Combination detector, high-performance liquid chromatography

An electrochemical detector using a static mercury drop electrode has been optimized for combination with high-performance liquid chromatography. Parameters like pump noise, oxygen in mobile phase and sample solution, nozzle, flow rate, working potential in the d.c. - and the d.p.p.- mode, have been examined. The application of the method in routine analysis has been illustrated by the analysis of the anticancer agent mitomycin C in plasma. 

GC-EAD Gas chromatography combined with an EAG detector GC-MS Gas chromatography combined with mass spectrometry HPLC High performance liquid chromatography KI Kovats retention index... 

Lanina et al. 1992 Oishi 1990). These methods include gas chromatography (GC) combined with mass spectrometry (MS) and high-performance liquid chromatography (HPLC) combined with an ultraviolet detector (UV). No comparisons can be made between methods since no data were given regarding sensitivity, recovery, or precision. 

As seen in Chapter 9.C.2, a very wide variety of organics are found in particles in ambient air and in laboratory model systems. The most common means of identification and measurement of these species is mass spectrometiy (MS), combined with either thermal separation or solvent extraction and gas chromatographic separation combined with mass spectrometry and/or flame ionization detection. For larger, low-volatility organics, high-performance liquid chromatography (HPLC) is used, combined with various detectors such as absorption, fluorescence, and mass spectrometry. For applications of HPLC to the separation, detection, and measurement of polycyclic aromatic hydrocarbons, see Wingen et al. (1998) and references therein. 

High-performance liquid chromatography (HPLC) is one of the premier analytical techniques widely used in analytical laboratories. Numerous analytical HPLC analyses have been developed for pharmaceutical, chemical, food, cosmetic, and environmental applications. The popularity of HPLC analysis can be attributed to its powerful combination of separation and quantitation capabilities. HPLC instrumentation has reached a state of maturity. The majority of vendors can provide very sophisticated and highly automated systems to meet users needs. To provide a high level of assurance that the data generated from the HPLC analysis are reliable, the performance of the HPLC system should be monitored at regular intervals. In this chapter some of the key performance attributes for a typical HPLC system (consisting of a quaternary pump, an autoinjector, a UV-Vis detector, and a temperature-controlled column compartment) are discussed [1-8]. 

Reversed-phase high-performance liquid chromatography (RP-HPLC) is the usual method of choice for the separation of anthocyanins combined with an ultraviolet-visible (UV-Vis) or diode-array detector (DAD)(Hebrero et al., 1988 Hong et ah, 1990). With reversed-phase columns the elution pattern of anthocyanins is mainly dependent on the partition coefficients between the mobile phase and the Cjg stationary phase, and on the polarity of the analytes. The mobile phase consists normally of an aqueous solvent (water/carboxylic acid) and an organic solvent (methanol or acetonitrile/carboxylic acid). Typically the amount of carboxylic acid has been up to 10%, but with the addition of a mass spectrometer as a detector, the amount of acid has been decreased to as low as 1 % with a shift from trifluoroacetic acid to formic acid to prevent quenching of the ionization process that may occur with trifluoroacetic acid. The acidic media allows for the complete displacement of the equilibrium to the fiavylium cation, resulting in better resolution and a characteristic absorbance between 515 and 540 nm. HPLC separation methods, combined with electrochemical or DAD, are effective tools for anthocyanin analysis. The weakness of these detection methods is a lack of structural information and some nonspecificity leading to misattribution of peaks, particularly with electrochemical... 

Virtually every type of high-performance liquid chromatography (HPLC) detector can be combined with SCIC refractive index, UV absorbance (direct and indirect), electrochemical, and so forth. 

The advantages of an on-line LC-MS approach are many. Both techniques show high separation power and their combination on-line is a powerful tool for identification purposes as well as quantitative studies. Many detectors are available for high-performance liquid chromatography (HPLC) ultraviolet (UV), conductivity, electrochemical, fluorescence, refractometer, and so forth. Unfortunately, most of them lack specificity, selectivity, and sensitivity. Hence, identification of unknown compounds is actually impossible. 

The IMER approach does not require that the enzyme be placed in close proximity to the detector if the transducer signal is generated by a soluble product or cosubstrate of the enzymatic reaction. In the latter case, a variety of flow systems and postreactor detectors can be utilized to produce simultaneous determinations of the concentrations of several analytes. For example, an IMER can be combined with a high-performance liquid chromatography (HPLC) instrument (perhaps also in combination with mass spectroscopy) for purposes of both qualitative and quantitative analysis. The chemo-, stereo-, and regio-selectivities of enzymes facilitate separation and/or identification of analytes that may be present as different isomers (e.g., in peptide analysis based on use of peptidase IMERs in combination with these techniques to obtain structural information about the sequence of amino acids in peptides). 

Mixtures can be identified with the help of computer software that subtracts the spectra of pure compounds from that of the sample. For complex mixtures, fractionation may be needed as part of the analysis. Commercial instruments are available that combine ftir, as a detector, with a separation technique such as gas chromatography (gc), high performance liquid chromatography (hplc), or supercritical fluid chromatography (96,97). Instruments such as gc/ftir are often termed hyphenated instruments (98). Pyrolyzer (99) and thermogravimetric analysis (tga) instrumentation can also be combined with ftir for monitoring pyrolysis and oxidation processes (100) (see Analytical methods, hyphenated instruments). 

More recently for ultratrace determination and speciation of antimony compounds the so-called hyphenated instrumental techniques have been applied which combine adequate separation devices with suitable element-specific detectors. They include high-performance liquid chromatography (HPLC) connected on-line with heated graphite furnace (HGF) AAS (HPLC-HGF-AAS), hydride-generation atomic fluorescence spectrometry (HPLC-HG-AFS) or inductively coupled plasma (ICP) mass spectrometry (MS) (HPLC-ICP-MS) capillary electrophoresis (CE) connected to inductively coupled plasma mass spectrometry (CE-ICP-MS) and gas chromatography (GC) coupled with the same detectors as with HPLC. Reliable speciation of antimony compounds is still hampered by such problems as extractability of the element, preservation of its species information, and availability of Sb standard compounds (Nash et al. 2000, Krachler etal. 2001). Variants of anodic stripping voltammetry for speciation of antimony have also been applied (Quentel and Eilella 2002). 

---