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 ```Please comment on "first order process". I would just like to know what is it all about, in reference to protein purification or isolation. Ted.```
 ```Hello Ted, Nice to see you back here again. Your question takes me back to my early days of college biochemistry classes. A first order process is one that follows a fairly simple dynamic. As "A" doubles, "B" doubles. If "A" is halved, then "B" is halved as well. Another way of saying this is that the relationship betwen "A" and "B" is linear. "A" and "B" can be a lot of different things, but the term "first order process" probably finds most use in describing chemical processes. And in the context of chemistry (and biochemistry, and protein separations), first-order processes often refer to the rate of a reaction, or to the concentration of chemical constituents, which can make for some complext math, but the overall idea remains the same. Here's an example of the use of the term pertaining to protein purification (not the clearest example, but on point for your question): ----- http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3443699&dopt=Abstract Isoelectric protein purification by orthogonally coupled hydraulic and electric transports in a segmented immobilized pH gradient. ...Macromolecules and small ions leave the flow chamber at a rate corresponding to a first order reaction kinetics (the plot of log C vs. time being linear). ----- In other words, the "A" and "B" of this situation -- the variables involved -- are time and protein concentration, and the two follow first-order process dynamics -- plotting time and log C (concentration) on a graph gives you a smooth, straight line. Here are some other references to the term, with some fairly straightforward definitions: http://www.biology-online.org/dictionary/first-order_reaction first-order reaction A reaction the rate of which is proportional to the concentration of the single substance undergoing change; radioactive decay is a first-order process, defined by the equation -(dN/dt)=kN, where N is the number of atoms subject to decay (reaction), t is time, and k is the first-order decay (reaction) constant, i.e., the fraction of all atoms decaying per unit of time. http://www.bio.hw.ac.uk/edintox/glossall.htm SOME TERMS USED IN TOXICOLOGY AND CHEMICAL SAFETY First-order process A first order process is a chemical process where the rate is directly proportional to the amount of chemical present. Any process changing at a constant fractional rate. ----- http://www.sci.tamucc.edu/pals/moslen/LECTURE3.htm Toxicokinetics One compartment model: Plot of plasma concentration versus time yields a straight line Rapidly equilibrate between blood and tissues relative to the rate of elimination Assumes that changes occurring in the plasma also reflect changes in the tissue conc. Usually a First order process: The rate of elimination is directly proportional to the amount of chemical in the body at that time. Semilogarithmic plot of plasma concentration versus time yields a single straight line Half-life is independent of dose The concentration of the chemical in plasma and other tissues decreases by some constant fraction per unit time. ----- ----- http://64.233.187.104/search?q=cache:92DrAvsKriAJ:clinicaloptions.com/x/module/module.asp%3FmodSpec%3Dpk_fletcher%26site%3D/hiv/+(dictionary+OR+definition)+%22first+order+process%22+protein&hl=en Elimination The elimination phase is reached after absorption is largely completed and after equilibrium between plasma and tissues occurs. For most drugs, elimination of drug from the body is a first-order process. This means that the rate of elimination is proportional to the amount of drug in the body. This rate of elimination is often referred to as a first-order rate constant (k or ß). The elimination half-life (t1/2) is defined as the length of time it takes for the plasma concentration to fall by 50% during the elimination phase. A characteristic of the elimination phase for a drug that has first-order elimination is that the half-life is constant. For example, if a drug has a 4-hour half-life, it would take 4 hours for the drug concentration to drop from 80 to 40 mg/L; following another half-life (4 hours), the concentration would again decrease by half to 20 mg/L. After 5 half-lives, 97% of the drug would be eliminated, and this is the basis for the dosing principle that it takes 5 elimination half-lives to eliminate a drug from the body. ----- I trust this information offers a useful explanation for you. However, please don't rate this answer until you are satisfied that you have everything you need. If you'd like more information, just post a Request for Clarification to let me know, and I'll be sure to get back to you. Cheers, pafalafa-ga search strategy: Google search on [ (definition OR glossary) "first order process" ]```