I. S. Pytskii

MALDI/SELDI mass-spectrometric surface investigation of AMg-6 and Ad-0 materials

Matrix-assisted and surface-enhanced laser desorption/ionization mass-spectrometry is carried out in order to investigate the surfaces of structural materials using marker substances. The method is shown to provide estimates of the surface heterogeneity and can be used for the quantitative comparison of the heterogeneity of different surfaces. In the domains where homogeneity is distorted, a larger amount of the marker substance is observed. Properly selected marker substances and the high sensitivity of mass-spectrometry make it possible to use the method for the express estimation of the surface heterogeneity.

Laser desorption/ionization mass-spectrometric study of surface chemistry of Ad-0 and AMg-6 alloys

Ad-0 and AMg-6 alloy surfaces are studied using matrix-enhanced laser desorption/ionization mass spectrometry. Inorganic salts, namely, nickel chloride and silver halides, which form cluster ions at the ionization, were taken as test molecules. Mass spectra revealed a principal difference between the desorption/ionization mechanisms depending on the surface kind and its prehistory. Qualitative and quantitative investigation of the mass spectra led to certain suppositions about the photoionization mechanisms of the cluster structures of inorganic nickel and silver salts. It is shown that, on the studied surfaces, parameters that characterize the surface chemistry can be estimated based on the mass spectra of the salts.

Chromatographic and mass-spectrometric study of the surfaces of construction materials after contact with 1,1-dimethylhydrazine

The products of conversion of 1,1-dimethylhydrazine after contact with the surface of AMg-6 alloy, which is a model of construction materials that contact with rocket fuel components, were characterized by use of chromatographic and mass-spectrometric methods. Alkyl phthalates, the homologues of triphenyl phosphate, and numerous polymer-homologues related to acetone condensation products were detected in acetone extracts taken from the test surfaces. The presence of such products makes it possible to identify fuel components that contacted with the construction materials; this is important for the utilization of the detachable parts of launch vehicles.

Application of contact angle analysis and surface-assisted laser desorption/ionization mass spectrometry to studying the surface state of AMg-6 and Ad-0 aluminum alloys

Surface- and matrix-assisted laser desorption/ionization mass spectrometry and analysis of contact angles have been employed to examine the surfaces of structural materials (Ad-0 and AMg-6 aluminum alloys). The combination of methods used has been shown to enable one to compare the degrees of nonuniformity of different surfaces and determine the effect of the chemical composition of surface impurities on surface properties. Owing to the high sensitivity and informativity, the proposed combination of the methods can be used to determine the nonuniformity of surfaces subjected to the action of rocket fuel components.

Application of mass spectrometry with laser desorption/ionization for studies of lead clusters on surfaces of different types

Ionization of model compounds is studied using the example of lead halides with the method of mass spectrometry with surface-activated laser desorption/ionization (SALDI) on surfaces of different types. Clusters of lead halides are determined in a wide range of masses, up to 2 kDa. The dependence of ionization on the concentration, support type, and method of application of model samples is shown. The surface of a fragment of the combustion chamber of a liquid rocket engine is studied using the method of SALDI mass spectrometry. Lead and oxides and chlorides thereof are detected on the surface of a combustion-chamber fragment. It is suggested that peeling of a nickel coating may be caused by the presence of lead clusters at the nickel-bronze interface.

Evaluation of the chemical risk factor of ultrahigh-molecular-weight polyethylene and hydroxyapatite used in endoprosthetic replacement

The concentration of chemical compounds migrating from ultrahigh-molecular-weight polyethylene powders of various molecular weights and hydroxyapatite powders processed by different methods, suggested for use in the endoprosthetic replacement, is identified and determined using integrated gas chromatography mass spectrometry and elemental analysis techniques. It is established that the values of integral parameters, as well as the concentration levels of identified products of migration, do not exceed the permissible levels. Optimum samples are recommended for application in endoprosthetic replacement.

Surface-assisted laser desorption/ionization mass spectrometry for the detection of low-molecular-weight and oligomeric products of 1,1-dimethylhydrazine transformation on the surfaces of construction materials

Surface-assisted laser desorption/ionization mass spectrometry (SALDI) was applied to study the products of 1,1-dimethylhydrazine transformation on the surfaces of construction materials. The approach proposed makes it possible to distinguish the transformation products of 1,1-dimethylhydrazine from the low-molecular-weight compounds and oligomers utilized in the production of construction materials, which undergo different transformations in the course of operational processes.

Methodological features of mass-spectrometric studies of oxidized metal surfaces

Clustering of silver halides under the conditions of photoionization has previously been studied by laser desorption/ionization mass spectrometry. Some features of desorption/ionization of silver halides from different metal surfaces (stainless steel and different partially oxidized aluminum alloys) are discussed in this study. The data on the m/z values determination accuracy, resolving power, ionization efficiency, and distortion of isotope distribution in the studies of oxidized surfaces are statistically generalized. It is shown that the results can be used to gain insight into the chemical nature and morphology of examined surfaces and, in particular, to plot diagrams for distribution of analyzed compounds over the surfaces.

Mass Spectrometry Detection of Nitrobenzoic Acids and Their Salts on the Surface of Construction Materials

The application of mass spectrometry to the detection of m-nitrobenzoic and 3,5-dinitrobenzoic acids and their salts on the surface of construction materials used in rocketry is described. Analytes are washed with acetonitrile from the studied surface and then analyzed by HPLC−MS with electrospray ionization or the matrix assisted laser desorption/ionization (MALDI). For electrospray ionization, the limit of detection is 6 μg/L and for MALDI ionization, 2 μg/L. The MALDI technique also ensures the direct investigation of samples without washing out; in this case, mass spectra can be visualized by constructing 2D diagrams of the distribution of nitrobenzoic acids over the surface.

Inorganic and Organic Clusters Formed upon Surface-Assisted Laser Desorption/Ionization

Examples of cluster formation from inorganic and organic compounds upon surface-assisted laser desorption/ionization have been considered. It has been shown that the cluster formation is especially efficient upon ionization of silver halides. The addition of silver salts to salts of other metals, in particular, lead and nickel salts and sodium stannate, leads to the formation of mixed clusters. The peak intensities of the ions of such clusters are higher than those of the clusters of initial salts, thereby indicating a higher efficiency of their formation. Nonpolar amino acids and short-chain peptides predominantly form adducts with alkali-metal ions.