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.
Due to the rapid development of nanotechnologies, engineered nanomaterials (ENMs) and nanoparticles (ENPs) are becoming a part of everyday life: nanotechnologies are quickly migrating from laboratory ...benches to store shelves and industrial processes. As the use of ENPs continues to expand, their release into the environment is unavoidable; however, understanding the mechanisms and degree of ENP release is only possible through direct detection of these nanospecies in relevant matrices and at realistic concentrations. Key analytical requirements for quantitative detection of ENPs include high sensitivity to detect small particles at low total mass concentrations and the need to separate signals of ENPs from a background of dissolved elemental species and natural nanoparticles (NNPs). To this end, an emerging method called single-particle inductively coupled plasma mass spectrometry (sp-ICPMS) has demonstrated great potential for the characterization of inorganic nanoparticles (NPs) at environmentally relevant concentrations. Here, we comment on the capabilities of modern sp-ICPMS analysis with particular focus on the measurement possibilities offered by ICP-time-of-flight mass spectrometry (ICP-TOFMS). ICP-TOFMS delivers complete elemental mass spectra for individual NPs, which allows for high-throughput, untargeted quantitative analysis of dispersed NPs in natural matrices. Moreover, the multi-element detection capabilities of ICP-TOFMS enable new NP-analysis strategies, including online calibration via microdroplets for accurate NP mass quantification and matrix compensation.
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•Tailored rf-irradiation schemes allow the control of proton-driven spin diffusion.•Polarization transfer can be restricted to the area of interest.•Rate constants of polarization ...transfer are maximized.
Spin-diffusion type polarization transfer among heteronuclei, e.g., 13C or 15N, plays an important role in many solid-state NMR experiments for structure determination of proteins. In such experiments, chemical-shift compensation is provided by the proton bath (‘proton-driven’) which can be improved by radio-frequency irradiation of the protons. Here, we address the problem that the polarization-transfer rates depend not only on the intermolecular distance but also on the chemical-shift difference of the two spins. We introduce rf-modulation schemes that allow eliminating the chemical-shift dependence to a large extent over a predefined range. At the same time, the rate constants are maximized.
The increasing release of engineered nanoparticles (NPs) into aquatic ecosystems makes it crucial to understand the interactions of NPs with aquatic organisms, such as algae. In this study, the ...association of CeO2 NPs with unicellular algae (Raphidocelis subcapitata) and changes to the cellular elemental profile were investigated using three exposure concentrations (1, 50, and 1000 µg CeO2/L) at two different algal growth conditions—exponential and inhibited growth (1% glutaraldehyde). After a 24 h-exposure, algal suspensions were settled by gravity and CeO2-NP/algae association was analyzed by single-cell inductively coupled plasma quadrupole mass spectrometry (sc-ICP-QMS) and ICP time-of-flight MS (sc-ICP-TOFMS). Concurrent detection of the cellular fingerprint with cerium indicated NP association with algae (adsorption/uptake) and changes in the cellular elemental profiles. Less than 5% of cells were associated with NPs when exposed to 1 µg/L. For 50 µg/L exposures in growing and inhibited cell treatments, 4% and 16% of cells were associated with CeO2 NPs, respectively. ICP-TOFMS analysis made it possible to exclude cellular exudates associated with CeO2 NPs due to the cellular fingerprint. Growing and inhibited cells had different elemental profile changes following exposure to CeO2 NPs—e.g., growing cells had higher Mg and lower P contents independent of CeO2 concentration compared to inhibited cells.
The work described herein assesses the ability to characterize gold nanoparticles (Au NPs) of 50 and 100 nm, as well as 60 nm silver shelled gold core nanospheres (Au/Ag NPs), for their mass, ...respective size, and isotopic composition in an automated and unattended fashion. Here, an innovative autosampler was employed to mix and transport the blanks, standards, and samples into a high-efficiency single particle (SP) introduction system for subsequent analysis by inductively coupled plasma-time of flight-mass spectrometry (ICP-TOF-MS). Optimized NP transport efficiency into the ICP-TOF-MS was determined to be >80%. This combination, SP-ICP-TOF-MS, allowed for high-throughput sample analysis. Specifically, 50 total samples (including blanks/standards) were analyzed over 8 h, to provide an accurate characterization of the NPs. This methodology was implemented over the course of 5 days to assess its long-term reproducibility. Impressively, the in-run and day-to-day variation of sample transport is assessed to be 3.54 and 9.52% relative standard deviation (%RSD), respectively. The determination of Au NP size and concentration was of <5% relative difference from the certified values over these time periods. Isotopic characterization of the
Ag/
Ag particles (
= 132,630) over the course of the measurements was determined to be 1.0788 ± 0.0030 with high accuracy (0.23% relative difference) when compared to the multi-collector-ICP-MS determination.
Multiple analytical techniques to measure microplastics (MPs) in complex environmental matrices are currently under development, and which is most suited often depends on the aim(s) of the research ...question and the experimental design. Here, we further broaden the suite of possible techniques which can directly detect MPs in suspension while differentiating the carbon contained in MPs from other natural particles and dissolved organic carbon (DOC). Single particle inductively coupled plasma mass spectrometry (sp-ICP-MS) is well suited to measuring particles at trace concentrations, and the use of ICP time-of-flight-MS (ICP-TOFMS) allows one to simultaneously monitor the entire elemental spectrum to assess the full elemental composition of individual particles through developing elemental fingerprints. Because carbon is not detected in a standard operation mode with icp TOF, a dedicated optimization was necessary. Subsequently, to assess the feasibility of monitoring 12C particle pulses for the detection of MPs in more complex natural waters, two proof-of-principle studies were performed to measure MPs in waters with environmentally relevant DOC backgrounds (≤20 mg/L) and in the presence of other carbon containing particles, here, algae. Elevated DOC concentrations did not impact the enumeration of particles in suspension, and individual MPs, single algae, and aggregates of MPs and algae were clearly distinguished. The simultaneous identification of different analytes of interest allows for multiplexed sp-ICP-TOFMS experiments utilizing elemental fingerprinting of particles and is a step forward in quantifying MPs in aqueous environmental samples.
In this work, we evaluate the capabilities of a new commercially available inductively coupled plasma time-of-flight mass spectrometry (ICP-TOFMS) instrument, the icp TOF (TOFWERK AG, Thun, ...Switzerland), for analysis of liquid samples with a standard pneumatic nebulizer – cyclonic spray chamber sample-introduction system and a microdroplet sample-introduction system. The ICP-TOFMS instrument provides simultaneous, high-speed detection across almost the entire elemental mass range, from around 7–275 amu. The instrument provides a standard mass resolving power ( R m ) of ∼2500 and can provide R m greater than 4000 through the use of collisional cooling prior to the TOF mass analyzer. In standard operation mode (without collision gas), a sensitivity of 60 000 cps ppb −1 is routinely achieved for heavy elements such as U, with two orders of magnitude decrease in sensitivity from high-to-low masses. Limits of detection (LODs) are in the low parts-per-trillion to high parts-per-quadrillion. The data acquisition system of the TOFMS instrument provides a linear dynamic range greater than 10 6 . The native abundance sensitivity of the ICP-TOFMS is 6.5 × 10 −4 on an adjacent mass and is characterized by a non-linear sloping baseline beyond the adjacent mass channel. To obtain simultaneous high-dynamic-range detection, post-acquisition peak fitting and baseline subtraction can be used to reduce the effect of peak tailing on adjacent masses. Simultaneous quantification of adjacent isotopes across six orders of magnitude of signal intensity is possible after baseline subtraction. Advantages of ICP-TOFMS are apparent for high-speed transient analysis. Here, we assess the performance of the icp TOF for the multi-elemental analysis of single microdroplets, with specific emphasis on the characteristics of this approach for 100% transport of liquid samples and for the analysis of nanoparticles. Absolute limits of detection are in the attogram range for single droplets and concentration LODs for the detection of ensembles of droplets are competitive with those attained with pneumatic nebulization sample introduction.
Single-particle inductively coupled plasma mass spectrometry ( sp -ICP-MS) has become an effective tool for the detection and quantification of inorganic nanoparticles (NPs). While sizing of NPs ...suspended in water is relatively straightforward by sp -ICP-MS, accurate mass quantification of NPs in complex media, such as consumer products and natural systems still remains a challenge. When NPs are suspended in a complex medium, the matrix may affect the analyte sensitivity and lead to inaccurate NP sizing. Here, we investigate the use of an online microdroplet calibration system to size NPs in a single step. In this setup, microdroplets—which are used as the calibrant to determine elemental sensitivities—and nebulized NP-containing solutions are introduced concurrently into the ICP via a dual-inlet sample introduction system. Because calibrant microdroplets and analyte NPs experience the same plasma conditions, both the microdroplets and the NPs are subjected to the same matrix-related signal enhancement or suppression. In this way, the microdroplet calibration standards are automatically matrix matched with the NP-containing solution. The online microdroplet calibration system is combined with an ICP-TOFMS instrument for simultaneous measurement of multiple elements in microdroplets and NPs. We investigate the ability of online microdroplet calibration to compensate for matrix effects through a series of experiments, in which Ag and Au NPs are measured with variable plasma-sampling positions, varying concentrations of HCl and HNO 3 , varying concentrations of single element solutions, and high concentrations of a salt matrix, i.e. phosphate buffered saline (PBS). Through these experiments, we demonstrate that the online microdroplet calibration strategy provides a matrix-independent mass quantification of analyte NPs in the presence of several established types of matrix effects, including acid effects, space-charge effects, and ionisation suppression. In results presented here, we focus on the size determination of the NPs.
Herein we investigate the capabilities of near ultraviolet femtosecond laser ablation - inductively coupled plasma – time-of-flight mass spectrometry (NUV-fs-LA-ICP-TOFMS) for sub-100 nm depth ...profile analysis of a Cr/Ni metal thin film. For this purpose, the laser beam is guided through a homogenization scheme, which is based on aperture-assisted diffraction and reassembly of the beam by an optical lens. Using this set up, craters with well-defined cylindrical shapes are formed. Fluences between 0.6 and 1 J/cm2 were applied, resulting in mean LA up-take rate of 27 nm/pulse. Discrepancies between LA up-take rates and depth resolutions were examined by a Gaussian depth resolution function, commonly used in SIMS or AES. In this study, depth resolutions ranging from 47 nm up to 80 nm were determined.
Depth profile of SRM NIST 2135c analyzed by fs-LA-ICP-TOFMS. Display omitted
•Homogenization unit for femtosecond-laser ablation (fs-LA), which is based on a 2 stage Fourier optical processing•High-resolution depth profiling by fs-LA – inductively coupled plasma – mass spectrometry•Achieved depth resolution: 47 nm•Adaption of the well-defined formalism described by Hofmann for the evaluation of the depth resolution (S. Hofmann, Surface and Interface Analysis, 1986, 8 (2), 87-89.)•Detailed discussion of detrimental effects leading to increasing depth resolution values for increasing depth of transition
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