Biomedical subjects

Vladimir I Baranov

Publications and source records attributed to Vladimir I Baranov.

9 recordsLinked to original sources

PubMed2006

Study of the enhancement of dipolar resonant excitation by linear ion trap simulations.

Resolution improvements in dipolar resonant excitation have been examined in a round-rod quadrupolar collision cell for values of the Mathieu characteristic exponent beta equal to n/p, where n and m are small integers (prime beta values) versus other beta values where n and p are not small (ordinary beta values). The trajectories of ions moving in the time-varying electric fields of a quadrupole with and without buffer-gas molecules were calculated to determine the relationship of prime and ordinary beta values to frequency resolution for resonant ion excitation and ejection. For prime beta values, the ion trajectory in the hyperbolic quadrupole field will be exactly periodic with a period of at most 4 pi p/Omega, where Omega is the angular frequency of the main drive radio-frequency (RF) potential. Ion trajectory simulations with prime beta versus ordinary beta values show that the motion of ions with prime beta values have simpler trajectories of shorter periods. Frequency response profiles (FRPs) for round-rod quadrupoles at zero pressure show that dipolar resonant excitations with prime beta values exhibit significantly narrower bandwidths than those with ordinary beta values. Simulations show that at 0.05 to 0.8 mTorr of nitrogen, it is possible to reduce the FRP bandwidth by 20% (measured at 50% depth).

Journal Article↗

PubMed2006

Clustering of pentacene and functionalized pentacene ions in a matrix-assisted laser desorption/ionization orthogonal TOF mass spectrometer.

A high-performance orthogonal time-of flight (TOF) mass spectrometer, in combination with the matrix assisted laser desorption/ionization (MALDI) source operating at elevated pressure ( approximately 1 torr in N(2)), was used to perform MALDI-TOF analyses of pentacene and some of its derivatives with and without an added matrix. These molecules are among the most interesting semiconductor materials for organic thin film transistor applications (OTFT). The observation of ion-molecule reactions between "cold" analyte ions and neutral analyte molecules in the gas phase has provided some insight into the mechanism of pentacene cluster formation and its functionalized derivatives. Furthermore, some of the matrices employed to assist the desorption/ionization process of these compounds were observed to influence the outcome via ion-molecule reactions of analyte ions and matrix molecules in the gas phase. The stability and reactivity of the compounds and their clusters in the MALDI plume during gas-phase expansion were evaluated; possible structures of the resulting clusters are discussed. The MALDI-TOF technique was also helpful in distinguishing between two isomeric forms of bis-[(triisopropylsilyl)-ethynyl]-pentacene.

Journal Article↗

PubMed2005

The high-pressure segmented quadrupole collision cell (HP-SQCC) as an ion molecule reactor.

A high-pressure 20-segment quadrupole collision cell (HP-SQCC), which replaces a collision cell in a modified triple-quadrupole mass spectrometer is investigated in this work as an ion-molecule reactor with an inherent heat source. The highest working pressure achievable is 20 mTorr. The 20 quadrupole segments permit superimposition of linear axial electric field over the conventional quadrupole field in the radial direction. The axial and radial fields are employed to control ion temperature. Heat is transferred to the reactants through ion frictional heating. The HP-SQCC utilizes a combination of several physicochemical phenomena and an attempt is made to examine a range of ion-molecule reactions. Due to a sufficiently large number of reactive collisions, the reactor is used to promote sequential exothermic ion-molecule reactions. To characterize the performance of the HP-SQCC, the various ion-molecule reactions between the fragment ions of ferrocene (Cp(2)Fe), cobaltocene (Cp(2)Co) and nitrogen, oxygen, water and carbon monoxide are investigated.

Journal Article↗

PubMed2004

Chemical resolution of Pu+ from U+ and Am+ using a band-pass reaction cell inductively coupled plasma mass spectrometer.

Determination of the concentration and distribution of the Pu and Am isotopes is hindered by the isobaric overlaps between the elements themselves and U, generally requiring time-consuming chemical separation of the elements. A method is described in which chemical resolution of the elemental ions is obtained through ion-molecule reactions in a reaction cell of an ICPMS instrument. The reactions of "natural" U(+), (242)Pu(+), and (243)Am(+) with ethylene, carbon dioxide, and nitric oxide are reported. Since the net sensitivities to the isotopes of an element are similar, chemical resolution is inferred when one isobaric element reacts rapidly with a given gas and the isobar (or in this instance surrogate isotope) is unreactive or slowly reactive. Chemical resolution of the m/z 238 isotopes of U and Pu can be obtained using ethylene as a reaction gas, but little improvement in the resolution of the m/z 239 isobars is obtained. However, high efficiency of reaction of U(+) and UH(+) with CO(2), and nonreaction of Pu(+), allows the sub-ppt determination of (239)Pu, (240)Pu, and (242)Pu (single ppt for (238)Pu) in the presence of 7 orders of magnitude excess U matrix without prior chemical separation. Similarly, oxidation of Pu(+) by NO, and nonreaction of Am(+), permit chemical resolution of the isobars of Pu and Am over 2-3 orders of magnitude relative concentration. The method provides the potential for analysis of the actinides with reduced sample matrix separation.

Journal Article↗

PubMed2003

Analytical approach for description of ion motion in quadrupole mass spectrometer.

Implementation of the analytical method of the solution of the Mathieu equation in conjunction with the algebraic presentation of Mathieu functions is discussed in this work. This approach is used for the analytical expression of fundamental properties of the quadrupole field such as ion trajectory stability and transmission. Extensive comparison with the matrix method is presented with demonstration of the fundamental advantages of the analytical method. However, contrary to the matrix method, the analytical method is limited to the cos trapping waveforms.

Energy Transfer↗

PubMed2003

Particle discriminator interface for nanoflow ESI-MS.

An atmosphere to vacuum interface was designed to exploit the different mobility and momentum characteristics of ions, and charged and neutral particles in electrospray ionization-mass spectrometry. The purpose of this device is to transmit with high efficiency the ions created at atmospheric pressure into the mass analyzer and to deflect the large charged and neutral particles prior to entrance into the vacuum system, thereby maintaining system cleanliness and stability. This interface is particularly suitable for low flow rate electrospray ionization-mass spectrometry where the close proximity of the electrospray emitters to the vacuum entrance, and near total consumption of the entire spray, leads to the production of large quantities of non-desolvated droplets and large charged and neutral particles. The improvement involves the application of potential gradients to a particle discriminator space located between the gas restricting ion entrance orifice of the mass spectrometer and the exit of a heated laminar flow chamber to divert large particles from the gas conductance limiting orifice. A counter-current flow of drying gas is used to deflect neutral particles and solvent vapor. Two stages of desolvation are achieved with the combined effects of the curtain gas and heated laminar flow chamber. This enhances the efficiency of desolvation and ion production, and stabilizes the resulting ion current under a wide variety of solvent compositions. In addition, this system eliminates the problems associated with the boiling of solution in nanospray tips when operated in close proximity to a heated mass spectrometer inlet. The particle discriminator interface gives approximately a 2-fold improvement in ion count rates, and a 3-fold improvement in stability (as measured by the signal relative standard deviation).

Algorithms↗

PubMed2002

Detection of ultratrace phosphorus and sulfur by quadrupole ICPMS with dynamic reaction cell.

A method of detection of ultratrace phosphorus and sulfur that uses reaction with O2 in a dynamic reaction cell (DRC) to oxidize S+ and P+ to allow their detection as SO+ and PO+ is described. The method reduces the effect of polyatomic isobaric interferences at m/z = 31 and 32 by detecting P+ and S+ as the product oxide ions that are less interfered. Use of an axial field in the DRC improves transmission of the product oxide ions 4-6 times. With no axial field, detection limits (3sigma, 5-s integration) of 0.20 and 0.52 ng/mL, with background equivalent concentrations of 0.53 and 4.8 ng/mL, respectively, are achieved. At an optimum axial field potential (200 V), the detection limits are 0.06 ng/mL for P and 0.2 ng/mL for S, respectively. The method is used for determining the degree of phosphorylation of beta-casein, and regular and dephosphorylated alpha-caseins at 10-1000 fmol/microL concentration, with 5-10% v/v organic sample matrix (acetonitrile, formic acid, ammonium bicarbonate). The measured degree of phosphorylation for beta-casein (4.9 phosphorus atoms/molecule) and regular alpha-casein (8.8 phoshorus atoms/molecule) are in good agreement with the structural data for the proteins. The P/S ratio for regular alpha-casein (1.58) is in good agreement with the ratio of the number of phosphorylation sites to the number of sulfur-containing amino acid residues cysteine and methionine. The P/S ratio for commercially available dephosphorylated alpha-casein is measured at 0.41 (approximately 26% residual phosphate).

Caseins↗

PubMed2002

A sensitive and quantitative element-tagged immunoassay with ICPMS detection.

We report a set of novel immunoassays in which proteins of interest can be detected using specific element-tagged antibodies. These immunoassays are directly coupled with an inductively coupled plasma mass spectrometer (ICPMS) to quantify the elemental (in this work, metal) component of the reacted tagged antibodies. It is demonstrated that these methods can detect levels of target proteins as low as 0.1-0.5 ng/mL and yield a linear response to protein concentration over 3 orders of magnitude.

Animals↗

PubMed2002

Inductively coupled plasma mass spectrometer with axial field in a quadrupole reaction cell.

A novel reaction cell for ICP-MS with an electric field provided inside the quadrupole along its axis is described. The field is implemented via a DC bias applied to additional auxiliary electrodes inserted between the rods of the quadrupole. The field reduces the settling time of the pressurized quadrupole when its mass bandpass is dynamically tuned. It also improves the transmission of analyte ions. It is shown that for the pressurized cell with the field activated, the recovery time for a change in quadrupole operating parameters is reduced to <4 ms, which allows fast tuning of the mass bandpass in concert with and at the speed of the analyzing quadrupole. When the cell is operated with ammonia, the field reduces ion-ammonia cluster formation, further enhancing the transmission of atomic ions that have a high cluster formation rate. Ni x (NH3)n+ cluster formation in a cell operated with a wide bandpass (i.e., Ni+ precursors are stable in the cell) is shown to be dependent on the axial field strength. Clusters at n = 2-4 can be suppressed by 9, 1200, and >610 times, respectively. The use of a retarding axial field for in-situ energy discrimination against cluster and polyatomic ions is shown. When the cell is pressurized with O2 for suppression of 129Xe+, the formation of 127IH2+ by reactions with gas impurities limits the detection of 129I to isotopic abundance of approximately 10(-6). In-cell energy discrimination against 127IH2+ utilizing a retarding axial field is shown to reduce the abundance of the background at m/z = 129 to ca. 3 x 10(-8) of the 127I+ signal. In-cell energy discrimination against 127IH2+ is shown to cause less I+ loss than a post-cell potential energy barrier for the same degree of 127IH2+ suppression.

Journal Article↗