J. C. de Andrade

Extraction of boron from soil by microwave heating for ICP‐AES determination

Abstract Extraction with hot water is the most widely used procedure to determine boron (B) in soils for the diagnosis of the nutrient availability for plants. However, this procedure is tedious for routine conditions and requires some special precautions. An alternative extraction procedure was developed, consisting in the extraction of B with a 1.25 g/L solution of barium chloride (BaCl2) or with water heated in a domestic microwave oven. Boron was determined either by inductively coupled argon plasma emission spectrometry (ICP‐AES) and by spectrophotometry with azomethine‐H. Good correlations were found between the extraction by boiling water under reflux and the extraction by the microwave heating for 13 Brazilian soils, and the contents of B obtained by spectrophotometry did not differ significantly from those obtained by ICP‐AES. Considering the calculated standard deviations, it can be concluded that microwave heating followed by ICP‐AES determination is an adequate procedure for the determination ...

Determination of organic matter in soils by FTIR/diffuse reflectance and multivariate calibration

A non‐destructive method avoiding the utilization of toxic and corrosive reagents is presented as an alternative for the determination of organic matter (OM) in soils. This method is based on a multivariate calibration procedure using partial least squares (PLS) regression to establish the relationship between the organic matter content in soils determined by conventional chemical measurements and by diffuse reflectance spectra in the mid‐infrared region. The spectra are presented as reflectance (R) or log(1/R) and in Kubelka–Munk (K/S) units. Several data pretreatments such as multiplicative scatter correction (MSC), smoothing, derivation and normalization of the spectral data were employed to improve the performance of the method. The PLS analysis on the data expressed as R and log(1/R) after smoothing, differentiation and normalization showed better results, with RMSEPs equal to 0·63% (for R) and 0·69% (for log(1/R)) and linear correlation coefficients between reference and predicted OM values equal to 0·981 (for R) and 0·972 (for log(1/R)). Copyright

Cold Vapor Atomic Absorption determination of mercury by Flow Injection Analysis using a Teflon membrane phase separator coupled to the absorption cell

Abstract A Flow Injection Analysis (FIA) procedure for the determination of trace amounts of mercury by the Cold Vapor Atomic Absorption (CVAA) method is presented. In order to make efficient use of the FIA technique, a new flow cell was developed to permit a rapid separation of elemental mercury from the carrier solution. The design of this device is based on the permeability of Hg 0 in commercially available Teflon (PTFE) tape, which acts as a membrane phase separator. The calibration curve is linear up to 70 ng.ml −1 ( A = 0.005 + 0.008 Hg(ng.ml −1 ); r = 0.9996) using a 15-cm open cell approach, with a detection limit of 1.4 ng. ml −1 (0.66 ng of mercury), considering a signal to noise ratio of three. The standard deviation is s = ±0.004 absorbance units, calculated at a level of 50 ng.ml −1 of Hg 2+ . The sampling rate was 110 samples per h.

A flow injection/hydride generation system for the determination of arsenic by inductively-coupled plasma atomic emission spectrometry

Abstract A flow-injection system is described for the semi-automatic determination of arsenic (10–1000 μg l −1 ) by hydride generation and inductively-coupled plasma atomic emission spectrometry. The elements which were found to interfere were Co, Ni, Ag, Au, Bi, Te and Sn. Standard reference materials were analyzed with good accuracy. Approximately 200 injection h −1 are possible. The detection limit is 1.4 ng arsenic.

Efficiency of multinutrient extractants for the determination of available copper in soils

Abstract Experiments under greenhouse conditions were carried out at the Instituto Agronomico de Campinas in order to determine the efficiency of some multinutrient extradants on the determination of available copper in soils from the State of Sao Paulo, Brazil. These experiments employed 31 soils using wheat and beans as test plants. All soil samples were limed to increase the soil pH to 6.0 and manured with copper‐free fertilizer. Copper was extracted from the soils before liming and before each planting using the Mehlich‐1, Mehlich‐3, or the TEA‐DTPA as extracting reagents followed by its determination using the inductively coupled plasma emission spectrometry (ICP‐AES) technique. The wheat and beans plants were also analysed for their copper content. The results showed that the extraction of the available copper decreased in the order: Mehlich‐3, TEA‐DTPA and Mehlich‐1. The Mehlich‐3 (R2 = 0.80**) and the TEA‐DTPA (R2 = 0.74**) methods explained well the variation in the copper concentration found in ...

Comparison of methods to evaluate heavy metals in organic wastes.

Abstract The conventional method for the digestion of residues using a mixture of nitric and perchloric acids was compared with the microwave procedure using both aqua regia and nitric acid as extractants, in order to determine which method fits better the routine measurements using inductively coupled plasma emission spectrometry (ICP‐AES). Urban domestic wastes, swine and dairy manure and NIES pond sediment certified reference material were used as samples. The microwave digestions were performed on sealed vessels by taking 500 mg of each residue and aqua regia (16 mL) or concentrated nitric acid (10 mL). The conventional nitric‐perchloric digestion was performed by heating 500 mg of each sample with 6 mL of HNO3 ‐HClO4 5+1 v/v in Pyrex digestion tubes until complete digestion. All extracts were analysed for Fe, Mn, Zn, Cu, Pb, Ni, Cr and Cd by ICP‐AES. Microwave extraction with aqua regia extracted higher amounts of metals from the certified pond sediment reference material than the USEPA‐SW 846‐method...

The effects of the DTPA extraction conditions on the determination of micronutrients in Brazilian soils

Abstract Extraction steps of the DTPA procedure for copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) determinations were tested in four representative soils from the State of Sao Paulo (Brazil), namely Red‐Yellow Latosol (LV), Red‐Yellow Podzolic (PV), Dusk‐Red Latosol (LR), and Sand Soil (AQ). The results indicated that the use of volume sampling, although possible, may cause biased results. Thus, direct soil sampling in terms of mass is recommended. Variations in the pH of the extraction solution from 7.1 to 7.5 can be critical for acid soils, but the best results for the soils tested were observed by keeping the extraction solution pH at 7.3. Some sort of equilibrium seems to be reached after a soil/extraction solution shaking time of 150 min for all soils tested. No significant changes in the micronutrient concentrations are observed if the soil suspension is filtered up to 120 min after shaking, but changes may occur upon storing the filtrate for more than 7 days at temperatures of 25°C‐30°C.

Revisiting titration procedures for the determination of exchangeable acidity and exchangeable aluminum in soils

Abstract The use of 1 mol L‐1 ammonium chloride (NH4Cl) or ammonium nitrate (NH4NO3) solutions as alternative soil extractants were evaluated for the determination of the exchangeable acidity and exchangeable aluminum (Al) in twelve soil samples by the traditional titration/back‐titration method. The exchangeable Al results were compared with those obtained by inductively coupled plasma emission spectrometry (ICP‐AES) measurements while the exchangeable acidity results, using either NH4Cl or NH4NO3 solutions as alternative soil extractants, were compared against those using 1 mol L‐1 potassium chloride (KCl) and bromothymol blue as the indicator. The results indicated that the use of ammonium (NH4) salts in these determinations is not recommended since the exchangeable acidity found using these extractants was systematically higher than that found in KCl extracts due to the additional acidity caused by the presence of comparatively higher concentrations of NH4 + ions. In addition, the reaction media also ...

An improved method for purifying α-metallophthalocyanines for use as radionuclide preparation targets

Modifications of the conventional precipitation method for purifying α-metallophthalocyanines give a product essentially free of the usual occluded impurities, significantly decreasing the total metallic content of extracted radionuclides. Application of the improved method to the preparation of an α-CoPc target is described.

An improved analytical protocol for the routine spectrophotometric determination of exchangeable aluminum in soil extracts with xylenol orange.

The proposed analytical protocol is applicable to potassium chloride and ammonium chloride soil extracts. It makes use of ethanol as a reaction accelerator. Full color development is achieved after a standing period of 2 hours and the absorbance measurements were performed at 555 nm, against the blank. Under these conditions the interference of other elements usually found in the soil extracts were not important. The calibration graphs, in the range from 0 to 1.0 mg L -1 Al +3 , were fitted by 2nd order polynomial regressions. The protocol was tested with 10 representative soil samples from the State of Sao Paulo (Brazil), containing exchangeable aluminum varying from 30 to 200 mg Al kg -1 of soil and variable amounts of iron. All samples were run in triplicate and the results averaged. The correlation among the proposed procedure and the measurements obtained by ICP-AES were [Al,XO] = 0.96[Al,ICP] - 7.38 with r 2 =0.9950 and [Al,XO] = 1.06[Al,ICP] - 6.43 with r 2 =0.9970, for the KCl and NH 4 Cl extractions. For absorbance readings above 0.9 or below 0.1 it is advisable to repeat the determinations by taking sample aliquots of 1.00 or 10.00 mL, respectively. This analytical approach proved to be appropriate for routine work.Abstract The proposed analytical protocol is applicable to potassium chloride and ammonium chloride soil extracts. It makes use of ethanol as a reaction accelerator. Full color development is achieved after a standing period of 2 hours and the absorbance measurements were performed at 555 run, against the blank. Under these conditions the interference of other elements usually found in the soil extracts were not important. The calibration graphs, in the range from 0 to 1.0 mg L‐1 Al+3 were fitted by 2nd order polynomial regressions. The protocol was tested with 10 representative soil samples from the State of São Paulo (Brazil), containing exchangeable aluminum varying from 30 to 200 mg Al kg‐1 of soil and variable amounts of iron. All samples were run in triplicate and the results averaged. The correlation among the proposed procedure and the measurements obtained by ICP‐AES were [Al,XO] = 0.96[Al,ICP] ‐ 7.38 with r2=0.9950 and [Al,XO] = 1.06[Al,ICP] ‐ 6.43 with r2=0.9970, for the KCl and NH4Cl extractions. For absorbance readings above 0.9 or below 0.1 it is advisable to repeat the determinations by taking sample aliquots of 1.00 or 10.00 mL, respectively. This analytical approach proved to be appropriate for routine work.