Comparison of Lead Extraction and Detection Procedures for Six Canadian Soils

The effects of acid digestion procedures and instrumentation on extracted lead (Pb) concentrations from several soils, including a mildly Pb-contaminated soil, were determined using a two-factor factorial experiment. The two factors were (i) digestion procedure [seven levels: U.S. EPA, AOAC (dry ashing), nitric acid (NA), three aqua regia procedures (AR1, AR2, and AR3), and hydrofluoric acid (HF)] and (ii) instrumentation [two levels: atomic absorption spectrometry (AAS) and inductively coupled plasma (ICP) spectroscopy]. The greatest Pb recovery was obtained when soils were digested with HF and analyzed by AAS. The results suggest that the AOAC procedure (a standard procedure for recovery of soil nutrients and trace elements in Canadian laboratories) and EPA procedure (a standard procedure in American laboratories) may underestimate Pb concentrations in some Atlantic Canadian soil types. The AAS procedure is more accurate than ICP for determining Pb concentrations in soil with a history of PbHAsO₄, at least for Atlantic Canadian soils.     

A rapid method for nitrogen determination in plant tissue

Abstract

A method is described for determining the total N content of plant tissue by a modified Kjeldahl digestion employing a Technicon Auto‐Analyzer. It is faster than the manual AOAC Kjeldahl method. Reproducibility is not as good as that for the AOAC method, but coefficients of variability are comparable with those for the analyses of mineral elements in plant tissue by emission spectroscopy.     

Sewage sludge incinerator ash effects on soil chemical properties and growth of lettuce and corn

Abstract

Incineration reduces sewage sludge volume, but management of the resulting ash is an important environmental concern. A laboratory incubation study and greenhouse pot experiments with lettuce (Lactuca sativa L.) and corn (Zea mays L.) were conducted to examine the potential for recycling elements in sewage sludge incinerator ash in agricultural systems. Ash rates in both the laboratory and greenhouse were 0, 0.95, 3.8, 15.2, and 61.0 g/kg soil (Typic Hapludoll). Ash was also compared to equivalent rates of citrate soluble P from superphosphate fertilizer in a soil‐less growth medium. During soil: ash incubation, Olsen P and DTPA extractable copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) increased with incubation time at the higher ash rates. Release rates diminished rapidly, however, and the limited release of these elements after 280 days was associated with decreasing pH. In the greenhouse, ash amendment increased extractable soil P, plant tissue P, and the growth of lettuce and corn. Ash was a less effective P source than superphosphate fertilizer in the soil‐less growth medium and Olsen P levels were more consistent with these differences than Bray P. Ash increased extractable soil levels and plant tissue concentrations of calcium (Ca), magnesium (Mg), sodium (Na), Cu, and Zn, but extractable soil manganese (Mn) and plant tissue Mn decreased. Ash increased soil pH and extractable SO₄‐S. DTPA extractable Cd and Pb increased, but chromium (Cr) and nickel (Ni) decreased. Lettuce accumulated higher amounts of these trace metals than corn, but tissue concentrations were at control levels or below detection limits in both crops.     

A single plant tissue digestion for macronutrient analysis

Abstract

A method was tested for determinations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) in one single digestion of plant tissue. Traditionally, for determinations of these five elements in plant tissue, at least two digestion or ashing procedures are used, totaling about 6 hours of tissue mineralization time. The method tested involved using a digesting medium of concentrated H₂SO₄ and a mixed catalyst of Na₂SO₄ and CuSO₄. The total digestion time was about 60 minutes on a hot plate. After tissue digestion, determinations were by volumetric analysis (N), colorimetry (P), and atomic absorption (Ca, Mg) or emission spectrophotometry (K). Leaves of eight different species, including one standard tomato leaf sample and one internal quality‐control apple leaf sample were analyzed. High correlations occurred between the results obtained with the new procedure and with the standard digesting methods (furnace ashing and Kjeldahl digestion). The new method used much less reagents, electrical energy, and labor than standard methods. The new method appears acceptable for routine macronutrient analysis.     

Improved recovery of fluoride in plant material using a low temperature sealed chamber digestion technique in conjunction with a fluoride ion‐specific electrode

Abstract

Seven different sample preparation methods (five ashing and fusion methods, an acid digestion method, an oxygen flask combustion method) and the AOAC extraction method (975.04) were compared with a newly developed sealed chamber digestion method for the determination of fluoride (F) in vegetation. Subterranean clover tissue was the test material. Fluoride concentration in digests was measured using a F ion‐selective electrode. The sealed chamber digestion carried out with nitric acid in Teflon chambers at 120°C for 6 hours gave the highest F concentration in the plant material and the highest recovery of added F of all methods. Tests on several types of plant material confirmed the superiority of the closed chamber digestion. The superiority of the method is attributed to the complete solubilisation of F in the sample and elimination of losses of volatile F.     

Corn uptake of bromide under greenhouse and field conditions

Abstract

Bromide (Br) has been used frequently to trace the movement of fertilizer derived nitrate (NO₃) through the soil profile. Although not required for plant growth, Br is readily absorbed by plants. Consequently, the pulse of an anion tracer moving through the soil can be attenuated by actively growing plants. Greenhouse and field experiments were conducted to determine the amount of Br absorbed by corn, and to better understand potential competitive interactions between nitrogen (N) and Br in plant uptake. Under greenhouse conditions, over 85 percent of applied Brwas recovered by corn tops. Results from both greenhouse and field experiments demonstrated that the addition of Br or Cl neither reduced yield nor inhibited N uptake. Therefore, either Br or Cl could be used in N trials without concern for competitive inhibition of N uptake. However, both experiments demonstrated that N treatments affected Br concentration in the tissue, but this difference may have been due to increased yield of N treated plants causing Br dilution. Nitrogen treatments significantly affected plant Br uptake, but only in the greenhouse study. In the field experiment, corn recovery of 100 kg Br/ha applied in the spring of 1988 was as high as 38 percent in 1988, and 11 percent in 1989. This high rate of recovery demonstrates that the pulse of Br can be significantly reduced in the presence of developing plants, and should be taken into account when it is used as a tracer in leaching studies.     

An analytical survey of aflatoxins in tissues from swine grown in regions reporting 1988 aflatoxin-contaminated corn.

A joint project was undertaken by the Food Safety and Inspection Service (FSIS) and the Agriculture Research Service branches of the U.S. Department of Agriculture to determine the presence of aflatoxins in the U.S. meat supply during a drought year. In 1988, high incidences of aflatoxins occurred in corn grown in regions of the Midwest, Southeast, and South. Six states were identified as having serious aflatoxin contamination in their corn crop: Virginia, North and South Carolina, Texas, Iowa, and Illinois. Swine liver and pillars of diaphragm (muscle) tissues were sampled by federal FSIS Inspectors in plants located in these states. A worstcase sampling plan was conducted. Samples were taken in January 1989 from hogs fed corn soon after harvest and in April 1989 from hogs fed corn originally stored and then fed in the spring. A modification of the official AOAC method for the thin-layer chromatography (TLC) determination of aflatoxins in animal tissue was used to permit quantitation by LC with fluorescence detection. The official AOAC TLC confirmation of identity method was used to confirm all positive samples with B1 concentrations greater than 0.04 ppb and M1 concentrations greater than 0.1 ppb. Sixty samples in the January group and 100 samples in the April group were assayed. Concentrations of aflatoxins B1 and M1 in the first group of pig livers ranged from 0.04 to 0.06 ppb. The identity of aflatoxin B1 was confirmed in all positive samples. Aflatoxin M1 could not be confirmed in any of the positive liver samples because the method was insufficiently sensitive for this aflatoxin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of gelatin on recovery of hair fragments in filth analysis

Prior literature has recommended the use of gelatin capsules or gelatin film for transferring spike elements to samples being examined for recovery studies. It was believed that gelatin had no effect on the recovery of filth spike elements. However, this study shows that hair recovery is lower when gelatin is present in direct trap-off procedures. Two types of gelatin capsules, gelatin film, and strips of filter paper were used to transfer spike filth elements. A comparison study employing an acid digestion and wet sieving procedure was also performed and showed that gelatin had little or no effect on the recovery of hairs using this type of procedure. An additional test was performed using gelatin added to water containing the same type of spiked filth elements. No hair fragments were recovered but all insect fragments were recovered. All recovery studies were performed using only water in the liquid phase of the trap flask extractions, with mineral oil or heptane as the flotation medium. No food product was used.     

Comparison of a microwave digestion system to other digestion methods for plant tissue analysis

Abstract

Most digestion procedures for the preparation for plant tissue for elemental analysis are often very laborious. Elemental contents of plant tissue prepared by microwave digestion were compared to those obtained by conventional dry ashing and sulfuric acid‐hydrogen peroxide wet digestion. All three digestion methods produced comparable quantitative values for the elements P, K, Ca, Mg, Fe, Mn, Zn, and Cu for all plant materials used. Thus, the microwave digestion technique was shown to be a viable rapid method for digesting relatively small numbers of samples prior to elemental analysis.     

Rapid perchloric acid digest methods for analysis of major elements in plant tissue

Abstract

The nutrient element composition of tissue from a plant species is not fixed. Composition in the plant varies among different plant parts at the same or different physiological stages of maturity, as soil type changes, from day to day, even hour to hour on the same day due to past and current environmental conditions. These observations seem to undermine the general trend in plant tissue analysis to develop quantitative procedures that are time consuming and, therefore, foster insufficient nutrient status monitoring within and/or between different physiological stages of maturity of like or different plant parts. Therefore, until tissue sampling becomes more definitive, a digest procedure with 90–100% recovery should be more than adequate for major elemental analysis. The HClO₄ digestion procedures described here meet that requirement and take only 15 to 30 min to complete. N recovery was greater than 100% with the H₂O₂‐HClO₄ digestion procedure. However, when HNO₃ was combined with H₂O₂ and HClO₄, N was lost, although even then N volatilization occured only when digestion was extended past clearing.     

不同前处理方法对秸秆金属元素原子吸收光谱分析结果的影响

秸秆中金属元素是关系农作物秸秆科学利用的重要组成部分,目前还没有统一的秸秆中金属元素原子吸收光谱(atomic absorption spectroscopy,AAS)测定方法标准,该研究采用原子吸收光谱测定黄芪(GBW10028)标准物质、玉米秸秆、小麦秸秆和棉花秸秆中金属元素含量,比较了不同前处理方法对样品中K、Cu、Fe、Zn和Mg分析结果的影响。结果表明:微波消解、干法灰化和湿法消解测定黄芪(GBW10028)标准物质中金属元素含量差异性显著(P<0.05),微波消解比干法灰化、湿法消解准确度高。微波消解对玉米秸秆、小麦秸秆和棉花秸秆中各金属元素的影响与黄芪(GBW10028)标准物质趋于一致。微波HNO3与微波HNO3-H2O2测定结果差异性不显著(P>0.05),微波HNO3比微波HNO3-H2O2和微波HNO3-H2SO4测定结果稳定。微波HNO3是进行秸秆样品金属元素含量测定时较准确简便的前处理方法。     

Trace Element Analysis via Open‐Vessel or Microwave‐Assisted Digestion in Calcareous Mediterranean Soils

Abstract

Different digestion methods can be applied for analyzing trace elements in soils. Selection of the most useful and convenient method is critical for the adequate determination of their concentrations in each type of soil to appropriately detect potential environmental pollution. Open‐vessel digestion using a digester block (method 1) and microwave‐assisted digestion (method 2) were compared using a certified reference material (CRM) with similar properties and characteristics to calcareous Mediterranean soils. Both methods were contrasted in terms of accuracy by calculating the recovery of cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) in the CRM and precision of replicate analysis through the relative standard deviation (RSD). Recoveries from the digester block method were slightly higher than recoveries from microwave digestion because the use of perchloric acid (HClO₄), whereas RSD values for microwave digestion were generally lower but with higher measured precision than values obtained by open‐vessel digestion. The digestion methods were compared for analyzing trace elements in calcareous agricultural soils devoted to vegetable crops in the Alicante province (southeast Spain), as a representative area of the European Mediterranean region. Results of the paired‐sample t‐test showed significant differences between both methods for Co, Cr, Cu, and Pb in calcareous Mediterranean soils, whereas regression analysis indicated a good correlation between both methods for Cu, Ni, Pb, and Zn. Consequently, the choice of the digestion method is more relevant for minor elements such as Co and Cr. Microwave‐assisted digestion seems to be the best option to determine most of the trace elements in calcareous Mediterranean soils, because closed‐vessel digestion exhibited lower variability according to the RSD values obtained in the study area, particularly for Co and Cr. Trace element concentrations were in agreement with background levels, except for Cu and Pb in some soils, which seem to be related to anthropic activities.     

Rapid digestion and flameless atomic absorption spectroscopy of mercury in fish: collaborative study

A collaborative study of the determination of mercury in fish has been completed in which wet oxidation of fish tissue in nitric acid, using vanadium as a catalyst, is compared with the AOAC official final action digestion technique, 25.103-25.105, involving a nitric-perchloric acid mixture. The study used tuna fish samples of known mercury content and included spike recovery studies in which methyl mercury solutions of known composition were provided to each laboratory. The study was designed to provide recovery information that bracketed the regulatory level of mercury in fish. The results indicate that the proposed digestion method is at least as precise and accurate as the AOAC method. The proposed method is also more rapid and less hazardous. It has been adopted as official first action.     

Elemental analysis of solid samples by low temperature plasma ashing and microwave acid digestion

Sixteen elements (Mn, Zn, Cu, Fe, B, Sr, Ba, Cr, Pb, As, Cd, Ni, Co, Se, Sb, Hg) were determined in oils, sediments, plants and marine organisms by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) or by Graphite Furnace Atomic Absorption Spectroscopy (GF-AAS) after plasma ashing followed by microwave acid digestion with HNO₃/HCl/H₂O₂. Soil and sediment samples were treated directly in the microwave oven without ashing, but the complete procedure must be applied in case of high organic content. The method was tested on a variety of standard reference materials. Good recoveries were obtained for most of the considered trace elements with less time and reagents consumption than conventional open vessels acid digestion procedures. Hg was determined with good recovery in soil samples by the same method and in organic materials by a modified procedure involving digestion of fresh material with nitric acid in a reflux quartz system.     

A comparison between the H2SO4‐H2O2‐Li2SO4‐Se oxidation method and alternative digestion procedures for plant nutrient analysis.

Abstract

Ca, Mg, Na, K and P contents of 3 plant tissues obtained by H₂SO₄‐H₂O₂‐Li₂SO₄‐Se peroxidation digestion were compared with those determined by mixed acid (HNO₃‐H₂S0₄‐HC10₄) and dry ashing procedures. Differences between methods were not consistent between elements or tissue types but the mixed acid digestion generally yielded higher Ca, Mg and P values than did dry ashing and peroxidation. Tissue K contents estimated by both wet digestion techniques were not significantly (P ≤0.05) different. Differences in Na values between digestion methods were highly inconsistent between tissue types and the precision of the Ma data was poor. N contents determined by peroxidation digestion and a conventional Kjeldahl method agreed closely.     

Evaluation of some soil and plant analysis procedures as predictors of the need for sulfur for corn production

Abstract

The objective of this study was to evaluate the usefulness of measures of mineralized sulfur (S), soil sulfate‐sulfur (SO₄‐S), concentration of S in plant tissue, and the N: S ratio in plant tissue as predictors of the need for S in a fertilizer program for corn (Zea mays L.). Data to evaluate the use of plant analysis for S as a predictor were obtained from ten sites where various rates of N and S were applied to corn. Regression analysis was used to relate the S concentration in the ear leaf tissue as well as the N: S ratio in the same tissue to relative yield when the rate of applied N was held constant at a rate of 168 kg/ha. These measures of S in plant tissue were not significantly related to relative yield at sites where there was no response to fertilizer S as well as sites where added S increased yield.

Data from the same sites were used to assess the ability of soil tests to predict the need for fertilizer S. A measurement of extractable SO₄‐S in the surface soil (0–15 cm) was not reliable for predicting the need for S for corn grown on soils with a silt loam texture.

Static incubation techniques were used to evaluate the amount of S mineralized from soil collected from seven sites. The amount of SO₄‐S measured after four and twelve weeks of incubation was curvilinearly related (p <.05) to yield increase from a S fertilizer. Net mineralized S was less than 2.1 and 3.7 ppm SO₄‐S after four and twelve weeks of incubation, respectively, for soils taken from sites where response to fertilizer S was obtained. Data collected in this study indicate that a measure of mineralized S could improve the ability to predict S needs for corn production on soils with a silt loam texture and a low organic matter content.     

Total elemental analysis digestion method evaluation on soils and clays

Abstract

The standard digestion method for total elemental analysis of soil material by the Soil Survey Laboratory (USDA Natural Resources Conservation Service) uses a 2‐mL clay suspension with hydrofluoric acid (HF) in a closed Teflon digestion vessel (method HF‐SUS). The accuracy and efficiency of elemental recovery by method HF‐SUS was compared to: (a) modification of HF‐SUS by use of a dried sample (method HF‐DRI); (b) modification of HF‐SUS by use of a dried sample and HF+aqua regia (method HF+AR); (c) sample digestion by Li metaborate fusion (method FUS); and (d) microwave digestion of samples with HF+aqua regia in Teflon bombs (method MICRO). Three replications of three standard reference materials (SRMs), fine‐earth (<2 mm) from 12 soils, and the clay (<2 urn) from 10 of those soils were analyzed. Method HF+AR shows the most consistent statistical agreement with the certified SRM values. Analysis of variance (ANOVA) indicates significant effects (α=0.05) for method of digestion, nonsignificant effects for method times SRM and method times clay, but significant effects for method times fine‐earth. Composition and/or variability of material are significant factors in the method of digestion. Method HF+AR yields significantly higher experimental means of A1₂O₃, Fe₂O₃, and K₂O contents and oxide recovery (summation of experimental means for oxides of all reported elements) than all other methods.     

Determination of Major and Trace Elements in Plant Samples by Inductively Coupled Plasma–Mass Spectrometry

The determination of several trace elements [arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), molybdenum (Mo), nickel (Ni), and lead (Pb)] in plant samples using inductively coupled plasma–mass spectrometry (ICP‐MS) was evaluated. It was established experimentally that moderate amounts (0.2–2%) of dissolved solids decreased the analyte signals significantly. Internal standardization with Rh was efficiently used to compensate for these matrix effects. The accuracy of the method was verified using reference materials digested according to two different procedures: dry ashing and microwave digestion. No significant differences were observed between measured concentrations and certified values. The investigation was next extended for the determination of major elements [aluminum (Al), boron (B), calcium (Ca), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), sodium (Na), phosphorus (P), and zinc (Zn)] on the same reference materials. The ICP‐MS values agree well with the values supplied. However, it appeared that Sc was the most useful internal standard for major elements.     

Generation of corn tissue norms from a small,high‐yield data base

Abstract

The purpose of this study was to determine the practicality of generating plant tissue norms with analytical data from a few, extremely high‐yield observations. A set of ear leaf tissue norms for corn (Zea mays L.) were developed from a set of data consisting of 10 observations of field‐grown corn with yields greater than 18 Mg ha^‐1. The norms thus generated were compared with norms generated from 8494 observations from a wide geographical area. Norms for several elements (P, K, Mg, S, Mn, and B) calculated from the two data bases were significantly different, while norms for the other nutrients (N, Ca, Fe, and Cu) were not. The norms generated from the limited data base were tested with data from an N³P³K³S³ factorial greenhouse experiment. Results of this test indicate that the norms developed from the limited, high‐yield data base were slightly better at predicting yield increases than those from the broader worldwide data base. The increase in accuracy seemed to be largely due to lower S norms and higher P norms when derived from the smaller data base, resulting in less frequent determinations of S‐induced yield limitations. Using a few, extremely high‐yield observations appears to be an efficient, accurate, and relatively inexpensive means of generating plant tissue nutrient optima.     

Pericarp Fiber Separation from Corn Flour Using Sieving and Air Classification

In the dry‐grind process, starch in ground corn (flour) is converted to ethanol, and the remaining corn components (protein, fat, fiber, and ash) form a coproduct called distillers dried grains with solubles (DDGS). Fiber separation from corn flour would produce fiber as an additional coproduct that could be used as combustion fuel, cattle feed, and as feedstock for producing valuable products such as “cellulosic” ethanol, corn fiber gum, oligosaccharides, phytosterols, and polyols. Fiber is not fermented in the dry‐grind corn process. Its separation before fermentation would increase ethanol productivity in the fermenter. Recently, we showed that the elusieve process, a combination of sieving and elutriation (air flow), was effective in fiber separation from DDGS. In this study, we evaluated the elusieve process for separating pericarp fiber from corn flour. Corn flour remaining after fiber separation was termed “enhanced corn flour”. Of the total weight of corn flour, 3.8% was obtained as fiber and 96.2% was obtained as enhanced corn flour. Neutral detergent fiber (NDF) of corn flour, fiber, and enhanced corn flour (dry basis) were 9.0, 61.5, and 5.7%, respectively. Starch content of corn flour, fiber, and enhanced corn flour (dry basis) were 68.8, 23.5, and 71.3%, respectively. Final ethanol concentration from enhanced corn flour (14.12% v/v) was marginally higher than corn flour (13.72% v/v). No difference in ethanol yields from corn flour and enhanced corn flour was observed. The combination of sieving and air classification can be used to separate pericarp fiber from corn flour. The economics of fiber separation from corn flour using the elusieve process would be governed by the production of valuable products from fiber and the revenues generated from the valuable products.