Atmospheric pressure (AP) liquid matrices for ultraviolet (UV) matrix-assisted laser desorption/ionization (MALDI) are presented. Doping a known organic chromophore, alpha-cyano-4-hydroxycinnamic acid (CHCA), into liquid media yielded a homogenous sample system with simplified sample preparation, increased sample lifetime, and added utility for APMALDI ion sources. Compared with vacuum situations, AP matrices are not as limited by vapor pressure, so liquid matrix formulations can focus on desorption and ionization versus vacuum stability and source contamination. The parameters studied include chromophore concentration, liquid support variations, and quantitation capability. Chromophore concentration adjustments provided insight into the necessary absorbance for UV-APMALDI and demonstrated the importance of laser penetration depth. Liquid support variations allowed adjustments of sample lifetime and analyte solvents. Extended sample lifetime is beneficial for instrument tuning and source optimization; however, increased liquid viscosity lowers signal intensity. The shot-to-shot reproducibility, as examined with individual ion packets, suggests that the liquid matrix can alleviate some inconsistencies seen with solid MALDI, suggesting a possibility for better quantitation. The measurements for laser penetration depth, solution viscosity, and solvent additives could add to the information on MALDI mechanisms. The liquid matrix offers advantages that complement current MALDI methods. 相似文献
With its highly fluctuating ion production matrix-assisted laser desorption/ionization (MALDI) poses many practical challenges for its application in mass spectrometry. Instrument tuning and quantitative ion abundance measurements using ion signal alone depend on a stable ion beam. Liquid MALDI matrices have been shown to be a promising alternative to the commonly used solid matrices. Their application in areas where a stable ion current is essential has been discussed but only limited data have been provided to demonstrate their practical use and advantages in the formation of stable MALDI ion beams. In this article we present experimental data showing high MALDI ion beam stability over more than two orders of magnitude at high analytical sensitivity (low femtomole amount prepared) for quantitative peptide abundance measurements and instrument tuning in a MALDI Q-TOF mass spectrometer. Samples were deposited on an inexpensive conductive hydrophobic surface and shrunk to droplets <10 nL in size. By using a sample droplet <10 nL it was possible to acquire data from a single irradiated spot for roughly 10,000 shots with little variation in ion signal intensity at a laser repetition rate of 5-20 Hz. 相似文献
A new atmospheric pressure (AP) infrared (IR) matrix-assisted laser desorption/ionization (MALDI) ion source was developed and interfaced with a Thermo Finnigan LCQ ion trap mass spectrometer. The source utilized a miniature all-solid-state optical parametric oscillator (OPO)-based IR laser system tunable in the lambda = 1.5-4 microm spectral range and a nitrogen ultraviolet (UV) laser (lambda = 337 nm) for use in comparative studies. The system demonstrated comparable performance at 3 microm and 337 nm wavelengths if UV matrices were used. However, AP IR-MALDI using a 3 microm wavelength showed good performance with a much broader choice of matrices including glycerol and liquid water. AP IR-MALDI mass spectra of peptides in the mass range up to 2000 Da were obtained directly from aqueous solutions at atmospheric conditions for the first time. A potential use of the new AP IR-MALDI ion source includes direct MS analysis of biological cells and tissues in a normal atmospheric environment as well as on-line coupling of mass spectrometers with liquid separation techniques. 相似文献
We have used an infrared laser to ablate materials under ambient conditions that were captured in solvent droplets. The droplets
were either deposited on a MALDI target for off-line analysis by MALDI time-of-flight mass spectrometry or flow-injected into
a nanoelectrospray source of an ion trap mass spectrometer. An infrared optical parametric oscillator (OPO) laser system at
2.94 μm wavelength and approximately 1 mJ pulse energy was focused onto samples for ablation at atmospheric pressure. The
ablated material was captured in a solvent droplet 1–2 mm in diameter that was suspended from a silica capillary a few millimeters
above the sample target. Once the sample was transferred to the droplet by ablation, the droplet was deposited on a MALDI
target. A saturated matrix solution was added to the deposited sample, or in some cases, the suspended capture droplet contained
the matrix. Peptide and protein standards were used to assess the effects of the number of IR laser ablation shots, sample
to droplet distance, capture droplet size, droplet solvent, and laser pulse energy. Droplet collected samples were also injected
into a nanoelectrospray source of an ion trap mass spectrometer with a 500 nL injection loop. It is estimated that pmol quantities
of material were transferred to the droplet with an efficiency of approximately 1%. The direct analysis of biological fluids
for off-line MALDI and electrospray was demonstrated with blood, milk, and egg. The implications of this IR ablation sample
transfer approach for ambient imaging are discussed. 相似文献
The mass spectra of peptides obtained with different matrices were compared using a matrix-assisted laser desorption/ionization (MALDI) ion source and a multi-turn time-of-flight (TOF) mass spectrometer, MULTUM-IMG, which has been developed at Osaka University. Two types of solid matrices, alpha-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB), and a liquid matrix made from a mixture of 3-aminoquinoline and CHCA were used. When measuring the peak signal intensity of human angiotensin II [M+H]+ from a fixed sample position, the liquid matrix produced a stable signal over 1000 laser shots, while the signal obtained with CHCA and DHB decayed after about 300 and 100 shots, respectively. Significant differences in the mass resolving power were not observed between the spectra obtained with the three matrices. Signal peak areas were measured as a function of the cycle number in a multi-turn ion trajectory, i.e., the total flight time over a millisecond time scale. For both [M+H]+ of human angiotensin II and bovine insulin, the decay of the signal peak area was the most significant with CHCA, while that measured with DHB was the smallest. The results of the mean initial ion velocity measurements suggested that the extent of metastable decomposition of the analyte ions increased in order of DHB, the liquid matrix, and CHCA, which is consistent with the difference in the decay of the signal peak area as the total flight time increased. 相似文献
Matrix-assisted laser desorption/ionization (MALDI) was used for the on-line analysis of single particles. An aerosol was generated at atmospheric pressure and particles were introduced into a time-of-flight (TOF) mass spectrometer through a single-stage differentially pumped capillary inlet. Prior to entering the mass spectrometer, a matrix was added to the particles using a heated saturator and condenser. A liquid matrix, 3-nitrobenzyl alcohol (NBA), and a solid matrix, picolinic acid (PA), were used. Particles were ablated with a 351 nm excimer laser and the resulting ions were mass-separated in a two-stage reflectron TOF mass spectrometer. Aerosol particles containing the biomolecules erythromycin and gramicidin S were analyzed with and without the matrix addition step. The addition of NBA to the particles resulted in mass spectra that contained an intact molecular ion mass peak. In contrast, PA-coated particles did not yield molecular ion peaks from matrix-coated particles. 相似文献
Solid phase microextraction (SPME) with matrix assisted laser desorption/ionization (MALDI) introduction was coupled to mass spectrometry and ion mobility spectrometry. Nicotine and myoglobin in matrix 2,5-dihydroxybenzonic acid (DHB), enkephalin and substance P in alpha-cyano-4-hydroxy cinnaminic acid were investigated as the target compounds. The tip of an optical fiber was silanized for extraction of the analytes of interest from solution. The optical fiber thus served as the sample extraction surface, the support for the sample plus matrix, and the optical pipe to transfer the laser energy from the laser to the sample. The MALDI worked under atmospheric pressure, and both an ion mobility spectrometer and a quadrupole/time-of-flight mass spectrometer were used for the detection of the SPME/MALDI signal. The spectra obtained demonstrate the feasibility of the SPME with MALDI introduction to mass spectrometry instrumentation. 相似文献
A transfer of energy into the internal modes of the matrix and analyte is expected to occur during matrix-assisted laser desorption/ioniziation (MALDI) processes. Both the physical and thermochemical properties of the MALDI matrix used can influence the ion internal energy and analyte ion fragmentation. Here we report the effect of several MALDI matrices on the relative internal energy of the 2'-deoxyadenylyl-(3',5')-2'-deoxyguanosine (AG) anion. Relative internal energies were probed by low-energy collision-induced dissociation in a Fourier transform ion cyclotron resonance mass spectrometer. Sublimation temperatures of the matrices under study were also determined and found to lie between 409 and 455 K. Analyte ion internal and initial kinetic energies did not correlate with matrix sublimation temperatures. In contrast, a strong correlation between the relative internal energy of the analyte anions and the gas-phase basicity of the matrix anions was found. These results suggest that gas-phase proton transfer reactions play an important role in MALDI analyte ion formation and influence their internal energy and fragmentation behavior. Copyright 2000 John Wiley & Sons, Ltd. 相似文献
We have recently presented a new method for direct coupling of high-performance thin-layer chromatography (HPTLC) with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), illustrated by the analysis of a complex ganglioside mixture. In the current communication, an adaptation of this procedure to mixtures of native oligosaccharides from human and from elephant milk is described. The key features in this method are (1) glycerol as a liquid matrix, to provide a homogeneous wetting of the silica gel and a simple and fast MALDI preparation protocol, (2) an infrared (IR) laser for volume material ablation and particular soft desorption/ionization conditions, and (3) an orthogonal time-of-flight mass spectrometer for a high mass accuracy, independent of any irregularity of the silica gel surface. Chromatographic "mobility profiles" were determined by scanning the laser beam across the analyte bands. The current limit of detection for the MS analysis was determined to approximately 10 pmol of individual oligosaccharides spotted for chromatography. A liquid composite matrix, containing glycerol and the ultraviolet (UV-)MALDI matrix alpha-cyano-4-hydroxycinnamic acid, allows a direct HPTLC-MALDI-MS analysis with a 337 nm-UV laser as well. Compared to the IR-MALDI mode, the analytical sensitivity in UV-MALDI was found to be lower by one order of magnitude, whereas unspecific analyte ion fragmentation as well as adduct formation was found to be more extensive. 相似文献
A major problem hampering the use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for quantitative measurements is the inhomogeneous distribution of analytes and matrices in solid sample preparations. The use of ionic liquids as matrices for the qualitative and quantitative analysis of low molecular weight compounds like amino acids, sugars and vitamins was investigated. The ionic liquid matrices are composed of equimolar combinations of classical MALDI matrices (sinapinic acid, alpha-cyano-4-hydroxycinnamic acid or 2,5-dihydroxybenzoic acid) with organic bases. These matrix systems allow a homogenous sample preparation with a thin ionic liquid layer having negligible vapour pressure. This leads to a facilitated qualitative and quantitative measurement of the analytes compared with classical solid matrices. 相似文献
Recent research has focused on increasing the evidentiary value of latent fingerprints through chemical analysis. Although researchers have optimized the use of organic and metal matrices for matrix‐assisted laser desorption/ionization‐mass spectrometry imaging (MALDI‐MSI) of latent fingerprints, the use of development powders as matrices has not been fully investigated. Carbon forensic powder (CFP), a common nonporous development technique, was shown to be an efficient one‐step matrix; however, a high‐resolution mass spectrometer was required in the low mass range due to carbon clusters. Titanium oxide (TiO2) is another commonly used development powder, especially for dark nonporous surfaces. Here, forensic TiO2 powder is utilized as a single‐step development and matrix technique for chemical imaging of latent fingerprints without the requirement of a high‐resolution mass spectrometer. All studied compounds were successfully detected when TiO2 was used as the matrix in positive mode, although, generally, the overall ion signals were lower than the previously studied CFP. TiO2 provided quality mass spectrometry (MS) images of endogenous and exogenous latent fingerprint compounds. The subsequent addition of traditional matrices on top of the TiO2 powder was ineffective for universal detection of latent fingerprint compounds. Forensic TiO2 development powder works as an efficient single‐step development and matrix technique for MALDI‐MSI analysis of latent fingerprints in positive mode and does not require a high‐resolution mass spectrometer for analysis. 相似文献
This report focuses on the heterogeneous distribution of small molecules (e.g. metabolites) within dry deposits of suspensions and solutions of inorganic and organic compounds with implications for chemical analysis of small molecules by laser desorption/ionization (LDI) mass spectrometry (MS). Taking advantage of the imaging capabilities of a modern mass spectrometer, we have investigated the occurrence of “coffee rings” in matrix-assisted laser desorption/ionization (MALDI) and surface-assisted laser desorption/ionization (SALDI) sample spots. It is seen that the “coffee-ring effect” in MALDI/SALDI samples can be both beneficial and disadvantageous. For example, formation of the coffee rings gives rise to heterogeneous distribution of analytes and matrices, thus compromising analytical performance and reproducibility of the mass spectrometric analysis. On the other hand, the coffee-ring effect can also be advantageous because it enables partial separation of analytes from some of the interfering molecules present in the sample. We report a “hidden coffee-ring effect” where under certain conditions the sample/matrix deposit appears relatively homogeneous when inspected by optical microscopy. Even in such cases, hidden coffee rings can still be found by implementing the MALDI-MS imaging technique. We have also found that to some extent, the coffee-ring effect can be suppressed during SALDI sample preparation. 相似文献
The mechanism of atmospheric pressure (AP) laser ionization of water and water/glycerol liquid samples at a 3-microm wavelength is studied experimentally. For the ion desorption, an in-house built Yb : YAG-pumped optical parametric oscillator (OPO) infrared (IR) laser has been coupled with AP MALDI ion source interfaced to an ion trap mass spectrometer (MS). It has been shown that water is primarily responsible for ion generation in water/glycerol samples, while glycerol increases the solution viscosity and decreases the water evaporation rate and sample losses. In contrast to AP UV-MALDI, the electric field in the case of AP IR-MALDI does not assist in ion production. It was found that the absence of the electrical field provides the optimum ionization condition both for water and water/glycerol liquid samples at the 3-microm laser irradiation. A two-stage ion formation mechanism, which includes the initial emission of microdroplets and release of molecular ions at the second stage, can explain the experimentally observed ion signal dependencies upon the voltage applied between MS inlet and the MALDI sample plate. Postionization using additional corona discharge APCI increases the observed signal by approximately 50%, which indicates that some portion of the analyte is desorbed in the form of neutral molecules. 相似文献
Native mass spectrometry (MS) encompasses methods to keep noncovalent interactions of biomolecular complexes intact in the gas phase throughout the instrument and to measure the mass-to-charge ratios of supramolecular complexes directly in the mass spectrometer. Electrospray ionization (ESI) in nondenaturing conditions is now an established method to characterize noncovalent systems. Matrix-assisted laser desorption/ionization (MALDI), on the other hand, consumes low quantities of samples and largely tolerates contaminants, making it a priori attractive for native MS. However, so-called native MALDI approaches have so far been based on solid deposits, where the rapid transition of the sample through a solid state can engender the loss of native conformations. Here we present a new method for native MS based on liquid deposits and MALDI ionization, unambiguously detecting intact noncovalent protein complexes by direct desorption from a liquid spot for the first time. To control for aggregation, we worked with HUαβ, a heterodimer that does not spontaneously rearrange into homodimers in solution. Screening through numerous matrix solutions to observe first the monomeric protein, then the dimer complex, we settled on a nondenaturing binary matrix solution composed of acidic and basic organic matrices in glycerol, which is stable in vacuo. The role of temporal and spatial laser irradiation patterns was found to be critical. Both a protein-protein and a protein-ligand complex could be observed free of aggregation. To minimize gas-phase dissociation, source parameters were optimized to achieve a conservation of complexes above 50% for both systems.