Study on the resonance Rayleigh scattering and resonance non‐linear scattering spectra of ion‐association complexes of [PdI4]2−‐protein systems and their analytical applications

In an acid medium solution, proteins such as bovine serum albumin, human serum albumin, ovalbumin, hemoglobin, lysozyme, γ‐globulin, α‐chymotrypsin and papain could react with [PdI₄]^2? by virtue of electrostatic attraction and hydrophobic force to form ion‐association complexes. As a result, the resonance Rayleigh scattering (RRS) and resonance nonlinear scattering such as second‐order scattering (SOS) and frequency doubling scattering (FDS) intensities were enhanced greatly and new scattering spectra appeared. The maximum scattering peaks of RRS, SOS and FDS were at 367, 720 and 370 nm, respectively. The enhanced RRS, SOS and FDS intensities were directly proportional to the concentrations of proteins. The detection limits for the different proteins were 2.4–11.8 ng/mL for RRS method, 9.5–47.9 ng/mL for SOS method and 4.6–18.5 ng/mL for FDS method. In this work, the influences of the interaction of [PdI₄]^2? with proteins on spectral characteristics of RRS, SOS and FDS were investigated and the optimum conditions were tested. Meanwhile, the effects of coexisting substances were tested and the results showed that the method exhibited a good selectivity. Based on the above research, a highly sensitive, simple and rapid method for the determination of trace amounts of proteins by resonance light scattering technique has been developed. It can be applied to the determination of proteins in tablet, human serum and urine samples. Copyright © 2009 John Wiley & Sons, Ltd.     

Direct determination of polymyxin B sulfate using resonance Rayleigh scattering and resonance non‐linear scattering methods with hexatungstate

At pH 1.3–1.6, tungstate WO₄^2–, can be converted to hexatungstate W₆O₁₉^2–, which can react with positively charged polymyxin B sulfate (PMB) to result in enhancement of resonance Rayleigh scattering (RRS) and resonance non‐linear scattering, including second order scattering and frequency doubling scattering. Linear relationships can be established between enhanced scattering intensity and PMB concentration. The detection limits (3σ) were 5.5 ng/mL (RRS), 10.1 ng/mL (second order scattering) and 34.6 ng/mL (frequency doubling scattering). The optimum reaction conditions, influencing factors and related analytical properties were tested. The interaction mechanism was investigated via absorption spectrum, circular dichroism spectra and atomic force microscopy imaging. The basis of scattering enhancement is discussed. PMB in eardrops, human serum and urine, were quantified satisfactorily by RRS. Copyright © 2013 John Wiley & Sons, Ltd.     

Study on the interaction between ligustrazine and 12‐tungstophosphoric acid using resonance Rayleigh scattering and resonance nonlinear scattering spectra,and its analytical applications

In an HCl medium (pH 1.5), ligustrazine (2,3,5,6‐tetramethylpyrazine, TMP) reacted with 12‐tungstophosphoric acid (TP) to form a 3 : 1 ion‐association complex. As a result, the intensities of resonance Rayleigh scattering (RRS), second‐order scattering (SOS) and frequency doubling scattering (FDS) were greatly enhanced and new scattering spectra appeared. The maximum RRS, SOS and FDS wavelengths of the ion‐association complexes were located at 379, 738 and 395 nm, respectively. The scattering intensity increments (ΔI_RRS, ΔI_SOS and ΔI_FDS) were directly proportional to the concentration of ligustrazine within certain ranges. The detection limits (3σ) of RRS, SOS and FDS were 1.6, 3.2 and 2.8 ng/mL. Optimal conditions for the RRS method and factors influencing the method were discussed, and the structure of the ion‐association complex and the reaction mechanism were investigated. Transmission electron microscopy (TEM) was used to characterize the structures of the ion‐association complex. Based on the ion‐association reaction and its spectral response, a rapid, simple and sensitive RRS method for the determination of TMP was developed. It was applied to the determination of TMP in tablet and urine samples with satisfactory results. Copyright © 2014 John Wiley & Sons, Ltd.     

Fluorescence spectroscopic studies on the interaction of Gemini surfactant 14‐6‐14 with bovine serum albumin

The interaction of the cationic Gemini surfactant hexamethylene‐1,3‐bis (tetradecyldimethylammonium bromide) (14‐6‐14) with bovine serum albumin (BSA) has been investigated by fluorescence quenching spectra and three‐dimensional (3D) fluorescence spectra. The Stern–Volmer quenching constants K_SV and the corresponding thermodynamic parameters ΔH, ΔG and ΔS have been estimated by the fluorescence quenching method. The results indicated that hydrophobic forces were the predominant intermolecular forces between BSA and the surfactant. Competitive experiments and the number of binding sites calculation show that 14‐6‐14 can be inserted in site‐II (in subdomain IIIA) of BSA. The effect of 14‐6‐14 on the conformation of BSA was evaluated by synchronous fluorescence spectroscopy and 3D fluorescence spectral methods. The results show that the conformation of BSA was changed dramatically in the presence of 14‐6‐14, by binding to the Trp and Try residues of BSA. The investigation provides interaction between BSA and 14‐6‐14 as a model for molecular design and industrial research. Copyright © 2011 John Wiley & Sons, Ltd.     

Study on the interaction between erythrosine B and the cardiac drug amiodarone using fluorescence,scattering, and absorbance spectra and their analytical application

In an acidic buffered solution, erythrosine B can react with amiodarone to form an association complex, which not only generates great enhancement in resonance Rayleigh scattering (RRS) spectrum of erythrosine B at 346.5 nm but also results in quenching of fluorescence spectra of erythrosine B at λ_emission = 550.4 nm/λ_excitation = 528.5 nm. In addition, the formed erythrosine B–amiodarone complex produces a new absorbance peak at 555 nm. The spectral characteristics of the RRS, absorbance, and fluorescence spectra, as well as the optimum analytical conditions, were studied and investigated. As a result, new spectroscopic methods were developed to determine amiodarone by utilizing erythrosine B as a probe. Moreover, the ICH guidelines were used to validate the developed RRS, photometric, and fluorimetric methods. The enhancements in the absorbance and the RRS intensity and the decrease in the fluorescence intensity of the used probe were proportional to the concentration of amiodarone in ranges of 2.5–20.0, 0.2–2.5, and 0.25–1.75 μg/mL, respectively. Furthermore, limit of detection values were 0.52 ng/mL for the spectrophotometric method, 0.051 μg/mL for the RRS method, and 0.075 μg/mL for the fluorimetric method. Moreover, with good recoveries, the developed spectroscopic procedures were applied to analyze amiodarone in its commercial tablets.     

Interaction of proteins with aluminum(III)–chlorophosphonazo III by resonance Rayleigh scattering method

In weak acid medium, aluminum(III) can react with chlorophosphonazo III [CPA(III), H₈L] to form a 1:1 coordination anion [Al(OH)(H₄L)]^2‐. At the same time, proteins such as bovine serum albumin (BSA), lysozyme (Lyso) and human serum albumin (HSA) existed as large cations with positive charges, which further combined with [Al(OH)(H₄L)]^2‐ to form a 1:4 chelate. This resulted in significant enhancement of resonance Rayleigh scattering (RRS), second‐order scattering (SOS) and frequency doubling scattering (FDS). In this study, we investigated the interaction between [Al(OH)(H₄L)]^2‐ and proteins, optimization of the reaction conditions and the spectral characteristics of RRS, SOS and FDS. The maximum RRS wavelengths of different protein systems were located at 357–370 nm. The maximum SOS and FDS wavelengths were located at 546 and 389 nm, respectively. The scattering intensities (ΔI) of the three methods were proportional to the concentration of the proteins, within certain ranges, and the detection limits of the most sensitive RRS method were 2.6–9.3 ng/mL. Moreover, the chelate reaction mechanism or the reasons for the enhancement of RRS were discussed through absorption spectra, fluorescence spectra and circular dichroism (CD) spectra. Copyright © 2013 John Wiley & Sons, Ltd.     

Study on the ternary system of MoO42‐–enzyme–PdCl2 by resonance Rayleigh scattering,second‐order scattering and frequency‐doubling scattering spectra and its analytical application

In pH 4.0 Britton–Robinson buffer medium, PdCl₂ was able to react with enzymes (EZ) such as lysozyme (LYSO) and papain (PAP) to form a coordination complex (EZ–PdCl₂), which further reacted with MoO₄^2‐ to form a ternary complex (MoO₄^2‐–EZ–PdCl₂). As a result, the absorption and fluorescence spectra changed; new spectra of resonance Rayleigh scattering (RRS), second‐order scattering (SOS) and frequency‐doubling scattering (FDS) appeared and their intensities were enhanced greatly. The maximum RRS, SOS and FDS wavelengths of two ternary complexes were located at 310, 560 and 350 nm, respectively. The increments of scattering intensity were directly proportional to the concentrations of EZ within certain ranges. The detection limits (3σ) of LYSO and PAP were 4.5 and 14.0 ng/mL (RRS method), 9.6 and 57.8 ng/mL (SOS method), and 5.2 and 106.0 ng/mL (FDS method). Taking the MoO₄^2‐–LYSO–PdCl₂ system, which was more sensitive, as an example, the effects of coexisting substances were evaluated. The methods showed excellent selectivity. Accordingly, new rapid, convenient, sensitive and selective scattering methods for the determination of LYSO and PAP were proposed and applied to determine LYSO in egg white with satisfactory results. The reaction mechanism and basis of the enhancement of scattering were discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Quantification of three triterpenic acids in dried rosemary using HPLC‐fluorescence detection and 4‐(4,5‐diphenyl‐1H‐imidazole‐2‐yl)benzoyl chloride derivatization

Functional triterpenic acids such as ursolic acid (UA), oleanolic acid (OA) and betulinic acid (BA) are representative ingredients in rosemary that may have health benefits. UA, OA and BA in rosemary extracts were derivatized with 4‐(4,5‐diphenyl‐1H‐imidazole‐2‐yl)benzoyl chloride (DIB‐Cl) and detected using HPLC‐fluorescence (FL). Dried rosemary (50 mg) was ground, added to 3 ml of ethanol, sonicated for 40 min, then the sample solution was added to a mixture of 1% trimethylamine and 1 mM DIB‐Cl in acetonitrile. The mixture was settled for 5 min at room temperature, then the DIB‐triterpenic acid derivatives were separated using a Wakopak Handy ODS column (250 × 4.6 mm, 6 μm) eluted with 25 mM acetate buffer (pH 4.5)/methanol/acetonitrile (= 8:10:82 v/v/v%). The fluorescence intensity of the eluent was monitored at 365 (λ_ex) and 490 nm (λ_em) and the maximum retention time of the derivatives was 30 min. Calibration curves constructed using rosemary extract spiked with standards showed good linearity (r ≥ 0.997) in the range 2.5–100 ng/ml. The detection limits at 3σ for internal BA, UA and OA peaks in rosemary extract were 0.2, 0.4 and 0.5 ng/ml, respectively. This method was used to quantify BA, UA and OA in commercially available dried rosemary products.     

High‐performance liquid chromatography study of gatifloxacin and sparfloxacin using erythrosine as post‐column resonance Rayleigh scattering reagent and mechanism study

Herein, a highly selective high‐performance liquid chromatography (HPLC) coupled with resonance Rayleigh scattering (RRS) method was developed to detect gatifloxacin (GFLX) and sparfloxacin (SPLX). GFLX and SPLX were first separated by HPLC, then, in pH 4.4 Britton–Robinson (BR) buffer medium, protonic quaternary ammonia cation of GFLX and SPLX reacted with erythrosine (ERY) to form 1:1 ion‐association complexes, which resulted in a significant enhancement of RRS signal. The experimental conditions of HPLC and post‐column RRS have been investigated, including detection wavelength, flow rate, pH, reacting tube length and reaction temperature. Reaction mechanism were studied in detail by calculating the distribution fraction. The maximum RRS signals for GFLX and SPLX were recorded at λ_ex = λ_em = 330 nm. The detection limits were 3.8 ng ml^?1 for GFLX and 17.5 ng ml^?1 for SPLX at a signal‐to‐noise ratio of 3. The developed method was successfully applied to the determination of GFLX and SPLX in water samples. Recoveries from spiked water samples were 97.56–98.85%.     

Redox‐triggered chiroptical switching activity of ruthenium(III)‐bis‐(β‐diketonato) complexes bearing a bipyridine‐helicene ligand

The charged, electroactive bipyridine‐helicene‐ruthenium(III) complex [ 4 ] ^{. +},PF₆^? has been prepared from 3‐(2‐pyridyl)‐4‐aza[6]helicene and a Ru‐bis‐(β‐diketonato)‐bis‐acetonitrile precursor (β‐diketonato: 2,2,6,6‐tetramethyl‐3,5‐heptanedionato). Its chiroptical properties (electronic circular dichroism and optical rotation) were studied both experimentally and theoretically and suggest the presence of 2 diastereoisomers, namely (P,Δ)‐ and (P,Λ)‐[ 4 ] ^{. +},PF₆^? (denoted jointly as (P,Δ*)‐[ 4 ] ^{. +},PF₆^?) and their mirror‐images (M,Λ)‐ and (M,Δ)‐[ 4 ] ^{. +},PF₆^? ((M,Δ*)‐[ 4 ] ^{. +},PF₆^?). The electrochemical reduction of (P,Δ*)‐[ 4 ] ^{. +},PF₆^? to neutral complex (P,Δ*)‐ 4 was performed and revealed strong changes in the UV‐vis and electronic circular dichroism spectra. A reversible redox‐triggered chiroptical switching process was then achieved.     

Determination of doxepin hydrochloride in spiked human plasma and capsule after derivatization with eosin Y using resonance Rayleigh scattering,second-order scattering and frequency doubling scattering methods

Doxepin hydrochloride (DOX) is a tricyclic antidepressant drug. Three sensitive spectrofluorimetric methods, namely resonance Rayleigh scattering (RRS), frequency doubling scattering (FDS) and second-order scattering (SOS), were developed and validated for their estimation of doxepin in spiked human plasma and formulation using liquid–liquid extraction method through the formation of an ion pair complex with eosin Y at a pH of 4.5. Various factors affecting fluorescence intensity were optimized, and the reaction kinetics was determined using the Arrhenius equation method. Different scattering methods such as RRS, FDS and SOS were developed at maximum scattering wavelengths λ_ex/λ_em = 567/567 nm for RRS, 720/360 nm for SOS and 260/520 nm for FDS, respectively. The methods exhibited high sensitivities, and the detection limits for DOX were found to be 0.82, 1.20 and 1.03 ng/ml for RRS, FDS and SOS methods, respectively. The FDS method exhibited the highest sensitivity. The methods were validated using the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use guidelines and applied to determine DOX in capsule and spiked human plasma samples.     

Synthesis of CuPF6‐(S)‐BINAP loaded resin and its enantioselectivity toward phenylalanine enantiomers

A type of resin‐anchored CuPF₆‐(S )‐BINAP was synthesized and identified. The PS‐CuPF₆‐(S )‐BINAP resin was used to adsorb the phenylalanine enantiomers. The results showed that the adsorption capacity of PS‐CuPF₆‐(S )‐BINAP resin toward L‐phenylalanine was higher than that of resin toward D‐phenylalanine. PS‐CuPF₆‐(S )‐BINAP resin exhibited good enantioselectivity toward L‐phenylalanine and D‐phenylalanine. The influence of phenylalanine concentration, pH, adsorption time, and temperature on the enantioselectivity of the resin were investigated. The results showed that the enantioselectivity of the resin increased with increasing the phenylalanine concentration, pH, and adsorption time, while it decreased with an increase in temperature. The causes for these influences are discussed. The highest enantioselectivity (α = 2.81) was obtained when the condition of phenylalanine concentration was 0.05 mmol/mL, pH was 8, adsorption time was 12 h, and temperature 5°C. The desorption test for removing D/L‐phenylalanine on PS‐CuPF₆‐(S )‐BINAP resin was also investigated. The desorption ratios of D‐phenylalanine and L‐phenylalanine at pH of 1 were 95.7% and 94.3%, respectively. This result indicated that the PS‐CuPF₆‐(S )‐BINAP resin could be regenerated by shaking with an acidic solution. The reusability of the PS‐CuPF₆‐(S )‐BINAP resin was also assessed and the resin exhibited considerable reusability.     

A rapid and sensitive resonance Rayleigh scattering spectra method for the determination of quinolones in human urine and pharmaceutical preparation

A new method based on resonance Rayleigh scattering (RRS) was proposed for the determination of quinolones (QNS) at the nanogram level. In pH 3.3–4.4 Britton–Robinson buffer medium, quinolones such as ciprofloxacin, pipemidic acid (PIP), lomefloxacin (LOM), norfloxacin (NOR) and sarafloxacin (SAR) were protonated and reacted with methyl orange (MO) to form an ion‐pair complex, which then further formed a six‐membered ring chelate with Pd(II). As a result, new RRS spectra appeared and the RRS intensities were enhanced greatly. RRS spectral characteristics of the MO–QNS–Pd(II) systems, the optimum conditions for the reaction, and the influencing factors were investigated. Under optimum conditions, the scattering intensity (∆I) increments were directly proportional to the concentration of QNS with in certain ranges. The method had high sensitivity, and the detection limits (3σ) ranged from 6.8 to 12.6 ng/mL. The proposed method had been successfully applied for the determination of QNS in pharmaceutical formulations and human urine samples. In addition, the mechanism of the reaction system was discussed based on IR, absorption and fluorescence spectral studies. The reasons for the enhancement of scattering spectra were discussed in terms of fluorescence‐scattering resonance energy transfer, hydrophobicity and molecular size. Copyright © 2014 John Wiley & Sons, Ltd.     

Bimolecular fluorescence quenching reactions of the biologically active coumarin composite 2‐acetyl‐3H‐benzo[f]chromen‐3‐one in different solvents

A study on fluorescence quenching was carried out for the coumarin derivative 2‐acetyl‐3H‐benzo[f]chromen‐3‐one (2AHBC) with aniline at room temperature. Efficient fluorescence quenching was observed and Stern–Volmer (S–V) plots showed upward curves from linearity in all solvents of different polarities. For the solute 2AHBC, ground state complex formation does not hold in our study. The kinetic distance (r) value was found to be greater than the encounter distance (R) and indicated that the quenching reaction was held within the sphere of action. Diffusion‐limited reactions were found to be more prominent in high polarity solvents, namely dimethyl sulfoxide (DMSO), DMF, ACN, methanol, ethanol, propanol and DCM. The relationships between quenching constant (K_SV) and dielectric constants (ε) of the different solvents were studied.     

Spectroscopic investigation of alloyed quantum dot‐based FRET to cresyl violet dye

Quantum dots (QDs), bright luminescent semiconductor nanoparticles, have found numerous applications ranging from optoelectronics to bioimaging. Here, we present a systematic investigation of fluorescence resonance energy transfer (FRET) from hydrophilic ternary alloyed quantum dots (CdSeS/ZnS) to cresyl violet dye with a view to explore the effect of composition of QD donors on FRET efficiency. Fluorescence emission of QD is controlled by varying the composition of QD without altering the particle size. The results show that quantum yield of the QDs increases with increase in the emission wavelength. The FRET parameters such as spectral overlap J(λ), Förster distance R₀, intermolecular distance (r) , rate of energy transfer k_T (r), and transfer efficiency (E) are determined by employing both steady‐state and time‐resolved fluorescence spectroscopy. Additionally, dynamic quenching is noticed to occur in the present FRET system. Stern–Volmer (K_D) and bimolecular quenching constants (k_q) are determined from the Stern–Volmer plot. It is observed that the transfer efficiency follows a linear dependence on the spectral overlap and the quantum yield of the donor as predicted by the Förster theory upon changing the composition of the QD. Copyright © 2015 John Wiley & Sons, Ltd.     

Spectroscopic investigation of water‐soluble alloyed QDs with bovine serum albumin

We present here a systematic investigation on the interaction between a water‐soluble alloyed semiconductor quantum dot and bovine serum albumin using various spectroscopic techniques i.e. fluorescence quenching, resonance light scattering and synchronous fluorescence spectroscopy. The analysis of fluorescence spectrum and fluorescence intensity indicates that the intrinsic fluorescence of bovine serum albumin (BSA) gets quenched by both static and dynamic quenching mechanism. The Stern‐Volmer quenching constants, energy transfer efficiency parameters, binding parameters and corresponding thermodynamic parameters (ΔH⁰, ΔS⁰ and ΔG⁰) have been evaluated by using van 't Hoff equation at different temperatures. A positive entropy change with a positive enthalpy change was observed suggesting that the binding process was an entropy‐driven, endothermic process associated with the hydrophobic effect. The intermolecular distance (r) between donor (BSA) and acceptor (CdSeS/ZnS quantum dots) was estimated according to Förster's theory of non‐radiative energy transfer. The synchronous fluorescence spectra revealed a blue shift in the emission maxima of tryptophan which is indicative of increasing hydrophobicity. Negative ΔG⁰ values implied that the binding process was spontaneous. It was found that hydrophobic forces played a role in the quenching process. Copyright © 2016 John Wiley & Sons, Ltd.     

Study of the interaction between sodium salts of (2E)‐3‐(4'‐halophenyl)prop‐2‐enoyl sulfachloropyrazine and bovine serum albumin by fluorescence spectroscopy

Three sodium salts of (2E)‐3‐(4'‐halophenyl)prop‐2‐enoyl sulfachloropyrazine (CCSCP) were synthesized and their structures were determined by ¹H and ¹³C NMR, LC‐MS and IR. The binding properties between CCSCPs and bovine serum albumin (BSA) were studied using fluorescence spectroscopy in combination with UV–vis absorbance spectroscopy. The results indicate that the fluorescence quenching mechanisms between BSA and CCSCPs were static quenching at low concentrations of CCSCPs or combined quenching (static and dynamic) at higher CCSCP concentrations of 298, 303 and 308 K. The binding constants, binding sites and corresponding thermodynamic parameters (ΔH, ΔS, ΔG) were calculated at different temperatures. All ΔG values were negative, which revealed that the binding processes were spontaneous. Although all CCSCPs had negative ΔH and positive ΔS, the contributions of ΔH and ΔS to ΔG values were different. When the 4'‐substituent was fluorine or chlorine, van der Waals interactions and hydrogen bonds were the main interaction forces. However, when the halogen was bromine, ionic interaction and proton transfer controlled the overall energetics. The binding distances between CCSCPs and BSA were determined using the Förster non‐radiation energy transfer theory and the effects of CCSCPs on the conformation of BSA were analyzed by synchronous fluorescence spectroscopy. Copyright © 2012 John Wiley & Sons, Ltd.     

Solvatochromic study of 3‐N‐(N′‐methylacetamidino)benzanthrone and its interaction with dopamine by the fluorescence quenching mechanism

The change in photophysical properties of the organic molecule due to solvatochromic effect caused by different solvent environments at room temperature gives information about the dipole moments of 3‐N‐(N′‐methylacetamidino)benzanthrone (3‐MAB). The quantum yield, fluorescence lifetime of 3‐MAB was measured in different solvents to calculate radiative and non‐radiative rate constants. The results revealed that the excited state dipole moment (μ_e) is relatively larger compared to the ground state dipole moment (μ_g), indicating the excited state of the dye under study is more polar than the ground state and the same trend is noticed with theoretical calculations performed using the CAM‐B3LYP/6‐311+G(d,p) method. Further, the study on preferential solvation was carried out for 3‐MAB dye in ethyl acetate–methanol solvent mixture. The fluorescence quenching method has been employed for the detection of dopamine using 3‐MAB as fluorescent probe, using steady‐state and time resolved methods at room temperature. The method enables dopamine in the micro molar range to be detected. Also, an attempt to verify the quenching process by employing different models has been tried. Various rate parameters are measured using these models, our results indicates the quenching process is diffusion limited.     

Synthesis of a novel fluorescent probe based on 7‐nitrobenzo‐2‐oxa‐1,3‐diazole skeleton for the rapid determination of vitamin B12 in pharmaceuticals

A new fluorescent probe, 4‐N,N‐di(2‐hydroxyethyl)imino‐7‐nitrobenzo‐2‐oxa‐1,3‐diazole (HINBD) was synthesized in a single step with reasonably good yield. The water‐soluble HINBD emits strongly in the visible region (λ_ex = 479 nm, λ_em = 545 nm) and is stable over a wide range of pH values. It was found that vitamin B₁₂ (VB₁₂) had the ability to quench the fluorescence of HINBD, and the quenched fluorescence intensity was proportional to the concentration of VB₁₂. A method for VB₁₂ determination based on the quenching fluorescence of HINBD was thus established. Interference effects of various substances, including sugars, vitamins, amino acids, inorganic cations and some organic substances have been studied. Under optimal conditions, the linear range is 0.0–2.4 × 10^–5 mol/L. The determination limit is 8.3 × 10^–8 mol/L. The method was applied to measure VB₁₂ in pharmaceutical preparations with satisfactory results. Copyright © 2013 John Wiley & Sons, Ltd.     

Study on the interaction between palladium(II)–lincomycin chelate and erythosine by absorption,fluorescence and resonance Rayleigh scattering spectra and its analytical applications

In pH 5.0–5.4 HAc–NaAc buffer solution, lincomycin (Linco) reacted with Pd(II) to form 1:1 cationic chelate, which could further react with erythrosine (Ery) to form 1:1 ion‐association complexes (Pd–Linco)Ery. As a result, not only were the absorption and fluorescence spectra changed, but also the resonance Rayleigh scattering (RRS) intensity was greatly enhanced. These phenomena offered useful means for the determination of Linco by spectrophotometry, fluorescence and RRS methods. The linear range and detection limit of Linco were 0.20–3.00 µg/mL and 0.057 µg/mL, 0.20–4.80 µg/mL and 0.061 µg/mL, 0.05–2.70 µg/mL and 0.015 µg/mL for the spectrophotometric, fluorescence quenching and RRS methods, respectively. Among these, the RRS method obtained the highest sensitivity. Therefore, the optimum reaction conditions and the influences of coexisting substances were investigated using the RRS method. A simple, sensitive and rapid method has been developed for the determination of Linco in either the pharmaceutical form or human body fluids, and the reasons for RRS enhancement are discussed. Copyright © 2008 John Wiley & Sons, Ltd.