On-line oxidation

Mineral and sea waters As K2S2Os-NaOH Domestic oven On-line oxidation HG-AAS 29... 

Total Hg determined by CVAAS after digestion with HNO, for 4 h at 80°C, and reduction with SnCU- For MeHg, 1000 mg was pre-treated by addition of HCI and toluene, back-extraction with thiosulphate, addition of acetate buffer, complexation and on-line oxidation (after HPLC), and reduction with SnCI, separation was by high performance liquid chromatography (HPLC), followed by CVAFS detection (Lab.OS)... 

Z.Q. Zhang, G.-X. Liang, Flow injection on-line oxidizing fluorometry coupled to dialysis sampling for the study of carbamazepine-protein binding, Anal. Chim. Acta 536 (2005) 145. 

Mascher, H. Kikuta, C. Determination of amoxicillin in plasma by high-performance liquid chromatography with fluorescence detection after on-line oxidation. J.Chromatogr., 1990, 506, 417-421... 

L.-J. Shao, W.-E. Gan, and Q.-D. Su. Determination of total and inorganic mercury in fish samples with on-line oxidation coupled to atomic fluorescence spectrometry. Analytica Chimica Acta 562 128-133, 2006. 

Figure 2.209 On-line oxidation of compounds eluting from the GC for the production of COj and Nj for IRMS measurement. (Thermo Fisher Scientific.)...

In reeent years, tire use of elevated temperatures has been reeognised as a potential variable in method development. Witlr inereased temperature, aqueous-organie mobile phases separations ean improve, viseosity deereases and diffusion inereases so baek pressures are redueed. At higher temperatures (usually with superheated water > 100 °C under modest pressures) water alone ean be used as the mobile phase and eair provide unique separation opportunities. The absenee of an organie solvent enables the use in HPLC of alternative deteetors sueh as FID or on-line LC-NMR using deuterium oxide as the eluent. 

Theories of the oxidation of tantalum in the presence of suboxide have been developed by Stringer. By means of single-crystal studies he has been able to show that a rate anisotropy stems from the orientation of the suboxide which is precipitated in the form of thin plates. Their influence on the oxidation rate is least when they lie parallel to the metal interface, since the stresses set up by their oxidation to the pentoxide are most easily accommodated. By contrast, when the plates are at 45° to the surface, complex stresses are established which create characteristic chevron markings and cracks in the oxide. The cracks in this case follow lines of pores generated by oxidation of the plates. This behaviour is also found with niobium, but surprisingly, these pores are not formed when Ta-Nb alloys are oxidised, and the rate anisotropy disappears. However, the rate remains linear it seems that this is another case in which molecular oxygen travels by sub-microscopic routes. 

Watmough, N.J.. Turnbull, D.M., Sherratt. H.S.A. Bartlett. K. (1989). Measurement of the acyl-CoA intermediates of p-oxidation by hplc with on-line radiochemical and photodiode-array detection. Application to the study of [U- C]hexadecanoate by intact rat liver mitochondria. Biochem. J. 262,261-269. 

Catalytic activity for the selective oxidation of H2S was tested by a continuous flow reaction in a fixed-bed quartz tube reactor with 0.5 inch inside diameter. Gaseous H2S, O2, H2, CO, CO2 and N2 were used without further purification. Water vapor (H2O) was introduced by passing N2 through a saturator. Reaction test was conducted at a pressure of 101 kPa and in the temperature range of 150 to 300 °C on a 0.6 gram catalyst sample. Gas flow rates were controlled by a mass flow controller (Brooks, 5850 TR) and the gas compositions were analyzed by an on-line gas chromotograph equipped with a chromosil 310 coliunn and a thermal conductivity detector. 

The isomer shift, d, arises from the Coulomb interaction between the positively charged nucleus and the negatively charged s-electrons, and is thus a measure for the s-electron density at the nucleus, yielding useful information on the oxidation state of the iron in the absorber. An example of a single line spectrum is fee iron, as in stainless steel or in many alloys with noble metals. 

The analyte must be converted into a volatile compound suitable for mass-spectrometric analysis. Procedures for C, N, and O follow those developed for conventional organic microanalysis— oxidation of organic C to COj, reduction of organic N to N2, and conversion of O2 into CO or COj. In most procedures, cryogenic purification of the products is carried out before mass spectrometry, and both off-line and on-line procedures have been developed. 

With respect to CO oxidation an activity order similar to that described above for CH4 combustion has been obtained. A specific activity enhancement is observed for Lai Co 1-973 that has provided a 10% conversion of CO already at 393 K, 60 K below the temperature required by LalMnl-973. This behavior is in line with literature reports on CO oxidation over lanthanum metallates with perovskite structures [17] indicating LaCoOs as the most active system. As in the case of CH4 combustion, calcination at 1373 K of LalMnl has resulted in a significant decrease of the catalytic activity. Indeed the activity of LalMnl-1373 is similar to those of Mn-substituted hexaaluminates calcined at 1573 K. Dififerently from the results of CH4 combustion tests no stability problems have been evidenced under reaction conditions for LalMnl-1373 possibly due to the low temperature range of CO oxidation experiments. Similar apparent activation energies have been calculated for all the investigated systems, ranging from 13 to 15 Kcal/mole, i.e almost 10 Kcal/mole lower than those calculated for CH4 oxidation. 

Zhang X, Cornelis R, De Kimpe J, and Mees L (1996) Arsenic speciation in serum of uraemic patients based on liquid chromatography with hydride generation atomic absorption spectrometry and on-line UV photo-oxidation digestion. Anal Chim Acta 319 177-185. 

Iwasita T, Vielstich W. 1986. On-line mass spectroscopy of volatile products during methanol oxidation at platinum in acid solutions. J Electroanal Chem 201 403-408. 

When the right-hand side of the above equation is zero, i.e., when either T = 0 or P0j equals one atmosphere, AG° must be zero. The intersection of the standard free energy change versus temperature line with the temperature axis, when AG° = 0, gives the temperature at which the oxygen equilibrium pressure, P0i, is equal to one atmosphere. This temperature is known as the decomposition temperature of the oxide and is denoted as TD on line 1 in Figure 3.5. 

Two lines on the Pourbaix diagrams (Figure 5.2) deserve reference. These are the sloping dashed lines, and they represent the stability limits for water they are essentially the domain of thermodynamic stability of water superimposed on potential-pH diagrams. At the upper line, oxidation of water goes according to ... 

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