Medical brain notes 35

  Kinetic  Methods of Analysis A system   under   thermodynamic   control   is   in   a   state   of   equilibrium, and   its   signal   has   a   constant,   or   steady-state   value   (Figure   13.1a).   When a   system   is   under   kinetic   control,   however,   its   signal   changes   with   time (Figure   13.1b)   until   equilibrium   is   established.   Thus   far,   the   techniques we   have   considered   have   involved   measurements   made   when   the system is at   equilibrium. By   changing   the   time   at   which   measurements   are   made,   an   analysis  can   be   carried   out   under   either   thermodynamic   control...

  Methods Based on Chemical Kinetics The   earliest   examples   of   analytical   methods   based   on   chemical   kinetics,   which   date from   the   late   nineteenth   century,   took   advantage   of   the   catalytic   activity   of   en- zymes.   Typically,   the   enzyme   was   added   to   a   solution   containing   a   suitable   sub- strate,   and   the   reaction   between   the   two   was   monitored   for   a   fixed   time.   The   en- zyme’s   activity   was   determined   by   measuring   the   amount   of   substrate   that   had  reacted.   Enzymes   also   were   used   in   procedures   for   the   quantitative ...

  Theory and Practice Every   chemical   reaction   occurs   at   a   finite   rate   and,   therefore,   can   potentially   serve as   the   basis   for   a   chemical   kinetic   method   of   analysis.   To   be   effective,   however,   the chemical   reaction   must   meet   three   conditions.   First,   the   rate   of   the   chemical   reac- tion   must   be   fast   enough   that   the   analysis   can   be   conducted   in   a   reasonable   time, but   slow   enough   that   the   reaction   does   not   approach   its   equilibrium   position   while the   reagents   are   mixing.   As   a   practical   limit,   re...