Band broadening caused by the multiple labeling of proteins in micellar electrokinetic chromatography with diode laser-induced fluorescence detection

Chemical and Instrumental Approaches for Capillary Electrophoresis (CE)-Fluorescence Analysis of Proteins

Capillary electrophoresis (CE) coupled to fluorescence detection is an invaluable technique for the quantitative analysis of proteins of interest in the field of clinical diagnosis and quality control of novel biotechnology products. The various chemical and instrumental approaches that have been reported to carry out such sensitive analysis are described in this paper. To illustrate the contribution of CE to the analysis of therapeutic proteins, a detailed protocol for impurities profiling of a recombinant antibody sample using CE-LEDIF is given.

Quantitative determination of methylene blue in environmental samples by solid-phase extraction and ultra-performance liquid chromatography-tandem mass spectrometry: a green approach

Industrial effluents with dyes may have appreciably high chemical oxygen demand and suspended solids, posing adverse effects to both humans and aquatic life; therefore, quantitative monitoring of these effluents is essential.

MEKC as a powerful growing analytical technique

This review summarizes the principle and the developments in MEKC in terms of separation power, sensitivity, and detection approaches more than 25 years after its appearance. Newly used surfactants are mentioned. Classical and new sample concentration techniques in MEKC are described. The different detection approaches in MEKC with advantages, limitations, and future prospects are also discussed. This review highlights the wider application of MEKC in different analytical fields. Various recent selected applications of this technique in different analytical fields are reported.

224nm deep-UV laser for native fluorescence, a new opportunity for biomolecules detection

A new highly sensitive and compact 224 nm laser-induced native fluorescence (LINF) detector was developed using a new generation of deep-UV laser and an innovating elliptical flow cell. The use of deep-UV excitation at 224 nm allows to achieve fluorescence detection of an important range of molecules containing a single aromatic ring. The LINF detector was first evaluated in liquid chromatography. An improvement of a factor 500 over a conventional fluorimeter is reached with a limit of detection (LOD) of 1.5 pmole for ibuprofen. LODs were in the nanomole range for phenylalanine and in the picomole range for tyrosine and tryptophan. The LINF detector is able to detect the same levels of peptides concentrations as an ESI-ion trap spectrometer used in scan mode. In this application, LINF outperforms the UV detection at 214 or 254 nm and could be used with different additives with no noticeable effect on the detection.

Quantification of polyamines in human erythrocytes using a new near-infrared cyanine 1-(ε-succinimidyl-hexanoate)- 1′-methyl-3,3,3′,3′-tetramethyl- indocarbocyanine-5,5′-disulfonate potassium with CE-LIF detection

A novel near-infrared (NIR) cyanine 1-(epsilon-succinimidyl-hexanoate)-1'-methyl-3,3,3',3'-tetramethyl-indocarbocyanine-5,5'-disulfonate potassium (MeCy5-OSu) has been developed in our laboratory. Simultaneous determination of MeCy5-OSu-derivatized polyamines spermine (Spm), spermidine (Spd), cadaverine (Cad), and putrescine (Put) based on the separation by CE combined with diode LIF detection has been accomplished. The highest derivatization efficiency was achieved in 0.2 mol/L borate buffer (pH 8.8) for 20 min at 25 degrees C. Polyamine derivatives were separated within 14 min in the phosphate running buffer (pH 3) containing 50 mmol/L phosphoric acid, 40 mmol/L SDS, and 35% methanol v/v. Linearity of response was obtained in the range of 10-200 nmol/L. The detection limits (S/N = 3) for Spm, Spd, Cad, and Put were 0.8, 1, 3, and 2 nmol/L, respectively. The proposed method has been successfully applied to the analysis of polyamines in erythrocytes of two healthy persons and one cancer patient. Average recoveries for erythrocyte samples were 93.6-106% and coefficients of variation ranged from 1.8 to 5.4%. The analysis of polyamines in erythrocytes can be used for studying the relationship between their changes and the carcinogenesis process involved in erythrocytes.

MEKC: An update focusing on practical aspects

This paper reviews recent methodological and instrumental advances in MEKC. Improvements in sensitivity arising from the use of on-line sample concentration (sweeping, stacking, and combination of both protocols) and derivatization (in-capillary reactions and coupling with flow-injection systems) and improvements in resolution obtained by changing the composition of the BGE (e.g., with organic modifiers, ionic liquids, nonionic and zwitterionic surfactants, mixed micelles, and vesicles) or using coated capillaries are discussed in detail. In addition, MS and LIF spectroscopy are examined in relation to their advantages and restrictions as applied to MEKC analysis. Some thoughts on potential future directions are also expressed.

Capillary-assembled microchip as an on-line deproteinization device for capillary electrophoresis

A capillary-assembled microchip (CAs-CHIP), prepared by simply embedding square capillaries in a lattice polydimethylsiloxane (PDMS) channel plate with the same channel dimensions as the outer dimensions of the square capillaries, has been used as a diffusion-based pretreatment attachment in capillary electrophoresis (CE). Because the CAs-CHIPs employ square-section channels, diffusion-based separation of small molecules from sample solutions containing proteins is possible by using the multilayer flow formed in the square section channel. When a solution containing high-molecular-weight and low-molecular-weight species makes contact with a buffer solution, the low-molecular-weight species, which have larger diffusion coefficients than the high-molecular-weight species, can be collected in a buffer-solution phase. The collected solution containing the low-molecular-weight species is introduced into the separation capillary to be analyzed by CE. This type of system can be used for CE analysis in which pretreatment is required to remove proteins. In this work a fluorescently labeled protein and rhodamine-based molecules were chosen as model species and a feasibility study was performed.

Micellar electrokinetic chromatography of fluorescently labeled proteins on poly(dimethylsiloxane)-based microchips

MEKC of standard proteins was investigated on PDMS microfluidic devices. Standard proteins were labeled with AlexaFluor(R) 488 carboxylic acid tetrafluorophenyl ester and filtered through a size-exclusion column to remove any small peptides and unreacted label. High-efficiency MEKC separations of these standard proteins were performed using a buffer consisting of 10 mM sodium tetraborate, 25 mM SDS, and 20% v/v ACN. A separation of BSA using this buffer in a 3.0 cm long channel generated a peak with a plate height of 0.38 microm in <20 s. Additional fast separations of myoglobin, alpha-lactalbumin, lysozyme, and cytochrome c also yielded peaks with plate heights ranging from 0.54 to 0.72 microm. All proteins migrated with respect to their individual pIs. To improve the separations, we used a PDMS serpentine chip with tapered turns and a separation distance of 25 cm. The number of plates generated increased linearly with increasing separation distance on the extended separation channel chips; however, the resolution reached an asymptotic value after about 7 cm. This limited the peak capacity of the separation technique to 10-12.

Rapid and sensitive determination of phosphorus-containing amino acid herbicides in soil samples by capillary zone electrophoresis with diode laser-induced fluorescence detection

A straightforward and sensitive method has been developed for the analysis of phosphorus-containing amino acid herbicides (glufosinate and aminomethylphosphonic acid, the major metabolite of glyphosate) in soil samples. For this purpose, the analytical features of two indocyanine fluorescent dyes, sulfoindocyanine succinimidyl ester (Cy5) and 1-ethyl-1-[5-(N-succinimidyl-oxycarbonyl)pentyl]-3,3,3,3-tetramethyl-indodicarbocyanine chloride, as labeling reagents for the determination of these herbicides by CZE with diode LIF detection were investigated. Practical aspects related to the labeling chemistry and CZE separation showed that the two probes behave similarly, Cy5 being the best choice for the determination of these herbicides on account of its higher sensitivity. The optimum procedure includes a derivatization step of the pesticides at 25 degrees C for 30 min and direct injection to CZE analysis, which is conducted within about 14 min using ACN in the running buffer. The lowest detectable analyte concentration ranged from 0.025 to 0.18 microg/L with a precision of 3.6-5.4%. These results indicate that indocyanine fluorescence dyes are useful as rapid and sensitive labels for the determination of these herbicides when compared with typical fluorescein dyes such as FITC and 5-(4,6-dichloro-s-triazin-2-ylamino) fluorescein, because they provide faster labeling reactions even at room temperature and the excess of reagent practically does not interfere the determination. Finally, the Cy5 method was successfully applied to soil samples without a preliminary clean-up procedure, and the herbicides were measured without any interference from coexisting substances. The recoveries of these compounds in these samples at fortification levels of 100-500 ng/g were 90-93%.

Determination of picomolar concentrations of proteins using novel amino reactive chameleon labels and capillary electrophoresis laser-induced fluorescence detection

Py-1 and Py-6 are novel amino-reactive fluorescent reagents. The names given to them reflect that they consist of a pyrylium group attached to small aromatic moieties. Upon reaction with a primary amine there is a large spectral shift in the reagent, rendering them effectively fluorogenic. In this study, these reagents were used to label a test protein, (human serum albumin), and the sample was analyzed by capillary electrophoresis and laser-induced fluorescence detection. Detection limits after a 60 min labeling reaction at 22 degrees C (Py-1) and 50 degrees C (Py-6) were 6.5 ng/mL (98 pM) for Py-1 and 1.2 ng/mL (18 pM) for Py-6. Separation of immunoglobulin G (IgG), human serum albumin, lipase, and myoglobin after labeling with Py-6 were performed. The method was further modified to make it amenable to automation. Unlike many other amino reactive reagents used to label protein amino groups, reaction with Py-1 and Py-6 do not alter the charge of the protein and the advantage of this with respect to electrophoretic separations is discussed.

On-Line Concentration of a Protein Using Denaturation by Sodium Dodecyl Sulfate

A novel method for the on-column sample stacking of proteins is described. The strategy takes advantage of interactions between protein molecules and sodium dodecyl sulfate (SDS) monomers. A long plug of a protein sample (either acidic or basic) is injected into a capillary filled with a background electrolyte (BGE) containing SDS. When a potential is applied, the proteins interact with SDS monomers in the BGE to form protein-SDS complexes that migrate more slowly than the corresponding uncomplexed protein, resulting in protein stacking. Both acidic and basic proteins migrate at an almost identical electrophoretic velocity after stacking, which indicates that the protein-SDS complexes formed in the BGE zone have a similar charge/mass ratio. The mechanism of stacking was investigated using a sample consisting of a basic protein, lysozyme, and a small molecule, methylene blue. The findings clearly show that two interactions with SDS occur, a stepwise binding interaction between protein molecules and SDS monomers and an interaction in which the small molecules enter into micelles formed by SDS molecules. The method was also applied to the detection of a protein labeled with a fluorescent labeling reagent at trace levels. The labeled protein was detected even under labeling conditions where the labeling efficiency was too low to detect by short-plug injection.