Free and HF-HO-extractable amino acids determined by high performance liquid chromatography in a loamy sand soil

Summary Amino acids were extracted from fertility plots of a loamy sand soil with 0.05 M HF-HCl and with a 10% ethanol solution (free amino acids) and analysed by reverse-phase high performance liquid chromatography (HPLC). The total quantities of amino-N compounds analysed were 4.4 g/g soil for the acid treatment and 22.6 g/g soil for the 10% ethanol extract. Glycine and glutamic acid were the most abundant of 15 amino-N compounds in the HF-HCl extracts, whereas glutamic acid and ornithine + NH⁺ ₄ were found in the highest concentration in the 10% ethanol extracts. The HF-HCI pretreatment is used to increase the efficiency of the extraction of soil organic matter. Although this pretreatment removed some amino acids, the acids extract less than 1% of the total amino-N content of the crude soil extracts. The pretreatment, therefore, was not overly destructive. Comparisons between the amino acids extracted from the fertility plots were not conclusive, except for glycine, which was greater in concentration in the higher fertilizer N plots of the same crop rotation.     

Evidence of peptides in low-molecular-weight fractions of soil organic matter

Summary Organic matter was extracted from three soils, a Berwick sandy loam, a Franklin loamy sand, and a Cumberland silty loam. The extracts were separated into high (>8000 daltons) and low-molecular-weight (<8000 daltons) fractions using gel filtration. Reverse-phase high performance liquid chromatography at 214 nm was used to separate the peptides into low-molecular-weight fractions. Peptide samples were collected with an integrated fraction collector and hydolyzed with an immobilized protease column reactor. High performance liquid chromatography with fluorescence detection was used to determine the amino-acid contents of the collected samples. The results indicated that peptide intermediates are present in soil size fractions. Greater quantities of several amino acids were released from the peptide hydrolyzates of the Berwick sandy loam and Franklin loamy sand, compared with the Cumberland silty loam, an uncultivated soil. These findings indicate that organic intermediates (e.g., peptides) are more prevalent in biologically active soils than in relatively inert soils.     

Relationship between molecular characteristics of soil humic fractions and glycolytic pathway and krebs cycle in maize seedlings

A humic acid (HA) isolated from a volcanic soil was separated in three fractions of decreasing molecular size (I, II and III) by preparative high performance size exclusion chromatography (HPSEC). The molecular content of the bulk soil HA and its size fractions was characterized by pyrolysis-GC-MS (thermochemolysis with tetramethylammonium hydroxide) and NMR spectroscopy. All soil humic materials were used to evaluate their effects on the enzymatic activities involved in glycolytic and respiratory processes of Zea mays (L.) seedlings. The elementary analyses and NMR spectra of the humic fractions indicated that the content of polar carbons (mainly carbohydrates) increased with decreasing molecular size of separated fractions. The products evolved by on-line thermochemolysis showed that the smallest size fraction (Fraction III) with the least rigid molecular conformation among the humic samples had the lowest content of lignin moieties and the largest amount of other non-lignin aromatic compounds. The bulk HA and the three humic fractions affected the enzyme activities related to glycolysis and tricarboxylic acid cycle (TCA) in different ways depending on molecular size, molecular characteristics and concentrations. The overall effectiveness of the four fractions in promoting the metabolic pathways was in the order: III>HA>II>I. The largest effect of Fraction III, either alone or incorporated into the bulk HA, was attributed to a flexible conformational structure that promoted a more efficient diffusion of bioactive humic components to maize cells. A better knowledge of the relationship between molecular structure of soil humic matter and plant activity may be of practical interest in increasing carbon fixation in plants and redirect atmospheric CO₂ into bio-fuel resources.     

水稻土中有机氯农药残留测定方法比较

研究国标方法对土壤中有机氯农药六六六、DDT 残留的测定结果,并与美国国家环境保护总局USEPA 8080 方法进行比较。结果表明,本研究条件下 USEPA 8080 方法对土壤中有机氯农药残留的测定结果显著高于国标方法,但 USEPA 8080 方法测定结果仅比国标方法测定结果高 14%,可以认为两种方法都适用于一般性的研究。     

鸡蛋中四环素类药物残留量测定的高效液相色谱法研究

建立了鸡蛋中土霉素、四环素、金霉素、多西环素残留量测定的高效液相色谱法。样品经弱酸性缓冲液提取后,HLB固相萃取柱净化后,反相液相色谱分离测定,本方法的检出限为10μg／kg,定量限为50μg／kg。四种四环素类药物在50～1000ng／mL范围内呈线性相关。在100～400ng／g添加浓度范围内,平均回收率为60％～110％,批内变异系数在3．2％～13．7％之间（n=5）,批间变异系数在0．9％-5．3％之间（n=4）。结果表明,该法简单、灵敏、特异性强,适用于鸡蛋中土霉素、四环素、金霉素、多西环素残留量的测定。     

Fractionation of hydrolase-humus complexes by gel chromatography

Summary Purification of soil phosphatase-, urease-, casein- and benzoylarginamide-hydrolysing proteases was obtained by exhaustively ultrafiltering a soil extract using 0.1M pyrophosphate solution at pH 7.1, separating the retained material into fractions of molecular weight higher (A_I) and lower (A_II) than 10⁵ and eluting the fractions on gel chromatography.Three peaks of phosphatase and urease activity were obtained after gel chromatography of fraction A_I on Sephadex G200 using 0.1M pyrophosphate solution as eluant. Only one distinct activity peak was observed when casein- and benzoylarginamide-hydrolysing proteases were assayed in the eluted fractions. Elution diagrams obtained by gel chromatography of fraction A_II on Sephadex G100, using a water as eluant, were characterized by one peak each of phosphatase-, casein- and benzoylarginamide-hydrolysing activity and by two peaks of urease activity.Gel chromatography of both A_I and A_II, generally, but not always, increased specific activity on a C and N basis of derivative fractions. Both proteases showed the highest increase in specific activity due to a marked decrease in organic C and N and an increase in total activity.     

Identification of ergosterol in vesicular-arbuscular mycorrhizae

Summary Ergosta-5,7,22-tri-3-enol (ergosterol) was identified by gas chromatography-mass spectrometry in roots of berseem (Trifolium alexandrinum L., cv. Landsorte) and sweet corn (Zea mays L., cv. Honeycomb-F1) infected with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus intraradices. The fungal-derived compound ergosterol was determined quantitatively in root extracts using reverse-phase high performance liquid chromatography. The concentrations of ergosterol in VAM-infected roots reached 72 g^-1 dry material in berseem and 52 g^-1 in sweet corn after 80 days of growth, whereas concentrations in non-infected roots remained below 8 g^-1 dry weight. Additionally, phytosterols such as -sitosterol, campesterol, and stigmasterol were detected in both infected and non-infected roots. Ergosterol, as a characteristic fungal substance, is proposed as an indicator of fungal biomass in the early stages of VAM infection.     

Structural studies on soil nitrogen by Curie-point pyrolysis — gas chromatography/mass spectrometry with nitrogen-selective detection

Curie-point pyrolysis-gas chromatography mass spectrometry with N-selective detection was used to characterize the structure of organic N compounds in four mineral soils. The technique was found suitable for the fast, sensitive, and highly specific identification of N-containing pyrolysis products from whole soils with total N contents between 0.08 and 0.46%. In order to optimize the methodology, one agricultural soil was pyrolyzed at final temperatures of 573, 773, and 973 K. Almost no chemical alterations to identifiable pyrolysis products were observed when the final pyrolysis temperature was increased from 573 to 973 K. More than 50 N-containing pyrolysis products were identified, and were divided into compound classes chracterized by specific molecular-chemical structures. These included pyrroles, imidazoles, pyrazoles, pyridines, pyrimidines, pyrazines, indoles, quinolines, N derivatives of benzene, alkyl nitriles, and aliphatic amines. Three additional soil samples different in origin and N content were analyzed at 773 K and each showed a specific thermosensitive N-selective chromatogram. Many N-containing pyrolysis products were identified in all samples, which indicated general qualitative regularities in the thermal release of N-containing pyrolysis products from the four soils. In the pyrolyzates of the investigated soils a number of compounds were identified, which is usually not detectable in pyrolysis-gas chromatography spectrometry analyses with N-selective detection of plants and microorganisms. Among these were N derivatives of benzene and long-chain alkyl nitriles, which appear to be soil-specific and suggest significant transformations of organic N in soils. Thus, our results contribute to a better understanding of the molecular-chemical structure of unknown N.     

超临界CO_2萃取结合高速逆流色谱分离八角茴香精油中的化学成分(英文)

建立了超临界CO2提取,高速逆流色谱分离纯化八角茴香中精油的分离方法。首先利用超临界CO2提取八角茴香中的精油,萃取压力为25 MPa,萃取温度为35℃。1.3 g粗提物经高速逆流色谱分离,两相溶剂体系为正己烷-乙酸乙酯-甲醇-水(体积比1∶0.2∶1∶0.1),一次分离出3种化合物,经EI-MS鉴定为茴香醛10.3 mg、异丁香酚甲醚7.1 mg和反式-茴香脑636.5 mg,纯度分别为98.9%、96.8%和99.7%。