The determination of extractable plant available selenium from soils by electrothermal atomic absorption spectroscopy

Abstract

Plant available selenate was measured in a soil extract by electrothermal atomic absorption spectroscopy. Selenate in soil was first extracted with potassium sulfate then extracted into toluene fron an iodide‐sulfuric acid media. Aliquots of the toluene were injected into the graphite furnace for selenium determination. Quantities of extractable selenium measured using the electrothermal atomic absorption method compared favorably with the results of determinations using a fluorometric technique on aliquots of the soil extract. The simplicity of the procedure allowed for the precise determination of soil selenate in a brief period of time.     

An automatic procedure for determination of available iron in Indian soils

Abstract

An on‐line automatic procedure for the flow injection analysis (FIA) determination of iron (Fe) in a variety of soil extracts with common laboratory reagents, i.e., thiocyanate, thiocyanate +1,10‐phenanthroline/bipyridine has been tested. The apparent molar absorptivity of the complexes lies in the range of (5.5–7.0)x10³ L mole^‐1 cm^‐1 at an absorption maximum between 470–495 nm. The detection limit of the method is 15 ppb Fe. The sample output is 100 samples/hr. Almost all ions associated with Fe in the soil extract do not interfere in this method. Optimization of FIA variables, composition of the complex, and effect of other ions on the determination of Fe are discussed. The method has been used for determination of Fe status in a variety of agricultural soils in east Madhya Pradesh, India.     

Cadmium copperization assays for the preparation of nitrate‐reducing columns

Abstract

An electrolytic method for the copperization of cadmium as a reducing agent for nitrate‐nitrogen (NO₃ ^‐‐N) determination is described. The conditions, medium, and time of copperization as well as the length of the cadmium reducing column has been studied in detail. This column was placed in a flow injection analyzer for the online determination of NO₃ ^‐‐N in soil extracts. The results obtained show that 1% copper sulfate (CuSO₄), 30 min and 55 mm are the optimal medium, time, and column length, respectively. With this reducing column, the method is linear between 0 and 12 ppm NO₃ ^‐‐N with a precision of 0.29% and a sampling frequency of 80 determinations per hour. The proposed method has been applied to the determination of NO₃ ^‐‐N in soil extracts and the results agree with those obtained by the reference method (r = 0.9998). The optimized electrolytic procedure for the copperization of cadmium permits more than 3000 determinations without any significant loss of sensitivity.     

Sequential Injection Determination of Nitrate in Vegetables by Spectrophotometry with Inline Cadmium Reduction

Abstract

A sequential injection system for the determination of nitrate (NO₃ ^?) in vegetables was developed to automate this determination, allowing for substantially reduced reagent consumption and generated waste using low‐cost equipment. After extraction with water and filtration, the extracted nitrate is reduced inline to nitrite in a copperized cadmium (Cd) column and determined as nitrite. According to the Griess–Ilosvay reaction, nitrate is diazotized with sulfanilamide and coupled with N‐(1‐naphtyl)‐ethylenediamine dihydrochloride to form a purple‐red azo dye monitored at 538 nm.

Nitrate can be determined within a range of 1.35–50.0 mg L^?1 of NO₃ ^? (corresponding to 0.270–10.0 g of NO₃ ^? per kg of vegetable), with a conversion rate of nitrate to nitrite of 99.1±0.8%. The results obtained for 15 vegetable extracts compare well with those provided by the classical procedure, with a sampling throughput of 24 determinations per hour and relative standard deviations better than 1.2%.     

Mercury pollution of effluent,air, and soil near a battery factory in Tanzania

Effluent, air, and soil samples near a battery factory in Dar es Salaam, Tanzania, where HgCl₂ is used to prevent mold growth, were collected to explore the potential for pollution of the environment from industrial discharge of Hg. Flameless atomic absorption spectrophotometry was used for Hg determinations. The concentration of Hg in the effluent ranged from <0.2 to 5.2 mg L^?1 and the Hg concentration varied greatly within and among sampling days, showing different peaks. Air contained a mean of 4.0 μg m^?3 with little variation within and between sampling days. Soils near the factory contained high Hg levels, from 6.7 to 472 mg kg^?1 in the immediate vicinity, the highest level being associated with disposal of solid waste (defective batteries). Downwind the concentration of Hg decreased with increasing distance from the factory resulting in a soil concentration of 1.0 mg Hg kg^?1 about 2 km away. Upwind the Hg concentration decreased drastically within a distance of 100 to 200 m.     

The determination of total lead in soil by atomic absorption spectrophotometry

A method is described for the determination of total lead in soil by atomic absorption spectrophotometry. The sample is digested with hot nitric acid. The dry residue is taken up in hydrochloric acid and excess iron is removed by extraction with acetylacetone‐chloroform. Lead is then extracted using the system DDC‐MIBK. The organic phase can be sprayed directly into the flame.

The method is not affected by elements occurring in contaminated soils. Iron is removed because a slow‐forming precipitate of the Fe‐DDC‐complex blocks the nebuliser system. The method is an improvement on other methods because no sulfuric acid is used for digestion, and therefore losses of lead by precipitation or occlusion are avoided. Tests confirm that the recommended method gives complete recovery of lead.

Lead can be determined in the range from 4 to 240 ppm in the soil. A standard soil sample has been analyzed, yielding a mean value of 125 μg Pb/g soil with a relative standard deviation of 2.4%.     

Determination of total boron in soils by inductively coupled plasma atomic emission spectrometry using microwave‐assisted digestion

Abstract

A method is described in which total soil boron (B) was determined by inductively coupled plasma atomic emission spectrometry (ICP‐AES). The method is based on microwave‐assisted digestion of soil samples with nitric acid (HNO₃), hydrofluoric acid (HF) and hydrogen peroxide (H₂O₂). Excess HF was eliminated by adding silicon (IV) oxide (SiO₂). The B 208.959 nm line was chosen as the analytical line to avoid the spectral interferences of iron (Fe). A detection limit of 0.0045 mg L^‐1 was obtained with the selected analytical line under the optimized operating conditions. Four National Institute of Standards and Technology (NIST) standard reference materials (three soils and one river sediment) and four different type of practical soils were analyzed to test the reliability of the method. The total B concentration in selected samples ranged from 19 to 76 mg kg^‐1. The excellent recoveries of the spike (98.5–101%) indicate that the proposed procedure is effective and feasible for the determination of total B in soils.     

Growth and cadmium accumulation in selected switchgrass cultivars

Abstract

Switchgrass (Panicum virgatum L.) has potential as a sustainable biofuel crop. Utilizing alternative sources of fertilizer nutrients could enhance production of switchgrass. However, alternative sources of fertilizer such as sewage sludge sometimes contain heavy metals such as cadmium (Cd) and the response of switchgrass to Cd is not known. Four switchgrass cultivars (Alamo, Blackwell, Cave‐in‐Rock, and Trailblazer) grown in sand culture were watered twice weekly with a nutrient solution containing Cd. Cadmium levels in solution were 0, 1, 2, 4, 8, and 16 mg Cd L^‐1. Plants were harvested 63 d after planting and separated into leaf blade, stem (culm + leaf sheath), and root components. Tissue Cd concentrations were determined using atomic absorption spectrophotometry. Cultivars differed (P<0.05) by less than 15% for biomass accumulation and allocation among plant parts. Cadmium levels of 16 mg L^‐1 reduced biomass yields by 31% for roots, 39% for leaf blades, and 47% for stems as compared to no added Cd. At 16 mg Cd L^‐1, Cd concentration in leaf blades was 9.9 mg kg^‐1. The highest levels of Cd (329 mg kg^‐1) were found in roots of Blackwell and Trailblazer grown at the highest Cd level. Cadmium at 16 mg Cd L^‐1 is phytotoxic to switchgrass and accumulates in all plant parts. The cultivars tested in this study did not differ in biomass accumulation in response to Cd; however, Cd accumulation in plant parts differed among cultivars. Consideration of Cd uptake should be a part of switchgrass cultivar selection when grown in the presence of Cd.     

Automatic spectrophotometric determination of copper in plant material,soil, and fertilizer mixtures by a kinetic method

Abstract

Knowledge of metal concentration in soils, plant material, and fertilizers is important both for plant nutrition as for environment contamination studies. In this paper, an automated spectrophotometric method using Flow Injection Analysis (FIA) for copper (Cu) determination was studied. That method was based on the catalytic effect of Cu²⁺ ions in the color fading of the red‐purplish complex formed when iron (Fe³⁺) and thiosulfate (S₂O₃ ^2‐) ions react. The principal feature of the studied method is its high selectivity, which allowed the Cu determination in a complex matrix as nitrogen (N):phosphorus (P):potassium (K) fertilizer mixtures without effect of interference. Soil and plant tissue samples were also analyzed with good precision and accuracy when compared with atomic absorption spectrophotometry.     

Application of the Multicomponent Spectral Fitting Algorithm in the Estimation of the Correct Value of Phosphorus determined by ICP OES in Soil Samples

ABSTRACT

Phosphorus (P) determination by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) in soil extracts is affected by copper (Cu) content and may lead to misinterpretation of the results. In this study, Multicomponent Spectral Fitting (MSF) method for the quantitative determination of P in the presence of Cu was tested. Phosphorus determination by UV/Vis molecular absorption spectrometry (COL) was free from copper interference. Phosphorus determination by ICP OES at wavelengths of 213.618 and 214.914 nm without use of MSF were subject to interference when Cu concentration was greater than 1.5 and mg L^?1 and 3.5 mg L^?1, respectively. When the P: Cu ratio in solution was 1:1 and 2:1, on average, there was no significant difference between the P determined by COL and by ICP-OES using MSF. In matrices containing Cu, it is indicated to use the P spectral line at 214.914 nm because it was less sensitive to Cu concentration than spectral line at 213.618 nm.     

Integrated Flow-based System Displaying an In-line Mini Soil Column to Monitor Iron Species in Soils Leachates

ABSTRACT

Contamination of ground water as a consequence of soil leaching processes is an issue of major concern. In this context, a simulation of the soil leaching process was designed. A sequential injection (SI) method to monitor the soil leaching of iron complexes with in-line rain simulation for leachate production is described. The developed methodology comprises the SI determination of both iron(III) and 3-hydroxy-4-pyridinones iron(III) complexes, coupled to a mini soil column (mSC) for displaying in-line rain simulations. The described SI method enabled iron(III) determination within the range 2.0–35 µmol L^?1, with a detection limit of 0.42 µmol L^?1, and determination of iron(III) complexes in the range 1.0–45 µmol L^?1. It was successfully applied to leachates from laboratory scale soil columns (LSSC), with good precision for both iron(III) and iron complexes determinations: calculated relative standard deviation (RSD) of 5% and 6%, respectively. A step further in automation and miniaturization was attained with the incorporation of a mini soil column for the in-line leachate production. The system enabled the soil leachate production and assessment in less than 5 min, including determinations in triplicate.     

Automated Modification of the Molybdenum Blue Colorimetric Method for Phosphorus Determination in Soil Extracts

A flow injection analysis (FIA) method capable of automation for molybdate reactive phosphorus (P) determination in soil extracts is described. Results obtained using this method in three soil extracts [calcium chloride (CaCl₂), Olsen, and Mehlich I] were the same as those provided by the manual molybdate blue colorimetric method. Linear range extending to 2 mg P L^?1, detection limits ranging from 6 to 26 µg L^?1 depending on the soil extract, and accurate recoveries from P‐spiked samples were achieved. The sensitivity of the system was around 0.3 absorbance units per mg P L^?1, and the sampling frequency was 72 samples h^?1, higher than those described for most of the flow injection methods.     

Determination of molybdenum in soil test extracts with potassium iodide plus hydrogen peroxide reaction

Abstract

The potassium iodide and hydrogen peroxide reaction (KI+H₂O₂) is catalyzed by molybdate. Our objective was to use this reaction to determine molybdenum (Mo) in Mehlich 1 (1:10) soil test extracts. A 350‐nm wavelength and 10‐minute reaction time were selected for the determination and absorbance was linear for 0.0 to 0.15 mg L^‐1 Mo. Ten samples of a LEd‐Iturama soil were extracted with Mehlich 1 and Mo determined. These extracts were also mixed and Mo determined on 10 aliquots of the mixture. Molybdenum concentration in the soil had a coefficient of variation (CV) of 23.5%, whereas that for the mixture was 3.95%. The low CV for the mixture indicates good precision for this method. The higher CV for the individual extracts indicates that most of the variation comes from the extraction phase of individual samples. To show the practical utility of the method, Mo maximum adsorption capacities (MoMAC) of 16 soils, primarily Oxisols, from Minas Gerais, Brazil were determined. The MoMAC varied from 0.15 to 2.02 mg g^‐1 and there were good correlations between MoMAC and soil clay content as well as between MoMAC and soil organic carbon content. From our experience, use of the KI+H₂O₂ reaction is a practical method of determining Mo in Mehlich 1 soil test extracts.     

Phosphate sorption characteristics of major soils in Okinawa,Japan

Abstract

Phosphate sorption isotherms were determined for 16 representative major soils developed from different parent materials on Okinawa. Phosphate sorption characteristics were satisfactorily described by the Langmuir equation, which was used to determine phosphorus (P) sorption maxima of the soils. Phosphate sorption maxima ranged from 630 to 2208 mg P kg^‐1 soil (mean 1,362 mg P kg^‐1). The standard P requirement (i.e., the amount of P required to attain 0.2 mg P L^‐1 equilibrium solution) followed the same trend as sorption maximum (r =0.94***), with values ranging from 132 to 1,020 mg P kg^‐1 soil (mean 615 mg P kg^‐1). This mean value corresponds to fertilizer addition of 923 kg P ha^‐1 indicating that the soils have high P fertilizer requirements. Results of simple linear regression analysis indicated that sorption maximum was significantly correlated with clay content, organic matter, oxalate iron (Fe), pyrophosphate Fe, DCB aluminum (Al), oxalate Al, and pyrophosphate Al, but not with DCB Fe, pH, or available P content. The best regression model for predicting sorption maximum was the combination of clay, organic matter, pyrophosphate Fe, and DCB Al which altogether explained 79% of the variance in sorption maximum. The equation obtained could offer a rapid estimation of P sorption in Okinawan soils.     

Dissolution of aluminum and iron phosphate by humic acids

Abstract

An investigation was conducted to study the effect of humic (HA) and fulvic acid (FA) on the dissolution of aluminum phosphate (AlPO₄) and iron phosphate (FePO₄), to analyze the dissolution products, and assess their availability to plants. The rate of dissolution was determined by shaking 10 mg of Al‐ or FePO₄ with 0 to 800 mg L^‐1 of HA or FA solutions at pH 7.0 for 0 to 192 hours. The phosphorus (P) concentration was measured in the extracts by spectrophotometry, whereas the nature of P‐humic acid complexes was determined by ³¹P NMR analysis. Availability of dissolution products was studied by growing corn plants in aerated hydroponic solutions receiving treatments of 50 mg Al‐ or FePO₄ and 0 to 800 mg L^‐1 of HA or FA at pH 5.0. The results indicated that the amount of P released by HA or FA increased with time. Humic acid was more effective than FA in dissolving the metal phosphates. The ³¹P NMR analysis showed that the dissolution products contained free orthophosphates and minor amounts of P‐humic acid complexes. This confirms the role of HA as a powerful chelator of Al and Fe, liberating in this way the orthophosphate anions. Corn plants grown in hydroponics, with AlPO₄ or FePO₄ as the source of P, exhibited better growth performance when HA or FA are present.     

Speciation of cadmium,copper, lead,and zinc in contaminated soils

Abstract

To investigate the activity of free cadmium (Cd²⁺), copper (Cu²⁺), lead (Pb²⁺), and zinc (Zn²⁺) ions and analyze their dependence on pH and other soil properties, ten contaminated soils were sampled and analyzed for total contents of Cd, Cu, Pb, and Zn (Cd_T, Cu_T, Pb_T, and Zn_T, respectively), 0.43 MHNO₃‐extractable Cd, Cu, Pb, and Zn (Cd_N, Cu_N, Pb_N, and Zn_N, respectively), pH, dissolved organic matter (DOC), cation exchange capacity (CEC), ammonium oxalate extractable aluminum (Al) and iron (Fe), and dissolved calcium [Ca²⁺]. The activity of free Pb²⁺, Cd²⁺, Cu²⁺, and Zn²⁺ ions in soil solutions was determined using Donnan equilibrium/graphite furnace atomic absorption (DE/GFAA). The solubility of Cd in soils varied from 0.16 to 0.94 μg L^‐1, Cu from 3.43 to 7.42 μg L^‐1, Pb from 1.23 to 5.8 μg L^‐1, and Zn from 24.5 to 34.3 μg L^‐. In saturation soil extracts, the activity of free Cd²⁺ ions constituted 42 to 82% of the dissolved fraction, for Cu²⁺the range was 0.1 to 7.8%, for Pb²⁺ 0.1 to 5.1% and for Zn²⁺2 to 72%. The principal species of Cd, Cu, Pb, and Zn in the soil solution is free metal ions and hydrolyzed ions. Soil pH displayed a pronounced effect on the activity of free Cd²⁺, Cu^2t, Pb²⁺, and Zn²⁺ ions.     

Use of Composting Manure to Improve Plant Iron and Zinc

Abstract

Laboratory experiments were conducted to determine the influence of three types of decomposing fresh organic materials [pig manure (PM), Astagalus sinicus (AS), and Alternanthera philoxeroides (AP)] on dissolution of Fe₂O₃ and ZnO and also the use of a loamy calcareous soil as an alternative source of iron (Fe) and zinc (Zn). Levels of Fe and Zn concentrations in composting solutions changed with composting time. The maximum levels of solution Fe resulting from the decomposition of the three organic materials were 20, 612, and 348 mg L^?1 for PM, AS, and AP, respectively, when the soil was supplied as the Fe source, and 17, 32, and 16 mg L^?1 when Fe₂O₃ was supplied as the Fe source. Corresponding maximum levels of solution Zn were 0.9, 0.7, and 1.3 mg L^?1 and 35, 171, and 103 mg L^?1 when the soil and ZnO was supplied as the Zn source respectively for the same three organic materials.     

Repeated Bray‐2 extractions of an Inceptisol and an Andisol

Abstract

Bray‐2 extractable phosphorus (Bray2‐P) is commonly used to measure plant‐available P in soil. The pool size of extractable P in the residual soil should be reduced after extraction. Phosphorus, once released with the Bray‐2 solution, is resorbed by the soil during the extraction‐filtration period. If P resorption is large, the Bray2‐P concentration is underestimated. The P absorption coefficient and composition of inorganic P [calcium (Ca)‐P, aluminum (Al)‐P, and iron (Fe)‐P] probably affect the Bray2‐P concentration. We investigated the effect of repeated Bray‐2 extractions on the Bray2‐P concentrations in relation to the P absorption coefficient and Ca‐P, Al‐P, and Fe‐P concentrations in two soils (an Inceptisol and an Andisol), which markedly differ in the P absorption coefficient. Test soil samples were the initial soil (S0) and soils after the 1st to 4th extractions (S1‐S4) for the Inceptisol, and S0, S1‐S4, and S7 for the Andisol. The Bray2‐P, Ca‐P, Al‐P, and Fe‐P concentrations in the S0 were 260, 75, 338, and 536 mg kg^‐1 in the Inceptisol, and 217, 31, 972, and 354 mg kg^‐1 in the Andisol, respectively. All of the extractable P concentrations in the Inceptisol decreased with increasing numbers of extractions, and the Bray2‐P, Ca‐P, Al‐P, and Fe‐P concentrations in the S4 were 5.3, 21, 5.7, and 30% of those in the S0, respectively. On the other hand in the Andisol, the Bray2‐P, Ca‐P, and Fe‐P concentrations did not decrease in the S1 and S2 compared with those in the S0, although the Al‐P concentration decreased with increasing numbers of extractions. The Bray2‐P, Ca‐P, Al‐P, and Fe‐P concentrations in the S7 were 23, 71, 16, and 79% of those in the S0, respectively. The P absorption coefficient in the S0 was higher in the Andisol (7,703 mg kg^‐1) than in the Inceptisol (1,582 mg kg^‐1), and it decreased with increasing numbers of extractions in both soils. The P absorption coefficient in the S7 Andisol was 51% of that in the S0, while the P absorption coefficient in the S4 Inceptisol was 24% of that in the S0. The results suggest that Presorption affects the efficiency of extraction with the Bray‐2 solution, and the composition of Ca‐P, Al‐P, and Fe‐P fractions. The Bray2‐P concentration in soil with high P absorption coefficient is underestimated due to P resorption.     

An evaluation of some manual colorimetric methods for the determination of inorganic nitrogen in soil extracts

Abstract

A number of manual colorimetric methods for the determination of inorganic nitrogen in 1 M KCl soil extracts were investigated to find techniques that were inexpensive, rapid, versatile and suitable for laboratories with limited analytical equipment. Three colorimetric methods for No^? ₃‐N determination were evaluated and only the copperised/cadmium reduction technique suffered no significant interference from the Cl^? present in the extracting solution. A phenol‐hypo‐chlorite (Berthelot) procedure for NH⁺ ₄‐N determination and the Griess‐Ilosvay method for NO^? ₂‐N determination were both found suitable for N determination in 1M KC1 soil extracts. The reliability and accuracy obtainable with the manual colorimetric methods described was shown to be comparable with that obtained from colorimetric analyses performed using an AutoAnalyser.     

Rapid and sensitive determination of nitrate in plant tissue using flow injection analysis

Abstract

The determination of nitrate in waters and soil extracts by the reduction of nitrate to nitrite by metallic or liquid reductants followed by the colorimetric determination of NO₂ ^‐using the Griess‐Ilosvay reaction has been automated for use with air‐segmented auto‐analyzers or flow injection techniques. However, this technique is not applicable to plant extracts as organic species in the extracts inactivate the reduction columns. The objective of this study was to develop an automated procedure that would allow the determination of NO₃ ^‐in plant extracts without the necessity of prior manual treatment. A flow injection technique was developed that successively traps and releases NO₃in an anion exchange column thereby removing pigments and other non‐ionic and cationic species that otherwise interfere with conversion of NO₃ ^‐ to NO₂ ^‐on a copperized cadmium column. This reduction step is subsequently followed by standard Griess‐Ilosvay colorimetric detection of this ion at a wavelength of 530 nm. The technique uses relatively simple and inexpensive equipment, principally a spectrophotometer equipped with a flow‐through cell and a pen recorder output, a 6‐channel peristaltic pump with accompanying tubing and a Perspex injector/commutator valve made in a laboratory workshop. The technique was found to avoid any significant interference of pigments or other organic compounds in the plant extracts, and the results compared favorably with those obtained using the manual transnitration technique. Analysis time was approximately 1.5 min per sample and could detect NO₃’ concentration as low as 0.1 ug NO₃’‐N ml/¹ in plant extracts (10 ug NO₃’‐N g‘¹of plant material).