Flow-Through Atmospheric Pressure-Atomic Layer Deposition Reactor for Thin-Film Deposition in Capillary Columns.

We demonstrate the development of a new atmospheric pressure-atomic layer deposition(AP-ALD) system to coat the inner walls of capillary columns for gas chromatography (GC). Unlike traditional ALD, this reactor operates at near-atmospheric pressure and addresses the challenges of depositing thin films inside capillaries, which include long pump down times, deposition in high-aspect-ratio materials, and temperature control. We show ALD of alumina in 5 and 12 m capillaries (0.53 mm ID) via sequential half reactions of trimethylaluminum and water. Our system yields pinhole-free, uniform thin films. It includes small witness chambers for witness silicon shards before and after the capillary. An engineering flow/transport analysis of the device is provided. Our ALD alumina thin films are characterized by spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy. Alumina film growth achieved is 1.4-1.5 Å/cycle, which is consistent with previously reported results. Film thickness measurements by SE on witness shards of silicon and by TEM at both ends of the capillary are in good agreement. A capillary column coated with alumina is used to separate different gases by GC, although the retention times of gases are essentially the same as with an untreated fused silica capillary. This successful deposition of ALD alumina in long capillaries opens the door for other possible ALD coatings, including hybrid organic-inorganic coatings, using the 450+ ALD precursors available today.

The Often-Overlooked Power of Summary Statistics in Exploratory Data Analysis: Comparison of Pattern Recognition Entropy (PRE) to Other Summary Statistics and Introduction of Divided Spectrum-PRE (DS-PRE).

Unsupervised exploratory data analysis (EDA) is often the first step in understanding complex data sets. While summary statistics are among the most efficient and convenient tools for exploring and describing sets of data, they are often overlooked in EDA. In this paper, we show multiple case studies that compare the performance, including clustering, of a series of summary statistics in EDA. The summary statistics considered here are pattern recognition entropy (PRE), the mean, standard deviation (STD), 1-norm, range, sum of squares (SSQ), and X4, which are compared with principal component analysis (PCA), multivariate curve resolution (MCR), and/or cluster analysis. PRE and the other summary statistics are direct methods for analyzing data-they are not factor-based approaches. To quantify the performance of summary statistics, we use the concept of the "critical pair," which is employed in chromatography. The data analyzed here come from different analytical methods. Hyperspectral images, including one of a biological material, are also analyzed. In general, PRE outperforms the other summary statistics, especially in image analysis, although a suite of summary statistics is useful in exploring complex data sets. While PRE results were generally comparable to those from PCA and MCR, PRE is easier to apply. For example, there is no need to determine the number of factors that describe a data set. Finally, we introduce the concept of divided spectrum-PRE (DS-PRE) as a new EDA method. DS-PRE increases the discrimination power of PRE. We also show that DS-PRE can be used to provide the inputs for the k-nearest neighbor (kNN) algorithm. We recommend PRE and DS-PRE as rapid new tools for unsupervised EDA.

6-Phenylhexyl silane derivatized, sputtered silicon solid phase microextraction fiber for the parts-per-trillion detection of polyaromatic hydrocarbons in water and baby formula.

We report the fabrication of 6-phenylhexylsilane derivatized, sputtered silicon, solid phase microextraction fibers that show parts per trillion detection limits for polyaromatic hydrocarbons, and negligible carry over and phase bleed. Their fabrication involves sputtering silicon on silica fibers under various conditions. Six different fibers were evaluated by generating three different thicknesses of sputtered silicon at two different throw distances, which altered the morphologies of the silicon surfaces. All of the fibers were coated with similar thicknesses of 6-phenylhexylsilane (ca. 2 nm). These fibers were characterized with multiple analytical techniques. The optimum fiber configuration was then used to analyze polyaromatic hydrocarbons via direct immersion, gas chromatography mass spectrometry. Our best fiber for the extraction of low molecular weight polyaromatic hydrocarbons in water had similar performance to that of a commercial fiber. However, our fiber demonstrated ca. 3 times the extraction efficiency for higher molecular weight polyaromatic hydrocarbons. In addition, it outperformed the commercial fiber by showing better linearity, repeatability, and detection limits. A method for analyzing polyaromatic hydrocarbons in baby formula was developed, which showed very good linearity (0.5-125 ppb), repeatability (2-26%), detection limits (0.12-0.81 ppb), and recoveries (103-135%). In addition, our fiber showed much less (negligible) carry over and phase bleed than the commercially available fibers.

Semiempirical Peak Fitting Guided by ab Initio Calculations of X-ray Photoelectron Spectroscopy Narrow Scans of Chemisorbed, Fluorinated Silanes.

Here, we address the issue of finding correct CF2/CF3 area ratios from X-ray photoelectron spectroscopy (XPS) C 1s narrow scans of materials containing -CH2CH2(CF2)nCF3 (n = 0, 1, 2, ...) moieties. For this work, we modified silicon wafers with four different fluorosilanes. The smallest had a trifluoropropyl (n = 0) moiety, followed by nonafluorohexyl (n = 3), tridecafluoro (n = 5), and finally, heptadecafluoro (n = 7) moieties. Monolayer deposition of the fluorosilanes was confirmed by spectroscopic ellipsometry, wetting, and XPS. Analysis of the trifluoropropyl (n = 0) surface and a sample of polytetrafluoroethylene provided pure-component XPS spectra for -CF3 and -(CF2)n- moieties, respectively. Initial XPS C 1s peak fitting, which follows the literature precedent, was not entirely adequate. To address this issue, six different fitting approaches with increasing complexity and/or input from the Hartree-Fock theory (HF) were considered. Ultimately, we show that by combining HF results with empirical analyses, we obtain more accurate CF2/CF3 area ratios while maintaining high-quality fits.

Versailles Project on Advanced Materials and Standards interlaboratory study on intensity calibration for x-ray photoelectron spectroscopy instruments using low-density polyethylene.

We report the results of a Versailles Project on Advanced Materials and Standards interlaboratory study on the intensity scale calibration of x-ray photoelectron spectrometers using low-density polyethylene (LDPE) as an alternative material to gold, silver, and copper. An improved set of LDPE reference spectra, corrected for different instrument geometries using a quartz-monochromated Al Kα x-ray source, was developed using data provided by participants in this study. Using these new reference spectra, a transmission function was calculated for each dataset that participants provided. When compared to a similar calibration procedure using the NPL reference spectra for gold, the LDPE intensity calibration method achieves an absolute offset of ∼3.0% and a systematic deviation of ±6.5% on average across all participants. For spectra recorded at high pass energies (≥90 eV), values of absolute offset and systematic deviation are ∼5.8% and ±5.7%, respectively, whereas for spectra collected at lower pass energies (<90 eV), values of absolute offset and systematic deviation are ∼4.9% and ±8.8%, respectively; low pass energy spectra perform worse than the global average, in terms of systematic deviations, due to diminished count rates and signal-to-noise ratio. Differences in absolute offset are attributed to the surface roughness of the LDPE induced by sample preparation. We further assess the usability of LDPE as a secondary reference material and comment on its performance in the presence of issues such as variable dark noise, x-ray warm up times, inaccuracy at low count rates, and underlying spectrometer problems. In response to participant feedback and the results of the study, we provide an updated LDPE intensity calibration protocol to address the issues highlighted in the interlaboratory study. We also comment on the lack of implementation of a consistent and traceable intensity calibration method across the community of x-ray photoelectron spectroscopy (XPS) users and, therefore, propose a route to achieving this with the assistance of instrument manufacturers, metrology laboratories, and experts leading to an international standard for XPS intensity scale calibration.

Practical Guides for X-Ray Photoelectron Spectroscopy (XPS): First Steps in planning, conducting and reporting XPS measurements.

Over the past three decades, the widespread utility and applicability of X-ray photoelectron spectroscopy (XPS) in research and applications has made it the most popular and widely used method of surface analysis. Associated with this increased use has been an increase in the number of new or inexperienced users which has led to erroneous uses and misapplications of the method. This article is the first in a series of guides assembled by a committee of experienced XPS practitioners that are intended to assist inexperienced users by providing information about good practices in the use of XPS. This first guide outlines steps appropriate for determining whether XPS is capable of obtaining the desired information, identifies issues relevant to planning, conducting and reporting an XPS measurement, and identifies sources of practical information for conducting XPS measurements. Many of the topics and questions addressed in this article also apply to other surface-analysis techniques.

Performance Comparison of Three Chemical Vapor Deposited Aminosilanes in Peptide Synthesis: Effects of Silane on Peptide Stability and Purity.

Silicon oxide substrates underwent gas-phase functionalization with various aminosilanes, and the resulting surfaces were evaluated for their suitability as a solid support for solid phase peptide synthesis (SPPS). APTES (3-aminopropyltriethoxysilane), APDEMS (3-aminopropyldiethoxymethylsilane), and APDIPES (3-aminopropyldiisopropylethoxysilane) were individually applied to thermal oxide-terminated silicon substrates via gas-phase deposition. Coated surfaces were characterized by spectroscopic ellipsometry (SE), contact angle goniometry, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and spectrophotometry. Model oligopeptides with 16 residues were synthesized on the amino surfaces, and the chemical stabilities of the resulting surfaces were evaluated against a stringent side chain deprotection (SCD) step, which contained trifluoroacetic acid (TFA) and trifluoromethanesulfonic acid (TFMSA). Functionalized surface thickness loss during SCD was most acute for APDIPES and the observed relative stability order was APTES > APDEMS > APDIPES. Amino surfaces were evaluated for compatibility with stepwise peptide synthesis where complete deprotection and coupling cycles are paramount. Model trimer syntheses indicated that routine capping of unreacted amines with acetic anhydride significantly increased purity as measured by MALDI-MS. An inverse correlation between the amine loading density and peptide purity was observed. In general, peptide purity was highest for the lowest amine density APDIPES surface.

Porous, High Capacity Coatings for Solid Phase Microextraction by Sputtering.

We describe a new process for preparing porous solid phase microextraction (SPME) coatings by the sputtering of silicon onto silica fibers. The microstructure of these coatings is a function of the substrate geometry and mean free path of the silicon atoms, and the coating thickness is controlled by the sputtering time. Sputtered silicon structures on silica fibers were treated with piranha solution (a mixture of concd H2SO4 and 30% H2O2) to increase the concentration of silanol groups on their surfaces, and the nanostructures were silanized with octadecyldimethylmethoxysilane in the gas phase. The attachment of this hydrophobic ligand was confirmed by X-ray photoelectron spectroscopy and contact angle goniometry on model, planar silicon substrates. Sputtered silicon coatings adhered strongly to their surfaces, as they were able to pass the Scotch tape adhesion test. The extraction time and temperature for headspace extraction of mixtures of alkanes and alcohols on the sputtered fibers were optimized (5 min and 40 °C), and the extraction performances of SPME fibers with 1.0 or 2.0 µm of sputtered silicon were compared to those from a commercial 7 µm poly(dimethylsiloxane) (PDMS) fiber. For mixtures of alcohols, aldehydes, amines, and esters, the 2.0 µm sputtered silicon fiber yielded signals that were 3-9, 3-5, 2.5-4.5, and 1.5-2 times higher, respectively, than those of the commercial fiber. For the heavier alkanes (undecane-hexadecane), the 2.0 µm sputtered fiber yielded signals that were approximately 1.0-1.5 times higher than the commercial fiber. The sputtered fibers extracted low molecular weight analytes that were not detectable with the commercial fiber. The selectivity of the sputtered fibers appears to favor analytes that have both a hydrophobic component and hydrogen-bonding capabilities. No detectable carryover between runs was noted for the sputtered fibers. The repeatability (RSD%) for a fiber (n = 3) was less than 10% for all analytes tested, and the between-fiber reproducibility (n = 3) was 0-15%, generally 5-10%, for all analytes tested. The repeatabilities of our sputtered fibers and the commercial 7 µm PDMS fiber are essentially the same. Fibers could be used for at least 300 extractions without loss of performance. More than 50 compounds were identified in a gas chromatography-mass spectrometry headspace analysis of a real world botanical sample with the 2.0 µm fiber.

Multi-instrument characterization of five nanodiamond samples: a thorough example of nanomaterial characterization.

Here, we report the most comprehensive characterization of nanodiamonds (NDs) yet undertaken. Five different samples from three different vendors were analyzed by a suite of analytical techniques, including X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), inductively coupled plasma mass spectrometry (ICP-MS), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), Brunauer-Emmett-Teller (BET) surface area measurements, and particle size distribution (PSD) measurements. XPS revealed the elemental compositions of the ND surfaces (83-87 at.% carbon and 12-14 at.% oxygen) with varying amounts of nitrogen (0.4-1.8 at.%), silicon (0.1-0.7 at.%), and tungsten (0.3 at.% only in samples from one vendor). ToF-SIMS and ICP showed metal impurities (Al, Fe, Ni, Cr, etc. with unexpectedly high amounts of W in one vendor's samples: ca. 900 ppm). Principal component analyses were performed on the ToF-SIMS and ICP data. DRIFT showed key functional groups (-OH, C=O, C-O, and C=C). BET showed surface areas of 50-214 m(2)/g. XRD and TEM revealed PSD (bimodal distribution and a wide PSD, 5-100 nm, for one vendor's samples). XRD also provided particle sizes (2.7-27 nm) and showed the presence of graphite. EELS gave the sp(2)/sp(3) contents of the materials (37-88% sp(3)). PSD measurements were performed via differential sedimentation of the particles (mean particle size ca. 17-50 nm). This comprehensive understanding should allow for improved construction of nanodiamond-based materials.

Polyallylamine as an Adhesion Promoter for SU-8 Photoresist.

Resist lithography is an important microfabrication technique in the electronics industry. In this, patterns are transferred by irradiation onto a photosensitive polymer. SU-8 has emerged as a favorite photoresist for High Aspect Ratio (HAR) lithography, showing high chemical and mechanical stability and biocompatibility. Unfortunately, its poor adhesion to substrates is a drawback, with possible solutions being the use of low-viscosity SU-8, surface modification with a low molecular weight adsorbate like hexamethyldisilazane (HMDS), or a commercial adhesion promotion reagent. However, HMDS and the commercial reagent require surface dehydration and/or curing, and a modified form of SU-8 is not always desirable. Here, we demonstrate the use of a water-soluble, amine-containing polymer, polyallylamine (PAAm), which spontaneously adsorbs to silica surfaces, as a simple, easy-to-apply, and reactive adhesion promoter for SU-8. Conditions for the use of PAAm are explored, and the resulting materials are characterized by X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), and wetting.

Separation of cannabinoids on three different mixed-mode columns containing carbon/nanodiamond/amine-polymer superficially porous particles.

Three mixed-mode high-performance liquid chromatography columns packed with superficially porous carbon/nanodiamond/amine-polymer particles were used to separate mixtures of cannabinoids. Columns evaluated included: (i) reversed phase (C18 ), weak anion exchange, 4.6 × 33 mm, 3.6 µm, and 4.6 × 100 mm, 3.6 µm, (ii) reversed phase, strong anion exchange (quaternary amine), 4.6×33 mm, 3.6 µm, and (iii) hydrophilic interaction liquid chromatography, 4.6 × 150 mm, 3.6 µm. Different selectivities were achieved under various mobile phase and stationary phase conditions. Efficiencies and peak capacities were as high as 54 000 N/m and 56, respectively. The reversed phase mixed-mode column (C18 ) retained tetrahydrocannabinolic acid strongly under acidic conditions and weakly under basic conditions. Tetrahydrocannabinolic acid was retained strongly on the reversed phase, strong anion exchange mixed-mode column under basic polar organic mobile phase conditions. The hydrophilic interaction liquid chromatography column retained polar cannabinoids better than the (more) neutral ones under basic conditions. A longer reversed phase (C18 ) mixed-mode column (4.6 × 100 mm) showed better resolution for analytes (and a contaminant) than a shorter column. Fast separations were achieved in less than 5 min and sometimes 2 min. A real world sample (bubble hash extract) was also analyzed by gradient elution.

Dual patterning of a poly(acrylic acid) layer by electron-beam and block copolymer lithographies.

We show the controllable patterning of palladium nanoparticles in both one and two dimensions using electron-beam lithography and reactive ion etching of a thin film of poly(acrylic acid) (PAA). After the initial patterning of the PAA, a monolayer of polystyrene-b-poly-2-vinylpyridine micelles is spun cast onto the surface. A short reactive ion etch is then used to transfer the micelle pattern into the patterned poly(acrylic acid). Finally, PdCl2 is loaded from solution into the patterned poly(acrylic acid) features, and a reactive-ion etching process is used to remove the remaining polymer and form Pd nanoparticles. This method yields location-controlled patches of nanoparticles, including single- and double-file lines and nanoparticle pairs. A locational accuracy of 9 nm or less in one direction was achieved by optimizing the size of the PAA features.

Hydrogen plasma treatment of silicon dioxide for improved silane deposition.

We describe a method for plasma cleaning silicon surfaces in a commercial tool that removes adventitious organic contamination and enhances silane deposition. As shown by wetting, ellipsometry, and XPS, hydrogen, oxygen, and argon plasmas effectively clean Si/SiO2 surfaces. However, only hydrogen plasmas appear to enhance subsequent low-pressure chemical vapor deposition of silanes. Chemical differences between the surfaces were confirmed via (i) deposition of two different silanes: octyldimethylmethoxysilane and butyldimethylmethoxysilane, as evidenced by spectroscopic ellipsometry and wetting, and (ii) a principal components analysis (PCA) of TOF-SIMS data taken from the different plasma-treated surfaces. AFM shows no increase in surface roughness after H2 or O2 plasma treatment of Si/SiO2. The effects of surface treatment with H2/O2 plasmas in different gas ratios, which should allow greater control of surface chemistry, and the duration of the H2 plasma (complete surface treatment appeared to take place quickly) are also presented. We believe that this work is significant because of the importance of silanes as surface functionalization reagents, and in particular because of the increasing importance of gas phase silane deposition.

Improved efficiency of reversed-phase carbon/nanodiamond/polymer core-shell particles for HPLC using carbonized poly(divinylbenzene) microspheres as the core materials.

Here, we report efficiencies up to 112,000 plates per meter (a reduced plate height, h, of 2.22) for RP, carbon/nanodiamond/aminopolymer particles using conventional injection conditions in HPLC. This efficiency greatly exceeds our best previously reported value of 71,000 N/m (h = 3.52). The carbon cores used in this study were derived from carbonized poly(divinylbenzene) spheres that were either made in-house by a two-step polymerization procedure or obtained commercially. The resulting particles showed good uniformity and were oxidized in nitric acid to increase their dispersability. X-ray photoelectron spectroscopy confirms particle oxidation and subsequent aminopolymer deposition. Layer-by-layer (LbL) growth of poly(allyamine) and nanodiamond was demonstrated to produce core-shell particles. After LbL growth, the particles were functionalized, sieved, and packed into columns. The column functionalization and packing were reproducible. Van Deemter curves indicated that the commercially obtained poly(divinylbenzene) spheres outperformed those synthesized in our laboratory. The columns appear to be stable at 120°C in a pH 11.3 mobile phase. Longer columns (2.1 × 50 mm) than previously reported were packed. Four essential oils were separated by gradient elution.

Controlling the surface silanol density in capillary columns and planar silicon via the self-limiting, gas-phase deposition of tris(dimethylamino)methylsilane, and quantification of surface silanols after silanization by low energy ion scattering.

Surface silanols (Si-OH) play a vital role on fused silica surfaces in chromatography. Here, we used an atmospheric-pressure, gas-phase reactor to modify the inner surface of a gas chromatography, fused silica capillary column (0.53 mm ID) with a small, reactive silane (tris(dimethylamino)methylsilane, TDMAMS). The deposition of TDMAMS on planar witness samples around the capillary was confirmed with X-ray photoelectron spectroscopy (XPS), ex situ spectroscopic ellipsometry (SE), and wetting. The number of surface silanols on unmodified and TDMAMS-modified native oxide-terminated silicon were quantified by tagging with dimethylzinc (DMZ) via atomic layer deposition (ALD) and counting the resulting zinc atoms with high sensitivity-low energy ion scattering (HS-LEIS). A bare, clean native oxide - terminated silicon wafer has 3.66 OH/nm2, which agrees with density functional theory (DFT) calculations from the literature. After TDMAMS modification of native oxide-terminated silicon, the number of surface silanols decreases by a factor of ca. 10 (to 0.31 OH/nm2). Intermediate surface testing (IST) was used to characterize the surface activities of functionalized capillaries. It suggested a significant deactivation/passivation of the capillary with some surface silanols remaining; the modified capillary shows significant deactivation compared to the native/unmodified fused silica tubing. We believe that this methodology for determining the number of residual silanols on silanized fused silica will be enabling for chromatography.

Area-Selective Atomic Layer Deposition of ZnO on Si\SiO2 Modified with Tris(dimethylamino)methylsilane.

Delayed atomic layer deposition (ALD) of ZnO, i.e., area selective (AS)-ALD, was successfully achieved on silicon wafers (Si\SiO2) terminated with tris(dimethylamino)methylsilane (TDMAMS). This resist molecule was deposited in a home-built, near-atmospheric pressure, flow-through, gas-phase reactor. TDMAMS had previously been shown to react with Si\SiO2 in a single cycle/reaction and to drastically reduce the number of silanols that remain at the surface. ZnO was deposited in a commercial ALD system using dimethylzinc (DMZ) as the zinc precursor and H2O as the coreactant. Deposition of TDMAMS was confirmed by spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS), and wetting. ALD of ZnO, including its selectivity on TDMAMS-terminated Si\SiO2 (Si\SiO2\TDMAMS), was confirmed by in situ multi-wavelength ellipsometry, ex situ SE, XPS, and/or high-sensitivity/low-energy ion scattering (HS-LEIS). The thermal stability of the TDMAMS resist layer, which is an important parameter for AS-ALD, was investigated by heating Si\SiO2\TDMAMS in air and nitrogen at 330 °C. ALD of ZnO takes place more readily on Si\SiO2\TDMAMS heated in the air than in N2, suggesting greater damage to the surface heated in the air. To better understand the in situ ALD of ZnO on Si\SiO2\TDMAMS and modified (thermally stressed) forms of it, the ellipsometry results were plotted as the normalized growth per cycle. Even one short pulse of TDMAMS effectively passivates Si\SiO2. TDMAMS can be a useful, small-molecule inhibitor of ALD of ZnO on Si\SiO2 surfaces.

Chemical alignment of DNA origami to block copolymer patterned arrays of 5 nm gold nanoparticles.

We have used block copolymer patterned arrays of 5 nm gold nanoparticles (AuNPs) for chemically aligned surface attachment of DNA origami. Addition of single-stranded DNA-thiol to AuNPs allowed a base paired attachment of sticky end modified DNA origami. Results indicate a stable, selective attachment between the DNA origami and ssDNA modified AuNPs. Yield data showed 74% of AuNP binding sites forming an attachment with a DNA origami rectangle, and control surfaces showed less than 0.5% nonspecific adsorption.

Pellicular particles with spherical carbon cores and porous nanodiamond/polymer shells for reversed-phase HPLC.

A new stationary phase for reversed-phase high performance liquid chromatography (RP HPLC) was created by coating spherical 3 µm carbon core particles in a layer-by-layer (LbL) fashion with poly(allylamine) (PAAm) and nanodiamond. Unfunctionalized core carbon particles were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and Raman spectroscopy. After LbL of PAAm and nanodiamond, which yields ca. 4 µm core-shell particles, the particles were simultaneously functionalized and cross-linked using a mixture of 1,2-epoxyoctadecane and 1,2,7,8-diepoxyoctane to obtain a mechanically stable C(18)/C(8) bonded outer layer. Core-shell particles were characterized by SEM, and their surface area, pore diameter, and volume were determined using the Brunauer-Emmett-Teller (BET) method. Short stainless steel columns (30 × 4.6 mm i.d.) were packed and the corresponding van Deemter plots obtained. The Supporting Information contains a MATLAB program used to fit the van Deemter data. The retentions of a suite of analytes were investigated on a conventional HPLC at various organic solvent compositions, pH values of mobile phases, including extreme pH values, and column temperatures. At 60 °C, a chromatogram of 2,6-diisopropylphenol showed 71,500 plates/m (N/m). Chromatograms obtained under acidic conditions (pH 2.7) of a mixture of acetaminophen, diazepam, and 2,6-diisopropylphenol and a mixture of phenol, 4-methylphenol, 2-chlorophenol, 4-chlorophenol, 4-bromophenol, and 1-tert-butyl-4-methylphenol are presented. Retention of amitriptyline, cholesterol, and diazinon at temperatures ranging from 35 to 80 °C and at pH 11.3 is reported. A series of five basic drugs was also separated at this pH. The stationary phase exhibits considerable hydrolytic stability at high pH (11.3) and even pH 13 over extended periods of time. An analysis run on a UHPLC with a "sandwich" injection appeared to reduce extra column band broadening and gave best efficiencies of 110,000-120,000 N/m.

Core-shell diamond as a support for solid-phase extraction and high-performance liquid chromatography.

We report the formation of core-shell diamond particles for solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) made by layer-by-layer (LbL) deposition. Their synthesis begins with the amine functionalization of microdiamond by its immersion in an aqueous solution of a primary amine-containing polymer (polyallylamine (PAAm)). The amine-terminated microdiamond is then immersed in an aqueous suspension of nanodiamond, which leads to adsorption of the nanodiamond. Alternating (self-limiting) immersions in the solutions of the amine-containing polymer and the suspension of nanodiamond are continued until the desired number of nanodiamond layers is formed around the microdiamond. Finally, the core-shell particles are cross-linked with 1,2,5,6-diepoxycyclooctane or reacted with 1,2-epoxyoctadecane. Layer-by-layer deposition of PAAm and nanodiamond is also studied on planar Si/SiO(2) surfaces, which were characterized by scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA). Core-shell particles are characterized by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), environmental scanning electron microscopy (ESEM), and Brunauer-Emmett-Teller (BET) surface area and pore size measurements. Larger (ca. 50 microm) core-shell diamond particles have much higher surface areas and analyte loading capacities in SPE than nonporous solid diamond particles. Smaller (ca. 3 microm), normal and reversed-phase, core-shell diamond particles have been used for HPLC, with 36,300 plates/m for mesitylene in a separation of benzene and alkyl benzenes and 54,800 plates/m for diazinon in a similar separation of two pesticides on a C(18) adsorbent.