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.     

Characterisation and quantification of organic phosphorus and organic nitrogen components in aquatic systems: a review

This review provides a critical assessment of knowledge regarding the determination of organic phosphorus (OP) and organic nitrogen (ON) in aquatic systems, with an emphasis on biogeochemical considerations and analytical challenges. A general background on organic phosphorus and organic nitrogen precedes a discussion of sample collection, extraction, treatment/conditioning and preconcentration of organic phosphorus/nitrogen from sediments, including suspended particulate matter, and waters, including sediment porewaters. This is followed by sections on the determination of organic phosphorus/nitrogen components. Key techniques covered for organic phosphorus components are molecular spectrometry, atomic spectrometry and enzymatic methods. For nitrogen the focus is on the measurement of total organic nitrogen concentrations by carbon hydrogen nitrogen analysis and high temperature combustion, and organic nitrogen components by gas chromatography, high-performance liquid chromatography, gel electrophoresis, mass spectrometry, nuclear magnetic resonance spectrometry, X-ray techniques and enzymatic methods. Finally future trends and needs are discussed and recommendations made.     

吉林省主要旱田土壤有机碳·氮和碳氮比的空间分布特征

土壤中的有机碳和全氮是评定土壤肥力的关键因素,快速准确测定土壤中的有机碳和全氮对于评价土壤肥力、研究碳氮与植物生长代谢关系、进一步提高作物产量与质量有重要的意义. 针对目前土壤中有机碳和全氮测量时间长、批量测试效率低的问题,采用红外吸收-热导法同时测定土壤中有机碳和全氮的含量,进一步提高了分析效率. 讨论了样品量、燃烧催化剂、无机碳干扰对有机碳和全氮测定的影响. 结果表明,试验最优条件为样品质量0.12 g,0.04 g氧化铜为燃烧催化剂,4 mol/L盐酸消除无机碳干扰. 以土壤标准样品建立仪器标准曲线,碳和氮的定量限分别为0.008 2%、0.043%. 方法应用于实际土壤样品测量,方法精密度小于3.0%,测量结果与标准方法对比,测量值在标准允许误差范围内.

     

Determination of nitrogen and carbon in refractory nitrides and carbonitrides by means of Dumas gas chromatography

The applicability of an automated Dumas-GC method for the determination of nitrogen and carbon in refractory materials was investigated. Analyses were carried out to determine nitrogen and carbon in TiN, ZrN and Ti(C,N) using CuO, V₂O₅ and Pb₃O₄ as oxidizing additives. The reproducibility of the analyses obtained with V₂O₅ was better than ± 1 rel% for major constituents. An estimation of the accuracy of the Dumas-GC method shows that this rapid and low-cost method can compete with other methods, at least for the refractory nitrides and carbonitrides of the transition metals.     

Detection of banned meat and bone meal in feedstuffs by near-infrared microscopic analysis of the dense sediment fraction

In this paper we present an alternative method for detection of meat and bone meal (MBM) in feedstuffs by near-infrared microscopic (NIRM) analysis of the particles in the sediment fraction (dense fraction (d >1.62) from dichloroethylene) of compound feeds. To apply this method the particles of the sediment fraction are spread on a sample holder and presented to the NIR microscope. By using the pointer of the microscope the infrared beam is focussed on each particle and the NIR spectrum (1112–2500 nm) is collected. This method can be used to detect the presence of MBM at concentrations as low as 0.05% mass fraction. When results from the NIRM method were compared with the classical microscopic method, a coefficient of determination (R²) of 0.87 was obtained. The results of this study demonstrated that this method could be proposed as a complementary tool for the detection of banned MBM in feedstuffs by reinforcement of the monitoring of feeds.     

Determination of trace metals by ICP-OES in plant materials after preconcentration of 1,10-phenanthroline complexes on activated carbon

In this work, 1,10-phenanthroline was used as a complexing agent for the separation and preconcentration of Cd(II), Co(II), Ni(II), Cu(II) and Pb(II) on activated carbon. The metals were adsorbed on activated carbon by two methods: static (1) and dynamic (2). The optimal condition for separation and quantitative preconcentration of metal ions with activated carbon for the proposed methods was for (1) in the static methods in the pH range 7-9. The desorption was found quantitative with 8 mol dm⁻³ HNO₃ for Cd(II) (92.6%), Co(II) (95.6%), Pb(II) (91.0%), and with 3 mol dm⁻³ HNO₃ for Cd(II) (95.4%), Pb(II) (100.2%). The preconcentration factor was 100 with R.S.D. values between 1.0 and 2.9%. For (2), the dynamic method (SPE), the pH range for the quantitative sorption was 7-9. The desorption was found quantitative with 8 mol dm⁻³ HNO₃ for Cd(II) (100.6%), Pb(II) (94.4%), and reasonably high recovery for Co(II) (83%), Cu(II) (88%). The optimum flow rate of metal ions solution for quantitative sorption of metals with 1,10-phenanthroline was 1-2 cm³ min⁻¹ whereas for desorption it was 1 cm³ min⁻¹. The preconcentration factor was 50 for all the ions of the metals with R.S.D. values between 2.9 and 9.8%.The samples of the activated carbon with the adsorbed trace metals can be determined by ICP-OES after mineralization by means of a high-pressure microwave mineralizer. The proposed method provides recovery for Cd (100.8%), Co (97.2%), Cu (94.6%), Ni (99.6%) and Pb (100.0%) with R.S.D. values between 1.2 and 3.2%.The preconcentration procedure showed a linear calibration curve within the concentration range 0.1-1.5 μg cm⁻³. The limits of detection values (defined as “blank + 3s” where s is standard deviation of the blank determination) are 5.8, 70.8, 6.7, 24.6, and 10.8 μg dm⁻³ for Cd(II), Pb(II), Co(II), Ni(II) and Cu(II), respectively, and corresponding limit of quantification (blank + 10s) values were 13.5, 151.3, 20.0, 58.9 and 33.2 μg dm⁻³, respectively.As a result, these simple methods were applied for the determination of the above-mentioned metals in reference materials and in samples of plant material.     

Western blot detection of brain material in heated meat products using myelin basic protein and neuron-specific enolase as biomarkers

An assay based on Western blotting and detection of central nervous system (CNS)-specific antigens was developed to detect brain tissue in processed (heated) meat products. Bands of antigen-bound primary antibodies were visualised through secondary anti-antibodies labelled with peroxidase, which generated chemiluminescence documented by a photographic film. Ponceau-S staining before antibody incubation and molecular mass information on detected antigens after immunoreactions added information supporting correct identification of brain tissue in the meat products. In this approach B50/growth-associated protein (B50), glial fibrillary acidic protein (GFAP), myelin basic protein (MBP), neurofilament (NF), neuron-specific enolase (NSE) and synaptophysin (Syn) proteins were detected in raw luncheon meat and a liver product enriched with brain tissue at a level of 5% (m/m). Only MBP and NSE were considered suitable biomarkers for detection of 1% (m/m) brain tissue in meat products pasteurised at 70 °C or sterilised at 115 °C. The use of an anti-monkey MBP instead of anti-human MBP enabled speciation of the CNS material whether from bovine and ovine brains or from porcine brain tissue. This immunoblot assay potentiates the analysis of approximately 70 samples within 8 h, including sample preparation and the simultaneous probing of NSE and MBP target antigens.     

Determination of trace elements in inorganic and organic materials by x-ray fluorescence spectroscopy

A new, almost universally applicable method for the trace analysis of inorganic and organic materials is described. The trace element (or elements) together with a suitable coprecipitating element is isolated from interfering elements by precipitation with a suitable organic or inorganic precipitant. The precipitate is then filtered on a paper disk and the collected trace element (or elements) is determined by X-ray analysis.     

Standardization of BSE rapid test performances and experiences gathered during the implementation of large-scale testing

The accumulation of pathological prion protein is used as a diagnostic marker for transmissible spongiform encephalopathies. According to European Union (EU) regulations cattle older than 30 months of age (Germany, France, Italy, and Spain by national law >24 months) and slaughtered for human consumption must be tested by using rapid tests for bovine spongiform encephalopathy (BSE). Likewise fallen stock and clinically affected animals must be tested. This article gives a short overview of the incidence of BSE in Europe. The diagnostic hierarchy, i.e., the officially approved methodology for the confirmation of suspect rapid test cases, and the organization of the numerous laboratories involved in this large-scale testing for BSE are described. Special emphasis is given to necessary quality control measures currently in place for BSE rapid testing laboratories and to measures intended to assure a consistent performance of the commercially available rapid test kits.Presented at BERM-9—Ninth International Symposium on Biological and Environmental Reference Materials, 15–19 June 2003, Berlin, Germany.     

Determination of trace elements in bone by two-jet plasma atomic emission spectrometry

This paper describes an analytical method for trace element determination in bone tissues. The study of the influence of the bone matrix showed that the addition of 25% ground bone to graphite powder with introduced impurities did not affect the analytical signal of elements in the spectral excitation in a two-jet plasma. On basis of these investigations a method for direct multielement analysis of bone tissues was suggested. The sample preparation procedure consisted in mixing powdered bone (particle size 30 μm or less) with a spectroscopic buffer (graphite powder plus NaCl) in ratio 1:3 or to a greater extent depending on the analyte concentration. Reference samples based on graphite powder were used for construction of calibration curves. The NaCl concentration in analyzed and calibration samples was 15 wt%. The effect of particle size was revealed from the determination of Ba, Sr, and Mg. To eliminate this effect, treatment of the samples with nitric acid was proposed. The validation of the technique was confirmed by comparison of the analysis results of a bone sample with those obtained by inductively coupled plasma atomic emission spectrometry after wet acid digestion. The limits of detection estimated for 20 elements were the following (μg g^-1): 0.1 (Ag), 1.0 (Al), 1.0 (Ba), 0.1 (Be), 1.2 (Bi), 0.4 (Cd), 1.0 (Co), 0.2 (Cu), 0.6 (Cr), 1.9 (In), 2 (Fe), 0.3 (Ga), 0.4 (Mn), 0.4 (Mo), 0.7 (Ni), 1.0 (Pb), 0.7 (Sn), 0.8 (Tl), 5 (Sr), 1.0 (Zn).     

A novel single-run dual temperature combustion (SRDTC) method for the determination of organic, in-organic and total carbon in soil samples

The quantification of organic (OC) and inorganic carbon (IC) in soils provides an essential tool for understanding biogeochemical processes. Examples of its potential application are the assessment of the humification degree of soil organic matter, the calculation of carbon fluxes and budgets in terrestrial systems on a regional and global scale and the investigation of the carbon storage potential of soils. The verification of changes in carbon stocks requires an extensive number of samples as well as precise and reliable analyses.Due to the wide variation in the concentrations of the two forms of carbon in solid samples, the exact distinction is very difficult. We present the advantages of a single-run dual temperature combustion method (SRDTC) at 515 °C for OC and 925 °C for IC, which allows the determination of OC, IC and total carbon (TC) within one single analytical run. The three parameters are analyzed in less than 30 min. Additionally, the method is characterized by a significantly reduced variability and low operator bias, as there is no need of chemical sample pre-treatment. It is applicable to a broad range of varying OC and IC contents, which is demonstrated by the use of numerous synthetic soil mixtures that have been analyzed. Furthermore, SRDTC indicates the presence of thermally instable carbonates, like magnesite, in the sample. Use of silver boats as a catalytic agent results in an improved distinction between OC and IC in this case. To examine the accuracy and reliability of the SRDTC method, it was compared to other techniques frequently used for carbon determination in soil samples: total combustion by elemental analysis to determine TC and acidification of the sample prior to combustion to determine OC. We will show that the rugged SRDTC method offers a substantial progress for both the reliable and rapid OC and IC determination in soil samples where elemental carbon is negligible.     

还原性物质对土壤中有机碳测定的影响研究

土壤中还原性物质会使得有机碳/质测定值偏高,尤其是矿区还原性土壤检测时,经常会因为还原性物质过高而影响土壤有机碳的测定,本文通过室内添加外源的方式来考察二价铁、二价锰、氯离子、亚硝酸根离子、亚硫酸根离子对有机碳/质测定的干扰。并且通过预烘烤的方式,考察烘烤温度,暴露时间对干扰去除效果的影响。此外研究中还考察了硫酸银的添加量对去除氯离子的干扰的影响。研究表明在50℃下,预烘24h,可以有效去除20%的二价铁、二价锰及亚硝酸根离子、亚硫酸根离子的影响;添加0.10g硫酸银可以有效去除20%的含量氯离子对有机质测定的干扰。将五种离子综合考虑,在50℃烘箱烘干24h后,加入0.10g硫酸银去除氯离子干扰,其检测值与原标准值一致,方法精密度（RSD）在2.94%~7.67%之间,方法准确度（RE）在0.69%～-3.19%之间,结果准确可靠。     

Preparation of nitrogen doped clews-like carbon materials and their application as the electrode in supercapacitor

Nitrogen doped clews-like hierarchical porous carbon materials, fabricated by means of a one-pot hydrothermal reaction and post treatment, exhibit superior supercapacitive performances.     

CE determination of quinolones in the presence of bovine serum albumin

This article describes the influence of bovine serum albumin (BSA) as an additive on the capillary electrophoresis–potential gradient determination of five quinolones, enoxacin, norfloxacin, ofloxacin, fleroxacin, and pazufloxacin. With 10 mg/L of BSA present in the buffer of 30 mM Tris and 3 mM phosphoric acid at pH 9, the detection limits of the five quinolones were in the range of 0.24–0.68 mg/L, i. e. 5.8–16.5‐fold lower than those obtained with the buffer devoid of BSA, and the analysis time was shortened. We suggest that the inner wall‐adsorbed BSA suppresses the adsorption of quinolones and simultaneously enhances the electroosmotic flow rate. Our experiments indicated that adopting the potential gradient detection technique could eliminate the interference of the UV‐active proteins on the detection of quinolones that would occur with conventional optical detection, and therefore offer high detection sensitivity. As a demonstration, the method was applied to the determination of QNs in fortified chicken muscle sample with satisfactory results.     

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.     

高频燃烧红外吸收法测定钢铁中超低碳硫

通过对气体净化,坩埚处理,试样处理及称样量选择,助熔剂种类及用量等因素的优化,建立了钢铁中超低含量碳硫的测定方法,实验结果表明：比较器水平设为1%,分析时间设为45 s,坩埚在1350 ℃下预烧45 min,选择钨作为助熔剂且使用前在140 ℃烘3 h,助熔剂用量为1.5 g,称样量为0.5 g时,是分析钢铁中碳硫含量在0.01～0.001 %的最佳条件,方法重复性好,准确度高,在实际操作中切实可行。     

重铬酸钾容量法测定地质样品中的有机碳

目前,地质样品中有机碳的测定方法有干烧法（高温电炉灼烧）和湿烧法（重铬酸钾氧化）两大类。另外还有ICP-AES法、微波消解法、过硫酸钾法、电导法、石墨电热消解法、比色法等,然而这些有机碳测定方法仍然存在许多不尽如人意的地方。干烧法要求实验条件苛刻,操作繁琐,不易掌握,受碳酸盐的干扰。湿烧法虽然操作比较简单,但方法受样品中还原性物质的干扰,如氯根、亚铁等,上述方法都有待完善和优化改进。如：探索因不同样品基体差异而产生的干扰元素消除方法;寻找更合适的指示剂;本文采 用重铬酸钾-容量法测定地质样品中的有机碳,在220±10℃恒温电热板上,用0.4 mol/mL重铬酸钾溶解样品。通过优化熔矿温度、熔矿时间、熔剂浓度的优化选择,进行了氯离子的干扰试验。样品中含氯化物低的样品通过加入0.1 g硫酸银消除,样品中含氯化物高的样品通过高温灼烧减量消除。氧化指示剂选用邻菲啰啉或苯二氨基苯甲酸。本方法适用于土壤、水系沉积物、岩石等地质调查样品中有机碳的测定,方法相对标准偏差（RSD）在0.80%～4.41%之间,准确度（RE）在-3.15%～+1.15%之间。通过标准物质验证,方法技术指标满足地质行业规范DZ/T0130.4-2006中有机碳的分析要求,建立了一种简单、快捷、经济、准确的测定地质样品中有机碳的测定方法,满足地球化学调查批量样品生产的需要。     

Simultaneous measurement of the solubility of nitrogen and carbon dioxide in polystyrene and of the associated polymer swelling

New experimental results for the solubility of nitrogen and carbon dioxide in polystyrene are reported, accompanied by data on the change in volume of the polymer caused by the sorption process. The two phenomena were measured simultaneously with a combined technique, in which the quantity of penetrating fluid introduced into the system was evaluated by pressure‐decay measurements in a calibrated volume, whereas a vibrating‐wire force sensor was employed for weighing the polymer sample during sorption inside of the high‐pressure equilibrium cell. The use of the two techniques was necessary because the effects of swelling and solubility could not be decoupled in a single gravimetric or pressure‐decay measurement. The sorption of nitrogen in polystyrene was studied along three isotherms from 313 to 353 K at pressures up to 70 MPa. The sorption of carbon dioxide was measured along four isotherms from 338 to 402 K up to 45 MPa. The results are compared with values from the literature when possible, although our data extend significantly the pressure ranges of the latter. The uncertainties affecting our measurements with nitrogen are 1 mg of N₂/g of polystyrene in solubility and 0.1% of the volume of the polymer. For carbon dioxide, the uncertainties are 5 mg of N₂/g of polystyrene and 0.5% respectively, carbon dioxide being about 1 order of magnitude more soluble than nitrogen. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2063–2070, 2001     

Stability against aggregation of bovine casein micelles in the presence of acidic and alkaline gelatin

The effect of the presence of colloidal dispersed and molecular dispersed acidic (type A) and alkaline (type B) gelatins with similar molecular weight and size but different isoelectric points (7.9 and 4.9) on the stability against aggregation of bovine casein micelles was investigated by turbidimetric titration and laser techniques, over a wide range of biopolymers concentrations, gelatin/casein ratio in the initial mixture (0.03–20), pH (4.9–6.7) and ionic strength (10⁻³(milk salts)–1.0 NaCl), using glucono-δ-lactone (GL) as acidifier. Aggregates of acid gelatin A interact with the oppositely charged micellar casein at an ionic strength of around 10⁻³(milk salts) and pH 6.7 resulting in the formation of an electroneutral complex by ionic bonds between the carboxyl groups of casein and the amino groups of the gelatin molecules. The complexes obtained are polynuclear, the aggregation of which is not as sensitive to pH as that of free casein micelles. Aggregation of such complexes is the result of bridging flocculation. The “molar” ratio gelatin aggregates/casein micelles in the mixed aggregates is 4/1. The complexes are formed and stabilised via electrostatic interaction rather than through hydrogen bonds or hydrophobic interaction. In the presence of an excess of gelatin molecules in the initial mixture a charged gelatin–casein complex forms and some dissociation of casein micelles occurs and, as a consequence, soluble complexes are obtained. During the addition of alkaline gelatin B aggregates to the micellar casein solution and subsequent acidification of the mixture by GL, no effect of the presence of gelatin B on the stability of micellar casein was observed. Received: 28 March 2000 Accepted: 5 October 2000