The effect of acidification on the determination of organic carbon, total nitrogen and their stable isotopic composition in algae and marine sediment

We investigated the effects of sample acidification on the stable carbon and nitrogen isotopic composition (delta13C and delta15N), as well as the organic carbon (OC) and total nitrogen (TN) composition, of an algal culture and a marine sediment. Replicate measurements of untreated and acid-treated samples were made using 1 M, 2 M and 6 M HCl, 6% H2SO3 and 1 M H3PO4. For all treatments the precision of the analysis for the acid-treated sample was equal to or less than that in the non-acidified sample. For the algae, analysis of variance (ANOVA) indicated no significant differences in the mean OC and TN concentration, or delta13C and delta15N composition, between any acid treatment and non-acidified samples. For the sediment sample a comparison could only be made between the different acid treatments because the untreated contained significant amounts ( approximately 30%) of carbonate carbon. ANOVA indicated that the mean OC determined in sediment samples after the 1 M HCl treatment and the mean delta13C values after the 6% H2SO3 and 1 M H3PO4 treatments were significantly different (p < 0.013 and < .05, respectively) from all other treatments. Mass balance calculations indicate that in some instances delta13C values were biased due to a contribution from unreacted carbonate carbon. There were no significant differences in the mean TN between any acid-treated and non-acidified samples. The mean delta15N values after 6 M HCl, 6% H2SO3 and 1 M H3PO4 treatments were significantly different from the untreated sediment sample (p < 0.044). Based on the significant bias observed for the delta15N and delta13C values, a weak (1-2 M) HCl solution is confirmed as the most appropriate acid for the removal of inorganic carbon from natural materials requiring elemental and isotopic analysis.     

Effects of sample preparation on methylmercury concentrations in Arctic organisms

The biogeochemical cycling of mercury (Hg) in the marine environment is an issue of global concern, as consumption of marine fish is a major route of human exposure to the toxic specie methylmercury (MeHg). The most widely utilised and accepted technique for preparing biological tissue samples for the analysis of MeHg involves an alkaline digestion of the sample. Recent studies suggest, however, that this technique is inadequate to produce satisfactory recoveries for certain biological samples, including fish, fur, feathers and other ‘indicator’ tissues which contain relatively high levels of MeHg. Thus an improved acidic extraction method has been proven to produce more satisfactory results for a wide range of biological tissues. The present study compares the two methods on real sample material from different organisms of an Arctic marine food chain, and shows how this could lead to misinterpretation of analytical results. Results show significantly (p < 0.05) lower concentrations for alkaline digestion for large parts of the food chain; especially in fish and birds. The mean differences in concentrations found between the two different methods were 28, 31 and 25% for fish (Polar and Atlantic cod), Little Auk and Kittiwake, respectively. For samples lower in the food chain (i.e. zooplankton and krill) no significant differences were found. This leads to a clear underestimation of the levels of MeHg found higher up in these food chains; the ratio of MeHg to Hg in biological samples; and thus potentially erroneous conclusions drawn from these results concerning the biological cycling of mercury species. We hypothesise that the main reasons for these differences are poor extraction efficiency and/or matrix effects on the ethylation step prior to analysis. This is the first study to examine the effects of these artefacts on real environmental samples covering a complete food chain.     

基于稳定同位素比和元素分析技术的何首乌产地识别研究

元素分析仪主要用于测试样品中的元素含量,是重要的定量分析仪器,测试过程中影响测试结果准确性的因素较多. 以欧维特EA3000元素分析仪的CHNS测试模式为例,分析各个元素测试的干扰因素并提出切实可行的解决方案,从而提高测试结果的可靠性和准确性.     

不同前处理制样方法对钢中氧、氮测定结果的影响

讨论了不同物理和化学制样方法对钢中氧、氮测定结果的影响。试验结果表明,物理制样采用锉刀打磨样品表面后剪切,再用乙醚清洗除去油污;化学制样先用20%盐酸溶液溶解样品表面氧化层,再用滴加了4滴30%过氧化氢的10%草酸溶液浸泡,取出后依次用水、无水乙醇浸洗,风干。用以上两种方法制样,钢标准样品中氧、氮含量测定值与标示值一致。在测定钢中氮含量时,可用乙醚清洗后直接测定,以缩短检测周期和减轻劳动强度。该研究结果可用于指导钢样品中氧、氮含量测定时样品的处理。     

The effects of sample preparation,pyrolysis and pyrolyzate transfer conditions on pyrolysis mass spectra

Two different biopolymers, bovine serum albumin and glycogen, were examined by pyrolysis-mass spectrometry under various experimental conditions. The parameters tested include the method of cleaning the pyrolysis wire, the choice of the sample solvent, the sample size, the temperature-time profile and the temperature of the mass spectrometric inlet system.In order to determine quantitatively the effects of changes in experimental conditions on reproducibility of the spectra, the differences observed between the pyrolysis mass spectra represented as numerical dissimilarity values.It is concluded that the long-term differences observed are only partly explained by fluctuations in the conditions studied. However, it appears feasible to define a set of standard conditions with respect to the production of the pyrolyzate which should afford a reasonable degree of interlaboratory reproducibility.     

Microdetermination of carbon,hydrogen, nitrogen and oxygen in petroleum compounds with an automatic elemental analyzer

Summary The Perkin-Elmer Elemental Analyzer has been evaluated for the analysis of carbon, hydrogen, nitrogen and oxygen in typical petroleum samples. Comparison of the Elemental Analyzer results were made with carbon and hydrogen analyses by the Pregl method, oxygen by the Unterzaucher method, and nitrogen results from the automated micro Dumas Analyzer. The results obtained by the automated method were found comparable to those obtained by conventional methods. The automated method was found useful for the analysis of nitrogen in petroleum samples ranging from 0.05 to 0.1% N, a borderline level that presents difficulty for conventional methods. Samples of transformer oil containing known amounts of added phenol were analyzed for oxygen at the 0.2 to 1.0% O level.

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Zusammenfassung Der Verbrennungsautomat von Perkin-Elmer wurde für die Bestimmung von C, H, N und O in bestimmten Erdölprodukten verwendet und die Ergebnisse mit jenen des Preglschen Verfahrens, der Methode nachUnterzaucher bzw. mit den Resultaten der automatischen Dumas-Bestimmung verglichen. Die erhaltenen Werte sind mit denen konventioneller Methoden durchaus vergleichbar. Das automatische Verfahren ist für die Bestimmung des Stickstoffs in Erdölproben mit 0,05 bis 0,1% N gut geeignet, eine Größenordnung, die bei konventionellen Verfahren Schwierigkeiten bietet. Proben von Transformatorenöl, die bekannte Mengen Phenol enthielten, wurden auf ihren Sauerstoffgehalt analysiert, der zwischen 0,2 und 1,0% lag.

     

Stannic oxide as a combustion aid in elemental analysis for carbon,hydrogen and nitrogen

Summary The properties of stannic oxide as a combustion aid in elemental analysis for carbon, hydrogen and nitrogen, and its modification with silver for the retention of halogens and oxides of sulphur are described. The optimum combustion temperature with stannic oxide is 1000±50° C. It is suitable as a combustion tube packing for automated methods. A universal packing for analysis of various types of compounds is shown.

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Zinn(IV)oxid als Oxydationsmittel für die Elementaranalyse von C, H und N

Zusammenfassung Die Eigenschaften des Zinnoxids als Katalysator für die Bestimmung von C, H und N und seine Modifikation mit Silber für die Retention der Halogene und der Schwefeloxide wurden beschrieben. Die Optimaltemperatur für die Verbrennung mit Zinnoxid ist 1000±50° C. Es eignet sich als Rohrfüllung für automatisierte Methoden. Eine Universalfüllung für Analysen verschiedener Verbindungstypen wurde angegeben.

     

Advances in sample preparation in electromigration, chromatographic and mass spectrometric separation methods

The quality of sample preparation is a key factor in determining the success of analysis. While analysis of pharmaceutically important compounds in biological matrixes has driven forward the development of sample clean-up procedures in last 20 years, today's chemists face an additional challenge: sample preparation and analysis of complex biochemical samples for characterization of genotypic or phenotypic information contained in DNA and proteins. This review focuses on various sample pretreatment methods designed to meet the requirements for the analysis of biopolymers and small drugs in complex matrices. We discuss the advances in development of solid-phase extraction (SPE) sorbents, on-line SPE, membrane-based sample preparation, and sample clean-up of biopolymers prior to their analysis by mass spectrometry.     

The determination of selenium in sea water,silicates and marine organisms

Spectrophotometric procedures are described for the determination of selenium in sea water, silicates (especially marine sediments) and marine organisms. Coprecipitation with iron(III) hydroxide at pH 4–6 is used to concentrate selenium and to separate it from many of the commoner elements. Separation from iron and other cations is achieved by ion exchange. Selenium is determined photometrically with diaminobenzidine. Isotope dilution with selenium-75 is used to correct results for the small losses occurring during the analysis. Silicates can be decomposed without loss of selenium by means of a mixture of hydrofluoric and nitric acids. The method of Cummins et al., with sulphuric and perchloric acids in presence of molybdate ion, is highly satisfactory for the decomposition of bio-materials. For sea water, which contains ca. 0.4–0.5 <mg Se/l, a standard deviation of 0.03 μg/l was obtained. A silicate sediment and a sea weed containing ca. 1.5 μg Se/g and 0.8 μg Se/g respectively gave coefficients of variation of 8.0% and 4.7%. The U.S. Geological Survey standard granite G1 was found to contain 2.5 ± 0.1 μg Se/g.     

Comparison of sample preparation methods for determination of free carbon in boron carbide by X-ray powder diffraction

Several sample preparation methods were evaluated for determination of free carbon in boron carbide powders by quantitative X-ray diffraction method, including ultrasonication, wet ball milling and dry ball milling–wet mixing. Quantitation was based on measuring the integral peak area ratio of the diffraction lines of graphite (002) to boron carbide (012) in samples spiked with pure graphite. The dry milling–wet mixing method provided the best precision and accuracy in all the measurements as well as in determination of free carbon in a boron carbide reference material. There was a linear relationship between the integral peak area ratios and graphite added to boron carbide samples which were purified from their free carbon content. The method provided a low detection limit of 0.05 wt% free carbon.     

Effect of sample preparation methods on the D,L-enantiomer ratio of extracted selenomethionine

Effects of the two most widespread sample preparation techniques on the d,l-enantiomer ratio of extracted selenomethionine were monitored through the analysis of the certified reference material selenium-enriched yeast and the isolated protein fraction of high selenium monkeypot nut. The extracted selenomethionine (SeMet) fractions were orthogonally cleaned up with anion exchange chromatography before carrying out the enantiomer-specific detection to increase the robustness and the efficiency of the subsequent o-phthal-aldehyde and n-isobutyril-cysteine-based derivatisation process and reversed phase-high-performance liquid chromatography-inductively coupled plasma mass spectroscopy (ICP-MS) detection. The two techniques, namely methanesulphonic acid (MSA) based digestion and proteolytic digestion with protease XIV, resulted in significantly different ratio of d,l-selenomethionine with the final results of 2.2–2.7% and 0.5–0.6% of d-SeMet, respectively. The study revealed significant differences in the ICP-MS-related sensitivity of the derivatised selenomethionine enantiomers, which calls attention to the quantification of this selenoamino acid after MSA hydrolysis.     

Centrifugal concentrator for the substitution of nitrogen blow-down micro-concentration in dioxin/polychlorinated biphenyl sample preparation

A centrifugal concentrator was applied for the substitution of nitrogen blow-down micro-concentration in dioxin/PCB sample preparation. Automation was achieved through this apparatus and resulted in significant improvements in sample preparation productivity, along with excellent reproducibility and recovery rate of dioxin/PCB. Mean recoveries of dioxin congeners were 90-106%, respectively.     

Determination of carbon, hydrogen and nitrogen in inorganic compounds by means of an automatic organic elemental microanalyzer

The Hewlett Packard Model 185 CHN Analyzer, which is based on an automated modified Dumas combustion technique and was designed for the analysis of organic materials, has been applied to the determination of carbon, nitrogen and hydrogen in inorganic compounds.With minor modifications to the procedure routinely used for the organic analysis, the instrument has proved to be able to broaden its original application field giving in general good performances in the inorganic domain.A particular emphasis has been put in testing nitrates, carbonates, ammonium salts and different kinds of carbon. Till now it appears that the only materials really difficult to analyze are the refractory nitrides, carbides and carbonitrides.Finally some considerations have been made in respect of the determination of the percent weight composition of mixtures through their carbon, nitrogen and hydrogen content.     

废弃线路板化学分析采样、制样及检测方法

介绍废弃线路板中有回收价值元素和有害物质分析的采样、制样及检测技术。样品经过分类采样、剪切破碎和高温灰化制样,采用样品全分析或副批混合样分析。通过提高称样量、多次测定求平均值的办法,火试金富集-重量法测定贵金属金、银。湿法王水溶解样品,碘量法测定主体元素铜。电感耦合等离子体发射光谱(ICP-AES)法测定其它杂质元素,被测元素质量浓度在0~10μg/mL范围内与光谱强度呈良好线性关系,相关系数均大于0.9998。测定结果的相对标准偏差小于10%(n=5),加标回收率为97.0%~102.5%。该方法简单、快速,有效地解决了线路板样品不均匀而难采样,以及硬度、韧性强制样难,金属易包裹难分解的技术瓶颈,测定结果准确,具有代表性。该方法适用于废弃线路板化学成分分析,其它废弃电子产品检测可参考此方法。     

Chemical forms of radioactive iodine in seawater and its effects upon marine organisms

Chemical forms of radioactive iodine and its effects upon marine organisms were studied by the tracer experiments. Seaweeds or fish were held in the aquarium in which the 125I tracer in either iodide or iodate form was inoculated. Iodide form of 125I was taken by Dorome (Chasmichthys gulosus) with the concentration factor of about 10 and excreted with the biological half-life of 15 days, while iodate form of 125I was not taken up appreciably and the concentration factor did not greatly exceed unity. Uptake and loss of 125I were studied as well for 3 species of seaweeds, Hijiki(Hizikia fusiforme), Nejimoku (Sargassum sagamianum) and Tsunomata (Chondrus ocellatus). Iodate form of 125I was accumulated less than iodide form by these seaweeds but the concentration factor of iodate by these seaweeds was very high compared to those by fish.     

A study of the determination of low levels of carbon, hydrogen, and nitrogen using an elemental analyzer

A study was made of the results obtained with an automatic CHN analyzer.     

Effect of ecosystem retrogression on stable nitrogen and carbon isotopes of plants,soils and consumer organisms in boreal forest islands

In the prolonged absence of catastrophic disturbance, ecosystem retrogression occurs, and this involves increased nutrient limitation, and reduced aboveground and belowground ecosystem processes rates. Little is known about how the nitrogen and carbon stable isotope ratios (δ¹⁵N and δ¹³C) of plants, soils and consumer organisms respond to retrogression in boreal forests. We investigated a 5000 year chronosequence of forested islands in the boreal zone of northern Sweden, for which the time since lightning‐induced wildfire increases with decreasing island size, leading to ecosystem retrogression. For this system, tissue δ¹⁵N of three abundant plant species (Betula pubescens, Vaccinium myrtillus and Pleurozium schreberi) and humus all increased as retrogression proceeded. This is probably due to enhanced ecosystem inputs of N by biological fixation, and greater dependency of the plants on organic N during retrogression. The δ¹³C of B. pubescens and plant‐derived humus also increased during retrogression, probably through nutrient limitation increasing plant physiological stress. Unlike the plants, δ¹⁵N of invertebrates (lycosid spiders and ants) did not increase during retrogression, probably because of their partial dependence on aquatic‐derived prey that had a variable δ¹⁵N signature. The δ¹³C of the invertebrates increased as retrogression proceeded and converged towards that of an aquatic prey source (chironomid flies), suggesting increased dependence on aquatic‐derived prey during retrogression. These results show that measurement of δ¹⁵N and δ¹³C of plants, soils, and consumers across the same environmental gradient can provide insights into environmental factors that drive both the aboveground and belowground subsystems, as well as the linkages between them. Copyright © 2009 John Wiley & Sons, Ltd.