Supersonic gas chromatography/mass spectrometry.
Journal - Rapid communications in mass spectrometry : RCM (England )
A new gas chromatography/mass spectrometry (GC/MS) system was designed and evaluated which we have named 'Supersonic GC/MS'. It is based on a modification of a commercially available GC/MS system to include a supersonic molecular beam (SMB) MS interface. In this system the standard electron ionization (EI) ion source was replaced with a fly-through EI ion source mounted in the path of the SMB. A hyperthermal surface ionization (HSI) ion source combined with a 90 degrees ion mirror (for the EI-produced ions) was also added, and placed inside the quadrupole mass analyzer in place of its original EI ion source. The 'Supersonic GC/MS' system requires 18 cm added bench space plus the addition of an air-cooled 60 L/s diffusion pump and a 537 L/min rotary pump. The system is user friendly since all the gas flow rates, heated zones, sampling and data analysis are performed the same way as the original system and are computer-controlled via the original software. Similar EI sensitivity was obtained as with the original system for hexachlorobenzene and octafluoronaphthalene, while improved EI detection limits were demonstrated for methyl stearate and eicosane due to the significant enhancement of their molecular ion abundances. A GC/MS detection limit of 500 ag for pyrene was demonstrated using HSI. Good supersonic expansion cooling was achieved with large alkanes, despite the use of a rotary pump at the nozzle chamber instead of a diffusion pump. High temperature GC/MS analysis was demonstrated for large polycyclic aromatic hydrocarbons (PAHs) including ovalene and decacyclene (ten rings). Library searches with EI mass spectra are demonstrated, and it is explained why the enhancement of the molecular ion actually improves the library search in most cases. The analysis of large phthalate esters is also described, and the improvement obtained is shown to originate from their enhanced molecular and high mass fragment ions.Copyright 2001 John Wiley & Sons, Ltd.
|ISSN : ||0951-4198|
|Mesh Heading : ||Environmental Pollutants Equipment Design Gas Chromatography-Mass Spectrometry Pesticides Phthalic Acids Polycyclic Hydrocarbons, Aromatic Sensitivity and Specificity Temperature Vibration instrumentation|
|Mesh Heading Relevant : ||analysis methods analysis chemistry chemistry|
Simultaneous pulsed flame photometric and mass spectrometric detection for enhanced pesticide analysis capabilities.
Journal - Journal of chromatography. A (NETHERLANDS )
Analysis of pesticides by simultaneous pulsed flame photometric detection (PFPD) and mass spectrometric (MS) detection was performed with column-effluent splitting between these two detectors. The resulting PFPD chromatograms were always much simpler due to the PFPD selectively and were further characterized by better sensitivity than that of MS. Accordingly, the PFPD chromatogram served as a marker for the exact elution time of the suspected pesticide. At this exact elution time, the resulting mass spectra were examined of unique high-mass peaks and a precise background subtraction was performed for improved library identification. If no definite identification was achieved, reconstructed mass chromatograms were performed, inspected for suspected major ions and confirmed with the PFPD chromatogram. A sequential search was then performed with the NIST library. The presence of P or S atoms was introduced into the search algorithm and two of the major suspected fragment mass peaks were included with an estimate of their minimum relative abundance. Under these conditions, the library search provided the correct pesticide identification, at a considerably lower concentration than achievable with standard GC-MC analysis. If only information on a single ion was available, such as with very pronounced matrix interferences, or with single-ion monitoring MS analysis, the NIST library sequential search was operated with this single-on information and PFPD provided information on both P and S (the majority of organophosphorus pesticides contain both P and S). The incorporation of one major ion and two heteroatoms' (P and S) information enabled an effective library identification, at an even further reduced pesticide concentration. The simultaneous PFPD-MS analysis approach is demonstrated and discussed with several examples of authentic pesticides in vegetable and spices. The merits of this method are analyzed and discussed with an emphasis on the unique suitability of PFPD for combination with MS.
|ISSN : ||0021-9673|
|Mesh Heading : ||Chromatography, Gas Gas Chromatography-Mass Spectrometry Mass Spectrometry Pesticide Residues Pesticides Photometry Spices Vegetables analysis analysis chemistry|
|Mesh Heading Relevant : ||analysis|