Showing papers in "Analytical Abstracts in 2012"

Simultaneous determination of human and veterinary antibiotics in various environmental matrices by rapid resolution liquid chromatography-electrospray ionization tandem mass spectrometry.

Abstract: A robust and sensitive analytical method is presented in which 11 classes of antibiotics are simultaneously extracted and determined in surface water, lagoon wastewater, influent, effluent, sediment, manure and sludge. Water samples with different volumes were adjusted to pH 3, added with 0.2 g Na2EDTA and then extracted using Oasis hydrophilic-lipophilic balance (HLB) cartridges. Extraction of solid samples was carried out by a combination of ultrasonic and vortex mixing using a mixture of acetonitrile and citric buffer at pH 3 as the extraction solution. The extracts of the solid samples were then cleaned-up by a tandem solid phase extraction (SPE) method using a strong anion exchange cartridge (SAX) and a HLB cartridge, followed by analysis using rapid resolution liquid chromatography-tandem mass spectrometry (RRLC-MS/MS) equipped with electrospray ionization source. Among the 50 target compounds, the recoveries in the range of 50-150% were obtained for 39, 40, 36, 40, 38, 33 and 36 antibiotics in the spiked samples of surface water, lagoon wastewater, influent, effluent, sediment, manure and sludge with three concentrations, respectively. Method quantification limits (MQLs) for the target compounds (except sulfaguanidine and sulfanilamide) were in the range of 0.52-5.88 ng/L, 2.36-65.8 ng/L, 1.73-20 ng/L, 1.42-9.52 ng/L, 0.64-6.67 ng/g (except bacitracin and cloxacillin), 1.33-17.4 ng/g (except salinomycin, narasin, monensin, cloxacillin and novobiocin) and 1.50-28.6 ng/g (except salinomycin, narasin, monensin and cloxacillin) in surface water, lagoon wastewater, influent, effluent, sediment, manure and sludge, respectively. The developed analytical method was successfully applied in the determination of target compounds in wastewater and sludge samples from Huiyang wastewater treatment plants, and in ground water, lagoon wastewater, manure and sediment collected from a pig farm, in South China.

‘Emerging’ mycotoxins in cereals processing chains: Changes of enniatins during beer and bread making.

Abstract: Enniatins represent an emerging food safety issue because of their extensive incidence, documented in recent decades, in various small grain cereals. This study was concerned with the fate of these Fusarium mycotoxins within malting, brewing, milling and baking, when employed for the processing of contaminated barley and wheat. Besides enniatins A, A1, B and B1, also deoxynivalenol and its conjugated form (deoxynivalenol-3-glucoside) were determined in almost all tested cereal-based samples. Significant decline of enniatins occurred within all technologies, with the largest drop in their concentrations observed in the brewing process. While enniatins were not detectable in final beers, they were almost quantitatively transferred to spent grains, probably because of their limited water solubility. Regarding bread baking, levels of enniatins decreased down to 30% of their concentration in the initial flour used for baking. In this case, degradation at higher temperatures might be assumed.

SERS substrate for detection of explosives.

Abstract: A novel gold coated femtosecond laser nanostructured sapphire surface - an “optical nose” - based on surface-enhanced Raman spectroscopy (SERS) for detecting vapours of explosive substances was investigated. Four different nitroaromatic vapours at room temperature were tested. Sensor responses were unambiguous and showed response in the range of 0.05-15 µM at 25 °C. The laser fabricated substrate nanostructures produced up to an eight-fold increase in Raman signal over that observed on the unstructured portions of the substrate. This work demonstrates a simple sensing system that is compatible with commercial manufacturing practices to detect taggants in explosives which can undertake as part of an integrated security or investigative mission.

Recent applications in derivative ultraviolet/visible absorption spectrophotometry: 2009-2011 : A review.

Abstract: Derivative spectrophotometry (DS) has been introduced for the resolution of overlapping peaks. DS method has been widely used to enhance the signal and resolve the overlapped peak-signals due to its advantages in differentiating closely adjacent peaks, and identifying weak peaks obscured by sharp peaks. In this work, the analytical applications of derivative UV/VIS region absorption spectrophotometry produced in the last 3 years (since 2009) are reviewed (review).

A method for determining the free (unbound) concentration of ten beta-lactam antibiotics in human plasma using high performance liquid chromatography with ultraviolet detection.

Abstract: With the clinical imperative to further research in the area of optimising antibiotic dosing in the intensive care setting, a simple high performance liquid chromatography method was developed and validated for routinely determining the free (unbound) concentration of ten beta-lactam antibiotics in 200 µL of human plasma. Antibiotics determined include three cephalosporins (ceftriaxone, cephazolin and cephalotin); two carbapenems (meropenem and ertapenem); and five penicillins (ampicillin, piperacillin, benzylpenicillin, flucloxacillin and dicloxacillin). There was a single common sample preparation method involving ultracentrifugation and stabilisation. Chromatography was performed on a Waters XBridge C18 column with, depending on analytes, one of four acetonitrile-phosphate buffered mobile phases. Peaks of interest were detected via ultraviolet absorbance at 210, 260 and 304 nm. The method has been validated and used in a pathology laboratory for therapeutic drug monitoring in critically ill patients. The significant variability in the level of protein binding that is common with antibiotics traditionally considered to have high protein binding (e.g. ceftriaxone, cephazolin, ertapenem, flucloxacillin and dicloxacillin) suggests that this assay should be preferred for measuring the pharmacologically active concentration of beta-lactam antibiotics in a therapeutic drug monitoring programme.

Enhanced fluorescence sensing of melamine based on thioglycolic acid-capped CdS quantum dots.

Abstract: A sensitive and simple method for the determination of melamine (MA) was developed based on the fluorescence enhancement effect of MA for thioglycolic acid-capped (TGA-capped) CdS quantum dots (QDs). Under optimum conditions, a good linear relationship was obtained from 2.0 × 10–9 to 5.0 × 10–5 M. The detection limit was 1.0 × 10–9 M, which was much lower than the safety limit (2.5 ppm in USA and the UK; 1 ppm for infant formula in China). The solution pH, the adding sequence of the buffer solution and MA and surface modifiers of CdS QDs greatly influenced the enhancement extent of MA for CdS QDs. The fluorescence enhancement was attributed to the surface passivation of the surface states of QDs by amine group of MA. The method was applied to detect MA in raw milk with satisfactory results. The proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation.

Development and validation of an HPLC method for the determination of six penicillin and three amphenicol antibiotics in gilthead seabream (Sparus aurata) tissue according to the European Union decision 2002/657/EC.

Abstract: A confirmatory high performance liquid chromatography method for the determination of six penicillin antibiotics and three amphenicol antibiotics in gilthead seabream (Sparus Aurata) tissue was developed. Ampicillin (AMP), penicillin G (PG), penicillin V (PV), oxacillin (OXA), cloxacillin (CLO), dicloxacillin (DICLO), thiamphenicol (TAP), florfenicol (FFC) and chloramphenicol (CAP) were separated on an Inertsil, C8 (250 × 4 mm, 5 µm) column by gradient elution with a mobile phase consisting of ammonium acetate 0.05 M and acetonitrile at 25 °C. Diode array detection with monitoring at 225 nm (for the determination of AMP, PG, PV, TAP and FFC), 240 nm (for OXA, CLO and DICLO) and 278 nm (for CAP) was applied. Examined antibiotics were isolated from gilthead seabream tissue by liquid-liquid extraction and further clean-up was performed by solid phase extraction using Oasis HLB (200 mg/6 mL) cartridges. The developed method was fully validated in terms of selectivity, linearity, accuracy, precision, stability and sensitivity according to the European Union Decision 2002/657/EC.

Species-specific expression of various proteins in meat tissue: Proteomic analysis of raw and cooked meat and meat products made from beef, pork and selected poultry species.

Abstract: The aim was to search for proteins differentiating the six species (cattle, pig, chicken, turkey, duck and goose) and relatively stable during the meat aging and only slightly degraded in ready-made products. The two-dimensional electrophoresis was used for analysis of the protein profiles from raw meat and frankfurters and sausages (15 products). The observed species-specific differences in protein expression in raw meat were retained in processed products after finishing the entire technological process. Regulatory proteins, metabolic enzymes, some myofibrillar and blood plasma proteins were identified, which were characterised by the electrophoretic mobility specific to the given species. Large differences in the primary structure were observed in serum albumin, apolipoprotein B, HSP27, H-FABP, ATP synthase, cytochrome bc-1 subunit 1 and alpha-ETF. Some of these proteins have potential to be used as markers in authentication of meat products.

Development of a gas chromatography-mass spectrometry method for the determination of pesticides in gaseous and particulate phases in the atmosphere.

Abstract: A reliable multi-residue method for determining gaseous and particulate phase pesticides in atmospheric samples has been developed. This method, based on full scan gas chromatography-mass spectrometry (GC-MS), allowed the proper determination of sixteen relevant pesticides, in a wide range of concentrations and without the influence of interferences. The pesticides were benfluralin, bitertanol, buprofezin, chlorfenvinphos, chlorpyrifos, chlorpyrifos-methyl, ethalfluralin, fenthion, lindane, malathion, methidathion, propachlor, propanil, pyriproxifen, tebuconazol and trifluralin. Comparisons of two types of sampling filters (quartz and glass fibre) and four types of solid-phase cartridges (XAD-2, XAD-4, Florisil and Orbo-49P) showed that the most suitable supports were glass fibre filter for particulate pesticides and XAD-2 and XAD-4 cartridges for gaseous pesticides (>95% recovery). Evaluations of elution solvents for ultrasonic-assisted extraction demonstrated that isooctane is better than ethylacetate, dichloromethane, methanol or a mixture of acetone:hexane (1:1). Recovery assays and the standard addition method were performed to validate the proposed methodology. Moreover, large simulator chamber experiments allowed the best study of the gas-particle partitioning of pesticides for testing the sampling efficiency for the validation of an analytical multiresidue method for pesticides in air. Satisfactory analytical parameters were obtained, with a repeatability of 5 ± 1%, a reproducibility of 13 ± 3% and detection limits of 0.05-0.18 pg m–3 for the particulate phase and 26-88 pg m–3 for the gaseous phase. Finally, the methodology was successfully applied to rural and agricultural samples in the Mediterranean area.

An ICT based “turn on/off” quinoline armed calix(4)arene fluoroionophore: Its sensing efficiency towards fluoride from waste water and Zn2+ from blood serum.

Abstract: A novel structurally simple calix(4)arene appended 8-amidoquinoline linked conjugate was synthesized and has been used as a turn-on fluorescence probe for Zn2+ and turn off fluorescence probe for F–. Moreover, this probe has been applied for Zn2+ detection in blood serum upto 8.7 µM and fluoride detection upto 22 nM in waste water samples, using emission spectra.

Liquid chromatography-tandem mass spectrometry method for determination of five antidepressants and four atypical antipsychotics and their main metabolites in human serum.

Abstract: The rapid and simple ultra performance liquid chromatography-tandem mass spectrometry method was developed and validated for simultaneous determination parent drugs: sertraline, fluoxetine, citalopram, paroxetine, venlafaxine, clozapine, olanzapine, quetiapine, risperidone, and their active and nonactive metabolites N-desmethylsertraline, norfluoxetine, desmethylcitalopram, didemethylcitalopram, N-desmethylvenlafaxine, O-desmethylvenlafaxine, N-desmethylclozapine, N-desmethylolanzapine, 2-hydroxyolanzapine and 9-hydroxyrisperidone in human serum. Precipitation of serum proteins was performed with a precipitation reagent consisting of 0.05% solution of ZnSO4·7H2O in acetonitrile/methanol (40:60, v/v). Alprenolol was used as an internal standard. Chromatographic separation was carried out on a BEH C18 column using gradient elution mobile phase A (2 mmol/L ammonium acetate, 0.1% formic acid in 5% acetonitrile, v/v/v) and B (2 mmol/L ammonium acetate, 0.1% formic acid in 95% acetonitrile, v/v/v). Electrospray in positive mode was used for ionization. Detection was performed on a triple-quadrupole tandem mass spectrometer by multiple reaction monitoring. Analysis time was 5 min. Drugs were separated into three groups with low, medium and high levels. Correlation coefficients of calibration curves were in the range 0.995-1.000. Coefficients of variation were 4.2-9.5% for intra-assay and 3.0-11.9% for inter-assay. Recoveries were 87.1-110% for intra-assay and 88.1-108.2% for inter-assay. The method was fully validated and can be successfully applied for routine analyses.

Liquid chromatography-tandem mass spectrometry analysis allows the simultaneous characterization of C-glycosyl and O-glycosyl flavonoids in stingless bee honeys.

Abstract: The analysis of the phytochemicals present in stingless bee honey samples has been a difficult task due to the small amounts of samples available and to the complexity of the phytochemical composition that often combines flavonoid glycosides and aglycones. Honey samples produced in Venezuela from Melipona species were analyzed using a combination of solid-phase extraction and HPLC-DAD-MSn/ESI methodologies with specific study of the fragment ions produced from flavonoid glycosides. The analyses revealed that flavonoid glycosides were the main constituents. The honey samples analyzed contained a consistent flavonoid pattern composed of flavone-C-glycosides, flavonol-O-glycosides and flavonoid aglycones. The HPLC-DAD-MSn/ESI analysis and the study of the fragment ions obtained allowed the characterization and quantification for the first time of five apigenin-di-C-glycosides, and ten quercetin, kaempferol and isorhamnetin O-glycosides (di- and tri- glycosides), and the aglycones pinobanksin, quercetin, kaempferol and isorhamnetin in the different samples. This is the first report of flavonoid-C-glycosides in honey. The results show that the content of flavonoid-glycosides (mean values of 2712 µg/100 g) in stingless bee honeys is considerably higher than the content of flavonoid aglycones (mean values of 315 µg/100 g). This differs from previous studies on Apis mellifera honeys that consistently showed much higher aglycone content and smaller flavonoid glycoside content. The occurrence of relevant amounts of flavonoid glycosides, and particularly C-glycosides, in stingless bee honeys could be associated with their putative anticataract properties.

Integrated printed circuit board device for cell lysis and nucleic acid extraction.

Abstract: Preparation of raw, untreated biological samples remains a major challenge in microfluidics. We present a novel microfluidic device based on the integration of printed circuit boards and an isotachophoresis assay for sample preparation of nucleic acids from biological samples. The device has integrated resistive heaters and temperature sensors as well as a 70 µm × 300 µm × 3.7 cm microfluidic channel connecting two 15 µL reservoirs. We demonstrated this device by extracting pathogenic nucleic acids from 1 µL dispensed volume of whole blood spiked with Plasmodium falciparum. We dispensed whole blood directly onto an on-chip reservoir, and the system's integrated heaters simultaneously lysed and mixed the sample. We used isotachophoresis to extract the nucleic acids into a secondary buffer via isotachophoresis. We analyzed the convective mixing action with micro particle image velocimetry (micro-PIV) and verified the purity and amount of extracted nucleic acids using off-chip quantitative polymerase chain reaction (PCR). We achieved a clinically relevant limit of detection of 500 parasites per microliter. The system has no moving parts, and the process is potentially compatible with a wide range of on-chip hybridization or amplification assays.

Analysis of synthetic endocrine-disrupting chemicals in food: A review.

Abstract: This work focuses on a revision of analytical methodologies for the determination of industrial chemicals that have an endocrine-disrupting effect on food commodities. These food commodities have been divided into two major categories: crops and food of animal origin. The reviewed methods have been commented on in terms of sample preparation, analytical methods, and the occurrence of the studied compounds (review).

Comparison of electrospray ionization, atmospheric pressure chemical ionization and atmospheric pressure photoionization for a lipidomic analysis of Leishmania donovani.

Abstract: A comparison of electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) for the analysis of a wide range of lipids has been performed on standard mixtures and extracts of Leishmania donovani promastigotes resistant to Amphotericin B (AmB). Calibration model, precision, limits of detection and quantification (LOD and LOQ) were assessed for each source. APPI provided the highest signal, signal-to-noise (S/N), and sensitivity for non-polar and low-polarity lipids, while ESI and APCI gave better results for the most polar ones. The linear model was valid for all lipids, except for one class with APPI, six classes with ESI, and eleven classes with APCI. LODs ranged from 0.2 to 20 µg mL–1 for ESI, from 0.1 to 10 µg mL–1 for APCI, and from 0.02 to 9.5 µg mL–1 for APPI. LOQs ranged from 0.2 to 61 µg mL–1 for ESI, from 0.4 to 31 µg mL–1 for APCI, and from 0.1 to 29 µg mL–1 for APPI. Each source provided similar lipid composition and variations in a comparison of three different L. donovani samples: miltefosine-treated, miltefosine-resistant and treated miltefosine-resistant parasites. A treated miltefosine-resistant sample was finally analyzed with each ion source in order to verify that the same lipid molecular species are detected.

Development of a liquid chromatography-tandem mass spectrometry assay of six antimicrobials in plasma for pharmacokinetic studies in premature infants.

Abstract: This method provides a simple extraction procedure, as well as a validated, sensitive, and specific liquid chromatography-tandem mass spectrometry assay for the simultaneous quantification of ampicillin, piperacillin, tazobactam, meropenem, acyclovir, and metronidazole in human plasma. The method was validated over concentration ranges specific for each compound, with a lower limit of quantification of 50-300 ng/mL and a sample volume of 50 µL. The method is accurate and precise, with within- and between-day accuracy ranging from 85 to 110% and 92 to 110%, respectively, and within- and between-day precision of 89-111% and 91-109%, respectively. Simplicity, low plasma volume, and high throughput make this method suitable for clinical pharmacokinetic studies in premature infants.

Analysis of fluoxetine and norfluoxetine in human plasma by liquid-phase microextraction and injection port derivatization GC-MS.

Abstract: A two-phase liquid phase microextraction using a hollow fiber combined with injection port derivatization and gas chromatographic analysis was developed for extracting and detecting fluoxetine (FLU) and norfluoxetine (NOR) in human plasma. Simultaneous extraction in a multiple tube shaker was used and, afterward, the organic phase was simply injected together with the derivatizing agent n-methyl-bis(trifluoroacetamide) (MBTFA). Factors influencing injection port derivatization, and several extraction parameters were optimized. Under optimal conditions the proposed method provided linearity between 10 and 500 ng mL–1 (R2 = 0.9973) for FLU, and between 15 and 500 ng mL–1 (R2 = 0.9972) for NOR. Intra-assay precision (RSD) between 4.8 and 13.1% and inter-assay between 5.4 and 14.2% were obtained, with detection and quantification limits of 3 and 10 ng mL–1, and of 5 and 15 ng mL–1 for FLU and NOR, respectively, using selected ion monitoring mode. Selectivity, short term stability and extraction efficiency were also evaluated. This method was simple, cheap, and environmentally friendly, yielding significant reduction of solvents and derivatizing agent consumption. The method was successfully applied to the analysis of samples from 5 patients under fluoxetine treatment.

Levels of Se, Zn, Mg and Ca in commercial goat and cow milk fermented products: Relationship with their chemical composition and probiotic starter culture.

Abstract: We determined Se, Zn, Mg and Ca levels in 42 samples of goat and cow fermented milks which are widely consumed in Spain were determined. Atomic absorption spectrometry (hydride generation for Se and flame atomisation for remaining elements) was used as an analytical technique. Reliability of the procedure was checked. Only Mg levels in goat fermented milks were significantly higher to those found in cow fermented milks (p 0.05). It was concluded that goat fermented milks are a better source for Mg than cow samples.

Evolution of chemico-physical characteristics during manufacture and ripening of Castelmagno PDO cheese in wintertime.

Abstract: Biochemical, volatile and textural profiles during manufacture and ripening were determined in samples of Castelmagno PDO cheese obtained from three different batches in the main artisan cheese plant of Castelmagno PDO production area. At the end of manufacture, samples were characterised by a pH of 6.57% and 52.4% moisture content. The HPLC analysis of organic acids and sugars showed the exhaustion of lactose content, while Urea-PAGE indicated extensive primary proteolysis of both β-casein and αs1-casein. During ripening, cheeses were characterised by high degradation of β-casein and αs1-casein, due to bacterial action. RP-HPLC profiles showed a high production of peptides eluted between 20 and 30 min. In total, 92 volatile compounds were identified in cheese headspace. Texture profiles showed an increase in hardness, gumminess, chewiness and adhesiveness values, as well as a decrease in cohesiveness during ripening.

Multiclass residues screening of 105 veterinary drugs in meat, milk, and egg using ultra high performance liquid chromatography tandem quadrupole time-of-flight mass spectrometry.

Abstract: A high-throughput and robust method for analyzing multiclass residues of veterinary drugs in meat, milk, and egg by ultra-high performance liquid chromatography (UHPLC)-quadrupole time-of-flight mass spectrometry (QTOF) was established. The method successfully applied to the screening, quantification, and confirmation of 105 compounds from 9 different classes of drugs, including beta-agonists, benzimidazoles, corticoides, triphenylmethane, nitromidazoles, quinolones, sulfonamides, tetracylines, and benzodiazepams. The samples are extracted by a single extraction using acetonitrile containing 0.1% formic acid, followed by an easy solid phase extraction (SPE) clean-up on HLB column and finally analyzed by LC/MS QTOF MS. The separation was achieved within 30 min at the optimized chromatographic conditions. More than 92% compounds in this study can be reliably identified based on accurate mass measurement (within the 3 ppm mass error) at the 5 µg/kg concentration levels in the complex food matrix with further MS/MS confirmation. Our study demonstrated a reliable, high-efficient and high-sensitive strategy for the fast and high throughput screening of multiclass of veterinary drugs in foodstuffs of animal origin.

Electrochemical behavior of azithromycin at graphene and ionic liquid composite film modified electrode.

Abstract: An electrochemical method has been successfully demonstrated for sensitive determination of azithromycin (Azi) with room temperature ionic liquid (IL) of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) - graphene (Gr) composite modified glassy carbon electrode (GCE). The cyclic voltammetric results indicate that Gr/IL/GCE can remarkably enhance electrocatalytic activity towards the oxidation of Azi in neutral solutions. Azi produce an anodic peak at about 0.82 V at this electrode. The electrocatalytic behavior was further exploited as a sensitive detection scheme for the Azi determination by differential-pulse voltammetry (DPV). Under optimized conditions, the concentration range and detection limit were 0.49-28.57 µg ml–1 and 0.19 µg ml–1 (S/N = 3) respectively for Azi. The method was successfully applied assay of the drug in the pharmaceutical dosage forms.

Development and validation of RP-UPLC method for the determination of darifenacin hydrobromide, its related compounds and its degradation products using design of experiments.

Abstract: A selective stability-indicating ultra-performance liquid chromatographic (UPLC) method was developed for the quantitative determination of darifenacin hydrobromide (DFN) and its related compounds in API and pharmaceutical dosages. The chromatographic separation was achieved on an Acquity UPLC BEH C18 column (100, 2.1 mm and 1.7 µm) at a flow rate of 0.3 mL/min, and detection was performed at 210 nm. The typical retention behaviors of impurities at various pH values were depicted graphically. The LC conditions were optimized by design of experiments (DOE) to obtain optimal separation in the shortest possible run time. A central composite design (CCD) was employed to study the main effects and interactions of the independent variables. The drug and its thirteen impurities were eluted within 13 min. The method exhibited consistent, high-quality recoveries (93.8 ± 2.1 to 99.8 ± 1.5 (mean ± RSD)) with a high precision for the drug and impurities. Linear regression analysis revealed an excellent correlation between peak responses and concentrations (R2 values of 0.9991-0.9999) for the drug and impurities. The stability-indicating capability of the method was verified by forced degradation experiments and mass balance study. LC-MS revealed protonated molecular ion peaks (M + H)+ at m/z 428.20, m/z 425.20 and m/z 281.30 for the acid (Imp-4), oxidized (Imp-6) and N-dealkylated (Imp-1) forms of DFN, respectively. Possible degradation pathways were established based on the known reactivity of the drug through hydrolysis, oxidation, N-dealkylation, phenyl hydroxylation, dihydrobenzofuran ring hydroxylation and ring opening. The m/z values of unknown degradation products were matched with the proposed structures and reported DFN metabolites.

Matrix solid-phase dispersion method for the determination of macrolide antibiotics in sheep's milk.

Abstract: A simple and effective extraction method based on matrix solid-phase dispersion (MSPD) was developed for the simultaneous cleaning-up and quantitative extraction of macrolide antibiotics (erythromycin, oleandomycin, roxithromycin, josamycin, spiramycin, tylosin and ivermectin) from manchega sheep milk samples. Solid support, defatting and elution solvents were evaluated thoroughly to find the optimal MSPD conditions. The best results were obtained using washed sea sand as dispersant sorbent, hexane as defatting agent and a mixture methanol/ethyl actetate (50:50) as elution solvent. Quantitative analyses were performed by liquid chromatography (LC) with diode-array ultraviolet detector (DAD-UV). The chromatographic separation was performed on a Hypersil ODS column (5 µm, 250 × 4.6) with a gradient system of KH2PO4 25 mM (pH = 7) and acetonitrile as the mobile phase at the flow rate of 1.2-1.5 mL min–1 and 60 °C of temperature. Under these conditions antibiotics recoveries were between 74% and 97% and relative standard deviations ranging from 1.6% to 9.0%. The analytical figures of merit of the optimised method have been performed using spiked milk samples at two different concentration levels (96.5 and 482.6 µg kg–1). The proposed method has been successfully applied to the determination of macrolides on milk samples.

Voltammetric determination of Δ9-THC in glassy carbon electrode: An important contribution to forensic electroanalysis.

Abstract: A new voltammetric method for the determination of Δ9-tetrahydrocannabinol (Δ9-THC) is described. The voltammetric experiments were accomplished in N-N dimethylformamide/water (9:1, v/v), using tetrabutylammonium tetrafluoroborate (TBATFB) 0.1 mol/L as supporting electrolyte and a glassy carbon disk electrode as the working electrode. The anodic peak current was observed at 0.0 V (vs. Ag/AgCl) after a 30 s pre-concentration step under an applied potential of –1.2 V (vs. Ag/AgCl). A linear dependence of Δ9-THC detection was obtained in the concentration range 2.4-11.3 ng/mL, with a linear correlation coefficient of 0.999 and a detection limit of 0.34 ng/mL. The voltammetric method was used to measure the content of Δ9-THC in samples (hemp and hashish) confiscated by the police. The elimination of chemical interferences from the samples was promptly achieved through prior purification using the TLC technique, by employing methanol/water (4:1, v/v) as the mobile phase. The results showed excellent correlation with results attained by HPLC.

Electrochemical determination of tryptophan, uric acid and ascorbic acid at a gold nanoparticles modified carbon paste electrode.

Abstract: A carbon paste electrode (CPE) modified with gold nanoparticles was used as a selective electrochemical sensor for the determination of tryptophan (Trp), uric acid (UA) and ascorbic acid (AA). Cyclic voltammetric, chronoamperometric, and differential pulse voltammetric methods were used to investigate the electrocatalytic oxidation of Trp in aqueous solution. The Au nanoparticles modified carbon paste electrode (AuNPs/CPE) showed very efficient electrocatalytic activity for anodic oxidation of Trp, UA, and AA. The linear calibration range for Trp in the presence of 100 µM AA and 50 µM UA was 6-200 µM, with a detection limit of 0.65 µM (S/N = 3). A linear relationship was found for UA in the range of 6-180 µM containing 100 µM AA and 25 µM Trp, with a detection limit of 0.71 µM. The linear calibration range for AA in the presence of 50 µM UA and 50 µM Trp was 20-250 µM, with a detection limit of 2.05 µM. The diffusion coefficient (D) for the oxidation of Trp at the modified electrode was calculated as 2.82 × 10–5 cm2 s–1. The modified electrode showed good sensitivity and selectivity, and was employed for the determination of Trp, UA, and AA in biological and pharmaceutical samples.

Highly specific triple-fragment aptamer for optical detection of cocaine.

Abstract: For the first time an anti-cocaine aptamer was cut into three fragments, which were still able to specifically assemble with cocaine and render the sensitive and highly selective optical detection of cocaine. The assembly process possesses significantly different thermodynamic signature compared to the interactions involved monolithic aptamer and double-fragment aptamer.

LC-ESI-MS quali-quantitative determination of phenolic constituents in different parts of wild and cultivated Astragalus gombiformis.

Abstract: High-performance liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS) profiling of the MeOH extract of Astragalus gombiformis Pomel (Fabaceae) aerial parts guided the isolation of seven phenolic compounds among which 7-methylquercetin 3-O-α- L-rhamnopyranosyl-(1→2)-β- D-galactopyranoside (2) and 7-methylquercetin 3-O-α- L-rhamnopyranosyl-(1→2)-(6-O-(3-hydroxy-3-methylglutaryl)-β- D-galactopyranoside) (7) whose structures were elucidated by NMR and ESI-MS experiments. The radical scavenging activities of isolated compounds were investigated, by using the TEAC assay. Furthermore quantitative analyses were performed by LC-ESI-MS and applied to the comparative profiling of different parts (aerial parts, leaves and stems) of cultivated and wild A. gombiformis samples, confirming the interest of these compounds as markers of the species. Finally, a Principal Component Analysis was carried out in order to highlight the differences between different parts of cultivated and wild plants.

Selective spectrophotometric and spectrofluorometric methods for the determination of amantadine hydrochloride in capsules and plasma via derivatization with 1,2-naphthoquinone-4-sulphonate.

Abstract: New selective and sensitive spectrophotometric and spectrofluorometric methods have been developed and validated for the determination of amantadine hydrochloride (AMD) in capsules and plasma. The methods were based on the condensation of AMD with 1,2-naphthoquinone-4-sulphonate (NQS) in an alkaline medium to form an orange-colored product. The spectrophotometric method involved the measurement of the colored product at 460 nm. The spectrofluorometric method involved the reduction of the product with potassium borohydride, and the subsequent measurement of the formed fluorescent reduced AMD-NQS product at 382 nm after excitation at 293 nm. The variables that affected the reaction were carefully studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients (0.9972-0.9974) and low LOD (1.39 and 0.013 µg mL–1) were obtained in the ranges of 5-80 and 0.05-10 µg mL–1 for the spectrophotometric and spectrofluorometric methods, respectively. The precisions of the methods were satisfactory; RSD ≤ 2.04%. Both methods were successfully applied to the determination of AMD in capsules. As its higher sensitivity, the spectrofluorometric method was applied to the determination of AMD in plasma; the recovery was 96.3-101.2±0.57-4.2%. The results obtained by the proposed methods were comparable with those obtained by the official method

Determination of unbound fraction of imatinib and N-desmethyl imatinib, validation of an UPLC-MS/MS assay and ultrafiltration method.

Abstract: Imatinib is a small-molecule tyrosine kinase inhibitor with large inter-individual but low intra-individual pharmacokinetic variability with consistent concentration-efficacy and concentration-toxicity relationships. For these reasons imatinib therapeutic drug monitoring is based on total plasma concentrations. However, since a significant impact of unbound imatinib concentrations on clinical response and/or toxicity evaluation has been suggested, the quantification of free fraction of imatinib and its active metabolite are of interest for therapeutic monitoring. Hence a reliable method for both separation and assay of the free fraction is needed. Using plasma samples spiked with imatinib (from 1000 to 7500 ng/mL) and its metabolite (from 1000 to 2500 ng/mL), an ultrafiltration procedure and an UPLC assay which give reproductive values for unbound fractions of imatinib (mean 3.0 ± 1.0%) and metabolite N-desmethyl imatinib (3.6 ± 1.8%) have been developed. The validation of the analytical UPLC-MS/MS method associated to ultrafiltration for quantification of imatinib and N-desmethyl imatinib was reported. The LOQ was set at 10 ng/mL for imatinib and 20 ng/mL for N-desmethyl imatinib, intraday CV (%) ranged from 2.7 to 4.8% for imatinib and from 5.4 to 12.4% for N-desmethyl imatinib and interday CV (%) ranged from 5.6 to 6.5% for imatinib and from 5.4 to 16.1% for N-desmethyl imatinib. Methodological modifications were attempted to overcome non specific binding (NSB) on the ultrafiltration device. Two types of devices previously used for unbound determination of drugs were tested. Our results clearly showed that the methodology and the features of devices used for ultrafiltration could totally compromise the determination of unbound concentrations of a drug.

Determination of lead in medicinal plants by high-resolution continuum source graphite furnace atomic absorption spectrometry using direct solid sampling.

Abstract: A procedure is proposed for Pb determination in medicinal plants by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) using direct solid sampling. Among Pd(NO3)2, Pd/Mg(NO3)2, NH4H2PO4 and the W-coated platform tested as chemical modifiers, Pd(NO3)2 presented the best performance. Calibration plots (10-1000 pg Pb) with regression coefficients better than 0.999 were typically obtained. Accuracy was checked for Pb determination in five plant certified reference materials. Results were in agreement with reference values at a 95% confidence level (paired t-test). Medicinal plant samples were analyzed by the proposed procedure and line-source GF AAS using slurry sampling as a comparative technique. The RSD was 10% (n = 3) for a sample containing 0.88 µg g–1 Pb. The limit of quantification (dry mass) was 0.024 µg g–1. The contents of Pb in medicinal plant samples varied in the 0.30-1.94 µg g–1 range.