Alexssandra Luiza Rodrigues Molina Rossete

Production of single superphosphate labeled with 34S

Single superphosphate is currently one of the mostly used fertilizers as an alternative source for phosphorus and sulphur. Sulphur presents four stable isotopes (32S, 33S, 34S, and 36S) with natural abundances of 95.00; 0.76; 4.22; and 0.014% in atoms, respectively. Single superphosphate labeled with the 34S isotope was obtained from a chemical reaction in stoichiometric amounts between Ca(H2PO4)2 and Ca34SO4.2H2O. Calcium sulphate (Ca34SO4.2H2O) was enriched with 5.85 ± 0.01 atoms % of 34S. The Ca(H2PO4)2 reagent was obtained from a reaction between CaCl2.2H2O and H3PO4. The reaction between the Ca(H2PO4)2 thus produced and the labeled Ca34SO4.2H2O compound was then performed to obtain the 34S-labeled single surperphosphate. The thermal decomposition of the labeled superphosphate for the production of gaseous 34SO2 was carried out under a vacuum line at 900oC in the presence of NaPO3. The isotopic determination of S (atoms % of 34S) was carried out on an ATLAS-MAT model CH-4 mass spectrometer. The production yield of Ca(H2PO4)2 and labeled single superphosphate were approximately 97 and 99% respectively, and the purity level of the labeled single superphosphate was estimated as 96%. No isotopic fractionation was observed in the production process of 34S-labeled single superphosphate.

Versatile Flow Injection System for Spectrophotometric Determination of Silicon in Agronomic Samples

Abstract A versatile flow injection system for spectrophotometric determination of silicon (Si) in agronomic samples is proposed. For plant and slag analysis (1.0–10.0 mg L−1 Si), the method involves monitoring the yellowish molybdosilicic acid at 410 nm. Soil, fertilizer, water, and sugarcane juice analysis (0.5–5.0 mg L−1 Si) were accomplished by adding a reducing agent, and the molybdenum blue compound that formed was monitored at 735 nm. Flexibility of the method allows determination in a variety of matrices involving a wide range of concentrations. Beers law is followed up to 20.0 mg L−1 Si (r<0.9997; n=6) for analysis at 410 nm and up to 10.0 mg L−1 Si (r<0.9998; n=6) at 735 nm. For the yellow‐color and blue‐color methods, the detection limits were estimated as 0.5 and 0.1 mg L−1 Si. Measurement frequency for both methods is approximately 75 h−1 using 48 mg of ammonium heptamolybdate, 80 mg of oxalic acid, and 24 mg of ascorbic acid per determination. Results are precise (r.s.d.>0.1%, n=10) and in agreement with inductively coupled plasma–optical emission spectroscopy (ICP‐OES). Statistical differences between data sets were not confirmed after applying the Students ttest at the 95% confidence level (texp=0.195>ttab=2.57) related to n=6.

Isotopic Determination of Silicon by Mass Spectrometry in Plants and Soils Labeled with 30Si

Abstract A method for isotopic determination of silicon by mass spectrometry in plants and soils labeled with 30Si is reported. The development of this method is for use with studies involving the physiological process of absorption, transport, and redistribution of Si in the soil-plant system by use of the stable isotope 30Si as a tracer. The procedure leads to SiF4 formation, and the isotopic determination of Si was based on the measurements of the 28SiF3 +, 29SiF3 +, and 30SiF3 + signals. Relative standard deviation of 30Si abundance measurements (n = 6) were lower than 0.1%, and the detection limit was 0.5 mg Si (dry mass).

15N-labeled glyphosate synthesis and its practical effectiveness

O glifosato e o herbicida de maior participacao no mercado mundial, sendo utilizado intensivamente na agricultura ha mais de 30 anos, principalmente devido ao custo relativamente baixo e a alta eficiencia sobre diferentes especies. Descreve-se um metodo para a sintese do glifosato na forma do sal isopropilamina enriquecido no isotopo estavel do nitrogenio (15N). A sintese do herbicida-15N foi realizada utilizando-se da reacao de fosfometilacao com diaquil fosfito e glicina-15N. Os testes foram realizados em microescala e em quantidades equimolares. Foi possivel obter um rendimento de 20%. Para testar a eficiencia do glifosato sintetizado, realizou-se experimento em câmara de crescimento com a planta daninha Lolium multiflorum (azevem), a qual e eficazmente controlada segundo a bula dos produtos a base do sal de isopropilamina (glifosato). O delineamento experimental foi inteiramente casualizado, com quatro repeticoes, sendo os tratamentos provenientes de fontes de sal de isopropilamina na dose comercial recomendada do produto (720 g i.a. ha-1). Avaliou-se a producao de fitomassa fresca e seca, da parte aerea e radicular, aos 21 dias apos a aplicacao (DAA), e a toxicidade dos tratamentos aos 7, 14 e 21 DAA. As fontes de sal de isopropilamina empregados nao diferiram, o que devera permitir sua utilizacao como tracador isotopico.

Organic sulfur oxidation to sulfate in soil samples for total sulfur determination by turbidimetry

O S no solo pode ocorrer como S-orgânico e S-inorgânico, sendo a forma orgânica responsavel por 95 % do S na maioria dos solos. A eficiencia da oxidacao do S-orgânico a sulfato, na determinacao de S-total em amostras de solo, foi avaliada com o emprego de metodos de oxidacao por via umida (acida) e via seca (alcalina). Com o proposito de avaliar o metodo por via umida e possivelmente emprega-lo como referencia na avaliacao do metodo por via seca, proposto no presente trabalho, fez-se uso de um padrao de referencia da National Institute of Standards Tecnology (NIST), Montana Soil (NIST 2710). A oxidacao por via seca com agentes oxidantes alcalinos e um dos metodos mais simples para oxidacao de S-orgânico a forma de sulfato e foi comparado com o metodo por via umida. O objetivo deste trabalho foi desenvolver um metodo de facil execucao que possibilite a determinacao do elemento (S-total) em amostras de solo por turbidimetria. A avaliacao da eficiencia da oxidacao do S-orgânico a sulfato foi realizada com tres misturas oxidantes alcalinas: NaHCO3 + Ag2O, mistura Eschka (17 % de Na2CO3, 66 % de MgO e 17 % de K2CO3) e NaHCO3 + CuO. O procedimento na quantificacao da concentracao de sulfato foi baseado na reacao com cloreto de bario e deteccao por turbidimetria. A quantificacao do S na amostra-padrao, pelo uso do metodo por via umida, mostrou-se adequada com boa precisao e exatidao. Deve-se ainda destacar que nao foram encontradas diferencas significativas (confiabilidade de 95 %) entre os metodos por via umida e via seca (mistura oxidante de NaHCO3 e Ag2O) em seis diferentes solos brasileiros, o que possibilita o uso do metodo proposto por via seca no preparo de amostras de solos para determinacao de S total.Sulfur in the soil occurs in two basic forms, organic and inorganic S. The organic form accounts for 95 % of S in most soils. The effectiveness of organic S to oxidate to sulfate was evaluated for total S determination in soil samples by wet (acid) and dry-ash (alkaline) oxidation methods. To evaluate the wet method and the possible use as a reference when evaluating the dry method proposed here, a reference standard from the US National Institute of Standards and Technology (NIST) was used (Montana Soil - NIST 2710). The dry-ash oxidation process with alkaline oxidizing agents is one of the simplest oxidation methods of organic S to the sulfate form and was compared with the wet process. The objective of the study was to develop a dry method that would be easy to apply and allow the complete conversion of organic S to sulfate in soil samples and later detection by turbidimetry. The effectiveness of organic S oxidation to sulfate was evaluated by means of three alkaline oxidation mixtures: NaHCO3 + Ag2O, Eschka mixture (17 % Na2CO3, 66 % MgO, and 17 % K2CO3), and NaHCO3 + CuO. The procedure to quantify the sulfate concentration was based on the reaction with barium chloride and turbidimetric detection. Sulfur quantification in the standard sample by the wet method proved adequate, precise and accurate. It should also be pointed out that no significant differences were found (95 % reliability) between the wet and dry processes (NaHCO3 and Ag2O oxidation mixture) in six different Brazilian soils. The proposed dry method can therefore be used in the preparation of soil samples for total S determination.

Production of 34S-labeled gypsum (Ca34SO4.2H2O)

O gesso agricola (CaSO4.2H2O) destaca-se como fonte eficiente de calcio e enxofre e na reducao da saturacao de aluminio no solo. O 34S como tracador isotopico pode elucidar aspectos importantes no ciclo do enxofre. Para tanto o Ca34SO4.2H2O foi obtido por reacao quimica entre o Ca(OH)2 e solucao de H234SO4, realizada sob agitacao lenta. O acido foi produzido por cromatografia de troca ionica, utilizando resina cationica Dowex 50WX8 e solucao eluente de Na234SO4. Apos a precipitacao foi separado o precipitado e realizada a secagem em estufa ventilada a temperatura de 60oC. Nos testes, a partir de 2,2 L de H2SO4 0,2 mol L-1 e 33,6 g de Ca(OH)2, foram produzidos em media 73,7 ± 0,6 g de Ca34SO4.2H2O representando um rendimento medio de 94,6 ± 0,8%, com pureza de 98%. A partir do Ca34SO4.2H2O na presenca de NaPO3, em linha de alto vacuo, obteve-se o gas 34SO2 utilizado para a determinacao isotopica do S no espectrometro de massas ATLAS-MAT modelo CH-4.

ACCUMULATION AND TRANSLOCATION OF SILICON IN RICE AND BEAN PLANTS USING THE 30SI STABLE ISOTOPE

The 30Si silicon isotope stable was used for assessing the accumulation and translocation of Si in rice and bean plants grown in labeled nutritive solution. The isotopic silicon composition in plant materials was determined by mass spectrometry (IRMS) using the method based on SiF4 formation. Considering the total-Si added into nutritive solutions, the quantity absorbed by plants was near to 51% for rice and 15% for bean plants. The accumulated amounts of Si per plant were about 150g in rice and 8.6g in bean. Approximately 70% of the total-Si accumulated was found in leaves. At presented experimental conditions, the results confirmed that once Si is accumulated in the old parts of rice and bean plant tissues it is not redistributed to new parts, even when Si is not supplied to plants from nutritive solution.

Production of 15N-enriched nitric acid (H15NO3)

Techniques that employ 15N have proved to be an important tool in many areas of the agronomic and biomedical sciences. Nevertheless, their use is limited by methodological difficulties and by the price of compounds in the international market. Nitric compounds (15NO3-) have attracted the interest of researchers. However, these compounds are not currently produced in Brazil. Thus, in the present work H15NO3 was obtained from the oxidation of anhydrous 15NH3. The method we used differs from the industrial process in that the absorption tower is replaced with a polytetrafluoroethylene-lined, stainless-steel hydration reactor. The process output was evaluated based on the following parameters: reaction temperature; ratio of reagents; pressure and flow of 15NH3(g) through the catalyst (Pt/Rh). The results showed that, at the best conditions (500 oC; 50 % excess O2; 0.4 MPa; and 3.39 g.min-1 of 15NH3), a conversion percentage (N-15NH3 to N-15NO3-) of 62.2 %, an overall nitrogen balance (N-15NH3 + N-15NO3-) of 86.8 %, and purity higher than 99 % could be obtained.

Isotope determination of sulfur by mass spectrometry in soil samples

Sulphur plays an essential role in plants and is one of the main nutrients in several metabolic processes. It has four stable isotopes (32S, 33S, 34S, and 36S) with a natural abundance of 95.00, 0.76, 4.22, and 0.014 in atom %, respectively. A method for isotopic determination of S by isotope-ratio mass spectrometry (IRMS) in soil samples is proposed. The procedure involves the oxidation of organic S to sulphate (S-SO42-), which was determined by dry combustion with alkaline oxidizing agents. The total S-SO42- concentration was determined by turbidimetry and the results showed that the conversion process was adequate. To produce gaseous SO2 gas, BaSO4 was thermally decomposed in a vacuum system at 900 oC in the presence of NaPO3. The isotope determination of S (atom % 34S atoms) was carried out by isotope ratio mass spectrometry (IRMS). In this work, the labeled material (K234SO4) was used to validate the method of isotopic determination of S; the results were precise and accurate, showing the viability of the proposed method.

Synthesis of 15N-enriched urea (CO(15NH2)2) from 15NH3, CO, and S in a discontinuous process

CO(15NH2)2 enriched with the stable isotope 15N was synthesized based on a reaction involving CO, 15NH3, and S in the presence of CH3OH. The method differs from the industrial method; a stainless steel reactor internally lined with polytetrafluoroethylene (PTFE) was used in a discontinuous process under low pressure and temperature. The yield of the synthesis was evaluated as a function of the parameters: the amount of reagents, reaction time, addition of H2S, liquid solution and reaction temperature. The results showed that under optimum conditions (1.36, 4.01, and 4.48 g of 15NH3, CO, and S, respectively, 40 ml CH3OH, 40 mg H2S, 100 oC and 120 min of reaction) 1.82 g (yield 76.5%) of the compound was obtained per batch. The synthesized CO(15NH2)2 contained 46.2% N, 0.55% biuret, melting point of 132.55 oC and did not exhibit isotopic fractionation. The production cost of CO(15NH2)2 with 90.0 at. % 15N was US