Josiane M. T. Carneiro

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).

Spectrophotometric determination of total nitrogen in plant materials using a flow-injection system with an AgCl(s) reactor

Abstract An improved flow-injection system with an AgCl (s) reactor is proposed for the spectrophotometric determination of total nitrogen in Kjeldahl digests of plant materials. After sample injection, the established sample plug is alkalinised and allowed to flow through the mini-column where Ag + ions are displaced as the soluble [Ag(NH 3 ) 2 ] + complex. Bromopyrogallol red and o -phenanthroline are then added and a coloured ternary complex is formed under neutral conditions. The system is very stable, and baseline drift is usually −1 . The analytical curve is linear up to 6.00% (w/w) N (dry basis), regression coefficient has been estimated as >0.999 ( n =6) and detection limit is 0.2% (w/w) N. Accuracy was confirmed by running standard reference materials and typical samples already assayed by conductimetry.

Spectrophotometric flow-injection determination of zinc in plant digests based on a spot test

A spot test was implemented in a flow-injection system for the spectrophotometric determination of zinc in digests of plant materials. It is based on the influence of Zn(2+) on the oxidation rate of 1-naphthylethylenediamine (NED) by hexacyanoferrate(III) under acidic conditions. In order to control the precipitate formation and to maintain the resulting suspension, a micellar medium was established by adding Triton X-100. The proposed system handles about 65 samples per hour, meaning 72mug NED and 9.0mg K(3)[Fe(CN)(6)] per determination. Baseline drift is usually <0.01 absorbance per hour and the analytical signals for 0.5-2.5mgl(-1) Zn range within ca. 0.07-0.45 absorbance. Linearity of the analytical curve is fair (r>0.999, n=6) and detection limit was estimated as 0.2mgl(-1) Zn. Results are precise (R.S.D.<1%, n=10) and in agreement with flame atomic absorption spectrometry and with certified values of standard reference materials.

Determinação indireta de N-total em plantas por espectrometria de absorção atômica com chama empregando uma mini-coluna de AgCl(s)

Um sistema de analises quimicas por injecao em fluxo empregando uma mini-coluna de AgCl(s) e proposto para a determinacao de nitrogenio total em plantas por espectrometria de absorcao atomica com chama. O metodo se baseia na remocao de ions Ag+ por amonia com formacao do complexo diamino argentato(I) e posterior direcionamento da amostra a um espectrometro de absorcao atomica onde prata e monitorada. Nitrogenio foi determinado em sete amostras de referencia (tres replicatas) com precisao e exatidao comparaveis as do procedimento condutimetrico. O sistema e estavel, apresentando apenas pequenas variacoes em sensibilidade (< 2 %) durante periodos de operacao de 4 horas. A velocidade analitica e de aproximadamente 100 h-1 e a repetibilidade das medidas e satisfatoria (desvio padrao relativo em geral < 0,02).

Determinação de enxofre em amostras vegetais por oxidação via seca em meio alcalino com detecção espectrofométrica

The sulphur take an essential role in plants and it is one of the main nutrients in several metabolic processes. The dry ash oxidation, using alkaline oxidizers agent, is the simplest and most economical form for the oxidation of Organic S to sulfate in plants. The objective of this work is to propose a method for sulfur determination in plants samples using dry ash oxidation and agent oxidizers alkaline. The quantification of S-SO42- in samples was accomplished by turbidimetric method. The results demonstrated that the proposed method for oxidation alkaline was appropriate.