A specialized isotope mass spectrometer for determining the isotopic ratio of lithium by ERIAD (electrospray with atomization in an ion source) is described. The device uses a Mattuha-Herzog-type mass analyzer with double focusing to use ion beams with a large spread in energy and simultaneous registration of signals of both lithium isotopes (6Li and 7Li), and a two-channel receiver based on a doublet of microchannel plates. The gas-dynamic interface is built according to the Kontorowitz-Gray scheme; from the gas-dynamic point of view, it is "long", that is, the distance between the nozzle and the skimmer is 4 times the size of the "Mach barrel" at the operating pressure (200 Pa). The device is desktop, its weight does not exceed 20 kg. The measurement time is 1000 s, sample replacement time is 100 s, measurement accuracy is ~ 0.1%. Keywords: mass spectrometry, electrospray, ion source, isotopes of lithium.

We developed a specialized mass-spectrometer for measuring the lithium isotopic ratio using electrospray ionization with controlled in-source fragmentation and atomization (in-source atomization, ERIAD). We used a Mattauch–Herzog double-focusing mass analyzer suspended under accelerating voltage; this makes its coupling with the gas-dynamic interface much easier. The mass analyzer is optimized up to the second degree; it can operate with ion beams with a broad energy spread, typical for ERIAD. Both isotopes, 6 Li and 7 Li, are detected simultaneously by a two-channel microchannel plate detector. The gas-dynamic interface is of the Kontorovitz–Gray type; it is gas-dynamically “long”: the nozzle-skimmer distance is four times longer than the Mach barrel at the operation pressure (200 Pa). The instrument is a desktop; it weighs approximately 20 kg. It is suitable for rapid analysis: one run takes 1000 s, and sample replacement takes only 100 s. The measurement precision in a series of 11 LiCl conventional measurements was 0.3%.

Описан специализированный изотопный масс-спектрометр для определения изотопного отношения лития методом ЭРИАД (электрораспыление с атомизацией в источнике ионов). В приборе используются масс-анализатор типа Маттауха-Герцога с двойной фокусировкой для использования пучков ионов с большим разбросом по энергии и одновременной регистрации сигналов обоих изотопов лития (6Li и 7Li) и двухканальный приемник на основе дублета микроканальных пластин. Газодинамический интерфейс построен по схеме Конторовица-Грея (с газодинамической точки зрения он "длинный", т. е. расстояние между соплом и скиммером в 4 раза превышает размер "бочки Маха" при рабочем давлении 200 Pa). Прибор настольный, его вес не превышает 20 kg. Время измерения 1000 s, время замены пробы 100 s, точность измерения содержания изотопа 7Li~ 0.1%. Ключевые слова: масс-спектрометрия, электрораспыление, источник ионов, изотопы лития.

The significance of the problem of determining the concentration of beryllium in solutions is substantiated. A method of ERIAD mass-spectrometry (atmospheric pressure electrospray with in-source atomization) is compared with a number of other common procedures used for solving the aforementioned problem and a number of advantages of ERIAD mass-spectrometry are highlighted. The possibility of measuring the beryllium concentration in various chemical forms (sulfate, nitric acid and chloride salts) using ERIAD mass-spectrometry is studied. The layout and the principle of operation of a small-size mass spectrometer MI-20 Low Mass (MS-Bio, Russia), which is intended for the determination of beryllium in solutions, are described. A method is proposed for the preparation of a beryllium salt solution using a lithium salt as an internal standard. The resolution of the instrument made it possible to separate lithium isotopes (6Li and 7Li). It is shown that beryllium can be detected from the salts of chloride and nitric acids with close relative sensitivity coefficients. The obtained detection limit for beryllium chloride in those measurements was ~1–2 × 10–8 M. At the same time, the analytical signal of beryllium cannot be detected during electrospray of the solution of beryllium sulfate under any experimental conditions. It has been suggested that this effect may be attributed to the features of dissolution of beryllium sulfate, in particular, to hydrolysis and formation of complex compounds with sulfate, including complex polymer and colloidal forms.

The significance of the problem of determining the concentration of beryllium in solutions is substantiated. A method of APESI mass-spectrometry (atmospheric pressure electrospray ionization with in-source atomization) is compared with a number of other common procedures used for solving the aforementioned problem and a number of advantages of APESI mass spectrometry are highlighted. The possibility of measuring the beryllium concentration in various chemical forms using APESI mass-spectrometry is studied. We used sulfate, nitric acid and chloride salts of beryllium. The measurements were carried out on a specialized small-sized mass spectrometer MI-20 «LowMass» developed at MS-Bio Company, Russia. A schematic diagram of the device designed to determine the concentration of beryllium in solutions is presented and described. A technique of solution preparation and measurement procedure are proposed. Presented ass spectra obtained on the samples containing beryllium and lithium isotopes were used as an internal standard. It is shown that beryllium can be detected from the salts of chloride and nitric acids with close relative sensitivity coefficients. The obtained detection limit for beryllium chloride in those measurements was ~1 – 2 × 10–8 M. At the same time, the analytical signal of beryllium cannot be detected during electrospray of the solution of beryllium sulfate under any experimental conditions. It has been suggested that this effect may be attributed to the features of dissolution of beryllium sulfate, in particular, to hydrolysis and formation of complex compounds with sulfate, including complex polymer and colloidal forms.

For the first time, electron-stimulated desorption (ESD) of K atoms from the K layer adsorbed on W covered with an Au film was detected and recorded, and the ESD yield was measured by a direct method depending on the electron energy, concentration K, and the thickness of the Au film. A model is proposed that explains the processes of ESD of potassium atoms from the surface.

Carbon C + ions formed in a mass-spectrometric electrospray source with controlled in-source fragmentation and atomization interface have been observed for the first time. The measurements were performed in a special MI-20 LowMass mass spectrometer (MS-Bio LLC) using aqueous methanol solutions of lithium and beryllium salts. The peak of C + ions was substantially broadened as compared to the peaks of metal ions. A model is proposed that explains the formation of C + ions due to charge exchange immediately at the high-vacuum boundary near the skimmer output.

AbstractThe transport of charged particles generated during electrospray in a longitudinal gasdynamic field has been studied in a model system comprising two coaxial electrodes and a collector grid. The process has been numerically simulated with omission of the role of a space charge. A comparison of the results shows that the space charge is a key factor determining the transport of charged particles: the model transport efficiency in the absence of space charge reaches 80–100%. In experiment, the efficiency strongly depends on the space charge and amounts to 70–80% for its minimum values, while decreasing to 20–30% with increasing electrospray current.

AbstractCarbon C^+ ions formed in a mass-spectrometric electrospray source with controlled in-source fragmentation and atomization interface have been observed for the first time. The measurements were performed in a special MI-20 LowMass mass spectrometer (MS-Bio LLC) using aqueous methanol solutions of lithium and beryllium salts. The peak of C^+ ions was substantially broadened as compared to the peaks of metal ions. A model is proposed that explains the formation of C^+ ions due to charge exchange immediately at the high-vacuum boundary near the skimmer output.

The paper discusses some peculiarities of the design and development of scientific equipment, particularly mass spectrometers, which provide implementation of high standard scientific and technological analytical testing methods.

The transport of charged particles generated during electrospray in a longitudinal gasdynamic field has been studied in a model system comprising two coaxial electrodes and a collector grid. The process has been numerically simulated with omission of the role of a space charge. A comparison of the results shows that the space charge is a key factor determining the transport of charged particles: the model transport efficiency in the absence of space charge reaches 80–100%. In experiment, the efficiency strongly depends on the space charge and amounts to 70–80% for its minimum values, while decreasing to 20–30% with increasing electrospray current.

AbstractWays to reduce ion beam intensity losses in a mass spectrometric ion source, which are caused by chromatic aberration of its immersion ion-optical system, are considered. These losses are rather significant in forming a beam from ions with a large energy spread. The reduction of aberration losses is especially important when ion sources are used jointly with mass analyzers with energy focusing. It is shown that these losses can be reduced significantly by using a new type of ion-optical system of the ion source, which includes achromatic elements. A special method for calculating such elements is given. Computer simulations have shown high efficiency of such elements in the ion-optical path of ion sources of mass spectrometers.

Ways to reduce ion beam intensity losses in a mass spectrometric ion source, which are caused by chromatic aberration of its immersion ion-optical system, are considered. These losses are rather significant in forming a beam from ions with a large energy spread. The reduction of aberration losses is especially important when ion sources are used jointly with mass analyzers with energy focusing. It is shown that these losses can be reduced significantly by using a new type of ion-optical system of the ion source, which includes achromatic elements. A special method for calculating such elements is given. Computer simulations have shown high efficiency of such elements in the ion-optical path of ion sources of mass spectrometers.

A model of a gas-dynamic interface with a high-vacuum ion-pulling system has been developed. The main part of the ion source is the ERIAD electrospray with in-source atomization (ion extraction from solution elements at atmospheric pressure), owing to which it is possible to measure concentrations of elements that are capable of being cations in a solution. The interface is constructed according to the Kontrovitsa–Gray type with a slight misalignment of the inlet and outlet. From the gas-dynamic point of view, the interface is “long,” since its length is several times longer than the resulting “Mach barrel.” Tests have shown that the interface circuit allows application of a voltage as high as 800 V between the nozzle and the skimmer, thus providing atomization of elements of not only the first, but also the second group of elements of the periodic system. The developed interface model can be used as a prototype for upgrading dual-focusing mass spectrometers for future elemental measurements.

Поступило в Редакцию 27 декабря 2017 г

Fragment analysis of DNA by the capillary gel-electrophoresis method is an effective tool for studying the DNA structure, which has a large number of applications (in particular, for genetic expertise of breeds and breed samples of a number of important crops). Fragment analysis of DNA is carried out in several stages. The stage of processing of the results of investigations includes the procedure of detection of peaks for standard DNA fragments. We list the features of the spectrum of the DNA fragment distribution, which necessitate the development of a new method for detecting peaks of a standard. We propose a method for their search based on comparison of the aggregate of standard lengths of DNA fragments and spectral peaks and describe the algorithm for implementing this method. We also consider in detail the critical stage of the algorithm, i.e., the choice of the threshold for the procedure of detection of peaks in the spectrum. The advantages and disadvantages of the method are enumerated and the results of testing are considered.

Проведено экспериментальное изучение распределения тока электрораспыления, генерируемого в системе с двумя противоэлектродами. Показано, что при малых значениях общего тока его распределение между электродами пропорционально потоку электрического поля, приходящегося на данный электрод. С ростом тока электрораспыления эта пропорциональность нарушается в направлении более равномерного распределения, видимо, вследствие роста роли объемного заряда, расталкивающего заряженные частицы. DOI: 10.21883/PJTF.2017.10.44624.16641

We have experimentally studied the distribution of current in an electrospray system with two counter-electrodes. It is established that, at low values of the total current, its distribution between these electrodes is proportional to the electric field flux to a given electrode. As the total current grows, this proportionality changes toward more uniform distribution, probably, due to increased role of a space charge producing mutual repulsion of charged particles.