Laura Sánchez-Hernández

Recent approaches in sensitive enantioseparations by CE.

The latest strategies and instrumental improvements for enhancing the detection sensitivity in chiral analysis by CE are reviewed in this work. Following the previous reviews by García‐Ruiz et al. (Electrophoresis 2006, 27, 195–212) and Sánchez‐Hernández et al. (Electrophoresis 2008, 29, 237–251; Electrophoresis 2010, 31, 28–43), this review includes those papers that were published during the period from June 2009 to May 2011. These works describe the use of offline and online sample treatment techniques, online sample preconcentration techniques based on electrophoretic principles, and alternative detection systems to UV–Vis to increase the detection sensitivity. The application of the above‐mentioned strategies, either alone or combined, to improve the sensitivity in the enantiomeric analysis of a broad range of samples, such as pharmaceutical, biological, food and environmental samples, enables to decrease the limits of detection up to 10−12 M. The use of microchips to achieve sensitive chiral separations is also discussed.

Sensitive determination of d-carnitine as enantiomeric impurity of levo-carnitine in pharmaceutical formulations by capillary electrophoresis–tandem mass spectrometry

In this work, capillary electrophoresis-electrospray ionization-tandem mass spectrometry was applied to the determination of l- and d-carnitine in pharmaceutical formulations. A simple sample treatment procedure consisting of the use of a dilution or an extraction step with water was employed prior to derivatization with 9-fluorenylmethoxycarbonyl (FMOC). The method was validated in terms of selectivity, linearity, accuracy, precision and sensitivity, with a LOD of 10ngmL(-1) for each enantiomer, which was enough to detect enantiomeric impurities up to 0.002% of d-carnitine with respect to the main enantiomer (l-carnitine). Eleven pharmaceutical formulations were analyzed including ampoules, oral solutions, sachets, and tablets. Results showed contents for carnitine comprised between 77 and 101% with respect to the labeled ones in the case of those formulations marketed with the racemate, and from 97 to 102% in those cases where the single enantiomer (l-carnitine) was employed as active ingredient. Percentages for the enantiomeric impurity (d-carnitine) ranging from 0.6 to 1.3% were obtained exceeding the limits established for impurities in drug products. These results corroborate the need of validated analytical methodologies enabling the quality control of pharmaceutical formulations containing carnitine.

Capillary electrophoresis in two‐dimensional separation systems: Techniques and applications

The analysis of complex samples requires powerful separation techniques. Here, 2D chromatographic separation techniques (e.g. LC‐LC, GC‐GC) are increasingly applied in many fields. Electrophoretic separation techniques show a different selectivity in comparison to LC and GC and very high separation efficiency. Thus, 2D separation systems containing at least one CE‐based separation technique are an interesting alternative featuring potentially a high degree of orthogonality. However, the generally small volumes and strong electrical fields in CE require special coupling techniques. These technical developments are reviewed in this work, discussing benefits and drawbacks of offline and online systems. Emphasis is placed on the design of the systems, their coupling, and the detector used. Moreover, the employment of strategies to improve peak capacity, resolution, or sensitivity is highlighted. Various applications of 2D separations with CE are summarized.

Resistant Starch Production from Non-conventional Starch Sources by Extrusion

The production of resistant starch from non-conventional sources using an extruder was studied. Starch was isolated from unripe banana and mango fruits, commercial corn starch was used for comparison purposes. Moisture, ash and fat content were higher in non-conventional starch sources than in corn starch, but corn starch presented a lower protein and dietary fibre content than banana and mango starches. Amylose content was higher in banana and mango starches than in corn starch. Besides, mango had the smallest granule size (5–10 m). Extruded mango had the lowest solubility which may be related with the granule size, and in the case of the swelling, extruded products from corn starch had the highest values, a pattern that may be due to the amylose/amylopectin ratio, because corn starch had the lowest amylose content of the starches studied. Extruded products from mango presented a resistant starch (RS) content that decreased when the screw speed increased, for banana starch, the RS values from the extruded products was similar at 30 rpm and 65 rpm, and at 40 rpm it was the highest. In the case of retrograded resistant starch (RRS), the values of the extruded products prepared with non-conventional starches had a defined pattern, because they decreased when screw speed increased.

A capillary electrophoresis-tandem mass spectrometry methodology for the determination of non-protein amino acids in vegetable oils as novel markers for the detection of adulterations in olive oils.

A new analytical methodology based on capillary electrophoresis-mass spectrometry (CE-MS(2)) is presented in this work, enabling the identification and determination of six non-protein amino acids (ornithine, β-alanine, GABA, alloisoleucine, citrulline and pyroglutamic acid) in vegetable oils. This methodology is based on a previous derivatization with butanol and subsequent separation using acidic conditions followed by on-line coupling to an ion trap analyzer for MS(2) detection established through an electrospray-coaxial sheath flow interface. The electrophoretic and interface parameters were optimized obtaining the separation of all compounds in less than 15 min and with resolutions higher than 5. The proposed method was validated by assessing its accuracy, precision (RSD<7% for corrected peak areas), LODs and LOQs (between 0.04-0.19 ng/g and 0.06-0.31 ng/g, respectively) and linearity range (R(2)>0.99), and it was used in order to identify the selected non-protein amino acids in soybean oils, sunflower oils, corn oils and extra virgin olive oils. MS(2) experiments performed the fingerprint fragmentation of these compounds allowing to corroborate ornithine and alloisoleucine in seed oils but not in olive oils. The method was applied to identify and quantify olive oil adulterations with soybean oil detecting in a single run the amino acids in mixtures up to 2% (w/w). The results showed a high potential in using these compounds as novel markers for the detection of adulterations of extra virgin olive oils with seed oils. Thus, the developed method could be considered a simple, rapid and reliable method for the quality evaluation of extra virgin olive oil permitting its authentication.

Development of a CE-ESI-ITMS method for the enantiomeric determination of the non-protein amino acid ornithine

Unequivocal enantiomeric determination by CE‐MS2 of the non‐protein amino acid ornithine (Orn), previously derivatized with FITC, was carried out in this work. A CE‐tandem MS system was used to combine the potential of CE in chiral separations with the sensitivity and selectivity of tandem MS detection. The electrospray‐coaxial sheath flow interface conditions were optimized and an IT analyzer working in the MS2 mode was employed to provide the best sensitivity and selectivity. Satisfactory results were obtained in terms of linearity (r2>0.99), precision (RSD from 1.3 to 2.3% for migration times and from 11.0 to 18.6% for corrected peak areas), and LOD (2×10−9 M). Interestingly, the CE‐MS2 method developed allowed a sensitivity enhancement of 100 folds with respect to UV detection. The results demonstrated the feasibility for carrying out quantitative CE‐ESI‐MS2 determinations of Orn enantiomers in beers. Thus, L‐Orn was found in the 16 beer samples analyzed at concentrations ranging from 1×10−6 to 2×10−5 M, whereas the percentages of D‐Orn with respect to the total amount of Orn reached values between 1.5 and 10.0%.

Potential of vancomycin for the enantiomeric resolution of FMOC‐amino acids by capillary electrophoresis‐ion‐trap‐mass spectrometry

The potential of the antibiotic vancomycin (VC) as chiral selector for the enantiomeric separation of amino acids by CE‐ESI‐MS/MS2 was investigated for the first time in this work. Derivatization of amino acids with FMOC‐Cl was carried out to enable their interaction with VC as well as the formation of precursor ions with larger m/z which were employed in MS2 experiments. The partial filling of a coated capillary was employed to avoid the loss in MS sensitivity originated by the introduction of VC in the ionization source. Under optimized conditions, the simultaneous enantiomeric separation and unequivocal identification of 17 amino acids (two of them being nonprotein amino acids) took place in about 20 min with LODs in the micromolar range.

New approaches in sensitive chiral CE

CE has shown to have a big potential for chiral separations, with advantages such as high efficiency, high resolution, and low sample and reagents consumption. Nevertheless, when UV detection is employed, CE has some drawbacks, especially the low sensitivity obtained due to the short optical path length. Notwithstanding, sensitivity improvements can be achieved when different approaches are employed, such as sample treatment strategies (off‐line or on‐line), in‐capillary sample preconcentration techniques, and/or alternative detection systems to UV–Vis (such as fluorescence, conductimetry, electrochemiluminiscence, MS, etc.). This article reviews the most recent methodological and instrumental advances reported from June 2011 to May 2013 for enhancing the sensitivity in chiral analysis by CE. The sensitivity achieved for the enantioseparated analytes and the applications carried out using the developed methodologies are also summarized.

Recent approaches for enhancing sensitivity in enantioseparations by CE

This article reviews the latest methodological and instrumental improvements for enhancing sensitivity in chiral analysis by CE. The review covers literature from March 2007 until May 2009, that is, the works published after the appearance of the latest review article on the same topic by Sánchez‐Hernández et al. [Electrophoresis 2008, 29, 237–251]. Off‐line and on‐line sample treatment techniques, on‐line sample preconcentration strategies based on electrophoretic and chromatographic principles, and alternative detection systems to the widely employed UV/Vis detection in CE are the most relevant approaches discussed for improving sensitivity. Microchip technologies are also included since they can open up great possibilities to achieve sensitive and fast enantiomeric separations.

Determination of betaines in vegetable oils by capillary electrophoresis tandem mass spectrometry--application to the detection of olive oil adulteration with seed oils.

A CE–tandem mass spectrometry (MS2) methodology enabling the simultaneous determination of betaines (glycine betaine, trigonelline, proline betaine and total content of carnitines) in vegetable oils was developed. Betaines were derivatized with butanol previous to their baseline separation in 10 min using a 0.1 M formic acid buffer at pH 2.0. Ion trap conditions were optimized in order to maximize the selectivity and sensitivity. Analytical characteristics of the proposed method were established by evaluating its selectivity, linearity, precision (RSDs ranged from 4.8 to 10.7% for corrected peak areas) and accuracy by means of recovery studies (from 80 to 99%) and LODs and LOQs at 0.1 ppb level. The method was applied for the determination of the selected betaines in seed oils and extra virgin olive oils. MS2 experiments provided the fingerprint fragmentation for the betaines identified in vegetable oils. In extra virgin olive oils, carnitines were not detected, making it possible to propose them as a feasible novel marker for the detection of adulterations of olive oils. Application of the developed method for the analysis of different mixtures of extra virgin olive oil with seed oil (between 2 and 10%) enabled the detection and quantitation of the total content of carnitines. The results obtained show the high potential of the developed method for the authentication and quality control of olive oils.