When released to the environment, the rocket fuel unsymmetrical dimethylhydrazine (UDMH) undergoes oxidative transformations, resulting in the formation of an extremely large number of nitrogen-containing transformation products, including isomeric compounds which are difficult to discriminate by common chromatography techniques. In the present work, supercritical fluid chromatography–tandem mass spectrometry (SFC-MS/MS) was proposed for resolving the problem of fast separation and simultaneous quantification of 1-formyl-2,2-dimethylhydrazine (FADMH) as one of the major UDMH transformation products, and its isomers—1,1-dimethylurea (UDMU) and 1,2-dimethylurea (SDMU). 2-Ethylpyridine stationary phase provided baseline separation of analytes in 1.5 min without the distortion of the chromatographic peaks. Optimization of SFC separation and MS/MS detection conditions allowed for the development of rapid, sensitive, and “green” method for the simultaneous determination of FADMH, UDMU, and SDMU in environmental samples with LOQs of 1–10 µg L⁻¹ and linear range covering three orders of magnitude. The method was validated and successfully tested on the real extracts of peaty and sandy soils polluted with rocket fuel and UDMH oxidation products. It was shown that both UDMU and SDMU are formed in noticeable amounts during UDMH oxidation. Despite relatively low toxicity, UDMU can be considered one of the major UDMH transformation products and a potential marker of soil pollution with toxic rocket fuel.

Supercritical fluid chromatography (SFC) is a promising alternative to conventional chromatographic methods and has several advantages over them in selectivity, efficiency, speed of separation, and environmental friendliness. Its combination with atmospheric pressure chemical ionization (APCI) mass spectrometric detection is one of the central areas of method development and requires an understanding of the APCI specificity in using carbon dioxide-based mobile phases. In the present study, the composition of negatively charged ions formed under APCI conditions for carbon dioxide–organic modifier (methanol, isopropanol, acetonitrile) systems, and also the influence of the mobile phase and ion source parameters (corona discharge needle voltage, temperature) on it are studied using high-resolution mass spectrometry. The results obtained testify to a significant role of carbon dioxide as a direct precursor for the formation of reaction particles (hydrocarbonate and percarbonate anions, carbonate radical anion) and as a reagent capable of shifting the ion-molecular equilibrium in corona discharge plasma and forming compounds with the organic modifier (alkylcarbonic acid anions in the case of alcohols, adduct with a deprotonated acetonitrile molecule). Ion-molecular equilibria involving carbon dioxide result in the formation of a large number of reactive particles that can take part in the ionization processes of analytes in SFC–APCI-MS.

Nitrogen-containing heterocyclic compounds (NHCs) are common environmental pollutants that need to be monitored due to their high toxicity. Typically, gas or liquid chromatography combined with mass spectrometric detection is used for this task. However, many NHCs are highly polar compounds, which can cause difficulties when using these methods. On the other hand, supercritical fluid chromatography is well-established in the analysis of polar compounds and could provide an alternative to conventional techniques. The presented work proposes an approach to the simultaneous determination of 20 NHCs in soils by supercritical fluid chromatography–tandem mass spectrometry with the limits of quantification in the range 0.08–1.23 mg kg⁻¹. The separation is carried out in gradient mode on a cyanopropyl stationary phase in 6 min. The approach was validated and tested on real objects—peat and sandy soils contaminated with rocket fuel transformation products.

Supercritical fluid chromatography with mass spectrometric detection (SFC–MS) represents a rapidly evolving analytical method that offers an alternative to conventional mass spectrometric chromatography techniques. This approach boasts notable advantages, such as high efficiency, flexibility, rapidity, and environmental friendliness. One field of development within this methodology involves the integration of various ionization techniques, notably atmospheric pressure photochemical ionization (APPI). In this study, the component composition of negatively charged ions generated under APPI conditions for the systems carbon dioxide–organic modifier (methanol, isopropanol, acetonitrile)–dopant (toluene, acetonitrile, anisole) was studied. The impact of mobile phase composition and ion source temperature on the generated ions was explored. The results obtained demonstrate the pivotal role of carbon dioxide as both a direct precursor of the formation of reactive particles (including carbonate radical anions, hydrocarbonate and percarbonate anions) and a reagent capable of forming compounds with the organic modifier (resulting in alkyl alcohol anions for alcohols and adducts with deprotonated acetonitrile molecules) and the dopant (yielding acetoacetic acid in the case of acetone). As a result, a plethora of reactive particles capable of participating in the ionization processes of analytes in SFC-APPI–MS was observed.

Сверхкритическая флюидная хроматография с масс-спектрометрическим детектированием (СФХ-МС) – быстро развивающийся метод анализа, выступающий в качестве альтернативы традиционным хроматомасс-спектрометрическим техникам. К его достоинствам можно отнести высокую эффективность, универсальность, экспрессность и экологичность. Одним из направлений развития этого метода является сопряжение с различными техниками ионизации, в частности – фотохимической ионизации при атмосферном давлении (ФИАД). В настоящем исследовании изучен компонентный состав отрицательно заряженных ионов, образующихся в условиях ФИАД для систем диоксид углерода – органический модификатор (метанол, изопропанол, ацетонитрил) – допант (толуол, ацетонитрил, анизол), влияние на него состава подвижной фазы и температуры ионного источника. Полученные результаты свидетельствуют о значительной роли диоксида углерода как непосредственного предшественника для образования реакционных частиц (карбонат-ион-радикал, гидрокарбонат- и перкарбонат-анионы), а также как реагента, способного образовывать соединения с органическим модификатором (анионы алкилугольных кислот в случае спиртов, аддукт с депротонированной молекулой ацетонитрила) и допантом (ацетоуксусная кислота в случае ацетона). В результате наблюдается большое количество реакционноспособных частиц, способных принимать участие в процессах ионизации аналитов в СФХ-ФИАД-МС.