System or Instrument Blank

 It is a measure of system contamination and isthe instrumental respo  n se    in  the abs ence of any sample. When the background signal is constant and  measurable, the usual practice is to considerthat level to be the zero setting. It is generally used for analytical instrumentsbut is also applicable for instruments for sample preparation The instrument blank also identifies memory effects or carryover fro mprevious samples. It may become significant when a low-concentrationsample is analyzed immediately after a high concentration sample. This isespecially true where preconcentration and cryogenic steps are involved. Forexample, during the purge and trap analysis of volatile organics, somecomponents may be left behind in the sorbent trap or at a cold spot in theinstrument. So it is a common practice to run a deionized water blankbetween samples. These blanks are critical in any instrument, where samplecomponents may be left behind only to emerge during the next analysis