Current air quality analytics and monitoring: A review

This review summarizes the different tools and concepts that are commonly applied in air quality monitoring. The monitoring of atmosphere is extremely important as the air quality is an important problem for large communities. Main requirements for analytical devices used for monitoring include a long period of autonomic operation and portability. These instruments, however, are often characterized by poor analytical performance. Monitoring networks are the most common tools used for monitoring, so large-scale monitoring programmes are summarized here. Biomonitoring, as a cheap and convenient alternative to traditional sample collection, is becoming more and more popular, although its main drawback is the lack of standard procedures. Telemonitoring is another approach to air monitoring, which offers some interesting opportunities, such as ease of coverage of large or remote areas, constituting a complementary approach to traditional strategies; however, it requires huge costs.     

A Mechanistic Study on the Oxidative Degradation of Dibenzazepine Derivatives by Manganese(III) Complexes in Acidic Sulfate Media

The oxidative degradation of tricyclic antidepressants (TCA) was studied in the presence of a large excess of the oxidizing agent manganese(III) and its reduced form manganese(II) sulfate in acidic media. The products were detected and identified using UV–vis, ESI‐MS, IR, and EPR methods. The mechanism of the reaction was studied for the following two classes of TCA: 10,11‐dihydro‐5H‐dibenz[b, f]azepines and dibenz[b, f]azepines. The oxidative degradation between dibenz[b, f]azepines and the manganese(III) ions resulted in the formation of substituted acridine with the same substituent as in the origin dibenz[b, f]azepine derivative. The pseudo–first‐order rate constants (k_obs) were determined for the degradation process. The dependences of the observed rate constants on the [Mn^III] with a zero intercept were linear. The reaction between 10,11‐dihydro‐5H‐dibenz[b, f]azepines, and the manganese(III) sulfate ion resulted in oxidative dehydrogenation, which proceeded via the formation of the following two intermediates: a free organic radical and a dimer. Further oxidation of the second intermediate led to a positively charged radical dimer as the single final product. Linear dependences of the pseudo–first‐order rate constants (k_obs) on the [Mn^III] with a zero intercept were established for the degradation of 10,11‐dihydro‐5H‐dibenz[b, f]azepines. The observed rate constants were dependent on the [H⁺] and independent of the [TCA] within the excess concentration range of the manganese(III) complexes used in the isolation method. The radical product of the degradation of 10,11‐dihydro‐5H‐dibenz[b, f]azepines was not stable in the aqueous solution and was subsequently transformed to a nonradical dimer in the next slower step. The observed rate constants were independent of the [Mn^III], independent of the [H⁺] and increased slightly with increasing TCA concentrations when TCA was used in excess. The mechanistic consequences of all of these results are discussed.     

An invariance of geometric mean with respect to Lagrangian means

The invariance of the geometric mean G with respect to the Lagrangian mean-type mapping (Lf,Lg), i.e. the equation G○(Lf,Lg)=G, is considered. We show that the functions f and g must be of high class regularity. This fact allows to reduce the problem to a differential equation and determine the second derivatives of the generators f and g.     

Separation of Monovinyl and Divinyl Protochlorophyllides Using C30 Reverse Phase High Performance Liquid Chromatography Column: Analytical and Preparative Applications

A new, high performance liquid chromatography method has been developed for the separation of monovinyl- and divinyl-protochlorophyllides, using commercially available, C₃₀ reverse phase column and isocratic elution. This method can be used both for analytical applications and preparative scale purification of monovinyl- and divinyl-protochlorophyllides using the same column where submilimolar concentrations of the crude protochlorophyllide extract can be separated in one run. The purity of the obtained protochlorophyllides was demonstrated by spectroscopic methods, as well by the formation of aggregates in toluene.     

Equilibrated thermodesorption studies of adsorption of n-hexane and n-heptane on zeolites Y, ZSM-5 and ZSM-11

Gravimetric measurements of thermodesorption of n-hexane and n-heptane were performed under quasi-equilibrium conditions. Differential thermodesorption profiles for ZSM-5 and ZSM-11 showed two peaks, but for Y zeolites, only one thermodesorption peak was observed. A model function, derived from the Langmiur adsorption model, was fitted to the experimental data, and the model parameters (the adsorption entropy and enthalpy) were estimated. The two-step desorption profiles observed for ZSM-5 and ZSM-11 were attributed to the commensurate freezing effect, i.e. a transition in the adsorbed phase resulting in ordering of the adsorbed molecules in the zeolite channels. The results observed for ZSM-11 indicate that the zigzag channels typical for ZSM-5 micropore system are not necessary for this transition to occur.     

Densitometric Determination of Embelin in Lysimachia punctata

JPC – Journal of Planar Chromatography – Modern TLC - Athin layer chromatographic method with densitometric UV detection at λ = 285 nm has been developed for quantification of...     

A fading effect in the X-ray diffraction contrast of dislocations

Fringes in the dislocation image in X-ray section topography are shown to fade away partially when unpolarized radiation is used. The fading effect is explained in terms of an analogy with the polarization beat in a wedge crystal. The polarization nature of the phenomenon is confirmed through numerical simulations of the contrast.Dedicated to Professor Dr. Ulrich Bonse on the occasion of his 60th birthday     

Application of platinum gauze activated by hydrogen to the adsorption separation of silver traces and their determination by aas or spectrophotometry

A method ("electrosorption") has been developed for separation of silver from copper by its deposition through internal electrolysis with hydrogen adsorbed on a platinum surface. The silver can then be stripped and determined by atomic-absorption spectrometry or the dithizone method. The activation of the platinum surface with adsorbed hydrogen can be achieved either electrolytically or by passing hydrogen gas through the solution in which the platinum is immersed. The method of electrosorption has been successfully applied to determination of trace levels of silver in copper metal.     

Origin of organic gaseous products formed in the thermal decomposition of formates

The gaseous products of the thermal decomposition of formates have been investigated and compared with the products of formaldehyde and synthesis gas transformation under analogous conditions in the presence of the solids formed in the thermal decomposition of particular formates. It was found that formaldehyde transformation leads to organic compounds identical to those obtained in the thermal decomposition of the respective formates, while synthesis gas does not react under such conditions. This fact substantiates the hypothesis that formaldehyde is a precursor of the organic compounds identified in the thermal decomposition of formates. The nature of the organic componds obtained in the thermal decomposition of formates indicates that the formaldehyde formed in the initial stages is then transformed in the Cannizzaro or Tishchenko reactions.

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Zusammenfassung Die gasförmigen Produkte der thermischen Zersetzung von Formiaten wurden untersucht und mit den Produkten verglichen, die bei der Umwandlung von Formaldehyd und Synthesegas unter analogen Bedingungen in Gegenwart von bei der thermischen Zersetzung von speziellen Formiaten gebildeten Feststoffen entstehen. Formaldehydumwandlungen führen zu organischen Verbindungen, die identisch mit denen sind, die bei der thermischen Zersetzung des betreffenden Formiats gebildet werden, während Synthesegas unter solchen Bedingungen nicht reagiert. Dies erhärtet die Hypothese, daß Formaldehyd eine Vorstufe der bei der thermischen Zersetzung von Formiaten identifizierten organischen Verbindungen ist. Die Natur der bei der thermischen Zersetzung von Formiaten auftretenden organischen Verbindungen weist darauf hin, daß das in den ersten Reaktionsschritten gebildete Formaldehyd nach der Cannizzaro-oder Tishchenko-Reaktion weiterreagiert.

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