29 research outputs found
Single Particle Inductively Coupled Plasma Mass Spectrometry: Investigating Nonlinear Response Observed in Pulse Counting Mode and Extending the Linear Dynamic Range by Compensating for Dead Time Related Count Losses on a Microsecond Timescale
The article demonstrates the importance of using
a suitable approach to compensate for dead time relate count losses (a certain
measurement artefact) whenever short, but potentially strong transient signals are
to be analysed using inductively coupled plasma mass spectrometry (ICP-MS).
Findings strongly support the theory that inadequate time resolution, and
therefore insufficient compensation for these count losses, is one of the main
reasons for size underestimation observed when analysing inorganic
nanoparticles using ICP-MS, a topic still controversially discussed.</p
Single Particle Inductively Coupled Plasma Mass Spectrometry with Nanosecond Time Resolution
In this proof-of-principle study, we present our contribution to single particle inductively coupled plasma mass spectrometry (spICPÂMS) developments with a novel in-house built data acquisition system with nanosecond time resolution (nsDAQ) and a matching data processing approach. The new system can continuously sample the secondary electron multiplier (SEM) detector signal and enables the detection of gold nanoparticles (AuNP) as small as 7 nm with a commercial single quadru-pole ICPÂMS instrument. Recording of the SEM signal by the nsDAQ is performed with a dwell time of approximately 4 ns. A tailored method was developed to process this type of transient data, which is based on determining the temporal dis-tance between detector events that is denoted as event gap (EG). We found that the inverse logarithm of EG is proportional to the particle size and the number of detector events corresponding to a particle signal distribution can be used to calibrate and determine the particle number concentration of a nanoparticle dispersion. Due to the high data acquisition frequency, a statistically significant number of data points can be obtained in under 30 s and the main measurement time limitation for analyses is merely the sample uptake time and rinsing step between analyte solutions
Fast Separation, Characterization, and Speciation of Gold and Silver Nanoparticles and Their Ionic Counterparts with Micellar Electrokinetic Chromatography Coupled to ICP-MS
In
this study, a method for separation, size characterization,
and speciation of gold and silver nanoparticles was developed through
the use of micellar electrokinetic chromatography (MEKC) coupled to
inductively coupled plasma-mass spectrometry (ICP-MS) for the first
time. Figures of merit in this proof-of-principle study include peak
area precision of 4–6%, stable migration times (1.4% with internal
standard), and capillary recoveries on the order of 72–100%
depending on species and nanoparticle size, respectively. Detection
limits are currently in the sub-microgram per liter range. For example,
a total of 1500 50-nm-sized gold nanoparticles were successfully detected.
After careful optimization, MEKC-ICP-MS was used to separate engineered
nanoparticles (ENPs) of different composition. Speciation analysis
of ENPs and free metal ions in solution was feasible using a complexing
agent (penicillamine). Gold speciation analysis of a dietary supplement,
which contained approximately 6-nm-sized gold nanoparticles, was demonstrated
Characteristics of Low-Temperature Plasma Ionization for Ambient Mass Spectrometry Compared to Electrospray Ionization and Atmospheric Pressure Chemical Ionization
Ambient desorption/ionization mass spectrometry (ADI-MS)
is an
attractive method for direct analysis with applications in homeland
security, forensics, and human health. For example, low-temperature
plasma probe (LTP) ionization was successfully used to detect, e.g.,
explosives, drugs, and pesticides directly on the target. Despite
the fact that the field is gaining significant attention, few attempts
have been made to classify ambient ionization techniques based on
their ionization characteristics and performance compared to conventional
ionization sources used in mass spectrometry. In the present study,
relative ionization efficiencies (RIEs) for a large group of compound
families were determined with LTP-Orbitrap-MS and compared to those
obtained with electrospray ionization mass spectrometry (ESI-MS) and
atmospheric pressure chemical ionization mass spectrometry (APCI-MS).
RIEs were normalized against one reference compound used across all
methods to ensure comparability of the results. Typically, LTP analyte
ionization through protonation/deprotonation (e.g., 4-acetamidophenol)
was observed; in some cases (e.g., acenaphthene) radicals were formed.
Amines, amides, and aldehydes were ionized successfully with LTP.
A benefit of LTP over conventional methods is the possibility to successfully
ionize PAHs and imides. Here, the studied model compounds could be
detected by neither APCI nor ESI. LTP is a relatively soft ionization
method because little fragmentation of model compounds was observed.
It is considered to be an attractive method for the ionization of
low molecular weight compounds over a relatively wide polarity range
Separation of Silver Nanoparticles with Different Coatings by Capillary Electrophoresis Coupled to ICP-MS in Single Particle Mode
The
possibility of separating mixtures of Ag nanoparticles (NPs)
with similar sizes but different surface coatings using capillary
electrophoresis coupled to single particle inductively coupled mass-spectrometry
(CE-SP-ICP-MS) was investigated. In two-component mixtures, it was
possible to separate 40 nm sized polyvinylpirrolidone (PVP)- and citrate-coated
NPs, 40 nm sized polyethylene glycol (PEG)- and citrate-coated NPs,
and 60 nm sized PVP- and citrate-coated NPs. The separation of a more
complex mixture containing NPs with the different coatings and sizes
was successful, and each component, namely, 20, 40, and 60 nm sized
citrate-coated and 40 and 60 nm sized PVP-coated NPs, could be distinguished.
The theoretically expected migration order was confirmed by experimental
results with selected Ag NPs. On the basis of the experimental observations,
a separation mechanism that considers the effect of stable vs displaceable
coatings during NP migration in CE is suggested. The ICP-MS was equipped
with a prototype data acquisition system (ÎĽsDAQ) that provided
5 ÎĽs time resolution
Defective defence in Daphnia daughters: silver nanoparticles inhibit anti-predator defence in offspring but not in maternal Daphnia magna
Finanziert aus dem Open-Access-Publikationsfonds der Universität Siegen für Zeitschriftenartikel.One major environmental problem of our time are emerging contaminants in the aquatic environment. While nanoparticles exhibit attractive features such as antimicrobial properties in the case of silver nanoparticles (AgNPs), earlier studies suggest that NPs are not completely filtered out at wastewater treatment plants and may therefore be continuously introduced into the aquatic environment. Although adverse effects of AgNPs on aquatic organisms have been extensively studied, there is still a lack of knowledge on how this chemical stressor interacts with natural cues on the maternal and subsequent generation of aquatic organisms. We tested whether AgNPs (NM-300K, 14.9 ± 2.4 nm, concentration range: 2.5 µg/L – 20 µg/L) affect the kairomone-induced adaptive anti-predator defence mechanism in maternal Daphnia and their offspring. While maternal Daphnia developed typical anti-predator defence mechanisms when exposed to kairomones and AgNPs, their offspring could not develop such adaptive defensive traits. The lack of this defence mechanism in offspring could have dramatic negative consequences (e.g. reduced Daphnia population) for the entire complex food web in the aquatic ecosystem. For a realistic risk assessment, it is extremely important to test combinations of chemical stressors because aquatic organisms are exposed to several natural and artificial chemical stressors at the same time
Discrimination of Stressed and Non-Stressed Food-Related Bacteria Using Raman-Microspectroscopy
As the identification of microorganisms becomes more significant in industry, so does the utilization of microspectroscopy and the development of effective chemometric models for data analysis and classification. Since only microorganisms cultivated under laboratory conditions can be identified, but they are exposed to a variety of stress factors, such as temperature differences, there is a demand for a method that can take these stress factors and the associated reactions of the bacteria into account. Therefore, bacterial stress reactions to lifetime conditions (regular treatment, 25 °C, HCl, 2-propanol, NaOH) and sampling conditions (cold sampling, desiccation, heat drying) were induced to explore the effects on Raman spectra in order to improve the chemometric models. As a result, in this study nine food-relevant bacteria were exposed to seven stress conditions in addition to routine cultivation as a control. Spectral alterations in lipids, polysaccharides, nucleic acids, and proteins were observed when compared to normal growth circumstances without stresses. Regardless of the involvement of several stress factors and storage times, a model for differentiating the analyzed microorganisms from genus down to strain level was developed. Classification of the independent training dataset at genus and species level for Escherichia coli and at strain level for the other food relevant microorganisms showed a classification rate of 97.6%