Capillary Gas Chromatography Coupled with Microplasma Mass Spectrometry – Improved Ion Source Design Compatible with Bench-Top Mass Spectrometric Instrumentation

Capillary gas chromatography was performed with mass spectrometric detection using a novel microplasma ion source for operation in an element-selective mode. The ion source was a 350 kHz radio frequency helium plasma, which was sustained inside the 4 cm end of a 0.32 mm i.d. fused silica capillary column, and located inside the high vacuum chamber of the quadrupole mass spectrometer. Due to the low volume of the ion source, a stable low pressure discharge was produced utilizing only the 2.25 mL min⁻¹ of GC carrier gas (helium) for plasma support. Small amounts of oxygen (0.1–0.2% v/v) were added to the plasma gas in order to prevent carbon deposits and to enhance signal-to-noise ratios. Chlorine and bromine were selectively detected at the 5–20 pg s⁻¹ level (S/N = 2), and both produced a response that was linear within 3 orders of magnitude.     

Simultaneous Element-Selective Detection of C,F, Cl,Br, and I by Capillary Gas Chromatography Coupled with Microplasma Mass Spectrometry

Simultaneous element-selective detection of the halogens and carbon was accomplished with capillary gas chromatography coupled with microplasma mass spectrometry. The microplasma ion source was a radio frequency plasma contained inside the last 4–5 cm of the 0.32 mm i.d. fused silica capillary column. The ion source was located inside the high vacuum housing of the MS, and only the GC carrier gas (2.3 mL min⁻¹ of helium) was used for plasma generation. Atomic ions were detected in the positive mode. Detection limits were in the low picogram area, and the selectivity to carbon ranged from 8×10² for fluorine to higher than 10⁴ for the other halogens. By introduction of both hydrogen and oxygen as reagent gases, peak tailing was avoided by suppression of analyte reactions with the silica walls of the ion source. Special attention was given to the fluorine-selective detection due to an interfering background species at m/z 19, assumed to be H₃O⁺ originating from the reagent gases. The background signal was minimized by careful control of the power level.     

On Schrödinger operators with multipolar inverse-square potentials

Positivity, essential self-adjointness, and spectral properties of a class of Schrödinger operators with multipolar inverse-square potentials are discussed. In particular a necessary and sufficient condition on the masses of singularities for the existence of at least a configuration of poles ensuring the positivity of the associated quadratic form is established.     

Patavine, a new arylnaphthalene lignan glycoside from shoot cultures of Haplophyllum patavinum

A new arylnaphthalene lignan glycoside, patavine (1), together with five known lignans, justicidin B (2), diphyllin (3), tuberculatin (4), majidine (5), and arabelline (6) were isolated from shoot cultures of Haplophyllum patavinum. The structure of the new compound was elucidated by extensive one-dimensional (1D) and two-dimensional (2D) NMR experiments and mass spectrometry. The cytotoxicity of compounds 1, and 3-6 against LoVo human colon carcinoma cells was investigated.     

Nonaqueous electrochromatography on continuous bed columns of sol–gel bonded large-pore C18 material: separation of retinyl esters

A nonaqueous electrochromatographic reversed-phase separation method for retinyl esters using continuous bed columns has been developed. The packing material 7 μm Nucleosil 4000 Å C₁₈ was sol–gel bonded in 180 μm I.D. capillaries. The mobile phase used was 2.5 mM lithium acetate in N,N-dimethylformamide–acetonitrile–methanol (2+7+1, v/v). At 350 V/cm and 30°C, this mobile phase composition gave rise to an electroosmotic flow of 1 mm/s. No Joule heating nor bubble formation were observed even at 625 V/cm (17 μA). With a 36 cm L_eff column complete separation of the commercially available and synthesized standards (all-trans-retinyl acetate, palmitate, heptadecanoate, stearate, oleoate, and linoleoate) was obtained within 10 min. The within-day and between-day variations of retention times of all-trans-retinyl palmitate were <0.3% relative standard deviation (RSD) (n=3) and <2% RSD (n=6), respectively. The within-day and between-day variations of peak areas were both <2% (both n=3). The columns were used for more than 1 month without degradation. Liver extracts from arctic seal were analyzed.