Chemistry 155 Introduction to Instrumental Analytical Chemistry
Chemistry 155 Introduction to Instrumental Analytical Chemistry
Chemistry 155 Introduction to Instrumental Analytical Chemistry
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Chem <strong>155</strong> Unit 1 Page 54 of 3131.15.1 Internal Standards Example:In HPLC the sample is injected in<strong>to</strong> a flowing stream, and the signalis a peak in a plot of absorbance versus time (a chroma<strong>to</strong>gram).Often the volume of the injection will vary from injection <strong>to</strong> injection,so the peaks will vary in size!Peak 1 is theinternal standard.100 ppm NaNO 3 ,480 All mAu . sabsorbance10.5Peaks 2, 3 and 4 are otheringredients in the sample.1Peak 5 is theanalyte, a caffeinestandard, 25 ppm,530 mAu . sabsorbance100 ppm NaNO 3 ,520 mAu . sabsorbance00 400 800 1200 1600 2000 2400 2800 3200 3600 4000time / s10.500 400 800 1200 1600 2000 2400 2800 3200 3600 4000time / s10.523Chroma<strong>to</strong>gram1 is a standard.Did the caffeineconcentrationincrease fromchroma<strong>to</strong>gram1 <strong>to</strong> 2?Did the caffeineconcentrationincrease inchroma<strong>to</strong>gram1 <strong>to</strong> 3?Unknowncaffeine conc.630 mAu . s00 400 800 1200 1600 2000 2400 2800 3200 3600 4000time / sPage 54 of 313
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