Sample introduction capillary electrophoresis

Guttman, A. and Schwartz, H. E., Artifacts related to sample introduction in capillary gel electrophoresis affecting separation performance and quantitation, Anal. Chem., 34, 2279, 1995. 

Fang, Q., Wang, F.-R., Wang, S.-L., Liu, S.-S., Xu, S.-K., and Fang, Z.-L., Sequential injection sample introduction microfluidic-chip based capillary electrophoresis system, Anal. Chim. Acta, 390, 27, 1999. 

Chen, G. and J. Wang. Fast and simple sample introduction for capillary electrophoresis microsystems. Analyst 129, 507-511 (2004). 

The capillary column has to be pre-conditioned with buffer solution for 6 min. The sample introduction is carried out by pressurised injection of water, sample and buffer in the capillary column each at 5 kPa for 5 s subsequently. Electrophoresis is performed for 8 min at 500 V/cm at 35°C in the running buffer solution. UV detector is set to 195 nm for analysis. Then the column is washed subsequently for 3 min with 0.1 M sodium hydroxide, 4% phosphoric acid containing 20% acetonitrile and 20% acetonitrile in water. 

Determination of inorganic anions by capillary electrophoresis is critically compared with ion chromatographic determinations on the basis of recent literature in the field. After a very brief summary of the theoretical background, the selection and optimization of the running electrolyte system are discussed, especially in connection with modification of the electroosmotic flow. Preconcentration techniques are surveyed, as are the approaches to the sample introduction and analyte detection. The principal analytical parameters of the determinations are evaluated and illustrated on selected applications described in the literature. 1997 Elsevier Science B.V. 

Fang, Q., Xu, G.-M., Fang, Z.-L., High throughput continuous sample introduction interfacing for microfluidic chip-based capillary electrophoresis systems. Micro Total Analysis Systems, Proceedings 5th XTAS Symposium, Monterey, CA, Oct. 21-25, 2001, 373-374. 

Fig. 13. Rapid capillary electrophoresis (CE) microchip measurements of TNT obtained by direct sample introduction into the separation channel 80 alternate injections of (a) 10 and (b) 5ppm TNT solutions. Reproduced with permission from Chen and Wang [34],...

Other mass spectral techniques that use LC and capillary electrophoresis (CE) as the sample introduction method make it possible to analyze chemicals that should otherwise be derivatized for GC analysis, and also those nonvolatile and nonderiva-tizable chemicals that cannot be analyzed at all with GC. Many of these chemicals could be analyzed with FUR without GC separation, but in the environment, they may be in, for example, water or soil samples (which possibly have to be extracted with water). Water samples are difficult to analyze with FTIR since water is quite a poor solvent for FTIR due to very high molar absorptivity. 

Using these criteria as yardsticks, the first edition has been a success. It is now obsolete, however Because of the increases in both number and types of activities assayed, it is no longer an accurate catalog of enzymatic activities investigated by means of the HPLC method. For this work to continue to serve as a reference source, it would need updating. While it was the obsolescence of the first edition that in part prompted the development of a second edition, there were other considerations as well. These included the introduction of high performance capillary electrophoresis (HPCE) as a method for separation, the development of microdialysis as a method for collection of samples... 

While some techniques require the absence of electroosmotic flow during the separation itself (capillary gel electrophoresis and capillary isoelectric focusing), most common techniques exploit electroosmotic flow for sample introduction and detection. Electrophoresis in buffer-filled capillaries uses electroosmotic flow in an analogous manner to a chromatographic mobile phase the flow is used to transport analyte from cathode to anode and separation occurs continuously between introduction and detection. 

Two introduction methods are commonly employed in capillary electrophoresis. Hydrodynamic injection is based on siphoning, or gravity feeding the sample into the anodic end of the capillary. The anodic end is removed from the buffer reservoir and placed in the sample solution. The capillary end is then raised so that the liquid level in the sample vial is at a height Ah above the level of the cathodic buffer, and is held in this position for a fixed time t. This process has been automated for reproducibility, and the hydrodynamic flow rate has been shown to obey Eq. 12.9 ... 

As shown in Figure 33-6, the instrumentation for capillary electrophoresis is simple. A buffer-filled fused-silica capillary, typically 10 to 100 xm in internal diameter and 40 to 100 cm long, extends between two buffer reservoirs that also hold platinum electrodes. Sample introduction is performed at one end and detection at the other. A potential of 5 to 30 kV dc is applied across the two electrodes. The polarity of this high voltage can be as indicated in Figure 33-6 or can be reversed to allow rapid separation of anions. 

Smith, E. M., Xu, H., and Ewing, A. G. DNA separations in microfabricated partitioned channels with automated capillary sample introduction. Electrophoresis 22 363—370, 2001. 

The liquid volume of a sample required for analysis depends on the ionization technique, MALDI or ESI, and the introduction technique (see Table 4.1). The following statements assume that we are analyzing a sample near the detection limit of the analyte in a specific mass spectrometer. For MALDI-MS, the researcher typically spots 0.1 to 1 jL onto the MALDI sample plate. Thus, a minimum starting volume of 1 of 5 jL of sample is recommended. For ESI, the required sample volume is primarily dependent on the sample introduction technique. If the researcher uses a nanoflow electrospray technique, capillary EC, or capillary electrophoresis, then typically a l-pL voliune is required. However, larger sample volumes are recommended for ease of handhng. If the voliune is small, then the analysis may be limited to one experiment when additional MS or MS-MS experiments are desired. For higher flow rate ESI sources, the researcher should supply 50 pL or more for direct infusion experiments or for loading 5 to 20 pL onto an analytical EC column. 

Identification of components in environmental samples and in samples from laboratory studies of biodegradation and biotransformation is generally based on the application of MS coupled to either GC or LC systems. For environmental samples which may contain only small amounts of the relevant compounds, MS is particularly attractive in view of the extremely small amounts of samples — of the order of nanograms — which are required. An important additional advantage is that since the mass spectrometer can be interfaced with GC, LC, or capillary electrophoresis (CE) systems which incorporate separation procedures, pure samples are not required. Some salient issues in MS in the context of environmental application are summarized briefly as an introduction. Reference should be made to an exhaustive review (Burlingame et al. 1998) for instrumental details and aspects that are not covered here, such as MS of synthetic and natural polymers. 

Device for the introduction of sample into the machine. A sample may be injected into the spectrometer depending on the nature of the sample and the method of ionization. A sample is placed into the source of ionization in the spectrometer. It is usually introduced on a probe or a platform or via a capillary tube directly after the HPLC or capillary electrophoresis of proteins or peptides. A sample is always introduced through a lock system to maintain the high vacuum in the machine without any interruption. 

Huang, X.)., Pu, Q. S., Fang, Z. L., Capillary electrophoresis system with flow injection sample introduction and chemiluminescence detection on a chip platform. The Analyst 2001,126(3), 281-284. 

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