无信息变量消除法变量筛选优化烟草中总氮和总糖的定量模型

应用近红外光谱技术对烟草常规化学成分中总氮和总糖进行了测定。无信息变量消除(UVE)剔除光谱矩阵中没有有效信息的数据点,并用偏最小二乘方法(PLS)建立总氮和总糖的定量分析模型,外部检验对模型效果进行了评价。总氮定量模型校正集的决定系数R2为93.35%,标准偏差SEC为0.10;外部检验集的决定系数R2为94.09%,标准偏差SEP为0.11,相对标准偏差RSD为6.12%;总糖的定量模型校正集的决定系数R2为98.20%,标准偏差SEC为0.95;外部检验集样品的决定系数R2为98.01%,标准偏差SEP为0.78,相对标准偏差RSD为2.93%。结果表明:采用UVE建立的总氮与总糖的模型优于用全谱建立的模型,UVE提高了PLS模型的预测能力。     

基于UV-Vis-SWIR漫反射光谱的土壤多属性同时快速测定

采用紫外-可见-短波近红外漫反射光谱(UV-Vis-SWIRDRS)结合化学计量学对土壤中有机质(SOM)、总氮(TN)、碱解氮(AN)、速效钾(AK)、缓效钾(SAK)、有效磷(AP)及pH共7种属性建立了快速同时低成本的定量分析方法。土壤样本共81个,其中50个分为校正集,另16个为验证集,剩余15个为测试集。对每种土壤属性,考察了多种光谱预处理,变量选择以及它们的组合方法处理土壤光谱后建立的PLSR模型预测效果,选择出了最佳的光谱数据处理方法及其对应的最佳PLSR预测模型,并以独立的测试集样本对最佳模型预测性能进行客观评价。对于有机质和总氮,测试集决定系数(R2t)分别为0.94和0.97,模型可用于准确定量分析;对碱解氮和pH,R~2t分别为0.76和0.66,模型定量预测结果良好;对于有效磷,速效钾及缓效钾,R~2t小于0.6,但模型的预测效果和以往报道中的预测效果相差不大。研究表明,利用UV-Vis-SWIR DRS对土壤多属性进行快速同时低成本定量分析是可行的,有望用于土壤信息检测。     

凯氏定氮法测定土壤中水解性氮样品处理条件的三维响应曲面优化

利用三维响应曲面法优化LY/T 1228—2015测定土壤中水解性氮含量的实验条件。为了缩短反应时间,提高检测效率,使用三维响应曲面法对碱解蒸馏法的蒸馏条件进行优化,并据此建立凯氏定氮仪直接测定土壤中水解性氮含量的方法,优化后的实验条件:NaOH溶液的浓度为2.7 mol/L,蒸汽比率为100%,蒸馏时间为5 min。测定结果的相对标准偏差为1.76%～2.64%(n=5),优于碱解扩散法(2.66%～3.61%)。对3个国家一级标准物质进行测定,测定结果与推荐值相符。与标准方法相比,该方法成本低,可操作性强,特别适用于土壤环境质量评价、地区土壤抽样调查等大批量土壤样品分析。     

傅立叶变换近红外光谱法测定腐乳中总酸、蛋白质和水分

应用傅立叶变换近红外光谱技术,建立了腐乳中总酸、蛋白质和水分的分析模型。测定32份腐乳的近红外光谱数据,得到原始光谱信息,通过光谱预处理方法消除原始光谱噪声,最后采用偏最小二乘法建立回归方程。最终得到总酸、蛋白质和水分近红外光谱分析模型的决定系数(R2)依次为99.37%、99.70%、99.73%,交叉验证均方根差(RMSECV)依次为0.00871、0.11、0.0714。用该模型对11个未知腐乳样品进行外部验证,其总酸、蛋白质和水分外部验证的决定系数(R2)依次为98.74%、99.38%、99.48%,预测标准偏差(RMSEP)依次为0.00862、0.113、0.0683。内部交叉验证和外部验证均证明,近红外定量分析有较高的准确度,能满足腐乳生产中总酸、蛋白质和水分的检测精度要求。     

自动蒸馏装置-滴定法测定土壤中水解性氮

建立自动蒸馏装置–滴定法测定土壤水解性氮的方法。对样品处理程序进行了优化,加入25 mL硼酸,60 mL蒸馏水,10 mL 10 mol/L的NaOH,蒸馏时间为380 s,待测液用0.01006 mol/L的HCl溶液进行滴定,测定土壤中水解性氮。方法的检出限为2.34 mg/kg,分别对标准物质GBW 07412a、GBW 07413a、GBW 0715a和GBW 07460进行测定,测定结果的相对标准偏差为1.90-3.75%(n=6),用该方法与碱解扩散法同时对45个不同类型土壤样品的水解性氮进行测定,测定结果无明显差异。该方法适合于土壤水解性氮的检测。     

近红外光谱法快速测定推进剂中N-甲基对硝基苯胺

采用近红外光谱法快速测定固体推进剂中N-甲基对硝基苯胺(MNA)的含量。评价了滤波平滑、一阶导数、二阶导数、多元散射校正(MSC)和标准正态变量校正(SNV)这5种不同光谱预处理方法的优化效果，基于建模参数优化结果建立了MNA定量模型，并对模型进行了准确性和重复性验证。结果表明，光谱最佳预处理方式是SNV，模型最佳主因子数为7，模型校正决定系数(R_C²)和验证决定系数(R_P²)分别为0.998 6和0.987 2，交互验证均方根误差(RMSECV)和预测均方根误差(RMSEP)分别为0.012 0和0.009 8，重复性极差和绝对误差均低于0.2%。近红外光谱法与液相色谱法测定结果相比相对偏差在6%以内，经t检验，两种方法测定结果无显著性差异。近红外光谱法快速、准确，可用于推进剂老化进程监控。     

SmartChem140全自动化学分析仪测定土壤全氮全磷的研究

本文以胶州湾湿地土壤为样品,建立了基于SmartChem140全自动化学分析仪,同时测定土壤全氮和全磷的方法。利用全自动化学分析仪可以同时快速、准确测定土壤中的全氮和全磷,全氮和全磷分别在0~6.0mg·L-1和0~5.0mg·L-1范围内线性良好,相关系数(R2)分别为0.9994、0.9995;测定结果与凯氏定氮法、磷钼蓝比色法对比无显著差异,相对误差均小于4%,相对标准偏差分别为1.39%和1.07%,样品的加标回收率分别在97.68%~102.12%和97.35%~101.88%之间。研究结果表明,该方法准确度高、稳定性好,回收率高,操作简便,测定结果能满足对土壤全氮、全磷的监测要求。     

全自动凯氏定氮仪测定干旱区土壤中全氮含量

对采用全自动凯氏定氮仪测定干旱区土壤全氮量的方法以及实验中影响因素进行了研究,对消解时间和硫酸用量进行了选择性实验,结果表明,土壤中有机物在30min时消解完全,硫酸用量在10~15mL时为最佳,干旱区土壤中氮一般含量为(0.260±0.003)%(P=0.95)。方法的相对标准偏差(RSD)≤1%,用来测定硫酸铵标准物质,其检测结果与标准值基本吻合,检测的准确度和精密度都符合国家标准的要求。     

用人工神经网络-近红外光谱法测定冬虫夏草中的甘露醇

提出了用近红外漫反射光谱技术快速分析发酵冬虫夏草菌粉中甘露醇含量的新方法。采用比色法测定样品中的甘露醇，其含量范围为8．082％-14．548％。在7501．7-6097．8cm^-1与5453．7-4246．5cm^-1波段，分别采用PCR、PLSR和BP神经网络方法建立了样品近红外光谱的一阶微分光谱与其甘露醇含量之间的相关模型。BP神经网络模型的内部交叉验证误差均方根为0．475，预测误差均方根为0．608，均优于PCR和PLSR的处理结果。这表明，BP神经网络法对非线性检测对象具有较好的建模效果，可用于中药近红外光谱分析的非线性校正。     

近红外光谱快速分析青贮饲料pH值和发酵产物

采用近红外光谱技术,结合偏最小二乘回归法,研究了142个不同种类的秸秆青贮饲料样品的pH值和发酵产物(乳酸、乙酸、丙酸、丁酸和氨态氮),建立了干燥粉碎和新鲜样品的近红外漫反射光谱定量分析模型以及浸提液样品的近红外透射光谱定量分析模型。研究发现,pH值的近红外漫反射光谱和透射光谱的分析效果均较好,校正模型决定系数R2和验证集样品预测值与化学值的相关关系决定系数r2都大于0.80,并且干燥粉碎、新鲜和浸提液样品的RPD值分别为3.44、2.50和2.27;3种状态样品的乳酸、乙酸、丁酸和氨态氮的定量分析模型精度需进一步提高;R2在0.64~0.85之间;RPD值在1.38~1.93之间;丙酸含量的测定结果较差。方差分析显示,3种状态样品的测定结果之间均无显著性差异(P>0.05)。     

Rapid coulometric method for the Kjeldahl determination of nitrogen

A rapid coulometric method for the Kjeldahl determination of nitrogen is described. The samples are digested by means of the Tecator AB digestion system which permits forty samples to be digested at the same time. The digestion products are diluted to 75 ml and 1 ml is coulometrically titrated in 1-2 min: 20-30 determinations can be performed per hour. For substances containing nitrogen in the per cent range the relative standard deviations for eight different substances were 0.1-1%.     

Automation in organic analysis III. Micro- and ultramicrodetermination of nitrogen

A simple, rapid and accurate method of nitrogen determination in organic substances containing in addition to C, H, N also O, S, F, Cl, I, Se and Hg was elaborated. The method is based on pyrolytic decomposition of the substance in a flow of hydrogen at 1000–1100 °C and passing the hydropyrolytic products through layers of managenese-II oxide (absorbing sulfur and selenium) and nickel at 950 °C. On nickel elementary nitrogen is liberated from the nitrogenous hydropyrolytic products and the pyrolytic methane also decomposes on it. After elimination of interfering substances (carbon monoxide, water, hydrogen halides) the content of nitrogen is determined with a catharometer.The whole determination, including the sample weighing, requires 12 min and the precision is ±0.30% absolute.     

Beiträge zur Stickstoffbestimmung in organischen Substanzen durch katalytische Hydrogenolyse in der Gasphase. I

Zusammenfassung Die Anwendbarkeit der Methode nach ter Meulen zur Bestimmung des Stickstoffes in organischen Verbindungen wurde mit Rücksicht auf die Stickstoffbindung überprüft. Eine Reihe von Testsubstanzen aus verschiedenen Körperklassen wurde auf drei Nickelkatalysatoren (Nickelasbest, Nickel + Thoriumoxid + Asbest, granuliertes Nickel + Magnesiumoxid) hydriert. Substanzen, welche den Stickstoff in Form von Amino-, Azo-, Azoxy-, Isonitroso-, Mononitro-, N-N oder heterocyklischem Stickstoff enthielten, lieferten richtige Stickstoffwerte. Substanzen mit zwei oder drei Nitrogruppen oder einer Nitrosogruppe im Molekül gaben wesentlich zu niedrige Stickstoff werte im Vergleich zur Theorie. Versuche, die Hydrierungsbedingungen durch Abänderung des Standardverfahrens besser zu gestalten, schlugen fehl.

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Contributions to nitrogen assay in organic substances by catalytic hydrogenolysis in the gas phase. I

Summary The applicability of the method for determination of nitrogen in organic compounds according to ter Meulen was checked with regard to nitrogen binding. A series of test substances from various organic groups was hydrogenated on three nickel catalysts (nickel asbestos, nickel + thorium oxide + asbestos, granulated nickel + magnesium oxide). Substances which contained nitrogen in the form of amino, azo, azoxy, isonitroso, mononitro, N-N or heterocyclic nitrogen provided correct nitrogen values. Substances with two or three nitro groups or a nitroso group in the molecule gave nitrogen values which were far too low compared to theory. Attempts to improve the hydrogenation conditions by altering the standard procedure failed.

     

A calculation method to estimate the concentration and elemental composition of organic substances in natural Waters

The possibility of calculating the elemental composition and concentrations of organic substances in natural water based on the results of determining organic carbon and nitrogen and chemical oxygen demand is substantiated both theoretically and experimentally. Three types of substances differing in the electrochemical valence of carbon were among organic substances. The elemental composition of a number of water objects was analyzed. It was found that the concentrations of organic carbon, oxygen, hydrogen, and nitrogen are close to 50, 40, 4–5, and 2–5%, respectively.     

Analysis of light element compounds by means of proton elastic scattering

A non-destructive method sensitive above all to atoms of light elements is proposed for the analysis of compounds. Preliminary results to the analysis of organic substances and boron compounds are presented. The target was cooled to the temperature of liquid nitrogen. A proton beam with an energy of 3.2 MeV was obtained with a Van de Graaff accelerator.     

Application of activated carbon in the characterization of nitrogen compounds and phthalates in a landfill leachate

The goal of this work was the development of a methodology based on solid phase extraction (SPE) to characterize nitrogen compounds and phthalates from landfill leachate samples. Activated carbon (AC) was used to extract all the organic compounds from the samples. The samples were collected in Porto Alegre-South Brazil. As the AC used had small particle size, it was impossible to use it in the form of packed cartridges; hence, it had to be applied in a batch mode. The desorption of the organic compounds from the AC was made by sonication with dichloromethane. The extract was analyzed by gas chromatography with mass spectrometric detection (GC-MSD). Some aspects of the validation of the methodology were also established. Several nitrogen compounds and phthalates were identified in the samples, proving the efficiency of this method with regard to the selectiveness for these substances.     

Sequential injection system for on-line analysis of total nitrogen with UV-mineralization

An automatic method for the determination of total nitrogen in wastewater by sequential injection analysis and mineralization with UV radiation has been developed. The method is based on the mineralization of the samples with sodium persulphate in basic medium under UV radiation. Small volumes of sample and reagents are firstly aspirated into a single channel and then propelled by flow reversal to the UV reactor and then to the detector. The organic and inorganic nitrogen compounds are oxidized to nitrate that is then measured at 226 nm. The sequential injection procedure has been optimized and the factors affecting the efficiency of the oxidation have been studied with a number of test substances with different chemical structures and properties. Solutions in the concentration range 1-56 g l⁻¹ of nitrogen can be analyzed with the described procedure. The sample rate is of 30-40 samples h⁻¹. The LOD is 0.6 mg l⁻¹ N and the reproducibility is 1.8% (28 mg l⁻¹ N). Organic carbon in the form of glucose was added to a number of test solutions to study the potential interference of organic matter.The method was compared with the Kjeldahl digestion method by analyzing 15 wastewater samples with both methods. The nitrate and nitrite content of the non-oxidized samples were subtracted from the corresponding nitrogen content determined after photo-oxidation and the value compared with the Kjeldahl nitrogen content.     

Determination of the Total Nitrogen Content of Organic Substances Through the Ammonia Formed in Oxidation by Persulfate

Abstract

A new concept for the analytical application of persulfate oxidation in alkaline media is presented: The persulfate oxidation of organic compounds has been utilized to determine their nitrogen content. The ammonia formed in the oxidation coupled distillation was measured acidimetrically with an accuracy of ± 0.5 % (rel.). The applicability of the method proposed is shown in the determination of the organically bound nitrogen content of numerous model substances as well as industrial and natural matrices: vinasse, aluminate liquor, white- and soy-bean samples, eggprotein.     

高效液相色谱法同时测定尿液中4种非蛋白氮的含量

建立了高效液相色谱(HPLC)同时测定尿液中4种常见的非蛋白氮物质--肌酸(Cr)、尿肌酐(Cn)、尿酸(Ua)及假尿嘧啶核苷(Pu)含量的方法。尿液首先经丙酮沉淀法除去大分子化合物,然后冷冻干燥,复溶后直接进行HPLC分析。色谱分离选用Waters RP18 Column (150 mm×4.60 mm,3.5 μm),以10.0 mmol/L磷酸缓冲溶液 (pH 4.78)和乙腈为流动相进行梯度洗脱,流速为0.8 mL/min,于220 nm波长下检测,可在7 min内完成4种非蛋白氮的快速分离分析。结果表明Cr、Cn、Ua、Pu在0.1~250 mg/L范围内线性关系均良好(相关系数均大于0.999),检出限分别为9.31、26.19、4.70、6.30 μg/L,加标回收率为81%~111%,峰高的相对标准偏差(RSD, n=3)为0.23%~2.78%,满足定量要求。该法简便、快速,结果准确可靠,为2型糖尿病(T2DM)患者肾功能损坏的研究提供了检测手段。     

Some important moments in the development of organic elementary analysis

As early as 1784, Lavoisier carried out combustions of organic substances in a glass bell-jar filled with oxygen. No quantitative results were however obtained. In 1810, Gay-Lussac and Thenard burned organic material in a vertical tube with potassium chlorate as oxidizing agent, and analyzed the resulting mixture of gases. Later (1814–1817), Berzelius used a horizontal tube and a mixture of potassium chlorate and sodium chloride, and weighed the water and carbon dioxide formed. In 1831, Liebig described his potash apparatus and created a general method for the analysis of organic substances, in which cupric oxide was the oxidizing agent. The most important advance in organic analysis after LIEBIG is due to Pregl (1912). By his very well known methods of micro-analysis, progress in organic chemistry has been stimulated enormously. The volumetric determination of nitrogen suggested by Dumas in 1833, was developed by Pregl into a micro-method.