FLOW SYSTEM BASED ON A BINARY SAMPLING PROCESS FOR AUTOMATIC DILUTIONS PRIOR TO FLAME ATOMIC SPECTROMETRY

A microcomputer-controlled flow system to perform automatic dilutions exploiting a binary sampling process is proposed. Introduction of prec ise volumes of sample and solvent was achieved by solenoid valves. The possibility to get different volumetric fractions was realized by sof tware, which defined the time delays of the valves and could be used, e.g., for samples with analyte concentrations exceeding the analytical range. A noteworthy feature is that sample and standards processing i s not necessarily the same. The analytical performance was exhaustivel y investigated, in particular the precision of standard measurements g enerated after application of different dilutions, or repeatability of results of 20 and 40 times diluted real sample solutions. The feasibi lity of the approach was demonstrated by the on-line automatic dilutio n of plant digests for determining Ca and K by flame atomic absorption and emission spectrometry, Precision of measurements performed on a s olution produced by the automatic 10-fold dilution of a 100 mg/l solut ion was characterized by a R.S.D. < 1%, Accuracy was assessed by analy sing vegetal reference materials after diluting 10 or 20 times, Result s were in agreement at 95% significance level with the certified value s. Comparison of automatic and manual dilutions by using a paired t-te st on a set of samples with varying composition presented no statistic al difference at the 95% significance level.