Analysis Of Soil Extracts Research Articles

Use of ion-selective electrodes for determination of content of potassium in Egner-Rhiem soil extracts

Potassium is one of the most important nutrients for plants and its content in the soil should be monitored. In the precision agriculture, which is recommended now, the ion selective electrodes are tested to determine chemical properties of the soil. The objective of this work was an evaluation of use of the valinomycin-based ion selective sensors for determination of assimilated potassium in Egner-Rhiem soil extracts. Flame photometry was used as a reference method. Results obtained from potentiometric and photometric methods in soil extracts correlated linearly (<i>R</i><sup>2</sup> = 0.84). Analysis of soil extracts by the ion selective electrodes is simple and there is not a need for calcium ions precipitation.

Separation and identification of isomeric acidic degradation products of organophosphorus chemical warfare agents by capillary electrophoresis-ion trap mass spectrometry

Capillary electrophoresis (CE) coupled to ion trap mass spectrometry (MS) was evaluated for the separation and identification of chemical warfare agent degradation products (alkylphosphonic acids and alkyl alkylphosphonic acids). Different analytical parameters were optimized in negative ionization mode such as electrolyte composition (15 mM CH 3COONH 4, pH 8.8), sheath liquid composition (MeOH/H 2O/NH 3, 75:25:2, v/v/v), nebulization and ion trapping conditions. A standard mixture of five alkylphosphonic (di)acids and five alkyl alkylphosphonic (mono)acids containing isomeric compounds was used in order to evaluate CE selectivity and MS identification capability. The obtained electropherograms revealed that CE selectivity was very limited in the case of alkyl alkylphosphonic acid positional isomers, whereas isomeric isopropylphosphonic and propylphosphonic acids were baseline-separated. CE–MS–MS experiments provided an unambiguous identification of each isomeric co-migrating alkyl alkylphosphonic acids thanks to the presence of specific fragment ions. On the other hand, CE separation was mandatory for the identification of isomeric alkylphosphonic acids, which led to the same fragment ion and could not be differentiated by MS–MS. The developed method was applied to the analysis of soil extracts spiked with the analytes (before or after extraction treatment) and appeared to be very promising since resolution and sensitivity were similar to those observed in deionized water. Especially, analytes were detected and identified in soil extract spiked at 5 μg mL −1 with each compound before extraction treatment.

Electroanalytical and chromatographic determination of pentachlorophenol and related molecules in a contaminated soil: a real case example

Electroanalytical and chromatographic methodologies have been applied for the determination of pentachlorophenol (PCP) and some of its derivatives in real soil samples contaminated by industrial discharge. The analytes were extracted with hexane from soil samples collected at different points of the site and mixed to produce a representative sample. Square wave voltammetry (SWV) experiments were carried out on either a boron-doped diamond (BDD) electrode or a gold ultramicroelectrode (Au-UME) in an analyte composed by the Britton-Robinson (B-R) buffer at pH 5.5 with the direct addition of proper amounts of the extract. The voltammetric responses revealed an irreversible anodic peak at approximately 0.80 V vs. Ag/AgCl with a peak current showing a linear dependence on PCP concentration. This linear relationship yielded a detection limit (DL) of 2×10 −8 mol l −1 (or 5.5 μg l −1) for the BDD electrode and 6.9×10 −8 mol l −1 (18.4 μg l −1) for the Au-UME, while the independently measured HPLC detection limit was 1.1×10 −8 mol l −1 (3.0 μg l −1). The application of electroanalytical and chromatographic methodologies in the analysis of soil extracts revealed, besides the PCP responses, signals for some related molecules such as o-tetrachlorobenzoquinone ( o-chloranil), hexachlorobenzene and tetrachlorophenol. Recovering experiments for PCP showed a concentration of 27.5 mg kg −1 for the electroanalytical determinations and 26.8 mg kg −1 for the HPLC analysis, values exceedingly high if considering that the maximum residue limit established for natural waters by the Brazilian Environmental Agency is 10 μg l −1.

Benefits of inoculation of the common bean ( Phaseolus vulgaris ) crop with efficient and competitive Rhizobium tropici strains

Cropping in low fertility soils, especially those poor in N, contributes greatly to the low common bean (Phaseolus vulgaris L.) yield, and therefore the benefits of biological nitrogen fixation must be intensively explored to increase yields at a low cost. Six field experiments were performed in oxisols of Parana State, southern Brazil, with a high population of indigenous common bean rhizobia, estimated at a minimum of 103 cells g–1 soil. Despite the high population, inoculation allowed an increase in rhizobial population and in nodule occupancy, and further increases were obtained with reinoculation in the following seasons. Thus, considering the treatments inoculated with the most effective strains (H 12, H 20, PRF 81 and CIAT 899), nodule occupancy increased from an average of 28% in the first experiment to 56% after four inoculation procedures. The establishment of the selected strains increased nodulation, N2 fixation rates (evaluated by total N and N-ureide) and on average for the six experiments the strains H 12 and H 20 showed increases of 437 and 465 kg ha–1, respectively,in relation to the indigenous rhizobial population. A synergistic effect between low levels of N fertilizer and inoculation with superior strains was also observed, resulting in yield increases in two other experiments. The soil rhizobial population decreased 1 year after the last cropping, but remained high in the plots that had been inoculated. DGGE analysis of soil extracts showed that the massive inoculation apparently did not affect the composition of the bacterial community.

A technique to facilitate diffusions for nitrogen‐isotope analysis by direct combustion

A technique was developed that permits the use of boric acid‐indicator solution in carrying out diffusions for inorganic 15N analysis of soil extracts by direct combustion, so as to eliminate the need for a separate quantitative determination. In this technique, the titrated sample is acidified with 2.5 M KHSO4 and subsequently treated with methanol to remove H3BO3 The NH+4‐N is dissolved in 1 mL of deionized water, concentrated after transfer to a microcentrifuge tube, and freeze‐dried in a tin capsule. Isotope‐ratio analyses were accurate to within 5% when diffusions were performed on 100 to 1000 μg of NH+4‐N (0.2–10 atom % 15N), whereas errors of 8 to 17% occurred with 25 to 50 μg of labeled N, even after correction for isotopic dilution by atmospheric NH3 The technique described permits 15N analysis of any form of N that can be recovered by H3BO3 diffusion of soil, soil extracts, soil hydrolysates, Kjeldahl digests, water, or wastewater.

Optimization of the hyphenation between capillary zone electrophoresis and inductively coupled plasma mass spectrometry for the measurement of As-, Sb-, Se- and Te-species, applicable to soil extracts

The optimization of the hyphenation between capillary zone electrophoresis (CZE) and inductively coupled plasma mass spectrometry (ICP-MS) was studied for the simultaneous determination of metalloid species in the environment. Arsenic (arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid), selenium (selenite, selenate, selenomethionine, selenocystine), antimony (antimonate) and tellurium (tellurite, tellurate) species were simultaneously separated using a 75-μm i.d. fused silica capillary using either a chromate or a phosphate electrolyte. Different nebulizers were tested for introduction in the detector. A V-groove nebulizer (the Babington) and two concentric micronebulizers (the MCN-100 and the MicroMist) were studied in order to improve resolution, sensitivity and reproducibility. The optimization of CE-ICP-MS interface operating parameters is discussed for each nebulizer–interface combination, and special attention is given to the position of the capillary inside the nebulizer. Different nebulizer gas and liquid sheath flow rates were studied in detail and they hardly affect electrophoretic resolution and peak width. The best analytical performance characteristics were obtained with the MicroMist nebulizer. Detection limits with this nebulizer were found to range between 6 and 58 μg l −1 depending on the species investigated using pressure injection and below 1 μg l −1 for most of the species with electromigrative injection. Analysis of soil extracts showed that it was possible to carry out this technique on real samples.

Organic matter extracted with 0.01 M CaCl 2 or with 0.01 M NaHCO 3 as indices of N mineralisation and microbial biomass

A pot experiment was carried out with three soils at ambient temperature in which temporal changes in fractions of soil organic matter that were extractable with either 0.01 M CaCl2 or 0.01 M NaHCO3 were compared with changes in N mineralisation and microbial biomass C. UV spectral analysis of soil extracts was also carried out on sub-samples taken at the beginning of the experiment. The objective was to quantify the fractions of extractable soil organic matter and determine whether these could be used to estimate the mineralisable organic N content of the soils. The results suggested that part of the NaHCO3-extractable organic matter originated in the microbial biomass but that non-biomass material was also present. The non-biomass material was not identified directly, but was composed of compounds with high UV absorbance. In the case of CaCl2, the results suggested that extracellular proteins were contained in the extract and that some material released from the actively growing microbial biomass may also have been present. A supplementary study with 16 soils was carried out to determine the ability of the organic matter solubilised by either extractant to predict soil N uptake by barley seedlings. A significant relationship (P<0.01) was found between N uptake and CaCl2-extractable material only.

Direct‐Diffusion Methods for Inorganic‐Nitrogen Analysis of Soil

Determinations of exchangeable NH4, NO3, and NO2 in soil normally require the preparation of an extract, which is usually obtained with a neutral salt solution such as 2 M KCl. In cases where analytical speed and convenience are key factors, as in routine soil testing, a more practical approach would be to carry out the determination directly on the soil sample itself. Studies were conducted to ascertain whether this approach could be employed using Mason‐jar diffusion methods previously developed for inorganic‐N analysis of soil extracts. Direct diffusions were performed with MgO to recover NH4–N, or with MgO and Devarda's alloy to recover (NH4 + NO3 + NO2)–N, from 1‐ to 5‐g samples of a wide variety of air‐dried soils, following treatment of the soil with sufficient 2 M KCl to give a 1:10 ratio of soil to solution. Up to 4 mg of inorganic N was recovered quantitatively in 18 h to 6 d at room temperature, or in 1.75 to 5.5 h with gentle heating on a hot plate (45–50°C). Analyses by direct diffusion were in close agreement with results obtained by diffusion of soil extracts, and recoveries ranged from 97 to 102% when direct diffusions were performed on samples that had been treated with NH4–N or NO3–N. Besides being quantitative, direct diffusions were found to have potential for N‐isotope analysis. In diffusing 15N‐treated samples, isotope‐ratio analyses of NH4–N or (NH4 + NO3 + NO2)–N were accurate to within 3%. The latter finding virtually precludes interference by labile organic N or nonexchangeable NH4–N; however, interference did lead to an increase in inorganic‐N analyses when diffusion was prolonged beyond the recommended period.

Factors affecting degradation rates of five triazole fungicides in two soil types: 1. Laboratory incubations

Triazole fungicides are now widely used commercially and several are known to be persistent in soil. The degradation rates of five such fungicides were measured in laboratory tests with two soils over 720 days, with analysis of soil extracts by high-pressure liquid chromatography. Behaviour in a sandy loam and a clay loam were similar, and incubation of the compounds either singly or in admixture did not influence loss rates except for those of flutriafol which were lower in the latter. Triadimefon was quite rapidly reduced to triadimenol, though traces of the former were always found, indicating a possible redox equilibrium. Flutriafol, epoxiconazole and triadimenol (derived from triadimefon) were very persistent, breakdown following first-order kinetics with half-lives greater than two years at 10 degrees C and 80% field capacity. Propiconazole was moderately persistent, with a half-life of about 200 days under these conditions. Degradation rates increased about 3-fold as the temperature was increased from 5 to 18 degrees C, though decreasing soil moisture to 60% field capacity only slightly slowed degradation. The rate constants obtained are used in a companion paper describing field studies on these two soils to compare laboratory-measured degradation rates with losses in the field following commercial sprays. (C) 1999 Society of Chemical Industry.

Analysis of polycyclic aromatic hydrocarbons by supercritical fluid chromatography (SFC)

Usually, elution gradient high performance liquid chromatography using polymeric octadecyl bonded phases is chosen for this kind of separation. Due to the properties of carbon dioxide, low viscosity, high eluting power, separations obtained by supercritical fluid chromatography (SFC) are generally faster than by liquid solvents. This paper reports the study of the PAH separation by SFC. The effects of the nature and percentage of modifiers, pressure, tem- perature and the choice of the stationary phase (mono or polyfunctional, high or low bonded density) are discussed. Results show that coupling two different columns is needed to reach the complete separation of the 16 PAHs requires by the standard of the Environmental Protection Agency (EPA 610). The separation is achieved in 25 minutes with a linear acetonitrile/CO 2 mobile phase gradient. Applied to the analysis of soil extracts, this analytical technique is enable to separate numerous other compounds than standard PAHs.

In situ antigen immobilization for stable organic-phase immunoelectrodes.

A new method based on enzymatic single-step in situ synthesis of hapten-carrier conjugates on electrodes is described yielding stable, reproducible, and reusable organic-phase immunoelectrodes (OPIEs). The electrodes developed were tailored for analyte detection in organic solvents and allow for the analysis of soil extracts without further sample processing and cleanup. Catalyzed by transglutaminase from a variant of Streptoverticillium mobaraense, the reaction proceeds in aqueous solution with and without addition of organic media in only 1.5 hours. In this study, the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was chosen as model compound and chemically amino-functionalized prior to its enzymatic immobilization. The high reproducibility of the immobilization procedure allowed for batch calibration of the immunoelectrodes. Moreover, pure methanol or treatment with diluted sulfuric acid used for regeneration studies did not disturb the hapten layer. The OPIE consists of screen-printed carbon electrodes, monoclonal anti-2,4-D antibodies, and the immunochemical recognition reaction and was optimized with regard to a high stability in organic media. For electrochemical detection, horseradish peroxidase was used as enzyme label together with H2O2 as substrate and hexacyanoferrate (II)/(III) as mediator. The OPIE showed high stability upon storage over 93 days. Response times of 17 s (t95) were found to be advantageous compared to those of other biosensors. Including the immunochemical reactions, the complete assay takes 30 min. A calibration curve for 2,4-D in 30% methanol/buffer obtained with 70 electrodes within 4 weeks revealed a detection limit of 9 mg/L, a sensitivity of 1.3 nA L mg-1 cm-2, and a repeatability of 6.8%. Although we calculated a lowered repeatability for reused electrodes of 13.4% and a slightly decreased sensitivity of 0.9 nA L mg-1 cm-2, multiple-used OPIEs could also be applied for calibration.

Bioremediation of Oil-Contaminated Soils by Stimulating Indigenous Microbes

Abstract Two oil-contaminated sites were bioremediated by stimulating indigenous microbes by tilling, liming, and fertilizing; the hydrocarbon contents were reduced by 84% in 7 weeks at one site and by 83% in 56 weeks at the other site. The process was monitored by measuring the most probable number (MPN) of oil-degrading microbes and the total petroleum hydrocarbon (TPH) concentration in soils. Bioremediation occurred at MPNs of 105 to 106 cells g−1 soil, mean water-holding capacities of 54–82% and mean soil pH values of 4.75–5.97. The initial control TPH concentrations remained unchanged at the end of the study at both sites. Bioremediation was not required at depths greater than 6 in except at one location; tilling at 18 in was necessary and remediation took 19 weeks longer than the surface remediation of 56 weeks. As revealed by gas chromatographic analyses of soil extracts before and after bioremediation, the diversity and amounts of hydrocarbons were substantially reduced during bioremediation. There were 10 oil-degrading bacteria isolated from the sites, representing the following genera: Alcaligenes, Actinomyces, Bacillus, Citrobacter, Corynebacterium, Enterobacter, and Pseudomonas.

Improved diffusion methods for determination of inorganic nitrogen in soil extracts and water

Diffusion methods previously developed for inorganic-N analysis of soil extracts were modified to improve reliability, increase the dynamic range, extend the scope of applications, and simplify the processing of samples for N-isotope analysis. In these methods, the soil extract is treated with MgO, or MgO plus Devarda‘s alloy, in a 473-ml (1-pint) wide-mouth Mason jar to convert NH4 +-N, NO3 –-N, and/or NO2 –-N to NH3-N. The NH3 thereby liberated is collected in H3BO3-indicator solution in a Petri dish suspended from the Mason-jar lid and determined quantitatively by acidimetric titration. With the modifications described, analyses can be performed on 10- to 100-ml samples of water, 0.5MK2SO4, 1MKCl, 2MKCl, or 4MKCl, at temperatures between 20 and 30°C. Recovery from 10 or 20ml was quantitative in 18–80h with up to 4mgN; recovery from 50 or 100ml was quantitative in 3–13 days with up to 2mgN. Removal of H3BO3 for N-isotope analysis by the Rittenberg process was effected using methanol. Mason-jar diffusion methods are much simpler and more convenient than conventional steam distillations. Comparative studies showed that quantitative determinations are more accurate and precise by diffusion than by distillation.

Accelerated Diffusion Methods for Inorganic‐Nitrogen Analysis of Soil Extracts and Water

AbstractThe major limitation of diffusion methods for N analysis is the time required to obtain the results — typically from one to several days. Methods were developed that involve a much shorter period for diffusion. In these methods, 10‐ to 100‐mL samples of 2 or 4 M KCl soil extract or water were treated with MgO, or MgO plus Devarda's alloy, in a 473‐mL (1‐pint) wide‐mouth Mason jar to liberate NH4‐N, NO3‐N, and/or NO2‐N as NH3. The jar was placed on an electric griddle maintained at 45 to 50°C. Gaseous NH3 was collected in 5 mL of H3BO3 indicator solution in a petri dish attached to the Mason jar lid, for quantitative determination by acidimetric titration. Complete recovery of 4 mg of N was achieved from 10 or 20 mL in 1.5 to 5 h. Recovery from 50 or 100 mL was complete in 5 to 8.5 h with 1 to 2 mg of N. The methods permit 15N analysis of the diffused NH3‐N. Isotopic analyses of labeled soil extracts were accurate to within 3%, as determined by isotope‐dilution calculations. Diffusions from 10 to 50 mL were subject to very little, if any, interference from decomposition of alkali‐labile organic‐N compounds.

Anaerobic Degradation of PCB in Soils

Abstract The anaerobic degradation of PCB in loamy and clayey soils containing indigeneous microflora was studied. The anaerobic conditions were created by an argon atmosphere in the flasks containing soil flooded by a liquid medium with glucose. GC-ECD analysis of soil extracts after 40 day incubation showed, in addition to the concentration changes of the less chlorinated PCB congeners, a significant decrease in the concentration of highly chlorinated congeners in both soils. The results indicate that in both soil types reductive dehalogenation of PCB congeners was encountered.

Metabolism of the urease inhibitor n-( n -butyl)thiophosphoric triamide (nbpt) in soils

An experiment was conducted to relate the effectiveness of N-( n-butyl)thiophosphoric triamide (NBPT) and its oxon analog N-( n-butyl)phosphoric triamide (BNPO) in controlling urea hydrolysis in soils to their corresponding soil concentrations. Both compounds were applied to an acid soil (pH 4.9) and to the same soil that had been neutralized (pH 7.1) by long-term liming or by the recent application of Ca(OH) 2. Hydrolysis of urea applied with the inhibitors was monitored along with the disappearance of the compounds themselves. Both compounds controlled urea hydrolysis much more effectively in the neutral soils than in the acid soil. HPLC analysis of soil extracts demonstrated that both compounds disappeared more rapidly in the acid soil, and that the compounds disappeared at similar rates for both neutral soils, indicating that pH governed disappearance rates in these soils. Disappearance rates were generally first-order for both compounds, although NBPT disappeared at an accelerated rate at low concentrations, presumably due to its simultaneous conversion to BNPO. The effectiveness of both compounds in controlling urea hydrolysis was closely related to the concentrations of BNPO found in the soil. BNPO was generally maintained at higher concentrations following NBPT application than when BNPO was applied directly to soil.

Soil saccharide extraction and detection

Extraction of soil saccharides involves the use of reagents effective in breaking hydrogen and covalent bonds between soil constituents and the saccharides. Of the many extractants proposed for saccharide determination, water is commonly used for extraction of water-soluble mono- and polysaccharides in soil. Analysis of these water extracts by colorimetric assays (anthrone-sulfuric acid and phenol-sulfuric acid methods) often show color development indicating that saccharides are present. However, high performance liquid chromatography (HPLC) and gas chromatography analyses have indicated that these colorimetric assays are prone to errors due to interferences from inorganic soil constituents such as Cl−, NO3 − and Fe+3. When water extracts (25° or 80°C) are put through deionization resins to remove interferences little to no saccharides are present when assayed by the phenol-sulfuric acid analysis. The inability of water to extract saccharides from soil or microbial polymers was confirmed by HPLC analysis. The phenol-sulfuric acid assay was found to be acceptable for saccharide analysis of soil extracts only after being subjected to resin deionization for interference removal. The anthrone-sulfuric acid method is not considered acceptable for determining saccharides in soil.

Comparison of soil extraction parameters for Al, Mn, Ca, and Mg determinations

Abstract Inductively coupled argon plasma atomic emission spectroscopy (ICAP‐AES) is frequently used for analysis of soil extracts. Advantages include increased detection limits, simultaneous multi‐element capabilities, speed, and operator safety due to inert, non‐combustible source gas. Previous research showed that instrumentation problems increased with increasing salt content in soil extracting solutions. An ICAP‐AES was used to analyze AI, Mn, Ca, and Mg in KCl soil extracts under various KCl concentrations, soil: solution ratios, and shaking times for two acidic soils in Oklahoma. Changes in KCl concentration and soil: solution ratio resulted in differences in extractable Al, Mn, Ca, and Mg for both soils. Shaking time did not affect extractable Al in either soil, but did affect extractable Mn. Extractable Ca and Mg varied in one of the soils as a result of shaking time. The most effective extraction parameters selected based on these soils were 0.5M KCl, 10 min. shaking time, and 1: 15 soil: solution ratio.

The relative persistence of trifluralin (545 EC and 5 G) and ethalfluralin in prairie soils

The persistence in soil of trifluralin 545 EC, trifluralin 5 G, and ethalfluralin 360 EC was studied over a 2-yr period at three different sites in Saskatchewan. At two of the three sites both formulations of trifluralin were more persistent than ethalfluralin when a canola crop was grown in the treated soil. In the high organic matter soil at the third site the persistence of trifluralin and ethalfluralin was similar under both fallow and cropped conditions. Crop response data gathered from wheat, oat and millet stands plus gas chromatographic analysis of soil extracts indicated that trifluralin 545 EC and trifluralin 5 G persisted in soil for comparable lengths of time when applied at rates between 0.85 and 1.40 kg a.i. ha−1. At recommended application rates to summerfallowed fields, the amount of herbicide remaining in the different soils at seeding time the following season was least for ethalfluralin 360 EC. The average amount of trifluralin 545 EC, trifluralin 5 G and ethalfluralin 360 EC which remained in the soil at the three field locations the year following application was 13, 13 and 6%, respectively. Key words: Trifluralin, ethalfluralin, herbicide persistence

Use of diffusion for automated nttrogen‐15 analysis of soil extracts

Abstract Studies to evaluate the use of diffusion for automated 15N analysis of inorganic N in soil extracts showed that serious error can arise from use of the Devarda's alloy recommended for steam distillations and that the error can be avoided by using a commercial product of higher purity. These studies showed that serious error can also arise when NO3 ‐‐N is diffused following NH4 +‐N and that separate diffusions should be performed for NH4 +‐N and (NH4 + + NO3‐)‐N. Other work demonstrated that the plastic specimen containers employed for diffusion can be reused if acid‐washed, that diffusions can be performed using either light or heavy MgO without ignition to decompose carbonate, and that labeled NO2‐is completely removed from soil extracts by treatment with sulfamic acid before diffusion. A comparison of 15N analyses by steam distillation and diffusion using extracts from two soils revealed better agreement for the soil having a lower content of organic matter. Substantial differences in analyses by the two techniques for the soil having a higher organic‐matter content were attributed to enzymatic conversions of inorganic N during the 6‐d diffusion period.