Multiresidue determination of organophosphorus pesticides in ginkgo leaves by accelerated solvent extraction and gas chromatography with flame photometric detection

A rapid and simple method using accelerated solvent extraction and solid-phase extraction cleanup was developed and validated for the determination of 15 organophosphorus pesticides in ginkgo leaves by capillary gas chromatography with flame photometric detection. The pesticides were extracted at 100 degrees C under 1500 psi pressure in <20 min. The average recovery from 10 g ginkgo leaves, fortified at 3 levels ranging from 0.05 to 1.00 mg/kg, was 95.2% with a relative standard deviation of 4.6%. The limits of detection ranged from 1.11 x 10(-3) mg/kg (dimethoate) to 4.44 x 10(-3) mg/kg (dichlorvos). The proposed method showed acceptable accuracy and precision while minimizing environmental concerns, time, and labor. Furthermore, the method could be easily applied to the monitoring of these 15 organophosphorus pesticides in ginkgo leaves.     

Microwave assisted micellar extraction coupled with solid phase microextraction for the determination of organochlorine pesticides in soil samples

Microwave assisted micellar extraction (MAME) coupled with solid phase microextraction (SPME) and HPLC-UV determination have been used for the determination of five organochlorine pesticides from agricultural soil samples. A non-ionic surfactant, Polyoxyethlylene 10 Lauryl Ether was used, and the different variables for the optimization of MAME and SPME procedures were studied. This method was applied successfully to the determination of these pesticides in several kinds of agricultural soil samples with different characteristics. Most of the compounds studied can be recovered in good yields with R.S.D. lower than 9% and detection limit ranged between 56-96 ng g⁻¹ for the pesticides studied.     

Adsorptive stripping voltammetry determination of molybdenum(VI) in water and soil

A differential pulse stripping voltammetry method for the trace determination of molybdenum(VI) in water and soil has been developed. In 0.048M oxalic acid and 6 x 10(-5)M Toluidine Blue (pH 1.8) solution, Mo(V), the reduction product of Mo(VI) in the sample solution, can form a ternary complex, which can be concentrated by adsorption on a static mercury drop electrode at -0.1 V (vs. Ag/AgCl). The adsorbed complex gives a well-defined cathodic stripping current peak at -0.30 V, which can be used for determining Mo(VI) in the range 5 x 10(-10)-7 x 10(-9)M, with a detection limit of 1 x 10(-10)M (4 min accumulation). The method is also selective. Most of the common ions do not interfere but Sn(IV) and large amounts of Cu(2+), Ag(+) and Au(3+) affect the determination.     

Fluorimetric study of the interaction between human serum albumin and quinolones-terbium complex and its application

A highly sensitive spectrofluorimetric method is proposed for determination of human serum albumin (HSA) and some quinolone drugs. Using quinolones-terbium (Tb3+) complex as a fluorescent probe, in the buffer solution of pH 7.8, HSA can remarkably enhance the fluorescence intensity of the quinolones-Tb3+ complex at 545 nm and the enhanced fluorescence intensity of Tb3+ ion is in proportion to the concentration of HSA and quinolone drugs. Optimum conditions for the determination of HSA were also investigated. The linear ranges and limits of detection are 8.0 x 10(-9) to 8.0 x 10(-8) mol L(-1), 4.20 x 10(-9) mol L(-1) (for HSA); 1.0 x 10(-6) to 4.0 x 10(-6) mol L(-1), 1.87 x 10(-8) mol L(-1) (for norfloxacin) and 1.0 x 10(-7) to 1.0 x 10(-6) mol L(-1), 4.82 x 10(-8) mol L(-1) (for enoxacine), respectively. This method is simple, practical and relatively free interference from coexisting substances, as well as much more sensitive than most of the existing assays.     

A novel long path length absorbance spectroscopy for the determination of ultra trace organophosphorus pesticides in vegetables and fruits

A simple, rapid, sensitive and reproducible spectrophotometry for determination of ultra trace organophosphorus pesticides (OPs) with liquid core waveguide light intensity technique is presented. OPs were degraded into phosphate with UV light, potassium peroxydisulphate as oxidant and nanosized titanium dioxide as catalyst. Under the optimum selected conditions, linear light intensity response was obtained in the range of 2.0 x 10(-11) to 8.0 x 10(-10)g mL(-1) phosphate, and the limit of detection (LOD) 6.7 x 10(-12)g mL(-1) was achieved. Both the low limit of linear range and the LOD of the proposed method were lower over 1000-fold than that of classical spectrophotometry. The proposed method was applied to the determination of ultra trace OPs in vegetables and fruits samples.     

Polarographic determination of osmium with the osmium(VIII)-cerium(IV)-arsenic(III) system

A highly sensitive and novel polarographic method has been developed for determination of ultratrace amounts of osmium, based on the catalysis of the cerium(IV)-arsenic(III) reaction by osmium(VIII). The reaction rate is monitored by measuring the arsenic(III) with a single-sweep oscillopolarograph. Osmium concentrations from 7.0 x 10(-11) to 5.0 x 10(-9)M can be determined by the initial rate method. The method has been applied to determination of osmium in refined ore and chlorination residues with satisfactory results.     

Electrochemical determination of hydrogen peroxide using o -dianisidine as substrate and hemoglobin as catalyst

A new electrochemical method for the determination of microamounts of hydrogen peroxide utilizing o-dianisidine (ODA) as substrate and hemoglobin (Hb) as catalyst is described in this paper. Hb can be used as mimetic peroxidase and it can catalyse the reduction of hydrogen peroxide with the subsequent oxidation of ODA. The oxidative reaction product is an azo compound, which is an electroactive substance and has a sensitive second-order derivative polarographic reductive peak at the potential of -0.58 V (vs. SCE) in pH 80 Britton-Robinson (B-R) buffer solution. The conditions of Hb-catalytic reaction and polarographic detection of the reaction product were carefully studied. By using this polarographic peak and under optimal conditions, the calibration curve for the H₂O₂ was constructed in the linear range of 2.0 x 10^-7 ∼ 10 x 10^-4 mol/l with the detection limit of 5.0 x 10^-8 mol/l. This method can also be used to the determination of Hb content in the range of 20 x 10^-9 ∼ 30 x 10^-7 mol/l with a detection limit of 10 x 10^-9 mol/l. The proposed method was further applied to the determination of the content of H₂O₂ in fresh rainwater with satisfactory results. The catalytic reaction mechanism and the electrode reductive process of the reaction product were carefully studied.     

Adsorptive stripping voltammetry for the determination of nifedipine in human serum

Adsorptive stripping voltammetry is used for the determination of trace levels of nifedipine. The conditions for preconcentration on the mercury drop electrode have been studied and the final measurements are made by differential pulse voltammetry. The response is linear from 2 x 10(-9) to 1 x 10(-7)M and can be extended to 10(-6)M by a change in conditions. The stripping peak has been used for determination of the drug in formulations, with a relative standard deviation of 0.8%. The method is applicable to the determination of nifedipine in blood-serum with a detection limit of 4.1 ng/ml.     

A continuous flow system design for simultaneous determination of heavy metals in river water samples

A new design of a continuous flow system applied to the simultaneous determination of the concentration of zinc(II), cadmium(II), lead(II), copper(II), nickel(II), cobalt(II) and chromium(VI) in river water is described. A flow cell made in the laboratory, which has been patented, based on a 'wall-jet' configuration with a three-electrode system is described. Optimum conditions for the determination of the metal ions are reported. The detection limits and relative standard deviation values were 4.01x10(-9) M and 0.078 for Zn(II), 1.76x10(-10) M and 0.056 for Cd(II), 4.69x10(-10) M and 0.134 for Pb(II), 2.29x10(-10) M and 0.138 for Cu(II), 1.61x10(-9) M and 0.093 for Ni(II), 1.91x10(-9) M and 0.113 for Co(II), and 1.35x10(-9) M and 0.081 for Cr(VI). The procedure was applied to a sample of water from the Arlanzón river and the results were compared with inductively coupled mass plasma spectrometry (ICP-MS) as reference method. The final aim of this work is to design a flow system, which can be automated.     

Determination of trace amounts of estriol and estradiol by adsorptive cathodic stripping voltammetry.

Estriol and estradiol are electroinactive in the potential range from -200 to -1000 mV versus a silver-silver chloride electrode at a mercury electrode. The conversion of these estrogens into electroactive nitro derivatives of estrogens, which are used for voltammetric determination, was studied. Such nitro derivatives give a well defined cathodic stripping wave at -600 mV in pH 10.5 borate buffer. Estriol and estradiol are determined in the ranges 1 x 10(-9)-1.5 x 10(-6) and 5 x 10(-9)-2 x 10(-6) mol dm-3, respectively, by differential-pulse adsorptive stripping voltammetry at a hanging mercury drop electrode. Some steroids, such as estrone, interfere because the three estrogens have almost the same molecular structure and have similar nitro derivatives, but progesterone does not interfere and is reduced at significantly more negative potentials than the nitrated estrogens. It can be determined simultaneously with estriol or estradiol. A method was developed for the assay of estriol in pharmaceutical preparations.     

Determination of lanthanum in food and water samples by Zeeman-effect atomic absorption spectrometry using graphite tube lined with tungsten foil.

A sensitive, selective method for the determination of lanthanum in food and water samples by atomic absorption spectrometry using a graphite tube lined with tungsten foil is described. The atomization of lanthanum from the tungsten surface gives better analytical sensitivity, a lower atomization temperature and negligible memory effects. The characteristic mass and detection limit of the method were 8.1 x 10(-9) and 7.85 x 10(-9) g, respectively. The precision (relative standard deviation in the range 5.9-9.9%), accuracy and interferences of the method were also investigated. The method can be used directly for the determination of trace amounts of lanthanum in food and water without pre-dissociation of the matrices. The results obtained by this method are in good agreement with those obtained from inductively coupled plasma atomic emission spectrometry.     

Simultaneous determination of dissolved anthracene and pyrene in aqueous solution by synchronous fluorimetry

A synchronous fluorimetry for simultaneous determination of dissolved anthracene and pyrene in aqueous solution has been established. The linear ranges for determination of dissolved anthracene and pyrene were 1.00x10(-8) to 4.50x10(-7)molL(-1) and 5.00x10(-9) to 6.50x10(-7)molL(-1), and the limits of detection (LOD) for anthracene and pyrene were 2.23x10(-9) and 8.24x10(-10)molL(-1) with relative standard deviations (R.S.D.) of 2.90 and 2.34% (n=5), respectively. Satisfactory results were obtained when the established method was used to simultaneously determine anthracene and pyrene in spiked water samples.     

Cathodic stripping voltammetry of the anticancer agent 5-fluorouracil and determination in urine

Cathodic stripping voltammetry was used to determine 5-fluorouracil (5-FU) in the presence of traces of Cu(II). It was found that the addition of 5 x 10(-9) mol dm(-3) Cu(II) to the measurement cell greatly enhanced the peak current of the adsorbed molecule. Different parameters were tested to optimize the conditions for the determination of 5-FU. The adsorbed form is reduced irreversibly. It was observed that by controlling the deposition potential, the technique could be directed to the determination of Cu(II) or the drug. The linear range was from 5 x 10(-9) to 6 x 10(-8) mol dm(-3) for 5-FU and from 6 x 10(-9) to 5 x 10(-8) mol dm(-3) for Cu(II). Detection limits of 4.6 x 10(-10) and 5 x 10(-10) mol dm(-3) were obtained for 5-FU and Cu(II), respectively. The method was applied to urine and molecules or ions which may interfere were studied.     

Design of a new dodecyl sulfate-selective electrode based on conductive polyaniline.

A new, simple, sensitive, low cost and rapid potentiometric method for direct determination of ultra trace amounts of sodium dodecyl sulfate (SDS) with a new DS(-)-selective electrode is reported. The electrode was prepared by electropolymerization of aniline in acidified DS- ion on the surface of a Pt electrode. The cyclic voltammetry (CV) was used for electropolymerization of polyaniline (PA) in the potential range of -200 to +1000 mV vs. Ag/AgCl. This sensor showed a Nernstian behavior (59.0 +/- 2.3 mV/decade) over a very wide linear range (1.0 x 10(-9)-3.0 x 10(-6) M) with a detection limit of 1.0 x 10(-9) M. The response time of the electrode was 15 s for 1.0 x 10(-7) M of analyte; the electrode can be used for 4 weeks without any major deviation. This electrode can be used in the pH range of 3.5-9.8. The selectivity of electrode to DS- over some organic, inorganic and anionic surfactants was investigated with the fixed primary ion method. The results show that the electrode is highly selective to DS- ion over other ions. The proposed electrode was applied to the determination of DS- in real samples.     

Flow injection with inhibited chemiluminescence method for the determination of dopamine hydrochloride.

A simple rapid and accurate flow injection inhibitory chemiluminescence method has been developed for the determination of dopamine hydrochloride based on its inhibition of the chemiluminescence from the luminol-potassium hexacyanoferrate(III) system. The linear range of determination is 4.0 x 10(-9) - 4.0 x 10(-7) g ml(-1) for dopamine hydrochloride and the detection limit is 1.14 x 10(-9) g ml(-1). The method has been applied to determine the content of dopamine in pharmaceutical preparation with satisfactory results.     

Sensitive flow-injection amperometric detection of iodide using Mn3+ and As3+.

A rapid, selective, and sensitive kinetic flow-injection method for iodide content determination with amperometric detection on a platinum electrode was developed. The method is based on the catalytic effect of iodide on the Mn3+ reaction with As3+ in the presence of sulfuric acid. The calibration curve was linear in the concentration range from 5.0 x 10(-7) to 1.0 x 10(-4) mol/L iodide. The limit of detection (LOD) was found to be 5.0 x 10(-9) mol/L iodide. The relative standard deviations (RSD) were 1.68% and 3.03% for 1.0 x 10(-3) mol/L standard and 1.0 x 10(-6) mol/L iodide solution (n = 6), respectively. The method has been successfully applied for determination of iodide in waters, table salts, fodder, organic substances and human blood sera. The results were compared with those obtained by a standard AOAC (Association of Official Analytical Chemists) method, as well as with those obtained by a kinetic spectrophotometric procedure for determination of iodide.     

Determination of attapulgite and nifuroxazide in pharmaceutical formulations by sequential digital derivative spectrophotometry

A new method for the sequential determination of attapulgite and nifuroxazide in pharmaceutical formulations by first- and second-derivative spectrophotometry, respectively, has been developed. In order to obtain the optimal conditions for nifuroxazide stability, studies of solvent, light, and temperature effects were performed. The results show that a previous hydrolysis of 2 h in 1.0 x 10(-1)M NaOH solution is necessary in order to obtain stable compounds for analytical purposes. Subsequently, the first- and second-derivative spectra were evaluated directly in the same samples. The sequential determination of the drugs can be performed using the zero-crossing method; the attapulgite determination was carried out using the first derivative at 278.0 nm and the nifuroxazide determination, using the second derivative at 282.0 nm. The determination ranges were 5.7 x 10(-6)-1.0 x 10(-4) and 3.7 x 10(-8) -1.2 x 10(-4)M for attapulgite and nifuroxazide, respectively. Repeatability (relative standard deviation) values of 1.2 and 3.0% were observed for attapulgite and nifuroxazide, respectively. The ingredients commonly found in commercial pharmaceutical formulations do not interfere. The proposed method was applied to the determination of these drugs in tablets. Further, infrared spectroscopy and cyclic voltammetry studies were carried out in order to obtain knowledge of the decomposition products of nifuroxazide.     

Determination of adenosine disodium triphosphate (ATP) using oxytetracycline-Eu3+ as a fluorescence probe by spectrofluorimetry

A new spectrofluorimetric method was developed for determination of adenosine disodium triphosphate (ATP). We studied the interactions between oxytetracycline (OTC)-Eu3+ complex and adenosine disodium triphosphate (ATP) by using UV-vis absorption and fluorescence spectra. Using oxytetracycline (OTC)-Eu3+ as a fluorescence probe, under the optimum conditions, ATP can remarkably enhance the fluorescence intensity of the OTC-Eu3+ complex at lambda = 612 nm and the enhanced fluorescence intensity of Eu3+ ion is in proportion to the concentration of ATP. Optimum conditions for the determination of ATP were also investigated. The linear ranges for ATP are 8.00 x 10(-8)-1.50 x 10(-6) mol L(-1) with detection limits of 2.67 x 10(-9) mol L(-1). This method is simple, practical and relatively free interference from coexisting substances and can be successfully applied to determination of ATP in samples. The mechanism of fluorescence enhancement between oxytetracycline (OTC)-Eu3+ complex and ATP was also studied.     

Flow injection-chemiluminescence determination of phenol using potassium permanganate and formaldehyde system

It is found that phenol can react with potassium permanganate in the acidic medium and produce chemiluminescence, which is greatly enhanced by formaldehyde. The optimum conditions for this chemiluminescent reaction are in detail studied using a flow injection system. The experiments indicate that under optimum conditions, the chemiluminescence intensity is linearly related to the concentration of phenol in the range 5.0x10(-9) to 1.0x10(-6)gmL-1 with a detection limit (3sigma) of 3x10(-9)gmL-1. The relative standard deviation is 1.2% for 4.0x10(-7)gmL-1 phenol solution in 11 repeated measurements. This method has the advantages of simple operation, fast response and high sensitivity. The method is successfully applied to the determination of phenol in the waste water.     

Sensitive detection of tetracyclines using europium-sensitized fluorescence with EDTA as co-ligand and cetyltrimethylammonium chloride as surfactant

The determination of tetracyclines (TC) in aqueous solutions, based on europium-sensitized fluorescence, has been improved using EDTA as co-ligand and cetyltrimethylammonium chloride as surfactant. The method involves working in slightly alkaline solutions with the formation of a new chelate where the lanthanide ion is bound to the beta-diketone group. The method is about 6 times more sensitive than that with the Eu-TC-Triton system and LODs are 2.5 x 10(-10), 5 x 10(-10), 1.5 x 10(-9) and 2 x 10(-9) mol l-1 for TC, oxytetracycline, chlortetracycline and doxycycline, respectively. The method has been applied to the determination of TC in calf serum without sample pretreatment. The mean recovery was close to 102% and the lowest concentration attainable in serum samples was better than 0.1 microgram ml-1.