Quantitative colorimetric-imaging analysis of nickel in iron meteorites.

A quantitative analytical imaging approach for determining the nickel content of metallic meteorites is proposed. The approach uses a digital image of a series of standard solutions of the nickel-dimethylglyoxime coloured chelate and a meteorite sample solution subjected to the same treatment as the nickel standards for quantitation. The image is processed with suitable software to assign a colour-dependent numerical value (analytical signal) to each standard. Such a value is directly proportional to the analyte concentration, which facilitates construction of a calibration graph where the value for the unknown sample can be interpolated to calculate the nickel content of the meteorite. The results thus obtained were validated by comparison with the official, ISO-endorsed spectrophotometric method for nickel. The proposed method is fairly simple and inexpensive; in fact, it uses a commercially available digital camera as measuring instrument and the images it provides are processed with highly user-friendly public domain software (specifically, ImageJ, developed by the National Institutes of Health and freely available for download on the Internet). In a scenario dominated by increasingly sophisticated and expensive equipment, the proposed method provides a cost-effective alternative based on simple, robust hardware that is affordable and can be readily accessed worldwide. This can be especially advantageous for countries were available resources for analytical equipment investments are scant. The proposed method is essentially an adaptation of classical chemical analysis to current, straightforward, robust, cost-effective instrumentation.

Photo-induced fluorescence of magnesium derivatives of tetracycline antibiotics in wastewater samples.

An analytical strategy, for the determination of tetracyclines (TCs), based on a HPLC system coupled with a photo-reactor followed by post-column derivatization was developed. Higher fluorescence emission after coupling the resulting photo-fragments with magnesium ions was observed for the determination of minocycline (MC), epitetracycline (ETC), tetracycline (TC) and doxycycline (DC). The manifold included a HPLC system with a photo-reactor (PTFE tubing helically coiled around a low-pressure mercury lamp), a mixing T-piece and a fluorescence detector. The derivatization reagent was delivered at 0.5 mL min(-1) by a pump. After HPLC separation using a gradient system with a mobile phase containing oxalic acid 0.02 M and acetonitrile, TCs were irradiated for 60 s, and the resulting photo-fragments were mixed with the post-column derivatization reagent, and the magnesium derivatives of TCs were detected by fluorimetry (lambda(exc) 386 nm, lambda(em) 500 nm). The results obtained showed a significant increase of sensitivity due to photodegration of TCs, 45.4%, 37.6% and 25.3% for MC, TC and ETC respectively. For DC an increase of only 1.5% was observed. The developed method was successfully applied to TCs determination in hospital and municipal wastewater samples using solid phase extraction with Oasis HLB cartridges. The LOQs were 0.25, 0.15, 01 and 0.25 microg L(-1) for TC, ETC, MC and DC, respectively. The recovery values oscillated between 107.1% and 92.4% for fortification of 2.5 microg L(-1) of each antibiotic.

Use of QSAR methods for predicting the chemiluminescent behaviour of organic compounds upon reaction with potassium permanganate in an acid medium.

In previous work, molecular connectivity computations were successfully used to predict the chemiluminescent behaviour of organic compounds upon reaction with common strong oxidants and the native fluorescence too; both of them in a liquid phase. The obtained results were used to develop new analytical procedures to the given compounds. For the first time, connectivity methods were used for a purely analytical purpose. In this work, we went deeper into the knowledge of direct chemiluminescence processes by using molecular connectivity in the form of QSAR methods to predict the chemiluminescence intensity produced by reactions between organic compounds (pharmaceuticals mainly) and potassium permanganate in a liquid phase. The choice of this oxidant was dictated by its being the most active by far in producing chemiluminescence. We used discriminant analysis to examine the results for 63 substances the emission intensity of which upon reaction with acid potassium permanganate was experimentally measured in a continuous-flow manifold. Descriptors were chosen by applying stepwise linear dicriminant analysis (LDA) to Snedecor F-values, using the smallest Mahalanobis distance, the minimum error on the test set and the lowest value of the Wilks'lambda as sorting criterion. The theoretical predictions thus obtained were checked against the experimental results for a set of 16 compounds not used in the previous theoretical computations the chemiluminescent behaviour of which was also experimentally assessed. The result was a hit rate of 87.5% in the predictions.

Determination of the herbicide benfuresate by its photo-induced chemiluminescence using flow multicommutation methodology.

The present paper deals with an analytical strategy based on coupling photo-induced chemiluminescence in a multicommutation continuous-flow methodology for the determination of the herbicide benfuresate. The solenoid valve inserted as small segments of the analyte solution was sequentially alternated with segments of the NaOH solution for adjusting the medium for the photodegradation. Both flow rates (sample and medium) were adjusted to required time for photodegradation, 90 s; and then, the resulting solution was also sequentially inserted as segments alternated with segments of the oxidizing solution system, hexacyanoferrate (III) in alkaline medium. The calibration range from 1 microg L(-1) to 95 mg L(-1), resulted in a linear behaviour over the range 1 microg L(-1) to 4 mg L(-1) and fitting the linear equation: I=4555.7x+284.2, correlation coefficient 0.9999. The limit of detection was 0.1 microg L(-1) (n=5, criteria 3 sigma) and the sample throughput was 22 h(-1). The consumption of solutions was very small; per peak were 0.66 mL, 0.16 mL and 0. 32 mL sample, medium and oxidant, respectively. Inter- and intra-day reproducibility resulted in a R.S.D. of 3.9% and 3.4%, respectively. After testing the influence of a large series of potential interferents the method is applied to water samples obtained from different places, human urine and to one formulation.

Photo-induced chemiluminometric determination of Karbutilate in a continuous-flow multicommutation assembly.

The present paper deals with the chemiluminescent determination of the herbicide Karbutilate on the basis of its previous photodegradation by using a low-pressure Hg lamp as UV source in a continuous-flow multicommutation assembly (a solenoid valves set). The pesticide solution was segmented by a solenoid valve and sequentially alternated with segments of the 0.001 mol l(-1) of NaOH solution, the suitable media for the formation of photo-fragments; then it passes through the photo-reactor and was lead to the flow-cell after being divided in small segments which were sequentially alternated with the oxidizing system; 2 x 10(-5) mol l(-1) of potassium permanganate in 0.2% pyrophosphoric acid. The studied calibration range, from 0.1 microg l(-1) to 65 mg l(-1), resulted in a linear behaviour over the range 20 microg l(-1)-20 mg l(-1) and fitting the linear equation: I=(1180+/-30)C+(15+/-5) with the correlation coefficient 0.9998. The limit of detection was 10 microg l(-1) and the sample throughput 17 h(-1). After testing the influence of a large series of potential interfering species, the method was applied to water and human urine samples.

Photo-induced fluorescence of fluometuron in a continuous-flow multicommutation assembly.

This paper deals with the photo-induced fluorimetric determination of the herbicide Fluometuron with the aid of a continuous-flow assembly of the emergent and new methodology known as Multicommutation which was provided with an on-line photoreactor. Maximum fluorescence intensity was observed at basic pH solutions, 1x 10(-4) mol l(-1) NaOH, after 1.4 min of irradiation and being the maximum at lambda(exc) 247.0 nm and lambda(em) 325.0 nm. The influence of different experimental parameters either chemical (pH, surfactants presence, solvent polarity and temperature) or hydrodynamic (time of photo-degradation, size and number of different segments and flow-rate) was tested. The linear dynamic range was from 0.01 to 4.0 mg l(-1) of Fluometuron; the inter-day reproducibility (as R.S.D.) of the slope was 0.001% and 1.7% from the peaks intra-day reproducibility. A large series of potential interferents was studied and finally the method was applied to human urine, soil, formulation and water samples.

Chemiluminometric determination of the pesticide 3-indolyl acetic acid by a flow injection analysis assembly.

A new method is proposed for the chemiluminescent determination of the pesticide 3-indolyl acetic acid by means of an flow injection analysis system. The chemiluminescence emission is obtained by oxidation of the analyte with Ce (IV) in nitric acid and presence of beta-cyclodextrine. The continuous-flow method allows the determination of 159samplesh(-1) of 3-indolyl acetic acid in an interval of concentrations over the range 0.5-15.0mgl(-1). The limit of detection was 0.1mugl(-1) and the R.S.D. (n, 17) at 2.0mgl(-1) of the pesticide level was 2.7%. The method was applied to water samples.

Theoretical prediction of the photoinduced chemiluminescence of pesticides.

Although it is relatively easy to find chemiluminescent (CL) molecules working on the field of direct liquid phase (especially employing strong oxidants), the molecules found as chemiluminescent are normally very weak CL compounds for developing suitable analytical CL-procedures. Therefore, it is mandatory to develop new strategies to enhance in a simple way the native chemiluminescence of such a compounds, and even to increase the number of compounds to be determined by direct chemiluminescence. Photoinduced chemiluminescence (Ph-CL) results in a simple and easily on-line accessible strategy to solve these disadvantages. In the present paper, molecular connectivity, a topological method which allows an unique mathematical characterization of molecular structures by the so-named topological descriptors and their correlation with physical, chemical and biological properties of molecules was applied to predict the Ph-CL in liquid phase. Molecular connectivity calculations and discriminant analysis was applied to 72 pesticides for which either a Ph-CL or non Ph-CL behaviour was observed in an experimental screening. The screening test is based on the on-line photodegradation of pesticides by using an automated multicommutation based flow asssembly provided with a photoreactor consisting of 150 cm x 0.8mm PTFE tubing helically coiled around a 20 W low-pressure mercury lamp. Photodegraded pesticides are detected by direct chemiluminescence of the resulting photo-fragments and their subsequent reaction with potassium permanganate in sulfuric acid medium as oxidant. The screening comprised pesticides with different molecular structures and relevant members of the most important families of pesticides were tested (oxime carbamates, sulfonylcarbamates, thiocarbamates, 1,3,5-triazines, organophosphorous, hydroxybenzonitrile, sulfonylureas, phosphonic acid derivatives, imidazolinones, carboxamides, aryloxyalkanoic acids, 1,2,4-triazinones, etc.). The theoretical predictions agree with the empirical results obtained by means of the screening test performed in the multicommutation flow-assembly.

Chemiluminometric photo-induced determination of Strychnine in a Multicommutation flow assembly.

This paper deals on the determination of Strychnine, a potent and dangerous pesticide and the analytical procedure is based on the photo-induced chemiluminescence of the pesticide by means of the Multicommutation continuous-flow methodology. Small segments of the pesticide solution were sequentially alternated with segments of the solution for adjusting the suitable medium for the photodegradation. The required time of UV irradiation was obtained by stopped-flow during 150s; then, the resulting solution formed alternated segments with the oxidizing solution containing 5x10(-3)moll(-1) Ce(IV) in 0.6moll(-1) nitric acid. The calibration range, from 2mugl(-1) to 50mgl(-1), resulted in a linear behaviour over the range 25mugl(-1) to 20mgl(-1) and fitting the equation: I=4706x+624 with a correlation coefficient of 0.9955. The limit of detection was 2mugl(-1) and the sample throughput 15h(-1). After testing the influence of a large series of potential interferents, the method was applied to different kinds of samples.

Photo-induced chemiluminescence-based determination of diphenamid by using a multicommuted flow system.

This manuscript deals with the application of molecular connectivity calculations to predict the photo-induced chemiluminescent behaviour of the family of herbicides grouped as amides. Several compounds of this group were theoretically studied by means of a general discriminant equation formerly obtained, being 18 of them (plus eight from the chloroacetanilide sub-group) predicted with a high probability as photo-induced chemiluminescent. Empirical confirmation of the chemiluminometric behaviour was performed with some few commercially available amide herbicides. On the basis of these results, a new multicommutation-photo-chemiluminescent method is proposed for the determination of the diphenamid. The method is based on the photodegradation of the pesticide and then the resulting photo-fragment solutions are oxidized by K(3)[Fe(CN)(6)] in sodium hydroxide medium, at room temperature and 80 degrees C, for the photodegradation and chemiluminometric oxidation, respectively. The studied calibration up to 5.0mgl(-1), revealed a linear dynamic graph up to 20mgl(-1). The reproducibility between days resulted in a R.S.D. (in slope %) of 2.8 (n=5) and the repeatability with a %R.S.D. (n=20) of 4.3. LOD (s/n=3) of 1mugl(-1) and sample throughput of 20h(-1). The influence of foreign compounds is also tested and the optimized flow assembly is applied to different kind of samples.

FIA-fluorimetric determination of the pesticide 3-indolyl acetic acid.

The paper presents the determination of the pesticide 3-indolyl acetic acid based on its native fluorescence; the method has been optimised either in a flow injection analysis (FIA) assembly or in batch. Maximum fluorescence intensity was observed at basic pH solutions at lambda(exc) = 280 nm and lambda(em) = 364 nm. The influence of different empirical parameters as pH, surfactants presence, solvent polarity, solved oxygen amount, and temperature was studied; highest outputs only required the pH in aqueous solutions to be adjusted over the range 9.5-10.5. Different calibration ranges were obtained by working with three different sensitivity scales of the fluorimeter either in flow injection analysis or batch. With the high sensitivity scale and FIA, the linear dynamic range was from 0.005 to 0.6 mg L(-1) 3-indolyl acetic acid; with an relative standard deviation (RSD) of 4.9% inter-day reproducibility. A large series of potential interferents was studied and finally, the method was applied to several water samples.

Application of sequential injection analysis to pharmaceutical analysis.

Sequential injection analysis is a well established tool for automation of pharmaceutical analysis. A short historical background of this technique is given as well as a brief discussion on the basic principles and potentials. The current applications of SIA in the pharmaceutical analysis are also described and discussed. The manifolds developed offer good analytical characteristics and are suitable for analysis of drug formulations, process analysis, drug-dissolution, drug-release testing and functional assays for screening potential drugs. The results obtained are in good agreement with those furnished by the application of the reference methods presented in the pharmacopoeias.

Analytical strategy photodegradation/chemiluminescence/continuous-flow multicommutation methodology for the determination of the herbicide Propanil.

The present paper is dealing with an analytical strategy based on coupling photodegradation, chemiluminescence and multicommutation continuous-flow methodology for the determination of the pesticide Propanil, a common herbicide. The pesticide solution is inserted as small segments sequentially alternated with segments of the solution for adjusting the suitable medium for the photodegradation. Both flow-rates (sample and medium) are adjusted to required time for photodegradation, 2.0min; and then, the resulting solution is also sequentially inserted as segments alternated with segments of the oxidizing solutions system, 1.00x10(-4)moll(-1) potassium permanganate in 2.00moll(-1) sulphuric acid medium. The calibration range, from 10mugl(-1) to 25mgl(-1), resulted in a linear behaviour over the range 10mugl(-1)-5mgl(-1) and fitting the linear equation: I=780.30C+95.28; correlation coefficient 0.9999. The limit of detection was 8mugl(-1) and the sample throughput 20h(-1). After testing the influence of a large series of potential interferents the method is applied to water samples obtained from different places and to one formulation. The method is valid for the determination of other pesticides from the same chemical family, namely: alachlor, flumetsulam, furalaxyl and ofurace. Calibration graphs, limits of detection, repeatability and determination in water samples are obtained for each reported pesticide.

FI-on line photochemical reaction for direct chemiluminescence determination of photodegradated chloramphenicol.

A new, simple, clean and selective flow injection strategy based on the tandem photochemical reaction-chemiluminescence detection was applied to the determination of chloramphenicol. The determination is based on the on-line photodegradation of the drug in a glycine buffer at pH 8.8 by using a photoreactor consisting of 697 cmx0.5 mm PTFE tubing helically coiled around an 8 W low-pressure mercury lamp. Photodegradated chloramphenicol is detected by direct chemiluminescence of resulting photo-fragments and their subsequent reaction with potassium permanganate in sulfuric acid medium as oxidant. The method allows the chemiluminescence determination of compounds which do not exhibit native chemiluminescence. The calibration graph was linear up to 14 mug ml(-1) chloramphenicol, the limit of detection was 30 ng ml(-1), the relative standard deviation was 2.4% for 7 mug ml(-1) of the drug and the sample throughput was 60 h(-1). Taking into account the importance of the medium of photodegradation on the mechanism of photodegradation a comparative study in terms of selective was performed for different chemical media employed in the procedure of photodegradation. The proposed method was applied to the determination of chloramphenicol in commercially available pharmaceutical formulations.

Spectral and thermal properties of ondansetron

Realizou-se estudo das propriedades gerais da ondansetrona. A estabilidade térmica do sólido é ensaiada mediante determinação do comportamento termogravimétrico e do ponto de fusão. A descrição das características e a interpretação do comportamento térmico são complementadas por meio de estudos espectrométricos: IV, RMH-Hû, RMN-ûüC, UV-VIS e fluorescência