Background impurities

Cq ), where is the blended impurity concentration of impurity a Cq, the background impurity level and the multiplication constant. Possible sources of background response include instmment noise, sample system outgassing, or interference from other impurity response signals. Proper setup, purging, and operation of the instmment should reduce background levels weU below ippb. 

MS sensitivity depends on both the type of instrumentation and the nature of the analytes, but, typically, a minimum sample size of 5-10 ng is in most cases sufficient. Limited sensitivity in a certain application is often not due to the inherent sensitivity of the MS but rather the level of background impurities that are in the isolate. It is not always appreciated that very slowly eluting LC solutes from previous separations can create substantial MS background peaks that obscure analyte identification. Thus, it is important to use a blank sample to ensure that the background of the trapped fraction is adequately free of possible interferences to the desired identification. 

FIG. 3.33. (a) Comparison of the FDTO model (solid lines) with the experimental (symbols) of Crone et al. [59] for a Ca/MEH-PPV/Ca electron only device, (b) Comparison of the FDTO model (dashed line) and FDTO with background impurity model (solid curve) with the experimental data for A1/MEH-OPV5/ITO (curve 1) and for A1/MEH-OPV5/PEDOT/ITO (curve 2). The thickness of both samples is 110 nm. 

The system has been characterized with respect to background impurities in the chamber air and in the collected cloud water (Table I). Ammonia is a significant impurity. In the absence of intentionally added reagents, it balances the major anions in the cloud water which are carbonate and formate. The anion/cation balance of background (i.e., blank) cloud water is typically within 10% of unity. 

The most common background impurities in the SiC crystals grown by sublimation are nitrogen, boron and aluminium. These impurities are also the principal dopants employed in SiC device fabrication. Their behaviour and properties have been studied in a number of papers. 

Glaeser AM, Bowen HK, Cannon RM (1986) Background impurity effects on grainboundary migration in LiF. Mater Sci Eng 79 111—117... 

It is possible to operate the analyzer to ignore these common background impurities. They will be present to contribute to poor vacuum if these impurities result from a... 

Gerardi G, MileUa E, Gampanella F and Bernadi S (1996) SIMS-ETAAS characterization of background impurities in CdZnTe bulk samples. Material Science Forum 203 273 278. 

---