Simultaneous determination of positional isomers of benzenediols by capillary zone electrophoresis with square wave amperometric detection

Influence of anions on dispersion and physical properties of the A horizon of a Red-brown earth

Soluble Zn in soils and its availability to plants may be influenced by the presence of organic ligands, particularly in the rhizosphere, where soluble organic matter may be present in high concentrations. Zinc adsorption by a lateritic podzolic soil was measured in the presence of 0 to 3 mmol L ' of acetate, oxalate, citrate, tricarbally late, salicylate, or catechol, or 0 to 3 mmolc L ' of humate. Zinc remaining in solution was measured by atomic absorption spectrometry after shaking the soil for 17 h at a soil/liquid ratio of 1:5 in a 0.003 mol L ' KC1 solution containing 0 to 500 pmol L ' Zn and the ligands. In the absence of organic ligands, more than 95% of the zinc was adsorbed. The amount of adsorption was linearly correlated with pH and the concentration of ZnOH* in solution after shaking (r 0.98; multiple regression). Zinc adsorption and pH decreased in the pres ence of each of the ligands except catechol. Seventy four percent of the variation in adsorption was accounted for by the combined effects of the concentration of zinc-ligand complex (Zn-L) and the concen tration of ZnOH that were present in solution after adsorption. However, other factors such as changes in the number of sites avail able for adsorption, the point of zero salt effect (pzse) of the soil, and the charge of zinc species also contributed to the magnitude of zinc adsorption. I SOILS containing concentrations of plant-available Zn that are marginal for adequate plant growth, the presence of organic ligands in the rhizosphere may influence the concentration of Zn in solution and thereby its availability to plants (Norvell, 1972). The soil solution can contain many kinds of organic ligands (Stevenson and Ardakani, 1972; Tiller, 1983), which may have originated from plant exudates, decaying organic matter, or as the product of microbial activities. Concentrations of organic ligands found in the rhizosphere are usually higher than in the bulk soil solution. Generally, the ligand has a short existence, because microorganisms themselves can also use these ligands as their substrates (Lindsay, 1972). Stevenson and Ardakani (1972) reviewed the types of organic ligands in soils and divided them into two broad groups. The first group consists of defined biochemical compounds produced by root exudation and microorganisms, whereas the other group is made up of lessdefined molecules usually referred to as humic and fulvic acids. The latter type are the product of the microbial breakdown of dead plant and animal debris (Stevenson and Ardakani, 1972). The importance of these ligands, however, is that they are able to form complexes with micronutrients; and the complexes are more soluble than the free ion (Broadbent and Ott, Soil Science and Plant Nutrition, School of Agric., Univ. of Western Australia, Nedlands, Western Australia 6009. Received 13 Oct. 1988. \"\"Corresponding author. Published in Soil Sci. Soc. Am. J. 54:1242-1248 (1990). 1957; Hodgson et al., 1965, 1966; Norvell, 1972; Prasad et al., 1976). Some ligands, particularly those defined as humic acid, form strong complexes with metal ions and become insoluble. Adsorption is a major contributing factor to low concentrations of Zn in solution in Zn-deficient soils (Ellis and Knezek, 1972). Soil pH has been shown to affect Zn adsorption, either by changing the number of sites available for adsorption or by changing the concentration of the Zn species that is preferentially adsorbed (Barrow, 1986). Soluble organic ligands may also influence Zn adsorption by these two mechanisms. Adsorption of organic anions can increase the negative charge on surfaces (Parfitt and Russell, 1977; Barrow, 1985) and hence increase Zn adsorption. On the other hand, the presence of organic ligands in solution may decrease Zn adsorption by competing with the surface for the Zn. Indeed, Zn adsorption onto clays and hydrous oxides has been shown to increase (Pickering, 1980) or decrease (Kinniburgh and Jackson, 1974) in the presence of organic ligands. However, these studies were conducted at high Zn concentrations and ionic strengths, which are not normally found in unpolluted and nonsaline soils. The variable effect of ligands on Zn adsorption will also depend on pH, concentration of ligand and metal, the pzse of soil, the formation constant of the complex, and the ionic strength of the soil solution. The objective of this study was to examine the effect of three concentrations of seven organic ligands on Zn adsorption by a lateritic soil from Western Australia where Zn concentrations and ionic strengths are low (Robson and Gilkes, 1981; Dolling and Ritchie, 1985). MATERIALS AND METHODS Effect of pH on Zinc Adsorption in the Absence of Organic Ligands The adsorption of Zn by a lateritic podzolic soil (Northcote classification: Dy 5.51; soil taxonomy: Entisol) was measured at four pH values and five concentrations of added Zn. The soil was chosen because of its relatively low sorption capacity (maximum Zn adsorption was 12 jumol 8~' soil). The soil contained 4 nmol g~' of DTPA-extractable Zn, 3.1% of organic C, and 8.1 Mg g~' of NaHCO3-extractable P. The cation-exchange capacity of the soil was 6.9 cmolc kg' and Ca and Al occupied 70 and 2% of the exchange sites, re spectively. The soils were shaken with 3 mmol L\" KC1 so lutions containing 100, 200, 300, 400, and 500 Mmol L-' Zn(NO3)2 at a soil/liquid ratio of 1:5. The concentrations were chosen because a preliminary experiment indicated that the Zn concentrations after adsorption spanned the range normally found in soils (Tiller et al., 1972; Pendias and Pen dias, 1984). The pH of each sample was then adjusted by adding 0, 1, 1.5, and 2 mL of 0.1 mol L-' HC1. The soil suspensions were shaken for 17 h, centrifuged at a relative

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Zinc Adsorption by a Lateritic Soil in the Presence of Organic Ligands

Flow injection chemiluminescence determination of pyrogallol

In the present study, a new biosensor based on laccase from Paraconiothyrium variabile was developed for catechol. The purified enzyme entrapped into the Fe3O4/polyaniline/chitosan (Fe3O4/polyaniline (PANI)/chitosan (CS)) biocomposite matrix film without the aid of other cross-linking reagents by a one-step electrodeposition on the surface of carbon paste electrode (CPE). The formed layer of biocomposite was characterized with scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The biosensor was optimized with respect to biocomposite composition, enzyme loading, and solution pH by amperometry method. The biosensor exhibited noticeable eletrocatalytic ability toward catechol with a linear concentration range from 0.5 to 80 μM and a detection limit of 0.4 μM. The biosensor showed optimum response within 8 s, at pH 5, and 40 °C. The apparent Michaelis–Menten (K
 M
 app) was found to be 1.092 μM. The fabricated biosensor could be applied for determination of catechol in tea leaf samples.

A new amperometric biosensor based on Fe3O4/polyaniline/laccase/chitosan biocomposite-modified carbon paste electrode for determination of catechol in tea leaves.

Spectrophotometric determination of microgram amounts of hydroquinone, pyrogallol and resorcinol

Spectrophotometric determination of pyrocatechol, resorcinol and phloroglucinol with potassium iodate in dilute nitric acid

An accurate method has been described for the determination of cysteine, cystine and methionine at the mg level with the use of ammonium hexanitratocerate(IV) as the oxidant. The sample is reacted with an excess of Ce(IV) solution at room temperature (25°) for about 30 min; the unreacted Ce(IV) reagent is then determined by titrating against Fe(II) using ferroin indicator. The precision and accuracy are within ±0.5%.

Q. S. Usmani

Papers

Spectrophotometric determination of microgram amounts of hydroquinone, pyrogallol and resorcinol

Spectrophotometric determination of pyrocatechol, resorcinol and phloroglucinol with potassium iodate in dilute nitric acid

Milligram determination of cysteine, cystine and methionine using ammonium hexanitratocerate(IV) as the oxidant