An assessment of analytical performance of dissolved organic nitrogen and dissolved organic phosphorus analyses in marine environments: a review

To better understand the cycling of marine dissolved organic matter, analytical methods are required allowing for data on dissolved organic nitrogen and phosphorus (DON and DOP) to be acquired with high analytical performance. The coverage of documented DON and DOP analytical performance is very limited; instead analytical data are mostly available for total dissolved N and P (TDN and TDP) analyses. This substitution overestimates analytical performance for DON and DOP measurements due to the cumulative effect of Standard Deviation applied for detection limit and precision evaluations. The little available data obtained by photolytic, chemical, a combination of both, and high temperature combustion methods indicate that current detection limit is 0.30 µM for DON and 0.010 µM for DOP. Precision for both analytes, in general, is ≤4.5%. The data on accuracy is scarce despite availability of Reference Materials for TDN and NO₃^? + NO₂^? analyses, and for the TDN measurement is <5%; even fewer data exist for TDP due to a lack of reference material for this analysis. The Beer–Lambert law is linear up to 200 µM for TDN and 5–6 µM for TDP. Current analytical abilities for DON/DOP measurements are not ready yet to set the level of dissolved organic carbon analysis. The advance in the analytical performance for DON and DOP measurements depends upon the possibility to improve the analytical performance for dissolved inorganic N and P measurements involved in DON and DOP estimations. For the DOP analysis, an international standard method becomes necessary to develop and evaluate collaboratively. The chemical oceanographers’ community should reconsider requirements needed for the coverage of analytical performance for DON and DOP measurements to make this data more shareable and transparent. The lack of these data protracts marine analysts from attaining further methods improvement and development.     

Conversion efficiency of the high-temperature combustion technique for dissolved organic carbon and total dissolved nitrogen analysis

The measurements of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) in seawater are key in global change and coastal eutrophication studies. Nowadays, the high-temperature combustion (HTC) technique is a widely used method for DOC and TDN analysis. However, uncertainties exist about the operation of the catalyst in the conversion process of DOC and TDN in the HTC method. In this study, five different ‘catalyst’ materials were tested for their blanks, calibration slopes, and conversion efficiency of DOC and TDN using the Shimadzu TOC 5000A total organic carbon analyser coupled to a Sievers NCD 255 nitrogen chemiluminescence detector. The materials included four metallic catalysts (Shimadzu and Johnson 0.5% Pt–alumina, 13% Cu(II)O–alumina, 0.5% Pd–alumina) and quartz beads. The results indicated that DOC blank signals for the HTC approach using metallic catalysts with an alumina support are higher compared with quartz beads, as a result of the amphoteric nature of the alumina. However, the slopes of the standard calibration graphs were lowest for DOC and TDN determinations on the quartz beads. The DOC recoveries for the metallic catalysts were close to 100% for all compounds tested, with the exception of ammonium pyrrolidine dithiocarbamate. Using quartz beads, poor recoveries were obtained for a range of organic compounds, including the commonly used calibration compounds potassium hydrogen phthalate and glycine. The TDN recoveries for all compounds were typically >90%, with the exception of NaNO₂. Furthermore, analysis using the CuO–alumina and Pd–alumina catalysts and quartz beads showed low recoveries for NH₄Cl. This study showed that catalyst performance should be verified on a regular basis using model compounds and blank checks made during every run, and that the Shimadzu 0.5% Pt–alumina material was an efficient catalyst for DOC and TDN analyses using the coupled total organic carbon–nitrogen chemiluminescence detector (TOC-NCD) analyser.     

Influence of nitrogen speciation on the TDN measurement in fresh waters by high temperature catalytic oxidation and persulfate digestion

Analytical methodologies for the determination of total dissolved nitrogen (TDN) in waters are based on a conversion step able to transform selectively all the nitrogen species into a compound that is then quantified. A crucial requirement to meet accuracy is the quantitative recovery of all organic and inorganic nitrogen species during the conversion step. In this work, the N recoveries of two widely employed methodologies that use different conversion steps (high temperature catalytic oxidation (HTCO) and persulfate digestion (PD)) were assessed on a set of organic nitrogen compounds, representative of the structures of both dissolved organic matter (DOM) and anthropogenic contaminants. Low recoveries are due to poor selectivity during the conversion step, with the formation of nitrogen compounds other than nitrogen oxide (HTCO) and nitrate (PD). The results show that in many instances the TDN measurements give systematically low results depending on N speciation. PD could give lower results than HTCO even for samples containing only DOM of biological origin. In particular (i) low N recovery was always observed with compounds having two or more contiguous N atoms; (ii) the HTCO method is very effective for TDN quantification in the presence of s-triazine rings while PD method did not yield satisfactory N recovery; (iii) a full N recovery was observed with compounds having amido or amino groups or nitrogen atoms in imidazole, indole and pyrimidine rings; and (iv) the N recoveries for purine derivatives are almost complete with HTCO, but give systematically low results by PD.

Finally, the estimation of dissolved organic nitrogen (DON) fluxes and pools from TDN measurements can be affected by uncertainties larger than previously thought as a consequence of (i) the lower N recovery for some nitrogen compounds and (ii) the differences in the N recovery as a function of the adopted analytical methods.     

Metal distribution and binding in balneological peats and their aqueous extracts

Binding of metals in typical bath peat samples ("Grosses Gifhomer Moor", Sassenburg/North Germany) and their aqueous extracts was characterized by means of a multi-method approach. For that purpose a sequential extraction procedure based on peat-filled chromatography columns was developed. Water-soluble metal and DOM (dissolved organic matter) fractions were subdivided by use of a stepwise increased pH gradient (pH 3.8-5), finally by the chelator EDTA and 0.1 mol L(-1) hydrochloric acid. Metal fractions very strongly bound to peat were assessed by an aqua regia extraction. Metal determinations required were performed by atomic spectrometry methods (AAS, ICP-OES, and TXRF). The metal and DOM concentrations in the peat extracts varied significantly, depending on the natural variety of the peat matter under study (e.g., Al: 25-674, Cd: 0.05-0.2, Cu: 5-15.4, Fe: 77-1785, Mn: 21-505, Ni: 2-33, Pb: < 1, Zn: 9-715 (microg L(-1)); Na: 8-45, K: 1.3-14.9, Ca: 2-51, Mg: 1.1-7.9 (mg L(-1)); 26-73 mg L(-1) DOC). An increase of the pH increased the DOC (dissolved organic carbon) of the peat extracts, but hardly the concentration of heavy metals. The latter could only be re-mobilized by EDTA and dilute hydrochloric acid. Additional investigations of the peat extracts using tangential-flow ultrafiltration revealed that the heavy metals extracted at pH < 4 were predominantly dissociated. At higher pH (pH > 4.5) they were preferentially bound to macromolecular DOM. Moreover, using multistage ultrafiltration the size distribution of the DOM and their metal species was assessed.     

A suite of sensitive chemical methods to determine the δ15N of ammonium, nitrate and total dissolved N in soil extracts

Natural ¹⁵N abundances (δ¹⁵N values) of different soil nitrogen pools deliver crucial information on the soil N cycle for the analysis of biogeochemical processes. Here we report on a complete suite of methods for sensitive δ¹⁵N analysis in soil extracts. A combined chemical reaction of vanadium(III) chloride (VCl₃) and sodium azide under acidic conditions is used to convert nitrate into N₂O, which is subsequently analyzed by purge‐and‐trap isotope ratio mass spectrometry (PTIRMS) with a cryo‐focusing unit. Coupled with preparation steps (microdiffusion for collection of ammonium, alkaline persulfate oxidation to convert total dissolved N (TDN) or ammonium into nitrate) this allows the determination of the δ¹⁵N values of nitrate, ammonium and total dissolved N (dissolved organic N, microbial biomass N) in soil extracts with the same basic protocol. The limits of quantification for δ¹⁵N analysis with a precision of 0.5‰ were 12.4 µM for ammonium, 23.7 µM for TDN, 16.5 µM for nitrate and 22.7 µM for nitrite. Copyright © 2010 John Wiley & Sons, Ltd.     

Determination of dissolved organic nitrogen in natural waters using high-temperature catalytic oxidation

Studies on nitrogen in natural waters have generally focussed on dissolved inorganic nitrogen (DIN), primarily because of relative ease of analysis and the important influence of DIN on water quality. Advances in analytical techniques now permit the systematic study of dissolved organic nitrogen (DON), and this work has shown that DON is quantitatively significant in many waters. This article describes the sampling and analytical protocols required for rapid, precise and reliable determinations of DON, involving high-temperature catalytic oxidation (HTCO), coupled to chemiluminescence detection. This approach simultaneously determines dissolved organic carbon (DOC) and total dissolved nitrogen (TDN), and DON is derived by subtraction of DIN measured by colorimetry. The DON determination is simple to perform, exhibits excellent precision (<1% for C and 1.5% for N) and is applicable to a wide range of natural waters.     

Metal distribution and binding in balneological peats and their aqueous extracts

Binding of metals in typical bath peat samples (“Großes Gifhorner Moor”, Sassenburg/North Germany) and their aqueous extracts was characterized by means of a multi-method approach. For that purpose a sequential extraction procedure based on peat-filled chromatography columns was developed. Water-soluble metal and DOM (dissolved organic matter) fractions were subdivided by use of a stepwise increased pH gradient (pH 3.8–5), finally by the chelator EDTA and 0.1 mol L^–1 hydrochloric acid. Metal fractions very strongly bound to peat were assessed by an aqua regia extraction. Metal determinations required were performed by atomic spectrometry methods (AAS, ICP–OES, and TXRF). The metal and DOM concentrations in the peat extracts varied significantly, depending on the natural variety of the peat matter under study (e.g., Al: 25–674, Cd: 0.05–0.2, Cu: 5– 15.4, Fe: 77–1785, Mn: 21–505, Ni: 2–33, Pb: < 1, Zn: 9– 715 (μg L^–1); Na: 8–45, K: 1.3–14.9, Ca: 2–51, Mg: 1.1– 7.9 (mg L^–1); 26–73 mg L^–1 DOC). An increase of the pH increased the DOC (dissolved organic carbon) of the peat extracts, but hardly the concentration of heavy metals. The latter could only be re-mobilized by EDTA and dilute hydrochloric acid. Additional investigations of the peat extracts using tangential-flow ultrafiltration revealed that the heavy metals extracted at pH < 4 were predominantly dissociated. At higher pH (pH > 4.5) they were preferentially bound to macromolecular DOM. Moreover, using multistage ultrafiltration the size distribution of the DOM and their metal species was assessed.     

In Vitro Antioxidant and Prooxidant Activities of Red Raspberry (Rubus idaeus L.) Stem Extracts

Leaves and stems of red raspberry (Rubus idaeus) are used in Lithuanian folk medicine. Healing properties of raspberry are related to the content of bioactive compounds, mainly polyphenols. Extracts of raspberry leaves contained higher total phenolic content (TPC) (1290 mg/L, expressed in gallic acid equivalent) compared to that in extracts of stems or peeled bark (up to 420 mg/L and 598 mg/L, respectively). To find out whether the collection time of herbal material was critical for the properties of the extracts, the stems were collected at different times of the year. TPC in the extracts depended more on extraction conditions rather than on the sampling time. Antioxidant activity of raspberry stem and bark extracts tested by spectrophotometric (DPPH^● scavenging) and electrochemical (cyclic and differential pulse voltammetry) assays correlated with TPC. DPPH radical scavenging activity values for stem, leaf, and bark extracts were as follows: ≤1.18 ± 0.07, 1.63 ± 0.10, and ≤1.90 ± 0.04 (mmol/L, TROLOX equivalent), respectively. Assessed electrochemically, hydrogen peroxide-scavenging activity of extracts was independent on TPC. The latter activity was related to the presence of some protein in the extract as revealed by gel electrophoresis. Prooxidant activity of raspberry stem extracts was dependent on solution pH and temperature.     

Effect of Liquid Animal Manure Application on the Solubilization of Heavy Metals from Soil

Abstract

The effect of liquid animal manure on heavy metal solubilization in soil has been studied in the laboratory; three different types of experiments were carried out:

1) aerobic and anaerobic incubation of soil/manure mixtures

2) desorption of heavy metals from soil, as affected by manure liquid fraction

3) gel permeation chromatography of soil/manure aqueous extracts to identify components responsible for heavy metal solubilization.

Alf three different approaches showed that complexation involving high molecular weight dissolved organic matter from the soil/manure matrix is (together with pH) the most important driving force for heavy metal solubilization. As a consequence, chemical and microbial processes (e.g. nitrification) that influence dissolved organic matter concentrations in the soil solution, determine the degree of heavy metal solubilization in manured soil.     

Chitosan Elicitation Impacts Flavonolignan Biosynthesis in Silybum marianum (L.) Gaertn Cell Suspension and Enhances Antioxidant and Anti-Inflammatory Activities of Cell Extracts

Silybum marianum (L.) Gaertn is a rich source of antioxidants and anti-inflammatory flavonolignans with great potential for use in pharmaceutical and cosmetic products. Its biotechnological production using in vitro culture system has been proposed. Chitosan is a well-known elicitor that strongly affects both secondary metabolites and biomass production by plants. The effect of chitosan on S. marianum cell suspension is not known yet. In the present study, suspension cultures of S. marianum were exploited for their in vitro potential to produce bioactive flavonolignans in the presence of chitosan. Established cell suspension cultures were maintained on the same hormonal media supplemented with 0.5 mg/L BAP (6-benzylaminopurine) and 1.0 mg/L NAA (α-naphthalene acetic acid) under photoperiod 16/8 h (light/dark) and exposed to various treatments of chitosan (ranging from 0.5 to 50.0 mg/L). The highest biomass production was observed for cell suspension treated with 5.0 mg/L chitosan, resulting in 123.3 ± 1.7 g/L fresh weight (FW) and 17.7 ± 0.5 g/L dry weight (DW) productions. All chitosan treatments resulted in an overall increase in the accumulation of total flavonoids (5.0 ± 0.1 mg/g DW for 5.0 mg/L chitosan), total phenolic compounds (11.0 ± 0.2 mg/g DW for 0.5 mg/L chitosan) and silymarin (9.9 ± 0.5 mg/g DW for 0.5 mg/L chitosan). In particular, higher accumulation levels of silybin B (6.3 ± 0.2 mg/g DW), silybin A (1.2 ± 0.1 mg/g DW) and silydianin (1.0 ± 0.0 mg/g DW) were recorded for 0.5 mg/L chitosan. The corresponding extracts displayed enhanced antioxidant and anti-inflammatory capacities: in particular, high ABTS antioxidant activity (741.5 ± 4.4 μM Trolox C equivalent antioxidant capacity) was recorded in extracts obtained in presence of 0.5 mg/L of chitosan, whereas highest inhibitions of cyclooxygenase 2 (COX-2, 30.5 ± 1.3 %), secretory phospholipase A2 (sPLA2, 33.9 ± 1.3 %) and 15-lipoxygenase (15-LOX-2, 31.6 ± 1.2 %) enzymes involved in inflammation process were measured in extracts obtained in the presence of 5.0 mg/L of chitosan. Taken together, these results highlight the high potential of the chitosan elicitation in the S. marianum cell suspension for enhanced production of antioxidant and anti-inflammatory silymarin-rich extracts.     

A semi-automatic alkaline peroxodisulphate method for the routine determination of total dissolved nitrogen in sea water

Nydahl's method for the determination of dissolved organic nitrogen (DON) in distilled water has been modified for the determination of total dissolved nitrogen (TDN) in sea water. Samples (9 cm³) are digested batch-wise with alkaline potassium peroxodisulphate solution. An improved buffering system permits the automatic measurement of the nitrate formed, and allows the analysis of 50–80 samples per day. DON may be determined as the difference between TDN and the sum of inorganic nitrogen species. The standard deviation of TDN determinations is 0.7 μg N dm^-3 at about 15 μg TDN dm^-3. The method is applied to a range of samples including tanker ballast water, oil platform production water, and zooplankton.     

Stable isotope analysis of dissolved organic carbon in soil solutions using a catalytic combustion total organic carbon analyzer‐isotope ratio mass spectrometer with a cryofocusing interface

Stable carbon isotopes are a powerful tool to assess the origin and dynamics of carbon in soils. However, direct analysis of the ¹³C/¹²C ratio in the dissolved organic carbon (DOC) pool has proved to be difficult. Recently, several systems have been developed to measure isotope ratios in DOC by coupling a total organic carbon (TOC) analyzer with an isotope ratio mass spectrometer. However these systems were designed for the analysis of fresh and marine water and no results for soil solutions or ¹³C‐enriched samples have been reported. Because we mainly deal with soil solutions in which the difficult to oxidize humic and fulvic acids are the predominant carbon‐containing components, we preferred to use thermal catalytic oxidation to convert DOC into CO₂. We therefore coupled a high‐temperature combustion TOC analyzer with an isotope ratio mass spectrometer, by trapping and focusing the CO₂ cryogenically between the instruments. The analytical performance was tested by measuring solutions of compounds varying in the ease with which they can be oxidized. Samples with DOC concentrations between 1 and 100 mg C/L could be analyzed with good precision (standard deviation (SD) ≤0.6‰), acceptable accuracy, good linearity (overall SD = 1‰) and without significant memory effects. In a ¹³C‐tracer experiment, we observed that mixing plant residues with soil caused a release of plant‐derived DOC, which was degraded or sorbed during incubation. Based on these results, we are confident that this approach can become a relatively simple alternative method for the measurement of the ¹³C/¹²C ratio of DOC in soil solutions. Copyright © 2010 John Wiley & Sons, Ltd.     

A solid phase microextraction method to fingerprint dissolved organic carbon released from Eucalyptus camaldulensis (Dehnh.) (River Red Gum) leaves

A solid phase microextraction-gas chromatography (SPME-GC) method was developed to trace natural sources of dissolved organic carbon (DOC) in river systems. The effects of extraction time, temperature, salt concentration, rate of stirring, and silanisation of sampling container were examined. The optimum extraction conditions using a polydimethylsiloxane (PDMS) SPME fibre were found to be extraction for 15 min at 40 °C, pH 2, from a saturated NaCl matrix with rapid stirring in a non-silanised vial. The method gave good results for a series of six compounds representative of those likely to be present in dissolved organic carbon leached from River Red Gum leaves—cineole, terpineol, thymol, myristic acid, methyl palmitate and methyl stearate. Artificial dissolved organic carbon solutions prepared from River Red Gum leaf leachate were also examined and the effects of filtering and storage on the filtrate were noted. The method was demonstrated to have potential to track the leachate in aquatic environment, indicated by the large number of compounds extracted from leachate solutions, and the broad linear working ranges of extracted compounds.     

Influence of salinity and natural organic matter on the solid phase extraction of sterols and stanols: application to the determination of the human sterol fingerprint in aqueous matrices

Faecal sterols have been proposed as direct chemical markers for the determination of faecal contamination in inland and coastal waters. In this study, we assess the impact of (a) the concentration of dissolved organic carbon (DOC), (b) the nature of DOC, (c) the salinity and (d) the concentration of sterols and stanols on their solid phase extraction. When natural organic matter (NOM) is modelled by humic acid, increasing DOC concentration from 2.7 to 15.4 mg/L has no significant impact on the recovery of sterols and stanols. The modelling of NOM by a mixture of humic acid and succinoglycan induces a significant (24%) decrease in the recovery of sterols and stanols. For all concentrations of target compounds, no significant increase in recovery is associated with increasing the salinity. Moreover, an increase in the recovery of target compounds is induced by an increase in their concentration. The nine target compounds and the recovery standard (RS) exhibit the same behaviour during the extraction step. Thus, we propose that (a) the concentration of target compounds can be corrected by the RS to calculate more realistic concentrations without modifying their profile and (b) the sterol fingerprint can be investigated in the colloidal fraction of aqueous samples without altering the information it could provide about the source. The application of this analytical method to waste water treatment plant influent and effluents yields results in agreement with previous studies concerning the use of those compounds to differentiate between sources of faecal contamination. We conclude that this analytical method is fully applicable to the determination of sterol fingerprints in the dissolved phase (<0.7 μm) of natural aqueous samples.     

微滴液相微萃取技术用于气相色谱-质谱法测定食品中的酞酸酯

将一种新型、简单、快速、环境友好的萃取方法微滴液相微萃取(SDME)与气相色谱-质谱法结合用于快速分析食品中的几种酞酸酯(PAEs)。考察了萃取溶剂的种类及用量、微液滴在样品溶液中的深度、萃取时间及搅拌子的搅拌速度对微滴液相微萃取的影响。优化的萃取条件为:萃取溶剂为2.0 μL甲苯,微液滴在样品溶液中的深度为0.75 cm,搅拌速度为1000 r/min,萃取时间为20 min。该方法的线性范围为0.1～4000 μg/L,检测限为25 ng/L～0.8 mg/L,加标回收率为87.1%～114.4%,相对标准偏差为4.9%～11.6%。微滴液相微萃取所需的有机溶剂量很小,是一种快速、简单、安全、有效的水溶性样品的前处理方法。     

Dynamic behaviour of river colloidal and dissolved organic matter through cross-flow ultrafiltration system

Through cross-flow filtration (CFF) with a 1-kDa regenerated cellulose Pellicon 2 module, the ultrafiltration characteristics of river organic matter from Longford Stream, UK, were investigated. The concentration of organic carbon (OC) in the retentate in the Longford Stream samples increased substantially with the concentration factor (cf), reaching approximately 40 mg/L at cf 15. The results of dissolved organic carbon (DOC) and colloidal organic carbon (COC) analysis, tracking the isolation of colloids from river waters, show that 2 mg/L of COC was present in those samples and good OC mass balance (77-101%) was achieved. Fluorescence measurements were carried out for the investigation of retentate and permeate behaviour of coloured dissolved organic materials (CDOM). The concentrations of CDOM in both the retentate and permeate increased with increasing cf, although CDOM were significantly more concentrated in the retentate. The permeation model expressing the correlation between log[CDOM] in the permeate and logcf was able to describe the permeation behaviour of CDOM in the river water with regression coefficients (r(2)) of 0.94 and 0.98. Dry weight analysis indicated that the levels of organic colloidal particles were from 49 to 71%, and between 29 and 51% of colloidal particles present were inorganic. COC as a percentage of DOC was found to be 10-16% for Longford Stream samples.     

高效液相色谱法测定土壤中香豆素类灭鼠药残留

建立了测定土壤中杀鼠灵、杀鼠醚、溴敌隆、氟鼠灵、溴鼠隆5种香豆素类灭鼠药残留量的柱后衍生荧光检测高效液相色谱方法。样品在加入内标物氯杀鼠灵后用丙酮-氨水-甲醇（体积比为100：3：100）混合液提取,浓缩的提取液用5 mL正己烷-氯仿（体积比为3：1）混合液溶解,NH₂固相萃取小柱净化,用15 mL 50 mmol/L四丁基磷酸二氢铵甲醇溶液洗脱分析物,移除溶剂,用甲醇-0.25%（体积分数）乙酸水溶液（体积比为3：2）混合液溶解,过滤后,经高效液相色谱分离,以甲醇-氨水-水（体积比为1：1：8）混合液为衍生试剂进行柱后衍生,采用荧光检测器检测。杀鼠灵、杀鼠醚、溴敌隆、氟鼠灵、溴鼠隆5种鼠药在0.02～10.00 mg/L范围内线性关系良好,相关系数均大于0.999,定量限（LOQ,S/N=10）为2.2～18.5 μg/L。在0.1～0.3 mg/kg添加水平内,5种灭鼠药的回收率为94.6%～118.0%,相对标准偏差（RSD）为0.8%～10.2% （n=3）。实验结果表明该方法灵敏、准确,重复性好。     

Liquid chromatography/mass spectrometry stable isotope analysis of dissolved organic carbon in stream and soil waters

A commercial interface coupling liquid chromatography (LC) to a continuous‐flow isotope ratio mass spectrometry (CF‐IRMS) instrument was used to determine the δ¹³C of dissolved organic carbon (DOC) in natural waters. Stream and soil waters from a farmland plot in a hedgerow landscape were studied. Based on wet chemical oxidation of dissolved organics the LC/IRMS interface allows the on‐line injection of small volumes of water samples, an oxidation reaction to produce CO₂ and gas transfer to the isotope ratio mass spectrometer. In flow injection analysis (FIA) mode, bulk DOC δ¹³C analysis was performed on aqueous samples of up to 100 μL in volume in the range of DOC concentration in fresh waters (1–10 mg C.L^–1). Mapping the DOC δ¹³C spatial distribution at the plot scale was made possible by this fairly quick method (10 min for triplicate analyses) with little sample manipulation. The relative contributions of different plot sectors to the DOC pool in the stream draining the plot were tentatively inferred on the basis of δ¹³C differences between the hydrophilic and hydrophobic components. Copyright © 2011 John Wiley & Sons, Ltd.     

光化学降解溶解有机物及其对生物过程的影响

溶解有机物对控制海洋和淡水水生系统的化学、生物和物理特性有重要的影响.光化学降解溶解有机物改变了生态体系的溶解有机碳、有机物的分子量及光学特性,并且产生复杂的反应性氧化合物、二氧化碳、一氧化碳、小分子量的有机酸、氨基酸、二硫化碳等,对生物过程有重要的影响.本文简要综述了光化学降解溶解有机物的过程机理及其对生物过程的影响.     

超声波提取-气相色谱法测定土壤中21种酚类化合物

建立了超声波提取-气相色谱法同时测定土壤中21种酚类化合物的分析方法。用二氯甲烷和正己烷混合溶剂提取土壤中的酚类化合物,提取液经碱性水溶液分配净化,去除非酸性有机杂质,再酸化萃取酚类化合物,浓缩后采用气相色谱-氢火焰离子化检测器进行检测,外标法定量。以10 g土壤样品计,酚类化合物的检出限为0.01~0.06 mg/kg。实际样品添加回收试验的回收率为62.9%~111.4%,相对标准偏差为4.3%~24.0%(n=6),准确度和精密度均较好。结果表明:该法操作方便,净化效果好,可用于土壤中多种酚类化合物的测定。