Potential acidity estimated by SMP pH in soils of the state of Pará

The use of SMP pH to estimate the potential acidity (H + Al) is more practical than the method of 0.5 mol L-1 calcium acetate for routine laboratory analyses. The objective was to fit an equation to estimate the H + Al from SMP pH values of soils of the State of Pará. From various regions of the state, 177 soil samples were collected, in which the SMP pH was determined in 0.01 mol L-1 CaCl2 solution and H + Al in 0.5 mol L-1 calcium acetate and the results were related by regression analysis. The equation H + Al = 77.77 + 20.61 SMP pH - 1.435 SMP pH² (R² = 0.90) expressed the H + Al values (in cmol c dm-3) best. When the SMP pH values were used in equations referring to other regions or states in Brazil, the H +Al values were over- or underestimated. The potential acidity in soils of Pará can be estimated by the method of SMP pH.

Extractants to assess zinc phytoavailability in mineral fertilizer and industrial by-products

Efficient analytical methods for the quantification of plant-available Zn contained in mineral fertilizers and industrial by-products are fundamental for the control and marketing of these inputs. In this sense, there are some doubts on the part of the scientific community as well as of the fertilizer production sector, whether the extractor requested by the government (Normative Instruction No. 28, called 2nd extractor), which is citric acid 2 % (2 % CA) (Brasil, 2007b), is effective in predicting the plant availability of Zn via mineral fertilizers and about the agronomic significance of the required minimal solubility of 60 % compared to the total content (HCl) (Brasil, 2007a). The purpose of this study was to evaluate the alternative extractors DTPA, EDTA, neutral ammonium citrate (NAC), buffer solution pH 6.0, 10 % HCl, 10 % sulfuric acid, 1 % acetic acid, water, and hot water to quantify the contents of Zn available for maize and compare them with indices of agronomic efficiency of fertilizers and industrial by-products when applied to dystrophic Clayey Red Latosol and Dystrophic Alic Red Yellow Latosol with medium texture. The rate of Zn applied to the soil was 5 mg kg-1, using the sources zinc sulfate, commercial granular zinc, ash and galvanic sludge, ash and two brass slags. Most Zn was extracted from the sources by DTPA, 10 % HCl, NAC, 1% acetic acid, and 10 % sulfuric acid. Recovery by the extractors 2 % CA, EDTA, water, and hot water was low. The agronomic efficiency index was found to be high when using galvanic sludge (238 %) and commercial granular zinc (142 %) and lower with brass slag I and II (67 and 27 %, respectively). The sources galvanizing ash and brass ash showed solubility lower than 60 % in 2 % CA, despite agronomic efficiency indices of 78 and 125 %, respectively. The low agronomic efficiency index of industrial by-products such as brass slag I and galvanizing ash can be compensated by higher doses, provided there is no restriction, as well as for all other sources, in terms of contaminant levels of arsenic, cadmium, chromium, lead, and mercury as required by law (Normative Instruction No 27/2006). The implementation of 2nd extractor 2 % CA and the requirement of minimum solubility for industrial by-products could restrict the use of alternative sources as potential Zn sources for plants.

Boron Leaching Decreases withIncreases on Soil pH

ABSTRACT Management of boron fertilization depends on the magnitude of B leaching in the soil profile, which varies proportionally with the concentration of B in the soil solution, which, in turn, decreases as the soil pH increases due to the higher sorption of B on soil solid surfaces. The objective of this study was to quantify the effect of liming and rates of B applied to the soil on B leaching. The experiment was carried out in the laboratory in 2012, and treatments consisted of a factorial combination of two rates of liming (without and with lime to raise the soil pH to 6.0) and five rates of B (0, 10, 20, 50 and 100 mg kg-1, as boric acid). A Typic Rhodudalf was used, containing 790 g kg-1 clay and 23 g kg-1 organic matter; the pH(H2O) was 4.6. Experimental units were composed of PVC leaching columns (0.10 m in diameter) containing 1.42 kg of soil (dry base). Boron was manually mixed with the top 0.15 m of the soil. After that, every seven days for 15 weeks, 300 mL of distilled water were added to the top of each column. In the percolated solution, both the volume and concentration of B were measured. Leaching of B decreased with increased soil pH and, averaged across the B rates applied, was 58 % higher from unlimed (pH 4.6) than from limed (pH 6.6) samples as a result of the increase in B sorption with higher soil pH. In spite of its high vertical mobility, the residual effect of B was high in this oxisol, mainly in the limed samples where 80 % of B applied at the two highest rates remained in the soil, even after 15 water percolations. Total recovery of applied B, including leached B plus B extracted from the soil after all percolations, was less than 50 %, showing that not all sorbed B was quantified by the hot water extraction method.

Estudo microcalorimétrico da interação de tensoativos n-alquil-sulfato de sódio com tripsina a 298 k

Systematic study of the interactions of ionic surfactants with protein trypsin in buffer solution pH 3.5, 7.0 and 9.0, ionic strength 10 mM at 298 K was done using the microcalorimetric technique. In this study, anionic surfactant solutions of the sodium n-alkyl sulfates series (C8, C10, C12 and C14) were used. The enthalpy of interaction (ΔintHº) shows that the interaction of the surfactants C8, C10, C12 and C14 with trypsin in the solution pH 3.5 is an endothermic process with the value of ΔintHº decreasing linearly with increasing carbon chain length, which is attributed to the unfolding of the polypeptide chain. In the solution pH 7.0, we observed the same trend except for C14. In the solution pH 9.0, from C10 the enthapy of interaction didn't change with the increasing of the carbon chain length due to unfolding of the polypeptide. We concluded that when trypsin is folded, the enthalpy of interaction shows a linear relationship with the surfactant's hydrophobicity, in agreement with Traube's rule.

Determinação espectrofotométrica por injeção em fluxo de vitamina B6 (piridoxina) em formulações farmacêuticas

A flow injection (FI) spectrophotometric procedure is proposed for the determination of vitamin B6 (pyridoxine hydrochloride) in pharmaceutical preparations. Powdered samples containing from 2.5 to 4.5 mg, were previously dissolved in 0.1 mol L-1 phosphate buffer solution (pH 7.0) and a volume of 500 muL was injected directly into a carrier stream consisting of this same phosphate buffer solution, flowing at 4.4 mL min-1. The stable blue indophenol dye produced in the oxidation of pyridoxine hydrochloride by potassium hexacyanoferrate(III) and N,N-diethyl-p-phenylenediamine solution was directly measured at 684 nm. Vitamin B6 was determined in five pharmaceutical preparations in the 0.5 to 6.0 mg L-1 concentration range (calibration graph: A= -0.00499 + 0.11963 C; r= 0.9991, where A is the absorbance and C is the vitamin B6 concentration in mg L-1), with a detection limit of 0.02 mg L-1 (3 Sblank/slope). The recovery of this vitamin from three samples ranged from 97.5 to 103.3 %. The analytical frequency was 62 h-1 and r.s.d. were less than 2% for solutions containing 1.0 and 3.0 mg L-1 vitamin B6 (n= 10). The results obtained for the determination of vitamin B6 in commercial formulations were in good agreement with those obtained by a spectrophotometric procedure (r=0.9997) and also with the label values (r= 0.9998).

Determinação enzimática de dopamina em formulações farmacêuticas utilizando sistema de análise por injeção em fluxo com extrato bruto de abacate (Persea americana)

In this work, a spectrophotometric flow injection analysis system using a crude extract of avocado (Persea americana) as a source of polyphenol oxidase to dopamine determination was developed. The substrates and enzyme concentrations from 2.4x10-7 to 5.3x10-4 mol L-1 and 28 to 332 units mL-1 were evaluated, respectively. In addition, the FIA parameters such as sample loop (50 to 500 µL), flow rate (1.4 to 4.3 mL min-1) and reactor length (100 to 500 cm) were also evaluated in a 0.1 mol L-1 phosphate buffer solution (pH 7.0). Dopamine solution concentrations were determined using 277 units mL-1 enzyme solution, 400 mL enzyme loop, 375 µL sample loop, 2.2 mL min-1 flow rate and a reactor of 350 cm. The analytical curve showed a linearity from 5.3x10-5 to 5.3x10-4 mol L-1 dopamine with a detection limit of 1.3x10-5 mol L-1. The analytical frequency was 46 h-1 and the RSD lower than 0.5% for 5.3x10-4 mol L-1 dopamine solution (n=10). A paired t-test showed that all results obtained for dopamine in commercial formulations using the proposed flow injection procedure and a spectrophotometric procedure agree at the 95% confidence level.

Determinação potenciométrica em fluxo de cloreto de cetilpiridinio em desinfectantes bucais

The work describes a new procedure for cetylpyridinium chloride determination in oral disinfectants, based on a flow-injection system with potentiometric detection. The determination was based on the measurement of picrate concentration decrease as result of ion-pair reaction with the analyte present in the injected sample. In the optimised set-up the sample injection volume was kept at 400 µL and merged downstream with the reagent solution containing 1,0 x10-5 mol/L of picrate adjusted to pH 5.0 with citrate/citric acid buffer. The flow rate was fixed at 8 mL/min and the reactor length at 40 cm. The proposed procedure enables the determination of cetylpyridinium in the analytical range of 5,0x10-6 - 7,5x10-5 mol/L at a sampling rate of 60/h. The results for real samples had a precision better than 3% and were comparable to the labelled values.

Análise de ácidos graxos por eletroforese capilar utilizando detecção condutométrica sem contato

This article describes a novel approach to the separation of fatty acids ranging from 8 to 20 carbons using capillary electrophoresis with contactless conductivity detection. Complete separation of nine linear chain fatty acids (from C8:0 to C20:0) was achieved in 15 min under normal polarity operation. Limits of detection ranged from 35 to 319 µmol L-1 for C20:0 to C8:0, respectively. The optimized running electrolyte composition was 5.0 mmol L-1 phosphate buffer at pH 7, 4.0 mmol L-1 dimethyl-b-cyclodextrin, 2.0 mmol L-1 trimethyl-b-cyclodextrin, acetonitrile 50% (v/v), and methanol 20% (v/v). The applicability of the separation system was demonstrated by the analysis of coconut vegetable oil.

Determinação eletroanalítica de corante reativo presente como contaminante em proteínas purificadas por cromatografia de afinidade

Procion Green HE-4BD is a reactive dye currently used in affinity purification, and commonly present as a contaminant in the final biological preparation. An assay method is described to determine trace amounts of the dye in the presence of human serum albumin(HSA) and leakage from agarose as affinity sorbent by cathodic stripping voltammetry. The proposed method is based on the reductive peak at -0.55V in B-R buffer pH 3 (E=0V and t= 240s), obtained when samples of HSA 2% (m/v) containing dye concentrations in sodium hydroxide pH 12 are submitted to a heating time of 330 min at 80 ºC. Linear calibration curves can be obtained for RG19 dye concentrations from 5x10-9 mol L-1 to 8 x10-8 mol L-1. The detection limit (3sigma) is 1x10-9 mol L-1.

Utilização de um eletrodo de grafite-epóxi recoberto com [Zn(FEN)3][tetratris(4-clorofenil) borato]2 sensível a zinco(II) em meio 1,10-fenantrolina como eletrodo indicador em titulações potenciométricas de precipitação

The construction and analytical evaluation of a coated graphite-epoxy electrode sensitive to the zinc-1,10-phenantroline complex based on the [Zn(fen)3][tetrakis(4-chlorophenyl)borate]2 incorporated into a poly(vinylchloride) (PVC) matrix are described. A thin membrane film of this ion-pair, dibutylphthalate (DBPh) and PVC were deposited directly onto an electrically conductive graphite-epoxy support located inside a Perspex® tube. The best PVC polymeric membrane contains 65% (m/m) DBPh, 30% (m/m) PVC and 5% (m/m) of the ion-pair. This electrode shows a response of 19.5 mV dec-1 over the zinc(II) concentration range of 1.0 x 10-5 to 1.0 x 10-3 mol L-1 in 1,10-phenantroline medium, at pH 6.0. The response time was less than 20 seconds and the lifetime of this electrode was more than four months (over 1200 determinations by each polymeric membrane). It was successfully used as an indicator electrode in the potentiometric precipitation titration of zinc(II) ions.

Determinação simultânea de resíduos de cloranfenicol, tianfenicol e florfenicol em leite bovino por cromatografia eletrocinética micelar

A micellar electrokinetic chromatographic method (MEKC) is described for determining residues of amphenicols(chloramphenicol,thiamphenicol and florfenicol) in bovine milk. MEKC is conducted by using a separation buffer consisting of 20 mM Na2HPO4, 10 mM Na2B4O7, 50 mM SDS at pH 8.0; UV detection at 210 nm and 10 kV of voltage. The limit of detection ranged from 4.3-5.3 µg L-1. The MEKC method was applied for the simultaneous determination of amphenicols in milk samples spiked with amphenicols at three concentration levels: 10, 30 and 50 µg L-1. Recoveries ranging from 91-105% were obtained by following a simple extraction/preconcentration procedure.

Construção e aplicação de biossensores usando diferentes procedimentos de imobilização da peroxidase de vegetal em matriz de quitosana

Biosensors were developed by immobilization of gilo (Solanum gilo) enzymatic extract on chitosan biopolymers using three different procedures: glutaraldehyde, carbodiimide/glutaraldehyde and epichlorohydrin/glutaraldehyde. The best biosensor performance was obtained after the immobilization of peroxidase on chitosan with epichlorohydrin/glutaraldehyde. Linear analytical curves for hydroquinone concentrations from 2.5x10-4 to 4.5x10-3 mol L-1 with a detection limit of 2.0x10-6 mol L-1 and recovery of hydroquinone ranging from 95.1 to 105% were obtained. The relative standard deviation was < 1.0 % for a solution of 3.0x10-4 mol L-1 hydroquinone and 2.0x10-3 mol L-1 hydrogen peroxide in 0.1 mol L-1 phosphate buffer solution at pH 7.0 (n=8). The lifetime of this biosensor was 6 months (at least 300 determinations).

Determinação de lamivudina, estavudina e nevirapina, em comprimidos, por cromatografia líquida de alta eficiência

A high performance liquid chromatography method was developed to quantify lamivudine, stavudine and nevirapine combined in tablets. The separation was carried out in less than 10 min using a phosphate buffer of pH 3.0 and acetonitrile (75:25, v/v) as mobile phase, a LiChrospher ODS column and UV detection at 266 nm. The method was linear over the range of 15-135 µg/mL (lamivudine), 4-36 µg/mL (stavudine) and 20-180 µg/mL (nevirapine). The accuracy ranged from 98.56 to 102.04% and intra-day and inter-day precision was less than 1% for the three drugs. The method showed robustness, remaining unaffected by deliberate variations in relevant parameters.

Método titrimétrico para determinar fosfito em amostras agroindustriais

A new titrimetric method for the determination of phosphite in fertilizer samples, based on reaction of H3PO3 with standard iodine solution in neutral media, is proposed. Diluted samples containing ca. 0.4% m/v P2O5 are heated and titrated with 0.05 mol L-1 iodine standard until the solution becomes faint yellow. Back titration is also feasible: a slight excess of titrant is added followed by starch indicator and titration is completed taking as the end point the change in color from blue to colorless. The influence of chemical composition and pH of buffers, temperature and foreign species on waiting time and end-point detection were investigated. For the Na2HPO4/NaH2PO4 buffer (pH 6.8) at 70 °C, the titration time was 10 min, corresponding to about 127 mg iodine, 200 mg KI and 174 mg Na2HPO4 and 176 mg NaH2PO4 consumed per determination. Accuracy was checked for phosphite determination in seven fertilizer samples. Results obtained by the proposed procedure were in agreement with those obtained by spectrophotometry at 95% confidence level. The R.S.D. (n=10) for direct and back titration was 0.4% and 1.3% respectively.

Validação de metodologia analítica por cromatografia líquida para doseamento e estudo da estabilidade de pantoprazol sódico

Pantoprazole is a proton pump inhibitor used in the treatment of digestive ulcers, gastro-esophageal reflux disease and in the eradication of Helicobacter pylori. In this work, an analytical method was developed and validated for the quantification of sodium pantoprazole by HPLC. The method was specific, linear, precise and exact. In order to verify the stability of pantoprazole during dissolution assays, pantoprazole solution in phosphate buffer pH 7.4 was kept at room temperature and protected from light for 22 days. Pantoprazole presented less than 5% of degradation in 6 hours and the half live of the degradation was 124 h.