An improved technique for the spectrophotometric determination of nitrate with 2,4-xylenol

An improved method is proposed for the spectrophotometric determination of nitrate with 2,4-xylenol. The sample in aqueous (1.7 + 1 ) sulfuric acid is treated with 2,4-xylenol to produce 6-nitro-2,4-xylenol which is distilled into an ammoniacal water—isopropanol mixture. The intense yellow color of the ammonium salt of 6-nitro-2,4-xylenol is measured at 455 nm. The distillation is done in a Parnas—Wagner Kjeldahl Semimicro distillation apparatus. The isopropanol keeps the excess of 2,4-xylenol in solution. Two procedures are described. In the first (applicable to samples containing alkali nitrates but no chloride, alkaline earth, or ammonium salts), the solution is evaporated to dryness, and (1.7 + 1) sulfuric acid and 2,4-xylenol in acetone are added. In the second (applicable to samples containing chloride, alkaline earth, or ammonium salts), concentrated sulfuric acid is added dropwise to a cooled aliquot and the 2,4-xylenol reagent is then added; if chloride is present, it must be removed by prior precipitation with silver sulfate. Nitrite shows a slight interference which depends on the amount of nitrate and nitrite present.     

Further improvements in the 2,4-xylenol spectrophotometric method for nitrate

Improvements are described for the 2,4-xylenol spectrophotometric method for nitrate that reduce the elapsed and working time. Diluted (22 + 3) sulfuric acid is added quickly to the sample solution while the flask is immersed in tap water. 2,4-xylenol solution is added, the 6-nitro-2,4-xylenol formed is steam-distilled into a composite ammonia—isopropanol reagent, and the absorbance of the ammonium salt of 6-nitro-2,4-xylenol is measured. Further possible interferences are described. Br₂, I₂, ClO^-, CIO₃^-, BrO₃^-, and I0₄^-, cause low results by deactivating or destroying the 2,4-xylenol. Azide, hydrazine, and elemental carbon cause low results by reducing the nitrate in the strong sulfuric acid solution. Se⁺ causes low results because 2,4-xylenol is consumed in reducing Se⁴⁺ to the element. Pt⁴⁺ and Os⁸⁺ cause high results. Interferences from Br₂, I₂, ClO^-, ClO₃^- lO₃^-, and I0₄^- can be eliminated by reduction to the halide with sulfurous acid and precipitation with silver sulfate. Sulfurous acid reduction also eliminates interferences from V⁵⁺. Mn⁷⁺, Cr⁶⁺, S₂O₈^2-, and H₂0₂. Interferences from N₃^-, Br₂, I₂, and S₂0₈^2- are eliminated merely by boiling a 0.5% sulfuric acid solution for 30 min (and precipitating any residual halide with silver sulfate).     

Organic interferences and their elimination in the 2,4-xylenol spectrophotometric method for nitrate

The 2,4-xylenol spectrophotometric method for nitrate involves formation of 6-nitro-2,4-xylenol, which is steam-distilled into an ammonia—water—isopropanol mixture. The yellow color of the ammonium salt of 6-nitro-2,4-xylenol is measured at 455 nm. A detailed study of the possible interferences from 123 representative organic compounds is described; 61 compounds interfered (when present in amounts of 0.1 g in the original sample). The interfering compounds can be classified according to their mode of interference: (1) compounds that are readily nitrated or oxidized by nitrate in the sulfuric acid medium used cause low results; (2) compounds containing the ONO₂ group that hydrolyze to nitrate cause high results; (3) compounds that steam-distil to produce colored solutions; (4) compounds that steam-distil to produce turbid solutions; (5) compounds that hydrolyze, either in water or sulfuric acid solution, to produce inorganic ions or compounds (e.g. Cl^-, S^2-, and H₂O₂) that repress the color development. Three procedures are described for the elimination of the interferences: (1) oxidation of the organic compound with permanganate, reduction of the excess of permanganate with hydrogen peroxide, and destruction of the peroxide by boiling in the presence of Fe(III) catalyst (this is unsuitable for organic compounds containing nitrogen, as there is invariably some oxidation to nitrate); (2) extraction of interfering organic compounds with methyl isobutyl ketone; (3) precipitation—adsorption method involving treatment with zinc sulfate and sufficient sodium hydroxide to precipitate most of the zinc as zinc hydroxide, addition of 3 g of activated carbon, digestion at 55–65°C for 20 min. cooling, dilution, and filtration. Method (3) is applicable to all organic compounds tested except formaldehyde. The amount of organic compound used to test the methods was normally 0.25 g in the solution being treated.     

Analysis of nitrite and nitrate as 1-nitro-2,4,6-trimethoxybenzene derivatives by reversed-phase HPLC with UV-detection

Summary A reversed-phase HPLC method for the determination of nitrite and nitrate in aqueous solutions, biological buffers and human urine is described. The method is based on the conversion of nitrite and nitrate into their 1-nitro-2,4,6-trimethoxybenzene (NTBM) derivatives by using 1,3,5-trimethoxybenzene and concentrated sulphuric acid. NTMB is extracted by benzene, the solvent evaporated, the residue reconstructed in methanol/water (3/4, v/v) and subsequently analyzed by reversed-phase HPLC and UV detection (360 nm). The specificity of the nitration reaction, good reproducibility (C.V. 6.2%) and high sensitivity (8.4 ng nitrite) show the applicability of this method to the quantitative analysis of nitrite and nitrate in several matrices including human urine.     

Determination of nitrate in suspended particulate matter by high-performance liquid chromatography with u.v. detection

For the determination of nitrate in suspended particulate matter (s.p.m.), high-performance liquid chromatography (h.p.l.c.) with a u.v. detector at 210 mm gives precise and accurate results. Chloride, bromate, iodide, nitrite, thiocyanate and various cations do not interfere. Calibration graphs are linear over the range 0–20 ppm of nitrat-enitrogen, and the limit of detection is 0.25 ng of nitrate-nitrogen. The coefficients of variation at 5.0- and 10.0-ppm levels are 3.4 and 2.9%, respectively. Results obtained by the h.p.l.c. method and by two 2,4-xylenol spectrophotometric methods for aqueous extracts of s.p.m. are compared. Agreement is generally good, particularly when choride is removed in the 2,4-xylenol method, but the spectrophotometric methods are much more prone to interference.     

Inorganic interferences in the 2,4-xylenol spectro-photometric method for nitrate and their elimination

A study of inorganic interferences with the 2,4-xylenol spectrophotometric method for nitrate and their elimination is reported. Fifty-three substances do not interfere with the original method. Nitrite interferes somewhat by producing a faint yellow color. Certain reducing agents (Fe²⁺, S^2-, S₂O₃^2-, and SCN^-) cause low results by reducing the nitrate in the strong sulfuric acid solution, while some oxidizing agents (Mn⁷⁺, Cr⁶⁺, V⁵⁺, and ClO₃^-) cause low results by inactivating or destroying the 2,4-xylenol. Persulfate and small amounts of H₂O₂ produce a slight deepening of the color; larger amounts of H₂O₂; cause low results, as do Cl^-, Br^-, I^-, and metals. The recommended maximum permissible limits (mg per 10-ml aliquot) for the original method are NO₂^--N, Fe²⁺, S^2-, SCN^-, V⁵⁺, ClO₃^-, Cl^-, I^-, 0.2; Mn⁷⁺, Cr⁶⁺, S₂O₈^2-, 5; H₂O₂, 0.02; S₂O₃^2-, Br^-, 0.1; metals, none. Procedures for the elimination of most of the interferences are described. Nitrite is destroyed with sulfamic acid. The interferences of reductants (Fe²⁺, S^2-, S₂O₃^2-, and SCN^-) and oxidants (Mn⁷⁺ and Cr⁶⁺) are eliminated with hydrogen peroxide, the excess of which (and S₂O₈^2-) is destroyed by boiling in the presence of Fe³⁺. The interference of Cl^-, Br^-, and I^- is eliminated by precipitation with silver sulfate. An alternative to the sulfamic acid procedure is to oxidize nitrite to nitrate with peroxide and deduct NO₂^--N from the total NO₃^--N. After elimination of interferences, a 10-ml aliquot of sample solution is treated with 17.0 ml of sulfuric acid and 2,4-xylenol, the 6-nitro-2,4-xylenol is steam-distilled into an ammonia—water—isopropanol mixture, and the yellow color is measured.     

2,6-二甲酚分光光度法测定废水中的总氮

废水中的无机态氮和有机态氮被过硫酸钾氧化消解后转变为硝酸盐，在硫酸和磷酸混合酸介质中，硝酸盐与2，6—二甲酚反应生成4—硝基—2，6—二甲酚而显色。废水中的总氮在2～8mg/L范围内与337nm波长处的吸光度成正比，回归方程为A=0．1672X—0．0077，相关系数r=0．9996，回收率为96．5％～105．7％。氯离子浓度高于1．5g/L时有干扰，其它常见的阴、阳离子无干扰。     

Chemistry of novolac resins. II. Reaction of model phenols with hexamethylenetetramine

It is proposed that the reactions of hexamethylenetetramine (HMTA) with 2,4-xylenol and with 2,6-xylenol occur by different pathways. The rate of reaction and the final product distribution depend on the initial xylenol : HMTA ratio and are different in the two systems. Measured by HMTA consumption, with 2,4-xylenol the reaction rate increased with increasing xylenol : HMTA ratios, whereas with 2,6-xylenol the rate of reaction decreased with increasing 2,6-xylenol : HMTA ratio. In systems which contain both 2,4- and 2,6-xylenol, a strong preference for reaction of the HMTA with the ortho site of 2,4-xylenol was noted. This preference was apparent even in mixtures in which 2,6-xylenol was present in greater amounts than 2,4-xylenol. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1389–1398, 1997     

Selective determination of 2,4-xylenol by gas chromatography/supersonic jet/resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry

Gas chromatography/supersonic jet/resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry (GC/SSJ/REMPI/TOF-MS) was employed for isomer-selective determination of 2,4-xylenol in river and seawater samples. The sample containing 2,4-xylenol was measured using argon, rather than helium, as the GC carrier gas to cool the analyte molecule sufficiently. The instrumental detection limit (IDL) achieved at a flow rate of 1 mLmin(-1) was 14 pg. Although this value was comparable to the value (ca. 10 pg) obtained by gas chromatography/electron impact/quadrupole mass spectrometry (GC/EI/QMS). When the flow rate was increased to 8 mLmin(-1), interference from the 2,5-xylenol isomer was completely suppressed. The IDL was degraded to 83 or 160 pg at a flow rate of 5 or 8 mLmin(-1), respectively. The recovery of 2,4-xylenol from the river and the seawater samples was 85 and 93%, respectively. The time for analysis was only 10 min per one sample in GC/SSJ/REMPI/TOF-MS. These results suggest that GC/SSJ/REMPI/TOF-MS is useful for the selective measurement of 2,4-xylenol, which has been designated a Class I chemical substance in the Pollutant Release and Transfer Register (PRTR).     

Preparation of 1,8-naphthalimides as candidate fluorescent probes of hypoxic cells

A number of nitro- and dinitro-1,8-naphthalimides have been prepared as potential fluorescent probes of hypoxic cells. The susceptibility of 4-nitro-1,8-naphthalic anhydrides and -naphthalimides to nucleophilic displacement of the nitro group has been demonstrated by reaction with 1-butanethiol to yield 4-butylthio derivatives. Attempted nitration of these 4-butylthio derivatives with sodium nitrate and concentrated sulphuric acid yielded the corresponding sulphoxides in high yield.     

Gem-dinitro compounds in organic synthesis. 3. Syntheses of 4-nitro-1,2,3-triazoles from gem-dinitro compounds

Several chemoselective syntheses have been developed for 4-nitro-1,2,3-triazoles from sodium azide and gem-dinitroethylenes prepared from readily available transformation products of dinitroacetic acid ester: N-(,-dinitroethyl)-N,N-dialkylamines, 2,2-dinitroethanol acetate, a mixture of dinitroacetic acid ester with aliphatic aldehydes, or 1,1,1-trinitroalkanes. Hitherto-unknown 4-nitro-5-amino- and 4,5-dinitro-1,2,3-triazoles have been synthesized via successive transformations of the CH₃ groups in 5-nitro-4-methyltriazole. Nitration of 4-nitro-1,2,3-triazole with nitronium fluoroborate or acetyl nitrate gave an unknown 2,4-dinitro-1,2,3-triazole.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 958–966, April, 1992.     

Bestimmung der aciditätsfunktion Ho in konzentrierten wässrigen lödsungen der 1,3,5-trifluorbenzol-2,4-disulfonsäure

The acidity function H_o for 1,3,5-trifluorobenzene-2,4-disulfonic acid has been determined using the Hammett bases 4-nitro-, 2-nitro-, 4-chloro-2-nitro-, 2,5-dichloro-4-nitro- and 2,6-dichloro-4-nitroanilin in aqueous media. The experimental determination of the H_o value was possible up to 65 % 1,3,5-trifluorobenzene-2,4-disulfonic acid. Thereafter it was possible by extrapolation to ascertain the H_o values within the concentration range of 65 – 100 % 1,3,5-trifluorobenzene-2,4-disulfonic acid.     

The determination of silver in sulphide minerals by atomic absorption spectrophotometry

Silver can be determined in sulphide minerals by atomic absorption spectrophotometry after decomposition with nitric and/or sulphuric acid with addition of tartaric acid to prevent precipitation of antimonic acid. The amount of silver retained in the residue is negligible if the acids used are completely chloride-free or if mercury(II) nitrate is added.     

Voltammetric determination of the stabilizing additives acardite II, centralite I and diphenylamine in propellants

A method for the determination of the stabilizing additives Acardite II, Centralite I and diphenylamine in single- and double-base propellants has been developed, based on oxidative differential pulse voltammetry with a glassy-carbon electrode in a 1:1 v v acetonitrile-methanol medium. The voltammetric behaviour of Acardite II and Centralite I was briefly studied to find the proper experimental conditions. For analysis, aliquots of a crude sample extract in dichloromethane are added directly, with no prior treatment, to the measurement cell. The analysis is performed by the standard-addition method. The relative standard deviation is typically 1.0-1.5%. The concentration range accessible with the differential pulse technique, 0.5-100 muM, is quite sufficient for the levels of stabilizers used in powders and propellants. The utility of the method is exemplified by the monitoring of stabilizer consumption in three different propellants subjected to accelerated degradation at 90 degrees .     

A new principle of activation-analysis separations-X Substoichiometric determination of traces of gallium

A rapid method for the substoichiometric determination of gallium by neutron-activation analysis has been developed. After irradiation and dissolution of the test sample, gallium carrier is added and two preliminary separation steps are performed: the extraction into chloroform of cupferrates from 7N sulphuric acid and of diethyldithiocarbamates from 2-3N sulphuric acid. The pH of the remaining aqueous phase is then adjusted to 5.5, the solution extracted with a substoichiometric amount of 8-hydroxyquinoline in chloroform and the activity of the gallium hydroxyquinolate extract measured. A simultaneously irradiated gallium standard is treated in exactly the same way. From the activities of these two substoichiometric extracts the amount of gallium originally present in the test sample can be calculated. The method has been applied to the determination of 10(-6) to 10(-3)% of gallium in metallic aluminium and transistor-grade silicon.     

Colorimetric determination of boron in nitrate solutions

A method has been developed for the determination of microgram amounts of boron in nitrate solutions. Nitrate is destroyed with formic acid and sulphuric acid under reflux conditions. As much as 3 millimoles of nitrate are reduced completely by refluxing 1 ml of the nitrate solution with 1 ml of 88% formic acid for 15 minutes. Boron is determined by the carminic acid method after forming the colored complex in situ. This method has been applied to the determination of boron in uranyl nitrate solutions after extraction of uranium with tri-n-octylphosphine oxide dissolved in cyclohexane.     

碘量法与电重法测定氧化铜矿中酸溶铜的方法比较

试料用含亚硫酸钠的硫酸(10%)溶液浸取,使铜的氧化物矿物选择溶解,过滤后加入溴饱和盐酸掩蔽砷和锑等金属,补加少量硫酸,蒸干后用硫酸溶解,用硫代硫酸钠标准溶液滴定测定氧化铜矿中酸溶铜的含量,此方法快速、稳定、准确。选取14个日常分析的样品进行测定,其结果与电解重量法比对,结果令人满意。     

一类新型嘧啶苯氧(硫)醚的合成及生物活性

一类新型嘧啶苯氧(硫)醚的合成及生物活性;双乙烯酮; 氯硝基嘧啶; 苯氧（硫）醚; 嘧啶肼; 生物活性     

Chemical analysis of manganese nodules : Part II. Determination of uranium and thorium after anion-exchange separation

A method is described for the determination of uranium and thorium in manganese nodules. After dissolution of the sample in a mixture of perchloric and hydrofluoric acids, uranium is adsorbed on the strongly basic anion-exchange resin Dowex 1 (chloride form) from 6 M hydrochloric acid. The effluent is evaporated and the residue is taken up in 7 M nitric acid—0.25 M oxalic acid; thorium is then isolated quantitatively by anion-exchange on Dowex 1 (nitrate form). Thorium is eluted with 6 M hydrochloric acid and determined spectrophotometrically by the arsenazo III method. Uranium is eluted from the resin in the chloride form with 1 M hydrochloric acid and then separated from iron, molybdenum and other co-eluted elements on a column of Dowex 1 (chloride form); the medium consists of 50% (v/v) tetrahydrofuran, 40% (v/v) methyl glycol and 10% (vv) 6 M hydrochloric acid. After removal of iron and molybdenum by washing the resin with a mixture of the same composition and with pure aqueous 1 M hydrochloric acid, the adsorbed uranium is eluted with 1 M hydrochloric acid and determined by fluorimetry. The method was used successfully for the determination of ppm-quantities of uranium and thorium in 60 samples of manganese nodules from the Pacific Ocean.     

Methanolysis and hydrolysis of derivatives of methyl 2,5- and 4,5-dihydrofuran-2-carboxylates

Methyl 2,5-dimethoxy-2,5-dihydrofuran-2-carboxylate is formed in the reaction of HCl-CH₃OH with methyl 5-nitro-2-acetoxy-2,5-, 5-nitro-4-acetoxy-4,5-, and 2,5-diacetoxy-2,5-dihydrofuran-2-carboxylates, whereas methyl 2,5-dioxo-3-pentenoate bis(2,4-dinitrophenylhydrazone) and 4-oxo-2-penten-1,5-dioic acid 2,4-dinitrophenylhydrazone are isolated in the presence of 2,4-dinitrophenylhydrazine. Methyl 5-nitrofuran-2-carboxylate is formed by treatment of methyl 5-nitro-2-acetoxy-2,5-dihydrofuran-2-carboxylate with aqueous solutions of acetic or phosphoric acid.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1600–1603, December, 1977.