Effect of Saddle height on skin temperature measured in different days of cycling.

Infrared thermography can be useful to explore the effects of exercise on neuromuscular function. During cycling, it could be used to investigate the effects of saddle height on thermoregulation. The aim of this study was to examine whether different cycling postures, elicited by different knee flexion angles, could influence skin temperature. Furthermore, we also determined whether the reproducibility of thermal measurements in response to cycling differed in the body regions affected or not affected by saddle height. Sixteen cyclists participated in three tests of 45 min of cycling at their individual 50 % peak power output. Each test was performed in a different knee flexion position on the bicycle (20°, 30°, 40° knee flexion when the pedal crank was at 180°). Different knee angles were obtained by changing saddle height. Skin temperatures were determined by infrared thermography before, immediately after and 10 min after the cycling test, in 16 different regions of interest (ROI) in the trunk and lower limbs. Changes in saddle height did not result in changes in skin temperature in the ROI. However, lower knee flexion elicited higher temperature in popliteus after cycling than higher flexion (p = 0.008 and ES = 0.8), and higher knee flexion elicited lower temperature variation in the tibialis anterior than intermediate knee flexion (p = 0.004 and ES = 0.8). Absolute temperatures obtained good and very good intraday reproducibility in the different measurements (ICCs between 0.44 and 0.85), but temperature variations showed lower reproducibility (ICCs between 0.11 and 0.74). Different postures assumed by the cyclist due to different saddle height did not influence temperature measurements. Skin temperature can be measured on different days with good repeatability, but temperature variations can be more sensitive to the effects of an intervention

Potentiometric sensor for L-ascorbic acid based on EVA membrane doped with copper(II)

The development of a new potentiometric sensor for L-ascorbic acid based on the redox properties of copper(II) ions incorporated in a EVA membrane was carried out. The poly(ethylene-co-vinyl acetate) matrix (EVA 40 % wt.) was doped with CU2+ ions and dispersed on the surface of a graphite/epoxy electrode. The electrode displayed a Nernstian response (slope between 55 and 60 mV/decade), in the ascorbate concentration between 5.6 x 10(-6) and 3.7 x 10(-4) mol L-1, when 0.1 mol L-1 KH2PO4 buffer at pH 5.0 and 25.0 degrees C was employed. The sensor stability was assessed, allowing 280 determinations without significant decrease in the response. The relative standard deviation for vitamin C determination in pharmaceuticals samples by the proposed method was about 10%. Considering these deviations, the results obtained for both the methods (spectrophotometric and potentiometric) were similar.11747548

Determination of acetylsalicylic acid by FIA-potentiometric system in drugs after on-line hydrolysis

A potentiometric flow injection (FI) system was developed for the acetylsalicylic acid (ASA) determination in drugs, without previous treatment. The tubular potentiometric electrode for salicylate (SA) was based on tricaprylyl-trimethyl-ammonium-salicylate (aliquat-salicylate) as the ion-exchanger, supported on poly(ethylene-co-vinyl-acetate) (EVA) matrix and applied directly onto a conducting support. The standards and samples were freshly prepared in ethanol solution (0.10 mol l(-1) Tris-SO4 buffer, pH 8.0, containing 0.25 mol l(-1) Na2SO4 and 8.0% v/v ethanol) to facilitate the dissolution of ASA and were injected directly into the system. The SA formed due to the on-line alkaline hydrolysis of alcoholic ASA solution, with 0.50 mol l(-1) NaOH (coil, 50 cm length), was monitored by the tubular electrode after neutralization with 0.25 mol l(-1) H2SO4. A solution of 0.10 mol l(-1) Tris-SO4 buffer (pH 8.0), containing 0.25 mol l(-1) Na2SO4 was employed as carrier. In optimized conditions (flow rate of 2.1 ml min(-1) and volume of injection of 150 mu l), the tubular electrode showed a linear response to ASA in the concentration range between 4.0 x 10(-3) and 4.0 x 10(-2) mol l(-1). A conversion factor of ASA to SA of 85% occurs in these conditions with an increase of about 130% in the signal to the system with on-line hydrolysis (three-channel) in comparison to the system without (one-channel). The response time of the electrode was about 5 s with an analytical frequency of 28 samples per h and a relative standard deviation (R.S.D.) of 2.1% for 30 successive injections. Determinations of ASA in tablet samples by the proposed method exhibited relative differences of 1.0-3.5%, compared to the official method of the British Pharmacopoeia. The useful lifetime of the sensor was greater than I month, in continuous use. (C) 1999 Elsevier Science B.V, Ail rights reserved.50366166

Potentiometric determination of L-ascorbic acid in pharmaceutical samples by FIA using a modified-tubular electrode

A flow injection system using a tubular electrode based on the redox properties of copper (II) ions occluded in EVA membrane was developed for L-ascorbic acid determination. The polyethylene-co-vinyl acetate (EVA 40% m/m) matrix was doped with copper (II) ions and dispersed on the surface of a graphite/epoxy tubular electrode. The electrode showed a super-Nernstian response for L-ascorbic acid concentration between 10(-3) and 10(-1) mol L-1 with a detection limit of 8.5x10(-4) mol L-1, when 0.1 mol L-1 KH2PO4 buffer mixed with 0.1 mol L-1 hydrogen peroxide at pH 5.0 was employed as carrier The Potentiometric-FIA system allows an analytical frequency of 120 samples per hour with a precision of 3.6%. The results obtained for ascorbic acid determination in pharmaceutical samples, without any previous treatment, were similar to these obtained by the British Pharmocopoeia method.11218218

Paraformaldehyde as an end-point indicator in hydrolytic thermometric titration of metal ions and iodine

The use of paraformaldehyde (PF) as an end-point indicator in hydrolytic titrations involving precipitation, complexation and redox reactions was investigated. The decrease in temperature caused by depolymerization of PF, catalysed by hydroxyl ions produced by hydrolysis of excess of titrant, was employed to locate the end-point of the titration, The results of titrations of alkaline earth metals with carbonate, several metal ions with EDTA and iodine with arsenite are presented.121455956

Development of a new FIA-potentiometric sensor for dopamine based on EVA-copper(II) ions

A how injection analysis (FIA) system using a tubular electrode based on the redox properties of copper(II) ions immobilized in a poly(ethylene-co-vinyl acetate) (EVA) membrane was developed for dopamine determination. The Cu2+ was trapped in the EVA (40% m/m) matrix and dispersed on the surface of a graphite-epoxy flow-through electrode. The electrode based on the dopamine oxidation catalyzed by Cu2+ exhibited a near-Nernstian response (83.2 +/- 0.2 mV decade(-1)) for dopamine concentration between 1.0 x 10(-3) and 1.0 x 10(-2) mol l(-1) (r = 0.9992), employing 0.25 mol l(-1) KH2PO4 buffer, containing 0.1 mol l(-1) H2O2 at pH 7.0, as a carrier solution. The potentiometric-FIA system allows an analytical frequency of about 25 samples per hour with a good precision (variance lower than 4.2%). The best potentiometric response was achieved using an EVA membrane containing 5.0% (m/m) Cu2+ ions. The use of hydrogen peroxide in a flow-system makes an efficient reoxidation of the Cu1+ ions possible in the EVA membrane. The relative standard deviation for dopamine determination in pharmaceutical samples, without any previous treatment, was about 4.7%. The useful lifetime for the dopamine sensor was longer than 3 months, in continuous use, (C) 2000 Elsevier Science S.A. All rights reserved.4811344

Application of two- and three-way chemometric methods in the study of acetylsalicylic acid and ascorbic acid mixtures using ultraviolet spectrophotometry

In this work, mixtures of acetylsalicylic acid (ASA) and ascorbic acid (AA) were studied by ultraviolet spectrophotometry (210-300 nm) using parallel factor analysis (PARAFAC) and partial least square (PLS). The study was carried out in the pH range from 1.0 to 5.5 and with a concentration range from 1.0 x 10(-5) to 1.0 x 10(-4) mol l(-1) of both analytes. PARAFAC was used for spectra deconvolution, pK(a) estimation for both acids and to check the presence of salicylic acid (SA), due to the possible ASA decomposition. The estimated first pK(a) was equal to 3.41 and 4.10 for ASA and AA, respectively. Multivariate calibration models using PLS at different pH and N-way PLS were elaborated for simultaneous determination of ASA and AA in pharmaceutical samples. The best models for the system were obtained with N-way PLS2 and PLS2 at pH 1.1. The results obtained for simultaneous determination of ASA and AA in samples were in agreement to the values specified by the manufacturers and the recovery was between 97.6 and 103.6%. Nevertheless, these models failed to predict ASA decomposition to SA in simulated samples. Thus, a new PLS-pH1 model considering SA was built and applied successfully in simulated samples. (C) 2000 Elsevier Science B.V. All rights reserved.4094167115917

Use of self-plasticizing EVA membrane for potentiometric anion detection

In this work, five different types of membranes were developed responsible to anion-selective electrodes. The membranes were based on tri-caprylyl-trimethyl-ammonium chloride (Aliquat-336S) supported on poly(ethylene-covinyl-acetate) copolymer (EVA). The sensors were prepared by solubilizing the copolymer with the appropriate exchanger in chloroform, without using of any plasticizers. The ion-selective electrodes prepared using these membranes show the utility for anions determinations in the concentration range between 10(-5) and 10(-1) mol l(-1) in the steady-state. The membrane performance was also evaluated in FIA system using tubular electrode for salicylate and iodide. In FIA system, the electrode exhibited nernstian response for salicylate in the concentration range of 2.5 x 10(-3) and 1.0 x 10(-1), while for iodide from 5.0 x 10(-4) up to 1.0 x 10(-1) mol l(-1). The systems were employed for the salicylate and iodide determination in pharmaceutical samples obtaining a relative deviation of 1.6%,when compared to the reference method. (C) 2001 Elsevier Science B.V. All rights reserved.53480781

Study of NADH stability using ultraviolet-visible spectrophotometric analysis and factorial design

The chemical stability of nicotinamide adenine dinucleotide coenzyme (NADH/NAD(+)) and its derivatives (NADPH/NADP(+)) was investigated using changes in the UV-visible absorption spectra of these compounds. The spectra of cofactor (reduced form) were monitored at 340 nm wavelength in different buffers, showing a faster degradation in phosphate buffer. This was assigned to the adduct formation between phosphate and NADH (pyridine ring). The three-factor-two-level factorial design study evaluated the contributions: buffers (phosphate and Pipes 0.1 M), pH's (6.8 and 7.8), and temperature (25 and 30 degrees C). The freshly prepared aqueous solutions of coenzyme were analyzed after 40 min under the different conditions (eight assays in triplicate) of the experiment. The main observed effects of the NADH oxidation were, in increasing order, pH, temperature, and buffer without appreciable interactive effects. Therefore, it was verified that the better conditions for cofactor use were alkaline media employing Pipes buffer or its derivatives and low temperatures. (C) 1998 Academic Press.2601505