SnifProbe: new method and device for vapor and gas sampling

SnifProbe is based on the use of 15 mm short pieces of standard 0.53 mm I.D. capillary or porous layer open tubular columns for sampling airborne, headspace, aroma or air pollution samples. A miniaturized frit-bottomed packed vial named MicroSPE was also prepared which served for the sampling of solvent vapors and gases as well as liquid water. The short (15 mm) trapping column is inserted into the SnifProbe easy-insertion-port and the SnifProbe is located or aimed at the sample environment. A miniature pump is operated for pumping 10-60 ml/min of the air sample through the short piece of column to collect the sample. After a few seconds up to a few minutes of pumping, the short column is removed from the SnifProbe with tweezers (or gloved hands) and placed inside a glass vial of a direct sample introduction device (ChromatoProbe) having a 0.5 mm hole at its bottom. The ChromatoProbe sample holder with its glass vial and sample in the short column are introduced into the GC injector as usual. The sample is then quickly and efficiently desorbed from the short sample column and is transferred into the analytical column for conventional GC and/or GC-MS analysis. We have explored the various characteristics of SnifProbe and demonstrated its applicability and effectiveness in many applications. These applications include: the analysis of benzene, toluene and o-xylene in air, SO2 in air, perfume aroma on hand, beer headspace, wine aroma, coffee aroma, cigarette smoke, trace chemical warfare agent simulants, explosives vapors, ethanol in human breath and odorants in domestic cooking gas. SnifProbe can be operated in the field or at a chemical process. The sample columns can be plugged and stored in a small union storage device, placed in a small plastic bag, marked and brought to the laboratory for analysis with the full power of GC and/or GC-MS. Accordingly, we feel that the major and most significant feature of SnifProbe is that it brings the field and process to the laboratory. Thus, SnifProbe can extend the "arm" of the GC and GC-MS laboratory and enable high-quality field and process analysis.     

Fast,very fast,and ultra-fast gas chromatography-mass spectrometry of thermally labile steroids,carbamates, and drugs in supersonic molecular beams

Gas chromatography-mass spectrometry (GC-MS) analyses of thermally labile compounds have been studied by using a short column fast gas chromatograph, coupled with fly-through electron ionization in supersonic molecular beams. Thirty-two compounds, which include steroids, carbamate pesticides, antibiotic drugs, and other pharmaceutical compounds, have been analyzed and the details of their GC-MS analysis are provided. The ability to analyze thermally labile compounds is discussed in relation to the speed of analysis. A new term, “speed enhancement factor” (SEF), is defined as the product of column length reduction and the carrier gas linear velocity increase, as compared with normal GC-MS conditions. Fast, very fast, and ultra-fast GC-MS are defined with a SEF in the ranges of 5–30, 30–400, and 400–4000, respectively. Trade-offs in the degree of dissociation, speed, gas chromatograph resolution, and sensitivity were studied and examined with thermally labile molecules. The experimental factors that affect the dissociation are described with emphasis on its reduction. We claim that the use of supersonic molecular beams for sampling and ionization provides the ultimate capability in the GC-MS of thermally labile compounds. The obtained 70-eV electron ionization mass spectra are shown, and an enhanced relative abundance of the molecular ion is demonstrated together with library search capability of these mass spectra, which is better than that reported with particle beam liquid chromatography-mass spectrometry. The performance of fast GC-MS in supersonic molecular beams is compared with other methods of fast GC-MS and with particle beam liquid chromatography-mass spectrometry.     

General method for the preparation of beta,beta-difluoroacrylates using BrF3

Various esters were reacted with base, carbon disulfide, and methyl iodide, producing 2-carboalkoxy-1,1-bis(methyl sulfide)-1-alkenes (2). The reaction of 2 with BrF(3), followed by oxidation with HOF.CH(3)CN gave the bromodifluorosulfonyl derivatives 5. Subsequent treatment with Raney nickel led to alpha-substituted beta,beta-difluoroacrylates 6 in overall yields of 50-80%.     

Reactions of 2,7-Dimethyloxepin with Dimethyldioxirane and Methyl(trifluoromethyl)dioxirane: Ring Opening and Probable Observation of the Intermediate “2,3-Epoxyoxepin”

The reactions of dimethyldioxirane (7) and methyl(trifluoromethyl)dioxirane (8) with 2,7-dimethyloxepin (4) both yielded Z,Z-3,5-octadiene-2,7-dione (Z,Z-6) as their initial stable products. This is the first published reaction of a dioxirane with an isolable pure oxepin. Reaction of the dienedione Z,Z-6 with one mole equivalent of either 7 or 8 yielded the corresponding monoepoxide. Treatment of this monoepoxide with another equivalent of 8 yielded the corresponding diepoxides (probably meso and R,S). The suggestion of Murray and co-workers that dioxiranes may model some of the reactivities of monooxygenases and their rapid epoxidations of alkenes under neutral conditions at low temperatures suggested their use. Our initial attempts to directly observe the putative intermediate 1,3-dimethyl-2,8-dioxabicyclo-[5.1.0]octa-3,5-diene (2,7-dimethyl-2,3-oxepin (2)] at low temperatures (ca. –60°C) yielded promising but inconclusive results when dimethyldioxirane (7) was employed. The epoxidation reaction was sufficiently slow that it only occurred measurably above –30°C, a temperature at which thermal ring opening to the dienedione is competitive. Initial reactions with the much more reactive methyl)trifluoromethyl)dioxirane (8) led to immediate ring opening at temperatures as low as –80°C. Since 8 is known to isomerize to methyl trifluoroacetate and since water is present, a trace of trifluoroacetic acid was suspected of catalyzing the ring opening of 2. Thus, inclusion of either suspended Na₂HPO₄ or miscible 2,6-di-t-butylpyridine at –80°C yielded an intermediate stable up to ca. 0°C, which is likely to be the 2,3-epoxyoxepin 2.     

Nitrogen and hydrogen as carrier and make-up gases for GC-MS with Cold EI

Gas chromatography–mass spectrometry (GC-MS) with Cold EI is based on interfacing GC and MS with a supersonic molecular beam (SMB) and sample compounds ionization with a fly-through ion source as vibrationally cold compounds in the SMB (hence the name Cold EI). We explored the use of nitrogen and hydrogen as carrier and make-up gases with Cold EI and found:

1. Nitrogen is very effective in cooling compounds in SMB and while helium requires 60 ml/min nitrogen provides effective cooling with only 7–8 ml/min combined column and make-up flow rate. Hydrogen is less effective than helium and requires higher flow rates.
2. The transition from helium to nitrogen (or hydrogen) is simple and fast and requires just closing the helium valve and opening the nitrogen valve.
3. The same column used with helium can be used with nitrogen or hydrogen.
4. The same elution times could be obtained with nitrogen or hydrogen as with helium.
5. The GC separation with nitrogen was reduced compared with helium and peak widths were increased by an average factor of 1.5 for similar elution times. Hydrogen provided ~0.7 narrower peak widths than helium.
6. The signal with nitrogen was reduced compared with helium by an average factor of 3.3 and the signal loss was reduced with higher compounds mass. With hydrogen the signal loss was about a factor of 1.5 but the baseline noise was higher thus with similar S/N as with nitrogen.
7. USEPA 8270 semivolatile mixture was easily analyzed with both nitrogen and hydrogen carrier gases.

     

From ketones, aldehydes or alkyl halides to terminal 1,1-difluoroolefins using BrF3

Terminal difluoromethylenes were prepared by two different routes: (a) by treating ketones and aldehydes with bis(methylthio)methane, producing 2-alkyl-1,1-bis(methylthio)alkene (2) (b) reacting alkyl halides with tris(methylthio)methane forming 1-alkyl-1,1,1-tris(methylthio)alkane derivatives (7). The reaction of either 2 or 7 with BrF₃, followed by oxidation with HOF·CH₃CN gave the difluorosulfonyl derivatives 4. Consecutive treatment with Zn led to the target difluoroolefins (5) in overall yields of 60-75%.     

Benzannelated [9] and [13] annulenes: Formation,structural properties and the effect of benzannelation on the aromaticity of the (4n+2) π anionic sy

The synthesis of benzannelated [9] and [13] annulenenes is described, 1,2:3,4-dibenzocyclononatetraene 3 and its diphenyl derivative 10 show upon deprotonation the initial formation of a non-planar partially delocalized anions 4 and 11 respectively, which undergo into the planar aromatic-diatropic dibenzocyclononatetraenyl anions 4a and 12. The immediate formation of the aromatic 1,2:5,6 - dibenzocyclononatetraenyl anion 14 upon deprotonation of 1,2:5,6 - dibenzocyclononatetraene 13 precludes peri H-H repulsions in the aromaticity development of the dibenzocyclononatetraenyl anions. The deprotonation of tetrabenzo[13]annulene 15 afforded anion 17, which shows reduced diatropic character as compared with non-benzannelated[13] annulenyl anion. The spatial arrangement of 17 is discussed.     

The dynamics of equally spaced multilevel model systems

Coherent dynamics of multilevel systems is of interest for the elucidation of energy disposal and multiphoton chemistry of polyatomic molecules. We compare the analytical solutions for coherent multiphoton excitation of two sparse multilevel model systems: (1) The spin-J system consisting of N = (2J + 1) equally spaced levels with the radiative coupling being determined by the xth component of the angular momentum. (2) The equally coupled N level system. The transition amplitudes for system (1) are always periodic, which is in contrast to the nonperiodic behavior exhibited by system (2) for N > 3.     

Switch peptide via Staudinger reaction

A new transformation based on the Staudinger reaction is described, and its application in the design of a novel switch element to control peptide folding is demonstrated. We found that the azide switch is activated rapidly in water to promote acyl transfer using tris(2-carboxyethyl)phosphine hydrochloride (TCEP) via the Staudinger reaction. Our findings expand the repertoire of uses of the Staudinger reaction in chemical biology and the number of available triggers for use in switch peptides.     

Fast Heroin and Cocaine Analysis by GC–MS with Cold EI: The Important Role of Flow Programming

A fast GC–MS method was developed based on the use of GC–MS with Cold EI. This new method was applied for the analysis of the street drugs heroin and cocaine and it enabled 2 min chromatography time and 3 min full analysis cycle time. GC–MS with cold EI provides mass spectra with enhanced molecular ions that are library compatible (with increased identification probabilities) and allows the use of short, 5 m 0.25 mm ID columns, which facilitates fast GC–MS. A central ingredient of our unique cold EI-based fast GC–MS analysis method is the use of column flow programming from 1 up to 32 ml min^?1 column flow rate. Column flow programming can reduce the analysis time by about a factor of two and unlike temperature programs of GC ovens the carrier gas flow rate can be raised and lowered very quickly (in a few seconds). The fast GC–MS with Cold EI method is demonstrated by the analysis of heroin in its street drug powder and cocaine on paper money and it can be applied for other drugs of abuse as a general fast drugs analysis method.