Extraction region, correction

Several strategies were employed in order to reduce this effect. Myers et al. described the use of a pulsed ion optic to limit the access of ions to the extraction region [28]. By application of a voltage pulse to one of the quadrupole optics, the ion beam was swept across the slit at the end of the primary optic chain. By correct choice of delay parameters, the extraction region was filled with ions only immediately prior to a repeller event. Mahoney et al. described a different approach that relied on differences in the energies of signal and continuum background ion populations [42]. 

Figure 2.21 Schematic diagram of the orthogonal acceleration ICP-TOF-MS system. RP, repeller plate ER, extraction region AR, acceleration region EG, extraction grid d, extraction region width v, beam velocity FE, flight tube entrance grid (size relations not correct)...

Petroleum pollution monitoring laboratories in the Mediterranean region participated (1984-1986) in two intercalibration exercises (MEDCALI and II) to evaluate the International Oceanographic Commission (IOC) Manual for petroleum hydrocarbon determination in sediment (IOC, Manuals and Guides, No. 11). The main source of error in the analysis was the extraction/ partition step. When the results were corrected for recoveries, relative standard deviations for w-alkancs, UCM (unresolved complex mixture) and total aromatics, which had previously been 60, 56 and 49%, respectively, were reduced to 17, 30 and 6%, respectively. 

There are many different types of soil, and extractant formulations have been fine-tuned to suit the soil. The particular extractant may also be chosen on the basis of familiarity over the years, and because it is easier to compare results with those previously obtained, and hence make recommendations to correct deficiencies based on experience. Usually one is not interested in the total amount of a soil nutrient, rather in the amount that is in a form available to the roots of the plant. Regional advisory laboratories over a long period may have developed index tables relating to the found concentration of nutrient in local soil types and the corrective amount of fertilizer required. It would probably be wise to adopt the same methods that have been used to... 

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