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MINIATURE METALLIC DEVICE FOR COLLECTION OF HYDRIDE FORMING ELEMENTS Pavel Krejčí 1,2 Bohumil Dočekal 2 1 Department of Environmental Chemistry and Technology, Faculty of Chemistry, Brno University of Technology, Purkyňova 118, CZ-61200 Brno, Czech Republic, e-mail:krejci-p@fch.vutbr.cz 2 Institute of Analytical Chemistry, Czech Academy of Sciences, Veveří 97, CZ-60200 Brno, Czech Republic, e-mail: docekal@iach.cz INTRODUCTION Collection of hydride forming elements (As, Bi, Ge, In, Pb, Sb, Se, Sn and Te) has become a simple and useful tool for pre-concentration and separation purposes in the trace and ultratrace analysis by atomic spectrometric methods [1,2]. It is typically performed "in situ" using conventional graphite (GF) or tungsten (WETA) heated atomizers with subsequent analyte detection by electrothermal atomic absorption spectrometry (ETAAS) method [1]. Nevertheless, the trapping technique can also be applied in other spectrometry methods (atomic emission spectrometry, atomic fluorescence spectrometry and mass spectrometry). For this purpose, conventional electrothermal atomizers are modified and/or special, mostly laboratory made devices are designed [2-5]. Capability of trapping of hydrides on a prototype of a miniature electrothermal vaporization (ETV) device was studied employing antimony, arsenic, bismuth and selenium hydrides as volatile species of analytes. This device is based on a strip of the molybdenum foil (which is typically used in production of "halogen" bulbs) and combined with miniature hydrogen diffusion flame for specific analyte detection in atomic absorption spectrometry. Influence of trapping temperature, modification of the molybdenum surface with noble metals – Ir, Pt and Rh, distance between the orifice of the injection capillary and the strip and composition of the gaseous phase (argon-hydrogen-oxygen) was studied in order to clarify the general hydride trapping mechanism. EXPERIMENTAL A Perkin–Elmer (Norwalk, USA) model 3110 atomic absorption spectrometer equipped with a deuterium background correction system was employed in this study. The Photron Super Lamps® (Photron, Victoria, Australia) of antimony, bismuth, arsenic and selenium were used as a specific radiation sources. The device for electrothermal induced collection of hydrides and their subsequent electrothermal release was based on a piece of the molybdenum foil (Metallwerk Plansee, Reutte, Austria), 85 µm thick, 2.15 mm wide and 56 mm long. It was bent to form a U– profile. Both ends of the strip were pressed between boron nitride cylindrical body (6 mm in diameter) and two brass contacts. A part of the bent strip (9 mm) remained free. Boron nitride electric insulation and the brass contacts maintained also an efficient cooling of the strip providing reproducible temperature setting in series of experiments. In this arrangement, maximum power of about 130 W was supplied at the highest temperature applicable (2600°C). Sborník soutěže Studentské tvůrčí činnosti Student 2006 a doktorské soutěže O cenu děkana 2005 a 2006 Sekce DSP 2006, strana 206
Fig. 1: Scheme of the hydride generation aparature coupled with the heated molybdenum-foil trap system and simple hydrogen diffusion flame atomic absorption system. The implementation of the electrothermal trapping/vaporisation (ETV) device in the instrumental arrangement is shown in Fig. 1. Only a very simple atomiser based on a miniature hydrogen diffusion flame was used for atomic absorption spectrometry detection in trapping experiments. The flame was supported by the gas mixture of hydrogen and argon at a flow rate of 215 ml min -1 and 800 ml min -1 , respectively. The injection capillary, made of a wide bore quartz GC–capillary (8 cm × 0.53 mm id), was inserted through the narrow hole, drilled in the axis of the boron nitride body. The tip of the capillary was precisely positioned by means of an adjusting screw made of PEEK. A laboratory made pulse-width modulation power supply was used for heating the molybdenum strip. It was based on a high power MOS-FET transistor and a car battery (12 V, 60 Ah). The power supply was controlled by a PC by using software created in Visual Basic ver.3. In trapping experiments, the actual temperature of the heated central part of the molybdenum strip was simultaneously measured by pyrometers. A laboratory made flow injection hydride generation system is depicted also in Fig. 1. The peristaltic pump (model 72624–71, Ismatec, Switzerland) was fitted with Tygon tubes. The generation system was based on 3-channel peristaltic pump, PTFE-reaction loop and gasliquid separator with a forced outlet for liquid phase and with a PTFE-filter in an outlet for gaseous phase. The flow rates were 1.1, 3.6 and 5.0 ml min -1 for 0.5% m/v NaBH4 solution, sample solution in 1 mol l -1 HCl and waste solution, respectively. The sample channel was equipped with a Knauer (Berlin, Germany) 6–port injection valve made of PEEK with a 100 μl sampling loop for performing flow injection of the sample solution. Argon was introduced in two channels, upstream of the reaction loop as reaction gas and into the gas– liquid separator as stripping gas at a flow rate of 55 ml min -1 and 10 ml min -1 , respectively. Sborník soutěže Studentské tvůrčí činnosti Student 2006 a doktorské soutěže O cenu děkana 2005 a 2006 Sekce DSP 2006, strana 207
Page 1 and 2: PRODUCTION OF SELECTED SECONDARY ME
Page 3 and 4: containing ampicillin, IPTG and x-g
Page 5 and 6: THE SIMPLE METHOD FOR THE RECOGNITI
Page 7 and 8: Figure 1 Negative-ion mode MALDI-TO
Page 9: Table 1 Evaluation of negative-ion
Page 13 and 14: [4] H. Matusiewicz, M. Kopras, J. A
Page 15 and 16: - are hypotriglyceridemic; - exhibi
Page 17 and 18: HYDROPHOBIZED SODIUM HYALURONATE IN
Page 19 and 20: spectrophotometer (AMINCO-Bowman, S
Page 21 and 22: Hyaluronate derivatives showed with
Page 23 and 24: copolymers were additionally functi
Page 25 and 26: Each micelle has a hydrophobic core
Page 27 and 28: STUDY OF THE COPPER(II) IONS NON-ST
Page 29 and 30: CuSO4, Cu(ClO4)2 and Cu2P2O7 of the
Page 31 and 32: total flux [mol.m -2 ] 0.7 0.65 0.6
Page 33 and 34: number of free radicals is very low
Page 35 and 36: Differences can be caused by severa
Page 37 and 38: MEASUREMENT OF THERMOPHYSICAL PROPE
Page 39 and 40: The typical time responses of tempe
Page 41 and 42: Figure 4 illustrates the typical de
Page 43 and 44: sodium sulphate and filtered to a 5
Page 45 and 46: Compare all tested evening primrose
Page 47 and 48: IMPROVED FLUORIMETRIC DETERMINATION
Page 49 and 50: Al F i 80 70 60 50 40 30 20 10 0 0
Page 51 and 52: F i 60 50 40 30 20 10 Data UCL LCL
Page 53 and 54: PHYSICAL-CHEMICAL ASPECTS OF PAINT
Page 55 and 56: Finally, the solubility parameter o
Page 57 and 58: Study of the influence of different
Page 59 and 60: Fig.1: Chemical structures of pI ma
Page 61 and 62:
Identification of pI markers - Firs
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