Determination of psilocin and psilocybin using flow injection analysis with acidic potassium permanganate and tris(2,2'-bipyridyl)ruthenium(II) chemiluminescence detection respectively

A simple, rapid and sensitive method for the determination of psilocin and psilocybin is described. This is the first report on the determination of psilocin and psilocybin using flow injection analysis with acidic potassium permanganate and tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence. The limits of detection (signal-to-noise ratio = 3) are 9 × 10⁻¹⁰ M and 3 × 10⁻¹⁰ M for psilocin and psilocybin, respectively.A concise synthetic route for psilocin in three steps from readily available starting materials is also described. The structures were elucidated on the basis of spectroscopic data.     

Flow analysis-hydride generation-gas phase derivative molecular absorption spectrophotometric determination of antimony in oral homeopathic products ("AntimoniumTartaricum") formulated under alcoholic medium

In this work, a flow analysis-hydride generation-gas phase derivative molecular absorption-(UV) spectrophotometric method has been developed for the direct determination of antimony in aqueous and hydro-alcoholic samples. Antimony (III) from undiluted samples is directly transformed into the gaseous stibine (SbH₃) form by on-line reaction with sodium tetrahydroborate (NaBH₄) in acidic medium (HCl). The gaseous phase generated is separated from the liquid phase using a commercial gas-liquid separator, and swept - with the help of a carrier gas (N₂) stream - into a quartz gas cell (10 cm pathlength); where the corresponding absorption spectrum is acquired in a continuous mode over the 190-300 nm wavelength range, using a conventional spectrophotometer. A derivative strategy was selected in order to avoid the strong spectral interference of the ethanol vapor on the gaseous SbH₃ absorption spectrum. In this way, the peak height at 223 nm of the second order derivative spectrum appears as a clear, clean and interference free analytical signal, which allows the direct determination of antimony. The recovery values obtained from homeopathic formulations (prepared in alcoholic medium) spiked with know amounts of antimony ranged between 97.5 and 103%. The method provides a dynamic range from 0.20 to 30 mg Sb l⁻¹. The precision (RDS), evaluated by replicate analysis (n = 5) of samples and standard solution containing between 2.5 and 15 mg Sb l⁻¹ was in all cases lower than 1.2%. The proposed method was applied to the determination of antimony in commercial homeopathic products (“Antimonium Tartaricum”) prepared in hydro-alcoholic medium; and showed to be simple, precise, and accurate.     

Detection of Newcastle disease virus with quantum dots-resonance light scattering system

A sensitive QDs-based RLS assay method for the detection of Newcastle disease virus (NDV) antibody has been developed. CdTe quantum dots (QDs) were conjugated with Newcastle disease virus and used as RLS-based probes to detect NDV antibody. The electrostatic interaction between CdTe QDs and NDV resulted in enhanced resonance light scattering (RLS) signal characterized at 555 nm. Upon the addition of NDV antibody, QDs-NDV formed dispersive immunocomplex that can decrease the RLS signal. The decreased RLS intensity at 555 nm (ΔI_RLS) was linearly proportional to the concentration of NDV antibody (C_anti-NDV) in the range of 0.5-50 ng/mL, with correlation coefficient of 0.974 and detection limit of 0.1 ng/mL under the optimization conditions. The proposed method was applied to the determination of NDV antibody in spiked samples with satisfactory results.     

The use of anion-exchange disks in an optrode coupled to a multi-syringe flow-injection system for the determination and speciation analysis of iron in natural water samples

A combination of multi-syringe flow-injection analysis (MSFIA) technique with an optical fibre reflectance sensor for the determination of iron in water samples has been developed in this work. Anion-exchange solid phase extraction (SPE) disks have been used as solid phase. Ammonium thiocyanate has been chosen as chromogenic reagent for Fe(III). The complex Fe[SCN]₆³⁻ is retained onto the SPE disk and spectrophotometrically detected at 480 nm. The complex is eluted with 0.25 mol l⁻¹ hydrochloric acid in 75% ethanol. Total iron can be determined by oxidising Fe(II) to Fe(III) with hydrogen peroxide.A mass calibration was run within the range of 0.4-37.5 ng. The detection limit (3s_b/S) was 0.4 ng. The repeatability (RSD), calculated from 9 replicates using 0.5 ml injections of a 25 μg l⁻¹ concentration, was 3.6%. The repeatability between five anion-exchange disks was 5.4%. An injection throughput of 7 injections per hour for a sampling volume of 1 ml has been achieved.The applicability of the proposed methodology in natural water samples has been proved.The properties of anion-exchange and chelating SPE disks have been studied and compared.     

Determination of hydrogen peroxide by using a flow injection system with immobilized peroxidase and long pathlength capillary spectrophotometry

The development of a highly sensitive method for the determination of nanomolar concentrations of hydrogen peroxide in the liquid phase is described. This paper demonstrates for the first time a flow injection analysis (FIA) system with immobilized enzyme reactor combined with a total internal reflective cell (a liquid waveguide capillary cell (LWCC)) and spectrophotometric detection, for the development of an improved procedure for the determination of hydrogen peroxide. Moreover, the newly synthesized 4-aminopyrazolone derivative, 4-amino-5-(p-aminophenyl)-1-methyl-2-phenyl-pyrazol-3-one (DAP), is used as a color coupler in its oxidative condensation with the sodium salt of N-ethyl-N-sulphopropylaniline sodium salt (ALPS) which acts as a hydrogen donor. Immobilization of peroxidase is achieved by coupling the periodate-treated enzyme to aminopropyl controlled-pore glass (CPG) beads. The determination of hydrogen peroxide is carried out in a 0.1 M phosphate buffer and the product is monitored at 590 nm with a charge-coupled device (CCD) detector equipped with fiber optics in a fully computerized system. The interference of different species, mainly ionic, was investigated.The method permits detection down to 4 nmol l⁻¹ hydrogen peroxide (signal-to-noise ratio=3). A linear calibration graph was obtained over the range 20-700 nmol l⁻¹. The relative standard deviation (R.S.D.) at 300 nmol l⁻¹ H₂O₂ is 1.7% (n=7). The method was successfully applied for the determination of hydrogen peroxide in samples from a vat-cleaning process.     

Fluorescence and terbium-sensitised luminescence determination of garenoxacin in human urine and serum

Fluorescence and terbium-sensitised luminescence properties of new quinolone garenoxacin have been studied. The fluorimetric method allows the determination of 0.060-0.600 μg ml⁻¹ of garenoxacin in aqueous solution containing HCl/KCl buffer (pH 1.5) with λ_exc=282 nm and λ_em=421 nm. Micellar-enhanced fluorescence was also studied, leading to a higher than 400% increase in analytical signal in presence of 12 mM sodium dodecyl sulphate (SDS), allowing the determination of 0.020-0.750 μg ml⁻¹ of garenoxacin. The terbium-sensitised luminescence method allows the determination of 0.100-1.500 μg ml⁻¹ of garenoxacin in 12 mM SDS solution containing 0.08 M acetic acid/sodium acetate buffer (pH 4.1) and 7.5 mM Na₂SO₃ (chemical deoxygenation agent), with λ_exc=281 nm and λ_em=546 nm. Relative standard deviation (R.S.D.) values for the three methods were in the range 1.0-2.0%. The proposed procedures have been applied to the determination of garenoxacin in spiked human urine and serum.     

Determination of lamivudine and zidovudine in binary mixtures using first derivative spectrophotometric, first derivative of the ratio-spectra and high-performance liquid chromatography-UV methods

Three methods are presented for the simultaneous determination of lamivudine and zidovudine. The first method depends on first derivative UV spectrophotometry, with zero-crossing and peak-to-base measurement. The first derivative amplitudes at 265.6 and 271.6 nm were selected for the assay of lamivudine and zidovudine, respectively. The second method depends on first derivative of the ratio-spectra by measurements of the amplitudes at 239.5 and 245.3 nm for lamivudine and 225.1 and 251.5 nm for zidovudine. Calibration graphs were established for 1-50 μg/ml for lamivudine and 2-100 μg/ml for zidovudine. In the third method (HPLC), a reversed-phase column with a mobile phase of methanol:water:acetonitrile (70:20:10 (v/v/v)) at 0.9 ml/min flow rate was used to separate both compounds with a detection of 265.0 nm. Linearity was obtained in the concentration range of 0.025-50 μg/ml for lamivudine and 0.15-50 μg/ml for zidovudine. All of the proposed methods have been extensively validated. These methods allow a number of cost and time saving benefits. The described methods can be readily utilized for analysis of pharmaceutical formulations. There was no significant difference between the performance of all of the proposed methods regarding the mean values and standard deviations. The described HPLC method showed to be appropriate for simultaneous determination of lamivudine and zidovudine in human serum samples.     

Determination of nickel in natural waters by FAAS after sorption on octadecyl silica membrane disks modified with a recently synthesized Schiff's base

A simple, highly sensitive, accurate and selective method for the determination of trace amounts of Ni²⁺ ions in water samples is proposed. The method is based on the separation and preconcentration of Ni²⁺ on an octadecyl-bonded silica (ODBS) membrane disk modified by a recently synthesized Schiff’s base N,N′-bis (3-methylsalicylidene) ortho phenylene diamine (MSOPD) at pH 7. The synthesis of this extractant ligand is also described. The retained nickel on the membrane was eluted with 2×5 ml 0.5 M HNO₃ and measured by flame atomic absorption spectrometry (FAAS) at 232.0 nm. The extraction efficiency and the influence of the type and least amount of eluent for the stripping of Ni²⁺ from the disks, pH, flow rates of sample solution and eluent, amount of MSOPD, effect of other ions, and breakthrough volume were evaluated. The maximum capacity of the membrane disks modified by 3 mg of MSOPD was found to be 146±4 μg Ni²⁺. The 3σ limit of detection of the method was 30 ng per 1000 ml and also an enrichment factor of 250 was obtained. The proposed method has been applied to the determination of nickel in several water samples with satisfactory results.     

Determination of cadmium by an improved double chamber electrothermal vaporization inductively coupled plasma atomic emission spectrometry

An improved double chamber electrothermal vaporization (ETV) system was designed. A new inner chamber and its bottom plate made of quartz glass were attached with carrier support gas inlet port for the determination of cadmium by inductively coupled plasma atomic emission spectrometry (ICP-AES). The use of the inner chamber in combination with the plate played important roles to transport the metal vapor efficiently into argon ICP. Ten-μl sample aliquots were dried at 100 °C and subsequently heated at 1000 °C on the tungsten boat furnace. The evolved vapor was swept into the ICP source through PTFE tubing and the inner chamber by a 0.8 l/min H₂ (7%)-Ar carrier gas. The performance parameters of ETV-ICP-AES such as temperature program and gas flow rate were evaluated using cadmium standard solution. Under the optimized experimental conditions, the best attainable detection limit at Cd II 214.438 nm line was 0.2 ng/ml with linear dynamic ranges of 50 to 10,000 ng/ml for cadmium. The instrumental precision expressed as the relative standard deviation (RSD) from ten replicate measurements of 10,000 ng/ml for cadmium by ETV-ICP-AES was 0.85%. The present method has been successfully applied to the determination of cadmium in zinc-base materials.     

Simultaneous determination of two anti-inflammatory drugs in serum using isopotential fluorimetry

The simultaneous determination of 6-methoxy-2-naphthylacetic acid (6MNA) and diflunisal in serum samples using the combination of matrix isopotential synchronous fluorescence (MISF) and first derivative technique is proposed. 6MNA and diflunisal exhibit overlapped spectra and serum produces background fluorescence that precludes the direct determination of these anti-inflammatory drugs by conventional fluorimetry. This method provides good analytical results for determination of compounds in samples with unknown background fluorescence. The method was applied for the simultaneous determination of 6MNA and diflunisal in serum samples at concentrations between 20-200 and 100-1000 ng mL⁻¹, respectively, by means of absolute values of first derivative of synchronous scan at 247.9/364.0 and 262.6/392.4 nm for 6MNA and diflunisal, respectively. In order to obtain maximum sensitivity and adequate selectivity, factors affecting fluorescence intensity were studied. As a result, the analyses were performed in water at a pH of 7.2, adjusted by using sodium dihydrogen phosphate/hydrogen phosphate (0.1 M) as a buffer solution. Serum samples were diluted 200 times. Analytical parameters of the proposed method were calculated according to the error propagation theory. The limit of detection calculated according to Clayton was 15.8 and 63.0 ng mL⁻¹ for 6MNA and diflunisal, respectively. The sensitivity, repeatability and reproducibility achieved with the proposed method were adequate for the determination of these anti-inflammatory agents in serum samples.     

Determination of pKa values of some antihypertensive drugs by liquid chromatography and simultaneous assay of lercanidipine and enalapril in their binary mixtures

In this study, pK_a values were determined using the dependence of the retention factor on the pH of the mobile phase for three ionizable substances, namely, enalapril, lercanidipine and ramipril (IS). The effect of the mobile phase composition on the ionization constant was studied by measuring the pK_a at different methanol-water mixtures, ranging between 50 and 65% (v/v), using LC-DAD method. Two simple, accurate, precise and fully validated analytical methods for the simultaneous determination of enalapril and lercanidipine in combined dosage forms have been developed. Separation was performed on an X-Terra RP-18 column (250 mm × 4.60 mm ID × 5 μm) at 40 °C with the mobile phase of methanol-water 55:45 (v/v) adjusted to pH 2.7 with 15 mM orthophosphoric acid. Isocratic elution was performed in less than 12 min with a flow rate of 1.2 mL min⁻¹. Good sensitivity for the analytes was observed with DAD detection. The LC method allowed quantitation over the 0.50-20.00 μg mL⁻¹ range for enalapril and lercanidipine. The second method depends on first derivative of the ratio-spectra by measurements of the amplitudes at 219.7 nm for enalapril and 233.0 nm for lercanidipine. Calibration graphs were established for 1-20 μg mL⁻¹ for enalapril and 1-16 μg mL⁻¹ lercanidipine, using first derivative of the ratio spectrophotometric method. Both methods have been extensively validated. These methods allow a number of cost and time saving benefits. The described methods can be readily utilized for analysis of pharmaceutical formulations. The methods have been applied, without any interference from excipients, for the simultaneous determination of these compounds in tablets. There was no significant difference between the performance of the proposed methods regarding the mean values and standard deviations.     

Gas-diffusion flow injection assay for the selective determination of chlorine dioxide based on the fluorescence quenching of chromotropic acid

The present work reports the first spectrofluorimetric gas-diffusion flow injection (GD-FI) assay for the determination of chlorine dioxide in water samples (tap, mineral and soda water). The method is based on the fluorescence quenching of chromotropic acid (CA) (λ_ex. = 347 nm, λ_em. = 371 nm) caused by the analyte. The chemical and instrumental variables of the system were studied in terms of maximum sensitivity. The gas-diffusion cell was thermostated at 40 °C to enhance the vaporization of chlorine dioxide and thus the sensitivity of the method. The quenching effect of chlorine dioxide on CA was linear in the range 0.09-3.41 mg l^− 1, while the precisions either close to the quantitation limit or near to the middle of the linear section of the calibration graph were satisfactory in both cases (s_r = 2.6% and 1.5% (n = 10) at 0.17 and 1.71 mg l^− 1 level, respectively). The developed method proved to be adequately selective and sensitive with 3σ limit of detection equal to c_L = 0.03 mg l^− 1. The application of the assay to spiked tap, mineral and soda water samples yielded accurate results with recovery values in the range 94.1-105.9%.     

Residue determination of glyphosate in environmental water samples with high-performance liquid chromatography and UV detection after derivatization with 4-chloro-3,5-dinitrobenzotrifluoride

A pre-column derivatization high-performance liquid chromatographic method for glyphosate analysis has been developed. Derivatization of glyphosate was performed with 4-chloro-3,5-dinitrobenzotrifluoride (CNBF). In pH 9.5 H₃BO₃-Na₂B₄O₇ media, the reaction of glyphosate with CNBF completed at 60 °C for 30 min. The labeled glyphosate was separated on a Kromasil C18 column (250 mm × 4.6 mm, 5 μm) at room temperature and UV detection was applied at 360 nm. The separation of labeled glyphosate was achieved within 15 min by gradient elution mode. Compared to other pre-column derivatization, this derivatization was performed more mildly, the derivative was more stable, and the detection limits of a few reagents were higher than CNBF, except 9-fluorenylmethyl chloroformate (FMOC-Cl) using fluorescence and mass spectrometry, however, this reagent avoid to be removed after derivatization like FMOC-Cl. The detection limit of glyphosate was 0.009 mg L⁻¹ (S/N = 3) without preconcentration and reach MRL, which is set at the level of 0.1 mg L⁻¹ in China. The method linearity correlation coefficient was 0.9999, in concentrations ranging from 0.3 to 48.5 mg L⁻¹. The proposed method has been applied to the quantitative determination of glyphosate in environmental water with recoveries of 91.80-100.20% and R.S.D. of 2.27-6.80, depending on the sample investigated.     

Sensitive determination of phenothiazines in pharmaceutical preparation and biological fluid by flow injection chemiluminescence method using luminol-KMnO4 system

A flow injection chemiluminescence method was described for the determination of four phenothiazine drugs, namely, chlorpromazine hydrochloride, perphenazine hydrochloride, fluphenazine hydrochloride and thioridazine hydrochloride. Strong Chemiluminescence (CL) signal was produced when above-mentioned drug was injected into the mixed stream of luminol with KMnO₄. The linear ranges of the method were 0.0020-1.0 μg/mL chlorpromazine hydrochloride, 0.0040-3.0 μg/mL perphenazine hydrochloride, 0.0020-5.0 μg/mL fluphenazine hydrochloride and 0.0050-1.0 μg/mL thioridazine hydrochloride. The detection limits were 0.4 ng/mL chlorpromazine hydrochloride, 0.7 ng/mL perphenazine hydrochloride, 2 ng/mL fluphenazine hydrochloride and 0.7 ng/mL thioridazine hydrochloride. The proposed method was applied to the determination of chlorpromazine hydrochloride in injections and in mental patient's urine samples and the satisfactory results were achieved. The possible CL reaction mechanism was also discussed briefly.     

Highly sensitive spectrofluorimetric kinetic determination of ultratrace amounts of vanadium(V) based on the oxidation of 1,8-diaminonaphthalene by bromate

A highly sensitive catalytic quenching spectrofluorimetric method was described for the determination of V(V) based on its catalytic effect on the oxidation of 1,8-diaminonaphthalene by potassium bromate with Tiron as an activator in weakly acidic medium and the reaction mechanism was investigated. The reaction was followed spectrofluorimetrically by measuring the fluorescence intensity of 1,8-diaminonathphlene (DAN) (λ_ex=356 nm, λ_em=439 nm) at a fixed time of 5 min from initiation of the reaction. Under the optimum conditions, vanadium(V) can be determined in the range 0.05-50.0 ng ml⁻¹ with a S.D.=0.024 for 15 times measurements. The detection limit of the method was down to 0.0088 ng ml⁻¹ and the catalytic reaction activation energy was found to be 43.92 kJ mol⁻¹. The proposed method was tested for the determination of vanadium(V) in rice and natural water samples.     

Determination of lead in hair and its segmental analysis by solid sampling electrothermal atomic absorption spectrometry

A rapid and practical solid sampling electrothermal atomic absorption spectrometric method was described for the determination of lead in scalp hair. Hair samples were washed once with acetone; thrice with distilled-deionized water and again once with acetone and dried at 75 °C. Typically 0.05 to 1.0 mg of dried samples were inserted on the platforms of solid sampling autosampler. The effects of pyrolysis temperature, atomization temperature, the amount of sample as well as addition of a modifier (Pd/Mg) and/or auxiliary digesting agents (hydrogen peroxide and nitric acid) and/or a surfactant (Triton X-100) on the recovery of lead were investigated. Hair samples were washed once with acetone; thrice with distilled-deionized water and again once with acetone and dried at 75 °C. Typically 0.05 to 1.0 mg of dried samples were inserted on the platforms of solid sampling autosampler. The limit of detection for lead (3σ, N = 10) was 0.3 ng/g The addition of modifier, acids, oxidant and surfactant hardly improved the results. Due to the risk of contamination and relatively high blank values, the lead in hair were determined directly without adding any reagent(s). Finally, the method was applied for the segmental determination of lead concentrations in hair of different persons which is important to know when and how much a person was exposed to the analyte. For this purpose, 0.5 cm of pieces were cut along the one or a few close strands and analyzed by solid sampling.     

Spectrofluorimetric determination of human serum albumin using a doxycycline-europium probe

A new spectrofluorimetric method is proposed for determination of human serum albumin (HSA) with the limit of detection at ng levels. Using doxycycline (DC)-europium (Eu³⁺) as a fluorescent probe, in a buffer solution of pH 10.2, HSA can remarkably enhance the fluorescence intensity of the DC-Eu³⁺ complex at 612 nm and the enhanced fluorescence intensity of Eu³⁺ is proportional to the concentration of HSA. Optimum conditions for the determination of HSA are also investigated. The linear ranges for HSA are 0-9.2 and 9.2-34.5 μg ml⁻¹ with limits of detection of 64 and 115 ng ml⁻¹, respectively. This method is simple, practical and relatively free of interference from coexisting substances, as well as much more sensitive than most of the existing assays. The determination results for human serum and urine samples are identical to those by the AOAO method, with relative standard deviations of five determinations of 1.1-3.6%. By the Rosenthal graphic method, the binding number and association constant of human serum albumin with the probe are 1.8 and 3.71×10⁵ l mol⁻¹, respectively.     

Sequential injection fluorimetric determination of Sn in juices of canned fruits

The present work describes the development of a fast and robust sequential injection fluorimetric procedure for the determination of Sn in juices of canned fruits. The developed automatic methodology is based on the complexation of Sn with 8-hydroxyquinoline-5-sulfonic acid (HQSA) to form a fluorimetric product (λ_exc = 354 nm; λ_em = 510 nm). The influence of dimethylsulfoxide (DMSO) and cetylpyridinium bromide (CPB) on the sensitivity of the fluorimetric determination was evaluated.Linear calibration plots were obtained for Sn concentrations between 1 and 10 mg L⁻¹, with a detection limit of 0.38 mg L⁻¹. In each analytical cycle 0.006 mg of HQSA and 0.47 mg of CPB were consumed and 1.5 mL of effluent was generated.The developed methodology was applied to the determination of Sn in juices of canned fruits and the results complied with those furnished by an electrothermal atomic absorption spectrometry comparison procedure, with relative deviations lower than 5.2%.The automatic procedure exhibited good precision (R.S.D. < 1.4%) and the sampling rate was about 70 determinations per hour.     

Total internal reflected resonance light scattering determination of protein in human blood serum at water/tetrachloromethane interface with Arsenazo-TB and Cetyltrimethylammonium bromide

A direct quantification of protein in human blood serum samples is proposed based on the measurement of total internal reflected resonance light scattering (TIR-RLS) at water/tetrachloromethane (H₂O/CCl₄) interfaces. At pH 4.10 and in the presence of Cetyltrimethylammonium bromide (CTAB), the interaction of Arsenazo-TB (ATB) with human serum albumin (HSA) results in strong enhanced TIR-RLS signals with the maximum spectra peak located at 330 nm. The enhanced TIR-RLS intensity at 330 nm was found to be proportional to the concentration of HSA in the range 0.5-42.3 μg/ml and its limit of determination (3σ) is 198 ng/ml. The content of HSA in blood serum samples were determined with the recovery of 97-103% for standard addition experiment.     

Solid phase extraction-spectrophotometric determination of fluoride in water samples using magnetic iron oxide nanoparticles

A new, sensitive, fast and simple method using magnetic iron oxide nanoparticles (MIONs), as an adsorbent has been developed for extraction, preconcentration and determination of traces of fluoride ions. The determination method is based on the discoloration of Fe(III)-SCN complex with extracted fluoride ions which was subsequently monitored spectrophotometrically at λ_max = 458 nm. Various parameters affecting the adsorption of fluoride by the MIONs have been investigated, such as pH of the solution, type, volume and concentration of desorbing reagent, amount of adsorbent and interference effects. A linear response for the determination of fluoride was achieved in the concentration range of 0.040-1.250 μg mL⁻¹. The limit of detection (LOD) and limit of quantification (LOQ) for fluoride based on 3 times and 10 times the standard deviation of the blank (3S_b, 10S_b) were 0.015 and 0.042 μg mL⁻¹ (n = 20) for fluoride ion, respectively. A preconcentration factor of 50 was achieved in this method. The proposed procedure has been applied for determination of fluoride concentration in various water samples. The results obtained from this method were successfully compared with those provided by standard SPADNS method.