Detection limit nitrate

Two techniques for sorption-spectroscopic determination of ascorbic acid have been proposed. The first one is the recovery by silica modified with tetradecyl ammonium nitrate of blue form of molibdophosphoric HPA in the presence of vitamin C. And the second one is the interaction between the ascorbic acid in solution and immobilized on silica ion associate of molibdophosphoric acid with lucigenine. The detection limits of vitamin C are 0.07 and 2.6 mg respectively. The techniques were successfully applied to the determination of ascorbic acid in fmit juices. 

Using the luminol photochemiluminescence it is possible to determine not only the nitrates (as reported by us earlier), but also the nitrites. The urotropin is added to the water sample, and the solution obtained is illuminated by the Hg lamp. The chemiluminescence is measured after the addition of basic luminol solution to the illuminated solution. The detection limit is 2-10 M. The nitrates contained in the drinking water do not interfere at tenfold excess. 

While barbiturate metabolites are more intensely colored by the mercury(I) nitrate reagent (q.v.) the unaltered barbiturates react more sensitively to the mercury(II) diphenylcarbazone reagent the detection limits lie between 0.05 pg (Luminal ) and 10 pg (Prominal ) per chromatogram zone [6]. 

The detection limits per chromatogram zone are 50 ng substance for sterol peroxides [1], 20-100 ng for nitrate esters [3] and 5-25 ng for aromatic amines [5]. 

Note Uranyl nitrate can be used instead of uranyl acetate [1]. The detection limits for purines are 10 ng substance per chromatogram zone. 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

Simultaneous determination of both cations and anions in acid rain has been achieved using a portable conductimetric ion-exclusion cation-exchange chromatographic analyzer.14 This system utilized the poly(meth-ylmethacrylate)-based weak acid cation exchange resin TSK-Gel OA-PAK-A, (Tosoh , Tokyo, Japan) with an eluent of tartaric acid-methanol-water. All of the desired species, 3 anions and 5 cations, were separated in less than 30 minutes detection limits were on the order of 10 ppb. Simultaneous determination of nitrate, phosphate, and ammonium ions in wastewater has been reported utilizing isocratic IEC followed by sequential flow injection analysis.9 The ammonium cations were detected by colorimetry, while the anions were measured by conductivity. These determinations could be done with a single injection and the run time was under 9 minutes. 

To date, a few methods have been proposed for direct determination of trace iodide in seawater. The first involved the use of neutron activation analysis (NAA) [86], where iodide in seawater was concentrated by strongly basic anion-exchange column, eluted by sodium nitrate, and precipitated as palladium iodide. The second involved the use of automated electrochemical procedures [90] iodide was electrochemically oxidised to iodine and was concentrated on a carbon wool electrode. After removal of interference ions, the iodine was eluted with ascorbic acid and was determined by a polished Ag3SI electrode. The third method involved the use of cathodic stripping square wave voltammetry [92] (See Sect. 2.16.3). Iodine reacts with mercury in a one-electron process, and the sensitivity is increased remarkably by the addition of Triton X. The three methods have detection limits of 0.7 (250 ml seawater), 0.1 (50 ml), and 0.02 pg/l (10 ml), respectively, and could be applied to almost all the samples. However, NAA is not generally employed. The second electrochemical method uses an automated system but is a special apparatus just for determination of iodide. The first and third methods are time-consuming. 

Iodide was determined by an iodide-selective electrode (Ag2S/AgI) after other anions were separated by a rhodium nitrate element [101]. However, the electrode that was stabilised by 0.5 xm iodide responded to chloride ions in seawater, and the detection limit of iodide was 22 xg/l. 

Flow injection analysis is another technique that has been applied to the determination of nitrate and nitrite in seawater. Anderson [ 126] used flow injection analysis to automate the determination of nitrate and nitrite in seawater. The detection limit of his method was 0.1 imol/l. However, the sampling rate was only 30 per hour which is low for flow injection analysis. Reactions seldom go to completion in a determination by flow injection analysis [127,128] because of the short residence time of the sample in the reaction manifold. Anderson selected a relatively long residence time so that the extent of formation of the azo dye was adequate to give a detection limit of 0.1 pmol/l. This reduced the sampling rate because only one sample is present at a time in the post-injector column in flow injection analysis. Any increase in reaction time causes a corresponding increase in the time needed to analyse one sample. 

Johnson and Petty [129] reduced nitrate to nitrite with copperised cadmium, which was then determined as an azo dye. The method is automated by means of flow injection analysis technique. More than 75 determinations can be made per hour. The detection limit is 0.1 xmol/l, and precision is better than 1% at concentrations greater than 10 xmol/l. 

Dahiloef et al. [ 133] have described an ion chromatographic method for the determination of nitrate and phosphate in seawater. A small sample volume (20 pi) is needed, and detection limits of 0.5 and 1.0 pM were obtained for nitrate and phosphate, respectively. 

In this development of a flow injection method for the determination of nitrate andnitrite, Anderson [168] chose the Shinn [155] method to reduce nitrate and nitrite because of its high sensitivity and relative freedom from interferences. Anderson [168] used flow injection in the photometric determination of nitrite and nitrate with sulfanilamide and N-( 1-naphthyl) ethylenediamine as reagents, as discussed next. The detection limit is 0.05 xm for nitrite and 0.1 xm for nitrate at a total sample volume of 200 iL. Up to 30 samples can be analysed per hour with relative precision of about 1%. 

A submersible flow injection-based sensor has been used to determine nitrite and nitrate in seawater. Detection limits of 0.1 pm for nitrate and a linear range of 0.1-0.55 pM were achieved [173]. 

A new in situ probe [25] was presented for the continuous measurement of ammonium and nitrate in a biological wastewater treatment plant. Based on the use of electrochemical measurement, the sensor can be immersed and requires minimum maintenance. The tests carried out to compare its performance with those of other procedures (including UV for nitrate) showed that the results were rather close, with a detection limit of 0.1 mg L 1 for both analytes. 

Another principle, based on the use of UV photo-oxidation of reduced forms of nitrogen (ammonium and organic) into nitrate (measured by UV spectrophotometry), allows the selective determination of nitrate, ammonium and organic nitrogen, and thus of TKN [26], with a detection limit of 1 mg L This method is commercially available. 

A field test for the detection of TNT in contaminated soils (e.g., near ammunition plants) was based on the color reaction between TNT and alkalis (the Janowski reaction [7]) [26]. A few milligrams of the suspected soil are placed on filter paper and sprayed with 1 M NaOH acetone (1 1). A red color indicates the possible presence of TNT. Detection limits were reported to be 2-50 mg of TNT per 1 kg of soil, depending on the type of soil. The same group [55] used the oxidation of DPA in concentrated H2SO4 as the basis of a field test for nitrate esters and nitramines in soil. 

Another field technique for screening soils for the presence of TNT, 2,4-dinitrotoluene (2,4-DNT) and RDX was reported [99]. The color reagents were KOH for TNT (red color) and sodium sulfite for 2,4-DNT (blue-purple color). In screening soil for the presence of RDX, the first step would be to remove any potential contaminants - nitrite and nitrate ions - from the soil, using an ion exchange resin. The RDX is then reduced by zinc powder and the resulting N02 ions are detected by the Griess reaction. Detection limits were estimated to be 1 mg of TNT or RDX and 2 mg of 2,4-DNT per 1 kg of soil. 

The concentrations of thorium in both hard and soft tissues of humans have been determined by a few authors. The concentration of thorium-232 in the blood of normal populations (not occupationally or otherwise known to be exposed to levels higher than background level of thorium) in the United Kingdom was 2.42 pg/L. The thorium-232 level in the urine of the same population was below the detection limit of 0.001 pg/L, although the concentration in the urine of exposed workers ranged from less than 0.001-2.24 pg/L. The highest value (2.24 pg/L) was found in a worker in the thorium nitrate gas mantle industry (Bulman 1976 Clifton et al. 1971). 

In addition to the sensors dealt with in Section 3.3.1.1, which could equally have been included in this Section as they use consumable immobilized reagents and regenerable fluorophores, Frei et al. developed a sensor for HPLC determinations based on the solid-state detection cell depicted in Fig. 3.38.B, where they immobilized 1-bromonaphthalene for measuring phosphorescence quenchers. Experiments demonstrated the sensor s usefulness for determining nitrate with a detection limit of ca. 10" M and an RSD of 4% for an analyte concentration of M. However, the scope of application of this sensor to chromatographically separated anions is rather narrow owing to the low sensitivity of the quenched phosphorescence detection for iodide and other halides [268]. 

In the method proposed by van Staden for the determination of three halides, these are separated in a short colunm packed with a strongly basic ion-exchange resin (Dowex i-X8) that is placed in an FI manifold. A laboratory-made tubular silver/silver halide ion-selective electrode is used as a potentiometric sensor. Van Staden compared the response capabilities of the halide-selective electrodes to a wide concentration range (20-5000 pg/mL) of individual and mixed halide solutions in the presence and absence of the ion-exchange column. By careful selection of appropriate concentrations of the potassixun nitrate carrier/eluent stream to satisfy the requirements of both the ion-exchange column and the halide-selective electrode, he succeeded in separating and determining chloride, bromide and iodide in mixed halide solutions with a detection limit of 5 /xg/mL [130]. 

Elemental composition Cu 64.18%, Cl 35.82%. Copper(I) chloride is dissolved in nitric acid, diluted appropriately and analyzed for copper by AA or ICP techniques or determined nondestructively by X-ray techniques (see Copper). For chloride analysis, a small amount of powdered material is dissolved in water and the aqueous solution titrated against a standard solution of silver nitrate using potassium chromate indicator. Alternatively, chloride ion in aqueous solution may be analyzed by ion chromatography or chloride ion-selective electrode. Although the compound is only sparingly soluble in water, detection limits in these analyses are in low ppm levels, and, therefore, dissolving 100 mg in a liter of water should be adequate to carry out aU analyses. 

The vendor claims that the following metals have been successfully treated to parts per biUion (ppb) and detection limit levels aluminum, arsenic, cadmium, chromium, cobalt, copper, iron, lead, manganese, mercury, molybdenum, nickel, selenium, silver, tin, uranium, vanadium, and zinc. The system is also able to remove ammonia, nitrates, phosphates, potassium, fluorides, and sodium. Studies have also been performed using Aqua-Fix to remove radionuchdes such as uranium from waste streams. 

In order to prevent interference with such inorganic anions as fluoride, chloride, and nitrate which occurs with Na2C03/NaHC03 eluents, a weak aqueous eluent, i.e., Na2Bi+0y, was used to achieve adequate separation. The detection limit in such an ion chromatographic analysis is limited by the conductance of the suppressed eluents, but the development of ion chromatography exclusion (ICE),... 

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