Rapid screening method for alkaline phosphatase activity in cheese: collaborative study

The method developed for developed for determining alkaline phosphatase activity in cheese, in which phenolphthalein monophosphate is used as the substrate, was collaboratively studied. A 7.5% butanol extract of cheese is reacted with phenolphthalein monophosphate; phenolphthalein is released and yields a red solution that is compared visually with a standard (s) prepared from the same extract. Seven collaborators analyzed 8 samples of cheese, in duplicate, by the screening method and Scharer I method. Of the 208 observations returned, only 4 were incorrect. The alkaline phosphatase method has been adopted as official first action.     

Kurzmitteilung Bestimmung von Dicyandiamid,Nitrit und Nitrat in Bodenextrakten mit Hochdruckflüssigkeitschromatographie

Determination of dicyandiamide, nitrite and nitrate in soil extracts by high pressure liquid chromatography A method for simultaneous determination of dicyandiamide, nitrite and nitrate in soil extracts and percolation water by means of HPLC has been developed. Extraction is done with water or CaCl₂, followed by separation on a RP–C18 column with tetrabutylammonium hydrogen sulfate and sodium dihydrogen phosphate as mobile phase UV-absorbance is measured at 220 nm. Detection limit is 0.1 mg N/I.     

海绵铁缓解污水厌氧氨氧化反应器中硝酸盐积累的效果

该文旨在通过向厌氧氨氧化反应器中投加海绵铁来减轻厌氧SBR(sequencingbatchreactoractivatedsludge process)反应器中的硝酸盐积累,试验研究了海绵铁与硝酸盐和亚硝酸盐在静态条件下的反应。在静态条件下,部分硝酸盐和亚硝酸盐被海绵铁还原成了氨。对比动态试验表明投加海绵铁可以将SBR出水硝酸盐质量浓度控制在25～30 mg/L左右。相同条件下不投加海绵铁出水硝酸盐质量浓度不断累积,直至超过55 mg/L。这可能是由于铁将硝酸盐还原为亚硝酸盐并与厌氧氨氧化进行了耦合。采用高通量测序发现投加海绵铁的反应器中厌氧氨氧化菌在微生物群落中所占的比例(22.55%)约为不投加反应器(8.85%)的3倍,表明投加海绵铁有利于反应器中厌氧氨氧化(ANAMMOX)菌的生长和厌氧氨氧化反应器的启动。     

Simultaneous automated determination of chloride,nitrite, nitrate,and ammonia in water and wastewater

An automated system capable of simultaneous determination of chloride, nitrite, nitrate, and ammonia in about 2 ml of fresh water or wastewater is described. The four compounds are determined using modifications of established colorimetric procedures. Results can be reported at a true rate of five samples per hour with a relative standard deviation at optimum concentrations of less than 2%. Detection limits are 1 ppm Cl for chloride and 1, 5, and 5 ppb N for nitrite, nitrate, and ammonia, respectively. Sample pH adjustment is not required from 0.0002 N H₂SO₄ (pH 3.7) to 0.005 N NaOH (pH 11.2). Fresh water and wastewater samples were analyzed for nitrite and ammonia by the proposed procedure and by the manual sulfanilic-naphthylamine and nesslerization method. Analysis by the student t-test showed no significant difference between the paired sets of data (P > 0.5). When potable and wastewater samples were spiked with sodium chloride, potassium nitrate, sodium nitrite, and ammonium chloride and analyzed, average recoveries were 99 to 103%.     

Ion-exchange liquid chromatographic determination of nitrate and nitrite in biological fluids

A rapid, ion-exchange liquid chromatographic method for the determination of nitrate and nitrite in biological fluids is presented. Samples are deproteinated by ultrafiltration followed by removal of chloride using a silver form cation-exchange resin. Nitrate and nitrite are measured by ion-exchange liquid chromatography with conductivity detection. Recoveries from serum, ocular fluid, and water were determined for fortifications from 10 to 150 mg/L. Average recoveries ranged from 96 to 104% for nitrate and from 89 to 105% for nitrite. Pooled RSD values ranged between 1.5 and 1.9% for these analytes in all matrixes examined. The method of joint confidence hexagons was applied to the data to determine constant and relative bias of the method for each of the 3 matrixes in the study.     

Gas chromatographic-mass spectrometric determination of adipate-based polymeric plasticizers in foods

A method for the quantitative determination of adipate-based polymeric plasticizers in foods is described. The procedure involves extraction from the food and transmethylation of the polymeric plasticizer to form dimethyladipate (DMA). The derivative is cleaned up by size-exclusion chromatography and determined by capillary gas chromatography-mass spectrometry with selected ion monitoring. The use of a deuterated internal standard at the extraction stage enables quantitation by stable isotope dilution. A detection limit of 0.1 mg/kg of the polymeric plasticizer in foods and a relative standard deviation of 4% have been achieved routinely. The method has been applied successfully to the analysis of cheese, sandwiches, meat, biscuits, and cake that have been in contact with polymeric plasticized poly(vinyl chloride) films.     

粪产碱菌(Alcaligenes faecalis)的反硝化及固氮作用

粪产碱菌生长在NH_4~+和NO_3~-两种氮源的介质中时,优先利用NH_4~+,在好气条件下,NH_4~+的存在抑制了粪产碱菌对NO_3~-的同化作用。在厌氧条件下,粪产碱菌能以乳酸为碳源,NH_4~+为唯一氮源进行反硝化作用,NO_3~-作为最终电子受体,接受无氧呼吸链传递的末端电子,经NO_2~-等氮氧化物最终还原为N_2。在好气和厌气条件下,低浓度的NO_2~-对粪产碱菌生长有一定抑制作用,但NH_4~-的存在并不抑制细菌对NO_2~-的利用。粪产碱菌在厌氧条件下还具有需硝酸盐的固氮酶活性。当氧存在或以NO_2~-代替NO_3~-时,固氮活性均受抑制,硝酸盐或亚硝酸盐浓度愈高,抑制愈强。反硝化作用产生的N_2能为微好氧条件下生长的粪产碱菌所重新固定。     

铜绿微囊藻对亚硝态氮的利用

通过室内培养,研究了不同亚硝态氮浓度对铜绿微囊藻（Microcystis aeruginosa）生长的影响和藻对亚硝态氮的利用,实验分析了水体中亚硝态氮、硝态氮和铵态氮浓度的变化,测定了铜绿微囊藻的生长曲线、藻细胞内亚硝态氮含量和藻亚硝酸氧化酶（NOR）。结果显示,在10mgNO^-2-N·L^-1的处理组中,培养基中亚硝态氮和硝态氮浓度同时减少,说明铜绿微囊藻可以同时利用亚硝态氮和硝态氮;在20和30mgNO^-2-N·L^-1的处理组中,随着藻的生长培养基中亚硝态氮的浓度减少,硝态氮浓度增加,而且电泳实验显示此培养条件下铜绿微囊藻能产生亚硝酸氧化酶,表明培养基中的亚硝态氮被亚硝酸氧化酶氧化为硝态氮。本实验也表明高浓度的亚硝态氮（大于10mgNO^-2-N·L^-1）能够抑制藻的生长。     

Sequential Injection Determination of Nitrate in Vegetables by Spectrophotometry with Inline Cadmium Reduction

Abstract

A sequential injection system for the determination of nitrate (NO₃ ^?) in vegetables was developed to automate this determination, allowing for substantially reduced reagent consumption and generated waste using low‐cost equipment. After extraction with water and filtration, the extracted nitrate is reduced inline to nitrite in a copperized cadmium (Cd) column and determined as nitrite. According to the Griess–Ilosvay reaction, nitrate is diazotized with sulfanilamide and coupled with N‐(1‐naphtyl)‐ethylenediamine dihydrochloride to form a purple‐red azo dye monitored at 538 nm.

Nitrate can be determined within a range of 1.35–50.0 mg L^?1 of NO₃ ^? (corresponding to 0.270–10.0 g of NO₃ ^? per kg of vegetable), with a conversion rate of nitrate to nitrite of 99.1±0.8%. The results obtained for 15 vegetable extracts compare well with those provided by the classical procedure, with a sampling throughput of 24 determinations per hour and relative standard deviations better than 1.2%.     

Nitrification results in underestimation of soil urease activity as determined by ammonium production rate

The majority of soil urease activity measurements have been based on the rate of ammonium production under optimal conditions. However, such procedures do not exclude ammonium consumption by the nitrification process. The purpose of this study was to determine the percentage of soil urease activity that is underestimated due to soil nitrification. Six soils with diverse properties were incubated using a standard procedure for measuring soil urease activity. The dynamics of nitrite and nitrate were observed during the incubation. Our results showed that the percentage of underestimation ranged from 7.38% to 15.97%, depending on soil types and whether or not a buffer was used. We recommend that nitrification be taken into account when soil urease activity is assayed by the ammonium production rate method.     

Gas-liquid chromatographic determination of nitrate and nitrite in cheese, ham, fish sausage, cod roes, and salmon roes

The 2,4-xylenol method was modified and a gas-liquid chromatographic (GLC) method was developed for nitrate and nitrite determinations in several foods. Either a flame ionization (FID) or an electron capture detector (ECD) can be used. Proteins and fats are removed from warm alkaline water with zinc sulfate and filtered. The filtrate is evaporated to dryness, redissolved in water, and reacted with 2,4-xylenol in the presence of sulfuric acid to form 6-nitro-2,4-xylenol. Interfering chlorides are precipitated with silver sulfate and the nitrosylenol is extracted with hexane, concentrated, and injected. Nitrite in the filtrate is distilled at pH 5, collected in alkaline solution, and dried. The residue is oxidized to nitrate with permanganate in the presence of sulfuric acid, and then chromatographed in the same manner as nitrate. Recoveries from several foods were 83--100% for nitrate and 80--100% for nitrite. The limit of sensitivity was 0.1 ppm for both residues.     

Interaction of soluble peptides and proteins from skeletal muscle with volatile compounds in model systems as affected by curing agents

The effect of curing agents (salt, glucose, nitrate, nitrite, and ascorbic acid) on the binding of skeletal peptides (carnosine and anserine) and a sarcoplasmic protein (myoglobin) with key flavor compounds (hexanal, octanal, 2-pentanone, 2-methylbutanal, and 3-methylbutanal) has been studied by solid-phase microextraction (SPME). Curing agents had an effect on the interaction process between carnosine and volatile compounds, which was higher than the interactions observed with anserine and myoglobin. Sodium chloride decreased the interaction of volatiles with carnosine except for octanal, which was increased, and 2-pentanone, which was unaltered. Ascorbic acid exerted the highest effect by decreasing the interaction of carnosine with all of the volatile compounds except for octanal and 2-pentanone. The interaction with anserine was affected by sodium chloride, nitrate, and nitrite, producing a decrease in the interaction with hexanal, octanal, and methional. Finally, sodium chloride, glucose, and nitrite increased the interaction of myoglobin with hexanal, octanal, and methional. The effect of simulated stages of the curing process on the binding was also studied. A combined effect of the curing agents resulted in a change in the relative proportions of volatile compounds that can lead to different flavor perceptions of dry-cured meat products.     

Nitrate and nitrite reduction in flooded gamma-irradiated soil under controlled pH and redox potential conditions

Nitrate and nitrite reduction was studied in a waterlogged soil after γ-irradiation with 2.5 Mrad. Before irradiation and mineral-N addition the pH was controlled at 4.5, 6 and 8, and the redox potential controlled at 0, +200 and +400 mV Nitrate reduction rate increased with increasing pH as well as with decreasing redox potential. Nitrate reduction rate was doubled by decreasing the redox potential from +400 to 0 mV. At pH 4.5 almost no nitrite accumulated regardless of redox potential, while at pH 6 and 8 marked nitrite accumulation occurred at low redox potential. In relation to non-irradiation. γ-irradiation had a stimulating effect on nitrate reduction at pH 6 and 8 but a retarding effect at pH 4.5; nitrite reduction proceeded slower at pH 6 and 8 but at the same rate at pH 4.5. It has been demonstrated that nitrate and nitrite reduction can be carried out by radiation-resistant enzyme systems of non-proliferating cells of denitrifying organisms.     

Nitrate determination in baby food, using the nitrate ion selective electrode.

The nitrate electrode has been utilized in the determination of nitrate content in food products. The AOAC xylenol method was employed for comparative results. A reasonable correlation (r=0.91) was found between the 2 methods in the analysis of 49 samples containing 30-350 ppm nitrate. At the average nitrate content (100 ppm) of these foods, the standard error was 4.3 ppm. The electrode responds directly to the ionic activity of the nitrate ion. It has a linear concentration range of 1-6000 ppm nitrate and can be used over a wide pH range. The electrode does respond to some extent to anions other than nitrate, and some interferences do occur. These interferences are easily controlled by the use of cation exchange resins. The Corning known addition (spiking) method is used on all samples to insure correct electrode response in solutions containing variable background ionic composition. The electrode has the advantage of simplicity, speed, reproducibility, and accuracy. Work time saved using the electrode as opposed to the xylenol method is about 7 hr for the analysis of 20 samples. Error, and the need for repeating analysis, is much less frequent.     

钾、尿素与有机物料或双氰胺配施对菠菜体内硝酸盐、亚硝酸盐含量影响的研究

采用盆栽试验探讨了钾、尿素与有机物料或双氰胺配施对菠菜体内硝酸盐、亚硝酸盐累积量及与其相关的硝酸还原酶(NR)活性的影响。结果表明,菠菜体内硝酸盐含量的顺序为:尿素>尿素+鸭粪>尿素+猪粪>尿素+双氰胺; 亚硝酸含量顺序为:尿素>尿素与鸭粪配施>尿素与双氰胺配施>尿素与猪粪配施。有机物料的加入均可明显地增加植株体内NR的活性,在菠菜体内NR活性以:尿素+鸭粪>尿素+猪粪>尿素+双氰胺>尿素处理。在相同的氮肥处理条件下,配施适量的钾肥也能显著地降低菠菜体内硝酸盐、亚硝酸盐的累积和增加NR的活性。随着追肥时间的延长,菠菜体内的硝酸盐、亚硝酸盐含量也随之降低,特别是NR的活性在追肥后的第12天到18天之间有显著的降低过程。     

Determination of (Nitrate + Nitrite )‐N in alkaline permanganate solutions

Abstract

The quantitative reduction of nitrate in an acid medium with reduced Fe was applied to the alkaline permanganate solution used to absorb NO and NO₂ evolved from soils during denitrification reactions. The method involves addition of H₂SO₄ to acidify the solution and ensure oxidation of nitrite to nitrate, and treatment with reduced Fe at 100°C to reduce nitrate to ammonium. The solution is made alkaline with NaOH and ammonium determined by standard distillation procedures. It is simple and precise, and applicable to nitrogen isotope ratio analysis of NO and NO₂ evolved from soils.     

Determination of nitrate in soil by second derivative ultraviolet spectrometry

Abstract

A second derivative UV‐spectrometry method is described for the determination of nitrate in soils. Ammonium, nitrite, and urea may be determined in the same extract. The method generally requires no pretreatment of soil extracts, and hence is very rapid. It is largely free from interferences. Recoveries of added nitrate in four soils by the proposed method compared favourably with the phenoldisulphonic acid method.     

成都平原典型样区浅层地下水水质调查与污染评价

[目的]开展成都平原区浅层地下水水质调查与污染评价,为该区域开展土壤和地下水资源保护、合理开发利用地下水资源提供理论依据。[方法]在成都平原典型样区采集了60个浅层地下水样,分析水样的pH值、溶解性总固体、总硬度、氯化物、氨氮、氟化物、硝酸盐、亚硝酸盐、硫酸盐、铁、锰等11项指标。利用层级阶梯评价法和主成分分析法对研究区浅层地下水水质进行评价,并用MapGIS绘制了水质综合评价图。[结果]研究区浅层地下水部分指标超标,尤其是硝酸盐污染较严重,其次是总硬度、铁和锰。[结论]研究区地下水质量总体较好,局部地区有一定程度污染。     

Rapid and simple leaf tissue test for nitrate

Abstract

A simple and rapid procedure for the determination of nitrate in fresh leaf tissue, suitable for use by relatively untrained operators is presented. The method requires only 4 reagents and can be carried out in less than 20 min from start to finish. A 400 mg sample of fresh leaf tissue is macerated briefly with 5 drops of 10 N sulphuric acid, diluted with 10.0 ml of water and filtered. Nitrate‐N is estimated on an aliquot of the filtered extract by reducing the nitrate to nitrite by shaking with powdered zinc in ammonium hydroxide solution for 3 min. The reduced mixture is allowed to settle (5 min) and an aliquot is withdrawn through a cotton‐wool plug thus removing any particles of the zinc. The filtered aliquot is then reacted with a single colour reagent to yield a pink azo‐dye, the intensity of which is directly proportional to the amount of nitrate.

The method was found to have a coefficient of variation of about 4%. When compared with the phenoldisulphonic acid method for nitrate, on aliquots of the some plant extract, it yielded values which were on average 94.6% of those obtained with the former method. The coefficient of variation between the methods was 7%.     

Role of nitrite and nitric oxide in the processes of nitrification and denitrification in soil: Results from N tracer experiments

Recent research has proven soil nitrite to be a key element in understanding N-gas production (NO, N₂O, N₂) in soils. NO is widely accepted to be an obligatory intermediate of N₂O formation in the denitrification pathway. However, studies with native soils could not confirm NO as a N₂O precursor, and field experiments mainly revealed ammonium nitrification as the source of NO. The hypothesis was constructed, that the limited diffusion of NO in soil is the reason for this contradiction. To test this diffusion limitation hypothesis and to verify nitrite and NO as free intermediates in native soils we conducted through-flow (He/O₂ atmosphere) ¹⁵N tracer experiments using black earth soil in an experimental set up free of diffusion limitation. All of the three relevant inorganic N soil pools (ammonium, nitrite, nitrate) were ¹⁵N labelled in separate incubation experiments lasting 81 h based on the kinetic isotope method. During the experiments the partial pressure of O₂ was decreased in four steps from 20% to about 0%. The net NO emission increased up to 3.7 μg N kg⁻¹ h⁻¹ with decreasing O₂ partial pressure. Due to the special experimental set up with little to no obstructions of gas diffusion, only very low N₂O emission could be observed. As expected the content of the substrates ammonium, nitrate and nitrite remained almost constant over the incubation time. The ¹⁵N abundance of nitrite revealed high turnover rates. The contribution of nitrification of ammonium to the total nitrite production was approx. 88% under strong aerobic soil conditions but quickly decreased to zero with declining O₂ partial pressure. It is remarkable that already under the high partial pressure of 20% O₂ 12 % of nitrite is generated by nitrate denitrification, and under strict anaerobic conditions it increases to 100%. Nitrite is present in two separate endogenous pools at least, each one fed by the nitrification of ammonium or the denitrification of nitrate. The experiments clearly revealed that nitrite is almost 100% the direct precursor of NO formation under anaerobic as well as aerobic conditions. Emitted N₂O only originated to about 100% from NO under strict anaerobic conditions (0-0.2% O₂), providing evidence that NO is a free intermediate of N₂O formation by denitrification. To the best of our knowledge this is the first time that NO has been detected in a native soil as a free intermediate product of N₂O formation at denitrification. These results clearly verify the “diffusion limitation” hypothesis.