarography, 364 Pulsed NMR, 155 Pyroelectric, 175... 

Solute property detectors measure a characteristic of the solute alone. These detectors are generally more sensitive yielding a detectable signal for nanogram quantities of solute. Representative detectors of this type include, for example, ultra-violet (UV), solute transport, fluorescence, and conductivity monitors. Other less frequently employed detectors of this nature are those based on radioactivity, polarography, and... 

The feedstocks (straight-mn naphtha (SRN) and a blend of SRN and hydrocracked naphtha) and hydrotreated products were analysed by ASTM methods for density, carbon, hydrogen, hydrocarbon and boiling point distribution. Total sulfur was determined by ASTM D-4045 method, mercaptan sulfur by the potentiometric method (ASTM D-3227 and UOP-212), disulfides by the UOP-202 method, polysulfides by polarography [1], and elemental sulfur by the UOP-286 method. The Perkin-Elmer gas chromatograph (Model 8700), equipped with a flame photometric detector (GC/FPD) and a DB-1 fused silica capillary column (30 m x 0.53 mm), was used for identification of individual sulfur compounds [2-6]. The sensitivity of the GC/FPD technique was maximized by optimizing the gas flow rates and temperature programming as presented elsewhere [1]. 

The order of presentation of the electroanalytical methods will be direct potentiometry with ion-selective electrodes, potentiometric titrations, voltammetry/polarography, polarisation titrations (amperometric and potentiometric), conductometry/coulometry and electrochemical detectors. 

The microelectrodes of voltammetry/polarography Again in FIA and in high-performance liquid chromatography (HPLC) some of these electrodes may function as detectors. 

J. Wang, E. Ouziel, C. Yamitzky and M. Ariel, A flow detector based on square-wave polarography at the dropping mercury electrode. Anal. Chim. Acta 102 (1978) 99-999. 

The aldehyde functional groups can be tested by classical wet methods. Individual aldehydes can be analyzed by various instrumental techniques such as GC, HPLC, GC/MS, colorimetry, polarography, and FTIR. Of these, GC, GC/MS, and HPLC are referred to here because of their versatility and wide application. Although an FID is commonly employed in GC, a thermal conductivity detector can also be suitable, especially for lower aliphatic aldehydes. The advantage of FID is that aqueous samples can be injected straight into the column. 

Styrene may be analyzed by GC, nsing a flame ionization detector. Air analysis may be performed by charcoal adsorption, followed by desorption of the analyte with carbon disnl-fide and injection of the elnant into GC-FID (NIOSH Method 1501 see Section 26.2). Styrene intake in the body may be estimated by analyzing mandelic acid in the nrine by liquid chromatography, polarography, or GC. However, the presence of other aromatics may interfere, as these componnds also generate the same urinary metabolite. Styrene in exhaled air may be analyzed by absorption over ethanol or charcoal followed by GC, UV, or IR analysis. 

In practice, electrochemistry not only provides a means of elemental and molecular analysis, but also can be used to acquire information about equilibria, kinetics, and reaction mechanisms from research using polarography, amperometry, conductometric analysis, and potentiometry. The analytical calculation is usually based on the determination of current or voltage or on the resistance developed in a cell under conditions such that these are dependent on the concentration of the species under study. Electrochemical measurements are easy to automate because they are electrical signals. The equipment is often far less expensive than spectroscopy instrumentation. Electrochemical techniques are also commonly used as detectors for LC, as discussed in Chapter 13. 

A variety of electroanalytical methods are used as detectors for liquid chromatography. Detectors based on conductometry, amperometry, coulometry, and polarography are commercially available. 

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