Sensitive Determination of Felodipine in Human and Dog Plasma by Use of Liquid–Liquid Extraction and LC–ESI–MS–MS

Summary A sensitive and selective liquid chromatographic method coupled with electrospray ionization tandem mass spectrometry (LC–ESI–MS–MS) has been developed for quantification of felodipine in human and dog plasma. Compounds were separated on a 2.0 mm × 150 mm, 5.0 m particle, C₈ column with 1 m m ammonium acetate–acetonitrile, 20:80, pH 6.0, as mobile phase at a flow rate of 200 L min^–1. Nifedipine was used as internal standard. Plasma samples were extracted with diethyl ether, the centrifuged upper layer was evaporated, the residue was reconstituted with mobile phase, and the reconstituted samples were injected. The analytical column lasted for at least 1000 injections. By use of multiple reaction monitoring (MRM) mode in MS–MS felodipine and nifedipine were detected without severe interference from the human or dog plasma matrix. Felodipine produced a protonated precursor ion ([M + H]⁺) at m/z 384 and a corresponding product ion at m/z 338. And internal standard (nifedipine) produced a protonated precursor ion ([M + H]⁺) at m/z 347 and a corresponding product ion at m/z 315. Detection of felodipine in human and dog plasma was accurate and precise, with a limit of quantification of 0.05 ng mL^–1. The method has been successfully applied to preliminary pharmacokinetic study of felodipine in human and dog plasma.     

Pressurized Liquid Extraction Coupled with LC–ESI–MS–MS for the Determination of Herbicides Chlormequat and Mepiquat in Flours

This paper describes a new method for the rapid extraction and unequivocal confirmation of herbicides chlormequat and mepiquat in wheat flours and various flours utilized in infant foods. The highly automated extraction procedure is based on accelerated solvent extraction, followed by liquid chromatography-tandem mass spectrometry as a confirmatory analysis. Typical recoveries from flours and baby food samples ranged from 83 to 99% at a fortification level of 10 ppb, corresponding to the maximum residue limits established by the European Union; while relative standard deviations (RSD) were less than 10% for all samples. The limit of detection (signal-to-noise ratio = 3) of the method for the considered phenols in baby food samples are less than 0.1 μg g^?1. Traces of the selected herbicides have been detected in about 50% of baby foods, bought from different Roman supermarkets and butcher shops, applying the described methodology.     

A Dissipative Reaction Network Drives Transient Solid–Liquid and Liquid–Liquid Phase Cycling of Nanoparticles

Transient states maintained by energy dissipation are an essential feature of dynamic systems where structures and functions are regulated by fluxes of energy and matter through chemical reaction networks. Perfected in biology, chemically fueled dissipative networks incorporating nanoscale components allow the unique properties of nanomaterials to be bestowed with spatiotemporal adaptability and chemical responsiveness. We report the transient dispersion of gold nanoparticles in water, powered by dissipation of a chemical fuel. A dispersed state that is generated under non-equilibrium conditions permits fully reversible solid–liquid or liquid–liquid phase transfer. The molecular basis of the out-of-equilibrium process is reversible covalent modification of nanoparticle-bound ligands by a simple inorganic activator. Activator consumption by a coupled dissipative reaction network leads to autonomous cycling between phases. The out-of-equilibrium lifetime is tunable by adjusting the pH value, and reversible phase cycling is reproducible over several cycles.     

High-Throughput Screening of Drugs of Abuse in Urine by Supported Liquid–Liquid Extraction and UHPLC Coupled to Tandem MS

A qualitative method, involving supported liquid–liquid extraction (SLE) and ultra high pressure liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS–MS), was developed for the rapid tentative identification of various drugs of abuse in urine. In this study, 28 drugs and metabolites were covered by the screening procedure. Before analysis, urine samples were extracted by SLE and good extraction recoveries were obtained for most investigated compounds. The UHPLC strategy was then selected for the rapid separation of amphetamines, cocaine, opiates and related compounds in urine. Using columns packed with sub-2 µm particles, analysis time was reduced down to 2 min, while maintaining acceptable performance. Finally, the detection was by tandem MS operating in the single reaction monitoring (SRM) mode. The most intense transition was selected for the different drugs and SRM dwell times set at 5 ms, to maintain sufficient data points across the narrow UHPLC peaks. The tentative identification of the drugs of interest, including amphetamines, opiates and cocaine, was based on both, retention times and mass spectrometry information. With the proposed method, limits of detection were estimated at about 1 ng mL^?1 and the applicability was assessed by successfully analyzing several samples of drug abusers. Finally, this study demonstrates the potential of UHPLC coupled to tandem MS for the rapid screening of drugs of abuse in urine.     

Determination of Aristocularine Enantiomers by Dispersive Liquid–Liquid Microextraction and Chiral High-performance Liquid Chromatography

Here is reported a novel analytical approach for the extractive separation and determination of enantiomeric ratios of aristocularine in bovine serum albumin. The results demonstrate suitable analytical performances. The separation was performed by chiral high-performance liquid chromatography with a 5-µm column using a mobile phase of 1:1 n-hexane:ethanol at a flow rate of 0.7?mL?min^?1 with ultraviolet–visible absorption, circular dichroism, and polarimetric detection. The enantiomers were eluted at 13.2 and 15.6?min for (+) and (?)-aristocularine, with a resolution of 1.58 and a separation factor of 1.27. The analytical parameters for the dispersive liquid–liquid microextraction were optimized; under these conditions, the extraction recoveries were from 88.6% to 93.9% for a two-step extraction. The precision, reported as the percent relative standard deviation, had values from 2.9% to 3.2% for 0.5?µg?mL^?1 of analyte for five replicate measurements using ultraviolet–visible absorption and circular dichroism detection. The limits of detection were between 0.05 and 0.08?µg?mL^?1 with enrichment ratios up to a value of 12.     

Dynamic and Rheological Properties of Span 80 at Liquid–Liquid Interfaces

The adsorption characteristics of Span 80 at liquid/liquid interfaces were investigated. The equilibrium interfacial tension values were successfully fitted with a Langmuir isotherm resulting in the determination of a mean molecular area from 25 to 35 Å²/mol. The measured interfacial tension values and deduced adsorption parameters depend on the experimental technique used to obtain them, either Du Noüy ring or profile analysis tensiometry. Two possible explanations to such phenomenon are provided. Adsorption kinetics of Span 80 at liquid/liquid interfaces were studied, and it was concluded that the diffusion of Span 80 molecules from the bulk is the rate determining step of the adsorption. Finally the interfacial rheology properties were investigated and compared to the Lucassen–van den Tempel model. A good match was obtained when the isotherm parameters determined by profile analysis tensiometry were used.      

Determination of Mycotoxins Using Hollow Fiber Dispersive Liquid–Liquid–Microextraction (HF-DLLME) Prior to High-Performance Liquid Chromatography – Tandem Mass Spectrometry (HPLC - MS/MS)

A modified hollow-fiber-supported dispersive liquid-liquid microextraction (HF-DLLME) method was developed for the determination of aflatoxins and ochratoxin A in food samples. The various parameters affecting the efficiency of extraction, such as pH, salt addition, extraction time, stirring rate, desorption time, type and volume of extractant and disperser solvents were carefully studied and optimized using two step strategies. The linearity of the evaluated results was 0.1 to 30?μg L^?1 for aflatoxins and 0.1 to 20?μg L^?1 for ochratoxin A, with regression coefficients (R²) exceeding 0.9990. The precision was satisfactory with relative standard deviation values less than 11%. The method accuracy was within the recommended range from 70% to 120% and analyte accuracy between 83% and 101%. The limits of detection and quantification were in the range from 0.04 to 0.06?μg L^?1 and 0.08 to 0.13?μg L^?1, respectively, for multi-aflatoxins, and 0.02 to 0.04?µg L^?1 and 0.08 to 0.10?µg L^?1, respectively, for ochratoxin A. The developed method was successfully applied for the determination of mycotoxins in food samples.     

Quantitative determination of cationic modified polysaccharides on hair using LC–MS and LC–MS–MS

Cationic polysaccharides containing N-hydroxypropyl-N,N,N-trimethylammonium substituents are widely used as conditioning agents for hair-care products. A sensitive method has been developed for the quantitation of these polymers. After acidic extraction from hair the polysaccharides are hydrolyzed using trifluoroacetic acid. The cationic monoglycosides are determined using liquid chromatography–tandem mass spectrometry (LC–MS–MS). The developed method is independent of hair treatment. Even hair cut from test persons after customary hair wash can be analyzed. After treatment of natural and bleached hair tresses using a real-life treatment procedure 180 g and 300 g of polymer per gram hair were quantified, respectively. Additionally the fragmentation mechanism of the cationic N-hydroxypropyl-N,N,N-trimethylammonium group during electrospray ionization was investigated. A mass loss of 60 Da in combination with loss of a single charge is observed and associated with cleavage of trimethylamine and a proton. It is assumed that this process is promoted by the anionic counter-ion which might be hydroxide in an aqueous environment.     

Analysis of Phlebodium decumanum Fronds by High-Performance Liquid Chromatography by Ultraviolet-Visible and Quadrupole Time-of-Flight Tandem Mass Spectrometry (HPLC–UV–VIS–QTOF–MS/MS)

Phlebodium decumanum (P. decumanum), together with other tropical ferns commonly known as Calaguala, have been empirically applied since ancient times to ameliorate inflammatory disorders, skins diseases and even cancer. There are evidences of antineoplastic potential and anti-inflammatory, immunomodulatory and antioxidant properties of the extract. Preliminary studies have also shown direct antitumor activity of the extracts. In the present article, the phytochemical composition of a hydro-ethanolic extract of P. decumanum is investigated using high-performance liquid chromatography (HPLC) with ultraviolet–visible (UV–vis) diode array detection (DAD) and electrospray ionization (ESI) quadrupole time-of-flight tandem mass spectrometry (QTOF–MS/MS) detection. First, the chromatographic profile is established as a representative fingerprint of the compounds extracted from the fern. Then, a total of 122 chemicals, including 23 flavonoids, 47 phenolic acids (34 hydroxycinnamic acids and 13 hydroxybenzoic acids), 9 amino and amino-sugar derivatives, 24 organic acids and their derivatives, and other metabolites, have been characterized. Moreover, 12 unknown compounds were also detected, providing the first comprehensive characterization available on the phytochemical composition of the leaves of P. decumanum.     

Detection and Confirmation of Ginsenosides in Horse Urine by GC–MS and LC–MS

Ginseng has been used by the Chinese as a traditional herbal medicine for thousands of years. In view of the growing popularity in the use of ginseng preparations as natural remedies and food supplements worldwide, there is an increasing concern for their abuse in both human and animal sports. Ginsenosides are considered the major constituents of ginseng responsible for its pharmacological properties. In this study, a method was developed for the detection and confirmation of a number of ginsenosides in horse urine. The intact ginsenosides were detected and confirmed at 5–100 ng mL^?1 by LC–MS², and two deglycosylation metabolites, namely protopanaxadiol and protopanaxatriol, could both be detected and confirmed at 2 ng mL^?1 by GC–MS² after trimethylsilylation. The above GC–MS and LC–MS methods were then applied to study the in vitro metabolism of ginsenosides Rg1 and Rb1 and the in vivo urinary metabolites after oral administration of Rg1 to horses. Results obtained reveal the very first evidence for the existence of the metabolites, Rg1 and protopanaxatriol, as glucuronides in urine.     

Investigation of Euphrasia rostkoviana Hayne Using GC–MS and LC–MS

Gas and liquid chromatography coupled with mass spectrometry was applied to solve difficulties and reinvestigate the serious matrix problems affecting analysis of the active compounds in Euphrasia rostkoviana Hayne. The main groups of compounds were obtained by extracting the herb stepwise with n-hexane, chloroform, ethyl acetate and methanol. Polyamide column chromatography facilitated further separation. Phenolic/flavonoid- and terpenoid-type molecules were studied by GC–MS, HPLC and LC–MS–MS. The β-sitosterol content of the herb was determined by gas chromatography with flame ionisation detection (GC-FID). Caffeic acid, chlorogenic acid, coumaric acid and flavonoid glycosides of apigenin, luteolin, rhamnetine (hexoside), kaempferol (both hexoside and rutinoside) and quercetin (rutinoside) were identified in the fractions of the methanolic extract.     

LC–MS–MS Determination of Stabilizers and Explosives Residues in Hand-Swabs

The contribution of explosive trace detection in samples from the hands of suspects has been fundamental in several forensic cases involving terrorists. This paper describes a method for the rapid extraction and unequivocal confirmation of some high potential explosives (trinitrotoluene, cyclotrimethylenetrinitramine, pentaerythritol tetranitrate, nitroglycerin) and two stabilizer (diphenylamine and ethylcentralite) residues in hand-swabs using liquid chromatography–tandem mass spectrometry. The extraction procedure of the analytes from the swabs is realized by solvent elution and the extracts are directly analyzed. Recoveries from spiked swabs range from 78 to 96%; the limits of quantification are between 0.04 and 1.8 ng injected and the inter-day method precision is less than 15%. The developed procedure was applied to the detection of explosives traces in samples after handling tests.     

Homogeneous Liquid–Liquid Microextraction Via Flotation Assistance (HLLME-FA) Method for the Pretreatment of Organochlorine Pesticides in Aqueous Samples and Determination by GC–MS

This work proposes a new, rapid and simple homogeneous liquid–liquid microextraction via flotation assistance technique for the analysis of six organochlorine pesticides in water samples. A special extraction cell was used to facilitate collection of the low-density solvent extract. No centrifugation was required in this procedure. Determination was carried using gas chromatography–mass spectrometry. The water sample solution was then added into the extraction cell containing appropriate mixture of extract and homogeneous solvents. In the first step, a homogeneous solution and then with the continuation of water sample injection, a cloudy solution was formed. Using air flotation, the organic solution was collected at the conical part of the designed cell. The optimized levels of effective parameters were found based on response surface methodology approach. Applying the optimized conditions to the system understudy, the limits of detection of all target analytes were obtained in the range of 1.4–7 ng mL^?1, while the precisions were found to be in the range of 11.08–14.87 (RSD, n = 3). The linearity of the method lay in the range of 10–150 ng mL^?1 with the coefficients of correlation (r ² ) ranging from 0.998 to 0.999.     

Ionic Liquid–Liquid Extraction and Supported Liquid Membrane Analysis of Lipophilic Wood Extractives from Dissolving-Grade Pulp

In this study, the extraction of lipophilic wood extractives from dissolving pulp samples using ionic liquid–liquid extraction and a two phase hollow fibre supported liquid membrane was investigated. Ionic liquids are capable of dissolving a range of organic and polymeric compounds and are biodegradable, with a negligible vapour pressure. Pulp samples were dissolved in a suitable amount of molten 1-butyl-3-methylimidazolium chloride to give 5 % cellulose solution. Pure cellulose was regenerated by adding water and filtered off. The ionic liquid-aqueous filtrate was first extracted for lipophilic extractives using liquid–liquid extraction. Then, a two phase hollow fibre supported liquid membrane extraction of lipophilic extractives was performed to extract the derivatized compounds prior to analysis by gas chromatography mass spectrometry. The operational parameters of this sample preparation approach were optimised using sterols and fatty acid methyl esters. The variation of enrichment factors and extraction efficiency with respect to liquid membrane, extraction time, stirring speed and sample pH were observed and used to get the optimal parameters. The approach was used in the analysis of oxygen bleached dissolving pulp samples in which main compounds identified were fatty acids, sterols, fatty alcohols, steroid hydrocarbons and ketones. These compounds were similar to those obtained using molecular solvent extraction method, which indicated the absence of chemical reaction between extractives and ionic liquid used.

     

Liquid–Liquid Equilibrium Data for 1-Ethyl-3-methylimidazolium Acetate–Thiophene–Diesel Compound: Experiments and Correlations

Extraction of thiophene from cyclohexane, isooctane and toluene were performed using the ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]) at T=298.15 K. The liquid?Cliquid equilibrium (LLE) experiments were performed on three systems, namely: [EMIM][OAc]?Cthiophene?Ccyclohexane, [EMIM][OAc]?Cthiophene?Cisooctane and [EMIM][OAc]?Cthiophene?Ctoluene. The LLE data showed that [EMIM][OAc] has a higher selectivity at low concentration of thiophene and also showed that the hydrocarbon-rich phase is free of ionic liquid. This implies that there will be no cross contamination and the ionic liquid will be a non-pollutant in fuel after extraction. Further, the amount of hydrocarbon in the ionic-liquid-rich phase is very small. This implies that ionic liquid can be regenerated with negligible loss of fuel. LLE data was then correlated using the NRTL and UNIQUAC models. These showed root mean square deviation (RMSD) values of 0.82?% and 1.46?% for the isooctane system, 1.37?% and 1.57?% for the cyclohexane system and 1.39?% and 1.53?% for the toluene system.     

Application of CE–ICP–MS and CE–ESI–MS in metalloproteomics: challenges,developments, and limitations

Application of capillary electrophoresis (CE) as a high-resolution separation technique in metalloproteomics research is critically reviewed. The focus is on the requirements and challenges involved in coupling CE to sensitive element and molecule-specific detection techniques such as inductively coupled plasma mass spectrometry (ICP–MS) or electrospray ionisation mass spectrometry (ESI–MS). The complementary application of both detection techniques to the structural and functional characterisation of metal-binding proteins and their structural metal-binding moieties is emphasised. Beneficial aspects and limitations of mass spectrometry hyphenated to CE are discussed, on the basis of the literature published in this field over the last decade. Recent metalloproteomics applications of CE are reviewed to demonstrate its potential and limitations in modern biochemical speciation analysis and to indicate future directions of this technique.     

LC–UV Methodology for Simultaneous Determination of Lamivudine and Zidovudine in Plasma by Liquid–Liquid Extraction

This study describes an accurate, sensitive, and specific chromatographic method for the simultaneous quantitative determination of lamivudine and zidovudine in human blood plasma, using stavudine as an internal standard. The chromatographic separation was performed using a C8 column (150 × 4.6 mm, 5 μm), and ultraviolet absorbency detection at 270 nm with gradient elution. Two mobile phases were used. Phase A contained 10 mM potassium phosphate and 3% acetonitrile, whereas Phase B contained methanol. A linear gradient was used with a variability of A-B phase proportion from 98–2% to 72–28%, respectively. The drug extraction was performed with two 4 mL aliquots of ethyl acetate.     

Determination of Phthalates in Milk by Ultrasound-Assisted Dispersive Liquid–Liquid Microextraction and Gas Chromatography–Mass Spectrometry

Ultrasound-assisted dispersive liquid–liquid microextraction was coupled with gas chromatography—mass spectrometry for the determination of phthalate esters in milk. Dimethyl phthalate, diethyl phthalate, dibutyl phthalate, benzyl butyl phthalate, bis(2-ethylhexyl) phthalate, and dioctyl phthalate were analyzed in five brands of pasteurized Turkish milk. The efficiencies of the extraction procedure for the analytes were between 66 and 100%. The linear dynamic ranges of the calibration curves were from 0.025 to 1.000 µg/mL with correlation coefficients exceeding 0.99. The precision of the method is acceptable with relative standard deviation values below 5%. Dibutyl phthalate and bis(2-ethylhexyl) phthalate were commonly observed in milk.     

Determination of Aflatoxins in Plant-based Milk and Dairy Products by Dispersive Liquid–Liquid Microextraction and High-performance Liquid Chromatography with Fluorescence Detection

The consumption of plant-based milk has increased due to their nutritional attributes. However, these products may contain aflatoxins if contaminated raw materials were used, although little concern is present in international regulation regarding this topic. In this work, dispersive liquid–liquid microextraction (DLLME) was used for the determination of the most important aflatoxins (B₁, B₂, G₁, and G₂) in oat, rice, coconut, almond, and birdseed plant-based milk and milk-based products enriched with oats, almonds, and walnuts using high-performance liquid chromatography (HPLC) with photochemical derivatization and fluorescence detection. Calibrations in matrix were performed for all of the samples, obtaining satisfactory linearity, with correlation coefficients exceeding 0.994 for all of the aflatoxins. The precision in terms of repeatability and intermediate precision, expressed as the relative standard deviation, was lower than 9.7%, and recoveries ranged between 82 and 104%, fulfilling current legislation for the determination of aflatoxins. In addition, the limits of quantification were 0.5?µg?L^?1 for the aflatoxins, allowing the determination of these compounds below the maximum levels established by European Commission in these commodities. Finally, 23 commercial products were analyzed to characterize the presence of these toxins.