Computer vision-based analytical chemistry applied to determining iron in commercial pharmaceutical formulations.

Two different computer vision-based analytical chemistry (CVAC) methods were developed to quantify iron in the commercial pharmaceutical formulations Ferbisol® and Ferro sanol®. The methods involve using a digital camera or a desktop scanner to capture a digital image of a series of Fe2+ standard solutions and the unknown sample upon reaction with o-phenanthroline. The images are processed with appropriate software (e.g., the public domain programme ImageJ, from NIH) to obtain a numerical value (analytical signal) based on colour intensity. The fact that such a value is proportional to the analyte concentration allows one to construct a calibration graph from the standards and interpolate the value for the sample in order to determine its concentration. The results thus obtained were compared with those provided by a spectrophotometric method and the US Pharmacopoeia's recommended method. The differences never exceeded 2%. The two proposed methods are simple and inexpensive; also, they provide an effective instrumental alternative to spectrophotometric methods which can be especially beneficial in those cases where purchasing and maintaining a spectrophotometer is unaffordable.

QSPR studies on the photoinduced-fluorescence behaviour of pharmaceuticals and pesticides.

Fluorimetric analysis is still a growing line of research in the determination of a wide range of organic compounds, including pharmaceuticals and pesticides, which makes necessary the development of new strategies aimed at improving the performance of fluorescence determinations as well as the sensitivity and, especially, the selectivity of the newly developed analytical methods. In this paper are presented applications of a useful and growing tool suitable for fostering and improving research in the analytical field. Experimental screening, molecular connectivity and discriminant analysis are applied to organic compounds to predict their fluorescent behaviour after their photodegradation by UV irradiation in a continuous flow manifold (multicommutation flow assembly). The screening was based on online fluorimetric measurement and comprised pre-selected compounds with different molecular structures (pharmaceuticals and some pesticides with known 'native' fluorescent behaviour) to study their changes in fluorescent behaviour after UV irradiation. Theoretical predictions agree with the results from the experimental screening and could be used to develop selective analytical methods, as well as helping to reduce the need for expensive, time-consuming and trial-and-error screening procedures.

Using digital photography to implement the McFarland method.

The McFarland method allows the concentration of bacterial cells in a liquid medium to be determined by either of two instrumental techniques: turbidimetry or nephelometry. The microbes act by absorbing and scattering incident light, so the absorbance (turbidimetry) or light intensity (nephelometry) measured is directly proportional to their concentration in the medium. In this work, we developed a new analytical imaging method for determining the concentration of bacterial cells in liquid media. Digital images of a series of McFarland standards are used to assign turbidity-based colour values with the aid of dedicated software. Such values are proportional to bacterial concentrations, which allow a calibration curve to be readily constructed. This paper assesses the calibration reproducibility of an intra-laboratory study and compares the turbidimetric and nephelometric results with those provided by the proposed method, which is relatively simple and affordable; in fact, it can be implemented with a digital camera and the public domain software ImageJ.

Theoretical prediction of the native fluorescence of pharmaceuticals.

At present, to search fluorescent compounds or to increase the native fluorescence is an active research line specially and not only with analytical purposes. On some analytical areas and from the early times of applications of fluorescence (mid-fifties) the fluorimeter was defined as the suitable detector for determination of pharmaceuticals and subsequently, this detection mode has been widely applied. Therefore, it is mandatory to develop new strategies to discover or to enhance in a simple way the native fluorescence of organic compounds to increase the number of analytes to be determined by direct fluorescence. In the present paper are studied further applications of a new tool suitable to increase the research in analytical field. Calculations on molecular connectivity and discriminant analysis are applied to a certain number of pharmaceuticals (and some pesticides) on which fluorescence behaviour was observed in an experimental screening or obtained from scientific literature. The screening tests were based on the on-line fluorimetric measurement by using a continuous-flow assembly. The screening comprised pre-selected compounds with different molecular structures. The theoretical predictions agree with the empirical results from the screening test.

A tandem-flow assembly for the chemiluminometric determination of hydroquinone.

A direct chemiluminescent procedure for determination of hydroquinone based on the emergent flow methodology known as multicommutation or tandem-flow is presented for first time. The manifold was based on a set of three channels and three solenoid valves; and, the determination was performed at 60 degrees C and at flow-rate of 7.5mlmin(-1). The complete cycle lasted 35s, which resulted in a sample flow trough of 103h(-1). The chemical process was the hydroquinone oxidation with the system sulphuric acid-potassium permanganate; and the light emission was clearly enhanced by the presence of quinine sulphate and benzalkonium chloride reaching a detection limit of 30mugl(-1). The dynamic interval was over the range 0.1-15.0mgl(-1) and a large list of interferents were assayed; the chemical robustness was also tested. The method was applied to different type of samples: namely, pharmaceutical formulations, a photographic solution and irrigation and residual superficial waters.

Determination of tyrosine through a FIA-direct chemiluminescence procedure.

A new FI-direct chemiluminescence method is proposed for the determination of tyrosine, based on the oxidation of the amino acid by K(3)Fe(CN)(6) in potassium hydroxide medium, at room temperature and enhanced by the presence of beta-cyclodextrin and formic acid. The dynamic range was linear over the range 1.0-10.0 mgl(-1). A large study of the influence of foreign compounds was performed, including amino acids; and, the method showed high selectivity. The reproducibility between days resulted in a rsd (in slope%) of 4.8 and the repeatability with a rsd (n=50, 10.0 mgl(-1)) of 3.1%, the LOD (s/n=3) was 50 mugl(-1) and sample throughput 98 h(-1).

Prediction of the chemiluminescent behaviour of phenols and polyphenols.

A paper from this laboratory 'J. Anal. Chem. 73 (2001) 4301' was recently published and dealing with the first attempt to apply molecular connectivity calculations to predict a chemical property with analytical usefulness; namely, the chemiluminescent behaviour of substances when react with common strong oxidants in liquid phase. In the present work, the usefulness of molecular topology on the search for new chemiluminescent compounds is clearly demonstrated. The proposed discriminant equation, represented a success of 92.7% in the prediction. The present paper is the further step from the cited paper; it is dealing on the application of molecular connectivity calculations (former discriminant equation 'J. Anal. Chem. 73 (2001) 4301') to predict the chemiluminescent behaviour of phenols and polyphenols when they react with common oxidants in liquid phase. A number of phenols and polyphenols (close to 100) were theoretically studied by means of the discriminant equation 'J. Anal. Chem. 73 (2001) 4301', being some of them predicted as chemiluminescent with a high probability. These theoretical predictions have been empirically checked through a continuous flow manifold. A number of 33 compounds, selected between those which chemiluminescent behaviour was predicted, were assayed. A success of 100% over the theoretical predictions was obtained.

Determination of tannic acid by direct chemiluminescence in a FIA assembly.

The determination of tannic acid is performed in a FIA assembly on the basis of the analytical output obtained by oxidation of the acid. The analyte solution was daily prepared in a mixture of quinine as sensitiser and perchloric acid and it was injected into a pure water stream acting as a carrier. This solution merges with the mixture potassium permanganate in perchloric medium and the resulting chemiluminescence is monitored. The method was applied over the range 0.5-20 mg l(-1) of tannic acid with a LOD 100 mug l(-1). The reproducibility was 2.1% and the sample throughput 54 h(-1). The influence of foreign substances was studied and the new method is applied to the determination of tannic acid in pharmaceutical and galenic formulations in human urine and surface waters.

Prediction of the chemiluminescent behavior of pharmaceuticals and pesticides.

The present paper deals with the first attempt to apply molecular connectivity calculations to predict a chemical property with analytical usefulness: the chemiluminescent behavior of substances when reacted with common oxidants in a liquid phase. Preliminary evidence when searching for new direct CL methods consisted of the examination of analyte reaction with a wide range of oxidants and media. This task, which results in time-consuming and trial-and-error expensive procedures, is necessary due to ensure empirical or theoretical rules for CL prediction are available. On the other hand, in quantitative structure-activity relationship studies, molecular connectivity is a topological method capable of describing the structure of a molecule by means of numbers named indices; subsequent regression in relation to the experimental values of the physical, chemical, or biological properties yields a series of functions called connectivity functions. Discriminant analysis was applied to 200 either chemiluminescent or nonchemiluminescent substances found either bibliographically or in an experimental screening. The method used for the selection of descriptors was a stepwise linear discriminant analysis from the Snedecor F-parameter. The classification criterion used was the minimum value of Mahalanobis. The quality of the discriminant function was calculated through the Wilks U-statistical parameter. Finally, the function was applied to a database including of more than 50,000 structurally heterogeneous compounds. The theoretical predictions were faced with the empirical evidence obtained through a continuous-flow manifold.

Inhibition of the system luminol-H2O2-Fe(CN)6(3)-chemiluminescence by the Mn(II) indirect determination of isoniazid in a pharmaceutical formulation.

A flow injection procedure for the indirect chemiluminescent determination of isoniazid is proposed. The method is performed in a flow-injection manifold provided with a solid-phase reactor. The reactor was made from manganese dioxide physically entrapped by polymerization; the redox reaction isoniazid-manganese dioxide released Mn(II) which was monitored through its inhibitory effect on the reaction between luminol and hydrogen peroxide in presence of potassium hexacyanoferrate (III). The procedure resulted in a linear calibration graph over the range 5-15 mg/L of isoniazid with a sample throughput of 43 samples/h. The influence of foreign compounds was studied and the method was applied to determination of the drug in a pharmaceutical formulation.

Solid-phase reactors as high stability reagent sources in flow analysis: selective flow injection spectrophotometric determination of cysteine in pharmaceutical formulations.

The flow injection spectrophotometric determination of cysteine was carried out by reaction with cobalt(II) ions entrapped in a polymeric material and filling a packed-bed reactor; the released cobalt(II) complexed with the amino acid was monitored at 360 nm. The method worked with a high repeatability, even with independent reactors, days and solutions. Selectivity of the procedure was tested with twenty different foreign compounds found in pharmaceutical formulations containing cysteine, parent amino acids included; no serious interferences were observed. The calibration graph for cysteine was linear over the range 1-90 micrograms ml-1 with a relative standard deviation of 0.8% at 60 micrograms ml-1 (n = 158). The calculated sample throughput was 90 h-1. The method was applied to determine the content of cysteine in pharmaceutical formulations.