Current Analytical Chemistry - Volume 6, Issue 2, 2010

The hyphenation of separation methods with mass spectrometry (MS) is one of the major topics in analytical chemistry. This is not only true for pressure-driven methods like HPLC but also for electro-driven ones such as capillary electrophoresis (CE). Research during the first years of CE-MS was primarily focused on technical improvements leading to commercially available equipment, making this combination more reliable and robust. On the other hand investigations on the applicability of CE-MS for the solution of real-world analytical problems were already performed during the early stages of this hyphenated technique. Thereby, CE was able to impress with its exceptional separation efficiency, whereas in most cases low-resolution MS instruments were used as detectors. The further development of reasonably priced benchtop reflectron time-of-flight (TOF)-MS and quadrupole time-of-flight (QTOF) instruments also promoted their use in CEMS, now providing high resolution in both dimensions separation and detection. Although TOF-MS is the most abundant high-resolution mass spectrometer coupled to CE, also other types of MS instruments such as Orbitraps of Fouriertransform- ion- cyclotron-resonance (FTICR)-MS have been employed for this purpose. The main goal of this critical review is to give an overview on the current state in the hyphenation of high-resolution mass spectrometry with electroseparation methods and to discuss possible future trends in this field.

The determination of trace analytes in some types of samples by capillary electrophoresis (CE) requires their prior extraction from the sample matrix and preconcentration. The preconcentration step is the bottleneck of many analytical processes, which should ideally involve as few operations as possible in order to minimize potential errors and shorten analysis times. There is a growing search for more environmental friendly approaches capable of using smaller amounts of solvents and sample sizes. Although solid phase extraction (SPE) continues to be the most widely used concentration technique, some cleanup/ concentration methodologies involving the use of membranes, electrophoretic preconcentration, chromogenic reagents, microdialysis (MD), solid phase microextraction (SPME), hollow fibres (HF), supercritical fluid extraction (SFE), cloud point extraction (CPE) and stir bar sorptive extraction (SBSE) have proved effective alternatives for preconcentration purposes. This paper reviews available preconcentration techniques for use in CE analysis (mainly with UV-Vis detection) and supplements the information contained in previously published reviews about this emerging field of analysis.

In this study, we prepared two different type complex groups. One of them is based on Schiff base (A1 , A2 and A3) Cd(II) complexes, another one is β-blockers (acebutolol (ACE), atenolol (ATE) and propranolol (PRO)) Cu(II) complexes. The ligands and their metal complexes were characterized by elemental analyses, mass spectra, 1H(13C) NMR spectra, FT-IR, UV-vis, conductivity measurements and thermal analysis studies. Protonation constants of the ligands and stability constants of their complexes were determined by potentiometric titration method at 25.00±0.02 oC under nitrogen atmosphere and ionic strength of 0.10 M sodium perchlorate. For the Schiff bases, the solvent was 50% DMSO-water; for the β-blockers, it was 50% methanol-water media. The effects of these properties on the observed inhibition of chemiluminescence and the analytical implications of the results are also discussed. Two sets of novel coordination compounds were found to inhibit the intense chemiluminescence reaction in DMSO solution between luminol and dioxygen in the presence of a strong base.

A new solid-phase extraction method was developed for trace analysis of cobalt on Duolite XAD-761 resin by using flame atomic absorption spectrometry (FAAS). The optimum experimental conditions for the quantitative sorption of Co(II)-PAR (cobalt chelates with 4-(2-Pyridylazo) resorcinol), pH, effect of sample flow rate, concentration of eluent, sorption capacity of resin and the effect of diverse ions on the preconcentration of analytes have been investigated. The optimum pH values for quantitative sorption of Co (II)-PAR were between 5 and 7.5. Eluted process was performed by 4 mL ethanol. The sorption capacity of resin was determined to be 8.6 mg g–1 for cobalt with a preconcentration factor of 150. In optimized conditions, the detection limit for cobalt ions was found to be 0.36 μg L– 1. The accuracy of the proposed procedure was checked by using NIST 1573 a tomato leave as a standard reference material. The achieved results were in good agreement with certified values. The proposed method was applied for the determination of cobalt in different water samples, such as city line, geothermal, river and lake.

A potentiometric stripping method for the measurement of lithium ions at a carbon paste electrode modified with spinel-type manganese oxide is described. The procedure is based on the effective pre-concentration of lithium ions on an electrode surface containing spinel-type MnO2, with the reduction of Mn(IV) to Mn(III), and the consequent intercalation (insertion) of the lithium ions into the spinel structure. The best current constant stripping analysis (CCSA) response was reached for an electrode composition of 25% (m/m) spinel-type MnO2 in the paste, 0.1 mol L–1 TRIS buffer solution at pH 8.0, an accumulation potential of 0.3 V vs. the saturated calomel reference electrode (SCE), a preconcentration time of 90 s and the application of a small positive constant current (10 μA) during the stripping step. The obtained limit of detection was 2.0 x 10–7 mol L–1, and the relative standard deviation from five measurements of 2.5 × 10-6 mol L–1 lithium ions was 3.8%.

This paper describes a potassium ion-selective electrode based on 2,2'-dithiodibenzoic acid with a focus on the sub-Nernstian response characteristics. The topics including the experimental parameters that influence the response of the electrode, useful membrane compositions and applications were investigated. The membrane electrode demonstrate linear (R2= 0.999) sub-Nernstian responses, with the slop of 40.12 ± 0.15 mV/decade, toward potassium(I) ions over the range of 1.0 x 10– 5 to 1.0 M. The prepared electrode, with detection limit of 6.2 x 10-6 M, was successfully applied in the direct potentiometric measurement of sub-milimolar quantities of K+ in aqueous solutions. The results were compared with atomic absorption spectrometry measurements. There was good agreement between the results from the proposed electrode and those from the standard method.

The transparency of the eye lens is vital for maintenance of good image quality to the eye. This is lost when the lens develops a cataract which is a manifestation of changes to the structural proteins and their organisation. Understanding the complex arrangements and interactions of proteins in the lens and how these alter with opacification requires a means of probing the intact tissue. Nanoparticles offer such potential but need to be tested on lens cells and proteins to see whether they cause any detrimental changes. Cerium oxide nanoparticles (nanoceria) of around 5-6nm were prepared and characterised. A concentration of 10μg/ml was introduced into cell cultures from porcine eye lens epithelial cells and from a commercially available human cell line. Transmission electron microscopy of treated samples showed nanoparticles within cells. Proteins extracted from the cultured cells were subjected to chromatography and electrophoresis. Chromatographs and electrophoresis gels showed no difference between treated and control samples from human lens cell cultures. Some slight differences, between treated and control samples, were noted in porcine samples. The results suggest that introduction of nanoceria into cultured cells from the eye lens do not manifest any significant effects on chromatographic or electrophoretic profiles of eye lens proteins.

A method has been developed to determine a trace concentration of individual polycyclic aromatic hydrocarbons (PAHs) and organochlorinated pesticides (OCPs) in sewage sludge sample. Sewage sludge samples were collected from three wastewater treatment plants (WWTPs) located at different areas in Kuwait. The new method was based on, utilizing gas chromatography-mass spectrometry with ion trap technique for the simultaneous determination of OCPs and PAHs. The sludge samples were extracted with accelerated solvent extraction (ASE) using (1:1; v/v) dichloromethane; nhexane solvent mixture. The extract was passed through a gel permeation chromatography (GPC) followed by silica/ Al2O3 column, in order to eliminate the large interferences caused by organic compound and lipid. Sulfur was treated by a non destructive method, such as copper bars added to the extraction thimble before the extraction process. Average concentrations of 5.62 mg kg-1 of the 16 PAHs and 3.52 mg kg-1 of the 20 OCPs were found in the sewage sludge sample tested.