Liquid chromatography/ultraviolet/mass sensitivity

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

In such cases, the use of liquid chromatography—tandem mass spectroscopy (LC-MS/MS) is beneficial, since LC-MS/MS provides a sensitive and reproducible measurement compared with conventional methods such as LC—ultraviolet detection or LC—fluorescence detection (Hermo et al., 2008). Furthermore, particularly in the early stages of drug development, is frequently determined by measuring the reduction in the amount of substrate, not the formation of metabolites, because of the difficulty in synthesizing enough amounts of many kinds of metabolites. In such cases, it is necessary to carry out the in vitro reaction so that substrate reduction can be accurately determined. 

LC/MS/MS. LC/MS/MS is used for separation and quantitation of the metabolites. Using multiple reaction monitoring (MRM) in the negative ion electrospray ionization (ESI) mode, LC/MS/MS gives superior specificity and sensitivity to conventional liquid chromatography/mass spectrometry (LC/MS) techniques. The improved specificity eliminates interferences typically found in LC/MS or liquid chro-matography/ultraviolet (LC/UV) analyses. Data acquisition is accomplished with a data system that provides complete instmment control of the mass spectrometer. 

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 discussed in Chapter 6, the primary method of analyzing benzene in body fluids and tissues is gas chromatography (GC) in conjunction with either mass spectrometry (MS), photoionization detection (PID), or flame ionization detection (FID). For detection of benzene metabolites, both GC/FID and high-performance liquid chromatography (FIPLC) with ultraviolet detection (UV) have been used. A recent article describes the development of simple and sensitive methods for determination of blood and urinary benzene levels using gas chromatography headspace method (Kok and Ong 1994). 

High-pressure liquid chromatography (HPLC) with fluorescence detection, ion-trap mass spectrometry (ITMS), and capillary electrophoresis (CE) with ultraviolet detection, three novel detection techniques for the analysis of cocaine in hair, have been evaluated by Tagliaro et aU°- and Traldi et al. The HPLC technique was highly sensitive, capable of detecting 0.015 ng/mg of cocaine in hair. The CE method was sensitive and highly selective. ITMS analysis of hair readily demonstrated the presence of cocaine in hair, but cocaine metabolites were more difficult to identify. 

The detector is another of the critical components of a high pressure liquid chromatograph, and in fact, the practical application of liquid chromatography had to await a good detector system. Many types of detectors are now on the market. The four most common, the ultraviolet absorption (uv), fluorescence, refractive index (RI), and electrochemical (EC) detectors, will be discussed as well as the newer light scattering mass sensitive detector. 

EDCs in the environment are often analyzed using GC or LC based instrumental techniques. GC coupled with an electron capture detector (BCD), a nitrogen-phosphorus detector (NPD), or mass spectrometry (MS) has been the preferred method due to its excellent sensitivity and separation capability on a capillary column. High performance liquid chromatography (HPLC) with various detectors such as ultraviolet detection (UV), fluorescence detection (FLD), MS, and more recently tandem MS (MS/MS) has also been used for analysis of some EDCs, especially for the polar compounds. Analytical techniques for each class of EDCs will be discussed in the following section. 

Table 21.1 classifies popular LC detectors according to several criteria for purposes of comparison. At the present time, LC detectors are generally less sensitive than GC detectors, which can detect picograms of material under good conditions. Most LC detectors provide only limited structural information. However, spectrophotometers fitted with micro flow-cells can be used to obtain a stop-flow ultraviolet-or visible-absorption spectrum of an LC peak trapped in the flow cell. On-line coupling of liquid chromatographs with mass or infrared spectrometers offers sophisticated, but indeed expensive, detection/identification methods. Such systems have been described in the literature, but are quite limited by the solvents that can be used in the chromatography step. 

Several chemical analysis methods have been developed for the determination of palytoxin and/ or palytoxin analogues, based on chemical properties characteristic and intrinsic to the toxin. Such methods include (1) infrared spectrometry, (2) ultraviolet spectrometry, (3) mass spectrometry, (4) high-performance capillary electrophoresis, (5) thin-layer chromatography, and (6) liquid chromatography. A comparative table of the most important quantitative chemical analysis methods summarizes the main features of each method and could assist in selection of the most fit-for-purpose analysis method depending on available equipment and sensitivity required (Table 29.4). 

Hyllbrant B, Tyrefors N, Markides KE, Langstrom B. On the use of liquid chromatography with radio- and ultraviolet absorbance detection coupled to mass spectrometry for improved sensitivity and selectivity in determination of specific radioactivity of radiopharmaceuticals. J Pharm Biomed Anal 1999 20 493-501. 

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