Fluorimetric Determination of p -Hydroxybenzoic Acid in Beer as α -Cyclodextrin Inclusion Complex

Abstract

The inclusion complex of p-hydroxyenzoic acid and α- and β-cyclodextrin has been studied by fluorescence spectroscopy. To describe quantitatively complex formation between α-cyclodextrin (α-CD) and p-hydroxybenzoic acid, an association constant of 967 ± 14 M^?1 at 21°C was obtained. The inclusion complex has been used to determine p-hydroxybenzoic acid in the range 0.15–1.00 mg L^?1 (RSD 4.5%, n = 8). Application of the method to determination of p-hydroxybenzoic acid in beer samples gave an endogenous content of 1.25 mg L^?1.     

Sensitive Determination of Prulifloxacin by Its Fluorescence Enhancement on Terbium(III)–Sodium Dodecylbenzene Sulfonate System

Abstract

A terbium-sensitized fluorescence spectrophotometry method using an anionic surfactant, sodium dodecyl benzene sulphonate (SDBS), was developed for the determination of prulifloxacin (PUFX). It was found that SDBS significantly enhanced the fluorescence intensity of the PUFX–Tb³⁺ complex (about 13-fold). The optimal experimental conditions were determined as follows: excitation and emission wavelengths of 290 nm and 545 nm, pH 8.0, 4.0 × 10^?5 mol L^?1 terbium(III), and 4.0 × 10^?4 mol L^?1 SDBS. The enhanced fluorescence intensity of the system (ΔF) showed a good linear relationship with the concentration of PUFX over the range 6.0 × 10^?8 to 2.0 × 10^?6mol L^?1 with a correlation coefficient of 0.9991. The detection limit (S/N = 3) was determined as 8.5 × 10^?9 mol L^?1. This method has been successfully applied for the determination of PUFX in pharmaceuticals and human urine/serum samples. Compared with most other methods reported, the rapid and simple procedure proposed here offered higher sensitivity, wider linear range, and good stability. The luminescence mechanism of the system was also discussed in detail. In the fluorescence system of PUFX–Tb³⁺–SDBS, SDBS acted not only as the surfactant but also as the energy donor.     

Potentiometric Dipyridamole Sensors Based on Lipophilic Ion Pair Complexes and Native Ionic Polymer Membranes

Abstract

A new spectrofluorimetric method was developed for the determination of trace amounts of lecithin. Using enoxacine (ENX)‐terbium ion (Tb³⁺) as a fluorescent probe, in a buffer solution at pH=5.80, lecithin can remarkably reduce the fluorescence intensity of the ENX‐Tb³⁺ complex at λ=545 nm; the reduced fluorescence intensity of the Tb³⁺ ion is proportional to the concentration of lecithin. Optimum conditions for the determination of lecithin were also investigated. The linear range and detection limit for the determination of lecithin were 1.96×10^?7–9.8×10^?6 mol l^?1 and 9.74×10^?8 mol l^?1. This method is simple, practical and relatively free of interference from coexisting substances, and can be successfully applied to assess lecithin in serum samples.     

Facile and Sensitive Spectrophotometric Determination of Chromium

Abstract

A simple, sensitive, and selective spectrophotometric method is developed for the determination of trace amounts of chromium(VI) in various samples. The method is based on oxidation of 2,4-dinitrophenylhydrazine (DNPH) by chromium in an acidic medium and coupling with β-naphthol to give a red-colored dye, having an absorbance maximum at 663 nm, and/or coupling with α-naphthol to give a violet-colored dye, having an absorbance maximum at 503 nm. The method obeys Beer's law in the concentration range 0.02–4.0µg mL^?1 and 0.05–9.0 µg mL^?1, respectively. The optimum reaction conditions and other important analytical parameters were established. Interference caused by various nontarget ions was also investigated. The proposed method is applied to the analysis of chromium(VI) in environmental, pharmaceutical, and steel samples. The performance of the proposed method is evaluated using the student's t and F -tests.     

Study of Aqueous Biomolecules with Magnetic Flux Using Density,Viscosity, and Surface Tension Probe at 304.15 K

Doses of 0.0150 weber m^?2 magnetic flux for 30 minutes are given to four series of biomolecules in aqueous medium, densities (ρ), viscosities (η), and surface tension (γ) were measured at 304.15 K. The vitamins and carbohydrates decrease densities and viscosities and the difference of density from magnet to aqueous solution in order of dextrose (? 0.00025 kg m^?3) > fructose (? 0.00021 kg m^?3) = B6 (? 0.00021 kg m^?3) > starch (? 0.00018 kg m^?3) > B1 (? 0.0018 kg m^?3), while viscosity in order of starch (? 0.0044 kg m^?1s^?1) > fructose (? 0.0037 kg m^?1s^?1) > B1(? 0.0018 kg m^?1s^?1) > dextrose (? 0.0016 kg m^?1s^?1) > B6 (? 0.0012 kg m^?1s^?1). The surface tension also decreases in vitamin and carbohydrate. The proteins show increase in ρ, η, and γ value hence casein decrease the density and viscosity. The glutamine show increase in density and surface tension while decrease in viscosity and vice versa to alanine. These orders of the data indicate the intermolecular force between water and bimolecules in magnetic flux.     

Enantioselective Separation and Determination of Carnosine in Rat Plasma by Fluorescence LC for Stereoselective Pharmacokinetic Studies

A sensitive fluorescence liquid chromatographic analytical method was developed for the simultaneous determination of carnosine enantiomers in rat plasma. The method was applied to pharmacokinetic studies. Chiral separation of carnosine enantiomers was achieved by pre-column derivatization with o-phthaldialdehyde and the thiol N-acety-l-cysteine as derivating reagents. They were separated on an ODS column and detected by fluorescence detection (λ_ex = 350 nm, λ_em = 450 nm). γ-Aminobutyric acid was used as internal standard. The method was linear up to 6,000 ng mL^?1 for l-carnosine, 4,000 ng mL^?1 for d-carnosine. Low limit of quantitation (LLOQ) was 40 ng mL^?1 for each isomer. The relative standard deviations obtained for intra- and inter-day precision were lower than 12% and the recoveries were higher than 75% for both enantiomers. The method was applied to a stereoselective study on the pharmacokinetics of carnosine after oral administration with a single dose (carnosine, 75 mg kg^?1 for each isomer) to a rat. The initial data indicated that l-carnosine had a larger value of the highest plasma concentration than d-carnosine (C _max 5,344 vs. 1,914 ng mL^?1), and that of l-carnosine had a lower value of AUC_(0?∞) and t _1/2(h) (AUC_(0?∞) 5,306 vs. 6,321 ng h mL^?1, t _1/2 1.43 vs. 3.37 h). Our results indicated that the pharmacokinetic of l-carnosine and d-carnosine revealed enantioselective properties significantly.     

β-Cyclodextrin-Cross-Linked Polymer as Solid Phase Extraction Material Coupled Graphite Furnace Atomic Absorption Spectrometry for Separation/Analysis of Trace Copper

Abstract

The β-cyclodextrin cross-linked polymer (β-CDCP) was synthesized by the reaction of β-cyclodextrin with epichlorohydrin in NaOH and characterized by fourier transform infrared spectroscopy and thermoanalysis. The β-CDCP as a solid phase extraction (SPE) material was used to preconcentrate/separate trace copper using l-(2-pyridylazo)-2-naphthol (PAN) as a complexing agent for Cu-(II)-PAN coupled with a graphite furnace atomic absorption spectrometry (GFAAS) for analysis. The optimized experiment conditions and adsorption capacity were investigated. The detection limit (DL) was 1.11 µg.L^?1 with RSD 4.27% (n = 5, c = 25.0 µg L^?1). The linear range is 6.25–31.25 µg L^?1. Moreover, the β-CDCP could be used repeatedly and offered better a recovery and estimation of trace copper. In order to verify the accuracy of the method, a certified reference water sample was analyzed and the results obtained were in agreement with the certified values. The recovery for copper was 103.6%. The proposed method was applied to the analysis of copper in lake water samples.     

LC–MS–MS Simultaneous Determination of l-Dopa and Its Prodrug l-Dopa n-Pentyl Ester Hydrochloride in Rat Plasma

A sensitive, simple and rapid LC–MS–MS method has been developed and validated for the simultaneous determination of l-dopa and l-dopa n-pentyl ester hydrochloride in rat plasma in the present study. The analytes were separated on a C₁₈ column (5 μm, 2.1 × 150 mm) with a security guard C₁₈ column (5 μm, 4 × 20 mm) and a triple-quadrupole mass spectrometer was applied for detection. The method was linear over the concentration ranges of 25–5,000 ng mL^?1 for l-dopa and 12.5–2,500 ng mL^?1 for l-dopa n-pentyl ester hydrochloride. Finally, the method was successfully applied to support the pharmacokinetic study.     

UPLC-PDA Analysis for Simultaneous Quantification of Four Active Compounds in Crude and Processed Rhizome of Polygonum multiflorum Thunb

A novel, rapid and specific ultra performance liquid chromatography-photo diode array detection method was developed for the simultaneous determination of 2,3,5,4′-tetrahydroxystilbene-2-O-β-d-glucoside (TSG), emodin-8-O-β-d-glucoside (EMG), emodin (EM) and physcion (PS). The chromatographic separation was performed on an Acquity BEH C₁₈ column (100 × 2.1 mm i.d., 1.7 μm). The mobile phase was a mixture of 0.3% acetic acid–water and 0.3% acetic acid–acetonitrile employing gradient elution at the flow rate of 0.4 mL min^?1. The four compounds behaved linearly in the concentration range between 60.80–3040.00 μg mL^?1 (TSG), 0.50–25.00 μg mL^?1 (EMG), 2.16–108.00 μg mL^?1 (EM) and 1.56–78.00 μg mL^?1 (PS), respectively with correlation coefficients >0.999. The precision of the method were below 5% RSD. Recoveries of the four compounds ranged from 95.71 to 102.97%, with RSD values less than 2%.     

Pico-Level Monitoring of Ampicillin by Using a Novel Cerium Fluorescence Probe

In this work, for the first time, a simple and sensitive fluorimetric method for low level determination of ampicillin, a beta-lactam antibiotic drug, using a cerium quenching fluorescence signal was developed. Among the lanthanide ions, cerium has a broad band spectrum in 300–400 nm which is due to the 5d to 4f allowed transition. The employed methodology is based on the formation of a complex formed between Ce³⁺ and ampicillin molecule. The detection limit was 0.0115 ng mL^?1 (33 × 10^?12 mol L^?1).     

A Direct Chemiluminescence Method for the Determination of Prulifloxacin Using Tris-(4,7-Diphenyl-1,10-Phenanthrolinedisulfonic Acid) Ruthenium(II)–Cerium(IV) System

Abstract

A simple, rapid, injection chemiluminescence method is described for the determination of prulifloxacin, a commonly used antibiotic. A strong chemiluminescence signal was detected when a mixture of the analyte and tris-(4,7-diphenyl-1,10-phenanthrolinedisulfonic acid)ruthenium(II) was injected into cerium(IV) sulfate. The chemiluminescence signal is proportional to the concentration of prulifloxacin in the range 4.0 × 10^?8–9.0 × 10^?6 mol L^?1. The detection limit is 1.0 × 10^?8 mol L^?1, and the relative standard deviation is 2.2% (n = 11) for the determination of 8.0 × 10^?7 mol L^?1 prulifloxacin. The proposed method was successfully applied to the determination of prulifloxacin in pharmaceutical preparations in capsules, spiked serum, and urine samples.     

Application of Solid Sampling Device for Direct Determination of Chromium and Nickel in Lubricating Oils by Graphite Furnace Atomic Absorption Spectrometry

Abstract

One method using a solid sampling device for the direct determination of Cr and Ni in fresh and used lubricating oils by graphite furnace atomic absorption spectrometry are proposed. The high organic content in the samples was minimized using a digestion step at 400°C in combination with an oxidant mixture 1.0% (v v^?1) HNO₃ + 15% (v v^?1) H₂O₂ + 0.1% (m v^?1) Triton X-100 for the in situ digestion. The 3-field mode Zeeman-effect allowed the spectrometer calibration up to 5 ng of Cr and Ni. The quantification limits were 0.86 µg g^?1 for Cr and 0.82 µg g^?1 for Ni, respectively. The analysis of reference materials showed no statistically significant difference between the recommended values and those obtained by the proposed methods.     

Study on the Fluorescence System of Oxolinic Acid‐Tb(III) and the Determination of Oxolinic Acid

Abstract

In Tris‐HCl buffer (pH=7.43), Tb³⁺ can react with oxolinic acid (OA) and form a 1:2 complex, which emits the intrinsic fluorescence of Tb³⁺. Based on this, a new fluorimetric method of determination of OA is developed. Under the optimum conditions, the enhanced fluorescence intensity of the system is proportional to the concentration of OA in the range of 1.5×10^?7～2.5×10^?5mol/L, and the detection limit is 5.5×10^?9 mol/L. Recovery test was also satisfactory. The experiments indicated that the luminescence mechanism was attributed to the M*–M luminescence.     

Enantiomeric LC Separation of Epinephrine on Amylose based sorbent

A simple, rapid, and robust chiral HPLC method has been developed and validated for separation of the enantiomers of epinephrine, l-1-(3,4-dihydroxyphenyl)-2-(methylamino)ethanol, an antihypertensive drug, in the bulk drug. The enantiomers were resolved on an amylose-based stationary phase with n-hexane–2-propanol–methanol–trifluoroacetic acid–diethylamine 90:05:05:0.2:0.2 (v/v) as mobile phase at a flow rate of 1.0 mL min^?1. In the optimized method resolution between the enantiomers was not less than 3.0. The trifluoroacetic acid and diethylamine in the mobile phase were important for enhancing chromatographic efficiency and hence the resolution of the enantiomers. The method was extensively validated and proved to be robust. The calibration plot for the d enantiomer was highly linear over the concentration range 100–2,000 μg mL^?1. The limits of detection and quantification for the d enantiomer were 0.15 and 0.45 μg mL^?1, respectively. Recovery of the d enantiomer from bulk drug samples of epinephrine ranged between 99.5 and 101.5%. Epinephrine sample solution was stable for up to 48 h. The method was suitable for accurate quantitative determination of the d enantiomer in the bulk drug substance     

The Development and Validation of a Stability-Indicating UHPLC-DAD Method for Determination of Perindopril l-Arginine in Bulk Substance and Pharmaceutical Dosage Form

A stability-indicating ultra-high-performance liquid chromatography (UHPLC) method with a diode array detector was developed and validated for the determination of cis/trans isomers of perindopril l-arginine in bulk substance and pharmaceutical dosage form. The separation was achieved on a Poroshell 120 Hilic (4.6 × 150 mm, 2.7 µm) column using a mobile phase composed of acetonitrile–0.1 % formic acid (20:80 v/v) at a flow rate of 1 mL min^?1. The injection volume was 5.0 µL and the wavelength of detection was controlled at 230 nm. The selectivity of the UHPLC-DAD method was confirmed by determining perindopril l-arginine in the presence of degradation products formed during acid–base hydrolysis and oxidation as well as degradation in the solid state, at an increased relative air humidity and in dry air. The method’s linearity was investigated in the ranges 0.40–1.40 µg mL^?1 for isomer I and 0.40–2.40 µg mL^?1 for isomer II of perindopril l-arginine. The UHPLC-DAD method met the precision and accuracy criteria for the determination of the isomers of perindopril l-arginine. The limits of detection and quantitation were 0.1503 and 0.4555 µg mL^?1 for isomer I and 0.0356 and 0.1078 µg mL^?1 for isomer II, respectively.     

Enoxacin—Tb3+ Complex as an Environmentally Friendly Fluorescence Probe for Coenzyme A and Its Application

Abstract

A new spectrofluorimetric method was developed for the determination of trace amounts of coenzyme A using enoxacin–Tb³⁺ as a fluorescent probe. In the presence of periodic acid (H₅IO₆), coenzyme A could remarkably enhance the fluorescence intensity of the Tb³⁺–enoxacin complex at 545 nm at pH 5.4. The optimal conditions for the determination of coenzyme A were also investigated. This method could be successfully applied to assess coenzyme A in injection and biological samples. Moreover, the enhancement mechanism of the fluorescence intensity of the coenzyme A–Tb³⁺–enoxacin system in the presence of H₅IO₆ was also discussed.     

Evaluation of Monolithic Columns for Determination of Formaldehyde and Acetaldehyde in Sugar Cane Spirits by High-Performance Liquid Chromatography

Abstract

High-Performance Liquid Chromatography (HPLC) conditions are described for separation of 2,4-dinitrophenylhydrazone (2,4-DNPH) derivatives of carbonyl compounds in a 10 cm long C₁₈ reversed phase monolithic column. Using a linear gradient from 40 to 77% acetonitrile (acetonitrile-water system), the separation was achieved in about 10 min—a time significantly shorter than that obtained with a packed particles column. The method was applied for determination of formaldehyde and acetaldehyde in Brazilian sugar cane spirits. The linear dynamic range was between 30 and 600 µg L^?1, and the detection limits were 8 and 4 µg L^?1 for formaldehyde and acetaldehyde, respectively.     

Determination of Trace Copper by Fluorescence Spectrophotometry Based on Cu(DP)2+ and Cu‐4.0‐Generations Polyamidoamine Dendrimers Catalyze Cu2+ to Oxidize Fluorescein

Abstract

Fluorescein can emit strong and stable fluorescence. Cu²⁺ can oxidize fluorescein, which causes the fluorescence signal to diminish. Cu(DP)²⁺ (DP refers to α,α′‐dipyridyl) and Cu‐GPD‐4.0 (GPD‐4.0 refers to 4.0‐generations polyamidoamine dendrimers) both can catalyze Cu²⁺ to oxidize fluorescein, which causes the fluorescence signal to diminish sharply. The ΔF is directly proportional to the content of copper. Based on the facts above, a new catalytic fluorescence spectrophotometry for the determination of trace copper using Cu(DP)²⁺ and Cu‐GPD‐4.0 was established. The linear range of this method is 0.040–28 pg mL^?1. The regression equation for working curve is ΔF=209.5+14.39 C_Cu ²⁺ (pg mL^?1), n=7; correlation coefficient is 0.991. The detection limit of this method is 1.0×10^?14 g mL^?1. After replicate measurement times, RSDs are 3.1% and 4.2% for samples containing 0.040 and 28 pg mL^?1 Cu²⁺, respectively. This method is rapid and precise with high sensitivity and good repeatability. The method has been applied to the determination of trace copper in tea and human hair with satisfactory results. Meanwhile, the mechanism for the determination of trace copper by catalytic fluorescence spectrophotometry using Cu(DP)²⁺ and Cu‐GPD‐4.0 was also discussed.     

Determination of α-tocopherol in Cosmetic Products by Chronopotentiometry

Abstract

In the present study, a rapid chronopotentiometric method was developed for the determination of α-tocopherol in various cosmetic products. Determination of α-tocopherol is based on its irreverse oxidation by constant current at the planar glassy carbon electrode. The influence of the most important experimental parameters of chronopotentiometry was investigated. After optimization, an appropriate procedure for the sample preparation was developed. Under the defined experimental conditions, a detection limit of 7.5 mg L^?1 of α-tocopherol was obtained. The accuracy of the defined method was confirmed by means of recovery assay. The developed method was successfully applied to quantitation of α-tocopherol in various cosmetic products.     

GC–ECD Method for Determination of Glucosidically Bound Aroma Precursors in Fresh Tea Leaves

The possibility of using GC–ECD to determine glucosidically bound aroma precursors was investigated. Five β-d-glucopyranosides were derivatized with N-methyl-bis(trifluoroacetamide) (MBTFA) and then determined by GC-ECD, which showed these mono-glycosides (glucosides) could be separated and identified by GC. Repeatability, sensitivity and stability were tested, relative standard deviation (RSD) was in the range of 0.55–5.9%, the limit of detection (LOD) was lower than 10^?3 μg mL^?1, and the standard mixture was stable within 3 days (stored at 4 °C, peak areas RSD < 3%). Application of the developed derivatization and determination method to the fresh tea leaves showed that the glucosides could be accurately quantified (using phenyl β-d-glucopyranoside as internal standard). Because of its high sensitivity, the developed method was suitable for the determination of glucosides in fresh tea leaves.