Charge Detection Mass Spectrometry for the Characterization of Mass

Article pubs.acs.org/JPCC

Charge Detection Mass Spectrometry for the Characterization of Mass and Surface Area of Composite Nanoparticles Tristan Doussineau,† Anthony Désert,‡,§ Olivier Lambert,§ Jean-Christophe Taveau,§ Muriel Lansalot,∥ Philippe Dugourd,† Elodie Bourgeat-Lami,∥ Serge Ravaine,⊥ Etienne Duguet,‡ and Rodolphe Antoine*,† †

Institut Lumière Matière, UMR5306 Université Lyon 1-CNRS, Université de Lyon 69622 Villeurbanne cedex, France CNRS, ICMCB, UPR9048, §CNRS, CBMN, UMR5248, and ⊥CNRS, CRPP, UPR8641, Université de Bordeaux, F-33600 Pessac, France ∥ Laboratoire de Chimie, Catalyse, Polymères et Procédés (C2P2), LCPP group, UMR5265, Université de Lyon, Université Lyon 1, CPE Lyon, CNRS, F-69616 Villeurbanne, France ‡

S Supporting Information *

ABSTRACT: Binary colloidal particles of polyhedral morphology, obtained by an emulsion polymerization of styrene in the presence of silica seeds, are studied. Because of kinetic effects, composite particles usually exhibit polydispersity in size, shape, and composition. Thus, accurate techniques aiming at characterizing the size and the shape, as well as the composition and surface properties of such objects, are required. In this work, we use charge detection mass spectrometry (CD-MS) as a tool for the characterization of nanometer-sized composite (clusters of) particles. CD-MS measures both the mass and the charge for each ion. This single ion mass spectrometry technique enables one to construct a histogram of mass, yielding the mass distribution. CD-MS for molar mass determination and composition of composite particles is demonstrated to be complementary to transmission electron microscopy. The study of the charging capacity of these composite particles in the gas phase also appears as a valuable approach to probe the surface area of such complex nano-objects, thus giving some insight about their structure and morphology.

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counterparts of molecules made of atoms.5,6,8,9 However, fabricating, in a reproducible manner, large amounts of composite nanoparticles with appropriate size, composition, surface properties, and shape uniformity, remains challenging.7 Recently, polystyrene/silica binary colloidal assemblies of controlled polyhedral morphology were obtained by an emulsion polymerization of styrene in the presence of silica seeds.9,10 In contrast to atomic clusters, due to kinetic effects, these polystyrene/silica (PS/silica) “clusters” present polydispersity in size, shape, and composition. Thus, accurate techniques aiming at characterizing the size, the size distribution, and the shape as well as the composition and surface properties of such colloidal objects are required. Various analytical techniques are used to provide these characteristics, among which the most common are microscopy techniques, for example, transmission electron microscopy (TEM), and light scattering techniques, for example, dynamic light scattering (DLS).11,12 These techniques actually provide different morphological features,

INTRODUCTION Polyhedra, particularly the platonic solids, are ubiquitous in nature and appear at different length scales, from the electron and spin densities at the subatomic level up to everyday objects. In atomic cluster science, it is well-known that clusters containing specific number of atoms occur much more frequently than others. The preferred values of nuclearity (often called “magic number”) correspond to various symmetrical, close-packed polygons (in two dimensions) and polyhedra (in three dimensions).1 Strong evidence for certain “magic number” clusters was obtained largely from mass spectrometric experiments,2,3 the most famous example being C60 (buckminsterfullerene adopting the truncated icosahedron structure).4 This concept can be extended at larger scales, that is at micro- and nanometer length scales. Particles of highly complex morphology and composition can now be produced, dramatically increasing the potential of technological development toward (nano)materials with new properties, improved performance, or multifunctionality. In particular, one way to obtain particles of anisotropic shape and composite composition is to produce, in a controlled manner, “clusters” of spherical particles.5−7 If these composite objects exhibit colloidal properties, they are called “shape-anisotropic colloids”, “colloidal clusters” or even “colloidal molecules” as mesoscopic © XXXX American Chemical Society

Special Issue: Current Trends in Clusters and Nanoparticles Conference Received: October 6, 2014 Revised: November 21, 2014

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dx.doi.org/10.1021/jp510081v | J. Phys. Chem. C XXXX, XXX, XXX−XXX

The Journal of Physical Chemistry C

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such as an equivalent 2D projected dimension for TEM and an equivalent translator diffusion hydrodynamic diameter for DLS. Whether the measurement is based on single-particle or ensemble approaches affects the degrees of uncertainty and precision. Furthermore, DLS, as most of the other sizing techniques, reports particle size in terms of equivalent spheres only. Thus, orthogonal morphological characterization approaches are usually highly recommended. Conventional mass spectrometry (MS) has limitations for weighing nanoparticles. Mass-to-charge ratio (m/z) spectra become unsolvable because high mass ions may carry an unresolvable distribution of charges. Moreover, large ions may not all have exactly the same mass due to sample heterogeneity (i.e., size and morphology polydispersities). One solution to overcome these limitations is to measure both the m/z ratio and the charge (z) for each ion.13 This single ion mass spectrometry enables one to construct a histogram of mass, yielding the mass distribution. A convenient way to measure the charge of individual ions is to use image charge detection. This approach was pioneered by Shelton in 1960 for characterizing multiply charged microparticles.14 On the basis of this concept of image current detection, charge-detection mass spectrometry (CD-MS) coupled to electrospray ionization (ESI) was introduced by Benner and co-workers in 1995 for weighing macro-ions with masses higher than one megadalton.13 Very recently, Jarrold and co-workers further improved this approach by demonstrating the ability of this technique to detect late intermediates in a virus capsid assembly.15 A direct and accurate determination of the absolute molar mass distributions of electrosprayed synthetic self-assembled polymer nanoparticles was recently obtained by CD-MS measurements. 16 In particular, the pertinence of CD-MS for molar mass determination was demonstrated by comparison with other analytical techniques, namely TEM and DLS. In addition to mass measurements, CD-MS measures the charge (z) for each ion by image charge detection. This has permitted for the first time the charging capacity of electrosprayed polymer nanoparticles to be addressed.17,18 Besides the number of ionizable groups, their surface accessibility is a key parameter to charging capacity. For instance, for proteins, charge state distributions can deliver important structural information, the higher the structural compactness is , the lower the average net charge will be observed for any given protein.19 It is in this context that we report here on the use of CD-MS to characterize for the very first time composite clusters of nanoparticles, namely binary polystyrene/silica tetra-, hexa-, and dodecapods (abbreviated as TP, HP, and DDP, respectively), prepared by a seeded-growth emulsion polymerization of styrene. The studied objects are depicted in Figure 1. The results obtained by CD-MS are compared with those from TEM analysis. Furthermore, measured charging capacities of these nanostructures electrosprayed in the gas phase are used as a probe of their surface area.

Figure 1. Transmission and scanning electron micrographs of the tetrapods (TP), hexapods (HP), and dodecapods (DDP) along with schematic drawings of the sphere configurations and projected polyhedra formed by drawing lines from the center of each PS nodule to its neighbors. Platonic solids are also represented.

seeds” were fabricated through the slow hydrolysis/condensation of tetraethoxysilane (TEOS, 99%, Aldrich) on the top of a 6 mM L-arginine (98.5%, Aldrich) aqueous solution at 60 °C. (ii) To obtain a precise diameter, a controlled regrowth was performed at room temperature in a classical Stöber-like reaction medium with ethanol (99.9%, Scharlau) and ammonia (28−30% in water, J. T. Baker) where a calculated amount of TEOS was added at the rate of 0.5 mL h−1. To activate the silica surface, methacryloxymethyltriethoxysilane (MMS, 97%, ABCR) was added to the reaction mixture at the concentration of 0.5 functions nm−2 of silica (based on the estimate of the silica developed surface area from the average diameter and concentration values). Aqueous dispersions of purified MMSmodified silica seeds were finally obtained by the help of a rotary evaporator and then by dialysis against ultrapure water (18.2 MOhm·cm at 25 °C, Millipore). (iii) Seeded-growth emulsion polymerization of styrene at 100 g L−1 (99% purity, inhibited with 4-tert-butylcatechol, Aldrich) was performed according to unvaried conditions in a thermoregulated reactor at 70 °C under a nitrogen atmosphere, using Synperonic NP30 (Aldrich) and sodium dodecyl sulfate (99%, Aldrich) at a total surfactant concentration of 3 g L−1 and sodium persulfate (99%, Aldrich) introduced at 0.5% w/w relative to monomer as initiator. By modifying the concentration and diameter values of silica seeds and the SDS fraction (relative to the total surfactant concentration), various PS/silica composite samples were prepared: TP were predominantly obtained with 8.8 × 1015 L−1 of 85 nm-silica seeds and 1 wt % SDS, HP were obtained with 5.5 × 1015 L−1 of 85 nm-silica seeds and 5 wt % SDS, and DDP were obtained with 2.5 × 1015 L−1 of 146 nmsilica seeds and 5 wt % SDS. TEM. TEM images were obtained with a FEI CM120 microscope operating at an accelerating voltage of 120 kV. Typically, samples were diluted 100 times in ethanol and one drop was deposited on a copper grid coated with a carbon membrane. The average diameter of the silica or PS latex particles was measured directly from the transmission electron micrographs by using the ImageJ software. Statistical analyses of the particles morphology were performed on a minimum of 400 objects per batch. CD-MS . Experiments were performed on a custom-built charge detection-mass spectrometer with an electrospray ionization source. This instrument was described in details in

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EXPERIMENTAL SECTION Synthesis of Composite Nanoparticles. Some years ago, we have reported the high-yield synthesis of binary polystyrene (PS)/silica multipods with a controlled morphology by a seeded-growth emulsion polymerization of styrene9 which was recently optimized by taking advantage of the complementary roles of nonionic and ionic surfactants.10 Typically, they were obtained according to a three-stages process. (i) Silica “preB



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then adjusted to best fit the experimental mass distribution of the samples.

previous works.20,21 Briefly, aqueous mother dispersions of composite particles (TP, HP, and DDP) were dialyzed and 10fold diluted in a 1:1 water/methanol solvent mixture and gently vortexed (1 min, 10 Hz) before injection into the ESI source. Respective concentrations were estimated to 8.0 × 1013, 2.0 × 1013, and 1.6 × 1013 particles L−1. Dispersions were injected at flow rates of typically 200 μL h−1 and entered the electrospray chamber through a 0.1 mm internal diameter stainless steel capillary tube located inside the needle tip. Nitrogen gas was injected between the end-cap and the transfer glass capillary and was moved through a heater typically set at 200 °C. The vacuum interface was composed of a glass transfer capillary that passes the ions into the first stage of the vacuum system, an end-cap, a skimmer between the first and second vacuum stages, a hexapole ion guide and an exit lens. The signal induced on the tube was picked up by a junction field effect transistor, was amplified by a low-noise, charge-sensitive preamplifier, and then was shaped and differentiated by a home-built amplifier. The signal was recorded with a waveform digitizer card. The data were transferred to a desktop computer where they were analyzed to compute the charge and mass of each ion. Calibration in charge was performed using a test capacitor that allowed a known amount of charge to be pulsed onto the pick-up tube. The test pulses were generated with a shapingpulse generator so that the time-dependent signal response could be determined as well. The charge of a particle was then directly deduced from this calibration and from the average value of the voltage intensity of the two pulses generated by the particle on the detector. For a single ion measurement, the charge precision is ∼350 electrons. The charge precision is given by Δz/z. The average charge of our composite particles range from ∼4000 to ∼7000 e. The charge precision is CP ≈ 5% to 9%. However, the average value is extracted from N single ion measurements and then the precision on the average values is defined by CP/(N)1/2. The intrinsic precision on masses is mainly given by the charge precision. The mass-tocharge m/z ratio of an ion was determined from the time-offlight Δt (time delay between the positive and negative pulses that corresponds to the entrance and the exit from the detector tube).20,21 An external calibration was performed using NIST traceable size standards (70, 100, 150, 200, 250, 300, 350, 400, 450, and 500 nm PS nanospheres supplied by Polysciences Europe GmbH). The resulting calibration curve (Figure S1 in Supporting Information) allowed us to obtain an accurate value of mass over a large size range. These spherical size standards were chosen because of their appreciable monodispersity, with a coefficient of variation varying from 0.6% (450 nm) to 14.7% (70 nm) for the standards considered here according to the certificate of analysis given by the supplier. Over 5000 individual ion signals were collected for each standard in order to statistically minimize random errors. Overall uncertainties on m and z are specified accordingly. Mass histograms of the studied composite objects were built from the collection of a statistically relevant number N of single mass measurements for each sample (N > 1000, typically). Respective experimental mass distributions of composite particles were deconvoluted in a sum of individual mass distributions, each corresponding to a composite of particular composition possibly present in the synthesis product. These individual mass distributions were described by a LogNormal function where mean mass and width values were calculated using the experimental mass distributions of free silica seeds and free PS beads. The weight of each LogNormal function was

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RESULTS AND DISCUSSION Molar Mass Distributions. Representative electrospray CD-MS scatter plots together with the respective projection of the mass distribution for produced TP, HP, and DDP are depicted in Figure 2. In vis-à-vis are also shown representative

Figure 2. Charge vs mass 3D scatter plots for (a) TP, (b) HP, and (c) DDP together with their corresponding mass distribution (histogram in red). In vis-à-vis are shown the corresponding TEM images with projected polyhedra formed by drawing lines from the center of each PS nodule to its neighbors.

TEM images. At a first glance, CD-MS spectra clearly indicate the presence of two main populations for each sample. The one exhibiting the lightest molar mass is attributed to the presence of free PS beads in the colloidal suspensions. If one assumes that these free PS beads are perfect spheres of density 1.055 (density of bulk PS),22 mass-converted equivalent mean C



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Table 1. Relative Proportions of the Two Main Populations for Each Studied Sample, Calculated on the Basis of the Number N of Chemical Species (Cluster or Free PS Beads) Taken into Account in Both Techniques (TEM and CD-MS) TP % free PS beads (N) % clusters (N)

TEM CD-MS TEM CD-MS

10.7 (140) 8.5 (146) 89.3 (1163) 91.5 (1564)

HP 56.0 35.8 44.0 64.2

(659) (846) (517) (1519)

DDP 43.4 54.0 56.6 46.0

(319) (836) (416) (711)

diameters are 175.8, 178.1, and 185.8 nm, respectively (Figure 2 panels a to c). For the heavy ion population in each figure, mean mass values of 10369 ± 22, 15468 ± 28, and 30446 ± 59 MDa were determined from the fitting of the distribution using the LogNormal function:

where xc corresponds to the mean value of the distribution and w is a statistical indicator of the dispersity of the distribution. Polydispersity indexes (PDIs) of the distributions could be calculated out of this w value using PDI = exp(w2). PDIs of 1.042, 1.027, and 1.030 were thus determined for tetrapod, hexapod, and dodecapod samples, respectively indicating a relatively low polydispersity of the samples. These heavy ion populations correspond to objects composed by a different number of pods. A qualitative comparison deduced from CDMS and TEM analyses of the proportion of multipods versus free beads is given in Table 1. A first relatively good agreement is observed. Deconvolution of the Molar Mass Distribution. The ion population corresponding to the resulting composite particles was deconvoluted in a sum of several subpopulation contributions as shown in Figure 3. Distributions of these subpopulations were described by LogNormal functions. Mean molar mass of silica seeds were calculated using their mean physical diameters as estimated by TEM and applying a density of 2.3, that is 445 MDa for tetrapod and hexapod samples (85 nm) and 2256 MDa for the dodecapod sample (146 nm). To best fit the experimental mass distribution of the samples, a molar mass of 2500 MDa for the PS nodules was chosen and applied to the overall molar mass calculation of the respective multipods. The weight of the subpopulation distributions was finally tuned to best fit the experimental distributions. As an example, the HP experimental distribution is described by the sum of subpopulations of tripods (7945 MDa), tetrapods (10445 MDa), pentapods (12945 MDa), hexapods (15445 MDa), and heptapods (17945 MDa). The determined parameters on each subpopulation enable a remarkably well fit of the experimental distributions for each sample (red curves in Figure 3) and in particular, the specific asymmetrical distribution of the DDP sample exhibiting a shoulder at lower molar masses. In addition, the weights assigned for each subpopulation allowed us to provide an estimate of their relative proportion in the overall distribution. These data are compiled in Table 2 where they are compared to the similar quantitative analysis based on TEM images. Interestingly, it appears that there is a remarkably good agreement between the data obtained from both techniques. For instance, CD-MS quantitative analysis of tetrapod and hexapod samples exhibits a very high proportion of the respective expected morphology that is 86.2 and 84.8% as compared to 80.4 and 77.6% by TEM

Figure 3. Experimental mass distributions measured by CD-MS (histograms of empty black bars) for (a) TP, (b) HP, and (c) DDP. Experimental distributions are deconvoluted with a combination of subpopulations described by LogNormal distributions (green curves) with optimized parameters (see text for more details). The red curve corresponds to the sum of these functions.

analysis, respectively. Regarding the dodecapod sample quantitative CD-MS analysis, the proportion of the expected D



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Table 2. Relative Proportions of the Subpopulations Constituting the Cluster Distribution As Determined by TEM and CD-MS TP no. of pods 1 2 3 4 5 6 7 8 9 10 11 12

HP

TEM

CD-MS

0.5% 18.4% 80.4% 0.7%

0.5% 12.6% 86.2% 0.6%

DDP

TEM

CD-MS

2.1% 4.4% 15.3% 77.6% 0.6%

0.2% 0.2% 14.3% 84.8% 0.5%

TEM

CD-MS

6.7% 7.5% 22.8% 12.0% 51.0%

4.2% 4.2% 20.8% 8.3% 62.5%

Figure 4. Charge vs mass plot showing the mean values obtained experimentally by CD-MS for TP, HP, and DDP and their respective distributions (blue solid squares and bars). Black triangles represent the hypothetical number of charges corresponding to the sum of the number of charges carried by separated individual entities (SSeqZ model). Red triangles represent the number of charges that would carry a PS bead of the same molar mass as the cluster (PSBeqZ model). Green circles represent the total number of charges of colloidal clusters assuming polyhedral structures (i.e., tetrahedral, octahedral, and icosahedral as depicted).

morphology (n = 12, n being the number of pods) is also in qualitative good agreement with TEM analysis, with respective proportion of 62.5% and 51%. The significant contribution of the (n − 2) multipods to the overall distribution, as evidenced by TEM analysis, is also clearly demonstrated in CD-MS analysis with a proportion as high as 20.8% as compared to 22.8% in TEM analysis. Charging Capacity. In addition to mass measurements, CD-MS measures the charge (z) for each composite ion. Besides the number of ionizable groups, their surface accessibility is a key parameter to charging capacity. The charging capacity of the particles can be viewed as a morphology probe enlightening to some extent how the different building blocks are arranged together. Indeed, ionizable groups are equally distributed on the surface of the nano-objects, and the charging capacity of the objects is actually a function of their accessible surface area in the defined conditions. The experimental mean number of charges for each sample as a function of their mass, together with their respective distribution are shown in Figure 4 (blue solid squares). These experimental values (ExpZ) were compared with the expected number of charges that would carry an equivalent spherical PS bead of the same molar mass (PSBeqZ, red triangles). The diameter of the equivalent spherical PS bead was calculated assuming a density of 1.055. The number of charges that would carry this hypothetical object are then calculated using the relation PSBeqZ = 0.02907 m 1/2 (experimentally measured fraction of the Rayleigh limit charge for PS beads in water/methanol 50/50, with m in Da).16 Experimental values (ExpZ) were also compared with the sum of the number of charges that would carry every individual entity constituting the composite objects (SSeqZ), PS pods and silica seeds being hypothetically considered as fully separated spheres. This leads to the relation SSeqZ = n × ZPS + Zsilica where n is the number of PS pods constituting the object and ZPS and ZSilica are the experimentally measured number of charges of individual PS pods and silica seeds, respectively. For instance, a tetrapod sample is characterized by a mean molar mass of 10369 ± 22 MDa and a mean number of charges of 4177 ± 9 e. The latter (ExpZ) can be compared to a PSBeqZ of 2960 e and to a SSeqZ of 6294 e. Thus, ratios ExpZ/PSBeqZ and ExpZ/SSeqZ are 1.41 and 0.66, respectively. Interestingly, these ratios changed for hexapod and dodecapod samples. They are 1.37 and 0.58 for HP, and 1.34 and 0.37 for DDP. As the

ratio ExpZ/SSeqZ drastically decreases from 0.66 to 0.37 as the number of pods increases, this first demonstrates that the composite assembly cannot be considered as fully separated spheres. Moreover the fact that the ExpZ/PSBeqZ ratio simultaneously decreases indicates that the charging capacity of the objects gets closer to the PSBeqZ model as the number of pods increases. This is physically reasonnable with the concomitant decrease in the surface (accessible surface area)to-volume (molar mass) ratio as the number of pods increases. To be more quantitative, we calculated the outer accessible surface (Sout) of each composite object assuming tetrahedral, octahedral, and icosahedral structures. The total number of charges of such objects is given by the ratio n × ZPS × Sout/SPS, where n is the number of PS pods constituting the object and ZPS and SPS are the number of charge and the surface of individual PS pods, respectively. These calculated number of charges that would carry such polyhedral composite clusters of nanoparticles were compared to experimental values (ExpZ) as well (green triangles). A good agreement between measured and calculated charges was obtained, demonstrating that in addition to mass measurements, charge measurements extracted from CD-MS can be used to get a rough estimation of the accessible surface of the composite object and eventually information on its morphology, as already exploited protein structural studies in the gas-phase.23,24

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CONCLUSIONS In summary, we used charge detection mass spectrometry (CDMS) as a new tool for the characterization of nanometer-sized, shape-anisotropic composite objects. CD-MS measures both the mass and the charge for each ion. This single ion mass spectrometry technique enables one to construct a histogram of mass, yielding the mass distribution. The pertinence of CD-MS for molar mass determination and colloidal composition is demonstrated by comparison with another analytical technique, namely TEM. The study of the charging capacity of the gas phase composite particles also appears as a valuable approach to probe the accessible surface area of such complex nano-objects. E



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(14) Shelton, H.; Hendricks, C. D., Jr.; Wuerker, R. F. Electrostatic Acceleration of Microparticles to Hypervelocities. J. Appl. Phys. 1960, 31, 1243−1246. (15) Pierson, E. E.; Keifer, D. Z.; Selzer, L.; Lee, L. S.; Contino, N. C.; Wang, J. C. Y.; Zlotnick, A.; Jarrold, M. F. Detection of Late Intermediates in Virus Capsid Assembly by Charge Detection Mass Spectrometry. J. Am. Chem. Soc. 2014, 136, 3536−3541. (16) Doussineau, T.; Bao, C. Y.; Antoine, R.; Dugourd, P.; Zhang, W.; D’Agosto, F.; Charleux, B. Direct Molar Mass Determination of Self-Assembled Amphiphilic Block Copolymer Nanoobjects Using Electrospray-Charge Detection Mass Spectrometry. ACS Macro Lett. 2012, 1, 414−417. (17) Ouadah, N.; Doussineau, T.; Hamada, T.; Dugourd, P.; Bordes, C.; Antoine, R. Correlation between the Charge of Polymer Particles in Solution and in the Gas Phase Investigated by Zeta-Potential Measurements and Electrospray Ionization Mass Spectrometry. Langmuir 2013, 29, 14074−14081. (18) Doussineau, T.; Santacreu, M.; Antoine, R.; Dugourd, P.; Zhang, W.; Chaduc, I.; Lansalot, M.; D’Agosto, F.; Charleux, B. The Charging of Micellar Nanoparticles in Electrospray Ionization. ChemPhysChem 2013, 14, 603−609. (19) Kaltashov, I. A.; Bobst, C. E.; Abzalimov, R. R. Mass Spectrometry-Based Methods to Study Protein Architecture and Dynamics. Protein Sci. 2013, 22, 530−544. (20) Doussineau, T.; Bao, C. Y.; Clavier, C.; Dagany, X.; Kerleroux, M.; Antoine, R.; Dugourd, P. Infrared Multiphoton Dissociation Tandem Charge Detection-Mass Spectrometry of Single Megadalton Electrosprayed Ions. Rev. Sci. Instrum. 2011, 82, 084104. (21) Doussineau, T.; Kerleroux, M.; Dagany, X.; Clavier, C.; Barbaire, M.; Maurelli, J.; Antoine, R.; Dugourd, P. Charging Megadalton Poly(ethylene oxide)s by Electrospray Ionization. A Charge Detection Mass Spectrometry Study. Rapid Commun. Mass Spectrom 2011, 25, 617−623. (22) Sharp, D. G.; Beard, J. W. Size and Density of Polystyrene Particles Measured by Ultracentrifugation. J. Biol. Chem. 1950, 185, 247−253. (23) Beveridge, R.; Chappuis, Q.; Macphee, C.; Barran, P. Mass Spectrometry Methods for Intrinsically Disordered Proteins. Analyst 2013, 138, 32−42. (24) Konermann, L.; Vahidi, S.; Sowole, M. A. Mass Spectrometry Methods for Studying Structure and Dynamics of Biological Macromolecules. Anal. Chem. 2013, 86, 213−232.

CD-MS could become a valuable alternative technique for the direct and fast characterization of mixtures of complex colloidal nano-objects in terms of composition and morphology.

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ASSOCIATED CONTENT

S Supporting Information *

Calibration curve obtained using NIST traceable size standards. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +33 4 72 43 10 85. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to the Agence Nationale de la Recherche for supporting this work (Grants ANR-08-BLAN-0110-01 and ANR-11-PDOC-032-01). The authors would like to thank Xavier Dagany, Christian Clavier, Michel Kerleroux, Marc Barbaire, Jacques Maurelli, Franck Bertorelle, and Céline Hubert for their invaluable technical assistance.

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Charge Detection Mass Spectrometry for the Characterization of Mass

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