Dynamic double collector measurement with cup efficiency factor determination

Static multicollector isotope ratio measurements are only possible if the cup efficiency factors (CEFs) are precisely known for all cups. Otherwise, one has to apply the dynamic double collector method which cancels out the CEFs as well as the isotope fractionation. This work presents such a dynamic method, which makes use of the fact that nearly all masses are measured by three different cups each scan, and the CEFs are determined by a standard bilinear interpolation method. After the end of a run the CEFs, which turned out to differ up to more than one permil, have been determined more than a hundred times, are averaged, and the three statically measured isotope ratios are corrected for CEFs. They agree within the limits of error with the two dynamically obtained ratios. The average of the five ratios increases the precision of the result. The CEF-calibration represents a byproduct, obtained during the standard measuring routine which requires no additional measurements, and it is demonstrated for Sr measurements but may be applied for high precision Nd or Pb measurements as well.