Rapid and simple micro-determination of carvedilol in rat plasma by high-performance liquid chromatography

We studied the use of high-performance liquid chromatography (HPLC) with spectrofluorometric detection, using a solid-phase extraction for a simple, rapid and sensitive determination of plasma carvedilol levels in rats. Extracted aliquots were analyzed by HPLC, using a reversed-phase octadecyl silica column. The analytical mean recovery of carvedilol added to the blank plasma was 94.2%. The detection limit was 3.6 ng/ml in the plasma. The reproducibilities (C.V.) were 2.7–7.5% for the within-day assay, and 2.6–7.4% for the between-day assay, indicating that the method was effective for the determination of carvedilol plasma levels.     

A sensitive fluorescence quenching method for the detection of tartrazine with acriflavine in soft drinks

In this work, a simple, rapid, sensitive, selective spectrofluorimetric method was applied to detect tartrazine. The fluorescence of acriflavine could be efficiently quenched by tartrazine. The method manifested real time response as well as presented satisfied linear relationship to tartrazine. The linear response range of tartrazine (R² = 0.9995) was from 0.056 to 5 μmol L^?1. The detection limit (3σ/k) was 0.017 μmol L^?1, indicating that this method could be applied to detect traces of tartrazine. The accuracy and precision of the method was further assured by recovery studies via a standard addition method, with percentage recoveries in the range of 96.0% to 103.0%. Moreover, a quenching mechanism was investigated systematically by the linear plots at varying temperatures based on the Stern–Volmer equation, fluorescence lifetime and UV–visible absorption spectra, all of which proved to be static quenching. This sensitive, selective assay possessed a great application prospect for the food industry owing to its simplicity and rapidity for the detection of tartrazine.     

Spectrofluorimetric determination of nomifensine in human plasma and urine by derivatization with fluorescamine

A sensitive, simple and rapid spectrofluorimetric method was developed for the determination of nomifensine in human plasma and urine. The present method was based on the derivatization by fluorescamine in phosphate buffer at pH 4.0 to produce a highly fluorescent product which was measured at 488 nm (excitation at 339 nm). The method was validated according to the ICH guidelines with respect to linearity, limit of detection, limit of quantification, accuracy, precision, recovery and robustness. The assay was linear over the concentration ranges 100–2,000 and 50–2,000 ng/mL for plasma and urine, respectively. The limits of detection were calculated to be 13.9 and 7.5 ng/mL for plasma and urine, respectively. The method was successfully applied to the analysis of the drug in human plasma and urine. Copyright © 2011 John Wiley & Sons, Ltd.     

Detection of Indigo Carmine dye in juices via application of photoluminescent europium-doped carbon dots from tannic acid

Indigo Carmine is a hazardous dye and produces an allergic action for humans despite the excessive use of the dye in several industrial fields. A sensitive and simple fluorescent assay for determining Indigo Carmine relying on quenching of the fluorescent europium-doped carbon dots by the action of inner filter effect was developed. This sensing platform involved the preparation of europium-doped carbon dots from the hydrothermal carbonization of tannic acid and europium chloride, which was used as fluorescent reagent with a distinctive excitation/emission wavelength at 307/340 nm. Both excitation and emission fluorescence of prepared carbon dots can be successfully quenched by adding Indigo Carmine dye. The developed spectrofluorimetric method exhibits good linearity with the concentration of Indigo Carmine dye in the range of 1.5 to 10.0 μg/ml and provided a limit of detection (LOD) value of 0.40 μg/ml. Furthermore, the prepared carbon nanoparticles were identified and characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR), and ultraviolet (UV)-spectrophotometer techniques. In addition, the developed detecting approach was applied to determine Indigo Carmine in juice samples with acceptable recovery.     

Sensitive detection of cysteine based on fluorescent silver clusters

In this work, we report the application of novel, water-soluble fluorescent Ag clusters in fluorescent sensors for detecting cysteine, an important biological analyte. The fluorescence of poly(methacrylic acid) (PMAA)-templated Ag clusters was found to be quenched effectively by cysteine, but not when the other alpha-amino acids were present. By virtue of the specific response, a new, simple, and sensitive fluorescent method for detecting cysteine has been developed based on Ag clusters. The present assay allows for the selective determination of cysteine in the range of 2.5 x 10(-8) to 6.0 x 10(-6)M with a detection limit of 20 nM at a signal-to-noise ratio of 3. Based on the absorption and fluorescence studies, we suggested that cysteine quenched the emission by the thiol-adsorption-accelerated oxidation of the emissive Ag clusters. The present study shows a promising step toward the application of silver clusters, a new class of attractive fluorescence probes.     

One-step hydrothermal preparation of chiral carbon quantum dots and enantioselective sensing of glutamine enantiomeric isomers

A novel method for chiral identification of glutamine enantiomers based on chiral carbon quantum dots (cCQDs) fluorescent probes. cCQDs were prepared using a one-step hydrothermal method with L-tryptophan as the carbon source and chiral source, producing spherical nanoparticles exhibiting a blue colour luminescence. The fluorescence intensity (F) of cCQDs was enhanced or quenched following the addition of chiral enantiomeric glutamine (L/D-Gln), and therefore cCQDs, as a fluorescence probe, could be used for enantioselective sensing of the L/D-Gln. The fluorescence enhancement value (∆F_E) exhibited good linearity with L-Gln concentration in the range 0.23–10.00 mM, and the limit of detection was 0.14 mM. The fluorescence quenching value (∆F_Q) showed a good linear relationship with D-Gln concentration in the range 0.29–10.00 mM, and the detection limit was 0.18 mM. The mechanism of fluorescence enhancement/quenching was explored by molecular modelling and the type of quenching. The method was applied to the determination of L-Gln content in real samples, and the recovery rate was satisfactory. This study provided a novel approach for the synthesis of cCQDs and the recognition of amino acid enantiomers.     

A Highly Sensitive Resonance Scattering Assay for Immunoglobulin M Using Ag(I)–Hydroquinone–Immunonanogold Catalytic Reaction

Ten-nanometer nanogold showed the strongest catalytic effect on the particle reaction between Ag(I) and hydroquinone to form nanosilver particles that exhibited the strongest resonance scattering (RS) peak at 350 nm. The enhanced RS intensity was linear to the nanogold concentration in the range of 30–5,700 nM Au. The nanogold was used to label goat antihuman immunoglobulin M (GIgM) to obtain an immunonanogold probe (AuGIgM) for immunoglobulin M (IgM). Based on the nanogold-labeled immunoreaction between IgM and AuGIgM, centrifugation, and AuGIgM–Ag(I)–hydroquinone nanocatalytic reaction, a highly sensitive and selective immunonanogold-catalytic Ag particle RS assay for 0.2–300 ng mL^?1 IgM was proposed, with a detection limit of 0.1 ng mL^?1. This assay was simple and sensitive and was applied to assay IgM in serum samples, with satisfactory results.     

A fluorescent aptasensor for sensitive analysis oxytetracycline based on silver nanoclusters

A fluorescent aptasensor for detection of oxytetracycline (OTC) was presented based on fluorescence quenching of DNA aptamer‐templated silver nanoclusters (AgNCs). The specific DNA scaffolds with two different nucleotides fragments were used: one was enriched with a cytosine sequence fragment (C12) that could produce DNA–AgNCs via a chemical reduction method, and another was the OTC aptamer fragment that could selectively bind to the OTC antibiotic. Thus, the as‐prepared AgNCs could exhibit quenched fluorescence after binding to the target OTC. The fluorescence ratio of the DNA–AgNCs was quenched in a linearly proportional manner to the concentration of the target in the range of 0.5 nM to 100 nM with a detection limit of 0.1 nM. This proposed nanobiosensor was demonstrated to be sensitive, selective, and simple, introducing a viable alternative for rapid determination of toxin OTC in honey and water samples. Copyright © 2016 John Wiley & Sons, Ltd.     

Selective fluorescence quenching of papain–Au nanoclusters by self‐polymerization of dopamine

In this paper, we synthesized a papain‐stabilized fluorescent Au nanocluster (NC) probe and studied its interaction with dopamine. As fluorescence of papain–Au NCs is quenched in the presence of dopamine under alkaline conditions, we were able to establish a simple, selective analytical method for dopamine determination. By studying the fluorescence lifetime and dynamic light scattering of the NCs before and after interaction with dopamine, we found that this fluorescence quenching mechanism was possibly due to dopamine self‐polymerization that produced polydopamine that cross‐linked papain–Au NCs. Based on this new phenomenon, we proposed a highly selective analytical method for dopamine detection. Other small organic molecules, such as amino acids, ascorbic acid and uric acid did not interfere with dopamine detection. Dopamine in the range 20–100 μM can be linearly detected by the fluorescence quenching ratio of gold nanoclusters. Dopamine detection could be visually realized by watching color changes of papain–Au NCs under UV light or daylight, as both fluorescence and absorption of the papain–Au NCs changed during dopamine polymerization.     

Prevalidation statistical design to assess analytical methods example of a quick liquid chromatographic assay of itraconazole in serum

(A) An analysis-of-varience spreadsheet program is presented which allows to readily test and/or quantitate in a single run analytical linearity, matrix effect on recovery, repeatability of measurement and of extraction and the ruggedness of these features for up to three sessions. Owing to napierian logarithmic transformation, ANOVA mean squares directly read as relative standard deviations and checking linearity is straightforward. (B) A quick assay for therapeutic drug monitoring of itraconazole and its main metabolite was devised with the help of the program, and subsequently validated according to current quality control recommendations. The assay involves acetonitrile demixing extraction, reversed-phase HPLC and UV detection and shows acceptable performance from 0.06 to 5.0 mg/l (limit of detection about 0.03 mg/l). The prevalidation design fairly predicted precision and accuracy, was more informative about matrix effect and was even more demanding about analytical linearity.     

Tetramethyl-6-carboxyrhodamine quenching-based aptasensing platform for aflatoxin B1: Analytical performance comparison of two aptamers

In this study, a simple TAMRA (tetramethyl-6-carboxyrhodamine) quenching-based aptasensing platform was designed for the detection of aflatoxin B1 (AFB1). Here, we compared the analytical performance of two aptamer sequences: seqA and seqB. The AFB1 detection was based on the interactions of FAM (carboxyfluorescein)-labeled aptamer with TAMRA-labeled DNA complementary strand in the presence and absence of target analyte. Under optimized experimental conditions, TAMRA-labeled strand quenched the fluorescence response of FAM-labeled aptamer due to the noncovalent interaction between the two DNA strands. The binding of AFB1 induced the complex formation and weakened the interaction between FAM-labeled aptamer and TAMRA-labeled complementary strand, resulting in the fluorescence recovery. By using this principle concept, an assay was constructed for the detection of AFB1. The method exhibited good sensitivity, good selectivity with a limit of detection of 0.2 ng ml⁻¹, and a wide linear range from 0.25 to 32 ng ml⁻¹. For real sample application, the aptasensors were tested in beer and wine samples, with good recovery rates obtained for AFB1 detection.     

Simultaneous determination of reduced and oxidized glutathione in peripheral blood mononuclear cells by liquid chromatography–electrospray mass spectrometry

We developed a sensitive and specific liquid chromatography–electrospray mass spectrometric (HPLC–ESI-MS) assay for the simultaneous determination of reduced and oxidized glutathione (GSH and GSSG) in peripheral blood mononuclear cells (PBMC). Following derivatization with N-ethylmaleimide to prevent GSH auto-oxidation, addition of thiosalicylic acid as internal standard, and protein precipitation with cold acetonitrile, the samples were injected into a diol column, eluted with acetonitrile–1% aqueous acetic acid (25:75) and detected by the ESI-MS system. The optimized method exhibited a good detection limit for both analytes (0.01 and 0.05 μM for GSH and GSSG, respectively). Good linearity was reached in the 0.01–20 μM range for GSH and 0.05–20 μM for GSSG. The mean recoveries of GSH and GSSG were 98.5–100.6% and 105.8–111.5%, respectively. The run-to-run repeatability for retention time and peak area was RSD% 0.06 and 1.75 for GSH and 0.18 and 2.50 for GSSG. The optimized method was applied to GSH and GSSG assay in PBMC analyzing 20 healthy individuals.     

Determination of acyclovir by ultrafiltration and high-performance liquid chromatography

A simple, sensitive and rapid high-performance liquid chromatographic (HPLC) procedure to determine total serum acyclovir concentrations is described. The assay involves a heat inactivation step at 56°C to prevent risk of infection, ultrafiltration as a pretreatment step prior to ion-pair reversed-phase liquid chromatography using guanosine as internal standard, and ultraviolet detection at 254 nm. This method has excellent recovery (97–100%), linearity (0.5–100 mg/l) and precision (1.2–8.0% coefficient of variation). The detection limit is 50 μg/l. The assay proved to be suitable for therapeutic drug monitoring of acyclovir.     

Determination of pilocarpic acid in human plasma by capillary gas chromatography with mass-selective detection

A novel, highly sensitive method for the determination of pilocarpic acid (PA) in human plasma is described. In addition, the method provides for the conversion of the lactone, pilocarpine (P), to PA so that a total drug presence can be determined. Using novel high-performance liquid chromatographic conditions capable of separating P, isopilocarpine (I-P), PA and isopilocarpic acid (I-PA) from each other and from endogenous plasma impurities, it was confirmed that P exclusively and quantitatively converts to PA in heparinized human plasma during storage. For the determination of PA, the selective extraction of PA from protein-free plasma was accomplished using two different solid-phase extraction (SPE) cartridges in two consecutive SPE steps. After extraction, PA was lactonized with trifluoroacetic acid back to P, and both P and an internal standard were acylated using heptafluorobutyric anhydride (HFBA). The trifluoroacetylated derivatives were monitored using gas chromatography (GC) with mass spectrometric (MS) detection. This procedure allowed the sensitive and reliable determination of PA with a limit of quantification (LOQ) of 1 ng/ml, which could not be achieved using previously described methods. The assay was validated in the concentration range of 1 to 10 ng/ml with an intra-day precision (expressed as the coefficient of variation, C.V.) ranging from 9.9 to 0.5%. Inter-day precision for the quality control standard at 2.5 ng/ml showed a C.V. of 10.2%. Accuracy ranged from 94 to 102%. The assay was used to monitor the maximum systemic exposure to P, administered by the ocular route, in terms of total plasma PA (P and PA).     

Development and validation of a sensitive spectrofluorimetric method for the determination of amoxapine in human plasma and urine

A selective and sensitive spectrofluorimetric method was developed and validated for the determination of amoxapine in human plasma and urine. The developed method is based on labeling with 5‐dimethylaminonaphthalene‐1‐sulfonyl chloride (dansyl chloride) and monitoring at 397 nm (excitation)/514 nm (emission). The method was validated for linearity, limit of detection (LOD), limit of quantification (LOQ), precision, accuracy, recovery and robustness. The calibration curves were linear over a concentration range of 250–2500 and 50–1250 ng/mL for plasma and urine, respectively. The LOD values were calculated to be 13.31 and 13.17 ng/mL for plasma and urine, respectively. The proposed method was applied to study of amoxapine in human plasma and urine. Copyright © 2013 John Wiley & Sons, Ltd.     

A miniaturized analytical method based on molecularly imprinted absorbents for selective extraction of (S)-1,1′-binaphthyl-2,2′-diamine and combinatorial screening of polymer precursors by computational simulation

Chiral resolution of binaphthylamine is often a toilful conundrum in the field of analytical chemistry and biomedicine. The work puts forward a selective, sensitive, and miniaturized analytical method based on molecularly imprinted polymers (MIPs) as adsorbent for miniaturized tip solid-phase extraction (MTSPE) in the separation of binaphthylamine enantiomer. This method combines the advantages of MIPs (high selectivity), MTSPE (low consumption), and high-performance liquid chromatography (HPLC, high sensitivity). A simple synthesis methodology of MIP (P2) was conducted through bulk polymerization with (S)-(?)-1,1′-binaphthyl-2,2′-diamine (S-DABN) as template together with methacrylic acid monomer, and ethylene glycol dimethacrylate as cross-linker in proper porogen, realizing a selective recognition and efficient enrichment for S-DABN. The method exhibited appreciable linearity (0.06–1.00 mg ml^?1), low quantification limit (0.056 mg ml^?1), good absolute recoveries (45.70%–69.29%), and high precision (relative standard deviations ≤ 3.54%), along with low consumption (0.50 ml sample solution and 25.0 mg adsorbent). Based on the density functional theory, computational simulation was used to make a preliminary prediction for rational design of MIPs and gave a reasonable elaboration involving the potential mechanism of templates interacting with functional monomers. The adsorption kinetics and thermodynamics were investigated to evaluate the recombination process of substrates. In addition, the selectivity of MIPs for S-DABN was obtained by MIP-MTSPE coupled with HPLC, which supports the feasibility of this convenient design process. The proposed method was employed for selective extraction of S-DABN and exhibited promising potential in the application of chiral analysis.     

Ultrasensitive and selective colorimetric detection of uric acid using peroxidase mimetic activity of biogenic palladium nanoparticles

Uric acid (2,6,8-trihydroxypurine) is a metabolic product of purine, which is one of the important markers of human health. The development of a rapid, facile, highly sensitive, and selective method for uric acid detection is critical for the diagnosis of related diseases and is still a strategic challenge. In this study, we developed a highly sensitive and selective colorimetric assay for the detection of uric acid using biogenic palladium nanoparticles (Pd NPs). The synthesized nanoparticles were shown to acquire peroxidase mimetic activity that oxidized 3,3′,5,5′-tetramethylbenzidine and produced a blue colour in an assay. The developed colorimetric assay is instrument-free detection of uric acid with a limit of detection of 0.05 μM and a 1.11 μM limit of quantification (LOQ). This is the first report determining the LOQ for a colorimetric assay that gives the lowest quantity of analyte that can be evaluated with more precision under the specified conditions of the analysis. The developed assay had a linear response at low uric acid concentrations of 0.05 to 1 μM and a 0.99841 linear regression correlation coefficient. This colorimetric detection provides a rapid, cost-effective, and easy-to-use platform for the clinical diagnosis of uric acid biomarkers.     

Development and validation of a sensitive assay of valproic acid in human plasma by high-performance liquid chromatography without prior derivatization

Sensitive and selective determination of valproic acid in plasma by high-performance liquid chromatography (HPLC) is usually achieved with pre-column derivatization. In the present work, the derivatization is omitted due to using a simple but highly selective plasma extraction procedure and an optimized chromatographic condition. Valproic acid and the internal standard octanoic acid were extracted from plasma samples with n-hexane under acidic condition followed by back-extraction into diluted triethylamine. Chromatography was performed on a CN column (250 x 4.6 mm, 5 microm) under isocratic elution with acetonitrile-40 mM aqueous sodium dihydrogen phosphate (30:70, v/v), pH 3.5. Detection was made at 210 nm and analyses were run at a flow-rate of 1 ml/min. The method was specific and sensitive with a quantification limit of 1.25 microg/ml and a detection limit of 0.1 microg/ml in plasma. The mean absolute recovery for valproic acid using the present plasma extraction procedure was 75.8%. The intra- and inter-day coefficient of variation and percent error values of the assay method were all in acceptable range. Calibration curves were linear (r>0.999) from 1.25 to 320 microg/ml in plasma.     

Highly Simple Deep Eutectic Solvent Extraction of Manganese in Vegetable Samples Prior to Its ICP-OES Analysis

In the present work, simple and sensitive extraction methods for selective determination of manganese have been successfully developed. The methods were based on solubilization of manganese in deep eutectic solvent medium. Three deep eutectic solvents with choline chloride (vitamin B4) and tartaric/oxalic/citric acids have been prepared. Extraction parameters were optimized with using standard reference material (1573a tomato leaves). The quantitative recovery values were obtained with 1.25 g/L sample to deep eutectic solvent (DES) volume, at 95 °C for 2 h. The limit of detection was found as 0.50, 0.34, and 1.23 μg/L for DES/tartaric, DES/oxalic, and DES/citric acid, respectively. At optimum conditions, the analytical signal was linear for the range of 10–3000 μg/L for all studied DESs with the correlation coefficient >0.99. The extraction methods were applied to different real samples such as basil herb, spinach, dill, and cucumber barks. The known amount of manganese was spiked to samples, and good recovery results were obtained.     

Measurement of 5,10-dideaza-5,6,7,8-tetrahydrofolate (lometrexol) in human plasma and urine by high-performance liquid chromatography

Three high-performance liquid chromatographic methods are described for the detection of the novel antifolate anticancer drug (6R)-5,10-dideaza-5,6,7,8-tetrahydrofolate (lometrexol): one with fluorometric detection and two with detection by UV absorbance. An assay for plasma lometrexol using UV detection (288 nm) and reversed-phase chromatography was developed, with a quantitation limit of 0.2 μg/ml and linearity up to 10 μg/ml. This assay was modified for measurement of lometrexol in urine, with a quantitation limit of 2 μg/ml and linearity up to 25 μg/ml. An alternative assay for plasma lometrexol using derivatization and fluorescence detection (excitation at 325 nm, emission at 450 nm) was also developed, which proved twenty-fold more sensitive (quantitation limit of 10 ng/ml) than the UV assay, and which was linear up to 250 ng/ml. The fluoremetric method requires sample oxidation with manganese dioxide prior to analysis, and uses ion-pair chromatography with tetramethylammonium hydrogensulphate as an ion-pair reagent. All assays use a similar preliminary solid-phase extraction method (recovery as assessed by UV absorption >73%), with C10-desmethylene lometrexol added for internal standardisation. Each assay is highly reproducible (inter-assay precision in each assay is <10%). Applicability of the fluorescence-based assay to lometrexol in plasma and the UV-based assay lometrexol in urine is demonstrated by pharmacokinetic studies in patients treated as part of a Phase I clinical evaluation of the drug.