Matthieu Tubino

A simple device for quantitative colorimetric diffuse reflectance measurements

Abstract A very simple and low cost reflectometer, for colorimetric diffuse reflectance measurements is described. The proposed instrument uses a light dependent resistor (LDR), as a sensor, and a light emitter diode (LED), as light source. The performance of the device was compared with that of a commercial instrument, measuring the reflectance of the Pantone® Process Black Uncoated Palette. The quantitative analysis of nickel, in a catalyst, using dimethylglyoxime as colorimetric reagent, was also used to test the device. The observed precision was about 6% (R.S.D.). These results were compared with those obtained by the gravimetric method using the same reaction, through the statistical Student’s t-test procedure. A complete agreement was observed. The good quality of all the obtained results allows the recommendation of the instrument for diffuse reflectance measurements including quantitative analytical procedures.

Quantitative spot tests of Fe(III), Cr(VI) and Ni(II) by reflectance measurements

ABSTRACT This work shows that diffuse reflectance measurements, using fiber optical devices, can give rapid quantitative results for application with spot tests determination where little sample manipulation is a desirable feature. The experiments were performed with a Hewlett Packard diode array spectrophotometer HP8452A and a Labsphere RSA-HP-84 reflectance accessory. The quantitative reflectance measurements of different complexes such as Fe (III) with thiocyanate, Cr (VI) with diphenylcarbazide and Ni (II) with dimethylglyoxime could be obtained by forming the complexes on filter paper. Calibration curves were obtained for each metal by plotting the optical density of the reflectance signal (AR) vs. the log of the mol/dm3 concentration, from 1.5 × 103 to 3.6 × 102mol/dm3 for Fe (III), from 8.00 × 10−5 to 2.00 × 103 mol/dm3 for Cr (VI) and from 1.00 × 103 to 8.00 × 102 mol dm3 for Ni (II), with correlation coefficients of 0.9986 for Fe (III), 0.9878 for Cr (VI) and 0.9892 for Ni (II). The results obtai...

Determination of sodium, potassium, calcium and magnesium cations in biodiesel by ion chromatography

This work reports an ion chromatographic (IC) method for the quantitative determination of inorganic cations (Na(+), K(+), Mg(2+) and Ca(2+)) in biodiesel samples that were synthesized from different vegetable oils and fat. The proposed method uses water extraction, heating and ultrasound. The limits of detection (LOD) for each ion, in milligrams of the analyte per kilogram of biodiesel (mgkg(-1)), were respectively: 0.11 (Na(+)); 0.42 (K(+)); 0.23 (Ca(2+)); and 0.36 (Mg(2+)). The accuracy of the method was studied through recovery tests. For comparison, two samples were also analyzed using an Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) procedure. The paired Student t test and the Snedecor F test showed that both methods offer equivalent results in terms of accuracy and precision. The operational simplicity, accuracy and precision of the proposed method suggest that it can be a good alternative for the determination of inorganic cations in biodiesel samples.

Determination of diclofenac in pharmaceutical preparations by diffuse reflectance photometry

A quantitative analytical method for the determination of diclofenac in pharmaceutical preparations by diffuse reflectance in the visible region of the spectrum is presented. The color reaction is done directly in the measuring cell immediately after mixing, using small volumes of the analyte solution, of the reagent and of the buffer solutions. All reflectance measurements were carried out in a home made reflectometer equipped with a red LED as light source and a LDR as detector. The calibration curves were constructed from 1.0 to 18 mg mL(-1) (about 3.0 x 10(-3) to 5.5 x 10(-2)mol L(-1)) of sodium diclofenac or of potassium diclofenac in the analytical solution, with typical correlation coefficients equal to 0.999. The detection limit was estimated to be about 0.7 mg mL(-1) (2 x 10(-3)mol L(-1)). The method was applied to determine diclofenac in solid and liquid pharmaceutical preparations. The R.S.D. varied from 2% to 4% depending of the sample. The results were compared with those obtained with the HPLC procedure recommended by the United States Pharmacopoeia using the statistical Students t-test procedure.

Analytical methods for vancomycin determination in biological fluids and in pharmaceuticals

Vancomycin is a glycopeptide antibiotic employed in the treatment of infections caused by certain methicillin-resistant staphylococci. It is indicated also for patients allergic to penicillin or when there is no response to penicillins or cephalosporins. The adequate vancomycin concentration levels in blood serum lies between 5 and 10 mg/L. Higher values are toxic, causing mainly nephrotoxicity and ototoxicity. Various analytical methods are described in the literature: spectrophotometric, immunologic, biologic and chromatographic methods. This paper reviews the main analytical methods for vancomycin determination in biological fluids and in pharmaceutical preparations.

Biomimetic aqueous-core lipid nanoballoons integrating a multiple emulsion formulation: a suitable housing system for viable lytic bacteriophages.

The emergence of antibiotic-resistant bacterial strains and the weak penetration of antibiotics into bacterial biofilms put an emphasis in the need for safe and effective alternatives for antimicrobial treatments. The application of strictly lytic bacteriophages (or phages) has been proposed as an alternative (or complement) to conventional antibiotics, allowing release of the natural predators of bacteria directly to the site of infection. In the present research effort, production of bacteriophage derivatives (starting from lytic phage particle isolates), encompassing full stabilization of their three-dimensional structure, has been attempted via housing said bacteriophage particles within lipid nanovesicles integrating a multiple water-in-oil-in-water (W/O/W) emulsion. As a proof-of-concept for the aforementioned strategy, bacteriophage particles with broad lytic spectrum were entrapped within the aqueous core of lipid nanoballoons integrating a W/O/W multiple emulsion. Long-term storage of the multiple emulsions produced did not lead to leaching of phage particles, thus proving the effectiveness of the encapsulation procedure.

Kinetic Method for the Determination of α‐Methyldopa in Pharmaceutical Preparations: Analytical Procedure and Reaction Mechanism Considerations

Abstract A reliable and very simple kinetic method is proposed for the determination of α‐methyldopa in pharmaceutical preparations. It is based of the oxidation of α‐methyldopa, a catechol derivative, to quinone, by the ferric ion in the presence of salicylic acid and HCl. The deep blue complex formed between iron(III) and salicylate (λmax 525 nm) allows the reaction to be watched as absorbance decreases with the reduction of the ferric ions to ferrous with the consequent dissociation of the complex. Four pharmaceutical preparations were analyzed and the results were compared with those obtained with the spectrophotometric United States Pharmacopeia method. The statistical t‐Student and the F‐tests were applied to compare the results obtained with the two independent methods. In all cases complete agreement, in terms of accuracy and precision, was observed with a confidence level of 95% (α=0.05). Considering the four samples analyzed, using the proposed method, and five determinations for each sample, the observed mean relative standard deviation (RSD) is about 0.8%. The concentration range studied was from about 2×10−4 mol L−1 to 18×10−4 mol L−1 (about 40 µg/mL to 360 µg/mL) in the final solution and it is quite adequate for the analytical procedure at 25.0±0.1°C. A typical coefficient of determination, r2, of the calibration curve, is 0.9994. For the kinetic pseudo first order curves a typical observed r2 is 0.99998. The Arrhenius activation energy was found to be 84.2±3.4 kJ mol−1. A schematic mechanism of the reaction is proposed.

Separation of the Glycerol-Biodiesel Phases in an Ethyl Transesterification Synthetic Route Using Water

Biodiesel is obtained by the transesterification of vegetable oil (or fat) and alcohol, with methanol being the most used alcohol. Methanol can be replaced by ethanol; however, this alcohol acts as a surfactant in the reaction mixture, promoting a stable dispersion of the glycerol in biodiesel, which hinders the separation of the glycerol-biodiesel phases. In this study, it was found that the addition of 1% v/v water relative to the total volume of the reaction mixture expedites the separation of the phases by interrupting the emulsifying action of ethanol with an immediate separation of glycerol from biodiesel. The characterization of the produced biodiesels was performed using hydrogen nuclear magnetic resonance (1H NMR) and gas chromatography (GC). 1H NMR indicated a 96.9% conversion of triglycerides to biodiesel. The fatty acid compositions of the synthesized ethyl and methyl biodiesels determined using GC are essentially the same.

Development and Characterization of a Hydrogel Containing Silver Sulfadiazine for Antimicrobial Topical Applications

Development and optimization of a hydrogel with impregnated silver sulfadiazine was pursued, for antimicrobial topical applications. The selected hydrogel exhibited a homogeneous appearance, with whitish colloration and devoid of any fractures or cracks. The content in impregnated silver sulfadiazine was within established limits (1%, w/w) with a standard deviation of up to 1.28%. The hydrogel presented a good characteristic in relation to release of the active antimicrobial principle, verified through swelling tests and antimicrobial activity. The swelling tests indicated a higher increase in weight during the first 6 h of contact with a moist environment, with a maximum value of 266.00 ± 0.81, and with maintenance of the original shape of the hydrogel. The impregnated silver sulfadiazine presented antimicrobial activity, as expected, indicating a prolonged release of the drug. The infrared spectra of the hydrogel with impregnated silver sulfadiazine indicated that the drug did not engage in any bonds with the polymeric matrix, which otherwise could have reduced its antimicrobial activity. The mechanical resistance tests produced good results, indicating that the hydrogels may be utilized in different locations of the human body with skin lesions.

Structural and functional stabilization of phage particles in carbohydrate matrices for bacterial biosensing

Infections associated with health care services are nowadays widespread and, associated to the progressive emergence of microorganisms resistant to conventional chemical antibiotics, are major causes of morbidity and mortality. One of the most representative microorganisms in this scenario is the bacterium Pseudomonas aeruginosa, which alone is responsible for ca. 13-15% of all nosocomial infections. Bacteriophages have been reported as a potentially useful tool in the diagnosis of bacterial diseases, since they specifically recognize and lyse bacterial isolates thus confirming the presence of viable cells. In the present research effort, immobilization of these biological (although metabolically inert) entities was achieved via entrapment within (optimized) porous (bio)polymeric matrices of alginate and agar, aiming at their full structural and functional stabilization. Such phage-impregnated polymeric matrices are intended for future use as chromogenic hydrogels sensitive to color changes evolving from reaction with (released) intracytoplasmatic moieties, as a detection kit for P. aeruginosa cells.