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Homework Help: Analytical chemistry Problem

  1. Mar 25, 2008 #1
    This is the problem:

    You are doing a typical AA ( atomic absorption spectroscopy analysis)
    What you dont know is that the standard calibration curve is incorrect you have made your concentration twice as concentrated.

    For exable you believe that you have 2,4,6,8 ppm but actualy you have 4,8,12,16
    The curve that you have is completely linear and pass at (C=0).
    You are not allowed to go to you merk index or any table for that matter to check the molar absoptivity.

    Now how can I look at the concentration I have written and look at my abs and know that I have made all of my standards incorrectly?
    ( remeber line is linear and passes through 0 line but all your standards are wrong twice as concentrated)

    I was thinking you know your usualy A = epsilon*b*c
    A1+A2+A3/C1+C2+C3 = A1/C1

    But for some reason I I find something that works and I go to proove it and it doesnt work again. ( no matter what Im always reduced to solving the problem using molar absoptivity from a text book or a table)

    What other way is there to solve this problem I can feel the answer but for some unknown reason I cant seem to put it on paper.
    I would greatly appreciate some help on this and if you can make diagrams that would be the best. Thx
  2. jcsd
  3. Mar 25, 2008 #2


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    If this is a routine analysis you are performing repeatedly the simplest way would be to qualitatively compare absorption values from previous sets of standards.

    If you aren't allowed to consult literature the you have to fall back on your documentation.

    I work in a "Regulated Environment" (GLP) and we have some safeguards in our systems designed to avoid such errors:

    1. Primary STDs are prepared in duplicate and tested agaist each other to ensure replicate preparation accuracy.

    2. A validated STD preparation plan is used and a preparation record is made contemporaneously with the preparation of each STD in the curve.

    Without these records it is difficult to prove anything "after the fact".
  4. Mar 25, 2008 #3
    Oh darn it this question is messing me again it piss me off there not mathematical way to proove but hopefully by the early morning of tommorow ill have prooved withought a doudt that no matter what you do to the numbers or how dilute your solutions the only way is to check documentation, check tables for molar absorptivity or intuition since obviously the sample your anayzing for wont be on the graph that really then main one that usually gives it away for me lol.

    Hey thanks for answering man really appreciate it !
    If you need help with anything ill try to post some ideas
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