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The purpose of this project is to use a hyphenated technique to combine Nuclear Magnetic Resonance (NMR) spectroscopy and Gel Permeation Chromatography (GPC) to evaluate the chemical composition and molecular weight distribution of the polymer Estane with an emphasis on determining if the technique is sensitive enough to evaluate the aging of Estane.
The purpose of this project is to use a hyphenated technique to combine Nuclear Magnetic Resonance (NMR) spectroscopy and Gel Permeation Chromatography (GPC) to evaluate the chemical composition and molecular weight distribution of the polymer Estane with an emphasis on determining if the technique is sensitive enough to evaluate the aging of Estane.
In support of the Bioenergy Technologies Office in recovering coproducts in biorefineries this project evaluates the use of Counter Current Chromatography (CCC) in recovering co-products from Reductive Catalytic Fractionation (RCF) oil, Alkaline Pretreatment Liquor (APL), aqueous phase Hydrothermal Liquefaction (HTL) oil, and Catalytic Fast Pyrolysis (CFP) oil. The project addresses three technology barriers in developing the bioeconomy; (1) Cost of production (2) Selective separation of organic acid species, and (3) Advanced bioprocess development. CCC is a unique, scalable, chromatographic technology that operates with two immiscible liquid phases moving counter current to one another. Unlike Simulated Moving Bed (SMB) technology, CCC is a true moving bed and because it uses liquids as both the stationary and mobile phase it can handle solids directly in the feed. This aspect of CCC allows it to skip the expensive filtration step needed prior to traditional SMB, furthermore the liquid phases are composed on relatively inexpensive organics (e.g. hexane and ethyl acetate). This project develops CCC methods for direct isolation of co-products from RCF oil, APL, HTL aqueous, and CFP oil. TechnoEconomic Analysis and process modeling is presented to compare CCC to SMB and assess its applicability in a holistic biorefinery. Initial results indicate approximately 4x reductions in solvent demand and 2x reduction in energy consumption compared to SMB.
The goal of gcxgclab is to provide a comprehensive program for preprocessing and analysis of two dimensional gas chromatography data. It is equipped with functions for baseline correction, smoothing, peak identification, peak alignment, identification of EICs, Mass Spectra, targeted analysis, compound identification with NIST and non-targeted analysis, plus plotting and data visualization.
The use of gradient anion-exchange HPLC, with a simple post-column detection system, is described for the separation of myo-inositol phosphates, including "phytic acid" (myo-inositol hexaphosphate). Hexa-, penta-, tetra-, tri- and diphosphate members of this homologous series are clearly resolved within 30 min. This method should facilitate analysis and quantitation of "phytic acid" and other inositol phosphates in plant, food, and soil samples.
Selective π‐complexation capabilities of silver(I) and copper(I) ions can be effectively facilitated in ionic liquids. To understand the effects of environmental factors that influence the π‐complexation of these metal ions with analytes, techniques that employ small volumes of ionic liquid that can be readily analyzed are desired. In this study, headspace single drop microextraction coupled with HPLC is used to investigate a diverse set of environmental factors on the metal ion‐mediated complexation with aromatic compounds in ionic liquid media. Silver(I) and copper(I) bis[(trifluoromethyl)sulfonyl]imide salts were both studied by dissolving them in the 1‐decyl‐3‐methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ionic liquid and employing the mixture as extraction media for aromatic compounds. Water and acetonitrile within the sample solution were observed to interfere with the complexation of silver(I) ions and aromatic compounds, while ethylene glycol and triethylene glycol did not. The temperature and extraction times were optimized to fully facilitate the π‐complexation capabilities of metal ions in ionic liquid media. Partition coefficients between the sample headspace and metal ion were determined using a three‐phase equilibria model. Although no discernable difference in analyte partitioning between the headspace and ionic liquid solvent was observed, analyte partition coefficients to silver(I) ion tended to be greater compared to copper(I) ion.
Extraction chromatographic separations following a nuclear event will require both speed and accuracy. Ideally these separations will be carried out using commercially available products. Because 90Sr is a likely material to be used in a radioactivity dispersal device, commercially available products for the separation of strontium were tested to evaluate differences in their elution profiles that may affect elution procedures. Gravity flow columns show better resolution, but vacuum flow columns allow rapid processing and are still adequate for purification if multiple aqueous conditions can be employed in the elution strategy.
An automated online separation–direct analysis method, RAPID (rapid analysis of post-irradiation debris), has been developed for the measurement of the concentration and isotopic composition of over 40 elements down to the low-picogram level. Here we discuss the application of RAPID to irradiated highly-enriched uranium, demonstrating that it has the sensitivity required to achieve precise, low-level analyses of non-natural isotopes, even in the presence of a bulk uranium matrix. As a result, isotopic ratios have been successfully measured at the low-picogram level, and the accuracy of these ratios was confirmed using an isotopic depletion and decay modeling software to within 1–2%.
Here, the uptake behavior of 73 As and 75 Se was studied in HCl and HNO3 media with CL resin, ethanethiol resin and dimethyl sulfide resin. In HCl solutions, there was high extraction of selenium on CL resin and ethanethiol resin but lower uptake on dimethyl sulfide resin; arsenic was only extracted by CL resin. From HNO 3 , selenium was extracted only by ethanethiol resin and CL resin and there was no uptake of arsenic on any resin. While the sulfur-based resins have high selenium uptake and selectivity, column separations are challenging due to the chemical instability of these resins.
Paralytic shellfish toxins (PSTs) are neurotoxins produced by dinoflagellates and cyanobacteria that cause paralytic shellfish poisoning in humans. PST quantitation by LC-MS is challenging because of their high polarity, lability as gas-phase ions, and large number of potentially interfering analogues. Differential mobility spectrometry (DMS) has the potential to improve the performance of LC-MS methods for PSTs in terms of selectivity and limits of detection. This work describes a comprehensive investigation of the separation of 16 regulated PSTs by DMS and the development of highly selective LC-DMS-MS methods for PST quantitation. The effects of all DMS parameters on the separation of PSTs from one another were first investigated in detail. The labile nature of 11α-gonyautoxin epimers gave unique insight into fragmentation of labile analytes before, during, and after the DMS analyzer. Two sets of DMS parameters were identified that either optimized the resolution of PSTs from one another or transmitted them at a limited number of compensation voltage (CV) values corresponding to structural subclasses. These were used to develop multidimensional LC-DMS-MS/MS methods using existing HILIC-MS/MS parameters. In both cases, improved selectivity was observed when using DMS, and the quantitative capabilities of a rapid UPLC-DMS-MS/MS method were evaluated. Limits of detection of the developed method were similar to those without DMS, and differences were highly analyte-dependant. Analysis of shellfish matrix reference materials showed good agreement with established methods. The developed methods will be useful in cases where specific matrix interferences are encountered in the LC-MS/MS analysis of PSTs in complex biological samples. .
In relation to developing a micro HPLC cartridge, we have recently built a high-pressure electroosmotic pump (EOP). However, we do not recommend people to use this pump to deliver an organic solvent directly, because it often makes the pump rate unstable. We have experimented several approaches to address this issue, but none of them are satisfactory. Here, we develop an innovative approach to address this issue. We first create an abruption (a dead-volume) within a fluid conduit. We then utilize an EOP to withdraw, via a selection valve, a train of eluent solutions having decreasing eluting power into the fluid conduit. When these solutions are further aspirated through the dead-volume, these solutions are partially mixed, smoothening concentration transitions between two adjacent eluent solutions. As these solutions are pushed back, through the dead-volume again, a smooth gradient profile is formed. In this work, we characterize this scheme for gradient formation, and we incorporate this approach with a high-pressure EOP, a nanoliter injection valve, and a capillary column, yielding a micro HPLC system. Lastly, we then couple this micro HPLC with an electrospray ionization – mass spectrometer for peptide and protein separations and identifications.
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A new and complete GC–ICP-MS method is described for direct analysis of trace metals in a gas phase process stream. The proposed method is derived from standard analytical procedures developed for ICP-MS, which are regularly exercised in standard ICP-MS laboratories. In order to implement the method, a series of empirical factors were generated to calibrate detector response with respect to a known concentration of an internal standard analyte. Calibrated responses are ultimately used to determine the concentration of metal analytes in a gas stream using a semi-quantitative algorithm. The method was verified using a traditional gas injection from a GC sampling valve and a standard gas mixture containing either a 1 ppm Xe + Kr mix with helium balance or 100 ppm Xe with helium balance. Data collected for Xe and Kr gas analytes revealed that agreement of 6–20% with the actual concentration can be expected for various experimental conditions. To demonstrate the method using a relevant “unknown” gas mixture, experiments were performed for continuous 4 and 7 hour periods using a Hg-containing sample gas that was co-introduced into the GC sample loop with the xenon gas standard. System performance and detector response to the dilute concentration of the internal standard were pre-determined, which allowed semi-quantitative evaluation of the analyte. The calculated analyte concentrations varied during the course of the 4 hour experiment, particularly during the first hour of the analysis where the actual Hg concentration was under predicted by up to 72%. Calculated concentration improved to within 30–60% for data collected after the first hour of the experiment. Similar results were seen during the 7 hour test with the deviation from the actual concentration being 11–81% during the first hour and then decreasing for the remaining period. The method detection limit (MDL) was determined for the mercury by injecting the sample gas into the system following a period of equilibration. The MDL for Hg was calculated as 6.8 μg · m -3 . This work describes the first complete GC–ICP-MS method to directly analyze gas phase samples, and detailed sample calculations and comparisons to conventional ICP-MS methods are provided.
The purpose of this study was to perform a preliminary investigation of compound-specific isotope analysis (CSIA) of diesel fuels to evaluate whether the technique could distinguish between the diesel samples from different sources/locations. The ability to differentiate or correlate diesel samples could be valuable for detecting fuel tax evasion schemes. Two fractionation techniques were used to isolate the n-alkanes from the fuel. Both δ13C and δD values for the n-alkanes were then determined by CSIA in each sample. Plots of δD versus δ13C with sample n-alkane points connected in order of increasing carbon number gave well separated clusters with characteristic shapes for each sample. Principal components analysis (PCA) with δ13C, δD, or combined δ13C and δD data on the yielded scores plots that could clearly differentiate the samples, thereby demonstrating the potential of this approach for fingerprinting fuel samples using the δ13C and δD values.
Understanding the composition of complex hydrocarbon mixtures is important for environmental studies in a variety of fields, but many prevalent compounds cannot be confidently identified using traditional gas chromatography/mass spectrometry (GC/MS) techniques. In this study, we use vacuum-ultraviolet (VUV) ionization to elucidate the structures of a traditionally “unresolved complex mixture” by separating components by GC retention time, t R , and mass-to-charge ratio, m/z, which are used to determine carbon number, N C , and the number of rings and double bonds, N DBE . Constitutional isomers are resolved on the basis of t R , enabling the most complete quantitative analysis to date of structural isomers in an environmentally relevant hydrocarbon mixture. Unknown compounds are classified in this work by carbon number, degree of saturation, presence of rings, and degree of branching, providing structural constraints. The capabilities of this analysis are explored using diesel fuel, in which constitutional isomer distribution patterns are shown to be reproducible between carbon numbers and follow predictable rules. Nearly half of the aliphatic hydrocarbon mass is shown to be branched, suggesting branching is more important in diesel fuel than previously shown. Lastly, the classification of unknown hydrocarbons and the resolution of constitutional isomers significantly improves resolution capabilities for any complex hydrocarbon mixture.
Biomass storage operation is one major source of feedstock quality variability that impacts on downstream preprocessing, feeding, handling and conversion into biofuels, chemicals and products. In field Ccorn stover biomass bales undergoes degradation and cell wall components modification resulting from microbial biological heating occurring during storage. A molecular characterization of the modification was achieved to unveil and understand the changes of structural cell wall modification in corn stover samples by conducting low temperature (400°C) pyrolysis, comparing samples that were mildly biologicallyun heated to those that had been subjected to microbial severe biological heating (~60°C). Pyrolysis of the samples originating from biomass that had been heated during storage generated small oxygenates such as furfural, 5-methylfurfural and 2-(5H)-furanone with efficiencies that were as much as ten times greater than those measured for the mildly unheated samples. Most of the compounds having enhanced efficiencies were C5 oxygenates, suggesting that the pyrolysis products may be formed from hemicellulosic precursor polymers in the corn stover. The findings suggest that microbial heating may be disrupting the cell wall structure, fragmenting the hemicellulose or cellulose chains, generating more polymer termini that have higher efficiency for generating the oxygenates at lower temperatures. Pyrolysis variability with temperature may be a beneficial strategy for improved biomass cell wall characterization, and for guiding control strategies for enhanced control over product distributions , providing insights to understand and manage the feedstock variability as well as to inform harvest and storage best management practices.
The investigation of crimes involving chemical or biological agents is infrequent, but presents unique analytical challenges. The protein toxin ricin is encountered more frequently than other agents and is found in the seeds of the castor plant Ricinus communis. Typically, the toxin is extracted from castor seeds utilizing a variety of different recipes that result in varying purity of the toxin. Moreover, these various purification steps can also leave or differentially remove a variety of exogenous and endogenous residual components with the toxin that may indicate the type and number of purification steps involved. We have applied three gas chromatographic - mass spectrometric (GC-MS) based analytical methods to measure the variation in seed carbohydrates and castor oil ricinoleic acid as well as the presence of solvents used for purification. These methods were applied to the same samples prepared using four previously identified toxin preparation methods starting from four varieties of castor seeds. The individual data sets for seed carbohydrate profiles, ricinoleic acid or acetone amount each provided information capable of differentiating different types of toxin preparations across seed types. However, the integration of the data sets using multivariate factor analysis provided a clear distinction of all samples based on the preparation method and independent of the seed source. In particular the abundance of mannose, arabinose, fucose, ricinoleic acid and acetone were shown to be important differentiating factors. These complementary tools provide a more confident determination of the method of toxin preparation.