The gaseous hydrides were directed towards the center <strong>of</strong> the bent part <strong>of</strong> the molybdenum foil via a wide bore quartz GC–capillary. See Ref. [5] for more details. RESULTS The <strong>in</strong>fluence <strong>of</strong> the molybdenum foil temperature and concentration <strong>of</strong> hydrogen <strong>in</strong> the gaseous phase on trapp<strong>in</strong>g behavior <strong>of</strong> bismuth and antimony were <strong>in</strong>vestigated for a bare molybdenum surface and argon-hydrogen atmosphere <strong>of</strong> the flame support<strong>in</strong>g gas mixture. Maximum trapp<strong>in</strong>g efficiencies were found for antimony and bismuth <strong>in</strong> the temperature ranges <strong>of</strong> 650-750 °C and 500-600 °C, respectively. These optimum temperatures are approximately 300-500 °C lower than those found for arsenic and selenium (1100-1200°C). Capability <strong>of</strong> trapp<strong>in</strong>g antimony and bismuth hydrides on a modified surface <strong>of</strong> the molybdenum trap was also <strong>in</strong>vestigated. Rhodium, plat<strong>in</strong>um and iridium were chosen as permanent modifiers and were <strong>in</strong>troduced stepwise on the surface <strong>in</strong> amounts <strong>of</strong> 10, 30, 100 and 200 μg. Significant depletion <strong>of</strong> signals <strong>of</strong> collected antimony and bismuth was observed when the amount <strong>of</strong> any modifier used exceeded 30 μg. Evidently, all modifiers <strong>in</strong>hibit the <strong>in</strong>teraction <strong>of</strong> both analytes with active sites on the molybdenum surface. In contrary, these modifiers do not significantly affect trapp<strong>in</strong>g <strong>of</strong> arsenic and selenium on the molybdenum surface. The maximum trapp<strong>in</strong>g efficiency <strong>of</strong> arsenic and selenium was <strong>in</strong>dependent <strong>of</strong> the modifier amount applied <strong>in</strong> the range from 0 to 200 μg. Their signal pr<strong>of</strong>iles were higher, more reproducible and symmetrical when <strong>in</strong>creas<strong>in</strong>g modifier amount. The overall efficiency <strong>of</strong> generation <strong>of</strong> hydrides and their transport <strong>in</strong>to the trapp<strong>in</strong>g chamber is <strong>in</strong>dependent on the <strong>in</strong>jection gas flow rate between the m<strong>in</strong>imum and the maximum achievable rates <strong>of</strong> 40 ml m<strong>in</strong> -1 and 260 ml m<strong>in</strong> -1 , respectively. Maximum trapp<strong>in</strong>g efficiency was reached at a flow rate close to 70 ml m<strong>in</strong> -1 , and at a distance <strong>of</strong> 2 mm between the tip <strong>of</strong> the <strong>in</strong>troduction capillary and the foil surface. Obviously, aerodynamic conditions prevail<strong>in</strong>g near the capillary orifice and the molybdenum foil dur<strong>in</strong>g the trapp<strong>in</strong>g step play the same role <strong>in</strong> trapp<strong>in</strong>g <strong>of</strong> all analytes studied. Vaporization experiments showed that antimony, arsenic and selenium are strongly bonded to the molybdenum surface. Collected antimony is completely released at temperatures above 2200 °C and arsenic and selenium at temperatures above 2400 °C. To the contrary, bismuth exhibits a different behavior. A relative low temperature <strong>of</strong> 1200 °C is sufficient for complete vaporization <strong>of</strong> trapped Bi. The heat<strong>in</strong>g vaporization pulse should be very short to prevent losses <strong>of</strong> analyte on the <strong>in</strong>ner quartz wall <strong>of</strong> the trap chamber and to perform an efficient transport <strong>of</strong> the analyte <strong>in</strong>to the diffusion flame. In the present experimental arrangement, the optimum heat<strong>in</strong>g pulse <strong>in</strong> duration <strong>of</strong> 0.4 s was found. ACKNOWLEDGEMENT This work was supported by The Grant Agency <strong>of</strong> the Czech Republic (Project No. 203/06/1441) and by M<strong>in</strong>istry <strong>of</strong> Education, Youth and Sports <strong>of</strong> the CZ (FRVS 1054/2006). REFERENCES [1] J. Ded<strong>in</strong>a, D. L. Tsalev: Hydride Generation Atomic Absorption Spectrometry, Wiley & Sons, Inc., Chichester (1995). [2] H. Matusiewicz and R. E. Sturgeon, Spectrochim. Acta, Part B, 51 (1996) 377-397. [3] F. Barbosa Jr., S. Simiao de Souza, F.J. Krug, J. Anal. At. Spectrom., 17 (2002) 382-388. Sborník soutěže Studentské tvůrčí č<strong>in</strong>nosti Student 2006 a doktorské soutěže O cenu děkana 2005 a 2006 Sekce DSP 2006, strana 208
[4] H. Matusiewicz, M. Kopras, J. Anal. At. Spectrom., 18 (2003) 1415-1425. [5] P. Krejci, B. Docekal, Z. Hrusovska, Spectrochim. Acta, Part B, 61 (2006) 444-449. Sborník soutěže Studentské tvůrčí č<strong>in</strong>nosti Student 2006 a doktorské soutěže O cenu děkana 2005 a 2006 Sekce DSP 2006, strana 209