Many modern time-of-flight mass spectrometry (TOFMS) instruments use fast analog-to-digital conversion (ADC) with high-speed digitizers to record mass spectra with extended dynamic range (compared to ...time-to-digital conversion). The extended dynamic range offered by ADC detection is critical for accurate measurement of transient events. However, the use of ADC also increases the variance of the measurements by sampling the gain statistics of electron multipliers (EMs) used for detection. The influence of gain statistics on the shape of TOF signal distributions is especially pronounced at low count rates and is a major contributor to measurement variance. Here, we use Monte Carlo methods to simulate low-ion-count TOFMS signals as a function of Poisson statistics and the measured pulse-height distribution (PHD) of the EM detection system. We find that a compound Poisson distribution calculated via Monte Carlo simulation effectively describes the shape of measured TOFMS signals. Additionally, we apply Monte Carlo simulation results to single-particle inductively coupled plasma (sp-ICP) TOFMS analysis. We demonstrate that subtraction of modeled TOFMS signals can be used to quantitatively uncover particle-signal distributions buried beneath dissolved-signal backgrounds. On the basis of simulated signal distributions, we also calculate new critical values (L C) that are used as decision thresholds for the detection of discrete particles. This new detection criterion better accounts for the shape of dissolved signal distributions and therefore provides more robust identification of single particles with ICP-TOFMS.
This paper is a review of the basic principles and recent developments of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) as a method for the element- and isotope-selective ...trace analysis of solid materials. In the course of this review, the aerosol formation/transportation process, quantification issues, as well as technical aspects concerning the system configuration and ICP operating conditions are outlined. Furthermore, the performance of femtosecond (fs) LA-based analyses as one of the most important advancements made over the past years is discussed. The benefits offered by fs-LA in comparison to LA using nanosecond (ns) laser sources are demonstrated on the basis of oxide layer and silicate glass analyses with different applied calibration strategies.
Capabilities of the downwardly oriented inductively coupled plasma mass spectrometer (ICP-MS) recently reported (Vonderach
et al.
2021) were studied using a time-of-flight mass spectrometer (TOFMS) ...yielding benefits for the fast detection of short transient signals containing multi-element information. The previously reported sample inlet configuration for the analysis of microdroplets was equipped with two extra gas inlets for the supply of argon and helium, which enabled a more precise optimization of the sample introduction and operating conditions of the plasma. Furthermore, the sample supply system was operated at elevated temperatures to enhance the desolvation of the droplets prior to their introduction into the plasma. Transient droplet signals with frequencies of up to 1000 Hz were recorded for 74 μm (diameter) sized droplets. The upper detectable droplet size was limited by the droplet generator used and was measured at 93 μm (diameter). The droplets served as the transporter for biological cells so that the described setup could be used to analyze single cells. Mouse lung cells embedded into droplets were detected successfully according to their Cs droplet tracer, Ir nucleus marker, surface markers and the phosphorus content. Transient signals were recorded at a time resolution of 33 μs in order to investigate the signal structure of single droplet-cell events containing multiple elements. Signals between 200-400 μs (FW base) and ≤100 μs (FWHM) in duration were measured. To ensure that the droplet formation process did not affect the sampled cells, different types of cells were localized within the droplets using optical inspection directly after droplet formation and it was possible to observe that cells remained intact with random sampling. The results indicate that a downward-pointing ICP-MS in combination with the microdroplet-based approach can be considered as an alternative to commonly used ICP-MS systems for single cell analysis, and might be suitable for online coupling to flow cytometry.
A downward inductively coupled plasma (ICP) was coupled to a time-of-flight mass spectrometer (TOFMS) and monodisperse microdroplets were used to study its capabilities and analyze single biological cells.
Garnet is one of the most robust and ubiquitous minerals that record element zoning during crustal metamorphism. In addition to major elements, zoning in trace elements can provide a wealth of ...information to document the changing conditions of garnet growth and modification. However, mapping trace elements at low concentrations, over large areas and with high resolution has remained a major challenge. We present a comprehensive investigation of the TE distribution in garnet from three Alpine samples that underwent a complex evolution at different metamorphic conditions. The TE distribution in garnet grains is mapped in 2D in thin section with a novel approach using laser ablation inductively coupled plasma time of flight mass spectrometry (LA-ICP-TOFMS) to achieve a lateral resolution of 5 µm and limits of detection for the heavy rare earth elements (REE) down to 0.2 µg/g. Comparison with major element zoning measured by electron probe microanalysis and trace elements measured by conventional LA-ICPMS spot analysis testifies to the accuracy of the measurements. Garnet in an amphibolite-facies metapelite from Campolungo, Central Alps, that recorded metamorphism to 600 °C preserves Y + REE trace element zoning that closely matches that of Ca. In this sample, there is no notable diffusive modification for trace elements. Y + REE zoning is dominated by Rayleigh fractionation in the core and by the sporadic breakdown of accessory phases producing annuli in the rim of the garnet. A granulite-facies garnet from Malenco, Eastern Central Alps, formed during subsolidus heating, followed by peritectic melting reactions up to temperatures of 800–850 °C. Major and trace element zoning are decoupled indicating diffusional resetting of major elements, whereas trace elements still largely document the growth history. Enrichment of trace elements in the garnet mantle may be related to the consumption of biotite (V, Cr) and the dissolution of zircon (Zr) and monazite (Y + REE) in the melt. Diffusion of Y + HREE at the core–mantle boundary occurred over a length scale of ~ 200 µm. Garnet in an eclogite from the Sesia Zone, Western Alps (
P
~ 2 GPa,
T
~ 600 °C), displays pronounced fluid-related veinlets, visible in FeO, MgO and MnO, which cross-cut the primary growth zoning. Surprisingly, complex Y + REE and Cr zoning is not affected by the veinlets, indicating that they did not form by a crack-seal mechanism but are rather related to a selective replacement process. The trace element maps provide a detailed insight into the growth and modification of garnet and thus allow assessment of equilibrium versus disequilibrium processes, and assist in determination of
P
–
T
conditions, garnet dating, diffusion modelling as well as documenting fluid-induced modifications.
Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and luminescent properties are challenged by the lability of their surfaces, ...i.e., the interface of the NC core and the ligand shell. On the example of CsPbBr3 NCs, we model the nanocrystal surface structure and its effect on the emergence of trap states using density functional theory. We rationalize the typical observation of a degraded luminescence upon aging or the luminescence recovery upon postsynthesis surface treatments. The conclusions are corroborated by the elemental analysis. We then propose a strategy for healing the surface trap states and for improving the colloidal stability by the combined treatment with didodecyldimethylammonium bromide and lead bromide and validate this approach experimentally. This simple procedure results in robust colloids, which are highly pure and exhibit high photoluminescence quantum yields of up to 95–98%, retained even after three to four rounds of washing.
The acquisition speed in laser ablation inductively coupled plasma mass spectrometry element imaging depends significantly on the laser aerosol transport system. The faster the aerosol washout, the ...faster the acquisition can be carried out. Here, we introduce a modified ablation cell based on the tube cell design for laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOFMS) element imaging which provides shorter signal durations. The parallel flow ablation cell (PFAC) included a recess in the cover for improved gas flow pattern at the ablation site and achieved signal durations of 0.25 ms (FW0.1M) for
44
Ca and 0.29 ms (FW0.1M) for
238
U on NIST SRM 610 using a laser ablation repetition rate of 100 Hz. Shortest signal duration was achieved using an inner cell to sample surface distance (CSD) of 700 μm, which is several times larger compared to previous fast washout ablation cells published and shows high tolerance to variations in the CSD. A shift in arrival time from the ablation to TOFMS extraction was observed when comparing light to heavy ions. A H
2
collision and reaction cell was not able to correct for this shift and lead to extended signal durations, but still very short signals of approximately 0.4 ms (FW0.1M) were observed. The robustness of the washout in a wide range of CSD makes the PFAC a promising ablation cell for fast aerosol transport and quasi-simultaneous detection of ions using an ICP-TOFMS and element imaging using a ≥1000 Hz laser ablation rate while maintaining the possibility for pulse-to-pulse signal separation.
Here, we introduce a modified ablation cell based on the tube cell design which provides shortest signal durations reported for LA sample introduction.
This work investigated the potential of a high temporal resolution inductively coupled plasma time-of-flight mass spectrometer (ICPTOFMS) in combination with a microdroplet generator (MDG) for ...simultaneous mass quantification of different nanoparticles (NPs) in a mixture. For this purpose, a test system containing certified Au NPs, well characterized Ag NPs, and core–shell NPs composed of an Au core and an Ag shell was employed. Thanks to the full spectra coverage and rapid simultaneous detection of the TOFMS, the element composition of individual particles can be determined. The pure Ag NPs and the core–shell NPs could be differentiated despite the same mass of Ag they contain. Calibration with monodisperse droplets consisting of standard solutions allowed for the mass quantification of NPs without the use of NP certified materials. On the basis of this mass quantification, the sizes of NPs originating from the same aqueous suspension were simultaneously determined with an accuracy of 7–12%. The size-equivalent limits of detection estimated with the 3*σ criterion were 13 nm for Au and 16 nm for Ag. Estimation of the LODs using Poisson statistics resulted in 19 and 27 nm, respectively. In addition, the 30 μs temporal resolution of the ICPTOFMS allowed studying interactions of NPs with the ICP based on their transient MS signals. The results demonstrated a difference in vaporization behavior of the core–shell NPs and solutions and indicated that vaporization of the Ag shell takes place prior to the Au core.
The analytical capabilities of a nitrogen-sustained high-power microwave inductively coupled atmospheric-pressure plasma mass spectrometer (N2 MICAP-MS) were investigated using solution nebulization ...with and without aerosol desolvation. The reduced solvent load for the desolvated aerosol and the increased aerosol transfer resulted in a signal enhancement of ten times for most elements in samples without a significant amount of dissolved solids. An exception was boron, whose signal decreased by a factor of seven when a desolvator was used. To compare the accuracy, reproducibility, and matrix susceptibility of the N2 MICAP-MS, the mass fractions of 30 elements were determined in two certified water reference materials using external calibration and standard addition. The results were generally found to agree within 10% of the certified reference values with a maximum deviation of 17% in the case of 64Zn. Comparing external calibration and standard addition provided comparable results regardless of the sample introduction method. To assess the extent of matrix effects, multi-element standard solutions were doped with amounts of up to 100 mg kg−1 calcium. This resulted in a signal suppression of up to 30% and 70% for conventional nebulization and aerosol desolvation, respectively. This substantially reduced the improvement in sensitivity observed for the desolvated aerosol. To further investigate the fundamental characteristics of the N2 MICAP-MS, the plasma gas temperature was estimated using three methods. The determined temperatures for the two most reliable methods were in the range of ∼5000–6000 K and were found to be independent of the sample introduction method and similar to those of an Ar ICP.
Single particle inductively coupled plasma mass spectrometry (sp-ICPMS) is an attractive technique for fast measurement of elemental composition, mass and particle number concentration (PNC) of metal ...containing nanoparticles (NPs). In order to investigate NPs <10 nm using ICPMS, low instrumental background and high detection efficiency are primary requirements. This study evaluated the performance of a sector-field ICPMS with standard and enhanced sensitivity ("Jet") vacuum interfaces with different sample introduction setups: conventional pneumatic nebulization with (DSN) and without aerosol desolvation (PN) and microdroplet generation (MDG). Additionally, the influence of nitrogen gas as an addition to a dry aerosol was studied. In this study, transport efficiencies (TEs) and detection efficiencies (DEs) are determined for the different instrumental setups. Gold NP suspensions were analysed and evaluated for PNC and size. Applying counting statistics, the size limit of detection (LOD
size
) of gold nanoparticles (Au NPs) was estimated to be 6.1 nm and 4.7 nm for PN and MDG with the standard interface, and 3.6 nm and 3.1 nm for DSN and MDG with the "Jet" interface and nitrogen addition, respectively. Additionally, DEs for various elements were determined. 11 isotopes (
27
Al,
47
Ti,
63
Cu,
107
Ag,
111
Cd,
115
In,
133
Cs,
140
Ce,
193
Ir,
197
Au, and
238
U) were measured at a mass resolving power (MRP) of 300 while an MRP of 4000 was used for
56
Fe and
66
Zn. DEs obtained for the conventional nebulization system with a spray chamber (PN) were in the range of 10
−4
to 10
−2
counts per atom (low resolution) and 10
−6
to 10
−5
counts per atom (medium resolution), while significant improvement in DE was obtained for the MDG setup with the "Jet" interface and nitrogen addition resulting in the range of 10
−2
to 10
−1
counts per atom (low resolution) and 10
−4
to 10
−3
counts per atom (medium resolution). The enhancement in DE was most pronounced for isotopes of lower
m
/
z
indicating reduced mass discrimination of the "Jet" interface with nitrogen gas added to the sample aerosol. The corresponding LOD
SIZE
could thus be decreased by 10 or 2 times for example for Al- and Au-containing NPs, respectively. At the same time the use of an MDG for sample introduction allowed for 98.5% TE in the analyses of NP suspensions, while a TE of 10% (PN) or 23% (DSN) was obtained with pneumatic nebulizers.
Improved detection efficiency and microdroplet sample introduction in single particle inductively coupled plasma mass spectrometry allow for accurate sizing and counting of nanoparticles in suspension at the single digit nm scale.
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