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.

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.

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.