ngfeng Li

Applicability of Standardless Semiquantitative Analysis of Solids by High-Irradiance Laser Ionization Orthogonal Time-of-Fight Mass Spectrometry

A compact high-irradiance laser ionization time-of-flight mass spectrometry system has been developed for the multielemental analysis of solids. Helium was introduced into the ion source as a buffer gas to cool high kinetic energy ions and suppress the interference of multicharged ions. A special pulse train repelling mode was used to achieve explicit spectra. Two quantitative methods are described for the laser ionization mass spectrometry in this paper. The first of these is the routine calibration curve quantitation, in which various matrix-matched standards are required; the second method, which is based on the uniform correlation between the signal and elemental concentration of different samples, is more convenient and covers a typical dynamic range of 6 orders. All the investigations and results indicate satisfactory performance of the newly developed instrument and its applicability for simultaneous multielemental analysis of solid samples.

High irradiance laser ionization orthogonal time-of-flight mass spectrometry: a versatile tool for solid analysis.

This article reviews the development of and applications for high irradiance laser ionization orthogonal time-of-flight mass spectrometry (LI-O-TOFMS). LI-O-TOFMS has solved the bottleneck problems in traditional high irradiance laser ionization mass spectrometry, which allows the instrument to acquire explicit spectra with high resolution. A buffer-gas-assisted ion source effectively reduces the kinetic energy of the ions and suppresses the multiply charged ion interference. The pulse train data acquisition technique was applied to reduce the spectrum interference from multiply charged ions and polyatomic ions according to the temporal profiles of different ion packets in the repelling region. Relatively high laser irradiance (≥10(10) W/cm(2)) is preferable for achieving uniform relative sensitivities for different elements in the samples of different matrices. LI-O-TOFMS has been used in the standardless, semiquantitative analysis of solids, which is proved to be a fast and convenient technique for solid sample analysis. By increasing the laser irradiance and reducing the buffer gas pressure, the determination of nonmetallic elements in solids can also be achieved without losing spectral explicity. Recent applications, such as elemental analysis of a single egg cell and acquiring elemental, fragmental, and molecular information of chemicals, were given to demonstrate the potential of the new technique. All of these results reveal that LI-O-TOFMS is an advanced tool in the elemental analysis of solids in terms of modern mass spectrometry.

Laser Ionization Orthogonal Time-of-Flight Mass Spectrometry for Simultaneous Determination of Nonmetallic Elements in Solids

The simultaneous determination of nonmetallic elements in solid samples is difficult owing to their discrepant physical and chemical properties. We developed a high-irradiance laser ionization orthogonal time-of-flight mass spectrometry (LI-O-TOFMS) system and applied it for the determination of nonmetallic elements in solids. Helium was used as the buffer gas at 250 Pa in the source chamber; the laser irradiance was about 7 x 10(10) W/cm(2). A series of artificial standards containing B, C, N, O, F, Si, P, S, Cl, As, Br, Se, I, and Te were used. Explicit spectra were obtained with only a little interference from gas species and doubly charged matrix ions. Standardless semiquantitative analysis could be accomplished with a novel sampling methodology to obtain near-uniform sensitivity coefficients for different elements. Limits of detection (LOD) at microgram per gram level and a dynamic range of 6 orders of magnitude were achieved for most nonmetallic elements.

Analysis of solids with different matrices by buffer-gas-assisted laser ionization orthogonal time-of-flight mass spectrometry

A laser ionization orthogonal time-of-flight mass spectrometer with a low-pressure source and high laser irradiance was used to analyze 27 solid samples with 9 different matrices, including aluminium, soil, copper sulfide, zinc sulfide, iron, nickel, copper, zinc, and tungsten. The influence of laser energy on non-stoichiometric effects, such as matrix effects and elemental fractionation, has been investigated. The results indicate that matrix effects can be alleviated to a great extent at high laser irradiance. Additionally, with the irradiance of 1010–1011 W cm−2, most elements presented relatively stable relative sensitivity coefficients (RSC), while W, Pb, and Bi demonstrated unusual characteristics that their RSCs increased along with increasing laser energy.

High irradiance laser ionization mass spectrometry for direct speciation of iron oxides

A novel method has been developed that allows the direct speciation analysis of iron oxides based on a modified laser ionization orthogonal time-of-flight mass spectrometer. Time resolved mass spectra were acquired for the investigation of elemental ions and oxide ions generated by a laser ionization source. Speciation methodologies, including the identification of characteristic ions and the use of ion abundance ratios were evaluated for the differentiation of the oxides. The influence of operating parameters on the distribution of cluster ions was investigated, and their mechanism of formation discussed.

Femtogram Detection and Quantitation of Residues Using Laser Ionization Orthogonal Time-of-Flight Mass Spectrometry

A newly developed high irradiance laser ionization orthogonal time-of-flight mass spectrometer (LI-O-TOFMS) was employed for the elemental analysis of residues, which were prepared by evaporating mixed salt solutions. The residues were first characterized in terms of shape and elemental distribution. In TOFMS detection, all of the metal elements in the residue can be observed in the spectra. Relative sensitivity coefficients for different elements were within 1 order of magnitude, which meets semiquantitative analysis criteria. By calculating the individual masses from the ablated area due to a single laser shot, the absolute detection limit reached 7 x 10(-15) g for most metal elements. The results indicate that LI-O-TOFMS is capable of performing ultratrace elemental qualification and quantification, with an absolute limit of detection and an absolute limit of quantitation at the femtogram level.

Two-Dimensional Separation in Laser Ionization Orthogonal Time-of-Flight Mass Spectrometry

The capabilities of two-dimensional separation using a high irradiance laser ionization orthogonal time-of-flight mass spectrometer (LI-O-TOFMS) were demonstrated in this paper. Ions were separated via their initial kinetic energy in one dimension and their mass-to-charge ratios in the other dimension. Investigation of the transient ion profiles after laser pulses revealed that the separation of analyte ions from multiply charged ions and gas species ions was achieved. Comparison of mass spectra in the normal accumulation mode and in the two-dimensional separation mode indicated that the relative sensitivity coefficients are stable and close to their true values in the two-dimensional separation mode, especially for trace elements that are prone to interference.

Simultaneous Acquisition of Elemental, Fragmental, and Molecular Information on Organometallic Compounds

A novel method for obtaining elemental, fragmental, and molecular information of organometallic compounds has been developed using high irradiance laser induced time-of-flight mass spectrometry (LI-TOFMS) with a buffer-gas-assisted ion source. This technique permits direct and matrix-free analysis of solid analyte with minimal sample preparation. In addition, it shows special advantages in integrated acquisition of elemental, fragmental, and molecular information from a single target, on the basis of which identification of organometallic complexes is simplified and expedited.

Characteristics and comparison of different radiofrequency‐only multipole cooling cells

Various multipole cooling cells are widely used in mass spectrometry for their outstanding performance with regard to transmission and cooling effects. Among these, radiofrequency (RF)-only quadrupoles, hexapoles, and octopoles are routinely used in practical instrumentation. A study of their performance has been carried out using a house-built electrospray time-of-flight mass spectrometer equipped with three different multipole devices. In addition, a user-written program was developed using SIMION 7.0 to simulate ion transmission characteristics for the different devices utilized. Systematic experiments and simulations were performed with an RF-only quadrupole, hexapole, and octopole to study their theoretical and practical characteristics.