Fluorimetric Determination of Thiamine with Cobalt(II)

Abstract

A rapid fluorimetric method is reported for the determination of thiamine based upon its interaction with Co(II) ion in the presence of base and a nonionic Triton X-100 micellar medium. The effect of different experimental variables upon the fluorescence intensity were assessed. The detection limit for thiamine is 5.0 × 10^?8M (λ_ex =375nm, λ_em =433nm). The method was successfully applied for determination of thiamine in variety of samples with good accuracy being achieved.     

Fluorimetric reaction-rate method for the determination of aluminum with acid alizarin garnet R

The development and optimization of a fluorimetric reaction-rate method for the determination of aluminum is described. The rate of formation of the fluorescent aluminum chelate of 2,4,2′-trihydroxyazobenzene-5′-sulfonic acid is measured within 24 s after mixing with one reagent solution. The technique exhibits a detection limit of 0.1 ng ml^?1 and a linear dynamic range of over four orders of magnitude. The technique was successfully applied to the determination of aluminum in NBS spinach leaves and a sample of river water.     

Fluorimetric kinetic method for the determination of total ascorbic acid with o-phenylenediamine

A fluorimetric reaction-rate method for the determination of L-ascorbic acid (AA) in aqueous solution is presented. The technique is based on the rapid oxidation of AA by mercury(II) chloride to dehydro-L-ascorbic acid, which then reacts with o-phenylenediamine to form a fluorescent quinoxaline. The formation of the product is monitored fluorimetrically with a data acquisition system based on a microcomputer, a voltage-to-frequency converter and a timer-counter board. The initial rate is estimated with a fixed-time computational method. With a 20-s measurement time (after a 5-s delay from initiation of the reaction), the detection limit for AA is 0.02 μg ml^?1 with a linear dynamic range extending to 10 μg ml^?. The procedure is applied to the determination of the AA in vitamin pills and juice. The relative standard deviation is 1.9% or better.     

Fast Fourier Transform Continuous Cyclic Voltammetry Development as a Highly Sensitive Detection System for Ultra Trace Monitoring of Thiamine

Abstract

In this work, a highly sensitive method for the fast monitoring of thiamine hydrocholoride in flow‐injection systems has been developed. The fast Fourier transform continuous cyclic voltammetry (FFCV) in flowing solution as a detection system was applied for the very fast monitoring of thiamine in its pharmaceutical formulations. This technique is very simple, precise, accurate, time‐saving and economical, compared to all previous reported methods. The effects of various parameters on the sensitivity of the detection system were considered. The best condition was obtained within the pH value of 2, and scan rate value of 25 V s^?1, accumulation potential of ?400 mV, and accumulation time of 0.6 s. The proposed method has some advantages over other reported methods such as, there is no need for the removal of oxygen from the test solution, has a sub‐nanomolar detection limit, and finally the method is fast enough for the determination of any such compound, in a wide variety of chromatographic methods. This research also introduces a special computer‐based numerical method, for the calculation of the analyte signal and noise reduction. The electrode response was calculated based on partial and total charge exchanges on the electrode surface after subtracting the background current from that of noise. To obtain a sensitive determination, the integration range of currents was set for all the potential scan ranges, including oxidation and reduction of the Au surface electrode, while performing the measurements. The potential waveform, consisting of the potential steps for cleaning, accumulation and potential ramp of analyte, was applied on an Au disk microelectrode (12.5 µm in radius) in a continuous way. The detection limit of the method for thiamine was 1.0×10^?12 M. The relative standard deviation of the method at 1.0×10^?8 M was 2.2% for 8 runs.     

A reaction-rate method for the determination of thiocyanate,based on its inhibitory effect on the iodate-hypophosphite reaction

An automatic spectrophotometric reaction-rate method is described for the determination of thiocyanate in aqueous solutions, based on its inhibitory effect on the iodate-hypophosphite reaction. The time required for the reaction to proceed between two pre-determined levels is measured automatically and related directly to the thiocyanate concentration. The recommended reaction-rate method is fast, simple, sensitive, accurate (to 2%) and precise (1.7%, relative standard deviation). The useful analytical range of concentrations of thiocyanate is 4 × 10^?5 to 5 × 10^?4M. Maximum tolerable amounts of interfering ions are also presented.     

Individual and Simultaneous Stopped-Flow Fluorimetric Determination of Perphenazine and Chlorpromazine

Abstract

The stopped-flow technique is used to develop fluorimetric determinative methods for two phenothiazine drugs: perphenazine and chlorpromazine. The methods are based on the oxidation of these compounds to their corresponding fluorescent sulfoxides. Owing to the intrinsic characteristics of this technique, which allow rapid and thorough mixing of reactants, the oxidation is affected by dissolved oxygen itself, which therefore makes an oxidizing reagent unnecessary. Two methods are proposed for each phenothiazine, one based on initial rate and another on maximum fluorescence intensity measurements. Their linear ranges are 0.1–40 μg mL^?1 and their precision (%RSD) between 0.9 and 2.8%. These methods have been satisfactorily applied to the determination of both phenothiazines in several pharmaceutical preparations. On the basis of the additivity of the initial rate and maximum fluorescence intensity of perphenazine and chlorpromazine, the proportional equations principle is applied to the simultaneous determination of these compounds. Perphenazine/chlorpromazine mixtures in ratios between 1:8 and 8:1 are successfully resolved.     

Simultaneous voltammetric determination of carbendazim and carbaryl in medicinal plant infusions with a boron-doped diamond electrode

This study is aimed to develop an electroanalytical methodology using a boron-doped diamond electrode to determine simultaneously and selectively carbendazim (CBZ) and carbaryl (CAR). In previous studies using cyclic voltammetry oxidation, peaks were observed at 1.03 V (CBZ) and 1.44 V (CAR), with characteristics of an irreversible process controlled by diffusion of species, with a supporting electrolyte of BR buffer (0.1 mol L^?1) and pH adjusted to 6.0. The differences between the potentials for both pesticides, about 400 mV, indicate the possibility of selective determination of CBZ and CAR. The square-wave voltammetric parameters were optimised. The best separation conditions were pH 6.0, square-wave frequency of 100 s^?1, pulse amplitude of 50 mV and scan increment of 2.0 mV. These parameters were used to obtain the calibration curves of CBZ and CAR. An analytical curve was constructed in the range concentration of CBZ of 1.3 mg L^?1 to 15.3 mg L^?1 and CAR of 1.0 mg L^?1 to 11.4 mg L^?1, respectively. The limits of detection (LOD) and limits of quantification (LOQ) for CBZ were 0.40 mg L^?1 and 1.30 mg L^?1, respectively. For CAR, the LOD and LOQ were 0.30 mg L^?1 and 1.00 mg L^?1, respectively. Sensitivity values were 0.78 and 2.60 µA/mg L^?1 for CBZ and CAR, respectively. The electroanalytical method was applied in Mikania glomerata infusions. The recovery values were 106.2% and 116.5% for CBZ and CAR, respectively. The results show that the developed method is suitable for application in medicinal plant samples.     

Determination of S-Adenosylmethionine and S-Adenosylhomocysteine from Human Blood Samples by HPLC-FL

Abstract

S-adenosylmethionine plays an important role in many biochemical reactions, including human health maintenance and disease prevention. This paper proposes a simplified, rapid, and easy high performance liquid chromatography (HPLC) with fluorimetric detection method of S-adenosylmethionine and its product, S-adenosylhomocysteine. Determination of S-adenosylmethionine and S-adenosylhomocysteine was by HPLC with fluorimetric detection by the formation of the fluorescent 1,N ⁶-ethanoderivatives of these compounds, which showed a linear concentration range of 310^?6–310^?8 molL^?1 for S-adenosylmethionine and 510^?7–510^?9for S-adenosylhomocysteine; the detection limits of the method ranged in the nanomolar domain. The method applied to real plasma samples lead to values of 60.1±19.6 for S-adenosylmethionine and 24±14.1 nmolL^?1 for S-adenosylhomocysteine.     

Theoretical study on the chemical fate of adducts formed through free radical addition reactions to carotenoids

It is well known that free radicals are responsible for oxidative stress and cause numerous health disorders. As a result, the study of molecules that can scavenge free radicals is significant. One of the most important classes of free radical scavengers are carotenoids (CAR). In this work, the effectiveness of the CAR in terms of the radical adduct formation (RAF) reaction is studied using density functional theory calculations (in polar and non-polar environments). The reactions between four CAR [β-carotene (BC), zeaxanthin (ZEA), canthaxanthin (CANTA) and astaxanthin (ASTA)] with eight different radicals (^?OH, ^?OOH, ^?CH₃, ^?O–CH₃, ^?OO–CH₃, ^?SH, ^?O–CH₂–CH=CH₂, and ^?OO–CH₂–CH=CH₂), as well as substantial further reactions involved in the radical chain propagation, are analyzed. According to our results, the RAF reactions are controlled to a larger extent by the nature of the free radical than by the particular CAR they are reacting with. Thermochemistry calculations predict that each CAR molecule is able to scavenge at least two free radicals, which would lead to the termination of the radical chain process. Epoxy and diepoxy CAR species can be formed, being epoxy molecules as good free radical scavengers as their parent CAR. ASTA and CANTA are predicted to be less reactive, when reacting through RAF mechanism, than BC and ZEA.     

Study on a Fluorometric Method for the Determination of Protein in Serum Using Quercetin‐Lanthanum (III)‐Sodium Dodecyl Benzene Sulfonate‐Protein System

Abstract

It was found that the fluorescence intensity of lanthanum (III) (La³⁺)‐quercetin (Qu) complex is greatly enhanced by proteins in the presence of sodium dodecyl benzene sulfonate (SDBS). Based on this finding, a new fluorimetric method for the determination of proteins was developed. Under optimum conditions, the enhanced intensity of fluorescence is in proportion to the concentration of proteins in the range of 2.5×10^?8 to 1.0×10^?5 g/mL for bovine serum albumin (BSA), 5.0×10^?8 to 1.5×10^?5 g/mL for human serum albumin (HSA), and 1.0×10^?7 to 1.5×10^?5 g/mL for egg albumin (EA). Their detection limits (S/N=3) are 5.0×10^?9 g/mL, 7.0×10^?9 g/mL, and 2.1×10^?8 g/mL, respectively. The interaction mechanism was also studied.     

Simultaneous Potentiometric Determination of Thiamine and Pyridoxine in Multivitamins Using a Single Cyclodextrin-Based Thiamine-Selective Electrode

Abstract

In this work, a PVC tubular ion-selective electrode without internal reference [composed of 6.35% (w/w) of β-cyclodextrin as ionophore, 1.59% (w/w) of potassium tetrakis (p-chlorophenyl) borate as lipophilic additive, and 63.5% (w/w) of 2-fluorophenyl-2-nitrophenyl ether as mediator solvent] was used to accomplish the simultaneous determination of thiamine and pyridoxine in multivitamin products. The electrode responds selectively to thiamine but presents high initial diffusion potential contribution from pyridoxine. This fact was exploited under flow conditions for the quantitative assessment of both species. A multitask flow system was optimized to dilute appropriately real samples and prepare in-line the set of calibrating solutions. The potentiometric signal was modeled by partial least squares regression, enabling the prediction of the content of each vitamin in the range of 1 × 10^?3 to 1 × 10^?4 mol L^?1. Absolute errors of prediction inferior to 0.06 × 10^?4 mol L^?1 and 0.16 × 10^?4 mol L^?1 for pyridoxine and thiamine respectively were obtained when compared with the chromatographic method.     

Indication Ion Square Wave Voltammetric Determination of Thiamine and Ascorbic Acid

Abstract

Cd²⁺ ion was used as an electrochemical indicator to detect V_B1 or Vc using square ware voltammetry (SWV) at a mercury film‐coated glassy carbon (GC) electrode. At pH=10 NH₃‐NH₄Cl buffer, a new cathodic peak was found at ?0.360 V (vs.SCE) by addition of thiamine, and the peak current of SWV was linear with the concentration of thiamine in the range of 1×10^?6 to 4×10^?3 M. On the other hand, the SWV peak current of Cd²⁺ at ?0.856 V linearly decreased with addition of ascorbic acid in the range of 6×10^?6～10^?3 M. The effects of interference, such as citric acid, DL‐malic acid, and calcium panlothenate, on thiamine or ascorbic acid determination were investigated. This method was successfully applied to the determination of thiamine or in pharmaceutical preparation.     

Ocular Pharmacokinetic Study of l-Carnosine and N-Acetyl-l-carnosine in Rabbit by Microdialysis Coupled with UPLC-MS-MS

In order to provide useful information for rational drug design, the ocular pharmacokinetics of l-carnosine (CAR) and its acetylized prodrug N-acetyl-l-carnosine (NAC) were investigated. The in vivo microdialysis sampling coupled with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS-MS) was developed for continuously simultaneous monitoring of CAR and NAC in rabbit aqueous humor. The measured in vitro recoveries of the probe were 61.3% for CAR and 65.8% for NAC, while in vivo recoveries decreased to 43.1% for CAR and 43.0% for NAC, respectively. The method was sensitive with LLOQ 20.5 ng mL^?1 for CAR and 20.4 ng mL^?1 for NAC. The initial data indicated that the value of C _max and AUC_(0?C??) of NAC were higher than these of CAR (C _max 2305 vs. 1,802 ng mL^?1), (AUC_(0?C??) 1,337 vs. 1,891 ng h mL^?1), which indicated that the NAC exhibited better ocular bioavailability and duration. The method was rapid, specific and sensitive for continuously monitoring of aqueous humor and it was successfully applied to pharmacokinetic studies of CAR and NAC.     

Photochemical Fluorescence Enhancement of Terbuium-Fleroxacin System and Determination of Fleroxacin

ABSTRACT

The sensitized fluorescence of the terbium ion (Tb³⁺) can be observed when excited in the presence of fleroxacin (FLRX) in the aqueous solution because a Tb³⁺ -FLRX complex was formed. The sensitised fluorescence was greatly enhanced after the complex system was irradiated by 365nm ultraviolet light. The irradiation makes the complex system undergo photochemical reactions and a new terbium complex which is more favourable to the intramolecular energy transfer is formed. On this basis a new sensitive and selective photochemical fluorimetric method for the determination of FLRX was developed. Under the optimum experimental conditions, the linear range of the determination is 1.0—200×10^?7 mol 1^?1 for FLRX, and the detection limit is 1.2×10^?8mol 1^?1. Without any pre-treatment the recoveries of FLRX in human urine samples were determined with satisfaction.     

Kinetic determination of sulphonamides at the millimolar level by the continuous addition of reagent technique

A kinetic method for the determination of sulphonamides by the continuous addition of reagent (CAR) technique is reported. The method involves the formation of an azo dye between 1-naphthol and a diazonium salt, which is in turn obtained on reaction between the free primary aryl amine of the sulphonamide and sodium nitrite in a weak acid medium. The reaction is monitored via the initial rate of change of the absorbance of the azo dye formed at 470 nm, which is proportional to the sulphonamide concentration. Practical problems associated with this type of reaction for the determination of sulphonamides were readily avoided by using the CAR technique. Sulphonamides can be determined in the range 3 × 10^?6 ?3 × 10^?5 M with a relative standard deviation of about 1% and a sampling frequency of 25 h^?1 (triplicate runs). The proposed method is simple and rapid and insensitive to the presence of excipients; it proved useful for the determination of sulphonamides in pharmaceutical samples.     

Photometric and Fluorimetric Determination of Creatine Kinase Activity by Using Co-Immobilized Auxiliary Enzymes and an Open/Closed Flow Injection Manifold

Abstract

An open-closed configuration for the determination of creatine kinase activity based on fixed-time and reaction-rate measurements on a multipeak recording obtained by using a single conventional photometric or fluorimetric detector is proposed. The complexity of the biochemical reaction (three enzyme-catalysed steps) was partially overcome by using the two auxiliary enzymes that catalyse the two-step indicator reaction co-immobilized on controlled-pore glass. Both measurement methods provided excellent results (linear calibration ranges 0.01–0.80 U/L and 0.01–2.00 U/L, and r.s.d. smaller than 2%) and were checked by application to the determination of the analyte activity in serum samples. The results obtained agreed well with those provided by the standard method, and recoveries were between. 96 and 103% in all instances.     

A Sensitive Flow Injection Fluorimetry for the Determination of Carbamazepine in Human Plasma

Abstract

A simple, sensitive, and specific flow injection fluorimetric method has been developed for the determination of carbamazepine (CBZ). The proposed method is based on use of a solid‐phase reactor containing lead dioxide for on‐line oxidization of CBZ into a strongly fluorescent compound in a medium of phosphoric acid. The product has a green‐yellow fluorescence at a maximum excitation wavelength of 355 nm and an emission wavelength of 478 nm. Under the optimum conditions, the fluorescence intensity is proportional to the concentration of CBZ ranging from 0.0005 to 4.000 µg mL^?1. The detection limit is 5.7×10^?5 µg mL^?1 (2.4×10^?10 mol L^?1) and the relative standard deviation is 1.4% at the sampling rate of 45 h^?1. The proposed method has been applied to clinical estimation of CBZ in real patients' plasma samples with the results compared with those obtained by HPLC method.     

Using silica nanoparticles as a catalyst carrier to the highly sensitive determination of thiamine

The preparation and utilization of silica nanoparticles as a carrier of tetra-substituted carboxyl iron phthalocyanine (TCFePc, a novel mimetic peroxidase) is reported in this article. Compared with free TCFePc, the experimental results indicated that the TCFePc entrapped in silica nanoparticles exhibited an improved catalytic activity and good reusability. By using tetra-substituted carboxyl iron phthalocyanine-silica nanoparticles (TCFePc-SiO₂ Nps) to catalyze the oxidation reaction of thiamine by hydrogen peroxide, a new fluorimetric method was developed for the quantitative analysis of thiamine in pharmaceutical tablets. The influences of different conditions, such as the medium acidity, the reaction time and temperature, the concentrations of reagents and foreign substances, were all investigated. Under the optimum conditions, the calibration graph for thiamine was linear over the range of 5.0 × 10^− 9-1.0 × 10^− 6 mol L^− 1, with a detection limit of 2.0 × 10^− 9 mol L^− 1. The proposed method was successfully applied to the direct analysis of thiamine in two kinds of pharmaceutical tablets, and offered the advantages of simple pretreatment, rapid determination, high sensitivity and good reusability. Hence, as a carrier of the mimetic enzyme, the silica nanoparticles are effective for enzymatic reaction processes. This method is supposed to be hopeful for the determination of thiamine in other complex raw materials.     

Fluorimetric reaction-rate method for determination of mercury with 2,2′-dipyridylketone hydrazone

A simple and sensitive fluorimetric reaction-rate method for determination of mercury(II) (0.03-0.3 ppm), based on its catalytic effect on the autoxidation of 2,2′-dipyridylketone hydrazone, has been developed. The reaction is followed by the measurement of the rate of appearance of blue fluorescence (λ_ex = 359 nm, λ_em = 430 nm). The experimental variables and interferences in the determination are also reported.     

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.