Influence of temperature and relative humidity

Relative humidity and temperature are two variables which have influence on the chromatographic behavior of the solutes [2] but which can not always be set at desired levels. The relative humidity is expected to have a large influence, while temperature has a small influence. In reference [2] it is stated that a temperature change of 5 degrees seldom exceeds reproducibility limits of the standard working techniques. It is most feasible to discuss the effect of variation in relative humidity and temperature in terms of activity. Therefore in the following paragraphs first the concept of activity will be introduced. Then the concept will be applied in a short examination of the effect of relative humidity and temperature on the retention. 

In this equation both factors which determine the activity can be seen as independent. The first term is the surface component. In this factor is the surface component and Wyv is approximately the solvent volume on the layer after development. The second term is the energy component. In this term a a substance independent, and - for weak solvents - also solvent independent parameter and f(X,S) is a constant dependent on solvent, solute and sorbent. With increasing deactivation of the surface a decreases. 

This means that at higher temperatures the activity decreases, and that this decrease depends on both the solvent and the sorbent. There may even be an interaction between the temperature and the relative humidity, meaning that the effect of temperature is different at different relative humidities, since a is influenced by the general activity, which is partly controlled by the relative humidity. 

A more simple modification is use of a linear relation for the influence of the temperature. After all, the inverse of the temperature, with values aroimd 300 K, is almost as linear as the temperature itself. It is believed that the difference in the values can be neglected in the range covered in this paper. 

There are several approaches towards the optimization of TLC separations. First a distinction has to be made between the method (design) according to which the experiments are performed and the method by which the resulting chromatograms are evaluated. Although not every evaluation method can be combined with every optimization strategy, it is overly restrictive to let an optimization method be limited by an evaluation method. The common optimization methods for TLC are given by Nurok [1], who mentions, for systems with three or more solvents, three feasible methods  

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Surface resistivity. One side of the specimen is coated with a circle of silver paint surrounded by a ring of silver paint. The uncoated distance between the circle and the ring is an effective length on which surface resistivity is measured. The other surface of the specimen is fully coated with silver paint. Current and voltage are measured and surface resistivity calculated. If samples contain internal or external antistatics, the measurement is performed under a controlled atmosphere to eliminate the influence of temperature and relative humidity. Also, specimen conditioning is used to account for migration of the antistatic to the surface. The surface of specimen containing antistatics is not coated with silver paint, but electrodes are... 

Apart from the influence of temperature and relative humidity conditions during powder processing, different unit operations can provide unique settings for food powder materials to encounter compression and compaction phenomena. In the following sections, we discuss how compaction and compression events directly or indirectly intervene in different processing operations. 

Figure 4.19 reveals the influence of temperature and relative humidity on the morphology of the particles. All experiments were planned with the design of... 

R. Jiang, H.R. Kunz, J.M. Fenton, Influence of temperature and relative humidity on performance and CO tolerance of PEM fuel cells with Nafion -Teflon -Zr(HP04)2 higher temperature composite membranes. Electrochim. Acta 51, 5596-5605 (2006)... 

High temperatures and high relative humidity can result in odor problems in a room containing particleboard manufactured with UF resins [25]. The release of formaldehyde from UF particleboard is caused by two factors. It can be due to free formaldehyde present in the board that has not reacted, and it can be due to formaldehyde formed by hydrolysis of the aminoplastic bond as a result of temperature and relative humidity [2,25]. While the first type of release lasts only a short time after manufacture of the particleboard, the second type of release can continue throughout the entire working life of the board. A considerable number of variables influence the emission of formaldehyde from a UF-bonded particleboard. The main ones are the molar ratio of urea to formaldehyde (which influences both types of release), the press temperature, and in service, the ambient temperature and relative humidity. 

Tang et al. [69] studied the hygro and thermal stresses in the fuel cell caused by step-changes of temperature and relative humidity. Influence of membrane thickness was also studied, which shows a less significant effect. However, their model is two-dimensional, where the hygro-thermal stresses are absent in the third direction (flow direction). In addition, a simplified temperature and humidity profile was assumed, (constant temperature for each upper and lower surfaces of the membrane was assumed), with no internal heat generation. 

The time of wetness can be calculated either by meteorological measurements of temperature and relative humidity or by electrochemical cells. For practical purposes, meteorological measurements are used when the relative humidity is 80% at temperatures >32°F/0°C to determine the time of wetness. However, the time of wetness determined in this manner may not be the same, as the actual time of wetness because wetness is also influenced by the type of metal, pollution of the atmosphere, presence of corrosion products, and the degree of coverage against rain. Even so, the results from these measurements usually show a good correlation with corrosion data from field tests under ordinary outdoor conditions. 

A precise mastery of the chromatographic process also requires that the relative humidity be controlled. There are sufficient examples demonstrating that reproducible development is only possible if temperature and relative humidity are maintained constant. The influence of the latter on chromatographic behavior can be investigated using the Vario KS chamber (Fig. 59). When the relative humidity IS altered it is possible that not only the zone behavior will be changed but also the order of the zones on the chromatogram (Fig. 60). 

In chromatographic terms the purpose of this paper is to find a mixture composition which results in a good separation of the solutes, both under standard environmental conditions and for different temperatures and relative humidities. In this section this chromatographic purpose is combined with the Taguchi approach to robustness. This results in mathematical expressions which quantify the separation and the robustness against environmental influences. 

Chowhan [9] defined different pathways of physical instability of tablet formulations. These physical paths may involve one or more complex physical processes, e.g. change in polymorphism, crystallization, vaporization and adsorption. These pathways and thus the physical tablet parameters, are influenced by different types of variables formulation variables (e.g. solubility and hygroscopicity), in-process variables (e.g. moisture content) and aging variables (e.g. temperature and relative humidity). 

The influence of the adjustable variables (disintegrant concentration as well as storage temperature and relative humidity), on the SIR of crushing strength (SIR(S)) was calculated for each combination of disintegrant and filler-binder. This was expressed as in equation (10). 

Fluctuations in the leaf environment are normal the exposed plant can not offer the degree of stability or moderation of extremes as can soil. Temperature, humidity (relative air humidity and free water), precipitation, radiation and wind speed have the greatest impact on the leaf microclimate (42-44). These factors can be modified by plant density and development, and by the growth of individual plant leaves and shoots (45-47). The influence of plant density in turn depends upon such factors as direction of the crop row relative to the prevailing wind, irrigation or precipitation, and the plant height (45). Increasing plant density tends to reduce the fluctuations in temperature and relative humidity, and to alter the distribution of dew. 

There are two complementary ways to assess the influence of the origin of a precipitation on its isotopic content. First, the combined measurement of both 5D and 5 0 enables the calculation of a second-order isotopic parameter, the deuterium excess (d=5D —86 0) which (see Section 4.08.4.1) depends on the temperature and relative humidity of the evaporative source (and, to a lesser degree, on the wind speed). In turn, this parameter contains information about conditions prevailing in these source regions and it has been applied, as of early 2000s, only for Antarctic sites (Culfey and Vimeux, 2001 Stenni et al., 2001 Vimeux et al, 2002), to correct the conventional approach for source temperature... 

When studying chemical reactions in indoor air it can be of great value to obtain continuous data of a number of influencing parameters (Weschler and Shields, 1994). In addition to the concentration of the reactants indoors and outdoors, the real-time monitoring should preferably include also the air exchange rate, temperature and relative humidity. 

They are well lighted, ventilated and, if necessary, air-conditioned in order to be maintained under temperature and relative humidity conditions so as to prevent unfavorable effects on the drug during manufacture and storage and not to influence the precision or operation of laboratory instruments. 

Polymers are much more affected by variations in ambient conditions than are many other types of materials, such as metals, glasses, and ceramics. The ambient temperature and relative humidity conditions at the time of test can therefore be expected to influence the outcome of tests on polymers much more than for these other materials. For this reason it is necessary to specify the ambient conditions under which the tests are to be performed. In addition to the external conditions, the state of the material at the time of testing will also be important. The conditions prevailing prior to the commencement of testing may therefore be expected to have an influence on the outcome of the tests and so once again should be subject to controls. 

Wear trials can be performed to investigate the influence of the measured values on the wear comfort of a real person. Those wear trials take place in a climatic chamber under standardized conditions. Heart rate, body core temperature and skin temperature were recorded as well as temperature and relative humidity in the nticroclimate between skin and clothing. Furthermore, subjects have to state their perception of temperature, humidity, and wear. 

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