Studying Influences and Optimizing Analytical Procedures

According to Sect. 3.5 the influencing of an analytical signal by the environment of the experiment (influence factors), i.e. interferences and other stimuli can be estimated either in a way basing on chemical facts (Eq. 3.16a) or in a statistical way (Eq. 3.16b,c). Therefore, two ways are feasible to study the significance of influences as a requirement of a subsequent optimization. 

---

PFE procedures for the soil were carried out in an Accelerated Solvent Extractor (ASE, Dionex Corporation, Salt Lake City, Utah). The extraction method was optimized by varying extraction temperature and number of extraction cycles. The extraction solvent was acetonitrilermethanol (1 1, v v) and the pressure was kept constant at 1500 psi, which in previous studies pressure did not show a big influence on the extraction efficiency (13), The soil used for optimization was of the Helemano series (14), spiked in the laboratory by the organic solvent slurry method (15) at approximately 3 pg/g for each of the analytes. After extraction, the sanq)les were filtered through sodium sulfate and 0.2 pm nylon filter and concentrated with a gentle flow of nitrogen gas before GC-MS analysis. 

---