Fluorescence Detector FLD

Many publications exist in the field of food analyses. Gerda Morlock described in 2004 the determination of heterocyclic aromatic amines after a 6-step AMD-separation. She used an HPTLC-MS online extractor, developed by Luftmarm [93a]. In 2004 a patent application was made for the mode of operation of this so-called ChromeXtrakt device [93b]. In her latest paper (2006), the quantification of isopropylthioxanthon (ITX) in food using HPTLC/FLD coupled with ESI-MS and DART-MS was reported. The prepared samples were separated on a HPTLC-plate and determined by a fluorescence detector (FLD). Positive results have been verified by ESI-MS (Electrospray-Ionisation-Mass-Spectrometry) and DART-MS (Direct Analysis in Real Trme-Mass-Spectrometry) [93c]. 

Atomic emission detector (AED), electrochemical detection (ELCD), electron capture detection (ECD), evaporative light scattering detector (ELSD, including condensation nuclea-tion-CN), fluorescence detector (FLD, including laser-induced fluorescence), inductively coupled plasma-mass spectormetry (ICP-MS), mass spectrometry (MSD), MS/MS, MS(n), thermoionic detector (NPD), spectrometric detection (UV, Vis, DAD) ... 

In the introductory Section 2.1.3, it was discussed that an important aspect of optimization can be to improve a method for its applicability in trace analysis. The nature of the mode of detection is very relevant in this case whether the applied detector is concentration proportional like the very common UV detector or mass proportional hke nebulizer-based detectors, for example, evaporative light scattering detector (ELSD) or charged aerosol detector (CAD). This textbook contains dedicated chapters on nebulizer-based or aerosol detectors (Chapter 10 on trends in detection), as well as for the coupling of LC with mass spectrometry (Chapter 1). Here, the focus is on concentration proportional detectors UV detectors (VWD, DAD), fluorescence detectors (FLD), electrochemical detectors (ECD), and refractive index (RI) detectors. 

In the last twenty years, many of the developed and validated high performance liquid chromatography methods with conventional diode array or fluorescence detectors (DAD, FLD) were improved and substituted by new hyphenation with mass spectrometric instrumentation and/or NMR, especially for the analyses of raw materials derived from Natural sources. The main goal of this coupling is achieved by improvement of selectivity and sensitivity of new instrumental configurations [7], Furthermore, with these configurations it is possible to obtain, in only one analysis, the complete chemical structure elucidation, identification and quantification of targeted compounds. 

QF = quartz fiber, GF = glass fiber, PUF = polyurethane foam, FA = filter-adsorbent, FFA = filter-filter-adsorbent, DFA = denuder-filter-adsorbent, DDF = denuder-denuder-filter, DCM = dichloromethane, ACN = acetonitrile, HEX = n-hexane, GC-MS = gas chromatography-mass spectrometry, GC-ECD = gas chromatography-electron-capture detector, HPLC = high-performance liquid chromatography, FLD = fluorescence detector, SFE = supercritical fluid extraction, EA = electrostatic precipitator. 

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. 

Fig. 4. A comparison of typical fractograms for freshwater vs seawater. Cellulose membrane MUli-Q water carrier solvent HP 1100 FLD fluorescence detector (Ae dtation = 350 nm, Xemission = 450 nm) bulk natural water samples from Shark River and Florida Bay (South Florida)...

Detection systems used for LC analysis of pesticides are UV spectrometric detection (especially diode array detection - DAD - allowing peak confirmation by means of spectra comparison), fluorescence detection (FLD), electrochemical detection (ED), evaporative light scattering detection (ELSD), and MSD. Their characteristic sensitivities can be considered to vary in the following order ELSDdetection systems mentioned above, only ELS and MS are universal detectors. 

Consequently, analysis of PAHs is mainly accomplished by GC-MS in simple or tandem mode (GC-MS/MS) and HPLC coupled with fluorescence detector (HPLC-FLD) since most of the PAHs are strong fluorophores. Multiple reaction monitoring (MRM) in a triple quadrupole GC-MS/MS is inherently more selective and sensitive than either scan or selected ion monitoring (SIM) as many matrix interferences are minimized or even removed. For this reason various groups have used tandem MS (Matozzo et al. 2010 Xia et al. 2012), however sufficient detection was accomplished also with GC-MS-SIM (Webster et al. 2006). HPLC-UV has also been used with less sensitivity as expressed by LOD values, although in one work LOD values with UV detection are reported quite low (Cravo et al. 2012). PAHs as in almost all UV or FLD methods were identified on the basis of retention time and quantification on an external standard method. 

The last but not least part of an HPLC system is the detector. There are several ways to detect when a certain compound elutes from the colunm. Detection systems based on molecular absorption (UV, Visible, or DAD), fluorescence (FLD) or chemiluminescence, EC or MS are the most popular. It is worthy to highlight the high sensitivity and selectivity provided by detection systems based on fluorescence or chemiluminescence. 

FIA-FLD flow injection analysis with fluorescence detection, GC gas chromatography, MS mass spectrometry (quadrupole mass filter), BCD electron capture detector, FID flame ionisation detector, LOD limit of detection, HPLC high performance liquid chromatography, TIMS ion trap mass spectrometry... 

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