Evaluation of solution-cathode glow discharge atomic emission spectrometry for the analysis of nanoparticle containing solutions

https://doi.org/10.1016/j.sab.2020.106040Get rights and content

Highlights

  • The solution-cathode glow discharge (SCGD) is used for the direct analysis of nanoparticle-containing solutions.

  • Analytical response of the SCGD to solutions containing nanoparticles is examined with varying experimental parameters.

  • A nested-capillary design is developed to introduce nanoparticles directly into the SCGD/plasma interface.

  • Decreased sensitivity of 20%–80% for nanoparticle solutions was seen during the experiment. Sensitivity could be recovered by acid-digestion.

  • Results are interpreted to gain insights into the potential mechanisms occurring at the interface between the plasma and liquid sample.

Abstract

The Solution Cathode Glow Discharge (SCGD) is a novel atmospheric-pressure glow discharge plasma sustained in the ambient atmosphere that is an appealing alternative to the inductively-coupled plasma as a source for atomic emission spectrometry. Simple, low power, and inexpensive, the SCGD is an attractive source for continuous environmental monitoring applications such as the quantitation of metallic nanoparticle solutions by atomic emission spectrometry. Metallic nanoparticles (NP) with diameters from 5 nm-150 nm were directly analyzed by SCGD-AES and found to exhibit lower, and size-dependent, elemental sensitivity when compared to dissolved free-ion standard solutions. Acid digestion with matrix-matching was shown to be an effective approach to achieve accurate quantitation. The origin of these morphological matrix effects was studied by investigating experimental parameters such as discharge power, solution flow rate, and influence of added surfactants. Examination of the spatial distribution of atomic emission between cathode and anode showed a shift in peak atomic emission towards the anode of the SCGD for some NPs as compared to free-ion solutions. A novel nested capillary design was used to introduce NP into the SCGD without dissolution within the acidic solvent and showed difference in sensitivity from free-ion solutions to be a NP morphological effect. Correlation of NP boiling point with difference in sensitivity between free-ion and NP solutions supports the conclusion that delayed vaporization of nanoparticles is the source of the morphological matrix effect, due primarily to lower rate of vaporization within the SCGD by lower gas temperatures and short residence time. Analysis of NP of different chemical form, and alloyed nanoparticles composed of more than one element, showed correlation with boiling point. Implications of these results on the possible mechanisms by which material is transferred from the liquid cathode into the plasma are considered.

Introduction

The solution-cathode glow discharge (SCGD) is a very simple, inexpensive alternative to the inductively-coupled plasma (ICP) for atomic emission analysis. In contrast to the ICP, the SCGD uses relatively low operating power (<100 W), does not require radio-frequency electronics, operates in ambient air without supporting gas flow (e.g. Ar), and requires no external nebulization equipment. Through iterative improvement, the SCGD has developed to the point where it holds analytical figures of merit on par with radially viewed ICP-AES [1], and this level of analytical performance paired with its benefits suggests that SCGD-AES is an attractive approach for mobile, field-portable, continuous onsite analysis [2,3].

A variety of applications of the SCGD have also been reported. Environment samples have been analyzed for industrially relevant metals (Te, Rh, In) with detection limits below 1 mg/L [4], and even complex samples like honey have been analyzed for Na, Ca, Cu, Fe, Li, Mg, Mn, Rb and Zn with detection limits almost entirely below 1μg/g [5]. Because the SCGD is based on a flowing liquid stream, it is very well suited for analysis of transients such as those from chromatographic separations. The plasma has been used with flow injection analysis [6], as a chromatographic detector [7], and with a novel type of ion-exchange chromatography [8]. The SCGD has even been employed as an ionization source for molecular mass spectrometry for the fragmentation of peptides [9]. Recently, trace metal contaminants in colloidal samples have been analyzed by SCGD-AES. Wang et al. quantified trace Li, Na, Mg, and K in aqueous dispersions of 22 nm dia. silica nanoparticles using the SCGD, reporting concentrations with relative accuracy within 7%–20% of the true value in slurry samples containing up to 20 mg/mL using external calibration [10]. Previously, a maximum of 10 mg/mL was achieved [11]. This result has generated significant interest, since analysis of refractory material slurries and nanoparticles are notoriously difficult without extensive sample treatment and dissolution steps.

In this paper, we report the first systematic study of the viability of using SCGD-AES for the analysis of NPs. NPs are increasingly seen as a subject of environmental concern as they are increasingly manufactured, used, and released into the environment [[12], [13], [14]]. NPs of various types have been shown to be potentially useful as anti-cancer drugs and sensing techniques [15,16], but also to pose potential biological issues, with some showing toxic effects [[17], [18], [19]], while others appear relatively benign [20]. Thus, accurately determining the identity, presence, size, and concentration of these species is of significant interest [21]. Unfortunately, current analytical strategies are relatively expensive and not amendable to continuous field-based monitoring. For example, hyphenated ICP-based techniques are currently commonly used in the analysis of NP solutions [22]. Here, a chromatographic sizing step such as size-exclusion chromatography [23] or field flow fractionation [24] is followed by quantitation by atomic spectrometry. Alternatively, single-particle ICP-MS is able to directly analyze and size sample solutions without previous separation [25]. However, ICP-MS analysis comes at a higher cost as it requires vacuum conditions, high-power electronics, complicated data processing components, and high gas flow rates of purified Ar.

In this report we examine the efficacy of the SCGD for the analysis of nanoparticle materials likely to be encountered in environmental samples with the eventual goal of using SCGD-AES for on-site, portable, and continuous analysis of effluent streams for potential contaminants. Because elements within the NP are introduced into the plasma as particles, as opposed to solvated ions as in normal conditions, analysis of various metal particulate samples by SCGD-AES also provides insights into the mechanisms by which material is removed from the liquid cathode of the SCGD and vaporization within the plasma. Lastly, analysis of NP atomic emission also provides some insight into the possible factors influencing the synthesize NPs using the SCGD plasma [26].

Section snippets

Experimental

The SCGD used here is shown in Fig. 1 and was similar to that reported previously elsewhere [27]. Briefly, sample solution was introduced into a quartz capillary (0.38 mm I.D. and 1.1 mm O·D.) at a rate of 2.5 mL/min using a peristaltic pump, where it overflowed into a waste reservoir of roughly 175 mL volume. The SCGD discharge was sustained between the sample solution as it exited the capillary (cathode) and a tungsten electrode (anode) by the bias network shown in Fig. 1. A high voltage

Relative sensitivity of nanoparticle solutions

In order to accurately quantitate nanoparticle concentrations as total metal in a sample using a simple external calibration approach, the sensitivity of a measurement for the analyte element should be identical whether the element is present as free-ion in solution or present as nanoparticles, or at worst, these sensitivities should be related by a reproducible factor. To determine if nanoparticles and free-ion standard solutions showed similar atomic emission response in the SCGD, calibration

Conclusions

The analysis of dispersions of NPs by SCGD-AES has been reported for the first time. Direct analysis of NP showed a significant decrease in observed sensitivity as compared to free-ion standard solutions, with NPs showing lower sensitivity from 14.3 ± 7.1% to 93.2 ± 1.5% as compared to the fee-ion solutions depending upon the NP composition, size, and morphology. Conventional acid digestion and matrix matching was shown to permit accurate quantitation of NP solutions, with limits of detection

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This material is based upon work supported by the National Science Foundation under Grant No. (CHE-1622531). The authors also acknowledge support from the State University of New York at Buffalo. The authors gratefully acknowledge the contribution of the UB Department of Chemistry Mass Spectrometry Facility, the UB CAS Machine Shop, and the UB Department of Chemistry Electronic Shop. The authors also thank and acknowledge the ICP Information Newsletter and Professor Ramon Barnes, and Indiana

References (65)

  • H. Prestel

    Characterization of sewage plant hydrocolloids using asymmetrical flow field-flow fractionation and ICP-mass spectrometry

    Water Res.

    (2005)
  • A.J. Schwartz

    Visual observations of an atmospheric-pressure solution-cathode glow discharge

    Talanta

    (2012)
  • J.L. Venzie et al.

    Effects of easily ionizable elements on the liquid sampling–atmospheric pressure glow discharge

    Spectrochim. Acta B At. Spectrosc.

    (2006)
  • A.J. Schwartz

    Spatially resolved measurements to improve analytical performance of solution-cathode glow discharge optical-emission spectrometry

    Spectrochim. Acta B At. Spectrosc.

    (2016)
  • K. Greda et al.

    The improvement of the analytical performance of direct current atmospheric pressure glow discharge generated in contact with the small-sized liquid cathode after the addition of non-ionic surfactants to electrolyte solutions

    Talanta

    (2013)
  • K.-S. Ho

    Considerations of particle vaporization and analyte diffusion in single-particle inductively coupled plasma-mass spectrometry

    Spectrochim. Acta B At. Spectrosc.

    (2013)
  • D.B. Robb et al.

    State-of-the-art in atmospheric pressure photoionization for LC/MS

    Anal. Chim. Acta

    (2008)
  • X. Peng

    Battery-operated portable high-throughput solution cathode glow discharge optical emission spectrometry for environmental metal detection

    J. Anal. At. Spectrom.

    (2019)
  • K. Greda

    Direct elemental analysis of honeys by atmospheric pressure glow discharge generated in contact with a flowing liquid cathode

    J. Anal. At. Spectrom.

    (2015)
  • M.R. Webb et al.

    High-throughput elemental analysis of small aqueous samples by emission spectrometry with a compact, atmospheric-pressure solution-cathode glow discharge

    Anal. Chem.

    (2007)
  • A.J. Schwartz

    Universal anion detection by replacement-ion chromatography with an atmospheric-pressure solution-cathode glow discharge photometric detector

    Anal. Chem.

    (2013)
  • Z. Wang

    Determination of trace sodium, lithium, magnesium, and potassium impurities in colloidal silica by slurry introduction into an atmospheric-pressure solution-cathode glow discharge and atomic emission spectrometry

    J. Anal. At. Spectrom.

    (2013)
  • Z. Wang

    Design modification of a solution-cathode glow discharge-atomic emission spectrometer for the determination of trace metals in titanium dioxide

    J. Anal. At. Spectrom.

    (2014)
  • A.A. Keller

    Global life cycle releases of engineered nanomaterials

    J. Nanopart. Res.

    (2013)
  • Y. Yang

    Nanoparticles in road dust from impervious urban surfaces: distribution, identification, and environmental implications

    Environ. Sci. Nano

    (2016)
  • X.F. Zhang

    Silver nanoparticles: synthesis, characterization, properties, applications, and therapeutic approaches

    Int. J. Mol. Sci.

    (2016)
  • Hanna L. Karlsson et al.

    Copper oxide nanoparticles are highly toxic: a comparison between metal oxide nanoparticles and carbon nanotubes

    Chem. Res. Toxicol.

    (2008)
  • A. López-Serrano

    Nanoparticles: a global vision. Characterization, separation, and quantification methods. Potential environmental and health impact. Anal

    Methods

    (2014)
  • C. Yausheva Capital Ie et al.

    Intestinal microbiome of broiler chickens after use of nanoparticles and metal salts

    Environ. Sci. Pollut. Res. Int.

    (2018)
  • B. Meermann et al.

    ICP-MS for the analysis at the nanoscale – a tutorial review

    J. Anal. At. Spectrom.

    (2018)
  • S. Wagner

    First steps towards a generic sample preparation scheme for inorganic engineered nanoparticles in a complex matrix for detection, characterization, and quantification by asymmetric flow-field flow fractionation coupled to multi-angle light scattering and ICP-MS

    J. Anal. At. Spectrom.

    (2015)
  • S. Naasz

    Multi-element analysis of single nanoparticles by ICP-MS using quadrupole and time-of-flight technologies

    J. Anal. At. Spectrom.

    (2018)
  • Cited by (0)

    This paper is dedicated to Paul Farnsworth, following his retirement, in recognition of his outstanding contributions to the fields of optical emission spectroscopy and mass spectrometry.

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