Substance concentration

The formal name for molarity is the amount of substance concentration. ... 

This section examined small muscle preparations stimulated electrically or skinned muscle fibers maintained in superfused baths with different substance concentrations. The electrical stimulation was either continuous or intermittent for relatively short durations. 

Transport and dijfusion. With the exception of N2, O2, Ar, and numerous other long-lived species that are well-mixed in the bulk of the atmosphere, horizontal and vertical transport are closely coupled with chemical reactions in controlling atmospheric trace-substance concentrations. 

Xexc = 436 nm and X > 560 nm (cut off filter FI 56 (D)). Under the conditions used for scans B and C some substances appear as double peaks on account of fluorescence quenching at the center of the chromatogram zones as a consequence of the substance concentration being too high. 

Brock A. 1991. Inter and intraindividual variations in plasma cholinesterase activity and substance concentration in employees of an organophosphorus insecticide factory. Br J Ind Med 48 562-567. 

Fig. 3.14 Potential-pH diagram for the Bi-Te-H20 system, calculated for dissolved substance concentrations, Bi 0.75 x 10 M and Te 1 x 10 M in 1 M HNO3 at 25 °C, 1 atm. (Reproduced with permission from [223], Copyright 2009, The Electrochemical Society)...

The right part of equation [4], E = e c d, represents Lambert-Beer s law. E is called the extinction, c is the substance concentration, and d is the thickness of the sample. The E values span from 0 (this is the case when all light is transmitted and no absorption takes place, i.e., 1 = Iq) to inhnity, °o (this is the case of maximal extinction when no incident light is transmitted, i.e., 1 = 0). Realistic E values that can be correctly measured by normal spectrometers range between 0 and 2. Instead of using the E expression for extinction, A for absorbance is often used. E and A are dimensionless values, i.e., numbers without units. Nevertheless, OD, the symbol for optical density, is often added to E and A in order to clarify their meanings. 

The much used term molarity instead of amount-of-substance concentration (for short amount concentration or just concentration) is obsolete and should not be used. The same applies to specifications such as 0.5 AT or 0.5 m the correct statement is c = 0.5 mol/L. 

The membrane permeabilities Pm may be converted to intrinsic permeabilities P(h when the pKa is taken into consideration. An ionizable molecule exhibits its intrinsic permeability when it is in its uncharged form and there is no water layer resistance. The relationship between Pm and P0 is like that between the pH-dependent apparent partition coefficient (log Kd) and the true partition coefficient (log Kp), respectively. This relationship can be rationalized by the mass balance. Take, for example, the case of a monoprotic acid, HA. The total substance concentration is... 

The GLP requirements for mixtures with carrier (40 CFR 160.113) were originally intended to address problems associated with the incorporation of test and control substances into feed, water, and other media for toxicology studies however, now these same requirements pertain to all other GLP-required studies, including those pertaining to re-entry and worker safety. The requirement involves (1) substantiation of test, control, and reference substance concentration through periodic analyses (2) verification of homogeneity and (3) determination of stability and, if applicable, also solubility. All of these requirements usually require chemical analysis, although bioassay may be necessary for microbial pesticides. 

To use this method, the sample is dissolved in a system containing two phases (e.g., water and octanol) such that the solution is at least about 5 x 10-4 M. The solution is acidified (or basified) and titrated with base (or acid) under controlled conditions. The shape of the ensuing titration curve is compared with the shape of a simulated curve, which is created in silico. The estimated p0Ka values (together with other variables used to construct the simulated curve such as substance concentration factor, CO2 content of the solution and acidity error) are allowed to vary systematically until the simulated curve fits as closely as possible to the experimental curve. The p0Ka values required to achieve the best fit are assumed to be the correct measured p0Ka values. This computerized calculation technique is called refinement , and is described elsewhere [14, 15]. 

Erk and Altun [24] used a ratio spectra derivative spectrophotometric method and a high performance liquid chromatographic method for the analysis of miconazole nitrate and metronidazole in ovules. The spectral method depends on ratio spectra first derivative spectrophotometry, by utilizing the linear relationship between substances concentration and ratio spectra first derivative peak amplitude. The ratio... 

The amount of a substance present in a given mass or volume of another substance. The abbreviations w/w, w/v and v/v are sometimes used to indicate whether the concentration quoted is based on the weights or volumes of the two substances. Concentration may be expressed in several ways. These are shown in Table 1.2. 

S.No. Substance Concentration/Preparation of Solution Specific Optical Rotation [a]p°... 

When the test component content in the samples varies over a wider interval, a calibration curve must be constructed. Calibration curves with ISEs are usually linear over several concentration orders (usually from about 10" m to about 10" m) and their slope is close to the theoretical Nernstian value. Both at high and at low concentrations with respect to the linear part, the caUbration dependence becomes curved and, eventually, independent of the test substance concentration (see fig. 5.1). The upper limit of the ISE response is mostly given by saturation of the active sites in the electrode membrane (for example ion-exchange sites), whereas the lower limit is determined by solubility of the... 

It is desirable that the test substance concentrations in the samples lie within the linear part of the calibration curve, in order to keep the standard deviation of the measurement at an acceptable level. More concentrated sample solutions can be appropriately diluted, while a determinate amount of the test component can be added to less concentrated solutions to bring the total concentration up to the linear part of the calibration curve. However, the latter approach is of only limited importance because the presence of a constant amount of the test component may cause the relative changes in the sample concentration to become too small to measure precisely therefore, it is useful only when calibration curve slope varies rapidly with changing concentration [144). 

In addition techniques, the test substance concentration is determined from the difference in the ISE potentials obtained before and after a change in the sample solution concentration. The main advantage Ues in the fact that the whole measurement is carried out in the presence of the sample matrix, so that results with satisfactory accuracy and precision can be obtained even if a substantial portion of the test substance is complexed. Several addition techniques can be used, namely, single, double or multiple known addition methods, in which the sample concentration is increased by additions of a test substance standard solution single, double or multiple known subtraction methods, in which the sample concentration is decreased by additions of a standard solution of a substance that reacts stoichiometrically with the determinand and analyte addition and subtraction methods, in which the sample is added to a test substance solution or to a reagent solution. 

The term flux here refers to the amount of the diffusing substance passing through the cross section of a unit area in unit time. The term gradient refers to the change in substance concentration as a function of distance. Both quantities, which have directionality in addition to a numerical value, are viewed as vector quantities. 

Lyotropic liquid crystals are those which occur on the addition of a solvent to a substance, or on increasing the substance concentration in the solvent. There are examples of cellulose derivatives that are both thennotropic and lyotropic. However, cellulose and most cellulose derivatives form lyotropic mesophases. They usually have a characteristic "critical concentration" or "A point" where the molecules first begin to orient into the anisotropic phase which coexists with the isotropic phase. The anisotropic or ordered phase increases relative to the isotropic phase as the solution concentration is increased in a concentration range termed the "biphasic region." At the "B point" concentration the solution is wholly anisotropic. These A and B points are usually determined optically. 

Acute toxic effects are considered as being threshold effects, i.e., effects for which there are expected to be a threshold of substance concentration below which the effects will not be manifested. For the hazard and risk assessment, it is important to identify those dose levels at which signs of acute toxicity are observed, and the dose level at which acute toxicity is not observed, i.e., to derive a NOAEL for acute toxicity. However, it should be noted that a NOAEL is usually not derived in the classic acute toxicity smdies, partly because of the limitations in smdy design. 

Unless a threshold mechanism of action is clearly demonstrated, mutagenicity and genotoxicity are considered as being non-threshold effects, i.e., a threshold of substance concentration cannot be identihed below which the effects will not be manifested. For non-threshold mechanisms of... 

See Ammonia as a substrate or product AMOUNT-OE-SUBSTANCE CONCENTRATION AMP... 

Liver damage characterized by toxic jaundice, which may progress to fatal hepatic necrosis, results from the repeated inhalation of higher concentrations of the hot fumes of the molten substance." Concentrations of mixed penta- and hexachloronaph thalene between 1 and 2mg/m were measured in the air of industrial plants where fatal cases of yellow atrophy of the liver occurred. ... 

Increased fluid intake increases urinary output, lowering substance concentration involved in stone formation. Hydration is recommended to reduce new stone formation. 

Embryo medium is highly aqueous, and the potential for developmental toxicity increases when significant concentrations of solvents are added. Consequently, one of the greatest limitations of any zebrafish embryo assay is the need for adequate aqueous solubility of the test substance. Solubility in embryo medium with the intended vehicle should be tested over the desired concentration range prior to initiation of an embryo assay. An assay plate can be filled with embryo medium with the test substance concentrations to be evaluated, heated to 28.5°C, and viewed with a stereomicroscope in order to detect precipitation. 

The top of the chain is the SI unit of amount-of-substance concentration mol dm 3 (mol L1). A certificate from the National Measurement Institute gives confidence to the certifying authority that the amount-of-substance... 

---