Atomization temperature optimum

The i-poly(3HB) depolymerase of R. rubrum is the only i-poly(3HB) depolymerase that has been purified [174]. The enzyme consists of one polypeptide of 30-32 kDa and has a pH and temperature optimum of pH 9 and 55 °C, respectively. A specific activity of 4 mmol released 3-hydroxybutyrate/min x mg protein was determined (at 45 °C). The purified enzyme was inactive with denatured poly(3HB) and had no lipase-, protease-, or esterase activity with p-nitro-phenyl fatty acid esters (2-8 carbon atoms). Native poly(3HO) granules were not hydrolyzed by i-poly(3HB) depolymerase, indicating a high substrate specificity similar to extracellular poly(3HB) depolymerases. Recently, the DNA sequence of the i-poly(3HB) depolymerase of R. eutropha was published (AB07612). Surprisingly, the DNA-deduced amino acid sequence (47.3 kDa) did not contain a lipase box fingerprint. A more detailed investigation of the structure and function of bacterial i-poly(HA) depolymerases will be necessary in future. 

Once the optimum drying and atomize temperatures have been selected, the optimum ash temperature can be determined. Select the optimum dry and atomize temperatures and an ash temperature of 400°C. Note the peak area produced at atomization, and then repeat the experiment increasing the ash temperature to 1200°C in 200°C steps. A graph of ash temperature against signal should then be plotted. The optimum ash temperature is that just before the signal starts to decrease. 

Each metal has specific requirements of ashing and atomization temperatures. Temperature programs are normally provided by the instrument manufacturers and are often very general. As the mineral composition of foods varies widely, different sample matrices may require specifically designed temperature programs to yield optimum results. It is a simple process to optimize the ashing and atomization temperatures. In the first step, the ashing temperature is fixed (at a suitably low temperature) and the atomization temperature is increased stepwise until an... 

Atomization Temperature and Time. The maximum temperature of the heated graphite tube during the atomization step and the rate at which this temperature is achieved determines the rate of volatilization and atomization of the sample and, therefore, the peak atom population and sensitivity. For involatile elements, the peak height sensitivity increases with increasing temperature imtil a plateau is reached. The optimum atomization temperature is then the lowest temperature at which maximum sensitivity is obtained. For some volatile elements, the peak absorbance may reach a maximum with increasing temperature and... 

In order to determine Bi by GF AAS under stabilized temperature platform furnace (STPF) conditions using the Pd-Mg modifier, a pyrolysis temperature of 1200 °C must be applied (Hiltenkamp and Werth 1988). The optimum atomization temperature under these conditions is 1900 °C the characteristic mass with Zeeman effect background correction (BC) is 28 pg, while in a non-Zeeman instrument it is about 20 pg. 

Without a modifier, Bi can be determined at an optimum atomization temperature of... 

Pyrolysis and atomization curves of manganese are shown in Fig. 2. The pyrolysis curve was obtained using 2300°C as the atomization temperature. The selected pyrolysis temperature for Mn in THFA is about 1600°C. Using this pyrolysis temperature, the optimum atomization temperature corresponds to 2100°C. These pyrolysis and atomization temperatures do not correspond to the THGA suggested temperatures [21], as the furnace design is different and the rate of the vaporization process is also different. Some loss on manganese is observed above 2100 C, due to the volatility of the atomic species at hi temperature. 

Double curves (thermal pretreatment/atomization curves) are used to determine the limits for both thermal pretreatment and atomization temperatures for the elements and matrices involved. These curves can also be applied to drawing conclusions about the atomization mechanism. In the first curve the absorbance signal at the optimum atomization temperature is plotted versus the pretreatment temperature as the variable. In the second curve the absorbance at the optimum pretreatment temperature is plotted versus the atomization temperature as the variable (Figure 65). The pretreatment curve (ash curve) shows the temperature to which the sample can be heated without loss of the analyte. From this curve it is also possible to derive the lowest temperature at which the element is quantitatively volatilized. From the atomization curve can be derived the temperature at which the atomization is first evident, the appearance temperature, and the optimum atomization temperature at which the maximum atom cloud density is attained. 

Figure 65 Thermal pretreatment/atomization curve. A The absorbance measured at the optimum atomization temperature B The absorbance plotted versus the atomization temperature 1 The maximum thermal pretreatment temperature 2 The lowest temperature at which the analyte is quantitatively volatilized 3 The appearance temperature of the analyte 4 The optimum atomization temperature...

FIG. 5. Pyrolysis-atomization curves for electrothermal A AS. A = integrated absorbance signal plotted against applied pyrolysis temperature (pyrolysis curve) B = integrated absorbance signal plotted against atomization temperature (atomization curve). 1 = maximum pyrolysis temperature 2 = lowest temperature of complete volatilization 3 = appearance temperature 4 — optimum atomization temperature. (From Ref. 23 by permission.)... 

Following the general strategy of this book as a kind of supplement to the book Atomic Absorption Spectrometry by Welz and Sperling [150], this chapter repeats as little as possible of what is already written in that book. This includes particularly information about the occurrence, use, biological significance, environmental relevance and toxicity of the individual elements, as well as of particular species of these elements. There is also no information in this chapter about optimum pyrolysis and atomization temperatures or modifiers for the individual elements when GF AAS is used for their determination. For these details as well as for information about the stability of solutions, the volatility of individual compounds or the risk of contamination the authors ask the reader to refer to Reference [150]. 

Figure 8.13 Typical pyrolysis curve for GF AAS the integrated absorbance obtained at the optimum atomization temperature is plotted against the pyrolysis temperature...

Because of the complexity of designs and performance characteristics, it is difficult to select the optimum atomizer for a given appHcation. The best approach is to consult and work with atomizer manufacturers. Their technical staffs are familiar with diverse appHcations and can provide valuable assistance. However, they will usually require the foUowing information properties of the Hquid to be atomized, eg, density, viscosity, and surface tension operating conditions, such as flow rate, pressure, and temperature range required mean droplet size and size distribution desired spray pattern spray angle requirement ambient environment flow field velocity requirements dimensional restrictions flow rate tolerance material to be used for atomizer constmction cost and safety considerations. 

Fig. 21—AES depth profiles of the TiN coatings (a and b) and the TiN/Si3N4 coating with optimum Si content of 10.8 at. % and hardness of 47.1 GPa (c and d) annealed at the temperature of 600 or 800°C in ambient atmosphere. The oxidation depth of the coatings is the sputtering depth where the oxygen atomic percentage reaches the minimum level.

The layer of titanium and ruthenium oxides usually is applied to a titanium substrate pyrolytically, by thermal decomposition (at a temperature of about 450°C) of an aqueous or alcoholic solution of the chlorides or of complex compounds of titanium and rathenium. The optimum layer composition corresponds to 25 to 30 atom % of ruthenium. The layer contains some quantity of chlorine its composition can be written as Ruq 2sTio 750(2- c)Cl r At this deposition temperature and Ru-Ti ratio, the layer is a poorly ordered solid solution of the dioxides of ruthenium and titanium. Chlorine is completely eliminated from the layer when this is formed at higher temperatures (up to 800°C), and the solid solution decomposes into two independent phases of titanium dioxide and ruthenium dioxide no longer exhibiting the unique catalytic properties. 

To find the optimum temperature for boron neutralization by atomic hydrogen, a systematic study was performed in the 40 to 250°C range by... 

While Josiphos 41 also possessed an element of atom-centered chirality in the side chain, Reetz reported a new class of ferrocene-derived diphosphines which had planar chirality only ligands 42 and 43, which have C2- and C -symmetry, respectively.87 Rhodium(i)-complexes of ligands (—)-42 and (—)-43 were used in situ as catalysts (0.75 mol%) for the hydroboration of styrene with catecholborane 1 for 12 h in toluene at — 50 °C. The rhodium/ i-symmetric (—)-43 catalyst system was the more enantioselective of the two - ( -l-phenylethanol was afforded with 52% and 77% ee with diphosphines (—)-42 and (—)-43, respectively. In both cases, the regioselectivity was excellent (>99 1). With the same reaction time but using DME as solvent at lower temperature (—60 °C), the rhodium complex of 43 afforded the alcohol product with an optimum 84% ee. 

---