On-site calibration of a phase fraction meter by an inverse technique

The formal calibration procedure of a phase fraction meter is based on registering the outputs resulting from imposed phase fractions at known flow regimes. This can be straightforwardly done in laboratory conditions, but is rarely the case in industrial conditions, and particularly for on-site applications. Thus, there is a clear need for less restrictive calibration methods regarding to the prior knowledge of the complete set of inlet conditions. A new procedure is proposed in this work for the on-site construction of the calibration curve from total flown mass values of the homogeneous dispersed phase. The solution is obtained by minimizing a convenient error functional, assembled with data from redundant tests to handle the intrinsic ill-conditioned nature of the problem. Numerical simulations performed for increasing error levels demonstrate that acceptable calibration curves can be reconstructed, even from total mass measured within a precision of up to 2%. Consequently, the method can readily be applied, especially in on-site calibration problems in which classical procedures fail due to the impossibility of having a strict control of all the input/output parameters.

A dose-response curve for biodosimetry from a 6 MV electron linear accelerator

Biological dosimetry (biodosimetry) is based on the investigation of radiation-induced biological effects (biomarkers), mainly dicentric chromosomes, in order to correlate them with radiation dose. To interpret the dicentric score in terms of absorbed dose, a calibration curve is needed. Each curve should be constructed with respect to basic physical parameters, such as the type of ionizing radiation characterized by low or high linear energy transfer (LET) and dose rate. This study was designed to obtain dose calibration curves by scoring of dicentric chromosomes in peripheral blood lymphocytes irradiated in vitro with a 6 MV electron linear accelerator (Mevatron M, Siemens, USA). Two software programs, CABAS (Chromosomal Aberration Calculation Software) and Dose Estimate, were used to generate the curve. The two software programs are discussed; the results obtained were compared with each other and with other published low LET radiation curves. Both software programs resulted in identical linear and quadratic terms for the curve presented here, which was in good agreement with published curves for similar radiation quality and dose rates.

Determinação de paracetamol em produtos farmacêuticos usando um biossensor de pasta de carbono modificado com extrato bruto de abobrinha (Cucurbita pepo)

Crude extracts of several vegetables such as peach (Prunus persica), yam (Alocasia macrorhiza), manioc (Manihot utilissima), artichoke (Cynara scolymus L), sweet potato (Ipomoea batatas (L.) Lam.), turnip (Brassica campestre ssp. rapifera), horseradish (Armoracia rusticana) and zucchini (Cucurbita pepo) were investigated as the source of peroxidase (POD: EC 1.11.1.7). Among those, zucchini (Cucurbita pepo) crude extract was found to be the best one. This enzyme in the presence of hydrogen peroxide catalyses the oxidation of paracetamol to N-acetyl-p-benzoquinoneimine which the electrochemical reduction back to paracetamol was obtained at a peak potential of ¾0.10V. A cyclic voltammetric study was performed by scanning the potential from + 0.5 to ¾ 0.5 V. The recovery of paracetamol from two samples ranged from 97.3 to 106% and a rectilinear calibration curve for paracetamol concentration from 1.2x10-4 to 2.5x10-3 mol L-1 (r=0.9965) were obtained. The detection limit was 6.9x10-5 mol L-1 and the relative standard deviation was less than 1.1% for a solution containing 2.5x10-3 mol L-1 paracetamol and 2.0x10-3 mol L-1 hydrogen peroxide (n=12). The results obtained for paracetamol in pharmaceutical products using the proposed biosensor and Pharmacopoeial procedures are in agreement at the 95% confidence level.

Automated flow-injection method for cadmium determination with pre-concentration and reagent preparation on-line

The spectrophotometric determination of Cd(II) using a flow injection system provided with a solid-phase reactor for cadmium preconcentration and on-line reagent preparation, is described. It is based on the formation of a dithizone-Cd complex in basic medium. The calibration curve is linear between 6 and 300 µg L-1 Cd(II), with a detection limit of 5.4 µg L-1, an RSD of 3.7% (10 replicates in duplicate) and a sample frequency of 11.4 h-1. The proposed method was satisfactorily applied to the determination of Cd(II) in surface, well and drinking waters.

Determinação de zinco em solo utilizando colorimetria

In terms of soil fertility, zinc is a micronutrient that is very important in the culture of soy, maize, rice and coffee, because it is a structural and functional component of a great number of enzymes. Therefore, diverse methods have been used to determine zinc in soil. In this work we use colorimetry as a methods of zinc determination in soil using two methodologies of sample digesting, H2SO4/H2O2 and HNO3/H2O2. In order to compare the results, atomic absorption spectrometry (AAS) was used. Results show that colorimetric methods can be used due to good sensitivity and reproducibility, since the zinc calibration curve showed good linearity. Comparing colorimetric methods with AAS we observed that the results were equivalent, as proven by the statistical values of the F and t of Student tests. Furthermore, both methods of soil digesting can be used, leading to a flexible methodology of low-cost for routine zinc analyses in soil.

Electrooxidación de glifosato sobre electrodos de níquel y cobre

The electrochemical oxidation of glyphosate on an electrode of nickel and on one of copper was studied. With both electrodes electrochemical signals related to the glyphosate concentration were observed. However, the behaviour of the copper electrode was much better than that of the nickel electrode. A calibration curve was obtained of the electrical signal of this electrode as a function of the glyphosate concentration. The detection limit was 30 µM. In the case of nickel, an increase in the oxidation signal, which is related to the glyphosate concentration, was obtained. However, the results were less reproducible and additional information is necessary to propose an interaction mechanism between glyphosate and the electrode.

Determinação de metil-etil-cetona em amostras de urina com amostragem por micro extração em fase sólida (MEFS) em headspace associada à cromatografia gasosa com detector de ionização de chama (CG-DIC)

Methyl ethyl ketone (MEK) is a solvent commonly used in chemical, paint and shoe industry. The aim of this study was to develop and validate a method for urinary quantification of MEK, employing headspace solid phase micro extraction sampling (SPME) coupled to gas chromatography with flame ionization detection (GC-FID). The calibration curve (y=4.6851x-0.0011) presented good linearity with r²=0.9993. Accuracy (94-109%), intra-assay precision (4.07-5.91%) and inter-assay precision (3.03-5.62%) were acceptable. The quantification limit was 0.19 mg/L. This low cost method can be used routinely in the biological monitoring of occupational exposure to MEK, according to the requirements of the Brazilian legislation.

Determinação de ácido valpróico em soro por cromatografia líquida de alta eficiência com detector de arranjo de diodos (CLAE-DAD), após derivatização com brometo de fenacila

Valproic acid (VA) is a drug used to control seizures in several epileptic conditions. In VA pharmacotherapy, therapeutic drug monitoring is recommended to obtain adequate seizure control and avoid toxicity. The aim of this study was to validate a method for the determination of valproic acid in serum, employing high performance liquid chromatography with diode array detection (HPLC-DAD), after derivatization with phenacyl bromide. The calibration curve (y=0.0133x-0.0025) presented good linearity with r²=0.9999. Accuracy (101-115%), intra-assay precision (4.53-8.15%) and inter-assay precision (3.15-6.77%) were acceptable. The quantification limit was 2.0 µg/mL. The method presented similar results to enzyme immunoassay.

Determinação de olanzapina em formulações farmacêuticas por espectrofotometria: desenvolvimento e validação

Spectrophotometric methods of zero order, first and second derived order had been developed for olanzapine determination in tablets using ethanol and isopropanol as solvent. The two solvents revealed to be adequate. For the three methods the calibration curve coefficient of correlation had been greater than 0.9998 with limit of detection varying from 0.068 to 0.190 mg L-1, in ethanol, and 0.026 to 0.205 mg L-1, in isopropanol. The inter-day precision was inferior to 1.1 and 1.9 mg L-1 for ethanol and isopropanol, respectively. The average recoveries varied from 98 to 101%, in ethanol and 99 to 103% in isopropanol.

Projeto e construção de um picnômetro a ar para caracterização de insumos e produtos farmacêuticos

This paper describes a project, construction and test of a low cost air pycnometer, developed to be used preferentially in pharmaceutical research. A complete discussion of the construction, test and calibration of this equipment is presented and some measurements are made using pharmaceutical powders and dry granulations. The equipment performance has been estimated through its calibration curve, and the obtained value to its volume resolution is about 1%. This equipment is accomplished at the Applied Nuclear Physics Laboratory of University of Sorocaba (LAFINAU) in Sorocaba, SP, Brazil and it was denominated "Picnômetro a Ar Uniso - PICNAU".

Ion pair-dispersive liquid-liquid microextraction of trace amount of rhodium ion in water and road dust samples prior to flame atomic absorption spectrometry determination

A simple ion pair-dispersive liquid-liquid microextraction method was proposed for preconcentration trace amounts of rhodium. An ion association complex of RhCl4- and tetradecyldimetylbenzylamonium was extracted into cholorobenzene. The volume and the type of extractive and dispersive solvents, the extraction time and the pH of the aqueous solutions were optimized. The calibration curve was linear in the range of 0.6-500 ng mL-1 of rhodium. The limit of detection was 0.10 ng mL-1 in initial solution and preconcentration factor was 40. The proposed method was successfully applied to the extraction and determination of rhodium in road dust and water samples.

Extração de ácido trans-trans mucônico urinário com polímeros de impressão molecular e análise por cromatografia gasosa: espectrometria de massas

This paper describes selective molecularly imprinted solid-phase extraction of ttMA from urine samples followed by derivatization and analysis by gas chromatography/mass spectrometry (GC/MS). The analytical calibration curve ranged from 0.3 to 7.0 mg L-1 (r = 0.999) and the limit of quantitation (LOQ) was 0.3 mg L-1. The method was applied for the determination of ttMA in urine samples from smokers and concentrations detected ranged from < LOQ to 1.64 mg L-1. Thus, the proposed method proved adequate for the determination of urinary ttMA in the biomonitoring of occupational exposure to low levels of benzene.

Determinação espectrofotométrica de cloreto em cimento após preparo de amostra por piroidrólise

A method based on pyrohydrolysis was proposed for cement sample preparation and further chloride determination by spectrophotometry using flow injection analysis. Analytical parameters were evaluated and, under the selected conditions, the calibration curve was linear in the range of 0.2 to 10.0 µg mL-1 with r2 = 0.998. The limit of detection was5 µg g-1 of chloride and the relative standard deviation was less than 7%. The proposed pyrohydrolysis method is relatively simple and can be used for sample preparation for further spectrophotometric determination of low concentrations of chloride in cement.

A reliable method of quantification of trace copper in beverages with and without alcohol by spectrophotometry after cloud point extraction

A new cloud point extraction (CPE) method was developed for the separation and preconcentration of copper (II) prior to spectrophotometric analysis. For this purpose, 1-(2,4-dimethylphenyl) azonapthalen-2-ol (Sudan II) was used as a chelating agent and the solution pH was adjusted to 10.0 with borate buffer. Polyethylene glycol tert-octylphenyl ether (Triton X-114) was used as an extracting agent in the presence of sodium dodecylsulphate (SDS). After phase separation, based on the cloud point of the mixture, the surfactant-rich phase was diluted with acetone, and the enriched analyte was spectrophotometrically determined at 537 nm. The variables affecting CPE efficiency were optimized. The calibration curve was linear within the range 0.285-20 µg L-1 with a detection limit of 0.085 µg L-1. The method was successfully applied to the quantification of copper in different beverage samples.

Registrador portátil de odorantes basado en la modulación de temperatura de un sensor mos comercial

A simple, portable and low-cost system for odor detection was developed using a single MOS commercial sensor and a microcontroller. The temperature modulation technique was implemented applying a DC signal pulse to the sensor heater by a bipolar transistor. Two odorant profiles, ethanol and acetic acid vapors, were obtained and distinguished based on their amplitude versus time responses. Response for acetic acid was not reported by the sensor manufacturer. An ethanol vapor calibration curve was also obtained. Experimental data showed a potential behavior according to the theoretical equation of the MOS sensors. Values of logK=0.457 and α=-0.213 for a 95% confidence level were obtained.