Flow injection visible diffuse reflectance quantitative analysis of total sulfur in biodiesel, in plant leaves and in natural waters

Flow injection (FI) methodology, using diffuse reflectance in the visible region of the spectrum, for the analysis of total sulfur in the form of sulfate, precipitated in the form of barium sulfate, is presented. The method was applied to biodiesel, to plant leaves and to natural waters analysis. The analytical signal (S) correlates linearly with sulfate concentration (C) between 20 and 120 ppm, through the equation S=-1.138+0.0934 C (r = 0.9993). The experimentally observed limit of detection is about 10 ppm. The mean R.S.D. is about 3.0 %. Real samples containing sulfate were analyzed and the results obtained by the FI and by the reference batch turbidimetric method using the statistical Student's t-test and F-test were compared.

Flow-batch analyser for preparation of calibration standard mixtures in simultaneous multicomponent spectrometric analysis

The application of multivariate calibration techniques to multicomponent analysis by UV-VIS molecular absorption spectrometry is a powerful tool for simultaneous determination of several chemical species. However, when this methodology is accomplished manually, it is slow and laborious, consumes high amounts of reagents and samples, is susceptible to contaminations and presents a high operational cost. To overcome these drawbacks, a flow-batch analyser is proposed in this work. This analyser was developed for automatic preparation of standard calibration and test (or validation) mixtures. It was applied to the simultaneous determination of Cu2+, Mn2+ and Zn2+ in polyvitaminic and polymineral pharmaceutical formulations, using 4-(2-piridilazo) resorcinol as reagent and a UV-VIS spectrophotometer with a photodiode array detector. The results obtained with the proposed system are in good agreement with those obtained by flame atomic absorption spectrometry, which was employed as reference method. With the proposed analyser, the preparation of calibration and test mixtures can be accomplished about four hours, while the manual procedure requires at least two days. Moreover, it consumes smaller amounts of reagents and samples than the manual procedure. After the preparation of calibration and test mixtures, 60 samples h-1 can be carried out with the proposed flow-batch analyser.

Spectrophotometric flow injection system for determination of Zn2+ in ophthalmic formulations using Alizarin red S

A spectrophotometric flow injection method for the determination of Zn(II) in ophthalmic formulations was developed. In this work, Zn(II) ion was complexed with Alizarin red S in borate buffer solution (pH 9.0) and the chromophore produced was monitored at 520 nm. The analytical curve was linear in the Zn(II) concentration range from 6.05 x 10-6 to 1.50 x 10-4 mol L-1 with a detection limit of 3.60 x 10-6 mol L-1. Recoveries ranged from 96.3 to 105 % and a relative standard deviation of 1.2 % (n = 10) for 5.5x10-5 mol L-1 Zn(II) reference solution were obtained. The sampling rate was 60 h-1 and the results obtained of Zn(II) in ophthalmic products using this procedure are in close agreement with those obtained using a comparative spectrophotometric procedure at 95 % confidence level.

Estimation of transpiration of the 'Valencia' orange young plant using thermal dissipation probe method

Most studies on measures of transpiration of plants, especially woody fruit, relies on methods of heat supply in the trunk. This study aimed to calibrate the Thermal Dissipation Probe Method (TDP) to estimate the transpiration, study the effects of natural thermal gradients and determine the relation between outside diameter and area of xylem in 'Valencia' orange young plants. TDP were installed in 40 orange plants of 15 months old, planted in boxes of 500 L, in a greenhouse. It was tested the correction of the natural thermal differences (DTN) for the estimation based on two unheated probes. The area of the conductive section was related to the outside diameter of the stem by means of polynomial regression. The equation for estimation of sap flow was calibrated having as standard lysimeter measures of a representative plant. The angular coefficient of the equation for estimating sap flow was adjusted by minimizing the absolute deviation between the sap flow and daily transpiration measured by lysimeter. Based on these results, it was concluded that the method of TDP, adjusting the original calibration and correction of the DTN, was effective in transpiration assessment.

Air flow humidification for air-assisted boom sprayer

The air-assisted ground spray is fairly widespread. However, due to the unpredictable weather conditions, the operational efficiency is impaired by stops on grounds of low humidity and high temperatures. The aim of this work was to assess an air humidification method and evaluate its impact on temperature and air humidity for the air curtain of the air-assisted sprayer. With respect to relative air humidity, it has increased in 6.59%, being the maximum change when inserting 1.92 L min-1. So, it is concluded that the pipeline humidification might significantly reduce temperature and enhance air humidity. The treatments performed in this study consisted of a varied flow of a humidity device, related to weather conditions. Temperature and relative air humidity were measured at 1.0 m height from right to left of middle point of the machine, corresponding to the end of the spray boom, in the middle and end of right spray boom. The readings were also performed at three different distances from the end of the pipeline and at 0.25 and 0.50 m from that to the soil. The results show that 0.48 L min-1 in the humidification system has promoted a better efficiency in reducing air-temperature, on average 2.52 ºC when compared to the non-humidified one.

Low-flow estimates in regions of extrapolation of the regionalization equations: a new concept

ABSTRACT Knowledge of natural water availability, which is characterized by low flows, is essential for planning and management of water resources. One of the most widely used hydrological techniques to determine streamflow is regionalization, but the extrapolation of regionalization equations beyond the limits of sample data is not recommended. This paper proposes a new method for reducing overestimation errors associated with the extrapolation of regionalization equations for low flows. The method is based on the use of a threshold value for the maximum specific low flow discharge estimated at the gauging sites that are used in the regionalization. When a specific low flow, which has been estimated using the regionalization equation, exceeds the threshold value, the low flow can be obtained by multiplying the drainage area by the threshold value. This restriction imposes a physical limit to the low flow, which reduces the error of overestimating flows in regions of extrapolation. A case study was done in the Urucuia river basin, in Brazil, and the results showed the regionalization equation to perform positively in reducing the risk of extrapolation.

Salivary and serum cortisol levels, salivary alpha-amylase and unstimulated whole saliva flow rate in pregnant and non-pregnant

PURPOSE: To compare salivary and serum cortisol levels, salivary alpha-amylase (sAA), and unstimulated whole saliva (UWS) flow rate in pregnant and non-pregnant women. METHOD: A longitudinal study was conducted at a health promotion center of a university hospital. Nine pregnant and 12 non-pregnant women participated in the study. Serum and UWS were collected and analyzed every trimester and twice a month during the menstrual cycle. The salivary and serum cortisol levels were determined by chemiluminescence assay and the sAA was processed in an automated biochemistry analyzer. RESULTS: Significant differences between the pregnant and non-pregnant groups were found in median [interquartile range] levels of serum cortisol (23.8 µL/dL [19.4-29.4] versus 12.3 [9.6-16.8], p<0.001) and sAA (56.7 U/L [30.9-82.2] versus 31.8 [18.1-53.2], p<0.001). Differences in salivary and serum cortisol (µL/dL) and sAA levels in the follicular versus luteal phase were observed (p<0.001). Median UWS flow rates were similar in pregnant (0.26 [0.15-0.30] mL/min) and non-pregnant subjects (0.23 [0.20-0.32] mL/min). Significant correlations were found between salivary and serum cortisol (p=0.02) and between salivary cortisol and sAA (p=0.01). CONCLUSIONS: Serum cortisol and sAA levels are increased during pregnancy. During the luteal phase of the ovarian cycle, salivary cortisol levels increase, whereas serum cortisol and sAA levels decline.

On the development of an unstructured grid solver for inert and reactive high speed flow simulations

An unstructured grid Euler solver for reactive compressible flow applications is presented. The method is implemented in a cell centered, finite volume context for unstructured triangular grids. Three different schemes for spatial discretization are implemented and analyzed. Time march is implemented in a time-split fashion with independent integrators for the flow and chemistry equations. The capability implemented is tested for inert flows in a hypersonic inlet and for inert and reactive supersonic flows over a 2-D wedge. The results of the different schemes are compared with each other and with independent calculations using a structured grid code. The strengths and the possible weaknesses of the proposed methods are discussed.

A high frequency electronic transducer for multiphase flow measurements

This paper describes an electronic transducer for multiphase flow measurement. Its high sensitivity, good signal to noise ratio and accuracy are achieved through an electrical impedance sensor with a special guard technique. The transducer consists of a wide bandwidth and high slew rate differentiator where the lead inductance and stray capacitance effects are compensated. The sensor edge effect is eliminated by using a guard electrode based on the virtual ground potential of the operational amplifier. A theoretical modeling and a calibration method are also presented. The results obtained seem to confirm the validity of the proposed technique.

Application of the finite element method in cold forging processes

The demand for more efficient manufacturing processes has been increasing in the last few years. The cold forging process is presented as a possible solution, because it allows the production of parts with a good surface finish and with good mechanical properties. Nevertheless, the cold forming sequence design is very empirical and it is based on the designer experience. The computational modeling of each forming process stage by the finite element method can make the sequence design faster and more efficient, decreasing the use of conventional "trial and error" methods. In this study, the application of a commercial general finite element software - ANSYS - has been applied to model a forming operation. Models have been developed to simulate the ring compression test and to simulate a basic forming operation (upsetting) that is applied in most of the cold forging parts sequences. The simulated upsetting operation is one stage of the automotive starter parts manufacturing process. Experiments have been done to obtain the stress-strain material curve, the material flow during the simulated stage, and the required forming force. These experiments provided results used as numerical model input data and as validation of model results. The comparison between experiments and numerical results confirms the developed methodology potential on die filling prediction.

Direct Simulation Monte Carlo Method Applied to Aerothermodynamics

An axisymmetric supersonic flow of rarefied gas past a finite cylinder was calculated applying the direct simulation Monte Carlo method. The drag force, the coefficients of pressure, of skin friction, and of heat transfer, the fields of density, of temperature, and of velocity were calculated as function of the Reynolds number for a fixed Mach number. The variation of the Reynolds number is related to the variation of the Knudsen number, which characterizes the gas rarefaction. The present results show that all quantities in the transition regime (Knudsen number is about the unity) are significantly different from those in the hydrodynamic regime, when the Knudsen number is small.

Validation of transit-time flowmetry for chronic measurements of regional blood flow in resting and exercising rats

The objective of the present study was to validate the transit-time technique for long-term measurements of iliac and renal blood flow in rats. Flow measured with ultrasonic probes was confirmed ex vivo using excised arteries perfused at varying flow rates. An implanted 1-mm probe reproduced with accuracy different patterns of flow relative to pressure in freely moving rats and accurately quantitated the resting iliac flow value (on average 10.43 ± 0.99 ml/min or 2.78 ± 0.3 ml min-1 100 g body weight-1). The measurements were stable over an experimental period of one week but were affected by probe size (resting flows were underestimated by 57% with a 2-mm probe when compared with a 1-mm probe) and by anesthesia (in the same rats, iliac flow was reduced by 50-60% when compared to the conscious state). Instantaneous changes of iliac and renal flow during exercise and recovery were accurately measured by the transit-time technique. Iliac flow increased instantaneously at the beginning of mild exercise (from 12.03 ± 1.06 to 25.55 ± 3.89 ml/min at 15 s) and showed a smaller increase when exercise intensity increased further, reaching a plateau of 38.43 ± 1.92 ml/min at the 4th min of moderate exercise intensity. In contrast, exercise-induced reduction of renal flow was smaller and slower, with 18% and 25% decreases at mild and moderate exercise intensities. Our data indicate that transit-time flowmetry is a reliable method for long-term and continuous measurements of regional blood flow at rest and can be used to quantitate the dynamic flow changes that characterize exercise and recovery

A simple HPLC-fluorescence method for the measurement of R,S-sotalol in the plasma of patients with life-threatening cardiac arrhythmias

R,S-sotalol, a ß-blocker drug with class III antiarrhythmic properties, is prescribed to patients with ventricular, atrial and supraventricular arrhythmias. A simple and sensitive method based on HPLC-fluorescence is described for the quantification of R,S-sotalol racemate in 500 µl of plasma. R,S-sotalol and its internal standard (atenolol) were eluted after 5.9 and 8.5 min, respectively, from a 4-micron C18 reverse-phase column using a mobile phase consisting of 80 mM KH2PO4, pH 4.6, and acetonitrile (95:5, v/v) at a flow rate of 0.5 ml/min with detection at lex = 235 nm and lem = 310 nm, respectively. This method, validated on the basis of R,S-sotalol measurements in spiked blank plasma, presented 20 ng/ml sensitivity, 20-10,000 ng/ml linearity, and 2.9 and 4.8% intra- and interassay precision, respectively. Plasma sotalol concentrations were determined by applying this method to investigate five high-risk patients with atrial fibrillation admitted to the Emergency Service of the Medical School Hospital, who received sotalol, 160 mg po, as loading dose. Blood samples were collected from a peripheral vein at zero, 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 6.0, 8.0, 12.0 and 24.0 h after drug administration. A two-compartment open model was applied. Data obtained, expressed as mean, were: CMAX = 1230 ng/ml, TMAX = 1.8 h, AUCT = 10645 ng h-1 ml-1, Kab = 1.23 h-1, a = 0.95 h-1, ß = 0.09 h-1, t(1/2)ß = 7.8 h, ClT/F = 3.94 ml min-1 kg-1, and Vd/F = 2.53 l/kg. A good systemic availability and a fast absorption were obtained. Drug distribution was reduced to the same extent in terms of total body clearance when patients and healthy volunteers were compared, and consequently elimination half-life remained unchanged. Thus, the method described in the present study is useful for therapeutic drug monitoring purposes, pharmacokinetic investigation and pharmacokinetic-pharmacodynamic sotalol studies in patients with tachyarrhythmias.

The modified 2VO ischemia protocol causes cognitive impairment similar to that induced by the standard method, but with a better survival rate

Permanent bilateral occlusion of the common carotid arteries (2VO) in the rat has been established as a valid experimental model to investigate the effects of chronic cerebral hypoperfusion on cognitive function and neurodegenerative processes. Our aim was to compare the cognitive and morphological outcomes following the standard 2VO procedure, in which there is concomitant artery ligation, with those of a modified protocol, with a 1-week interval between artery occlusions to avoid an abrupt reduction of cerebral blood flow, as assessed by animal performance in the water maze and damage extension to the hippocampus and striatum. Male Wistar rats (N = 47) aged 3 months were subjected to chronic hypoperfusion by permanent bilateral ligation of the common carotid arteries using either the standard or the modified protocol, with the right carotid being the first to be occluded. Three months after the surgical procedure, rat performance in the water maze was assessed to investigate long-term effects on spatial learning and memory and their brains were processed in order to estimate hippocampal volume and striatal area. Both groups of hypoperfused rats showed deficits in reference (F(8,172) = 7.0951, P < 0.00001) and working spatial memory [2nd (F(2,44) = 7.6884, P < 0.001), 3rd (F(2,44) = 21.481, P < 0.00001) and 4th trials (F(2,44) = 28.620, P < 0.0001)]; however, no evidence of tissue atrophy was found in the brain structures studied. Despite similar behavioral and morphological outcomes, the rats submitted to the modified protocol showed a significant increase in survival rate, during the 3 months of the experiment (P < 0.02).

An HPLC-UV method for the measurement of permeability of marker drugs in the Caco-2 cell assay

The Caco-2 cell line has been used as a model to predict the in vitro permeability of the human intestinal barrier. The predictive potential of the assay relies on an appropriate in-house validation of the method. The objective of the present study was to develop a single HPLC-UV method for the identification and quantitation of marker drugs and to determine the suitability of the Caco-2 cell permeability assay. A simple chromatographic method was developed for the simultaneous determination of both passively (propranolol, carbamazepine, acyclovir, and hydrochlorothiazide) and actively transported drugs (vinblastine and verapamil). Separation was achieved on a C18 column with step-gradient elution (acetonitrile and aqueous solution of ammonium acetate, pH 3.0) at a flow rate of 1.0 mL/min and UV detection at 275 nm during the total run time of 35 min. The method was validated and found to be specific, linear, precise, and accurate. This chromatographic system can be readily used on a routine basis and its utilization can be extended to other permeability models. The results obtained in the Caco-2 bi-directional transport experiments confirmed the validity of the assay, given that high and low permeability profiles were identified, and P-glycoprotein functionality was established.