Capillary electrophoresis isotope separation

Zhao, J. and Jorgenson, J. W., Application of synchronous cyclic capillary electrophoresis Isotopic and chiral separations. Journal of Microcolumn Separations 1999,11, 439-449. 

Zhao 1, lorgenson IW (1999) Application of synchronous cyclic capillary electrophoresis isotopic and chiral separations. 1 Microcolumn Sep 11 439-449... 

The separation of isotopes can be used to show the efficiency of separation by capillary electrophoresis. Moreover, the interfacing of a mass spectrometer to the capillary can be used for the study of biological substances (cf. Fig. 16.7). 

Figure 26-31 Separation of natural isotopes of 0.56 mM Cl by capillary electrophoresis with indirect spectrophotometrlc detection at 254 nm. Background electrolyte contains 5 mM CrOJ to provide absorbance at 254 nm and 2 mM borate buffer, pH 9.2. The capillary had a diameter of 75 m, a total length of 47 cm (length to detector = 40 cm), and an applied voltage of 20 kV. The difference in electrophoretic mobility of 36C and 37CI is just 0.12%. Conditions were adjusted so that electroosmotlc flow was nearly equal to and opposite electrophoretic flow. The resulting near-zero net velocity gave the two isotopes maximum time to be separated by their slightly different mobilties. [From C. A Lucy and T. L McDonald, "Separation of Chloride Isotopes by Capillary 35 40 45 Electrophoresis Based on the Isotope Effect on Ion Mobility"Anal.

The optimum pH for separating cations is pK + 0.30 K. K.-C. Yeung and C. A. Lucy, Isotopic Separation of [14N]- and fI5N] Aniline by Capillary Electrophoresis Using Surfactant-Controlled Reversed Electroosmotic Flow, Anal. Chem 1998, 70. 3286. 

EDTA was determined in human plasma and urine by capillary electrophoresis/MS [85]. Using a BC stable labile isotope, the detection and quantitation limits were found to be 7.3 and 14.6 ng/mL, respectively. The running buffer was pH 3.5 ammonium formate/formic acid buffer, at an inlet pressure 50 mb and a separation potential of -30 KV. The same authors [86] utilized this technique for the determination of EDTA as the nickel chelate in environmental water. 

In past years, on line chromatographic coupling techniques such as HPLC and CE coupled to ICP-MS with the isotope dilution technique have been used for element quantification in speciation analysis. An interesting application of the isotope dilution technique in medical research was proposed recently by Prange and co-workers, who added highly enriched " S, Cu, Zn and Cd spikes to the interface of the CE-ICP-MS system. The authors separated isoforms of metallothionein (e.g., of rabbit liver) by capillary electrophoresis and quantified S, Cd, Cu and Zn concentrations in isoforms by ICP-SFMS using the isotope dilution technique. A new selenized yeast reference material (SELM-1) for methionine, selenomethionine (SeMet) and total selenium content has also certified by an intercomparison exercise. ... 

C. A. Lucy and T. L. McDonald, Separation of chloride isotopes by capillary electrophoresis based on the isotope effect on ion mobility, Anal. Chem., 67,1074,1995. 

Yeung, K. K. C. and Lucy, C. A., Ultrahigh-resolution capillary electrophoretic separation with indirect ultraviolet detection Isotopic separation of [14N]-and [15N]ammonium. Electrophoresis 1999, 20, 2554-2559. 

Protein quantitation by MS makes it possible to use in-line liquid-phase separation methods such as multidimensional chromatography and capillary electrophoresis. Quantitation can be carried out by comparing peptide ion currents but this is inherently inaccurate and is biased by instrument design. Instead, quantitation is often based on the use of stable isotopes. The general approach is to label alternative samples with equivalent reagents, one of which contains a heavy isotope and one of which contains a light isotope. The samples are mixed, separated into fractions, and analyzed by MS. The ratio of the two isotopic variants can be determined from the heights... 

Hyphenated techniques are the analytical methods most frequently used today for elemental speciation. For that purpose, a separation technique, such as high-performance liquid chromatography (HPLC), gas chromatography (GC), capillary electrophoresis (CE), or gel electrophoresis (GE), is coupled on-line with an elemental detection method, such as ICP-MS [67]. Hyphenated ICP-MS techniques can also be combined with the isotope dilution method for quantification of elemental species. Two different spiking modes are possible, the species-specific and spedes-unspedfic mode. Rottmann and Heumann were the first to present a setup for H PLC-ICP-IDMS enabling the use of these two spiking modes [68] (Figure 8.14). 

Prange et al. analyzed the isoforms of metallothioneins in human brain cytosol with capillary electrophoresis (CE) coupled to ICP-SFMS (inductively coupled plasma-sector field mass spectrometry). In the study, three metal-lothionein isoforms were separated by CE, and the enriched isotopes of Cu, Zn, Cd, and were mixed as a specific-unspecific spiking solution finally, the Cu, Zn, Cd, and S in metallothioneins were quantified with IDA. They found that the levels of MT-3 and MT-1 were lower in the brain samples from the patients with Alzheimer s disease in comparison with the controls (see Figure 4.8). The results indicated that quantification of metalloproteins gave additional information on its relationship with Alzheimer s disease. ... 

Synchronous cyclic capillary electrophoresis (SCCE) was proposed by Jorgenson s group as a technique which allows overcoming the dispersion problems in FCCE caused by the parabolic counterflow profile [31], High resolution is achieved in SCCE by driving the samples in a virtually closed loop until desired resolutions are achieved. This technique was applied for isotopic and chiral separations. In the third cycle, the chiral compound (a-hydroxybenzyl) methyltrimethylammonium with a selectivity as low as 1.0078 was almost baseline separated in 3.5 h [40]. As mentioned by the authors, similar separations with a multicycle LC system as described in [41] would also be possible but would have taken 43 h. 

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