Effect of organic matter content in the trace analysis of triazines in various types of soils with GC-NPD

Summary Recent work demonstrated that the combination of microwave assisted solvent extraction (MASE) and capillary gas chromatography with selective nitrogen detection (GC-NPD) is a viable approach for the efficient determination of triazine herbicides in soils. However, for soils with a high organic matter content or the injection of more concentrated extracts to obtain lower LOD's the performance of gas chromatographic analysis of uncleaned extracts is hampered. This results in both a decrease of the chromatographic response of analytes and a decrease in the life time of the column due to coextracted matrix substances. The effect of various types of soils on the chromatographic analysis of triazine herbicides was studied. It appeared that for the investigated samples with an organic matter content below 5% processing of uncleaned extracts is possible. Samples with a higher organic matter content required a cleanup step. A rapid procedure on 100 mg silica cartridges has been developed using solvents compatible with the MASE extracts and the instrumental analysis. Beside the testing with different standard soils, about 120 samples of an ongoing monitoring program involving three different types of soil (organic matter content: 3–37%) were analysed. The selected compounds atrazine, desethylatrazine, desisopropyl-atrazine and simazine could be assayed in the various soil types to a level of at least 2 μg kg⁻¹. For soil samples with a high organic matter content (>5%), the rapid cleanup procedure allowed the trace analysis of the triazines and considerably increased the life time of the capillary column. Recoveries at levels from 2 to 50 μg kg⁻¹ ranged from 70 to 100% with RSDs ranging from 5.1 to 9.5%. Confirmation of positive samples was carried out by gas chromatography mass spectrometry.     

Optimization of QuEChERS method for the analysis of organochlorine pesticides in soils with diverse organic matter

A QuEChERS method has been developed for the determination of 14 organochlorine pesticides in 14 soils from different Portuguese regions with wide range composition. The extracts were analysed by GC-ECD (where GC-ECD is gas chromatography-electron-capture detector) and confirmed by GC-MS/MS (where MS/MS is tandem mass spectrometry). The organic matter content is a key factor in the process efficiency. An optimization was carried out according to soils organic carbon level, divided in two groups: HS (organic carbon >2.3%) and LS (organic carbon <2.3%). The method was validated through linearity, recovery, precision and accuracy studies. The quantification was carried out using a matrix-matched calibration to minimize the existence of the matrix effect. Acceptable recoveries were obtained (70-120%) with a relative standard deviation of ≤16% for the three levels of contamination. The ranges of the limits of detection and of the limits of quantification in soils HS were from 3.42 to 23.77 μg kg(-1) and from 11.41 to 79.23 μg kg(-1), respectively. For LS soils, the limits of detection ranged from 6.11 to 14.78 μg kg(-1) and the limits of quantification from 20.37 to 49.27 μg kg(-1) . In the 14 collected soil samples only one showed a residue of dieldrin (45.36 μg kg(-1) ) above the limit of quantification. This methodology combines the advantages of QuEChERS, GC-ECD detection and GC-MS/MS confirmation producing a very rapid, sensitive and reliable procedure which can be applied in routine analytical laboratories.     

Characterization of soil organic matter fractions from grassland and cultivated soils via C content and delta13C signature

Variations in (13)C natural abundance and distribution of total C among five size and density fractions of soil organic matter, water soluble organic C (WSOC) and microbial biomass C (MBC) were investigated in the upper layer (0-20 cm) of a continuous grassland soil (CG, C(3) vegetation), a C(3)-humus soil converted to continuous maize cultivation (CM, C(4) vegetation) and a C(3)-humus soil converted to a rotation of maize cultivation and grassland (R). The amounts of WSOC and MBC were both significantly larger in the CG than in the CM and the R. In the three soils, WSOC was depleted while MBC was enriched in (13)C as compared with whole soil C. The relative contributions to the total C content of C stored in the macro-organic matter and in the size fraction 50-150 microm decreased with decreasing total C contents in the order CG > R > CM, while the relative contribution of C associated with the clay- and silt-sized fraction <50 microm increased. This reflects a greater stability and physical protection against microbial degradation associated with soil disruption (tillage) of the clay- and silt-associated organic C, in relation to the organic C in larger size fractions. The size and density fractions from the CG soil showed significant differences in (13)C enrichment, indicating different degrees of microbial degradation and stability of soil organic C associated with physically different soil organic matter (SOM) fractions. Delta(13)C analysis of the size and density fractions from CM and R soils reflected a decreasing turnover rate of soil organic C with increasing density among the macro-organic matter fractions and with decreasing particle size.     

Total concentration analysis of polycylic aromatic hydrocarbons in aqueous samples with high suspended particulate matter content

The European water framework directive (WFD) requires priority pollutants to be measured in the whole water sample and not only in the dissolved phase. However, it does not give clear definitions on how to achieve this. To overcome this limitation, a new methodology of sample preparation procedure for the analysis of polycyclic aromatic hydrocarbons on the basis of extraction disks is introduced here. The automatable procedure includes a “one-step” extraction of the analytes both dissolved in the liquid phase of the sample and sorbed to suspended particulate matter. The latter is extracted concurrently with the solid-phase extraction (SPE) material within the elution step of the procedure. Separation, identification, and quantification of the analytes is performed by GC–MS. Results from surface water samples spiked with certified sediment up to 1000 mg/l are presented in this work and compared with results derived from liquid–liquid extraction (LLE). Most measured values are within or at least near certified uncertainty limits of the sediment. The SPE disk method shows much higher recoveries and better precision (relative standard deviations between 2% and 11%) than the standard LLE method. For all substances under investigation, the limits of quantification achieved range between 0.001 and 0.005 μg/l.     

Determination of oligosaccharides (DP1-DP8) in samples with high content of salt and organic matter by reversed phase HPLC

Summary A method is described for the determination of oligosaccharides in samples of high salt content by RP-HPLC with water as eluent and refractive index detection. The samples, mussel processing wastes which are used as media for microfungus and yeast cultures and hence for enzymatic assays (amilolitic capacity) of these microorganisms that develop within the wastes, have been treated with ethanol to precipitate the macromolecular organic matter and desalted by a modified mixed bed resin before chromatographic analysis is carried out.     

Microwave digestion of sediment, soils and urban particulate matter for trace metal analysis

A microwave digestion technique was developed to determine the content of nine heavy metals in sediments and soils. The digests were subsequently analysed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The metals determined were Ca, Mg, Fe, Mn, Zn, Cr, Cd, Cu, Pb and V. The digestion was achieved by using an acid mixture of HNO₃, HF and distilled H₂O. The experimental study was conducted using four standard reference materials (SRMs): sewage sludge (LGC6136), marine sediment (PACS-1), urban particulate matter (NIST 1648) and coal carbonisation site soil (LGC6138). Two different programs were examined to determine which was optimal for the digestion of real environmental samples. The accuracy and precision of the two digestion programs for the analysis of the SRMs were compared. From the results obtained, the microwave program providing a maximum of power of 650 W and a cycle time of 51 min resulted in the best analytical performance. The experimental results obtained were in good agreement with the certified values and demonstrated that the proposed method is precise and accurate.     

Infrared and chemometrics study of the interaction between heavy metals and organic matter in soils

The study of the behavior of heavy metals in soils requires the knowledge of the complexation between soil constituents and metals and this information is not available from conventional analytical techniques such as atomic absorption. Since metals do not absorb mid infrared radiation, we wanted to characterize them using their interaction with the organic matter of soils. The use of chemometrics treatment of the spectroscopic data has demonstrated firstly that the interaction between soil constituents and metals takes place preferentially via organic matter, secondly the high difference between the complexation of lead and zinc into organic matter should be noted. The study of the infrared spectra shows that two bands at 1670-1690 and 1710 cm(-1) vary according to the concentration of lead, which seems to be preferentially complexed by the salicylate functionality.     

Influence of soluble organic matter on cadmium mobility in model compounds and in soils.

The role of soluble organic matter on the mobility of cadmium in model compounds and soils is discussed. For model compounds, a simple predictive model is proposed to describe the competition between metal adsorption and the formation of complexes in the solution, using conditional constants to predict the adsorption behaviour of metallic cations in the presence of an organic ligand. Experimental results are presented using a clay mineral and ethylenediaminetetraacetic acid as organic ligand to assess this model for cadmium. Soil experiments are also presented to illustrate the influence of soluble complexing organic matter on the mobility of cadmium. In this instance, mobility is shown to depend on three interactive parameters: pH, oxidation-reduction reactions and formation of complexes.     

Determination of organic matter in soils using radial basis function networks and near infrared spectroscopy

A relationship was established between the organic matter content in soils determined by conventional chemical measurements and by diffuse reflectance spectra in the near infrared region (1000-2500 nm). Radial basis function networks (RBFN) with regularized forward selection to control the model complexity were used for non-parametric regression, resulting in a RMSEP of 0.25%. The observed results using RBFN were better than those obtained by partial least squares regression (PLS) and multi-layer perceptron (MLP) feed-forward networks with a back-propagation learning algorithm. RBFN is a suitable tool to model this complex system, with additional advantages over MLP, since the training procedure is less dependent on the initial conditions.     

Microcalorimetric measurements of the metabolic activity by bacteria and fungi in some Brazilian soils amended with different organic matter

The effect of bacterial and fungal activities on organic matter degradation in Brazilian soils was studied by a microcalorimetric method. Bacteria and fungi isolated from tropical soils and added to: Rhodic eutrudox (R), Typic eutrudox (V) and Quartzipsamment (Q) soils amended separately with moisture (control) (A) and 25% of cattle manure (E), municipal refuse compost (L), earthworm casts (H) or 23 μg of trifluralin (T) were investigated. The number of colony forming units in soil suspension was quantified by microscopy and inoculated in respective soil. All processes were measured at intervals of 7 days over a period of 35 days. The exothermic thermal effect (μJ) per cm³ of bacteria or fungi per gram of dry soil, respectively, for each substrate was: [(9±1), (4±1)] RA; [(478±24), (105±5)] RE; [(121±6), (71±4)] RL; [(121±6), (71±4)] RH; [(8±1); (3±1)] RT; [(10±1), (9±1] VA; [(347±17), (261±13)] VE; [(71±4), (28±1)] VL; [(22±1), (33±2)] VH; [(7±1), (10±1)] VT; [(19±1), (12±1)] QA; [(1301±65), (46±2)] QE; [(89±4), (9±1)] QL; [(130±7), (11±1)] QH; [(32±2), (8±1)] QT. The calorimetric values are higher for bacteria than for fungi. In general, the results showed higher activities in the soil amended with cattle manure than with other additives.     

Influence of organic matter removal on competitive and noncompetitive adsorption of copper and zinc in acid soils

We studied competitive and noncompetitive adsorption of copper and zinc in four acid soils, and compared the behavior of the two metals in untreated samples and samples treated with hydrogen peroxide to remove organic matter in the soil. Copper exhibited stronger competitive adsorption than zinc in the untreated samples. However, removal of organic matter reduced copper adsorption to a greater extent than zinc adsorption, the two metals exhibiting a more similar adsorption pattern than the untreated samples. The presence of copper dramatically reduced zinc competitive adsorption in untreated samples; on the other hand, that of zinc only resulted in slightly reduced competitive adsorption of copper. The hydrogen peroxide treatment decreased competitive adsorption in both metals; however, copper continued to be more efficient than zinc in competing for binding sites on adsorbing surfaces. Desorption of Cu occurred much less readily than desorption of Zn and hysteresis is apparent especially for Cu.     

Optimization of conditions for the determination of the organic matter content of waters by reagentless oxithermography and its application to the analysis of natural waters

To determine the chemical oxygen demand (COD) of water by oxithermography, we studied a high-temperature reactor with two inputs of the gas flow. Such a design allowed the creation of an internal circuit of the oxygen–inert gas (argon) binary flow in the reactor for the oxidation of organic substances and the determination of COD by the decrease in the concentration of oxygen in the binary mixture. The optimum operation parameters of the instrument, affecting the analytical characteristics of the method, were determined. The detection limit for a water sample of the volume 10 µL was 3.4 mg O/L. It was shown that the oxithermograph and the proposed procedure can be used for the determination of COD in drinking and natural waters of Bryansk oblast. The approach developed has an advantage, consisting in the reagentless rapid determination of the COD of waters without preliminary sample preparation.     

Methodological considerations for using thermal analysis in the characterization of soil organic matter

Thermal analysis is primarily used in the field of materials science, but has a long history in the geosciences. Soil organic matter (SOM) has received a great deal of recent scientific interest because of its role in the global carbon cycle. Conventional methods of characterizing SOM quality are unsatisfactory because they do not adequately capture the complete quality continuum that SOM comprises or the various mechanisms that act to stabilize it in the soil matrix. Thermal analysis techniques have the potential to capture this quality continuum, but are dependent on numerous experimental conditions that limit the comparability of results among different studies. Published methodology on thermal analysis of soils and sediments has largely focused on the characterization of the mineral component, while the organic component has received little attention. We tested several experimental conditions for their effects on the exothermic region of curves generated by thermal analysis of easily dispersed soil clay fractions and non-protected light-density particulate organic matter fractions isolated from the surface horizon of a forest soil. Results were found to be highly repeatable but strongly sensitive to crucible material, heating rate, and sample amount, and relatively insensitive to the use of a reference material. Thermal analysis is an important addition to the set of analytical tools used to characterize SOM quality because it provides direct, quantitative information of the energy potentially available for microbial metabolism. However, users will need to balance the needs of specific scientific objectives with the need for standardized methods and comparability between studies.     

大气颗粒物中有机物色谱分析的样品制备技术

大气颗粒物中有机物成分分析对深入研究大气颗粒物对人类健康、环境、气候、生态的影响,解析气溶胶来源,制定颗粒物控制相关法规,以及风险管理方法具有重要意义。由于颗粒物中的有机组分种类繁多,分析复杂,目前仅10%~20%的有机物得到了定性和定量分析。因此,大气细颗粒中有机物的分析已成为环境分析领域的优先发展方向。色谱是大气颗粒物中有机物分析的主要方法,而样品制备则是影响分析速度和精度的关键步骤。本文对颗粒物中有机组分色谱分析前的样品制备方法进行了综述,介绍了索氏提取、超声辅助提取、微波辅助提取、加压溶剂提取等溶剂提取方法以及热解吸提取方法,并重点介绍了这些方法在大气颗粒物样品处理中的应用,总结了各种方法的优缺点。     

Determination of the total phenol content of soils by high speed liquid chromatography with electrochemical detection

The total phenol content of soil samples has been measured using high performance liquid chromatography with electrochemical detection. Soils are extracted with sodium hydroxide solution and the phenols present in the extract are recovered on solid phase C₁₈ cartridges after pH adjustment. The measurement stage employs a short (3 cm) reversed phase column and electrochemical detection. The short column focuses the phenolic species into a single peak which can be integrated. Electrochemical detection provides both sensitivity and selectivity. Hence high speed measurement of a composite peak representing total phenol content is achieved.     

Artificial neural network data analysis for classification of soils based on their radionuclide content

The artificial neural network (ANN) data analysis method was used to recognize and classify soils of an unknown geographic origin. A total of 103 soil samples were differentiated into classes according to the regions in Serbia and Montenegro from which they were collected. Their radionuclide (²²⁶Ra, ²³⁸U, ²³⁵U, ⁴⁰K, ¹³⁴Cs, ¹³⁷Cs, ²³²Th, and ⁷Be) activities detected by gamma-ray spectrometry were then used as inputs to ANN. Five different training algorithms with different numbers of samples in training sets were tested and compared in order to find the one with the minimum root mean square error (RMSE). The best predictive power for the classification of soils from the fifteen regions was achieved using a network with seven hidden layer nodes and 2500 training epochs using the online back-propagation randomized training algorithm. With the optimized ANN, most soil samples not included in the ANN training data set were correctly classified at an average rate of 92%. The text was submitted by the authors in English.     

Validation of the methods for heavy metal speciation in soils and sediments

The knowledge of the chemical forms of metals is used to assess their availability and uptake by plants, and in sediments the forms of metals determine their transport and mobility in the aquatic media. This information may be obtained by determining chemical forms of metals (speciation) or different phases in which the metals are bound, obtained by applying extraction schemes. The analytical methods used include different steps and all of them must be validated. We report here the recommendations to minimize the errors in this kind of analysis. For validation the use of Certified Reference Materials (CRMs) and the participation in interlaboratory exercises are highly recommended.     

Offline oxygen isotope analysis of organic compounds with high N:O

Although the advantages of online δ¹⁸O analysis of organic compounds make its broad application desirable, researchers have encountered NO⁺ isobaric interference with CO⁺ at m/z 30 (e.g. ¹⁴N¹⁶O⁺, ¹²C¹⁸O⁺) when analyzing nitrogenous substrates. If the δ¹⁸O value of inter‐laboratory standards for substrates with high N:O value could be confirmed offline, these materials could be analyzed periodically and used to evaluate δ¹⁸O data produced online for nitrogenous unknowns. To this end, we present an offline method based on modifications of the methods of Schimmelmann and Deniro (Anal. Chem. 1985; 57: 2644) and Sauer and Sternberg (Anal. Chem. 1994; 66: 2409), whereby all the N₂ from the gas products of a chlorinated pyrolysis was eliminated, resulting in purified CO₂ for analysis via a dual‐inlet isotope ratio mass spectrometry system. We evaluated our method by comparing observed δ¹⁸O values with previously published or inter‐laboratory calibrated δ¹⁸O values for five nitrogen‐free working reference materials; finding isotopic agreement to within ±0.2‰ for SIGMA® cellulose, IAEA‐CH3 cellulose (C₆H₁₀O₅) and IAEA‐CH6 sucrose (C₁₂H₂₂O₁₁), and within ±1.8‰ for IAEA‐601 and IAEA‐602 benzoic acids (C₇H₆O₂). We also compared the δ¹⁸O values of IAEA‐CH3 cellulose and IAEA‐CH6 sucrose that was nitrogen‐'doped' with adenine (C₅H₅N₅), imidazole (C₃H₄N₂) and 2‐aminopyrimidine (C₄H₅N₃) with the undoped δ¹⁸O values for the same substrates; yielding isotopic agreement to within ±0.7‰. Finally, we provide an independent analysis of the δ¹⁸O value of IAEA‐600 caffeine (C₈H₁₀N₄O₂), previously characterized using online systems exclusively, and discuss the reasons for an average 1.4‰ enrichment in δ¹⁸O observed offline relative to the consensus online δ¹⁸O value. Copyright © 2010 John Wiley & Sons, Ltd.