UHPLC combined with mass spectrometric study of as-synthesized carbon dots samples.

A fast and green approach to synthesize carbon dots (C-dots) by microwave-assisted pyrolysis of precursor chitosan as the carbon source and glacial acetic acid as the condensation agent has been developed. Ultra-high performance liquid chromatography (UHPLC) has been applied to study C-dots samples prepared with various synthetic conditions including amount of chitosan, concentration of acetic acid and reaction time. All the as-prepared C-dots samples are complex mixtures of C-dots species which can be separated by UHPLC within 16 min. All the separated C-dots peaks display a distinctive absorption bands at 261-271 nm corresponding to the n→π* transition of C=O bond. The obtained chromatograms indicate the composition and complexity of an as-synthesized C-dots sample which is commonly neglected. In addition, high-performance liquid chromatography is employed to fractionate the C-dots sample. The separated C-dots fractions are collected and characterized by photoluminescence (PL) spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The PL spectra of the fractions display emission peaks at 427-446 nm upon excitation at 340 nm. The C-dots fractions are fully anatomized by MALDI-TOF MS, displaying their fragmentation mass ion features and indicating the surface functionalities of C-dots. The findings highlight the virtues of UHPLC to separate and reveal the unique characteristics of individual C-dots product which may have potential applications in the fields of bioanalysis, bioimaging, catalysis, chemosensing, energy storage, and optoelectronics device.

Sensitive determination of kaempferol using carbon dots as a fluorescence probe.

In this study, a new sensitive and convenient method for the determination of kaempferol (Kae) based on the fluorescence quenching of fluorescent carbon dots (C-dots) was developed. The C-dots were prepared by simply mixing acetic acid, water and diphosphorus pentoxide. This green synthesis approach proceeds rapidly and gives large quantities of C-dots. The fluorescence of the C-dots decreased obviously with the increase of Kae concentration. The effect of other interfering substances on the fluorescence intensity of C-dots showed low interference. Under the optimum conditions, a linear correlation was established between fluorescence intensity ratio Fo/F and the concentration of Kae in the range of 3.5-49 µM with a detection limit (S/N=3) of 38.4 nM. The proposed method has been successfully applied to determination of Kae in xindakang tablets and human serum samples with recovery in the range of 94.6-109.0%. The C-dots could be a promising fluorescence probe for the detection of Kae owing to its low-cost production, easy operation, low cytotoxicity, and excellent biocompatibility.

Capillary electrophoretic study of green fluorescent hollow carbon nanoparticles.

CE coupled with laser-induced fluorescence and UV absorption detections has been applied to study the complexity of as-synthesized green fluorescent hollow carbon nanoparticles (HC-NP) samples. The effects of pH, type, and concentration of the run buffer and SDS on the separation of HC-NP are studied in detail. It is observed that phosphate run buffer is more effective in separating the HC-NP and the optimal run buffer is found to be 30 mM phosphate and 10 mM SDS at pH 9.0. The CE separation of this HC-NP is based on the difference in size and electrophoretic mobility of HC-NP. Some selected HC-NP fractions are collected and further characterized by UV-visible absorption and photoluminescence (PL) spectroscopy, MS, and transmission electron microscopy. The fractionated HC-NP show profound differences in absorption, emission characteristics, and PL quantum yield that would have been otherwise misled by studying the complex mixture alone. It is anticipated that our CE methodology will open a new initiative on extensive studies of individual HC-NP species in the biomedical, catalysis, electronic, and optical device, energy storage, material, and sensing field.

Facile synthesis of nitrogen-doped carbon dots for Fe(3+) sensing and cellular imaging.

A fast and facile approach to synthesize highly nitrogen (N)-doped carbon dots (N-CDs) by microwave-assisted pyrolysis of chitosan, acetic acid and 1,2-ethylenediamine as the carbon source, condensation agent and N-dopant, respectively, is reported. The obtained N-CDs are fully characterized by elemental analysis, transmission electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction pattern, X-ray photoelectron spectroscopy, UV-vis absorption, and photoluminescence spectroscopy. Doping N heteroatoms benefits the generation of N-CDs with stronger fluorescence emission. As the emission of N-CDs is efficiently quenched by Fe(3+), the as-prepared N-CDs are employed as a highly sensitive and selective probe for Fe(3+) detection. The detection limit can reach as low as 10 ppb, and the linear range is 0.010-1.8 ppm Fe(3+). The as-synthesized N-CDs have been successfully applied for cell imaging and detecting Fe(3+) in biosystem.

High-performance liquid chromatography coupled with mass spectrometry for analysis of ultrasmall palladium nanoparticles.

Metal nanoparticles (NPs) have recently attracted considerable attention in many areas of research including bioscience, chemistry and material science. Regrettably, most current and past work usually focuses on studies of multi-component NPs mixture where there is a plethora of NPs species co-existing. This work highlights the merits of reverse-phase high-performance liquid chromatography (RP-HPLC) for disclosing the genuine properties of individual palladium nanoparticles (PdNPs) species present in an as-synthesized N,N'-dimethylformamide-stabilized PdNPs product (DMF-PdNPs) which might have been previously hidden or misinterpreted. DMF-PdNPs is successfully separated by RP-HPLC that smaller DMF-PdNPs are approximately eluted first and then follow by the large ones on a C18 column. The separation fractions are further collected and determined their chemical compositions by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The results unambiguously reveal that the as-synthesized DMF-PdNPs product is indeed a complex mixture of ultrasmall PdxNPs (x=10-20) stabilized with different numbers of DMF ligands. It is anticipated that the separated fractions afforded by RP-HPLC will offer more accurate determinations of the catalytic, electronic, optical and toxicological properties of metal NPs which might have been previously misinterpreted.

High-performance liquid chromatographic and mass spectrometric analysis of fluorescent carbon nanodots.

Amino/hydroxyl-functionalized fluorescent carbon nanodots (C-NanoD) are conveniently synthesized based on hydrothermal carbonization of chitosan at 180°C. Dialysis membranes with small cut-off masses (500-1000 Da) were found useful for removing the side-products and low molecular mass species to purify the C-NanoD product. Herein, reversed-phase high-performance liquid chromatography (RP-HPLC) has been successfully applied to fractionate the C-NanoD product. The elution order of the C-NanoD species present in the sample follows approximately their core sizes from small to large. The separated C-NanoD fractions are collected and characterized by UV absorption spectroscopy, photoluminescence (PL) spectroscopy, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and transmission electron microscopy (TEM). All the C-NanoD fractions display a distinctive absorption band at 300 nm, attributing to the n→π* transition of C=O bond. The PL spectra of the fractions display emission peaks at 400-415 nm which are slightly red-shifted with their increase in relative molecular masses. The C-NanoD fractions are fully anatomized by MALDI-TOF MS, displaying their fragmentation mass ion features. The core sizes of some selected C-NanoD are determined as 1.6, 1.8, 2.5, and 3.1 nm by TEM which are in consistent with their HPLC elution order. The findings highlight the virtues of RP-HPLC to fractionate and reveal the unique characteristics of individual C-NanoD species present in an as-synthesized C-NanoD product which may have potential applications in the fields of bioanalysis, bioimaging, catalysis, chemosensing, energy storage, and optoelectronics device.

Red-green-blue fluorescent hollow carbon nanoparticles isolated from chromatographic fractions for cellular imaging.

An as-synthesised hollow carbon nanoparticle (HC-NP) sample has been proved to be a relatively complex mixture, and its complexity can be reduced significantly by high-performance liquid chromatography. An unprecedented reduction in such complexity can reveal fractions of HC-NP with unique luminescence properties. While the UV-vis absorption profile for the HC-NP mixture is featureless, the HC-NP fractions do possess unique absorption bands and specific emission wavelengths. The HC-NP fractions are fully anatomised by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry, displaying their fragmentation mass ion features. The shell thickness and crystal lattices of the selected HC-NP fractions are determined as 6.13, 8.31, 2.22, and 8.66 nm, and 0.37, 0.35, 0.33, and 0.32 nm by transmission electron microscopy, respectively. The fractionated HC-NP show profound differences in emission quantum yield, allowing for brighter HC-NP to be isolated from an apparent low quantum yield mixture. Finally, red, green and blue emissive HC-NP are isolated from the as-synthesised HC-NP sample. They show good photostability and have been demonstrated to be excellent probes for cellular imaging.

Better understanding of carbon nanoparticles via high-performance liquid chromatography-fluorescence detection and mass spectrometry.

RP-HPLC coupled with fluorescence detection for separation of carbon nanoparticles (CNP) synthesized with microwave-assisted pyrolysis of citric acid and 1,2-ethylenediamine is presented. The influence of methanol content and pH of mobile phase on the separation of CNP has been investigated. Under optimal mobile phase and elution gradient conditions, the effect of mole ratio of amine to carboxylic groups (NH2 /COOH) in the initial reagents on CNP product is studied. At NH2 /COOH = 0.67, the strongest fluorescence CNP sample is obtained. The separated CNP fractions are collected and further characterized by UV-visible absorption and photoluminescence (PL) spectroscopy, CE, transmission electron microscopy (TEM), and MALDI-TOF MS. The absorption and PL emission bands of the fractions are bathochromatically shifted with the elution order of CNP on RP-HPLC. The TEM images prove that CNP are eluted from the smallest to the largest. The MS data show that CNP undergo fragmentations, closely relating to their surface-attached carboxylic acid and amide/amine moieties. This work highlights the merit of RP-HPLC coupled with fluorescence detection, TEM, and MS for isolation and characterization of individual CNP species present in a CNP sample.

Capillary electrophoretic study of amine/carboxylic acid-functionalized carbon nanodots.

Capillary zone electrophoresis (CZE) coupled with UV absorption and laser-induced fluorescence detections has been applied to study the complexity of carbon nanodots (C-dots) products synthesized with microwave-assisted pyrolysis of citric acid (CA) and 1,2-ethylenediamine (EDA). The effects of pH and concentration of run buffer on the CZE separation of C-dots are studied in detail. The optimal acetate run buffer (30mM, pH 3.6) is subsequently employed to investigate the effect of reaction time and mole ratio of amine (NH2) to carboxylic acid (COOH) moieties of the precursors on the C-dots species present in C-dots products. Our results confirm that the synthesis of C-dots could be improved by lengthening the microwave irradiation time and optimizing the initial mole ratio of NH2/COOH in the precursors. Negatively charged C-dots are obtained only when the amount of CA exceeds that of EDA, i.e., the mole ratio of NH2/COOH is 0.25-0.80. By contrast, when the quantity (mole) of NH2 in EDA is equal to or larger than that of COOH in CA, only positively charged and neutral C-dots species are formed, inferring that the C-dots species are predominantly covered by the surface-attached ammonium and amido moieties. This work highlights the merit of CZE to identify the composition of an as-prepared C-dots product which is pretty much dependent on the mole ratio of NH2/COOH. It is anticipated that our CZE methodology will open a new avenue in optimizing the synthetic conditions for producing specific C-dots of desired composition.

High-performance liquid chromatographic analysis of as-synthesised N,N'-dimethylformamide-stabilised gold nanoclusters product.

Reverse-phase high-performance liquid chromatographic (RP-HPLC) separation and analysis of polydisperse water-soluble gold nanoclusters (AuNCs) stabilised with N,N'-dimethylformamide (DMF) were investigated. Under optimal elution gradient conditions, the separation of DMF-AuNCs was monitored by absorption and fluorescence spectroscopy. The UV-vis spectral characteristics of the separated DMF-AuNCs have been captured and they do not possess distinct surface plasmon resonance bands, indicating that all DMF-AuNCs are small AuNCs. The photoluminescence emission spectra of the separated DMF-AuNCs are in the blue-light region. Moreover, cationic DMF-AuNCs are for the first time identified by ion chromatography. Our proposed RP-HPLC methodology has been successfully applied to separate AuNCs of various Au atoms as well as DMF-stabilised ligands. Finally, the composition of the separated DMF-AuNCs was confirmed by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry and electrospray ionisation mass spectrometry, proving that the as-synthesised DMF-AuNCs product consists of Au10⁺, Au10, Au11, Au12, Au13, and Au14 NCs stabilised with various numbers of DMF ligands.

Ultrahigh performance liquid chromatographic analysis and magnetic preconcentration of polycyclic aromatic hydrocarbons by Fe3O4-doped polymeric nanoparticles.

This paper reports the synthesis of hydrophilic-hydrophobic magnetic Fe3O4-doped polymeric nanoparticles (MPNP) and its application for preconcentration of polycyclic aromatic hydrocarbons (PAHs) in environmental water samples for ultrahigh performance liquid chromatographic (UHPLC) analysis. The MPNP were prepared from highly charged poly(styrene-divinylbenzene-co-4-vinylbenzenesulfonic acid sodium salt) nanoparticles impregnated with Fe²âº via the electrostatic attraction and by microwave heating. The MPNP are relatively uniform in size with an average diameter of 50 nm and have a magnetic saturation value of 24.5 emu/g. The hydrophilic-hydrophobic MPNP could easily disperse in water. The phenyl moieties of MPNP assist the adsorption of PAHs via both hydrophobic and π-π interactions. The separation of the PAHs-adsorbed MPNP from water could be easily achieved by a permanent magnet and the adsorbed PAHs were back extracted into acetonitrile for UHPLC analysis. The UHPLC separation of PAHs is very quick and could be achieved within 1.6 min. Factors affecting the extraction and desorption were investigated in detail. Under the optimum experimental conditions, the recoveries of various PAHs including acenaphthylene, anthracene, fluoranthene, fluorene, phenanthrene, and pyrene in water samples at three different concentrations are 75.7-102.9, 77.8-101.2, 86.3-100.7, 88.5-99.7, 92.0-106.4, and 81.6-98.5%, respectively. The recovery SDs are 0.30-8.20% and the instrumental limits of detection are 10.83-18.53 nM. The proposed technique combining hydrophobic extraction and magnetic separation coupled with UHPLC could provide a fast, convenient and sensitive method for the determination of PAHs in water samples.

Mass spectrometric identification of water-soluble gold nanocluster fractions from sequential size-selective precipitation.

This paper presents a simple and convenient methodology to separate and characterize water-soluble gold nanocluster stabilized with penicillamine ligands (AuNC-SR) in aqueous medium by sequential size-selective precipitation (SSSP) and mass spectrometry (MS). The highly polydisperse crude AuNC-SR product with an average core diameter of 2.1 nm was initially synthesized by a one-phase solution method. AuNCs were then precipitated and separated successively from larger to smaller ones by progressively increasing the concentration of acetone in the aqueous AuNCs solution. The SSSP fractions were analyzed by UV-vis spectroscopy, matrix-assisted laser desorption/ionization time-of-flight-MS, and thermogravimetric analysis (TGA). The MS and TGA data confirmed that the fractions precipitated from 36, 54, 72, and 90% v/v acetone (F(36%), F(54%), F(72%), and F(90%)) comprised families of close core size AuNCs with average molecular formulas of Au(38)(SR)(18), Au(28)(SR)(15), Au(18)(SR)(12), and Au(11)(SR)(8), respectively. In addition, F(36%), F(54%), F(72%), and F(90%) contained also the typical magic-sized gold nanoparticles of Au(38), Au(25), Au(18), and Au(11), respectively, together with some other AuNCs. This study shed light on the potential use of SSSP for simple and large-scale preliminary separation of polydisperse water-soluble AuNCs into different fractions with a relatively narrower size distribution.

A simple and sensitive CE method for the simultaneous determination of catecholamines in urine with in-column optical fiber light-emitting diode-induced fluorescence detection.

A simple and sensitive method has been developed for simultaneous analysis of three catecholamines: dopamine (DA), epinephrine (EP) and norepinephrine (NE) in urine by capillary electrophoresis (CE) coupled with in-column fiber-optic light-emitting diode-induced fluorescence detection (ICFO-LED-IFD). Fluorescein isothiocyanate was used as the fluorescence tagged reagent for derivatization of DA, EP and NE. The CE conditions for separation of these catecholamines were systematically investigated. It was found that catecholamines could be more effectively separated by adding ß-cyclodextin (ß-CD) and acetonitrile (ACN) to a background electrolyte (BGE) of sodium borate. The migration times are 10.61, 10.83 and 11.14 min for DA, EP and NE, respectively and the catecholamines are completely separated within 11.5 min under the optimal condition of a BGE containing 10% v/v ACN, 20 mM ß-CD and 20 mM sodium borate (pH 9.5), and an applied voltage of 13 kV. The relative standard deviations of migration time and peak area for these catecholamines are less than 0.16 and 2.0%, respectively. The limit of quantifications (LOQs) for DA, EP and NE are 3.5, 1.0 and 3.1 nM whereas the limit of detections (LODs) for DA, EP and NE are 1.0, 0.3 and 0.9 nM, respectively. Our proposed CE method provides low LOQ and LOD values. This CE-ICFO-LED-IFD methodology has been successfully applied to analyze catecholamines in human urine samples with good accuracy and satisfactory recovery.

Application of hydrophobic palladium nanoparticles for the development of electrochemical glucose biosensor.

An amperometric glucose biosensor based on an n-alkylamine-stabilized palladium nanoparticles (PdNPs)-glucose oxidase (GOx) modified glassy carbon (GC) electrode has been successfully fabricated. PdNPs were initially synthesized by a biphase mixture of water and toluene method using n-alkylamines (dodecylamine, C12-NH2 and octadecylamine, C18-NH2) as stabilizing ligands. The performance of the PdNPs-GOx/GC biosensor was studied by cyclic voltammetry. The optimum working potential for amperometric measurement of glucose in pH 7.0 phosphate buffer solution is -0.02 V (vs. Ag/AgCl). The analytical performance of the biosensor prepared from C18-PdNPs-GOx is better than that of C12-PdNPs-GOx. The C18-PdNPs-GOx/GC biosensor exhibits a fast response time of ca. 3s, a detection limit of 3.0 µM (S/N=3) and a linear range of 3.0 µM-8.0 mM. The linear dependence of current density with glucose concentration is 70.8 µA cm⁻² mM⁻¹. The biosensor shows good stability, repeatability and reproducibility. It has been successfully applied to determine the glucose content in human blood serum samples.

Preparation of gold nanoparticles on eggshell membrane and their biosensing application.

A facile green biosynthesis method has been successfully developed to prepare gold nanoparticles (AuNPs) of various core sizes (25+/-7 nm) using a natural biomaterial, eggshell membrane (ESM) at ambient conditions. In situ synthesis of AuNPs-immobilized ESM is conducted in a simple manner by immersing ESM in a pH 6.0 aqueous solution of HAuCl(4) without adding any reductant. The formation of AuNPs on ESM protein fibers is attributed to the reduction of Au(III) ions to Au(0) by the aldehyde moieties of the natural ESM fibers. Energy dispersive X-ray spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray powder diffraction unambiguously identify the presence of AuNPs on ESM. The effect of pH on the in situ synthesis of AuNPs on ESM has been investigated in detail. The pH of the gold precursor (HAuCl(4)) solution can influence the formation rate, dispersion and size of AuNPs on ESM. At pH < or =3.0 and > or =7.0, no AuNPs are observed on ESM while small AuNPs are homogeneously dispersed on ESM at pH 4.0-6.0. The optimal pH for AuNPs formation on ESM is 6.0. AuNPs/ESMs are used to immobilize glucose oxidase (GO(x)) for glucose biosensing. AuNPs on ESM can increase the enzyme activity of GO(x). The linear response range of the glucose biosensor is 20 microM to 0.80 mM glucose with a detection limit of 17 microM (S/N=3). The biosensor has been successfully applied to determine the glucose content in commercial glucose injections. Our work provides a very simple, non-toxic, convenient, and green route to synthesize AuNPs on ESM which is potentially useful in the biosensing field.

Separation and preconcentration of persistent organic pollutants by cloud point extraction.

Persistent organic pollutants (POPs) are recognized as a class of poisonous compounds which pose risks of causing adverse effects to human health and the environment. Thus, it is very important to detect POPs in environmental and biological samples. The identification and determination of very low levels of POPs in complex matrices is extremely difficult. Recently a promising environmentally benign extraction and preconcentration methodology based on cloud point extraction (CPE) has emerged as an efficient sample pretreatment technique for the determination of trace/ultra-trace POPs in complex matrices. The purpose of this paper is to review the past and latest use of CPE for preconcentrating POPs and its coupling to different contemporary instrumental methods of analysis. First, the comparison of various extraction techniques for POPs is described. Next, the general concept, influence factors and other methods associated with CPE technique are outlined and described. Last, the hyphenations of CPE to various instrumental methods for their determination are summarized and discussed.

Capillary electrophoretic study of thiolated alpha-cyclodextrin-capped gold nanoparticles with tetraalkylammonium ions.

Capillary zone electrophoresis (CZE) has been employed to characterize nanometer-sized thiolated alpha-cyclodextrin-capped gold nanoparticles (alpha-CD-S-AuNPs). The addition of tetrabutylammonium (Bu(4)N(+)) ions to the run buffer greatly narrows the migration peak of alpha-CD-S-AuNP. The optimal run buffer was determined to be 10mM Bu(4)N(+) in 30 mM phosphate buffer at pH 12 and an applied voltage of 15 kV. The effect of various tetraalkylammonium ions on the peak width and electrophoretic mobility (mu(e)) of alpha-CD-S-AuNP was studied in detail. Bu(4)N(+) ions assist in inter-linking the alpha-CD-S-AuNPs and narrowing the migration peak in CZE. This observation can be explained by the fact that each Bu(4)N(+) ion can simultaneously interact with several hydrophobic cavities of the surface-attached alpha-CDs on AuNPs. The TEM images show that alpha-CD-S-AuNPs with Bu(4)N(+) are linked together but in the absence of Bu(4)N(+), they are more dispersed. The migration mechanism in CZE is based on the formation of inclusion complexes between Bu(4)N(+) and alpha-CD-S-AuNPs which induces changes in the charge-to-size ratio of alpha-CD-S-AuNPs and mu(e). An inverse linear relationship (r(2)>0.998) exists between the mu(e) and size of alpha-CD-S-AuNPs in the core range 1.4-4.1 nm. The CZE analyses are rapid with migration time less than 4 min. A few nanoliters of each of the alpha-CD-S-AuNP samples were injected hydrodynamically at 0.5 psi for 5s. Our work confirms that CZE is an efficient tool for characterizing the sizes of alpha-CD-S-AuNPs using Bu(4)N(+) ions.

Application of HPLC and MALDI-TOF MS for studying as-synthesized ligand-protected gold nanoclusters products.

Samples of polydisperse gold nanoclusters (AuNCs) protected with monolayers of N-acetyl-L-cysteine (NAC) have been chromatographically separated by a C18 column (4.6 mm x 250 mm) using a gradient elution program with a mobile phase of methanol (MeOH)/water containing tetrabutylammonium fluoride (Bu(4)N(+)F(-)) and sodium chloride. The effects of Bu(4)N(+)F(-) and MeOH on the separation have been investigated in detail. In conjunction with absorbance-based, fluorescence, and electrochemical detectors, the elution order of these water-soluble AuNCs is confirmed according to their core size in an ascending order. The onset oxidation potential closely follows the core size of AuNC. The separated fractions from high-performance liquid chromatography (HPLC) were collected and analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry to determine the number of Au atoms in the fractions. The sizes of AuNCs in some selected HPLC fractions were also assessed by transmission electron microscopy and high-resolution transmission electron microscopy. Photoluminescence spectra of the fractions show that the luminescent shift in the visible/near-infrared region does not follow with the core size of AuNC. More importantly, the proposed HPLC methodology has been successfully applied to analyze various polydisperse AuNC products synthesized from different gold-to-ligand mole ratios (Au/NAC) and reaction temperatures. The results confirm that larger Au/NAC and higher temperature will produce larger core size AuNCs products with narrower dispersity. In addition, AuNC samples obtained from various synthesis reaction times were analyzed by our HPLC methodology, demonstrating that the reaction's behavior follows the nucleation-growth-disintegration process.

Application of capillary zone electrophoresis for separation of water-soluble gold monolayer-protected clusters.

An effective capillary electrophoretic technique for separating samples of negatively charged, polydisperse, water-soluble gold monolayer-protected cluster (Au MPC) protected by monolayers of N-acetyl-L-cysteine has been developed. The separation mechanisms of the Au MPC in CZE suggest that the larger core sizes Au MPC emerge first from the capillary. The electrophoretic separation depends on pH, buffer concentration, and organic modifiers. The addition of aliphatic alcohols to the run buffer can improve the separation of Au MPC by reducing the EOF and changing the selectivity between the Au MPCs. The enhancement of resolution is attributed to the more significant difference in the charge-to-size ratio between the Au MPCs. The run buffer containing 20 v/v % ethanol provides the best separation for water-soluble Au MPC. Our proposed CE method provides a powerful tool to evaluate and separate the water-soluble Au MPC products.

Capillary electrophoresis, mass spectrometry, and UV-visible absorption studies on electrolyte-induced fractionation of gold nanoclusters.

We describe a novel and simple electrolyte-induced fractionation method to separate a polydisperse water-soluble gold nanocluster (Au NC) product. Different particle sizes of Au NC fractions can be easily centrifuged down as a function of the electrolyte concentration or lipophilicity of the solution. The changes in the absorption characteristic of the Au NC fractions under different electrolyte/ethanol conditions demonstrate the change in particle size distribution of the Au NC. Small gold nanoclusters, Au10, Au11, Au12, and Au15, were separated from the Au10-Au50 polydisperse Au NC product under various phosphate/ethanol conditions. The core size separation of Au NC was evaluated by their migration trends in capillary zone electrophoresis, UV-visible absorption, and mass spectra. The electrolyte-induced fractionation not only provides a convenient method to separate small Au NC mixture but also assists in the study of the photophysical properties of smaller Au NCs that are present with the larger Au NCs in a polydisperse Au NC product.