Mass balance accounting

Bucks, D.A.W., Guy, R.H. Maibach, H.I. (1990) Percutaneous penetration and mass balance accountability technique and implications for dermatology. J. Toxicol, cutan. ocul. Toxicol., 9, 439-451... 

Step 3 Mass balance. This is a little tricky. From Reaction 8-30, we could say that the concentrations of all species containing OH equal two times the concentrations of all magnesium species. However, Reaction 8-32 also creates 1 OH for each H+. The mass balance accounts for both sources of OH- ... 

In this section, the concentration is represented by C. Mass balance accounting in terms of the number of moles and the fractional conversion is discussed in Sec. 7 and can be very useful. The rate of reaction is r the flow rate in moles is Na the volumetric flow rate is V reactor volume is Vr. Several equations are presented without specification of units. Use of any consistent unit set is appropriate. 

Direct evidence for accumulation of PAHs by species that are able to metabolize these compounds is often difficult to obtain because of the rapid rate of biotransformation to metabolites that are not routinely detected by standard analytical techniques. If appreciable metabolism is occurring, then the bioaccumulation study needs to be performed using radiolabeled compounds to allow a mass-balance accounting of parent compounds and metabolites. Hence, for metabolically active species that accumulate very little parent compound, it may be more appropriate to monitor the metabolic products for evidence of accumulation. Two techniques have been developed to measure PAH metabolites one utilizes HPLC fluorescence detection of metabolites in bile of teleosts and the other uses P-postlabeling for DNA adducts that occur as a result of the interaction of metabolites and cellular DNA. Both techniques have displayed a highly positive correlation with environmental concentrations, making them useful for monitoring populations in our coastal areas. 

It is complemented by the mass balance accounting for the concentration of ZnO in the liquid phase ... 

Knowing where waste is going is the key to reducing it. When reducing waste from process operations, a steady-state mass balance is not usually comprehensive enough. A balance that takes into account start-up, shutdown, and product changeovers is required. 

We can account for the effect of an auxiliary complexing agent, such as NH3, in the same way we accounted for the effect of pH. Before adding EDTA, a mass balance on Cd + requires that the total concentration of Cd +, Ccd, be... 

Stea.dy-Sta.teFeedforwa.rd, The simplest form of feedforward (FF) control utilizes a steady-state energy or mass balance to determine the appropriate manipulated variable adjustment. This form of feedforward control does not account for the process dynamics of the disturbance or manipulated variables on the controlled variable. Consider the steam heater shown ia Figure 15. If a steady-state feedforward control is designed to compensate for feed rate disturbances, then a steady-state energy balance around the heater yields ... 

Phase II Mass Balance. (/) Determine raw material iaputs. 2) Record water usage. 3) Assess present practice and procedures. (4) Quantify process outputs. (5) Account for emissions to atmosphere, to wastewater, and to off-site disposal. (6) Assemble iaput and output information. (7) Derive a preliminary mass balance. (8) Evaluate and refine the mass balance. 

The population balance accounts for the number of particles at each size in a continuous distribution and may be thought of as an extension of the more familiar overall mass balance to that of accounting for individual particles. 

Mass balance considerations apply tlie law of tlie conservation of mass to account for each constituent entering and leaving a system. Constituents that do not comprise the product are either retained by the system or released from tlie system as waste. This method requires a quantitative analysis of the influent and effluent streams and an understanding of chemical reactions occurring within tlie system. 

In transient elongational flow degradation, it was determined in the authors laboratory, by a detailed mass balance, that main chain scission accounted for >95% of the degradation in dilute solution. Any other type of depolymerization, if present, should then be of minor importance. 

A second kind of model is briefly treated, based on isotopic mass balance arguments, and it is shown that large isotopic discrimination during methano-genesis in ruminants may account for data trends when comparing herbivores and carnivores. A third class of model is sketched at the level of biochemical flows, where some fundamental points are made concerning points where the isotopic composition of metabolites may be altered. The relevance of this to nitrogen isotopic enrichment is considered. 

At small space times, the C5 hydrocarbons could not account for all the PA converted, although no PA was found in the reactor outlet a similar observation was reported by La Vopa and Satterfield (17). But at higher space time the C5 hydrocarbons do account for more than 90% of the PA converted. Thus only the data at very high space time were used to calculate Kn (Fig. 5). The adsorption constants of DHQ were obtained in the same way. The mass balance of DHQ and CHE was always good. The resulting adsorption constants are given in Table 4. 

However, conducting a complete LCA is very time consuming. Fortunately, simple mass balancing may already indicate most relevant requirements for action. This was illustrated by one case study concerning a pharmaceutical intermediate (Scheme 5.1). Compared to LCA, the system boundaries of mass balancing are relatively narrow. For instance, the case study focuses on the chemical reaction and does not take into account the production of substrates. In this respect, a look at two reduction reactions of the synthetic routes via B and via C is worthwhile (Scheme 5.1). 

Mass balance cannot be strictly obtained in any open field study however, in field-scale groundwater studies, accounting for as much of the applied material as possible in order to interpret the results is particularly important. With the pesticide diluted over a large mass of soil and groundwater, concentrations in some samples may be low and hard to detect, but the total mass leaching may be large. 

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