Laboratory buffers

The pH of blood is maintained at about 7.4. If the pK of C02 is 6.1, how can the HCOs/C02 help buffer blood at pH 7.4 Everything we have learned so far suggests that a buffer is effective only in the region of its pK. The key here is that in vivo the HCOr/C02 buffer is an open sysiem in which the concentration of dissolved COs is maintained constant. Any excess CO2 produced by the reaction H" + HCO -> H2O + CO2 is expelled by the lungs. In contrast, the usual laboratory buffer is a closed system. The concentration of conjugate acid increases when H reacts with the conjugate base. The effectiveness of the open system is illustrated below. 

Unhke the hydrophobic mechanism that forms Afi fibrils, metal-induced A precipitation proceeds through two pathways- 1. reversible, ionically-mediated oligomerization, 2. Cu-mediated A oxidation and cross-finking. High affinity chelators both inhibit and reverse Afi precipitation induced by metal ions, and dissolve deposits from post-mortem human brain tissue [ 143,183] (Table 2). A also recruits the contaminating metal ions in ordinary laboratory buffers to form the micronuclei that seed the precipitation of peptide solutions into fibrils. Therefore, even the formation of fibrils in the... 

These two buffer systems are common ones used in many laboratories. Take a closer look at the specific buffer chemistry of your blood, which operates just like these laboratory buffers. 

How Important buffers are for normal functioning of a body can be understood from the fact that the pH of blood is maintained strictly within the range 7.3 to 7.5. Death is more or less certain below a pH of 7.0 and above a pH of 7.9. In the laboratory, buffers are used for two main purposes (i) as reference standards for pH determination, and (ii) to maintain optimum acid-base reaction of a medium such as bacteria or tissue culture or an enzymatic reaction mixture. We will discuss more about some important biological buffers in a later section. 

This assay is not intended to yield the identities or exact concentrations of the carbamate and OP insecticides present, but rather the relative anticholinesterase activity. More specifically, this screening assay is intended to flag samples which, from a potential risk perspective, warrant further examination for specific carbamate and organophosphorus insecticide contamination. In this respect, the assay performed exceptionally well using standards in laboratory buffers. Although the assay underestimated the inhibition expected from laboratory standards, the AChE-based assay detected anticholinesterase activity present in all of the environmental samples. 

Even though the carbonic acid-hydrogen carbonate buffer system is crucial to the maintenance of the pH of blood, it has no practical use as a laboratory buffer solution. Can you think of a reason(s) for this [Hint Refer to data in Practice Example A of the Integrative Example in Chapter 16.]... 

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