Below detection, limit tailing

In 2004, the pH of pore water in the reduced tailings was 4.4 at <10 cm depth, increasing to 7 by 30 cm. Dissolved constituents follow pH, with concentrations of 36,000 ppm S042", 18,000 ppm Fe, and 9,600 ppm Zn at <10 cm depth. These concentrations decrease steadily with depth. Below 30 cm, most metals drop to below detection limits. 

Concentration levels of Mo and Se in the tailings were below the detection limit ( 100 ppm) of the instrument. 

Figure 4 shows calibration curves measured as the peak absorbance at 235 nm. This shows good linearity and high sensitivity for all substances. The detection limit is well below 10 ng for all substances and thus competes favourably with flame ionization detector - GC. The retention times were also measured at all concentrations since it was suspected, due to the apparent tailing, that the chromatography might be non-linear. This did not prove to be so. 

The mobile phases consisting of acetonitrile/methanol [16] or acetoni-trile/methanol/water [18] in different ratios with a few drops of ammonia solution were found to discriminate between two enantiomers of these three -blockers in one-dimensional (ID) ascending development mode. The mobile phase composition and values of chiral separation factor a are listed in Table 11.3. The zones of separated antipodes were detected using iodine vapor and the detection limit of both alprenolol and propranolol racemates was 2.6 ng, while that of metoprolol was 0.26 /rg [16]. The effects of temperature on the separation of these three jS-blockers were also investigated [16]. It was observed that no resolution of atenolol racemate was achieved at the temperatures higher than 15" C, as well as below 8°C. The best resolution of propranolol and metoprolol racemates was achieved at 22°C. Increase of the temperature above 22°C led to the tailing, while a decrease up to 6°C had little or no effect on the quality of resolution. 

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