Aqueous equilibria blood

Applications of Aqueous Equilibria Blood as a buffer system. Reactivity of strong and weak acids and bases. 

The human body generates a steady flow of acidic by-products during its normal metabolic processes. Foremost among these is carbon dioxide, which is a major product of the reactions the body uses to produce energy (see Section 14-). An average person produces from 10 to 20 mol (440 to 880 g) of CO2 every day. Blood carries CO2 from the cells to the lungs to be exhaled. In aqueous solution, dissolved CO2 is in equilibrium with carbonic acid H2 O + CO2 H2 CO3... 

Substances that undergo bioconcentration are hydrophobic and lipophilic, and therefore tend to undergo transfer from water media to fish lipid tissue. The simplest model of bioconcentration views the phenomenon on the basis of the physical properties of the contaminant and does not account for physiologic variables (such as variable blood flow) or metabolism of the substance. Such a simple model forms the basis of the hydrophobicity model of bioconcentration, in which bioconcentration is regarded from the viewpoint of a dynamic equilibrium between the substance dissolved in aqueous solution and the same substance dissolved in lipid tissue. 

The unbound drug in the systemic circulation is available to distribute extravascularly. The extent of distribution is mainly determined by lipid solubility and, for weak organic acids and bases, is influenced by the pK3/pH-dependent degree of ionization because only the more lipid-soluble non-ionized form can passively diffuse through cell membranes and penetrate cellular barriers such as those which separate blood from transcellular fluids (cerebrospinal and synovial fluids and aqueous humour). The milk-to-plasma equilibrium concentration ratio of an antimicrobial agent provides a reasonably... 

The MIPs have also been utilized as the recognition elements in pseudoimmunoassays. " In this approach, MIPs are substituted for antibodies to quantify the amount of analyte in a biological sample, such as blood plasma. Most MIP immunoassays are competitive binding studies in which a radio- or fluorescent-labeled analyte is added to a mixture of the MIP and imlabeled analyte. After equilibrium is reached, some fraction of the labeled species is bound to the polymer surface and thus can be separated from the supernatant. The supernatant is then analyzed via scintillation or fluorescence techniques to determine the concentration of the original unlabeled analyte. Mosbach et al. have demonstrated that MIP-based immunoassays can rival the selectivity of antibody-based assays. Imprinted polymers for the opioid receptor ligands enkephalin and morphine were prepared and showed submicromolar (pM) level selectivity in a radioligand competition assay in aqueous buffers. The analysis... 

Recall from Chapter 7 that, because the equilibrium constants of the blood buffer systems change with temperature, the pH of blood at the body temperature of 37°C is different than at room temperature. Hence, to obtain meaningful blood pH measurements that can be related to actual physiological conditions, the measurements should be made at 37°C and the samples should not be exposed to the atmosphere. (Also recall that the pH of a neutral aqueous solution at 3TC is 6.80, and so the acidity scale is changed by 0.20 pH unit.)... 

While analysing an equilibrium vapour phase, Sturtevant [132] developed a reaction method for determining ethanol in 20-jul blood samples. According to this method the sensitivity is increased by converting the ethanol and an internal standard (n-propanol) into nitrite derivatives. This technique was studied and further elaborated by Gessner [133], then used to determine ethanol and methanol in aqueous solutions [134]. The method is characterized by high speed, sensitivity (0.1 mg/ml) and reproducibility (the relative standard deviation for a blood sample containing 0.1 mg/ml of ethanol is 2.2%). 

As an example, we consider the equilibrium in aqueous solution between iron hexaquo complex cations and thiocyanate anions on the one hand and the blood red iron thiocyanate complex on the other which can be described in the following simplified manner ... 

The bloodstream is an aqueous environment so when a lipophilic molecule enters the bloodstream it will prefer to reside in fatty tissue. We can look at Figure 4.2.1.1 to think about this process. A lipophilic molecule will set up a dynamic equihbrium between the blood and fatty tissue (B-F), probably with the equilibrium heavily favoring the fatty tissue. This is equihbrium B-F in the figure. If more exposure occurs, then the concentration of the molecule in the blood increases and applying the LeChatelier effect we know that this will set up a new equilibrium with higher concentrations in both the blood and fatty tissue. 

A chemical equilibrium can only occur when the chemical system is closed. One reaction that gives a visual demonstration of aspects of a chemical equilibrium is based on a chemical test for iron(iii) ions (Fe ions) in solution. Aqueous iron(iii) ions react with thiocyanate ions (SCN ions) to produce a blood red colour (Figure 7.8). The red colour is due to the soluble complex ion, [Fe(SCN)] h... 

Two conditions must be met to extract an analyte from a matrix. First, there must be an exploitable difference in a chemical or physical property between the matrix and the analyte. Second, there must be an equilibrium condition that can be manipulated (equation 4-1). Consider a sample preparation protocol based on differences in volatility. A headspace method can be used to determine blood alcohol concentration. The premise underlying the extraction is a difference in volatility between ethanol and the aqueous-biological matrix of blood. The system is illustrated in Figure 4.2. The equilibrium at the requisite phase boundary is Phase boundar> ... 

The mode of action of PDMS-hydrophobed silica antifoams in aqueous surfactant solutions has been extensively stndied by Denkov et al. [53] and reviewed in detail in Chapter 4. Essentially the hydrophobed silica particles rupture the so-called air-water-oil pseudoemulsion film, thereby enabling the oil to emerge into the air-water surface. It is known that once they emerge into the air-water surface, drops of PDMS oils usually initially spread over that snrface, exhibiting either complete wetting or pseudo-partial wetting behavior (see Section 3.6.2). This means that the oil spreads as either a thick duplex layer or spreads and breaks up into lenses in equilibrium with a thin oil layer. Since such behavior is ubiquitous with aqueous surfactant solntions, it is reasonable to expect similar behavior when PDMS oil drops are introduced into the gas-blood surface. It is not, however, known whether complete or pseudo-partial wetting behavior is to be expected. 

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