Selection of Conditions for the Dynamic Sorption Preconcentration of a 1,1-Dimethylhydrazine Derivative (4-Nitrobenzaldehyde N,N-Dimethylhydrazone) on Hydrophobized Silica

The type of mass transfer in the sorption of 4-nitrobenzaldehyde N,N-dimethylhydrazone (BDH) on silica chemically modified with hexadecyl groups was determined using the linear model of sorption dynamics, and distribution and mass transfer coefficients of hydrazone were calculated. Optimal conditions of the dynamic sorption preconcentration and desorption of BDH and its subsequent determination by reversed-phase high-performance liquid chromatography were proposed. The detection limit of the compound for preconcentration from a sample of 100 mL was 1 g/L.     

A sensitive chromatographic determination of hydrazines by naphthalene-2,3-dialdehyde derivatization

A new high-performance liquid chromatography (HPLC) method for the sensitive simultaneous determination of hydrazine (Hy), monomethylhydrazine (MMH) and 1,1-dimethylhydrazine (UDMH) based upon the derivatization of hydrazines with naphthalene-2,3-dialdehyde and the separation of the derivatives on Zorbax Eclipse AAA column in a single chromatographic run under acidic conditions (pH 2.4) was developed. Hydrazine and monomethylhydrazine derivatives were found to be strongly fluorescent at λ_ex?=?273?nm, λ_em?=?500?nm. It was shown that UDMH derivative can be detected as non-fluorescent hydrazone at 290?nm by UV-detection. Limits of detection were 0.05?µg?·?L^?1 for Hy and MMH, and 1?µg?·?L^?1 for UDMH for the injection volume of 100?µL. The method was validated for water sample analysis. It proved to be selective, accurate and precise with the supplementary advantage of the simple and rapid sample preparation.     

Transformations of asymmetric dimethylhydrazine in soils

High-performance liquid chromatography and mass spectrometry were used to find that the decomposition of asymmetric dimethylhydrazine (I) in soils occurred with the formation of dimethylamine, formaldehyde dimethylhydrazone, methylhydrazine, trimethylhydrazine, N-nitrosodimethylamine, 1-methyl-1,2,4-triazole, formic acid dimethylhydrazide, 1,5,5-trimethylformazane, 1-methyl-1,6-dihydro-1,2,4,5-tetrazine, N,N-dimethylaminoguanidine, and several other products. High-reliability structure identification was achieved using independent methods, including gas chromatography-mass spectrometry, ¹H and ¹³C NMR, and UV spectroscopy, and by measuring retention times and spectral characteristics after the counter-synthesis of the suggested structures. The products of the decomposition of I potentially capable of forming initial I and characterized by high migration mobility in soils were identified.     

The effect of alkylating agent on the efficiency and selectivity of new polymeric anion exchangers

New anion exchangers for ion chromatography with functional groups of trimethylammonium and 3-chloro-2-hydroxypropyl-N,N-dimethylammonium were obtained. The synthesis included consecutive acetylation of a styrene-divinylbenzene copolymer containing 25% divinylbenzene, reductive amination of carbonyl groups, and subsequent alkylation. Iodomethane and epichlorohydrin were used as alkylating agents. The chromatographic properties of anion exchangers were studied by means of suppressed ion chromatography with conductometric detection. Anion exchangers with the 3-chloro-2-hydroxypropyl-N,N-dimethylammonium group are characterized by better selectivity and higher efficiency for polarizable nitrate and bromide ions, as well as for nonpolarizable chloride, fluoride, nitrite, phosphate, and sulfate ions, compared to those of sorbents with the trimethylammonium group.     

Simultaneous Determination of Hydrazine,Methylhydrazine and 1,1-Dimethylhydrazine in Waters by HPLC with Spectrophotometric Detection Using Catalysis to Obtain Derivatives

Journal of Analytical Chemistry - A simple, rapid, and sensitive method is developed for the simultaneous determination of hydrazine, methylhydrazine, and 1,1-dimethylhydrazine in waters based on...     

Poly(alkyl methacrylate) monolithic columns for HPLC

Several monolithic macroporous polymer sorbents (pore size 1–2 µm) based on alkyl methacrylates and ethylene glycol dimethacrylate as a cross-linking agent were prepared by free radical copolymerization in columns 3×150 mm. The influence of compositions of the reaction mixture and porogens and the nature of the alkyl radical in a mixture of monomers on the hydrodynamic and chromatographic characteristics of the monoliths was studied. The monoliths based on n-butyl methacrylate have rigid macroporous morphology and excellent hydrodynamic characteristics (flow rate up to 5 mL min^?1). The efficiency of separation of a mixture of benzene and its derivatives in the version of reversed-phase HPLC was shown to increase with an increase in the fraction of a lauryl methacrylate additive (LMA) in the reaction mixture. The maximum separation efficiency (number of theoretical plates (tp)) was 35 000 tp m^?1 for the monolith based on n-butyl methacrylate with 7% LMA in the reaction mixture.     

Sorption-chromatographic determination of phosphate and silicate ions in waters as molybdic heteropoly acids

Conditions were found for the group adsorption preconcentration of phosphomolybdic and silicomolybdic heteropoly acids (HPAs) in the dynamic mode on a microcolumn packed with an Amberlite XAD-8 polyacrylate adsorbent. A sorption-chromatographic method for determining phosphate and silicate ions in waters as molybdic HPAs is developed. It is based on the adsorption of HPAs followed by desorption with acetonitrile and determination by reversed-phase HPLC. The detection limits for phosphorus and silicon calculated by the 3s test were 0.5 and 0.1 μg/L, respectively.     

Effect of sample preparation conditions on the determination of the total concentrations of unsymmetrical dimethylhydrazine in soils

It is shown that, for a correct determination of the total concentration of unsymmetrical dimethylhydrazine (UDMH) in soil, it is necessary to consider the simultaneous presence of active products of its transformation, capable of hydrolysis to the parent compound, such as formic acid 1,1-dimethylhydrazide (FADMH). A comparative study is performed of the methods known in the literature for sample preparation to select conditions for the quantitative extraction of UDMH bonded by various mechanisms to organic and mineral fractions of soil, as well as FADMH as one of the most common active transformation products. It is found that the distillation with a 40% NaOH solution with an addition of Na₂S enables the quantitative recovery of UDMH and FADMH from soils of all types and the determination of the maximum concentration of UDMH in the analysis of real samples of contaminated soils, which allows us to recommend this option to determine the total concentration of UDMH.     

Identification of Spillages of Semi-Volatile Hydrocarbon Fuels in Soils by Gas Chromatography–Mass Spectrometry

A possibility of the identification of semi-volatile hydrocarbon fuels in soil samples by studying the distribution of biomarkers of the sesquiterpane class is shown. The extraction of a soil sample with methylene chloride and the subsequent analysis of the extract by gas chromatography–mass spectrometry ensured the detection of these hydrocarbons in RG-1 and T-1 rocket kerosenes, TS-1 aviation kerosene, and diesel fuel. It was found that the distribution of the compounds found is characteristic for each type of fuel and is preserved in their transformations in the soil. The parameters reflecting the distribution of biomarkers and ensuring the identification of the type of fuel at any stage of transformation are proposed.     

1-Formyl-2,2-dimethylhydrazine as a new decomposition product of 1,1-dimethylhydrazine

A new decomposition product of 1,1-dimethylhydrazine (UDMH), 1-formyl-2,2-dimethylhydrazine (FDMH), was found in water and soil samples. The formation of FDMH was confirmed by LC-MS and NMR studies. The possibility of FDMH conversion to initial UDMH by alkaline hydrolysis was shown.