Polymeric architecture as a tool for controlling the reactivity of palladium(II) loaded nanoreactors.

Self-assembled systems, like polymeric micelles, have become great facilitators for conducting organic reactions in aqueous media due to their broad potential applications in green chemistry and biomedical applications. Massive strides have been taken to improve the reaction scope of such systems, enabling them to perform bioorthogonal reactions for prodrug therapy. Considering these significant advancements, we sought to study the relationships between the architecture of the amphiphiles and the reactivity of their PdII loaded micellar nanoreactors in conducting depropargylation reactions. Towards this goal, we designed and synthesized a series of isomeric polyethylene glycol (PEG)-dendron amphiphiles with different dendritic architectures but with an identical degree of hydrophobicity and hydrophilic to lipophilic balance (HLB). We observed that the dendritic architecture, which serves as the main binding site for the PdII ions, has greater influence on the reactivity than the hydrophobicity of the dendron. These trends remained constant for two different propargyl caged substrates, validating the obtained results. Density functional theory (DFT) calculations of simplified models of the dendritic blocks revealed the different binding modes of the various dendritic architectures to PdII ions, which could explain the observed differences in the reactivity of the nanoreactors with different dendritic architectures. Our results demonstrate how tuning the internal architecture of the amphiphiles by changing the orientation of the chelating moieties can be used as a tool for controlling the reactivity of PdII loaded nanoreactors.

Cold Electron Ionization (EI) Is Not a Supplementary Ion Source to Standard EI. It is a Highly Superior Replacement Ion Source.

GC-MS usually employs a 70 eV electron ionization (EI) ion source, which provides mass spectra with detailed fragment ion information that are amenable for library search and identification with names and structures at the isomer level. However, conventional EI often suffers from low intensity or the absence of molecular ions, which reduces detection and identification capabilities in analyses. In an attempt to enhance the molecular ions, several softer ion sources are being used to supplement standard EI, including chemical ionization (CI), atmospheric pressure chemical ionization (APCI), field ionization (FI), photoionization (PI), and low electron energy EI. However, the most advantageous way to enhance molecular ions is to use cold EI, which employs 70 eV EI of cold molecules in supersonic molecular beams. Cold EI yields classical EI mass spectra with highly enhanced molecular ions, which still provides high detectability and library-searchable mass spectra. In this paper, we explain and discuss why cold EI is not a supplementary ion source to standard EI, but rather it is a highly superior replacement to standard EI. With cold EI, there is no need for standard EI or any other supplemental ion source. We describe 16 benefits and unique features of cold EI that not only yield better results for existing applications but also significantly extend the range of compounds and applications amenable for GC-MS analysis.

Open Probe: a device for ultra fast electron ionization mass spectrometry analysis.

Open Probe is based on a vaporization oven mounted on a transfer line of a gas chromatograph mass spectrometer (GC/MS) which is connected to the MS ion source via a short flow restriction capillary. The probe oven is open to room air while having helium purge flow protection to eliminate or significantly reduce air leakage into the oven and MS ion source. Sample analysis can be as simple as touch (the sample), push (the sample holder) into the open probe oven, and have the results. Experiments were performed with a GC/MS with supersonic molecular beams and with a standard Agilent 5975 MSD. Powders and tablets analysis were performed by touching the sample with the bottom side of a melting point vial and inserting it into the open probe oven with total analysis cycle time of <30 s. Similarly, trace trinitrotoluene (TNT) on human fingerprints was analyzed. Additional sample holder types included swabs, spoons, and vials. The open probe is a leak-proof MS probe which is characterized by fast analysis cycle time, and it uses a low cost mass spectrometer of GC/MS with the benefits of electron ionization of library search and uniform, quantitative response without ion suppression effects.

Classical electron ionization mass spectra in gas chromatography/mass spectrometry with supersonic molecular beams.

A major benefit of gas chromatography/mass spectrometry (GC/MS) with a supersonic molecular beam (SMB) interface and its fly-through ion source is the ability to obtain electron ionization of vibrationally cold molecules (cold EI), which show enhanced molecular ions. However, GC/MS with an SMB also has the flexibility to perform 'classical EI' mode of operation which provides mass spectra to mimic those in commercial 70 eV electron ionization MS libraries. Classical EI in SMB is obtained through simple reduction of the helium make-up gas flow rate, which reduces the SMB cooling efficiency; hence the vibrational temperatures of the molecules are similar to those in traditional EI ion sources. In classical EI-SMB mode, the relative abundance of the molecular ion can be tuned and, as a result, excellent identification probabilities and very good matching factors to the NIST MS library are obtained. Classical EI-SMB with the fly-through dual cage ion source has analyte sensitivity similar to that of the standard EI ion source of a basic GC/MS system. The fly-through EI ion source in combination with the SMB interface can serve for cold EI, classical EI-SMB, and cluster chemical ionization (CCI) modes of operation, all easily exchangeable through a simple and quick change (not involving hardware). Furthermore, the fly-through ion source eliminates sample scattering from the walls of the ion source, and thus it offers full sample inertness, tailing-free operation, and no ion-molecule reaction interferences. It is also robust and enables increased column flow rate capability without affecting the sensitivity.

Hydrocarbons and fuels analyses with the supersonic gas chromatography mass spectrometry--the novel concept of isomer abundance analysis.

Hydrocarbon analysis with standard GC-MS is confronted by the limited range of volatile compounds amenable for analysis and by the similarity of electron ionization mass spectra for many compounds which show weak or no molecular ions for heavy hydrocarbons. The use of GC-MS with supersonic molecular beams (Supersonic GC-MS) significantly extends the range of heavy hydrocarbons that can be analyzed, and provides trustworthy enhanced molecular ion to all hydrocarbons. In addition, unique isomer mass spectral features are obtained in the ionization of vibrationally cold hydrocarbons. The availability of molecular ions for all hydrocarbons results in the ability to obtain unique chromatographic isomer distribution patterns that can serve as a new method for fuel characterization and identification. Examples of the applicability and use of this novel isomer abundance analysis (IAA) method to diesel fuel, kerosene and oil analyses are shown. It is suggested that in similarity to the "three ions method" for identification purposes, three isomer abundance patterns can serve for fuel characterization. The applications of the Supersonic GC-MS for engine motor oil analysis and transformer oil analysis are also demonstrated and discussed, including the capability to achieve fast 1-2s sampling without separation for oil and fuel fingerprinting. The relatively fast analysis of biodiesel is described, demonstrating the provision of molecular ions to heavy triglycerides. Isomer abundance analysis with the Supersonic GC-MS could find broad range of applications including petrochemicals and fuel analysis, arson analysis, environmental oil/fuel spill analysis, fuel adulteration analysis and motor oil analysis.

Gas chromatography-mass spectrometry with supersonic molecular beams.

Gas chromatography-mass spectrometry (GC-MS) with supersonic molecular beams (SMBs) (also named Supersonic GC-MS) is based on GC and MS interface with SMBs and on the electron ionization (EI) of vibrationally cold analytes in the SMBs (cold EI) in a fly-through ion source. This ion source is inherently inert and further characterized by fast response and vacuum background filtration capability. The same ion source offers three modes of ionization including cold EI, classical EI and cluster chemical ionization (CI). Cold EI, as a main mode, provides enhanced molecular ions combined with an effective library sample identification, which is supplemented and complemented by a powerful isotope abundance analysis method and software. The range of low-volatility and thermally labile compounds amenable for analysis is significantly increased owing to the use of the contact-free, fly-through ion source and the ability to lower sample elution temperatures through the use of high column carrier gas flow rates. Effective, fast GC-MS is enabled particularly owing to the possible use of high column flow rates and improved system selectivity in view of the enhancement of the molecular ion. This fast GC-MS with SMB can be further improved via the added selectivity of MS-MS, which by itself benefits from the enhancement of the molecular ion, the most suitable parent ion for MS-MS. Supersonic GC-MS is characterized by low limits of detection (LOD), and its sensitivity is superior to that of standard GC-MS, particularly for samples that are hard for analysis. The GC separation of the Supersonic GC-MS can be improved with pulsed flow modulation (PFM) GC x GC-MS. Electron ionization LC-MS with SMB can also be combined with the Supersonic GC-MS, with fast and easy switching between these two modes of operation.

Flow modulation comprehensive two-dimensional gas chromatography-mass spectrometry with a supersonic molecular beam.

A new approach of flow modulation comprehensive two-dimensional gas chromatography-mass spectrometry (GC x GC-MS) with supersonic molecular beam (SMB) and a quadrupole mass analyzer is presented. Flow modulation uniquely enables GC x GC-MS to be achieved even with the limited scan speed of quadrupole MS, and its 20 ml/min column flow rate is handled, splitless, by the SMB interface. Flow modulation GC x GC-SMB-MS shares all the major benefits of GC x GC and combines them with GC-MS including: (a) increased GC separation capability; (b) improved sensitivity via narrower GC peaks; (c) improved sensitivity through reduced matrix interference and chemical noise; (d) polarity and functional group sample information via the order of elution from the second polar column. In addition, GC x GC-SMB-MS is uniquely characterized by the features of GC-MS with SMB of enhanced and trustworthy molecular ion plus isotope abundance analysis (IAA) for improved sample identification and fast fly-through ion source response time. The combination of flow modulation GC x GC with GC-MS with SMB (supersonic GC-MS) was explored with complex matrices such as diesel fuel analysis and pesticide analysis in agricultural products.

Extending the range of compounds amenable for gas chromatography-mass spectrometric analysis.

Gas chromatography-mass spectrometry (GC-MS) suffers from a major limitation in that an expanding number of thermally labile or low volatility compounds of interest are not amenable for analysis. We found that the elution temperatures of compounds from GC can be significantly lowered by reducing the column length, increasing the carrier gas flow rate, reducing the capillary column film thickness and lowering the temperature programming rate. Pyrene is eluted at 287 degrees C in standard GC-MS with a 30 m x 0.25 mm I.D. column with 1-microm DB5ms film and 1-ml/min He column flow rate. In contrast, pyrene is eluted at 79 degrees C in our "Supersonic GC-MS" system using a 1 m x 0.25 mm I.D. column with 0.1-microm DB5ms film and 100-ml/min He column flow rate. A simple model has been invoked to explain the significantly (up to 208 degrees C) lower elution temperatures observed. According to this model, every halving of the temperature programming rate, or number of separation plates (either through increased flow rate or due to reduced column length), results in approximately 20 degrees C lower elution temperature. These considerably lower elution temperatures enable the analysis of an extended range of thermally labile and low volatility compounds, that otherwise could not be analyzed by standard GC-MS. We demonstrate the analysis of large polycyclic aromatic hydrocarbons (PAHs) such as decacyclene with ten fused rings, well above the current GC limit of PAHs with six rings. Even a metalloporphirin such as magnesiumoctaethylporphin was easily analyzed with elution temperatures below 300 degrees C. Furthermore, a range of thermally labile compounds were analyzed including carbamates such as methomyl, aldicarb, aldicarbsulfone and oxamyl, explosives such as pentaerythritol tetranitrate, Tetryl and HMX, and drugs such as reserpine (608 a.m.u.). Supersonic GC-MS was used, based on the coupling of a supersonic molecular beam (SMB) inlet and ion sources with a bench-top Agilent 6890 GC plus 5972 MSD. The Supersonic GC-MS provides enhanced molecular ion without any ion source related peak tailing. Thus, the lower GC separation power involved in the analysis of thermally labile and low volatility compounds is compensated by increased separation power of the MS gained from the enhanced molecular ion. Several implications of these findings are discussed, including our conclusion that slower chromatography leads to better analysis of thermally labile compounds.

Fast, high-sensitivity, multipesticide analysis of complex mixtures with supersonic gas chromatography-mass spectrometry.

We developed a new instrumental approach, termed Supersonic GC-MS, which achieves fast, sensitive, confirmatory and quantitative analysis of a broad range of pesticides in complex agricultural matrices. Our Supersonic GC-MS system is a modification of a bench-top Agilent 6890 GC+5972 MSD with a supersonic molecular beam (SMB) interface and fly-through EI ion source. One of the main advantages of Supersonic GC-MS is an enhanced molecular ion (M+) in the resulting mass spectra. For example, the M+ was observed in all 88 pesticides that we studied using the Supersonic GC-MS whereas only 36 of 63 (57%) pesticides that we investigated in standard GC-MS exhibited a M+. We also found that the degree of matrix interference is exponentially reduced with the fragment mass by about 20-fold per 100 amu increasing mass. The enhancement of the M+ combined with the reduction in matrix background noise permit rapid full scan analysis of a potentially unlimited number of pesticides, unlike selected ion monitoring or MS-MS in which specific conditions are required in segments for targeted pesticides. Furthermore, unlike the case with chemical ionization, EI-SMB-MS spectra still give accurate identification of compounds using common mass spectral libraries. In practice,we found thatlibraries favor mass spectra in which the M+ appears, thus Supersonic GC-MS produced better spectra for compound identification than standard GC-MS. To achieve even lower identification limits, the M+ plus a second major ion (still using full scan data) gives higher signal-to-chemical noise ratios than the traditional 3-ion approach. The replacement of two low-mass ions with the M+ (supersonic two-ions method) results in a significant reduction of matrix interference by a factor of up to 90. Another main advantage of Supersonic GC-MS is its exceptional suitability for fast GC-MS with high carrier gas flow-rate. Fast Supersonic GC-MS was able to analyze thermally labile pesticides, such as carbamates, that are difficult or impossible to analyze in standard GC-MS. Large volume injection using a ChromatoProbe was also demonstrated, in the 6 min analysis of pesticides at 20 ng/g in a spice matrix.