Fluorescence detectors studies using

Another study employed CE for the determination of the stoichiometry of the conjugation reaction between immonuglobulin and Lissamine rhodamine-B sulphonyl chloride (LRSC). The chemical structure of the dye is shown in Fig. 3.162. Separation of the unconjugated dye from the conjugated end product was performed by CE using an uncoated fused-silica capillary column (60 cm X 75 //m i.d.). The running buffer consisted of 10 rnM borate and 0.5 mM sodium dodecyl sulphate. The separation voltage was 20 kV and analytes were detected by a fluorescence detector. It was concluded from the results that the CE method combined with... 

Figure 5.11 illustrates the basic performance of the on-line MS assay. For comparison, a homogenous fluorescence assay has been set up in parallel. For this purpose, the carrier flow was split after the second microcoU reactor, with 90% of the total flow being directed to a fluorescence detector (Fig. 5.11a) and 10% to the MS (Fig. 5.11b). The affinity interaction between streptavidin and biotin was chosen to study the characteristics of an on-line MS biochemical assay. Fluorescein-biotin was used as reporter ligand for both fluorescence and MS in the SIM mode (m/z 390) detection. In the fluorescence mode, the homogeneous biochemical assay is based on the quenching of the fluorescein-biotin fluorescence upon binding to streptavidin.

The authors have evaluated different C18 and C8 columns, studying the variation in capacity factors with the proportion of water in the mobile phase for all six acid derivatives. The detector was a fluorescence detector equipped with a 360-nm excitation and a 420-nm emission filter. They were unable to resolve derivatives of the six acids on three different C18, 5-/zm columns, despite using a wide range of solvent compositions. Table 3 shows capacity factor values for three critical acid derivatives on a number of columns. When a C8,5-/un column was used with an isocratic solvent system [acetonitrile/water (98 2)], they observed a marked improvement in the resolution of the six derivatives. However, it was not possible to achieve complete resolution of the six compounds under isocratic conditions, despite numerous experiments with a range of organic solvent mixtures consisting of acetonitrile, methanol, tetrahydrofuran, and water. 

In their study on the automation of the derivatization reaction of carboxylic acids, Wolf and Korf (34) chose bromomethylmethoxycoumarin (Br-MMC) as a label because of its commercial availability. The automation of this reaction is problematic, because elevated temperatures are required in the manual procedures and the reaction had to take place in an aprotic environment. The addition of a solid salt also complicates the procedure. They describe a solution to this problem using a suspension of potassium carbonate and appropriate reagent concentrations. The samples were detected by a fluorescence detector equipped with a 5-ju.l cell, using an excitation wavelength of 325 nm and a cutoff filter of 398 nm. 

The concentrates are analysed by High Performance Liquid Chromatography (HPLC) coupled to a fluorescence detector. Elution is performed using a gradient of methanol in a phosphate buffer on a Cj g radial compression column. In order to render the amino acids amenable to fluorescence detection ( X Xgjjj = 455 nm), it is first necessary to derivatize them using orthophtaldialdehyde (O.P.A.) in the presence of mercapto-2 ethanol. Up to 20 amino acids can thus be analysed and quantified, and the complete analysis takes only 35 minutes. Table 2 presents the most commonly determined amino acids during the course of this study. 

Only a few reports are available in the literature dealing with the limits of the detection for the chiral resolution of environmental pollutants by CE, indicating mg/L to fig/L as the limits of the detection. Tsunoi et al. " carried out an extensive study on the determination of the limits of the detection for the chiral resolution of herbicides. The authors used a 230-nm wavelength for the detection and the minimum limit of the detection achieved was 4.7 X 10 M for 2,4-dichhophenoxy acetic acid. On the other hand, Mechref and El Rassi reported better detection limits, for herbicides, in the derivatized mode, in comparison to the underivatized mode. For example, the limit of the detection was enhanced by almost 1 order of magnitude from 1x10 " M (10 pmol) to 3 x 10 M (0.36 pmol). In the same study, the authors reported 2.5 X 10 M and 1 x 10 M as the limits of detection for the herbicides by fluorescence and laser-induced fluorescence detectors, respectively. 

UV and fluorescence detectors can be used for SFC. Carbon dioxide and nitrous oxide have made possible the use of conventional GC flame detectors (24). Based on studies of aliphatic fraction of a solvent refined coal product with supercritical CO2 at 40 C and conventional FID detection, it was concluded... 

There are, unfortunately, no studies to date of the dissolved protein content of microlayer samples. With the recent development of many sensitive techniques for the analysis of amino-acid mixtures in seawater using liquid chromatography and fluorescence detectors (e.g., Dawson and Pritchard, 1978), it should be relatively simple to analyse for combined amino acids after hydrolysis of the microlayer samples. Analyses of free amino acids in the microlayer seem not to have been performed to date either, but since considerable degradation of surface-adsorbed proteins may take place as a result of UV irradiation, this may be a fruitful area for future research. 

Corn-based foods followed by fumonisin B2 (FB2).The problems and risks associated with fumonisin contamination have resulted in the development of precise, reliable and sensitive methods for its determination in corn and corn-based foods (Magan Olsen, 2004, as cited in Silva et al., 2009). Therefore, the quality parameters in the analysis of FBI and FB2 in corn-based products obtained with LC with fluorescence detector have been investigated (Silva et al, 2009). Furthermore, a comparison study between fluorescence detector (FD), mass spectrometry, and tandem mass spectrometry with a triple quadrupole (QqQ) analyzer using an electrospray ionization interface for the determination of fumonisin B1 and B2 in corn-based products has been performed. A comparative study of the three LC detectors, FD, single quadrupole, QqQ for the analysis of fumonisins in corn samples has been performed. The response achieved by the three detectors was sensitive enough to study the maximum contents established by the EU legislation. These LC detectors would be appropriate for quantification purposes but the acquisition of at least two transitions achieved with QqQ provided a univocal identification. 

There are also two detector devices that are gaining popularity for fluorescence lifetime studies due to their fast time response the microchannel plate photodetectors and streak cameras. MicroChannel plate photodetectors, similar to PMTs, are based on the use of multiplication of photoelectrons. Instead of using discrete dynodes, continuous semiconductor-coated glass multiplier tubes of 10 pm diameter... 

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