Метод ионизации, индуцированной лазерной плазмой при атмосферном давлении, исследован для решения задачи классификации чая по запаху без пробоподготовки. Изучены образцы листового чая, относящиеся к девяти различным товарным наименованиям. Полученные масс-спектрометрические данные кластеризовали методами хемометрики без детальной покомпонентной интерпретации масс-спектров. Проведено сравнительное исследование шести методов: метода главных компонент, K-средних и иерархической кластеризации (методы «без учителя») и метода опорных векторов, логистической регрессии и нейронная сеть вида многослойный перцептрон (методы с предварительным обучением). Показано, что наиболее эффективным методом классификации образцов чая является логистическая регрессия в сочетании с рекурсивным устранением признаков с кросс-валидацией.

The laser formation of positive and negative ions on a nanostructured metal surface is observed at laser fluence below the plasma formation threshold. The laser radiation energy dependences of the yield of positive and negative Au ions and charged clusters as well as electrons from the laser-induced nanostructures on the surface of gold are obtained at laser fluence below the plasma formation threshold using a pulsed laser with a wavelength of 355 nm and a pulse duration of 0.37 ns. It is shown that the ratio of the signals of positive and negative ions is constant over the entire range of the laser radiation energies, while the ion signal dependence on the laser radiation energy is described by a power function with an exponent of 9. The role of gold nanoparticles with a size of less than 5 nm in the formation of Au ions and charged Au clusters is discussed.

The process of $\text{Au}+$ and $\text{Au}$ -ions formation on a surface of nanostructured gold plate under pulsed laser irradiation with energy density below plasma threshold is studied. The role of nanoscale objects produced on the surface under laser irradiation higher than the plasma threshold in the ion formation process is discussed.

Background: Primary vesicoureteral reflux (VUR) is the most common congenital uropathy (CU) in children, leading to the development of reflux nephropathy and chronic kidney disease, reaching the terminal stage in 25-60% of patients. The insufficient sensitivity of modern methods of instrumental and laboratory diagnostics of the initial stages of renal parenchyma damage dictates the need to develop new non-invasive technologies for screening and monitoring kidney conditions in patients with CU. Aims: To evaluate the possibility of separating groups of healthy children and children with kidney damage with CU using the analysis of the mass spectra of volatile organic compounds (VOCs) in urine samples. Materials and methods: This study involved 42 patients (average age 5.4 + 2.3 years), divided into 2 groups: group 1 24 children with congenital uropathies (grade II-V PMR) and comparison group 2 - 18 patients with minor surgical pathology without pathology of the urinary system. Urine samples were collected before the start of treatment. Composition analysis of VOCs samples was carried out through express-analysis method for biological objects at atmospheric pressure without preliminary preparation using a mass spectrometer with ionization by laser plasma radiation. Urinary levels of markers of inflammation (MCP-1, IL-8, IL-18), angiogenesis (VEGF) and fibrosis (TGF-1) were measured by solid-phase ELISA. Results: Composition changes in urine VOCs were detected in group 1 patients with congenital uropathies (VUR). These changes made it possible to distinguish group 1 samples from the comparison group 2. Creatinine level and glomerular filtration rate (GFR) in both groups had no statistical difference. An increase in concentration of inflammatory markers MCP-1, IL-18, IL-8, VEGF angiogenesis and TGF-1 fibrosis was observed in the urine of children with congenital uropathies (VUR) (p0.001). In group 1 patients the concentration of markers did not correlate with the reflux level. Conclusions: The performed research allowed to find a set of peaks in the recorded mass spectra, according to which it is possible to divide groups into healthy and sick. It also demonstrated the potential of volatolom analysis to detect kidney damage in children with congenital uropathies. The use of standard methods: creatinine and GFR did not allow us to find a threshold value to divide patient into healthy and sick groups. The increase of biomarkers of inflammation, angiogenesis and fibrosis in the urine of children with congenital uropathies confirmed the presence of persistent kidney damage, parenchymal hypoxia, activation of fibrosis and inflammation in children with CU kidneys.

A method of laser mass spectrometric express analysis of volatile organic compounds (VOC) without sample preparation is proposed. VUV radiation of laser plasma is used for VOCs ionization. The method was applied for early diagnostics of kidney damage in children with congenital uropathy.

Trained detection dogs distinguish between urine samples from healthy organisms and organisms with malignant tumors, suggesting that the volatile urine metabolome contains information about tumor progression. The aim of this study was to determine whether the stage of tumor growth affects the chemical differences in the urine of mice and to what extent the "olfactory image of disease" perceived by dogs coincides with the "image of disease" recorded by the mass spectrometer. We used a novel laser ionization mass spectrometry method and propose a mass spectrometric analysis without detailed interpretation of the spectrum of volatile metabolomes in urine. The mass spectrometer we use works without sample preparation and registers volatile organic compounds in air at room temperature without changing the pH of the sample, i.e. under conditions similar to those in which dogs solve the same problem. The experimental cancer models were male BDF-f1 hybrid mice transplanted with hepatocarcinoma tissue, and similar mice transplanted with healthy liver tissue were used as controls. Our data show that both dogs and our proposed laser mass spectrometry method are able to detect both the entire spectrum of volatile organic compounds associated with the disease and minor changes in this spectrum during its course.

A laser plasma ion source was used to ionize volatile organic compounds in a gas sample. The plasma was generated on a metal target in the intermediate vacuum region of ~0.3 Torr using a pulsed Nd:YAG laser with a wavelength of 1 μm. The resulting ions mass spectra were acquired using orthogonal time-of-flight mass spectrometer (O-TOF MS). When using a copper target, the ions formed are simple complexes (CuM+ ) of copper ions with organic molecules. The possibility of online identification of trace amounts of alkanes in nitrogen and air, with a detection limit of ~10 ppb, was demonstrated. The ionization efficiency of volatile organic compounds through the formation of clusters with metal ions is 10-4 in terms of the quasimolecular complex ions. The rate constants of ion-molecular reactions of copper ions with octane and water molecules in nitrogen and air are estimated.

Laser-induced plasma generated by exposing a metal target to pulsed laser radiation with a power density of similar to 70 GW cm(-2) is used to ionize organic compounds in gases at atmospheric pressure. The estimation of the plasma temperature based on the analysis of the plasma emission spectra has shown that in the first few nanoseconds the temperature exceeds 5.5 x 10(4) K. The vacuum ultraviolet radiation of that plasma provides ionization of any organic compounds and water molecules. The main ionization channels of the studied compounds are proton transfer reactions, addition reactions with the formation of [M + NH4](+) and [M + H3O](+) ions and photoionization. Hydrocarbons are ionized by pre-oxidation and subsequent ionization of oxygenated molecules. The optimal surrounding gas for the analysis is pure argon, since the ionization efficiency of organic compounds in argon is up to a hundred times higher than that in atmospheric air and pure nitrogen. (C) 2020 Elsevier B.V. All rights reserved.

Vacuum UV radiation from laser-induced plasma is used to ionise volatile organic compounds (VOCs) released by living organisms during their mass spectrometric analysis at atmospheric pressure without sample preparation. It is shown that the probability of ionisation of organic compounds with different ionisation potentials and proton affinity at atmospheric pressure in the argon flow weakly depends on the compound parameters and can be 3.6 × 10−5 – 1.4 × 10−4. The VOC spectra of mouse and human biological fluids are obtained without sample preparation at room temperature of the sample. The possibility of using the proposed method for the diagnosis of pathological changes is demonstrated.

Pulsed vacuum ultraviolet (VUV) radiation (80–180 nm) emitted by laser plasma produced on a metal target is used in mass spectrometry to ionize volatile organic compounds at atmospheric pressure. The parameters of light emitted by the laser plasma generated by a pulsed Nd:YAG laser radiation at a wavelength of 1064 nm, power density of about 70 GW/cm2, and pulse energy of 250 µJ have been determined using emission spectroscopy. During the first several nanoseconds, the plasma emission spectrum does not contain any pronounced spectral lines and can be described as the emission spectrum of a blackbody with a temperature of 5.5 × 104–105 K (the temperature depends on the ambient gas pressure). This radiation provides ionization of water, oxygen, and nitrogen molecules, as well as argon atoms. It is shown that the mechanisms of ionization of organic compounds under VUV irradiation in argon are based on the reaction of proton transfer from ionized water molecules and reactions of organic compounds with oxygen ions.

Представлены результаты математического моделирования импульсного источника ионов при атмосферном давлении с ионизацией анализируемого вещества УФ излучением лазерной плазмы. Расчеты проводились на основе разработанной авторами математической модели, описывающей эволюцию ансамбля ионов под действием скрещенных газодинамических и электрических полей с учетом эффектов кулоновского взаимодействия. Модель включает в себя систему уравнений Навье-Стокса для описания формирования газодинамических течений в исследуемом объеме, уравнение Пуассона для определения результирующего распределения электрического поля в этом объеме и уравнение Лоренца для построения ионных траекторий ионов от места их рождения до собирающей диафрагмы. Показана сходимость метода релаксации при численном решении основных уравнений модели. Исследована зависимость ионного тока от приложенного напряжения и показано, что учет конечности времени жизни ионов за счет эффекта рекомбинации позволяет получить хорошее согласие между расчетными и экспериментальными данными. Ключевые слова: лазерная плазма, математическое моделирование, ионный источник, газодинамические и электростатические поля, масс-спектрометрия.

A method of rapid mass spectrometric analysis of volatile organic compounds (VOC) of biological samples at atmospheric pressure has been developed. The method uses laser plasma radiation for ionization of VOC molecules. Multivariate statistics was used for the mass spectra analysis. The possibility of identification of progressing oncological process in mice with analyzing the composition of VOCs of the urine samples was showcased.

A pulsed source of ions with ionization of the substance under study at atmospheric pressure by the UV radiation of laser plasma is numerically simulated. The calculations are based on an original mathematical model that describes evolution of an ensemble of ions in the presence of superimposed gas-dynamic and electric fields with allowance for the Coulomb interaction. The model contains a system of the Navier–Stokes equations for gas-dynamic flows in the volume under study, the Poisson equation for the resulting distribution of electric field in such a volume, and the Lorentz equation for construction of ion trajectories from the ionization place to collecting diaphragm. Convergence of the relaxation method is demonstrated for the numerical solution of the main model equations. The dependence of ion current on applied voltage is studied. It is shown that the calculated results are in good agreement with the experimental data when finiteness of the ion lifetime due to recombination effect is taken into account.

Laser desorption of organic compound ions from specially prepared surfaces is known as surface-assisted laser desorption/ionization (SALDI). In this work the properties of a SALDI ion emitter obtained by two-stage laser treatment of crystalline silicon surface have been investigated. The laser surface treatment leads to the formation of a layer with nanoscale objects—quantum dots (QDs) less than 10 nm in size, providing laser desorption of organic compound ions. A change in the desorbing laser wavelength from 351 to 263 nm at comparable laser-exposed spot sizes and fluences results in a sharp decrease in the formation efficiency for MH+ ions and appearance of ions M+ for the same analytes. The effect is apparently determined by the spectral properties of the quantum dots formed on the silicon surface under laser irradiation.

Two new versions of surface-assisted laser desorption/ionization method are considered. One version is based on a combination of this method with thermal desorption sample injection and may be applied for determination of chemical compounds that are transformed into a gas phase without decomposition by heating. Another version is based on laser-induced electron-transfer desorption/ionization and could be used for determination of compounds with low proton affinity. The possibilities of the new approaches are illustrated by the example of determination of aminoacids, medical compounds, chlorophyll, as well as gold in sulfide ores.

Four different substrates, namely, graphite, tungsten, amorphous silicon (α-Si) and titanium dioxide (TiO2) films, were compared in view of the laser-induced electron transfer desorption/ionization (LETDI) of metal coordination complexes. A rhenium complex with 8-mercaptoquinoline, a copper complex with diphenylthiocarbazone and chlorophyll A were studied as the test analytes. The dependencies of the ion yield and the surface temperature on the incident radiation fluence were investigated experimentally and theoretically. The temperature was estimated using the numerical solution of a one-dimensional heat conduction problem with a heat source distributed in time and space. It was found that at the same temperature, the ion yield from the different substrates varies in the range of three orders of magnitude. The direct comparison of all studied substrates revealed that LETDI from the TiO2 and α-Si films offer a better choice for producing molecular ions of metal coordination complexes.

The atmospheric pressure mass spectrometric detection efficiency of organic species (tofisopam and verapamil) was measured by means of the laser ablation of dried solution drops containing known amount of the analyte. Ablated molecules were ionized by an atmospheric pressure laser plasma cell and then introduced in the TOF mass-spectrometer. The spot was formed by dripping 2 mu l of solution on the stainless steel substrate and consequent drying. Then it was scanned by an intense ablating beam of various lasers (CO2, Nd:YAG and femtosecond fiber laser) until the spot was completely eroded during the non-stop MS-analysis of ablated material. The sensitivity was defined as the ratio of the total ion current integral of the relevant mass peaks to the amount of molecules in the spot. All the tested lasers are suitable for the ablation and subsequent MS-detection of organic species in dried solution spots given enough power deposition is provided. The measured sensitivity values reach 0.1 ions/fg of tested analytes.

A new method was developed for the mass spectrometric analysis of organic and bioorganic compounds, which involves laser ablation with the ionisation of its products by laser-plasma radiation and enables analysing gaseous, liquid, and solid substances at atmospheric pressure without sample preparation. The capabilities of this method were demonstrated by the examples of fast pharmaceutical composition screening, real-time atmosphere composition analysis, and construction of the mass spectrometric images of organic compound distributions in biological materials.