Rongfu Huang

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.

Elemental Imaging via Laser Ionization Orthogonal Time-of-Flight Mass Spectrometry

An elemental imaging method using a laser ionization orthogonal time-of-flight mass spectrometer system was developed for the simultaneous detection of all metal and nonmetal elements. The instrument control and data processing were realized by self-developed programs. This system is capable of simultaneous detection of metal and nonmetal elements, with a spatial resolution of 50 μm, the lowest detection limits of 3 × 10(-7) g/g (Li), and a dynamic range of 7 orders of magnitude. Moreover, this technique does not require standards for quantitative analysis and can be a powerful and versatile tool for elemental imaging.

A small high-irradiance laser ionization time-of-flight mass spectrometer

A small high-irradiance laser ionization time-of-flight mass spectrometer (LI-TOFMS) with orthogonal sample introduction was described. High irradiance of 6 x 10(10) W/cm(2) at 532 nm from a Nd:YAG laser was applied in the experiment to get a high ionization degree in plasma and to dissociate the interferential polyatomic ions. Meanwhile, the interferential multiply charged ions resulted by high-irradiance were nearly eliminated in the spectrum by utilizing helium as the buffer gas in the ion source due to three-body recombination, which resulted in a relatively clean background. Improved signal stability was obtained by automated step moving of the sample stage in short time intervals. By using two sets of Einzel lens in transport system, nearly uniform relative sensitivity coefficients (RSCs) were achieved for most of metal elements including light ions which were detected in extremely low sensitivity in previous hexapole transportation instrument. The resolving power reaches 2200, and the detection limits (DLs) are 10(-6) g/g for metal elements in the steel standard.

A spectroscopic investigation of the afterglow and recombination process in a microsecond pulsed glow discharge

The emission characteristics of afterglow in a microsecond pulsed glow discharge atomic source are studied to obtain insight into the excitation and recombination processes of analytes and fill gases. Each emission line features an initial intense peak at the beginning of the discharge pulse. The afterglow, which has been observed in the temporal behavior for some emission temporal profiles of analytes and discharge gases, exhibits an intense post-pulse signal maximized at 25–35 μs after plasma termination, with a broader profile than their initial peaks. The afterglow of Ar I and Cu I spectra last approximately 100 μs and 300 μs, respectively, after the argon discharge pulse at 2.0 torr pressure. The intensity of the afterpeak increases with the pulse width between 2 μs to 200 μs. A study of fourteen Ar I and twenty-seven Cu I lines show that transitions from high energy levels (5p [14.5–14.7 eV] for Ar and above 6 eV for Cu) are relatively stronger in the afterglow. The highly excited argon and copper atoms are thought to be generated via the recombination of ions and electrons. The results are explained primarily in terms of an electron-electron-ion three-body recombination process.

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.