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Continuous electrophoretic ion focusing is applied to the concentration and separation of extremely small quantities of tetraand pentavalent neptunium and of tri-and tetravalent plutonium. Two types of electrolyte systems are used: A three-zone system in which the analyte is introduced into the central zone with solutions of complexing agents flowing on both sides, and a system with a conductivity-and pH-gradient arranged in twelve steps with the analyte added to one of these solutions. With tartaric, glycolic and citric acid as complexing agents the different oxidation states are focused into narrow and well separated fractions.

Actinides, detection of trace amounts /Laser resonance ionization mass spectrometry /Isotope analysis of plutonium AbstractLaser resonance ionization mass spectrometry has been investigated as a method for the detection of trace amounts of actinides. High sensitivity and selectivity can be achieved by three-step photoionization followed by time-of-flight mass analysis. The laser system for photoionization consists of three dye lasers which are pumped simultaneously by a copper vapor laser. For mass determination a time-of-flight spectrometer with a mass resolution of about 1500 is used. By ionization via autoionizing states an overall efficiency of 4 X 10"' was determined for 23 ®Pu yielding a detection limit of less than 10 7 atoms. Isotope ratio measurements have been performed with synthetic plutonium samples.

Resonance ionization mass spectrometry (RIMS) is a very sensitiveanalytical technique for the detection of trace elements. This method is based on the excitation and ionization of atoms with resonant laser light followed by mass analysis. It allows element and, in some cases, isotope selective ionization and is applicable to most of the elements of the periodic table. A high selectivity can be achieved by applying three step photoionization of the elements under investigation and an additional mass separation for an unambiguous isotope assignment.An effective facility for resonance ionization mass spectrometry consists of three dye lasers which are pumped by two copper vapor lasers and of a linear time-of-flight spectrometer with a resolution better than 2500. Each copper vapor laser has a pulse repetition rate of 6.5 kHz and an average output power of 30 W.With such an apparatus measurements with lanthanide-, actinide-, and technetium-samples have been performed. By saturating the excitation steps and by using autoionizing states for the ionization step a detection efficiency of 4 x 10 -6 and 2.5 x 10 -6 has been reached for plutonium and technetium, respectively, leading to a detection limit of less than 107 atoms in the sample. Measurements of isotope ratios of plutonium samples were in good agreement with mass-spectrometric data. The high elemental selectivity of the resonance ionization spectrometry could be demonstrated.

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