Search on ruggedness of fast gas chromatography-mass spectrometry in pesticide residues analysis

In this study, suitability of fast gas chromatography-mass spectrometry (GC-MS) on a narrow-bore column with a programmed temperature vaporizer for the analysis of pesticide residues in non-fatty food was evaluated. The main objectives were ruggedness and stability of chromatographic system with regards to co-extractives injected. The chromatographic matrix induced response enhancement was found to be strongly dependent on the concentration of residues and is reaching up to 700% compared to the pesticides solutions in a neat solvent. However, the responses of pesticides in matrix-matched standards at different concentration levels do not significantly change during 130 injections. Response enhancement/or decrease is influenced by the sample preparation technique. External calibration with matrix-matched calibration standards should, therefore, provide results with good precision also at the concentration level of 0.005 mg kg(-1). Special attention is given to the performance of the chromatographic column and retention gap with regards to peak widths, peak tailing and different sample preparation methods. During approximately 460 matrix sample injections, the performance of the analytical column was acceptable. GC-MS set-up with 0.15 mm i.d. column can be successfully utilized for the pesticide residues analysis.     

Reproducibility of retention indices measurement of alkylbenzenes on crosslinked methyl silicone phase fused silica capillaries

Summary Reproducibility of the Kovats retention indices of alkylbenzenes was studied on conventional “PONA” fused-silica capillary columns coated with crosslinked dimethyl silicone phase, with a film thickness of 0.5 μm. The data were compared with those obtained on conventional OV-101 columns. The tested PONA columns showed reproducible chromatographic properties, capacity ratios and high efficiencies. Having a standard deviation of s=0.03 i.u. of the retention indices on a single column, the column-to-columns differences were found to be up to 0.3 i.u. Higher indices were determined for crosslinked columns, the difference being in most cases about one i.u.     

Practical aspects of splitless injection of semivolatile compounds in fast gas chromatography

Possibilities and practical aspects of implementation of splitless injection of larger volumes for fast GC purposes utilizing narrow-bore column, hydrogen as carrier gas, fast temperature programming under programmed flow conditions and commercial instrumentation were searched. As a model sample semivolatile compounds of a broad range of volatility and polarity (7 n-alkanes and 19 pesticides) were chosen. Peak shapes, peak broadening and peak areas and its repeatability were evaluated under various experimental set-ups (liner/injection technique combinations). Various factors, such as liner design, injection technique, retention gap length, compound volatility and polarity, the solvent used, initial oven temperature influenced compound focusation and/or maximal injection volume. Combination of analytical column (CP-Sil 13 CB 25 m long, 0.15 mm i.d., film thickness 0.4 microm) with normal-bore retention gap (1 m long, 0.32 mm i.d.) allowed maximal injection volume 8 microl for 4 mm i.d. liner used without any peak distortion when solvent recondensation in the retention gap was employed.     

Thermo-oxidation of polypropylene in the presence of triphenylphosphonium cyclopentadienylide

From measurements of weight losses of samples of isotactic polypropylene (IPP) with triphenylphosphonium cyclopentadienylide (TPCP) under various conditions and from the measurements of time courses of chemiluminescence, kinetic parameters of the process were determined. At concentrations of TPCP >1 wt%, the rate of loss of weight changes with the additive concentration. Compensation of the values of activation energy and pre-exponential term, determined from thermo-oxidation of IPP alone and IPP with TPCP, indicates that interaction of TPCP with oxidized polymer is complex.     

Screw-type transparency in a three-level medium

A solution is obtained for the system of Maxwell-Schrödinger equations describing the propagation of a laser pulse through a three-level Λ medium in which the initial atomic populations are in a specially prepared coherent superposition of low-energy states. This solution describes a new type of transparency which is characterized by the presence of conversion of the frequency of the incident pulse and can be used, specifically, to produce “optical keys” and frequency converters for laser radiation.     

Coherent population trapping in an ensemble of three-level atoms in the presence of cooperative relaxation

We derive equations that describe the dynamics of three-level atoms with a cascade system of levels interacting with two resonant coherent fields in conditions where cooperative relaxation dominates over incoherent spontaneous emission. We calculate the temporal dynamics of the values of the atomic populations. The possibility of coherent population trapping in the presence of the cooperative decay is established. Finally, we calculate the averaged population of the intermediate level as a function of detuning for different values of the coupling constant. Zh. éksp. Teor. Fiz. 112, 869–876 (September 1997)     

Nonlinear magnetic phenomena in atomic bose gas

Optically confined (j=1, j=2)-Bose gas is studied. The spin Hamiltonian and the ground state of a set of particles with spins j=1 and j=2 are obtained. Nonlinear magnetic phenomena in the set of particles with j=1 are considered.     

Oscillating course of thermooxidation of polypropylene under conditions of cool flame

Secondary multiple cool flame appearing under certain conditions during thermooxidation of polypropylene was interpreted on the basis of oxidation of the polymer surface being influenced by changes in the direction of the temperature gradient. The average period of the oscillation process, directly proportional to the amplitude of the first oscillation, expresses the effect on the oscillation process of all important factors such as the oxygen concentration, rate of delivery of volatile oxidation products and temperature of a cool flame in the gas phase.     

Possibilities and limitations of fast GC with narrow-bore columns

In this work, two narrow-bore capillary columns with different internal diameters (I.D.) 0.15 mm (15 m length, 0.15 microm film thickness) and 0.10 mm (10 m length, 0.10 microm film thickness) with the same stationary phase (5% diphenyl 95% dimethylsiloxane), phase ratio and separation power were compared with regard to their advantages, practical limitations and applicability in fast GC on commercially available instrumentation. The column comparison concerns fast GC method development, speed and separation efficiency, the sample transfer into the column utilizing split and splitless inlet, sample capacity, detection (analysing compounds of a wide range of polarities and volatilities--even n-alkanes C16-C28 and selected pesticides) and ruggedness (in the field of ultratrace analysis of pesticide residues in real matrix). Under conditions corresponding to speed/separation efficiency trade-off 0.10 mm I.D. versus 0.15 mm I.D. column provides a speed gain of 1.74, but all other parameters investigated were better for the 0.15 mm I.D. column concerning more efficient sample transfer from inlet to the column using splitless injection, no discrimination with split injection. Better sample capacity (three times higher for the 0.15 mm than for the 0.10 mm I.D. column) resulted in improved ruggedness and simpler fast GC-MS method development.