Medical brain notes 35

  The Language of Analytical Chemistry A nalytical   chemists   converse   using   terminology   that   conveys specific   meaning   to   other   analytical   chemists.   To   discuss   and   learn   analytical   chemistry   you   must   first   understand   its   language.   You   are probably already familiar with some analytical terms, such as “accuracy”   and   “precision,”   but   you   may   not   have   placed   them   in   their appropriate analytical context. Other terms, such as “analyte” and “matrix,”   may   be   less   familiar.

  Analysis, Determination, and Measurement The   first   important   distinction   we   will   make   is   among   the   terms   “analysis,”   “deter- mination,”   and   “measurement.”   An   analysis   provides   chemical   or   physical   infor- mation   about   a   sample.   The   components   of   interest   in   the   sample   are   called   ana- lytes,   and   the   remainder   of   the   sample   is   the   matrix.   In   an   analysis   we   determine the   identity,   concentration,   or   properties   of   the   analytes.   To   make   this   determina- tion   we   measure   one   or   more   of   the   analyte’s   chemical   or ...

  Techniques, Methods, Procedures, and Protocols Suppose   you   are   asked   to   develop   a   way   to   determine   the   concentration   of   lead   in drinking   water.   How   would   you   approach   this   problem?   To   answer   this   question   it helps   to   distinguish   among   four   levels   of   analytical   methodology:   techniques,   meth- ods,   procedures,   and   protocols. A   technique   is   any   chemical   or   physical   principle   that   can   be   used   to   study   an analyte.   Many   techniques   have   been   used   to   determine   lead   levels. 2   For   example,   in graphite   furnace   atomic   absorpt...

  Classifying Analytical Techniques Analyzing   a   sample   generates   a   chemical   or   physical   signal   whose   magnitude   is   pro- portional   to   the   amount   of   analyte   in   the   sample.   The   signal   may   be   anything   we can   measure;   common   examples   are   mass,   volume,   and   absorbance.   For   our   pur- poses   it   is   convenient   to   divide   analytical   techniques   into   two   general   classes   based on   whether   this   signal   is   proportional   to   an   absolute   amount   of   analyte   or   a   relative amount of   analyte. Consider   two   graduated   cylinders,   each   containi...

  Selecting an Analytical Method A   method   is   the   application   of   a   technique   to   a   specific   analyte   in   a   specific   matrix. Methods   for   determining   the   concentration   of   lead   in   drinking   water   can   be   devel- oped   using   any   of   the   techniques   mentioned   in   the   previous   section.   Insoluble   lead salts   such   as   PbSO 4   and   PbCrO 4   can   form   the   basis   for   a   gravimetric   method.   Lead forms   several   soluble   complexes   that   can   be   used   in   a   complexation   titrimetric  method   or,   if   the   complexes   are   highly   absorbi...