Control of soil solution interferences in an automated nitrate method

Abstract

An AutoAnalyzer method for nitrate nitrogen based on hydrazine reduction followed by diazotization was re‐examined after certain soil solutions had given poor recoveries. Modifications to the reaction parameters, particularly in the reduction stage improved the recovery of nitrate as nitrite. Soluble organic compounds in the samples were more critical than inorganic salts, but the proposed method allowed tolerance of up to 30 mgl^‐1 total organic carbon. Concentrations of various inorganic ions in soil solutions and natural waters were usually below the limits shown to be critical for the improved method.     

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%.     

Dynamics of nitrification in a continuous flow system

Ammonium sulphate was added at constant rates to a column containing a mixture of glass beads and marble chips inoculated with the nitrifying bacteria, Nitrosomonas europaea and Nitrobacter agilis. Changing the rate of NH₄⁺ addition caused nitrite and nitrate concentrations in the outflow to stabilize at characteristic steady state values after brief transition periods. The steady state concentrations were inversely related to the flow rate. The transition phases were characterized by overshoots in the concentrations of nitrite and nitrate when the flow was reduced and a smooth monotonic change to the new steady state values when it was increased. Three mathematical models were developed based on several simplifying assumptions and tested with the data. The best fit was obtained when it was assumed that growth of the organisms could be described by a modification of the Verhulst-Pearl logistic equation.     

Simplified procedure for rapid,manual analysis of nitrate in soil extracts by copper‐cadmium reduction

Abstract

An inexpensive modification of the commonly used manual nitrate (NO₃)‐nitrogen (N) analysis for soil extracts is described. This procedure uses multiple reductors of copperized cadmium (Cd) wire threaded through Teflon tubing and a peristaltic pump to rapidly pass a low volume of soil extract through the reductors at a constant flow rate. In excess of 150 prepared samples can be processed daily with minimum waste generation. Efficiency of reduction is >98% and precision of analysis (coefficient of variation) for replicate standards of known NO₃‐N concentration is excellent, at <0.5% over the concentration range 0.025 to 0.2 μg NO₃‐N mL^‐1. Column life and storage characteristics are high, at >250 samples per column and one month, respectively. Column activation and regeneration in these wire type reductors are simpler and less tedious than for reductors constructed of copperized Cd granules.     

Cadmium copperization assays for the preparation of nitrate‐reducing columns

Abstract

An electrolytic method for the copperization of cadmium as a reducing agent for nitrate‐nitrogen (NO₃ ^‐‐N) determination is described. The conditions, medium, and time of copperization as well as the length of the cadmium reducing column has been studied in detail. This column was placed in a flow injection analyzer for the online determination of NO₃ ^‐‐N in soil extracts. The results obtained show that 1% copper sulfate (CuSO₄), 30 min and 55 mm are the optimal medium, time, and column length, respectively. With this reducing column, the method is linear between 0 and 12 ppm NO₃ ^‐‐N with a precision of 0.29% and a sampling frequency of 80 determinations per hour. The proposed method has been applied to the determination of NO₃ ^‐‐N in soil extracts and the results agree with those obtained by the reference method (r = 0.9998). The optimized electrolytic procedure for the copperization of cadmium permits more than 3000 determinations without any significant loss of sensitivity.     

A modified autoanalyzer II method for the determination of NO3‐N in water using a hollow‐Cd reduction coil

Abstract

The Technicon AutoAnalyzer II (AAII) is used routinely by many laboratories for determination of NO₃‐N in water. The methodology involves the use of a packed‐Cd column for reduction of NO₃‐N to NO₂‐N, which subsequently is determined colorimetrically. A newer instrument, the Technicon TRAACS 800, uses a hollow‐Cd coil for NO₃ ‐N reduction. A method is described for adapting the hollow‐Cd coil to the AAII for determination of NO₃‐N in water samples. This adaptation was found to increase throughput rate and to decrease the time required for column preparation.     

Use of an AutoAnalyzer for total nitrogen determination in plants

Abstract

An AutoAnalyzer was evaluated as a means of determining ammonium concentration in semi‐micro Kjeldahl digests of plant tissue. Results of the AutoAnalyzer determination agree closely with distillation‐titration results. Advantages of the AutoAnalyzer method include speed, precision, and release of labor. Only a small aliquot of each digest is utilized.     

Development and Validation of a New Soil Universal Extractant: 0.02 Molar Strontium Chloride

Abstract

In this experiment, when the strontium chloride–citrate acid extractant (0.02 M SrCl₂–0.05 M citrate) was used for extraction of calcareous soils with calcium carbonate greater than 70 g kg^?1, the filtrate was turbid. Furthermore, white precipitation appeared when this extract was used for phosphorus determination with the Murphy and Riley method. As the concentration of citrate in strontium chloride–citrate acid extractant decreased to 0.025 or 0 M, the filtrate became clean. Further experiments indicated that the 0.02 M SrCl₂ extractant could be used as a universal extractant for soil nitrate+nitrite and potassium; the extracted nitrate+nitrite and potassium significantly correlated with nitrogen and potassium phytoavailability, respectively, determined with ryegrass pot experiment (P<0.05). Thus, the 0.02 M SrCl₂ was recommended as a universal extractant for soil nitrate+nitrite and potassium.     

Collaborative study of the colorimetric determination of nitrate and nitrite in cheese.

A quantitative colorimetric method for the determination of nitrate and nitrite in cheese has been subjected to collaborative study. The method includes clarification of an aqueous extract of cheese with zinc hydroxide, reduction of nitrate to nitrite via a spongy cadmium collumn (the nitrite originally present is unaltered), diazotization of sulfanilic acid with the nitrite, and coupling with 1-naphthylamine hydrochloride to form a pink azo dye whose absorbance is measured at 522 nm. The spectrophotometric responses are compared to a standard curve. In samples containing both nitrate and nitrite, nitrate is determined by difference. A standard deviation of 5.5 was obtained (5 of 6 collaborators) when a cheese sample spiked with 276 ppm sodium nitrate was analyzed by the method. The method has been adopted as official first action.     

Determination of nitrate in 2,0 M KC1 soil extracts using ion chromatography

Abstract

A simple and accurate ion chromatography method for the determination of nitrate in 2,0 M KC1 soil extracts is described. The method can be carried out on a commercially available chromatograph using a reverse phase column with tetrabutylammonium hydrogen sulphate as the mobile phase. Ultraviolet absorbance at 220 nm was used to quantify the nitrate. Statistical analyses showed that nitrate values obtained for 30 soils by this chromatographic method agree closely with those obtained by a colorimetric method. A notable advantage of this method is the direct determination of nitrate by ion chromatography in the most commonly used extractant     

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.     

Ion chromatography in nutrient depletion studies: Measurement of very low nitrate concentrations

Abstract

Determination of the extent to which plants can deplete nitrate from nutrient solutions (C_min) has been hindered in the past by insufficiently sensitive assay techniques. Now ion chromatography on a Dionex AS4A column can be used to separate and quantitate as little as 5 pmoles nitrate (a sensitivity of 0.02 + 0.005 μM NO₃ ^‐[0.3 ppb NO₃ ^‐N]) in nutrient medium containing other anions in more than 10⁵molar excess. To obtain this precision in actual depletion experiments, however, certain important precautions must be observed, including the avoidance of membrane filters with interfering extractables, i.e. all types tested. Under these conditions, other components of the medium do not interfere, nor apparently do root exudates. The sensitivity and absence of interference is compared with that of existing methods for nitrate estimation (nitrate electrode, salicylate, phenoldisulfonate, nitrate reductase/ nitrite diazotization, and ultraviolet absorption, alone, or coupled with high pressure liquid chromatography). The technique is used to demonstrate that pumpkins (Cucurbita moschataPoir.) growing in nutrient solutions can deplete nitrate at least to 0.16 μM, a concentration probably not measurable by any non‐chromatographic method, and measurable accurately at present only by the ion chromatography technique described here. Chloride uptake, and efflux, has also been measured simultaneously from the same chromatography profiles     

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.     

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.     

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%.     

Rapid and sensitive determination of nitrate in plant tissue using flow injection analysis

Abstract

The determination of nitrate in waters and soil extracts by the reduction of nitrate to nitrite by metallic or liquid reductants followed by the colorimetric determination of NO₂ ^‐using the Griess‐Ilosvay reaction has been automated for use with air‐segmented auto‐analyzers or flow injection techniques. However, this technique is not applicable to plant extracts as organic species in the extracts inactivate the reduction columns. The objective of this study was to develop an automated procedure that would allow the determination of NO₃ ^‐in plant extracts without the necessity of prior manual treatment. A flow injection technique was developed that successively traps and releases NO₃in an anion exchange column thereby removing pigments and other non‐ionic and cationic species that otherwise interfere with conversion of NO₃ ^‐ to NO₂ ^‐on a copperized cadmium column. This reduction step is subsequently followed by standard Griess‐Ilosvay colorimetric detection of this ion at a wavelength of 530 nm. The technique uses relatively simple and inexpensive equipment, principally a spectrophotometer equipped with a flow‐through cell and a pen recorder output, a 6‐channel peristaltic pump with accompanying tubing and a Perspex injector/commutator valve made in a laboratory workshop. The technique was found to avoid any significant interference of pigments or other organic compounds in the plant extracts, and the results compared favorably with those obtained using the manual transnitration technique. Analysis time was approximately 1.5 min per sample and could detect NO₃’ concentration as low as 0.1 ug NO₃’‐N ml/¹ in plant extracts (10 ug NO₃’‐N g‘¹of plant material).     

Determination of extractable sulfate and total sulfur from plant and soil material by an autoanalyzer

Abstract

The method has been modified from Sinclair^3,4 and tested for extractable sulfate and total sulfur on plant, soil, and water samples. Inorganic sulfur is extracted from plant and soil material by using dilute acidic extractants, and total sulfur is estimated from dry ashed or wet ashed material whereby various sulfur forms are oxidized to sulfate‐sulfur. The sulfate is precipitated in sample solutions as barium sulfate and determined turbidimetrically by AutoAnalyzer.

The method is rapid, precise, and sensitive enough to be used on a routine basis.     

Nitrogen metabolism in Nicotian a rustica L. grown with molybdenum. I. vegetative development

Abstract

The effect of 1 ppm of molybdenum on nitrate reductase (EC 1.6.6.1.3) and nitrite reductase (EC 1.7.7.1) activity, and the nitrate, nitrite, ammonium, total nitrogen, total protein content on vegetative development of Nicotiana rustica L. was studied. This molybdenum supply increased the ammonium and nitrite content in leaves and the protein content in the root. Variations in enzymatic activity was not observed. The vegetative stage was shorter in the plants grown with this molybdenum supply.     

Errors in the measurement of extractable soil inorganic nitrogen caused by impurities in filter papers

Abstract

Various grades and batches of filter papers were tested for their levels of inorganic nitrogen contamination (measured as ammonium, nitrate and nitrite‐N) by eluting them with 50 mL of 0.5 M potassium sulphate. Significant amounts of ammonium‐N were eluted from all the filter papers, however, most were low in nitrate and nitrite nitrogen. The amounts of ammonium‐N varied with the batch number, among boxes within a batch number and within filter papers from the same box. To minimise the effects of ammonium‐N contained in the filter papers, it is necessary to wash them with a salt solution, such as 0.5 M potassium sulphate, rinse them with deionized water and dry them prior to use     

A rapid colorimetric method for analysis of nitrate nitrogen by reduction to nitrite

Abstract

A new method was developed for the determination of nitrate based on a soluble powder containing zinc and a bluish diazotizing solution. In this procedure about 10% of the nitrate content of the sample is converted to nitrite, but the intensity of the color developed is proportional to the nitrate content. The color changes from blue through green to yellow. The nitrate concentration can be estimated visually or determined spectrophotometerically at λ_max 400 nm in the range of 4–40 mg/L N. When the color change is very small, a coupling solution is added, and the violet color that develops can be measured colorimetrically at λ _max 545 nm in the range of 0.5–5 mg/L N. This simple method employs harmless chemicals and is especially suitable for use in agriculture. Reliable results are obtained in less than 10 minutes.