A rapid and highly selective method for the estimation of pyro-, tri- and orthophosphates

A rapid, highly selective and simple method has been developed for the quantitative determination of pyro-, tri- and orthophosphates. The method is based on the formation of a solid complex of bis(ethylenediamine)cobalt(III) species with pyrophosphate at pH 4.2-4.3, with triphosphate at pH 2.0-2.1 and with orthophosphate at pH 8.2-8.6. The proposed method for pyro- and triphosphates differs from the available method, which is based on the formation of an adduct with tris(ethylenediamine)cobalt(III) species. The complexes have the composition [Co(en)(2)HP(2)O(7)]4H(2)O and [Co(en)(2)H(2)P(3)O(10)]2H(2)O, respectively. The precipitation is instantaneous and quantitative under the recommended optimum conditions giving 99.5% gravimetric yield in both cases. There is no interferences from orthophosphate, trimetaphosphate and pyrophosphate species in the triphosphate estimation up to 5% of each component. The efficacy of the method has been established by determining pyrophosphate and triphosphate contents in various matrices. In the case of orthophosphate, the proposed method differs from the available methods such as ammonium phosphomolybdate, vanadophosphomolybdate and quinoline phosphomolybdate, which are based on the formation of a precipitate, followed by either titrimetry or gravimetry. The precipitation is instantaneous and the method is simple. Under the recommended pH and other reaction conditions, gravimetric yields of 99.6-100% are obtainable. The method is applicable to orthophosphoric acid and a variety of phosphate salts.     

A sensitive chemiluminescence method for the determination of H2O2 in exhaled breath condensate

In this paper, a novel flow injection chemiluminescence (FI-CL) method is proposed for the determination of picomolar L(-1) levels of hydrogen peroxide (H(2)O(2)) in exhaled breath condensate (EBC). This method is based on the oxidation of a low concentration of luminol (10(-7) M) by H(2)O(2) at a low concentration level (< 10(-8) M) in an alkaline medium catalyzed by a complex, K(5)[Cu(HIO(6))(2)] (DPC), which is not interfered by other metal ions or horseradish peroxidase (HRP). Under the optimum conditions, H(2)O(2) was determined over the range of 1.0 x 10(-10) to 1.0 x 10(-8) mol L(-1) with a detection limit of (3sigma) of 4.1 x 10(-11) mol L(-1). The relative standard deviation (RSD) was 3.2% for 5 nmol L(-1) H(2)O(2) (n = 7). The proposed method offers the advantages of ultra-sensitivity, selectivity, simplicity and rapidity for H(2)O(2) determination. It was successfully applied to directly determine trace amounts of H(2)O(2) (nmol L(-1)) in human's EBC of both rheum and healthy volunteers. A statistically significant difference was found between patients with rheum (n = 11) and control subjects without rheum (n = 11).     

Role of binding entropy in the refinement of protein-ligand docking predictions: analysis based on the use of 11 scoring functions

We present results of testing the ability of eleven popular scoring functions to predict native docked positions using a recently developed method (Ruvinsky and Kozintsev, J Comput Chem 2005, 26, 1089) for estimation the entropy contributions of relative motions to protein-ligand binding affinity. The method is based on the integration of the configurational integral over clusters obtained from multiple docked positions. We use a test set of 100 PDB protein-ligand complexes and ensembles of 101 docked positions generated by (Wang et al. J Med Chem 2003, 46, 2287) for each ligand in the test set. To test the suggested method we compared the averaged root-mean square deviations (RMSD) of the top-scored ligand docked positions, accounting and not accounting for entropy contributions, relative to the experimentally determined positions. We demonstrate that the method increases docking accuracy by 10-21% when used in conjunction with the AutoDock scoring function, by 2-25% with G-Score, by 7-41% with D-Score, by 0-8% with LigScore, by 1-6% with PLP, by 0-12% with LUDI, by 2-8% with F-Score, by 7-29% with ChemScore, by 0-9% with X-Score, by 2-19% with PMF, and by 1-7% with DrugScore. We also compared the performance of the suggested method with the method based on ranking by cluster occupancy only. We analyze how the choice of a clustering-RMSD and a low bound of dense clusters impacts on docking accuracy of the scoring methods. We derive optimal intervals of the clustering-RMSD for 11 scoring functions.     

First derivative of the ratio spectra method for resolving iodide and thiocyanate in binary mixtures

A new method is described to analyse the binary mixture of iodide (I(-)) and thiocyanate (SCN(-)) ions, using the first derivative of the ratio spectra obtained by mathematical treatment of the data. The method is based on the formation of mixed ligand complexes between benzohydroxamic acid (BHA), vanadium (V) and I(-) or SCN(-) and their extraction in ammonium quaternary salt dissolved in toluene. Calibration graphs for 2-9 mug/ml of I(-) and for 2-6 mug ml of SCN(-) were established by measuring the analytical signals at 376 nm for I(-) and at 400.6 nm for SCN(-). The method has been applied for determining both ions in waste water of an power station at ng/ml levels after a preconcentration step with C(18), without any separation step.     

A combined spectrophotometric-AAS method for the analysis of trace metal, EDTA, and metal-EDTA mixture solutions in adsorption modeling experiments

The adsorption of free- and bound-metal ions (metal complexes) as well as of ligands onto various hydrous oxide type sorbents have been extensively modelled using EDTA as the model ligand. This type of modelling uses metal ion-EDTA mixture solutions containing stoichiometrically equivalent or excessive amounts of either constituent. Consequently, for mixture solutions equilibrated with the sorbent, the aim was to develop a suitable method for determining either metal complex+free ligand (MY(2-)+H(2)Y(2-)) or metal complex+free metal (MY(2-)+M(2+)) in the aqueous filtrate, the metal M being lead or cadmium. The conventional method of analyzing such filtrates is exchanging different metal-EDTA complexes with Fe(NO(3))(3) followed by HPLC using UV detection. The developed method utilizes Vis- and AA-spectrometry widespread in common laboratories, eliminating the need for HPLC and UV techniques that require higher operational cost, expertise and contaminant-free media. The developed procedure is based on the following analyses for the possible constituents of equilibrated solution (with the sorbent). All EDTA (free or bound, as H(2)Y(2-) or MY(2-)) species are converted into FeY(-) by adding Fe(NO(3))(3), and heating at 80 degrees C for 1 h. All metal (free or bound, as M(2+) or MY(2-)) species are determined by AAS. All unbound (free) Fe(3+) species are determined by the thiocyanate spectrophotometric method at 480 nm. Then 'EDTA-bound iron (III)' is defined as added Fe minus colorimetrically (thiocyanate method) found Fe, and 'AAS-found metal' (lead or cadmium) corresponds to M(2+) and/or MY(2-), depending on the analyzed solution. If EDTA-bound Fe(III) is greater than AAS-found metal, then one has a (MY(2-)+H(2)Y(2-)) mixture where AAS-found metal is (MY(2-)), and free EDTA, i.e. (H(2)Y(2-)), is calculated from the difference. If EDTA-bound Fe(III) is smaller than AAS-found metal, then one has a (M(2+)+ MY(2-)) mixture where EDTA-bound Fe(III) is (MY(2-)), and the free metal, i.e. (M(2+)), is calculated from the difference. If the two compared quantities are equal, then one has a pure MY(2-) solution. Since surface complexes on the hydrous oxide sorbent ( approximately SOH) as bound metal ( approximately SOM), bound ligand ( approximately SOL) or bound metal complex ( approximately SOML) are much more difficult to desorb and analyze, the simple procedure developed here applicable to more conventional instruments carried out in sorbent equilibrated solutions (filtrates) may effectively aid heavy metal adsorption modelling in realistic environmental simulations.     

Exploring intramolecular reactions in complex systems with metadynamics: the case of the malonate anions

We have determined the optimized structures, relative energies and intramolecular reactions for two anionic forms of malonic acid, anion malonate(-1) (HO(2)CCH(2)CO(2)(-)) and malonate(-2) ((-)O(2)CCH(2)CO(2)(-)). For this purpose we employed accurate quantum chemistry calculations using second-order M?ller-Plesset perturbation theory and Density Functional Theory with an aug'-cc-p-VTZ basis set to determine the structures and energies, and a novel metadynamics method based on Car-Parrinello molecular dynamics for the thermal reactions. For both malonates, we found new isomers (keto and enol structures) characterized by CO(2) rotations and intramolecular proton transfers. These proton transfers characterize the keto-enol tautomerism that takes place both in the monoanion and dianion. In all cases, the keto tautomer is the more stable configuration. The metadynamics method allows the system to explore the potential energy surface in a few picoseconds, crossing activation barriers of 20-50 kcal/mol.     

Fluorescence quenching method for the determination of sodium dodecyl sulphate with near-infrared hydrophobic dye in the presence of Triton X-100

A fluorophotometric method for the determination of anionic surfactant sodium dodecyl sulphate (SDS) was proposed. The method is based on the quenching effect of SDS on the fluorescence of near-infrared (NIR) hydrophobic dye, 2-[4'chloro-7'(3'hexadecyl-2'benzothiazolinylidene)-3',5'-(1',3'-propanediyl)-1',3',5'-heptatriene-1'-yl]-3-ethylbenzothiazolium iodide (dye I) in the presence of Triton X-100. The calibration graph is linear in the concentration range from 0 to 2 x 10(-6) mol L(-1) of SDS with a detection limit (LOD) of 8.3 x 10(-8) mol L(-1). The relative standard deviation for the determination of 7 x 10(-7) mol L(-1) SDS was 4.1%. Recoveries of 95.3-110.3% were found for the addition to 1.0 x 10(-6) mol L(-1) SDS in the analysis of environmental water samples. Preliminary research shows that the fluorescence quenching is due to the formation of dye aggregate facilitated by SDS.     

On the N2O correction used for mass spectrometric analysis of atmospheric CO2

To obtain accurate values of delta(13)C(CO(2)) and delta(18)O(CO(2)) on environmental CO(2) by mass spectrometry, the raw isotope data must be corrected for the isobaric N(2)O contribution. This is one of the analytical problems limiting inter-laboratory delta(13)C(CO(2)) data consistency. The key parameter, the N(2)O relative ionisation efficiency (E(N2O)), cannot be determined with sufficient accuracy by direct measurements of pure N(2)O. The determination of (E(N2O)) by analyses on N(2)O--CO(2) mixtures of known isotope composition and mixing proportions has been recently suggested. In this work we propose a new method of N(2)O correction which uses the m/z 30 signal as a measure of the N(2)O/CO(2) ratio, so that determinations of (E(N2O)) and N(2)O content are not required. The method uses the fact that fragment-ion spectra of N(2)O and CO(2) are very specific. The formalism of the correction is considered. Various tests demonstrate that the new method is robust, stable and easy to implement in practice. The effective value (E(N2O)) (the key parameter for the new correction) has to be calibrated on known N(2)O--CO(2) mixtures by measuring (30)R signals only. The method accuracy we presently achieved is around 2.5% and any error which appears to come mostly from our N(2)O--CO(2) mixture preparation. Based on our tests and error considerations, the error of the proposed method that may be achieved is as low as +/-1.5% (relative to the correction magnitude). For tropospheric CO(2) this means +/-0.003 per thousand and +/-0.005 per thousand for delta(13)C(CO(2)) and delta(18)O(CO(2)), respectively. The proposed method may be valuable for small samples where no separate N(2)O determinations are available (e.g. ice core samples and CF-IRMS measurements) as well as for determination of (E(N2O)) and testing the 'traditional' N(2)O correction based on mass balance calculations.     

Spectrophotometric determination of NO(2) in the working atmosphere

A method is described for determining NO(2) in workplace atmospheres, based on its reaction with bis(diethyldithiocarbamato)copper(II) in toluene. NO(2) is absorbed from an air sample by a toluene solution of Cu(dtc)(2) and the decrease in the initial absorbance at 437 nm is measured. The method has been compared with the Saltzman method. The interference of NO, Cl(2), O(3), SO(2) and other gases has been studied. The NO(2) concentration range of the method is 1-500 mg m (3).     

Fluorimetric determination of nitrogen oxides in the air by a novel red-region fluorescent reagent

A sensitive fluorimetric method for the determination of nitrogen oxides (NO(x): NO+NO(2)) in air is described. Nitrogen dioxide (nitrogen monoxide was previously converted to nitrogen dioxide in oxide tubes) was aspirated through a fritted glass bubble at a flow rate of 500 ml min(-1) for 120 min and fixed as nitrite, using 0.1 N NaOH as a trapping solution with the empirical absorption efficiency 0.74 and the stoichiometric factor 0.5. The method is based on the fluorescence quenching of a red-region fluorescent reagent, tetra-substituted amino aluminum phthalocyanine (TAAlPc), after being diazotized by nitrite. Under optimal conditions the linear range of the calibration curve for nitrite is 1-40 ng ml(-1) (NO(2) 0.24-9.6 ppb, v/v). The detection limit is 0.34 ng ml(-1) for nitrite (NO(2) 0.08 ppb, v/v) and the relative standard deviation for six replicate measurements of 15 ng ml(-1) nitrite is 3.2%. The method has been applied to the determination of nitrogen oxides in the air with satisfactory results. Typical gaseous co-pollutants such as SO(2), H(2)S and HCHO did not interference the determination.     

Equation-of-motion coupled-cluster method for the study of shape resonance

The equation-of-motion coupled-cluster method (EOM-CC) is applied for the first time to calculate the energy and width of a shape resonance in an electron-molecule scattering. The procedure is based on inclusion of complex absorbing potential with EOM-CC theory. We have applied this method to investigate the shape resonance in e(-)N(2), e(-)CO, and e(-)C(2)H(2).     

A novel chemiluminescent method for the determination of salicylic acid in bactericidal solutions

A new flow-injection procedure has been developed for the determination of salicylic acid based on the enhancement of the chemiluminescence from the cerium(IV)-Tween 20 reaction by salicylic acid in acidic medium. The method is simple, selective and sensitive with a detection limit of 2.5x10(-9) g mL(-1). It is applicable to the determination of salicylic acid in the concentration range of 4.0x10(-9)-1.1x10(-6) g mL(-1). The relative standard deviation (RSD) is 0.85% for 4.0x10(-7) g mL(-1) salicylic acid (n=11). The method has been successfully applied to the determination of salicylic acid in bactericidal solutions. Furthermore, it is suggested that light emission from cerium(IV)-Tween 20 reaction is probably because of the formation of singlet oxygen 1O2* and the emitter is excited oxygen molecular pairs O2(1delta(g))O2(1sigma(g)-).     

The use of 1-[pyridyl-(2)-azo]-naphthol-(2) in the presence of TX-100 and N,N'-diphenylbenzamidine for the spectrophotometric determination of copper in real samples

A simple and sensitive field detection and spectrophotometric method for determination of copper described herewith is based on the formation of a red coloured species of copper(II) with 1-[pyridyl-(2)-azo]-naphthol-(2) (PAN), TX-100 and N,N'-diphenylbenzamidine (DPBA) at pH range 7.8-9.4. The red coloured Cu(II)-PAN-(TX-100)-DPBA complex in chloroform shows maximum absorbance at 520 nm with molar absorptivity value of 1.14x10(5) l mol(-1) cm(-1). The detection limit of the method is 2 ng ml(-1) organic phase. The system obeys Beer's law up to 0.6 mug Cu(II) ml(-1) in organic solution. Most of the common metal ions generally found associated with copper do not interfere. The repeatability of the method was checked by finding relative standard deviation (RSD) (n=10) value for solutions each containing 0.2 mug ml(-1) of Cu(II) and the RSD value of the method was found to be 1.5%. The validity of the method has been satisfactorily examined for the determination of copper in soil and airborne dust particulate samples.     

Study of the electro-adsorptive behaviour of the herbicide nitralin by means of voltammetric techniques

The electroanalytical behaviour of the herbicide Nitralin has been studied by means of different voltammetric techniques. Nitralin is adsorbed on the mercury electrode and gives 2 reduction waves at -0.6 and -0.7 V versus Ag AgCl reference electrode, for pH values > 10. The electrochemical process is irreversible and strongly influenced by pH solution. A systematic study of the several instrumental and accumulation variables affecting the stripping response was carried out using square wave (SWV; Osteryoung's method) and differential pulse voltammetry (DPV) as redissolution techniques. The limits of detection were 4.4 x 10(-1) mol 1(-1) (AdS-SWV) and 3.5 x 10(-11) mol 1(-1) (AdS-DPV), with variation coefficients of 4.17 and 3.90% respectively, at a concentration level of 8 x 10(-9) mol 1(-1) (n = 10). A method, based on AdS-DPV, for the determination of Nitralin in ground-water is proposed. A detection limit of 8.7 x 10(-11) mol 1(-1) (AdS-DPV) was reached in real samples.     

Determination of trace formaldehyde by solid substrate-room temperature phosphorescence quenching method based on the rose bengal-potassium bromate-Tween-80 system

A new method for the determination of trace formaldehyde by solid substrate-room temperature phosphorescence quenching method has been proposed. It is based on the facts that rose bengal (R) can emit intense and stable room temperature phosphorescence on the solid substrate of filter paper (SS-RTP). Potassium bromate (KBrO(3)) can oxidize R, which causes the quenching of RTP. In the presence of HCHO, it can react with KBrO(3) to form Br(2) and Br(2) can oxidize R, which causes smart quenching of RTP. The phosphorescence intensity (DeltaI(p)) is directly proportional to the concentration of HCHO. In the presence of Tween-80, the DeltaI(p) will be increased to 9.1 times higher than that without it. The linear range of this method is 0.016-1.6fgspot(-1) (corresponding concentration: 0.040-4.0 pgml(-1), 0.40 microlspot(-1)) with the detection limit of 4.5agspot(-1) (corresponding concentration: 1.1 x 10(-14) gml(-1)). The regression equation for working curve is DeltaI(p)=136.6+28.28m(HCHO)fgspot(-1) (r=0.9935, n=6). This method is sensitive, simple, rapid and has been applied to the determination of trace formaldehyde in real samples with satisfactory results. The mechanism of determination of trace formaldehyde by SS-RTP quenching method based on the rose bengal-KBrO(3)-Tween-80 system is also discussed.     

Synthesis of a novel chemiluminescent reagent for the determination of hydrogen peroxide in snow waters

7-(4,6-Dichloro-1,3,5-triazinylamino)-4-methylcoumarin (DTMC) was synthesized as a completely new chemiluminescent reagent, and with it a novel chemiluminescence method was developed for the determination of hydrogen peroxide in the absence of any added catalyst or co-oxidant. The chemiluminescence intensity of the DTMC-H(2)O(2) system could be enhanced by the addition of cation surfactants. The chemiluminescence intensity was directly proportional to the concentration of H(2)O(2) in the range 1.0 x 10(-7)-4.0x10(-4) mol l(-1), and the detection limit was 4.0 x 10(-8) mol l(-1). The relative S.D. was 4.9% for 1.0 x 10(-6) mol l(-1) of H(2)O(2) (n=10). The selectivity of this method was high, and most of the transition metal ions have no effect on the determination. The proposed method has been applied to the determination of trace amounts of hydrogen peroxide in snow water. A possible mechanism of the chemiluminescence reaction is also discussed.     

Simple fluorimetric liquid chromatographic method for the analysis of undecylenic acid and zinc undecylenate in pharmaceutical preparations

A simple and selective liquid chromatographic method is described for the analysis of undecylenic acid (UA) and zinc undecylenate (ZnUA) in pharmaceutical preparations. The method is based on the derivatization of the analytes extracted from various samples with 2-(2-naphthoxy)ethyl 2-(piperidino)ethanesulfonate. The resulting derivative was analyzed by liquid chromatography with fluorimetric detection. The quantitation of the method is in the range of 3.0-50.0 microM UA with a detection limit of about 0.3 microM (S/N = 3 with 10 microl injection). We found that acetonitrile is a selective solvent for differentially dissolving UA from coexisted ZnUA in compound formulation. This results in the specific analysis of UA in the presence of ZnUA and simply analyzing the coexisted ZnUA by the value of total UA (UA+ZnUA) minus that of UA. Application of the method to the analysis of undecylenic acid and zinc undecylenate in ointment, powder and solution preparations proved feasible.     

Kinetic fluorimetric determination of nanogram amounts of manganese, based on its catalysis of the oxidation of 2-hydroxybenzaldehyde thiosemicarbazone with hydrogen peroxide

A kinetic method is described for the determination of trace amounts of manganese(II), based on its catalytic effect on the oxidation of 2-hydroxybenzaldehyde thiosemicarbazone by hydrogen peroxide. The reaction is followed by measuring the rate of change of fluorescence (lambda(ex) 365 and lambda(em) 440 nm). The calibration is linear over the manganese range 2-9 ng ml with a precision of +/-1%. The proposed method suffers from few interferences.     

The use of phenylfluorone in the presence of cetylpyridinium chloride and Triton X-100 for the spectrophotometric determination of copper(II) in blood serum

A simple and sensitive spectrophotometric method for determination of copper(II) is based on the formation of a blue coloured complex of Cu(II) with 9-phenyl-2,3,7-trihydroxy-6-fluorone (PF) in the presence of cetylpyridinium chloride (CP) and Triton X-100, has been developed. Optimum concentrations of PF, CP, Triton X-100 and pH ensuring maximum absorbance were defined. The complex Cu(II)-PF-CP-Triton X-100 shows maximum absorbance at 595 nm with a molar absorptivity value of 9.67x10(4) l mol(-1) cm(-1). The detection limit of the method is 0.028 mug ml(-1). Beer's law is obeyed for copper concentrations in the range 0.04-0.4 mug ml(-1). The studies of the effect of foreign ions on determination of copper, show that the selectivity of the method is poor. The cations of alkali metals and anions Br(-), Cl(-), I(-), F(-), NO(2)(-), NO(3)(-), CH(3)COO(-), SO(4)(2-), S(2)O(3)(2-), PO(4)(3-), citrates (examined in 1000-fold molar excess over copper) do not affect the determination. All cations forming complexes with PF have an interfering effect. The statistical evaluation of the method was carried out for six determinations using 10 mug of Cu and the following results were obtained: the standard deviation, SD=0.042, the confidence interval mu(95)=10.1+/-0.1 mug Cu. The method has been applied for determination of copper in blood serum.     

Determination of vitamin D(3) hydroxymetabolites in plasma at the sub-part per trillion levels using on-line cleanup/preconcentration and HPLC-fluorimetric post-column derivatisation

A new method for the determination of the hydroxymetabolites of vitamin D(3) (24,25-(OH)(2)-D(3), 1,25-(OH)(2)-D(3) and 25-OH-D(3)) in plasma is reported. The method is based on the integration of three subsystems: continuous cleanup/preconcentration, HPL separation and post-column fluorimetric derivatisation. The derivatising subsystem is based on the dehydration reaction undergone by the secosteriod molecules in a strong-acid medium. The calibration graphs were run between 0.1 pg ml(-1) and 100 ng ml(-1) for each analyte with excellent regression coefficients (>/=0.9933) in all cases. The precision at two concentration levels was established with acceptable RSDs (%) in all instances (values between 2.1 and 5.2%). The method was also checked by applying it to human plasma samples spiked with the target analytes and the recoveries ranged between 86 and 106%.