Solid-phase extraction of nitrophenols in water by using a combination of carbon nanotubes with an ionic liquid coupled in-line to CE.

This paper describes the combined use of carbon nanotubes and an ionic liquid directly coupled in-line to commercial CE equipment for sample treatment. The extraction unit operates as a spin column to preconcentrate the analytes. The extraction unit is inserted into the sample vial. The elution is performed in-line, placing the vial on the carrousel of the CE equipment. The joint use of carbon nanotubes and ionic liquids as sorbent is based on the high adsorption capacity of these materials, which makes them highly suitable for microextraction purposes. The LOQ of analytes were within the range of 0.65-0.83 µg/L with a RSD of less than 7%. The values of recovery range between 90 and 112%. The absolute recovery obtained from samples containing 1 µg/L of analytes was 38%.

Graphene nanoparticles as pseudostationary phase for the electrokinetic separation of nonsteroidal anti-inflammatory drugs.

The exceptional properties of graphene (G) were exploited here to facilitate capillary electrokinetic separations. Two types of commercially available G consisting of nanoparticles containing-one to three and-four to six G sheets, respectively, were compared for this purpose. Both proved effective in separating the arylpropyl derivatives of nonsteroidal anti-inflammatory drugs. The highest resolution and shortest migration times were obtained with G containing high amount of single and double G nanosheets. G affords higher resolution than other types of nanoparticles; stable suspensions can be easily prepared and used as BGE without the need of adding an additional surfactant. This results in a high reproducibility in migration times and stability in background noise. The LOD and LOQ obtained by using G nanoparticles as pseudostationary phases spanned the range 0.29-1.18 mg/L and 0.95-3.95 mg/L, respectively, and the RSD was less than 4.7% in all instances.

Microextraction by packed sorbents combined with surface-enhanced Raman spectroscopy for determination of musk ketone in river water.

Microextraction by packed sorbents (MEPS) combined with Surface-enhanced Raman spectroscopy (SERS) was investigated, and applied to the determination of musk ketone (MK) in river water samples. The full MEPS-SERS method includes analyte enrichment by MEPS preconcentration with C18 sorbent followed by SERS detection supported by silver nanoparticles. An eluent drop containing the analyte is deposited directly from the MEPS syringe on a CaF2 glass plate. When the drop has dried, a specific volume of silver nanoparticles solution is added on it before each SERS measurement. Several experimental variables were studied in depth; under the optimum experimental conditions MK can be extracted from a 500 µL sample with recoveries in the range 47-63 %. The limit of detection was 0.02 mg L(-1) and the relative standard deviation 15.2 % (n = 4). Although not investigated in this work, the proposed method might be suitable for in-situ monitoring, because of the portability of the Raman spectrometer used.

(CdSe/ZnS QDs)-ionic liquid-based headspace single drop microextraction for the fluorimetric determination of trimethylamine in fish.

Here, we propose the use of ionic liquid-modified QDs for the combination of ionic liquid-based headspace single drop microextraction technique (IL-HS-SDME) and QD-based fluorimetric detection. In that way, we exploit the advantages of ILs as extractant solvent and the use of QDs as fluorescence detection probe. After in situ generation of volatile trimethylamine (TMA) from fish samples, the analyte was extracted and preconcentrated directly onto a (QD)IL microdrop by HS-SDME. Then, TMA was quantified through the enhancing effect produced on the initial fluorescence of the (QD)IL dispersion. The working conditions for the (QD)IL-HS-SDME procedure were: 20 µL microdrop of (QD)IL exposed for 2 min to the headspace of a 5 mL aqueous sample (0.2 g of fish in 10 M NaOH) placed in a 10 mL vial with stirring and thermostatted at 50-60 °C. For the detection, the microdrop was transferred to a microcuvette with 300 µL of acetonitrile and the fluorescence was recorded (λ(em) = 570 nm, λ(exc) = 400 nm). Under the selected conditions, the analytical response was linear over the range from 0.05 to 0.25 mg L(-1) (R(2) = 0.997) with a detection limit of 0.014 mg L(-1) (0.35 µg TMA per gram of fish) and the relative standard deviation was 3.5% (n = 5). The proposed method was applied to the determination of TMA in hake fish samples with satisfactory results.

Capillary electrophoresis method for the characterization and separation of CdSe quantum dots.

This paper presents a simple and rapid methodology to separate and characterize free CdSe quantum dots (QDs) in aqueous medium by capillary electrophoresis (CE). First, we describe a controlled derivatization procedure to obtain water-soluble QDs through noncovalent interactions. This derivatization methodology was based on the formation of a complex between the QDs and several types of surfactants to enhance the hydrophilicity and stability of the CdSe QDs. The surfactants used to achieve the surface functionalization were trioctylphosphine oxide/trioctylphosphine (TOPO/TOP) and sodium dodecyl sulfate (SDS). Different CdSe QDs core sizes were synthesized as function of the nanocrystals growing time and then subjected to controlled coating. These free QDs were separated by capillary zone electrophoresis (CZE) based on the differences in the charge-to-mass ratio of the QDs-TOPO/TOP-SDS complexes, and the detection was carried out with UV-vis and laser-induced fluorescence (LIF) techniques obtaining detection limits 5 times lower with CE-LIF. Under the optimal working conditions, four different-sized QDs were successfully separated whose average sizes were 3.1, 3.6, 4.3, and 4.9 nm, and the size distribution was less than 7% for all of them [calculated from the full width at half-maximum (fwhm) of the fluorescence spectra and confirmed by high-resolution transmission electron microscopy (HTEM)]. Therefore, we were able to separate QDs that differ in only 0.5 nm in diameter and 19 nm in fluorescence emission maximum. This corresponds to the better resolution achieved in the analysis of these kinds of nanoparticles. Finally, a correlation between the migration times plus or minus peak width and the core sizes plus or minus size distribution was established.

Calix[8]arene coated CdSe/ZnS quantum dots as C60-nanosensor.

Here, we report an optical sensor for fullerene C(60) in water using CdSe/ZnS quantum dots coated by p-tertbutylcalix[8]arene. This C(60)-nanosensor is based on the selective host-guest interaction between fullerene C(60) and p-tertbutylcalix[8]arene. The procedure for the synthesis of p-tertbutylcalix[8]arene-CdSe/ZnS complex is described, and its fluorescent characteristics are also reported. We found that the interaction between C(60) fullerene and p-tertbutylcalix[8]arene-CdSe/ZnS complex quenches the original fluorescence of calix-QDs according to the Stern-Volmer equation. The mechanism of interaction is discussed. Finally, the potential application of the proposed method using the designed nanosensor for determination of C(60) in spiked environmental river water samples is demonstrated. For the analysis of river samples, a liquid-liquid extraction multistep preconcentration procedure is proposed. The method, which is simple and rapid, allows the detection of 5 µg L(-1) of fullerene. This sensor could be a useful tool for environmental and toxicological studies.

Determination of pyrimidine and purine bases by reversed-phase capillary liquid chromatography with at-line surface-enhanced Raman spectroscopic detection employing a novel SERS substrate based on ZnS/CdSe silver-quantum dots.

We have developed a new SERS substrate based on the reduction of silver nitrate in the presence of ZnS-capped CdSe quantum dots. This substrate showed higher sensitivities as compared to a hydroxylamine-reduced silver sol. On the basis of this new substrate, at-line SERS detection was coupled with capillary liquid chromatography (cap-LC) for the separation and selective determination of pyrimidine and purine bases. For this purpose, wells of a dedicated microtiter plate were loaded with 20 µL of the SERS substrate and placed on an automated x,y translation stage. A flow-through microdispenser capable of ejecting 50 pL droplets, at a frequency 100 Hz, was used as the interface to connect the cap-LC system to the wells loaded with SERS substrate. A detailed study of the dependence of both the separation and the surface-enhanced Raman spectra of each base on the pH was performed to optimize the system for maximum sensitivity and selectivity. Highly satisfactory analytical figures of merit were obtained for the six investigated bases (cytosine, xanthine, hypoxanthine, guanine, thymine, and adenine) with detection limits ranging between 0.2 and 0.3 ng injected on the capillary LC column, and the precisions were in the range of 3.0-6.3%.

In situ synthesis of magnetic multiwalled carbon nanotube composites for the clean-up of (fluoro)quinolones from human plasma prior to ultrahigh pressure liquid chromatography analysis.

Magnetic nanoparticles (MNPs) were deposited onto multiwalled carbon nanotubes (MWCNTs) by in situ high-temperature decomposition of the magnetic precursor [iron(III)] and MWCNTs, in ethylene glycol. This one-step synthetic method was applied to commercially available carbon nanotubes (CNTs). Scanning electron micrographs of the resulting products revealed that MNPs decorated the surface of the MWCNTs. The hybrid nanoparticles thus obtained were used for sampling and cleanup in the determination of eight fluoroquinolones (FQs) and two quinolones (Qs) at trace levels by ultra performance liquid chromatography (UPLC). A systematic study of analyte adsorption and desorption was conducted with MNPs and MWCNTs separately. Although both solid phases adsorbed the analytes to some extent, the much higher recoveries were obtained by using the MNP-MWCNT composite which was thus selected to treat plasma samples containing FQs and Qs. Lower accuracies were determined at spiked plasma compared to the standard solution caused by the complexation affinity of the analytes with proteins because high recoveries were observed when deproteinization was performed before treating the sample with the magnetic MWCNTs. The performance characteristics of the optimized method were determined, and the method was applied to the analysis of plasma samples from antibiotic-treated patients. On the basis of the results, the use of an in situ synthesized MWCNT-MNP composite allows the simple, expeditious sampling and treatment of such complex biological samples for the subsequent determination of FQs and Qs present at free form.

Fully automatic sample treatment by integration of microextraction by packed sorbents into commercial capillary electrophoresis-mass spectrometry equipment: application to the determination of fluoroquinolones in urine.

This paper describes a new and innovative way to integrate microextraction by packed sorbents (MEPS) into commercial CE equipment. The suggested integration allows the automatic sample cleanup and preconcentration requiring only a few microliters of sample and no additional hardware and software. The MEPS was integrated in the outlet region of a commercial CE equipment cartridge in order to provide easy manipulation and exchange. The robustness of the proposed integration was demonstrated by the design and use of a (MEPS)-nonaqueous capillary electrophoresis (NACE)-MS method used to determine fluoroquinolones "FQs" (namely, ofloxacin, marbofloxacin, enrofloxacin, danofloxacin, and difloxacin) in urine. The method allows the analysis of micrograms per liter of FQs to be carried out with only 48 microL of urine sample. The obtained LODs were in the range 6.3-10.6 microg/L. An analysis of spiked urine samples was used to validate the method. Absolute recoveries were in the range of 71-109% while the precision expressed as repetitivity of peak area was lower than 5.9%.

Selective quantification of carnitine enantiomers using chiral cysteine-capped CdSe(ZnS) quantum dots.

We report the first observation of selective and specific recognition of chiral L-cysteine (L-Cys)- or D-cysteine (D-Cys)-capped CdSe(ZnS) quantum dots (QDs) with carnitine enantiomers in aqueous solution. The intensity fluorescence of L-Cys-capped QDs decay in the presence of D-carnitine but are not affected by L-carnitine. On the other hand, the fluorescence of D-Cys-capped QDs was only affected by L-carnitine. The applicability of chiral Cys-capped QDs for the analysis of chiral mixtures on enantiomers has been demonstrated for 1:100 mixtures, and the results that were obtained had high precision (<2.3%) and low error (<2.7%).

Comparison of aromatic and alkyl micelles for the electrokinetic determination of phthalates in virgin olive oil.

Two electrokinetic methods for the separation of phthalates are proposed. One uses 25 mM sodium borate and 50 mM sodium taurodeoxycholate adjusted to pH 2.8, and the other uses 15 mM ammonium tetraborate, 100 mM SDS, 0.25% w:v hydroxypropylmethyl cellulose (HPMC) and 5% v:v methanol (MeoH) adjusted to pH 9. The BGE containing SDS micelles as the pseudo-stationary phase provided better analytical figures of merit, particularly as regards LOD (0.4-1.4 mg/L) and precision (1.1-6.5%). Adding MeoH and HPMC to the BGE proved essential in order to obtain narrow and symmetric peaks. The proposed method was successfully used to determine phthalates in virgin olive oil. Recoveries from spiked samples ranged from 96 to 106%. The precision obtained in the analysis of real samples, as RSD, was better than 6.8%.

Recent developments in capillary EKC based on carbon nanoparticles.

This paper provides an overview of the use of carbon nanoparticles (CNPs) as pseudo-stationary phases (PSPs) in EKC. Specifically, it describes the characteristics and properties of the major types of CNPs used as PSPs in EKC separations, namely C(60) fullerenes, carbon nanotubes and covalently modified carbon nanotubes. Based on such properties, a plausible mechanism for the interactions governing EKC separation with these materials is proposed. Also, the most salient uses of CNPs as PSPs are outlined. Finally, CNPs are compared in terms of performance with other well-established types of nanostructures used to enhance selectivity in EKC over the past decade.

Direct automatic determination of free and total anesthetic drugs in human plasma by use of a dual (microdialysis-microextraction by packed sorbent) sample treatment coupled at-line to NACE-MS.

This paper reports for the first time the use of microextraction by packed sorbent in combination with CE. The combined system was used to determine anesthetic drugs in human plasma. A microdialysis fiber was coupled on-line to the microextraction unit in order to distinguish between free and total concentrations of drugs. The system was automated by connecting the microextraction unit to a syringe pump and interfacing it to a computer. The ensuing method allows the determination of 10 microg/L concentrations of free drugs and 1 microg/L concentrations of total drugs from only 200 microL of sample with an RSD of less than 9%.

Capillary electrophoresis separation of microorganisms.

Microorganisms can be considered a bio-colloid. That is, they have a characteristic outer surface that carries, or can carry, a charge. Precisely, differences in the surface can be exploited for separation by capillary electrophoresis (CE). In fact, methods based on CE seem to be very promising because they should produce rapid and high-efficiency separations. Although CE can be used to separate microbial (i.e., bacteria, virus, fungi, and whole cells) and subcellular particles (i.e., mitochondria and nuclei), this chapter is focused mainly on the determination of bacteria and virus for their interest. At difference to the separation off molecules, microorganisms are characterized as living. This makes their analysis more difficult because several aspects such as possible lysis, aggregation, evolution, growing etc. must be taken into count.

Separation of carbon nanotubes in aqueous medium by capillary electrophoresis.

A robust and reproducible method for the dispersion of carbon nanotubes, either single-walled or multi-walled is presented. Dispersion of nanotubes was achieved as surfactant-coated species of sodium dodecyl sulphate. The addition of small amounts of hydroxypropyl methyl cellulose (HPMC) together with the surfactant, sodium dodecyl sulphate, was found critical to achieve reproducible nanotubes dispersion and to obtain an homogeneous and stable solution. This solution is further analyzed by capillary electrophoresis using a background electrolyte solution containing a polymer, 0.025% (w/v) HPMC solution prepared in 5 mM ammonium acetate at pH 8.03. This electrophoretic method presents a high reproducibility between runs, being an interesting alternative to study nanotube size distribution or characterization after synthesis. In addition, the methodology developed allowed the study of the interaction of the different types of carbon nanotubes with a molecular probe such as pentachlorophenol. This procedure was showed effective to detect small differences on the chemical/physical surface properties of the nanotubes. The different interaction behavior found within the two SWNTs selected was critically discussed.

Effects of escin on indinavir crystallization time in the urine of patients with HIV-I infection: a multicenter, randomized, open-label, controlled, four-period crossover trial.

BACKGROUND: The combination of indinavir, a protease inhibitor, and reverse-transcriptase inhibitors is widely used in the treatment of HIV-1 infection. However, precipitation of indinavir crystals in the renal tubular lumen due to the drug's aqueous insolubility may result in characteristic symptoms of flank pain or classic renal colic. An in vitro study has shown that addition of escin to synthetic urine containing indinavir delayed the crystallization time of indinavir. OBJECTIVE: This study examined the efficacy and tolerability of the addition of escin to highly active antiretroviral therapy containing indinavir to delay the crystallization time of indinavir in urine. METHODS: This was a multicenter, randomized, open-label, controlled, 4-period crossover trial in which each period lasted 4 weeks. HIV-1-infected adults receiving treatment with indinavir plus 2 nucleoside analogue reverse-transcriptase inhibitors in whom plasma viral loads had been undetectable (HIV-1 RNA <200 copies/mL) for at least 6 months were randomly assigned to 1 of 2 groups based on the timing of the initiation of escin. Group I received escin during the second and third treatment periods, and group II received escin during the first and fourth treatment periods. The primary end point was the in vitro crystallization time of indinavir in 24-hour urine specimens, determined at the end of each 4-week period. Tolerability was assessed based on the number of patients with a rebound in plasma viral load and on the numbers of clinically and biologically relevant adverse events (including those requiring discontinuation of treatment). Clinical and laboratory evaluations were performed throughout each 4-week period. RESULTS: Fifty HIV-1-infected patients were enrolled, 47 were randomized to treatment (40 [85.1%] men, 7 [14.9%] women; median [interquartile range] age, 36 [34-45] years), and 30 completed the study. Urine pH and plasma and urine indinavir concentrations were unaffected by the addition of escin to antiretroviral treatment. The mean time to the onset of crystallization was 14.7 minutes with escin (95% Cl, 11.8-17.5) and 9.9 minutes without it (95% Cl, 6.7-13.1). Therefore, the addition of escin increased the mean crystallization time by 5.5 minutes (95% Cl, 1.5-9.5; P = 0.008), representing the overall capacity of study treatment to inhibit indinavir crystallization in the urine. Three of 47 patients had mild gastrointestinal symptoms associated with escin treatment. No episodes of nephrolithiasis were recorded during the study or after the completion of study treatment. CONCLUSION: The results of this prospective clinical trial of the effect of escin on indinavir crystallization time support the possibility that indinavir-associated nephrolithiasis may be prevented by means other than overhydration. Further research is needed in greater numbers of patients over longer follow-up times.

Sialolithiasis: mechanism of calculi formation and etiologic factors.

BACKGROUND: Sialolithiasis is a common disease of salivary glands. The etiology of these calculi is little known and their exact mechanism of formation is unknown. METHODS: The composition and structure of 21 sialoliths were studied and the composition of the saliva of each corresponding patient was determined (pH, calcium, magnesium, phosphorus, citrate and phytate). RESULTS: Eighteen sialoliths exhibited similar macro and microstructure, being constituted by hydroxyapatite (HAP) and organic matter, normally arranged in a multilayer structure. The three remaining sialoliths were exclusively constituted by organic matter. The salivary Ca of patients with HAP calculi was significantly higher than that found in the saliva of the healthy group. The salivary phytate concentration of patients with HAP calculi was significantly inferior to that found in patients with calculi exclusively formed by organic matter, as well as to that found in saliva of healthy group. Significant differences between the salivary magnesium concentrations of patients with HAP calculi and the control group were also observed. No significant differences between pH and citrate concentrations of the three groups were found. CONCLUSIONS: It was concluded that the deficit of crystallization inhibitors such as myo-inositol hexaphosphate (phytate) was also an important etiologic factor implied in the sialolith development.

Effects of exogenous inositol hexakisphosphate (InsP(6)) on the levels of InsP(6) and of inositol trisphosphate (InsP(3)) in malignant cells, tissues and biological fluids.

InsP(6) is abundant in cereals and legumes. InsP(6) and lower inositol phosphates, in particular InsP(3), participate in important intracellular processes. In addition, InsP(6) possess significant health benefits, such as anti-cancer effect, kidney stones prevention, lowering serum cholesterol. Because of the insensitivity of existing methods for determination of non-radiolabeled inositol phosphates, little is known about the natural occurrence, much less on the concentrations of InsP(6) and InsP(3) in biological samples. Using gas chromatography-mass detection analysis of HPLC chromatographic fractions, we report a measurement of unlabeled total InsP(3) and InsP(6) (a) as they occur within cells culture, tissues, and plasma, and (b) their changes depending on the presence of exogenous InsP(6). When rats were fed on a purified diet in which InsP(6) was undetectable (AIN-76A) the levels of InsP(6) in brain were 3.35 +/- 0.57 (SE) micromol.kg(-1) and in plasma 0.023 +/- 0.008 (SE) micromol.l(-1). The presence of InsP(6) in diet dramatically influenced its levels in brain and in plasma. When rats were given an InsP(6)-sufficient diet (AIN-76A + 1% InsP(6)), the levels of InsP(6) were about 100-fold higher in brain tissues (36.8 +/- 1.8 (SE)) than in plasma (0.29 +/- 0.02 (SE)); InsP(6) concentrations were 8.5-fold higher than total InsP(3) concentrations in either plasma (0.033 +/- 0.012 (SE)) and brain (4.21 +/- 0.55 (SE)). When animals were given an InsP(6)-poor diet (AIN-76A only), there was a 90% decrease in InsP(6) content in both brain tissue and plasma (p < 0.001); however, there was no change in the level of total InsP(3). In non-stimulated malignant cells (MDA-MB 231 and K562) the InsP(6) contents were 16.2 +/- 9.1 (SE) micromol.kg(-1) for MDA-MB 231 cells and 15.6 +/- 2.7 (SE) for K 562 cells. These values were around 3-fold higher than those of InsP(3) (4.8 +/- 0.5 micromol.kg(-1) and 6.9 +/- 0.1 (SE) for MDA-MB 231 and K562 cells respectively). Treatment of malignant cells with InsP(6) resulted in a 2-fold increase in the intracellular concentrations of total InsP(3) (9.5 +/- 1.3 (SE) and 10.8 +/- 1.0 (SE) micromol.kg(-1) for MDA-MB 231 and K562 cells respectively, p < 0.05), without changes in InsP(6) levels. These results indicate that exogenous InsP(6) directly affects its physiological levels in plasma and brain of normal rats without changes on the total InsP(3) levels. Although a similar fluctuation of InsP(6) concentration was not seen in human malignant cell lines following InsP(6) treatment, an increased intracellular levels of total InsP(3) was clearly observed.

Enzymatic determination of pyrophosphate in urine by flow methods.

Two flow methods for the enzymatic determination of pyrophosphate are described that are used to diminish the consumption of reagents. One method is based on the use of an open-close circuit with manual injection using a syringe. The other is a sequential injection method. The analytical features of both methods are: a linear range of 0.4 - 20 mg L(-1), an LOD of 0.38 mg L(-1), and a CV of 2.0% for the sequential injection method, and a linear range of 0.3 - 15 mg L(-1), an LOD of 0.29 mg L(-1), and CV of 2.2% for the open-close circuit method. The methods were applied to the determination of pyrophosphate in urine. The pyrophosphate concentration determined in urine samples varied from 1.26 to 6.67 mg L(-1).

A sensitive extracto-photometric method for determination of residual chlorine in greywater.

A new photometric method for chlorine determination based on the oxidative transformation of iodide to iodine and subsequent extraction in ethyl acetate has been developed. The effects of several chemical variables (pH, ionic strength, and iodide concentration) have been studied. Characteristics of the method were linear range 0-0.6 mg C12/L, limit of detection 5 microg Cl2/L, and coefficient of variation 0.6%. The method has been applied to greywater without previous sample treatment.