An electron monochromator mass spectrometer was used to study the resonant electron energies versus negative ion masses of the organophosphate insecticides dicapthion, EPN, ethion, fenitrothion, leptophos, leptophosoxon, paraoxon, and parathion. Each compound yielded a unique two-dimensional electron energy/mass spectrum. The most abundant ions are produced with electrons of energies between 0.03 and 1 eV, but ions result also from capture of electrons with energies ranging to 8.5 eV. Both resonance electron capture ions and dissociative electron capture ions are produced with electrons of energies ranging from 0.03 to 8.5 eV, and ions may have as many as three observable resonance states from which they are formed. Substituted thiophenoxide ions are postulated to arise by rearrangement of the parent thiophosphate ions through a spiro intermediate. Most fragment ions can be rationalized as arising through simple homolytic cleavage of the parent radical anions.
The effect of different buffer gases on the intensity of negative ions was studied using a gas chromatography/electron monochromator mass spectrometer (GC/EM-MS). The buffer gas was introduced into the ion source not to moderate the electron energies, but specifically to investigate the process of collisional stabilization of negative ions. Three different designs of ion source were tested to study this phenomenon. It was found that collisional stabilization has a profound effect on the intensity of molecular radical anions and begins to play an important role at buffer gas pressures in the order of 10 mTorr. By using a partitioned ion-forming chamber, it was shown that for optimum stabilization to take place the buffer gas should be present in the region of negative ion formation. The gases possessing internal degrees of freedom which are capable of accommodating the excess energy of short-lived excited molecular anion states showed the largest increase in molecular radical anion intensities. At the same time helium, a widely used GC carrier gas, showed sufficient stabilization properties to allow detection of the molecular radical anions of typical electron-capturing molecules with positive electron affinities.
Accelerated corrosion leading to system failure has been observed on printed circuit boards present in industrial environments that contain abnormal levels of reduced sulfur gasses, such as hydrogen sulfide (H2S) and elemental sulfur. The problem is compounded by the fact that elemental sulfur is regulated by OSHA as a nuisance dust, and is allowed in a human working environment at the parts per thousand levels. Anecdotal data shows clearly that elemental sulfur gas present at the parts per million level can cause computer systems to fail within 2 months of use. Newer technologies such as immersion silver plating are especially susceptible to this type of corrosion. With the rapid growth of organically coated copper (OCC) and immersion silver platings, the number of failures due to reduced sulfur gasses in the environment has risen substantially.
The Directive 2002/95/EC (referred as ROHS) of the European Parliament and of the Council restricts the use of certain hazardous substances in electrical and electronic equipment. This article reports on a fast and inexpensive methodology for rapidly screening entire electronic assemblies that acts as a high-level screen for obvious ROHS violations. Using this methodology, this lab has been able to check entire product lines for basic ROHS compliance and has identified many cases where vendors needed to be informed of ROHS violations before a product could be certified as ROHS compliant. Four tests are employed. Each of them is described, along with the basic theory behind the test: pre-screening with x-ray fluorescence spectroscopy and electron dispersion spectroscopy; detection and identification of polybrominated biphenyl ethers using gas chromatography - mass spectrometry; and chromium 6 colorimetric testing based on diphenylcarbazide.
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