The aim of the present analysis was to study the influence of the sample concentration on the measured antioxidant capacity, since such investigations are scarce but necessary to ensure the ...reproducibility of the results. Pure substances (ascorbic acid, gallic acid, Trolox®, uric acid) and food extracts (strawberry nectar, tomato extract, white tea) were analysed using seven common antioxidant capacity assays (three versions of Trolox equivalent antioxidant capacity, TEAC; ferric reducing antioxidant power, FRAP; photochemiluminescence, PCL; oxygen radical absorbance capacity, ORAC and total phenolics assay). For all applied pure substances and in most of the assays effects of the sample concentration on the measured antioxidant capacity were observed. Since it remains speculative how sample concentration does affect the measured antioxidant capacity exactly, it is strongly recommended to use at least three sample concentrations for analysis to detect and to discuss concentration-dependent effects.
The finiteness and positive value of the slope of the saturation curve at the critical point according to its location in the region of a thermodynamic surface restricted by the curves of inversion ...and saturation are substantiated. It is shown that any two derivatives of the first order formed with respect to volume, internal energy, entropy, enthalpy, and the Helmholtz energy, one of which is taken at a fixed value of pressure and the other at a fixed value of temperature, are equal in the critical state. New sets of the critical conditions for a pure substance are obtained.
The paper reports work on the synthesis, purification and certification of pure substance (organic) reference materials as conducted within the National Analytical Reference Laboratory (NARL). Areas ...of interest include illicit drugs, agricultural and veterinary chemicals, and steroids and steroid metabolites and their deuterates. The discussion covers the prioritization of work requirements, procedures for synthesis and production, quality assurance, characterization, homogeneity, storage and stability testing, and certification of materials. Future plans for establishing traceability are also discussed.
Inorganic minerals such as C., O, N, Si, P, and Fe are necessary for the phytoplankton multiplication. It has been reported by Nakamura et al. 1 that some kinds of phytoplankton can grow quite ...rapidly once Fe, Si, P and N are supplied into seawater in the adequate proportion. One of the best candidates as a source of such minerals for the phytoplankton multiplication is steelmaking slag because of its cheap cost, sufficient quantity (15 million ton per year in Japan), adequate mineral concentration and its ionic nature (steelmaking slags basically consists of FetO, CaO, SiO2 and P2O5). On the other hand, steelmaking companies are now seeking new technologies to reduce the amount of steelmaking slag and to reuse the slag as new valuable resources 2. If such technologies are successfully developed, we will be able to regard steelmaking slag as a new ecomaterial.
Phase Equilibrium in Ideal Mixtures Hołyst, Robert; Poniewierski, Andrzej
Thermodynamics for Chemists, Physicists and Engineers
Book Chapter
In this chapter, we use the ideal mixture model to phase transitions and related phenomena that occur in two-component systems. In the context of liquid–gas equilibrium, we discuss Raoult’s and ...Henry’s laws. According to Raoult’s law the partial vapour pressure of a component above an ideal solution is proportional to the molar fraction of that component in the solution. Henry’s law is similar to Raoult’s law but applies only to dilute solutions, for instance, to a small amount of a gaseous component dissolved in a liquid solvent, in equilibrium with the gaseous phase. Then we discuss the liquid–solid equilibrium, in particular, solubility of solids in liquids and the phase diagram of a system called the simple eutectic. We also discuss osmotic equilibrium which occurs between a pure solvent and the solvent in a solution in the presence of a membrane permeable only to solvent molecules. Finally, we summarize the properties of solutions which depend only on the amount of the solute but not on its characteristics, called colligative properties. Examples of colligative properties are the boiling point elevation, freezing point depression and osmotic pressure.
So far we have treated the first and second laws separately, but in a real system both energy conservation and entropy play a role. The role of entropy in determining the spontaneous direction of a ...system was derived for an isolated system that exchanged neither energy nor material with its surroundings. There are few biological systems of interest that fulfill the requirements of this isolation. We need a state variable that will indicate the direction and equilibrium position of a system that undergoes radical changes in energy (usually measured as enthalpy) and entropy together. This state function exists. It is the Gibbs free energy, G.
Mixtures Hołyst, Robert; Poniewierski, Andrzej
Thermodynamics for Chemists, Physicists and Engineers
Book Chapter
In this chapter, we show that the thermodynamic formalism can be easily extended to mixtures, in particular, the thermodynamic potentials have the same definitions as for a pure substance. We also ...derive the conditions of internal stability of a mixture. Then the concept of a partial molar quantity is introduced, which is a generalization of a molar quantity for a pure substance. Another useful concept is a function of mixing. It expresses the change in a given extensive state function when pure substances form a mixture at constant temperature and pressure. Next we consider a mixture of ideal gases and determine the chemical potential of a gaseous component and functions of mixing. In particular, it follows from the form of the Gibbs free energy of mixing that mixing of gases is a spontaneous process. Then we introduce the model of ideal mixture which applies to mixtures of similar substances in the liquid and solid phases. In the case of real mixtures the concepts of fugacity, activity and excess functions are used. Finally, we derive the phase rule which is a general relation between the number of phases in equilibrium, number of components and number of independent intensive parameters in the system.
Introduction Khan, JaVed I.; Kennedy, Thomas J.; Christian, Donnell R.
Basic Principles of Forensic Chemistry
Book Chapter
Forensic science is the application of scientific principles to matters involving the law. This area of science is generally considered quite fascinating and it continues to experience growing ...popularity. Many would agree that the current public interest in forensics is a direct result of CSI-related television programming. These weekly shows have brought a once relatively unknown area of science to the forefront of public mainstream. Viewers are captivated and intrigued by well-informed scientists working in spotless labs with ominous lighting and a modern music background. The use of cutting-edge technology provides last-minute revelations culminating in the solution of a complex crime. These programs are entertaining and have certainly increased public awareness to the field of forensics; but alas, television is not reality. Although it is true that forensic science has experienced tremendous growth, few would (or should) believe this to be the result of fictional television programming.
