LIF instrumentation

There are numerous excitation sources available for LIF instruments. A xenon arc lamp is the most common light source within commercial LIF analyzers. While they offer uniform broad spectral coverage across the UV-vis range and sufficient uniform power output, they are low precision sources and do not offer sufficient real-time or dynamic optical power control. The white output also necessitates an excitation... 

Figure 11.44 is a schematic diagram of one LIF instrument (Stevens et al., 1994 Brune et al., 1998). An air-cooled copper-vapor laser pumps a dye laser whose output at 616 nm is doubled to generate the 308-nm exciting radiation. An OH reference cell in which OH is generated from the thermal dissociation of water... 

FIGURE 11.44 (a) Overall schematic diagram of an LIF instrument used for OH and H02 and (b) sample chamber in this instrument. (Adapted from Stevens et at., 1994.)... 

An intercomparison of the mass spectrometer method with an LIF instrument, however, was not as good. While the slope of the plot of LIF versus the MS measurements was 0.73, the r value was only 0.26, in part due to poor laser performance in the LIF instrument during the studies (Mather et al., 1997). 

Extensive intercomparisons using the radiocarbon technique have not been carried out. Campbell et al. (1995) compared measurements using the radiocarbon technique to those from an LIF instrument (Chan et al., 1990). The values obtained were frequently near the detection limits of the instruments, but despite that, were reasonably well correlated (r2 = 0.74). However, the slope of a plot of the radiocarbon versus LIF absolute concentrations was 2.9, i.e., there was a difference of about a factor of three. 

FIGURE 9.4 (a) Schematic diagram of a CCD-based wavelength-resolved CE-LIF instrument, (b) Wavelength-resolved electropherogram of a mixture of seven peptides containing tryptophan and tyrosine residues. (Adapted from Timperman, A. T., et al., Anal. Chem., 67, 3421, 1995. With permission.)... 

Lastly, the most popular detection technique for subcellular analysis is LIF due to the extremely low LODs that can be attained. Mass LODs on the order of attomoles can be achieved with commercial CE-LIF instruments and custom-built instruments, in conjunction with sheath-flow cuvettes, can reach down to the yoctomole (10 " mole) scale. LIF detection thus allows the quantification of minute amounts of analyte, and is the only detection method that has been used to detect individual organelles. We will therefore describe off-column LIF detection in further detail. 

LIF was initiated by R. Jankow in 1971 [1] it was adopted to various measurements. Until 2000, it was applied to the detector of microfluidics capillary electrophoresis by G. Jiang [2]. A confocal epifluorescence that utilized a photomultiplier tube (PMT) was firstly developed to obtain the LIF detection on a microfluidics, which also is the most popular LIF instrument for microfluidics/ nanofluidics. 

DRE Suffield is also investigating the use of CE and CE-Laser Induced Fluorescence (LIF) Detection for ultra-high sensitive analysis under field laboratory conditions. Some specific applications for highly polar, water soluble molecules, such as proteins, peptides and toxins, have been developed. DRE Suffield, in cooperation with the University of Alberta, is also developing miniaturized, silica-chip based CE instrumentation and field portable CE-LIF instruments for detection and identification of biological and chemical warfare agents. 

The high separation efficiency of capillary electrophoresis is valuable for the analysis of proteins (27) however the concentration detection limits for UV absorbance detection is limited to the micromolar range. Capillary zone electrophoresis with laser induced fluorescent detection (CE-LIF) is an attractive technology because of its ultra-low sensitivity detection limits. (28) Further sensitivity can be gained by using a state-of-the art sheath-flow cuvette flow chamber. (29) A field portable, sheath flow cuvette based CE-LIF instrument has been constructed (Figure 3) for analysis of proteins in field and portable laboratories. 

Despite some disadvantages of conventional fluorimeters (discussed by Chen and Bada, 1990), their use is described in this chapter, because the more suitable laser induced fluorescence (LIF) instruments are not as readily available. Accounts of LIF applications have been published by Chen and Bada (1990) and Donard et al. (1989). 

Kroll, J.H., Hanisco, T.F., Drarahue, N.M., Demerjian, K.L., Anderson, J.G. Accurate, direct measuremorts of OH yields frran gas-phase ozone-alkene reactions using an LIF Instrument. Geophys. Res. Lett. 28, 3863-3866 (2001)... 

Hard et al (reference 110, 125, and submitted to/. Geophys, Res. 1991) have developed a system for the chemical conversion of HO2 to HO via the reaction HO2 + NO —> HO -I- N02. The hydroxyl radical is then measured by their low-pressure laser-induced-fluorescence instrument. Their multi-sample-channel LIF PAGE system is thus capable of simultaneous measurements of [HO ] (directly) and [H02 ] (by conversion to HO ). 

Miniaturisation of scientific instruments, following on from size reduction of electronic devices, has recently been hyped up in analytical chemistry (Tables 10.19 and 10.20). Typical examples of miniaturisation in sample preparation techniques are micro liquid-liquid extraction (in-vial extraction), ambient static headspace and disc cartridge SPE, solid-phase microextraction (SPME) and stir bar sorptive extraction (SBSE). A main driving force for miniaturisation is the possibility to use MS detection. Also, standard laboratory instrumentation such as GC, HPLC [88] and MS is being miniaturised. Miniaturisation of the LC system is compulsory, because the pressure to decrease solvent usage continues. Quite obviously, compact detectors, such as ECD, LIF, UV (and preferably also MS), are welcome. 

Concentrations of OH and HO2 were determined, in situ, using Laser Induced Fluorescence (LIF) at low pressure, (FAGE technique). HO2 cannot be detected directly by LIF, and was converted to OH by titration with NO directly below the sampling nozzle. The detection limit for the FAGE instrument during SOAPEX-2, determined by calibration in the field, was 1.4 xlO5 molecule cm-3 for OH and 5.4x 105 molecule cm-3 for HO2. A description of the instrument, as set up in previous field campaigns and dur-... 

In the US market, there are two major brands of commercially available CE instruments Agilent (HP ° CE System) and Beckman (PA 800). Agilent uses a PDA detector, while the Beckman instrument uses a UV, PDA, or LIF detector. For CE-SDS, we have compared CE... 

FIGURE I CE-SDS separations of non-reduced and reduced preparations of a 5-TAMRA SE-labeled rMAb sample. Electrophoretic conditions were as follows Bio-Rad Biofocus 3000 instrument with LIF detection, effective length 19.4 cm, total length 30 cm, 50-pm ID, 375-pm OD uncoated fused-silica capillary both anode and cathode buffers were the Bio-Rad CE-SDS running buffer. The samples were injected at a constant electric field of 4l7V/cm for 20s and electrophoresed at 625 V/cm (21.2 pA) and 20 C. 

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