Dry mass determination: what role does it play in combined measurement uncertainty?

Elemental mass fractions are normally reported on a dry-mass basis. In addition, producers of reference material state their property values for dry masses and relate them to a defined dry mass determination method. This paper describes how biases and uncertainties in dry mass correction factors may affect values reported as ‘concentration per dry mass’. The influence of the use of different drying methods, accuracy of drying temperature, length of drying, environmental humidity, and the sample mass used for dry mass determination have been evaluated using two candidate International Atomic Energy Agency reference materials. Deviation from proposed drying methods was observed to lead to differences of up to 5% in dry mass correction factors. In addition, the heterogeneity of sample moisture as well as hygroscopic behaviour during weighing play an important role in the uncertainty estimation. Proposals are made regarding which sources of uncertainty arising from dry mass determination should be considered and included in the combined uncertainty of analytical results.     

P680: what is it and where is it?

Electron and X-ray crystallography have provided intermediate structural models for photosystem II (PSII), the membrane located multisubunit complex which uses light energy to split water into its elemental constituents. This reaction is thermodynamically demanding and involves the production of redox potentials in excess of 1 V. Structural analyses have now shown that the primary oxidant, P680, is not a 'special pair' of chlorophylls, as in other types of photosynthetic reaction centres, but a tetramer of equally spaced chlorophyll a molecules. Its high redox potential, and the involvement of four weakly coupled isoenergetic monomers rather than a strongly excitonically coupled 'special pair', has implications for redox mechanisms which are unique to PSII, and therefore not found in any other photosynthetic system. The importance of these features is discussed.     

Tritium measurement in the Western Caucasus

Measurement of tritium in water of rains, springs, wells, mud volcanoes and rivers, lakes of the Western Caucasus (Krasnodar region) has been carried out since 1997 for hydrogeology, engineering geology, ecology and seismology. Electrolytic cells with spiral electrodes and the big multiwire proportional chamber were used for low tritium concentration measurements on expeditions. With the new design of the cell the enrichment factor of 64.0 ± 1.5 % was obtained during the electrolytic process. Correlation of tritium concentration is observed in mud volcanoes and spring water with regional seismicity. The long-term tritium data are shown in natural waters in South Russia.     

Hydrogen exchange mass spectrometry: what is it and what can it tell us?

Proteins are undoubtedly some of the most essential molecules of life. While much is known about many proteins, some aspects still remain mysterious. One particularly important aspect of understanding proteins is determining how structure helps dictate function. Continued development and implementation of biophysical techniques that provide information about protein conformation and dynamics is essential. In this review, we discuss hydrogen exchange mass spectrometry and how this method can be used to learn about protein conformation and dynamics. The basic concepts of the method are described, the workflow illustrated, and a few examples of its application are provided.     

Flavonoids of the cotton plant and plants close to it

This review gives information on the distribution of flavonoids (flavonol and anthocyanin glycosides, catechins, and proanthocyanidins in plants of the family Malvaceae, namely the various species of the genera Gossypium, Hibiscus, Altheae, etc. It is shown that the flavonols are represented by glycosides of kaempferol, quercetin, myricetin, herbacetin. gossypetin, and hibiscetin, the most widespread being glycosides of quercetin and kaempferol. Characteristic for the majority of representatives of the families that were studied are flavonols having a hydroxy group in the C-8 position. Anthocyanins are represented by glycosides of cyanidin and of delphinidin. However, together with these, glycosides of methoxylated anthocyanins have also been detected — peonidin, petinidin, and malvidin. Sources of a food dye have been revealed among representatives of the family. Literature sources up to 1991 have been included.A. S. Sadykov Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax 627071. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 3–19, January–February, 1994.     

Microelectrodes for the measurement of cellular metabolism

The study of metabolism of cellular cultures is of great interest. Although some papers reports the monitoring of parameters such as pH, potassium, dissolved oxygen and temperature in cellular cultures using different kind of sensors, no definitive solution has been found to get reproducible and feasible results. The advantage of using sensors fabricated with microelectronic technology is focused on their small size, rapid response and the possibility of having an integrated array of microelectrodes, which favors the measurement of small volumes and fast cell metabolism changes. In this work, the viability of using a multisensor platform of microelectrodes, such as potassium and pH ISFETs, amperometric microelectrodes for dissolved O₂ and pseudo-reference microelectrodes for the study of metabolism of cellular cultures is described. Preliminary results of pH ISFETS’ response in neuronal cultures is reported.     

Measurement uncertainty in the pH measurement procedure

A measured value without even an approximate knowledge of the uncertainty is worthless. The uncertainty is part of every measured value and specification of the uncertainty is part of every analytical procedure. The uncertainty makes the value independent of its origin. The basis for estimation of the uncertainty is the "Guide to the Expression of Uncertainty in Measurement ". For some procedures, however, for example pH measurement, several problems arise in practice. This article describes a practical and inexpensive way of calculating the uncertainty of pH values.