An electronic tongue for gliadins semi-quantitative detection in foodstuffs

An all-solid-state potentiometric electronic tongue with 36 polymeric membranes has been used for the first time to detect gliadins, which are primarily responsible for gluten intolerance in people suffering from celiac disease. A linear discriminant model, based on the signals of 11 polymeric membranes, selected from the 36 above using a stepwise procedure, was used to semi-quantitatively classify samples of a “Gluten-free” foodstuff (baby milked flour), previously contaminated with known amounts of gliadins (<10, 20-50 or >50 mg/kg), as “Gluten-free”, “Low-Gluten content” or “Gluten-containing”. For this food matrix, the device had sensitivity towards gliadins of 1-2 mg/kg and overall sensitivity and specificity of 77% and 78%, respectively. Moreover, the device never identified an ethanolic extract containing gliadins as “Gluten-free”. Finally, the system also allowed distinguishing “Gluten-free” and “Gluten-containing” foodstuffs (15 foods, including breads, flours, baby milked flours, cookies and breakfast cereals) with an overall sensitivity and specificity greater than 83%, using the signals of only 4 selected polymeric membranes (selected using a stepwise procedure). Since only one “Gluten-containing” foodstuff was misclassified as “Gluten-free”, the device could be used as a preliminary tool for quality control of foods for celiac patients.     

Fast analysis of doping agents in urine by ultra-high-pressure liquid chromatography–quadrupole time-of-flight mass spectrometry: I. Screening analysis

The general strategy to perform anti-doping analyses of urine samples starts with the screening for a wide range of compounds. This step should be fast, generic and able to detect any sample that may contain a prohibited substance while avoiding false negatives and reducing false positive results. The experiments presented in this work were based on ultra-high-pressure liquid chromatography coupled to hybrid quadrupole time-of-flight mass spectrometry. Thanks to the high sensitivity of the method, urine samples could be diluted 2-fold prior to injection. One hundred and three forbidden substances from various classes (such as stimulants, diuretics, narcotics, anti-estrogens) were analysed on a C₁₈ reversed-phase column in two gradients of 9 min (including two 3 min equilibration periods) for positive and negative electrospray ionisation and detected in the MS full scan mode. The automatic identification of analytes was based on retention time and mass accuracy, with an automated tool for peak picking. The method was validated according to the International Standard for Laboratories described in the World Anti-Doping Code and was selective enough to comply with the World Anti-Doping Agency recommendations. In addition, the matrix effect on MS response was measured on all investigated analytes spiked in urine samples. The limits of detection ranged from 1 to 500 ng/mL, allowing the identification of all tested compounds in urine. When a sample was reported positive during the screening, a fast additional pre-confirmatory step was performed to reduce the number of confirmatory analyses.     

The economics of residue analysis

Since the onset of residue analysis some 40 years ago, much attention has been paid to several analytical aspects [e.g., the fight to achieve lower limits of detection (LODs), the gain in specificity, and quality assurance]. In recent years, “omic approaches” have also been introduced to accomplish these purposes. However, when reviewing the literature, one “omic” of residue analysis is not represented: the economic.Residue analysis covers a broad working area, including banned (group A) substances and registered veterinary drugs (group B). Some 40 years ago, only thin-layer chromatography and gas chromatography with electron-capture detection were used for A substances, in combination with laborious sample clean-up and thus small sample throughput. The nominal or money price of such an analysis remained relatively stable from 1970 to 2010. However, the operational costs of analysis increased considerably over the years, in particular, personnel and equipment costs. But, higher operational costs were countered by much greater sample throughput, although this phenomenon remains limited.For B substances, the strategy of screening with microbiological inhibition tests at a very low price competes with sophisticated ultra-high-performance liquid chromatography with (high-resolution) mass spectrometry systems, where the number of analytes/run can theoretically reach 122,500.The question that we address in this contribution from an economics point of view is: “How do laboratories keep the balance between price of analysis, specificity, LOD, number of analytes, quantification and quality assurance?”     

Development and application of a micro-digestion device for elemental analysis of biological samples

A commercially available piece of equipment for high pressure ashing was adapted for the digestion of micro-samples of biological origin by a supplementary device. This attachment is shown to be suitable for solids with a sample amount of some micrograms and for liquids with a volume of a few microliters. In addition, the homogeneity of two reference materials NBS SRM 1571 “Orchard Leaves” and BCR CRM 414 “Plankton” is tested. For that purpose, the results of elemental analysis of small portions down to the level of 1 mg are compared with those for larger portions recommended by the supplier. Elements are found to be homogeneously distributed in test portions down to 100 mg but a few elements show an inhomogeneous distribution in portions ≤3 mg. For multi-element determinations, total reflection X-ray fluorescence spectrometry was used after addition of an internal standard to the digestion solutions.     

RF-pulsed glow discharge time-of-flight mass spectrometry for glass analysis: Investigation of the ion source design

Radiofrequency (RF) millisecond pulsed glow discharge (PGD) coupled to time-of-flight mass spectrometry (TOFMS) was investigated for direct elemental analysis of glass samples. Aiming at achieving highest elemental sensitivity, appropriate discrimination from polyatomics, and good crater shapes on glasses, a new Grimm-type GD chamber (termed from now “UNIOVI GD”, designed and constructed in our laboratory) was coupled to TOFMS, and the results compared with those obtained with the former GD design (here denominated as “GD.1”) of the initial RF-PGD-TOFMS prototype. The critical differences distinguishing the two GDs under scrutiny are the GD chamber thickness (15.5 mm for the GD.1 and 7 mm for the UNIOVI GD) and the “flow tube” which is inserted in the GD.1 and inexistent in UNIOVI GD.     

Method development for liquid chromatographic/triple quadrupole mass spectrometric analysis of trace level perfluorocarboxylic acids in articles of commerce

An analytical method to identify and quantify trace levels of C5–C12 perfluorocarboxylic acids (PFCAs) in articles of commerce (AOCs) was developed and rigorously validated. Solid samples were extracted in methanol, and liquid samples were diluted with a solvent consisting of 60:40 (v/v) methanol and 2 mM ammonium acetate (NH₄Ac) aqueous solution. In both cases, the samples were spiked with an isotopically labeled recovery check standard. The samples were concentrated in a nitrogen atmosphere (solid samples only), filtered, and then analyzed by HPLC coupled with a tandem mass spectrometer. Method evaluation included selection of the extraction solvent and the sample preparation solvent used to facilitate sample injection into the analytical system, method comparison for extraction and sample concentration, determination of extraction efficiency, instrument and method detection limits, and determination of potential sample loss during filtration and sample storage. Results of consecutive extractions demonstrated that a single extraction step accounts for 70–100% of the “total” PFCAs in the AOCs with the exception of cookware. The instrument's detection limit was ≤0.05 ng/mL, and the method detection limit were 1.0–3.9 ng/g for solid AOCs and 1.1–6.8 ng/g for liquid AOCs. The method has been used to determine the PFCA content in a wide range of AOCs containing or treated with fluoropolymers and fluorotelomers.     

On the crystallization mechanism of ETS-10 titanosilicate synthesized in gels containing TAABr

Thermal analysis of the products resulted during crystallization of ETS-10 by using starting co gels with molar composition 5.0 Na₂O-3.0 KF-TiO₂-6.4 HCl-TAABr-7.45 SiO₂-197.5 H₂O, where tetralkylammonium (TAA) are tetramethyl (TMA), tetraethyl (TEA), tetrapropyl (TPA) and tetrabutylammonium (TBA), was performed. The effect of TAA⁺ cations (ionic radius in hydrated forms, shapes and hydrophilic/hydrophobic character) on the crystallization of ETS-10 is evident from the induction time, t_i (TMA⁺ ? TEA⁺ < TPA⁺ < TBA⁺), the rate of crystallization, R (TMA⁺ < TEA⁺ < TPA⁺ < TBA⁺), morphology and size of crystallites. Organic cations play a “pore filling” role rather than as a “structure-directing” agent. The relatively flexible molecules of the symmetric tetraalkylammonium cations mixed with alkali cations (Na⁺, K⁺) participate directly at prenucleation and nucleation steps by their interaction with the silicate and titanate in aqueous colloidal dispersion.     

Metabolism profile of scutellarin in urine following oral administration to rats by ultra performance liquid chromatography coupled to time-of-flight mass spectrometry

Scutellarin, a flavone glucuronide of 5,6,4′-trihydroxyflavone-7-O-glucoronide, is the main active component of the traditional Chinese botanic drug Erigeron breviscapus (Vant.) Hand.-Mazz. In this study, a method based on ultra performance liquid chromatography coupled with a time-of-flight mass spectrometer (UPLC/TOF MS) was established and validated to profile the metabolites of scutellarin in Sprague-Dawley rat urine following oral administration of single dose of scutellarin at 80.8 mg/kg. The column utilized was an Acquity BEH C18 (150 mm × 2.1 mm, 1.7 μm). The mobile phase was 0.2% formic acid and acetonitrile with gradient condition. Two standard curves of scutellarin were obtained for the concentration range of 1.065-10.65 μg/mL and 10.65-63.92 μg/mL, respectively. By automating the data processing of the software Masslynx developed by Waters Ltd., 17 metabolites of scutellarin were found and determined in rat urine, with the corresponding reactions in vivo such as isomerism, reduction, methylation, glucuronide conjugation, hydroxylation, hydroxylation and methylation, etc., most of which were discovered for the first time. For most metabolites, the time (T_p) of peak excretion was 8-12 h. Calculated as scutellarin, the cumulative urine excretion rate of the metabolites was 1.93%.     

Development and validation of an ultra-high performance liquid chromatography tandem mass spectrometry method for quantifying thyreostats in urine without derivatisation

Thyreostatic drugs, illegally administrated to livestock for fattening purposes, are banned in the European Union since 1981 (Council Directive 81/602/EC). For monitoring their illegal use, sensitive and specific analytical methods are required. In this study an UHPLC-MS/MS method was described for quantitative analysis of eight thyreostatic drugs in urine, this without a derivatisation step. The sample pretreatment involved a reduction step with dithiothreitol under denaturating conditions at 65 °C, followed by liquid-liquid extraction with ethyl acetate. This analytical procedure was subsequently validated according to the EU criteria (2002/657/EC Decision), resulting in decision limits and detection capabilities ranging between 1.1 and 5.5 μg L⁻¹ and 1.7 and 7.5 μg L⁻¹, respectively. The method obtained for all, xenobiotic thyreostats, a precision (relative standard deviation) lower than 15.5%, and the linearity ranged between 0.982 and 0.999. The performance characteristics fulfill not only the requirements of the EU regarding the provisional minimum required performance limit (100 μg L⁻¹), but also the recommended concentration fixed at 10 μg L⁻¹ in urine set by the Community of Reference Laboratories. Future experiments applying this method should provide the answer to the alleged endogenous status of thiouracil.     

Electronic micropipettor: a versatile fluid propulsion and injection device for micro-flow analysis

The shortage of ready to use small sized liquid propulsion and switching devices for microfluidic cells (μ-cell) is a bottleneck in the dissemination of micro-flow analysis (μ-FA), now that microfluidic electrochemical cells can be designed and assembled in any laboratory by thermal transfer of laser printed masks and CD-Rs. Microprocessor-controlled electronic pipettors, commercially available with minimum capacity of 10 μL, represent a compromise solution between oversized peristaltic pumps and tiny “on a chip” micropumps and valves. The versatility of the electronic pipette coupled with the μ-cell (13-μm deep longitudinal channel) was demonstrated in three operation modes: SIA like, FIA like and direct injection analysis (DIA). Injections of 100 nL K₄Fe(CN)₆ (0.1 mol L⁻¹ KCl) define a linear analytical curve (r = 0.999) in the range of 5 × 10⁻⁷ to 1.0 × 10⁻³ mol L⁻¹ for flow amperometry at a gold electrode potentiostated at 0.4 V versus Ag/AgCl. Methods for the amperometric μ-flow determination of promethazine (FIA like), dipyrone (SIA like) and chlorpromazine (DIA) in pharmaceutical formulations were developed and applied to real samples. Excellent linearity of analytical curves and high repeatability (R.S.D. < 3.0%) at the low picomole range was obtained and all results for real samples were in agreement with reference methods. The results reflect the stability and the reliability of the setups envisioned for the electronic pipette coupled with amperometric μ-cell and the validity of the μ-FA methods.     

High throughput analysis of 150 pesticides in fruits and vegetables using QuEChERS and low-pressure gas chromatography–time-of-flight mass spectrometry

A higher monitoring rate is highly desirable in the labs, but this goal is typically limited by sample throughput. In this study, we sought to assess the real-world applicability of fast, low-pressure GC–time-of-flight MS (LP-GC/TOFMS) for the identification and quantification of 150 pesticides in tomato, strawberry, potato, orange, and lettuce samples. Buffered and unbuffered versions of QuEChERS (which stands for “quick, easy, cheap, effective, rugged, and safe”) using dispersive solid-phase extraction (d-SPE) and disposable pipette extraction (DPX) for clean-up were compared for sample preparation. For clean-up of all sample types, a combination of 150 mg MgSO₄, 50 mg primary secondary amine (PSA), 50 mg C₁₈, and 7.5 mg graphitized carbon black (GCB) per mL extract was used. No significant differences were observed in the results between the different sample preparation versions. QuEChERS took <10 min per individual sample, or <1 h for two chemists to prepare 32 pre-homogenized samples, and using LP-GC/TOFMS, <10 min run time and <15 min cycle time allowed >32 injections in 8 h. Overall, >126 analytes gave recoveries (3 spiking levels) in the range of 70–120% with <20% RSD. The results indicate that LP-GC/TOFMS for GC-amenable analytes matches UHPLC–MS/MS in terms of sample throughput and turnaround time for their routine, concurrent use in the analysis of a wide range of analytes in QuEChERS extracts to achieve reliable quantification and identification of pesticide residues in foods.     

Comprehensive two-dimensional gas chromatography improves separation and identification of anabolic agents in doping control

The application of comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC-TOFMS) for the analysis of six anabolic agents (AAs) in doping control is investigated in this work. A non-polar–polar column configuration with 0.2 μm film thickness (d_f) second dimension (²D) column was employed, offering much better spread of the components on ²D when compared to the alternative 0.1 μm d_f²D column. The proposed method was tested on the “key” AA that the World Anti-Doping Agency (WADA) had listed at the low ng mL⁻¹ levels (clenbuterol, 19-norandrosterone, epimethendiol, 17α-methyl-5α-androstane-3α,17β-diol, 17α-methyl-5β-androstane-3α,17β-diol and 3′-OH-stanozolol). The compounds were spiked in a blank urine extract obtained by solid-phase extraction, hydrolysis and liquid–liquid extraction; prior to analysis they were converted to the corresponding trimethylsilyl (TMS) derivatives. The limit of detection (LOD) was below or equal to the minimum required performance limit (MRPL) of 2 ng mL⁻¹ defined by WADA, and the correlation coefficient was in the range from 0.995 to 0.999. The method allows choosing an ion from the full mass spectra which shows the least interference from the matrix and/or the best sensitivity; this can only be done if full scan mass spectral data are available. The advantage of GC × GC over classical one-dimensional GC (1D GC), in terms of separation efficiency and sensitivity, is demonstrated on a positive urine control sample at a concentration of 5 ng mL⁻¹. The obtained similarity to the in-house created TOFMS spectra library at this level of concentration was in the range from 822 to 932 (on the scale from 0 to 999). Since full mass spectral information are recorded, the method allows the retro-search of non-target compounds or new “designer steroids”, which cannot be detected with established GC–MS methods that use selected ion monitoring (SIM) mode.     

Worldwide interlaboratory study on the determination of ochratoxin A in different wine type samples

Interlaboratory studies are decisive tools to help the validation of a specific analytical methodology or to assess the reproducibility of the use of different methods to analyze a given compound or compounds in certain sample matrices. In this work, homogeneous samples of two white wines (“White Wine” and “White Liqueur Wine”) and one red wine (“Red Fortified Wine”) from Portugal with different production techniques and characteristics, namely in alcohol strength (10.5%, 16.0% and 19.0% ethanolic content, respectively), were analyzed for their contents in ochratoxin A (OTA), a mycotoxin generated from fungal contamination. White Liqueur Wine was naturally contaminated, whereas the other two wine type were spiked with ethanolic OTA solutions. The participation of 24 laboratories from 17 countries of five continents was ensured for this study. Although with no restrictions in terms of analytical methodology to employ, 75% of the laboratories resorted to immunoaffinity columns clean-up followed by high performance liquid chromatography with fluorescence detection (HPLC-FD), most of them in accordance with the European Standard EN 14133. For White Wine samples, the general mean OTA concentration was 1.96 μg/l (two outliers) with interlaboratorial standard deviation (s_L) of 0.53 μg/l; for White Liqueur Wine, mean of 1.59 μg/l (one outlier), with s_L = 0.59 μg/l; and for Red Fortified Wine, mean of 2.73 μg/l (no outliers), with s_L = 0.96 μg/l. Outliers were determined by Cochran and Grubbs tests. The Horrat index, recommended by the Association of Official Analytical Chemists (AOAC) for the quality assurance of the collaborative study was, on average, 1.7. This study proved that OTA determination in wines is reproducible, regardless of the methodology employed.     

Determination of aluminum by electrothermal atomic absorption spectroscopy in lubricating oils emulsified in a sequential injection analysis system

The sequential injection (SIA) technique was applied for the on-line preparation of an “oil in water” microemulsion and for the determination of aluminum in new and used lubricating oils by electrothermal atomic absorption spectrometry (ET AAS) with Zeeman-effect background correction. Respectively, 1.0, 0.5 and 1.0 ml of surfactants mixture, sample and co-surfactant (sec-butanol) solutions were sequentially aspirated to a holding coil. The sonication and repetitive change of the flowing direction improved the stability of the different emulsion types (oil in water, water in oil and microemulsion). The emulsified zone was pumped to fill the sampling arm of the spectrometer with a sub-sample of 200 μl. Then, 10 μl of this sample solution were introduced by means of air displacement in the graphite tube atomizer. This sequence was timed to synchronize with the previous introduction of 15 μg of Mg(NO₃)₂ (in a 10 μl) by the spectrometer autosampler. The entire SIA system was controlled by a computer, independent of the spectrometer. The furnace program was carried out by employing a heating cycle in four steps: drying (two steps at 110 and 130 °C), pyrolisis (at 1500 °C), atomization (at 2400 °C) and cleaning (at 2400 °C). The calibration graph was linear from 7.7 to 120 μg Al l⁻¹. The characteristic mass (mo) was 33.2 pg/0.0044 s and the detection limit was 2.3 μg Al l⁻¹. The relative standard (RSD) of the method, evaluated by replicate analyses of different lubricating oil samples varied in all cases between 1.5 and 1.7%, and the recovery values found in the analysis of spiked samples ranged from 97.2 to 100.4%. The agreement between the observed and reference values obtained from two NIST Standard Certified Materials was good. The method was simple and satisfactory for determining aluminum in new and used lubricating oils.     

A screening method for the simultaneous detection of glucocorticoids,diuretics, stimulants,anti-oestrogens,beta-adrenergic drugs and anabolic steroids in human urine by LC-ESI-MS/MS

This paper presents a general screening method, based on liquid chromatography/mass spectrometry (LC/MS), for the simultaneous detection in human urine of 72 xenobiotics (21 diuretics, 16 synthetic glucocorticoids, 17 beta-adrenergic drugs, 10 stimulants, 5 anti-oestrogens and 3 anabolic steroids), excreted free or as glucuro-conjugates in urine. Although the method has been specifically designed and evaluated in view of its potential application to anti-doping analyses, it can also be effective in other areas of analytical toxicology. Sample preparation was based on two liquid/liquid separation steps (performed at alkaline and at acid pH, respectively) of hydrolyzed human urine, and then an assay by LC/MS-MS in positive and negative ionization mode using an electrospray ionization source (ESI) and multiple reaction monitoring (MRM) as the acquisition mode. The overall time needed for an LC run was less than 15 minutes. All compounds showed good reproducibility in terms of both the retention times (CV%<1) and the relative abundances of the diagnostic transitions (CV%<10). The limits of detection (LOD) were in the range of 1–50 ng/mL for glucocorticoids, anti-oestrogens and steroids, and 50–500 ng/mL for diuretics, beta-adrenergic drugs and stimulants, thus satisfying the minimum required performance limits (MRPL) set by the World Anti-Doping Agency (WADA) for the accredited anti-doping laboratories.     

Fast analysis of catecholamine metabolites MHPG and VMA in human plasma by HPLC with fluorescence detection and a novel SPE procedure

A fast and sensitive high-performance liquid chromatographic method has been developed for the determination in human plasma of MHPG (3-methoxy-4-hydroxyphenylethylenglycol) and VMA (vanillyl mandelic acid), the main metabolites of epinephrine and norepinephrine. Analyses were carried out at 325 nm while exciting at 285 nm on a reversed-phase column (Atlantis C18, 150 mm × 4.6 mm I.D., 5 μm) using a mobile phase composed of 2% methanol and 98% aqueous citrate buffer at pH 3.0. A careful solid-phase extraction procedure, based on mixed-mode reversed-phase - strong anion exchange Oasis cartridges (MAX, 30 mg, 1 mL), was developed for the pre-treatment of plasma samples. Extraction yields were satisfactory, always higher than 90%. Calibration curves were linear over the 0.2-40.0 ng mL⁻¹ concentration range for MHPG and over the 0.5-40.0 ng mL⁻¹ concentration range for VMA. The method was successfully applied to plasma samples of former drug users undergoing detoxification therapy and subjects “at risk” of developing drug addiction.     

Exploiting in situ hydride trapping in tungsten coil atomizer for Se and As determination in biological and water samples

A flow injection hydride manifold was coupled to a 150 W tungsten coil electrothermal atomizer for in situ hydride collection followed by selenium and arsenic determination by ET AAS. Rhodium (200 μg), thermally reduced over the double layer tungsten atomizer, was very efficient at collecting selenium or arsenic hydrides. Prior to analysis, biological samples were digested in closed-vessels microwave digestion system. Prior to the hydride formation, both selenium and arsenic were reduced to valence state (IV) and (III), respectively. The detection limit was 35 ng L⁻¹ for selenium and 110 ng L⁻¹ for arsenic. Sample throughput was 70 h⁻¹ using 30 s of hydride trapping time. Method accuracy was evaluated by analyzing biological-certified reference materials from the National Institute of Standard and Technology (SRM-1577a and SRM-1577b “bovine liver” and RM-8414 “bovine muscle powder”) and from the International Agency for Energy Atomic (A-13 “animal blood”) and one water-certified reference material from the National Institute of Standard and Technology (SRM-1640 trace elements in natural water). By applying a t-test, there was no significant difference at the 95% probability level between the results obtained with the proposed method and those certified values.     

High throughput screening various abused drugs and metabolites in urine by liquid chromatography-heated electrospray ionization/tandem mass spectrometry

An integrated method of liquid chromatography-heated electrospray ionization/tandem mass spectrometry was evaluated for high throughput screening of various abused drugs in urine. Chromatographic analysis was performed on a C18 reverse phase column using a linear gradient of 10 mM ammonium acetate containing 0.1% formic acid-methanol as mobile phase and the total separation time was 7 min. A simple and rapid sample preparation method used was by passing urine samples through a 0.22 μm PVDF syringe filter. The detection limits of the studied abused drugs in urine were from 0.6 ng mL⁻¹ (ketamine) to 9.0 ng mL⁻¹ (norcodeine). According to the results, the linear range was from 1 to 1200 ng mL⁻¹ with relative standard deviation (R.S.D.s) value below 14.8% (intra-day) and 24.6% (inter-day). The feasibility of applying the proposed method to determine various abused drugs in real samples was examined by analyzing urine samples from drug-abused suspects. The abused drugs including ketamines and amphetamines were detected in suspected urine samples. The results demonstrate the suitability of LC-HESI-MS/MS for high throughput screening of the various abused drugs in urine.     

Double-ion imprinted polymer @magnetic nanoparticles modified screen printed carbon electrode for simultaneous analysis of cerium and gadolinium ions

A typical, reproducible, and rugged screen printed carbon electrode, modified with dual-ion imprinted beads, was fabricated employing the “surface grafting from” approach. For this, the acyl chloride functionalized magnetic nanoparticles were first immobilized and chemically attached with a typical functional monomer (but-2-enedioic acid bis-[(2-amino-ethyl)-amide]) on the electrode surface. This was subsequently subjected to the thermal polymerization in the presence of template ions (Ce(IV) and Gd(III)), cross-linker (ethylene glycol dimethacrylate), initiator (AIBN), and multiwalled carbon nanotubes. The modified sensor was used for the simultaneous analysis of both template ions in aqueous, blood serum, and waste-water samples, using differential pulse anodic stripping voltammetry which revealed two oxidation peaks for respective templates with resolution as much as 950 mV, without any cross reactivity, interferences and false-positives. The detection limits realized by the proposed sensor, under optimized conditions, were found to be as low as 0.07 ng mL⁻¹ for Ce(IV) and 0.19 ng mL⁻¹ for Gd(III) (S/N = 3) that could eventually be helpful for lanthanide estimation at stringent levels.     

"Off-On" based fluorescent chemosensor for Cu2+ in aqueous media and living cells

A novel Cu²⁺-specific “off-on” fluorescent chemosensor of naphthalimide modified rhodamine B (naphthalimide modified rhodamine B chemosensor, NRC) was designed and synthesized, based on the equilibrium between the spirolactam (non-fluorescence) and the ring-opened amide (fluorescence). The chemosensor NRC showed high Cu²⁺-selective fluorescence enhancement over commonly coexistent metal ions or anions in neutral aqueous media. The limit of detection (LOD) based on 3 × δ_blank/k was obtained as low as 0.18 μM of Cu²⁺, as well as an excellent linearity of 0.05-4.5 μM (R = 0.999), indicating the chemosensor of high sensitivity and wide quantitation range. And also the coordination mode with 1:1 stoichiometry was proposed between NRC and Cu²⁺. In addition, the effects of pH, co-existing metal ions and anions, and the reversibility were investigated in detail. It was also demonstrated that the NRC could be used as an excellent “off-on” fluorescent chemosensor for the measurement of Cu²⁺ in living cells with satisfying results, which further displayed its valuable applications in biological systems.