Amino acid analysis provides the best method for quantifying peptides and proteins yet remains one of the most difficult protein chemistry techniques to perform accurately. One approach taken to enhance the accuracy of AAA in our laboratory is to use in addition to an amino acid standard (Pierce Standard H) for instrument calibration, a standard protein solution of fixed concentration as a check that the calibration factors generate accurate protein quantification and that the system yields low error compositions. Any standard protein will serve this purpose; however we have found it convenient to use bovine serum albumin, Standard Reference Material 927, available from the National Institute of Standards and Technology (Standard Reference Materials Program, Building 202, Room 204, Gaithersburg, MD 20899-0001, Telephone 301-975-6776, Fax 301-948-3730). This BSA preparation is termed a 7% solution based on Biuret analysis and is provided in dilute NaCl primarily as a reference for clinical analyses of total protein by colorimetric methods. (Our AAA suggest that the concentration of NIST BSA solution 927a is lower than 7%; NIST BSA solution 927b is the currently available lot.) One vial of the BSA solution (2 ml) was diluted 1:35 with H2O and 50 equal aliquots frozen as stock solutions (yielding a life time supply for our needs). For AAA, a working solution was prepared by diluting the stock solution 1:10 with H2O and 10 ul aliquots (~1.6 ug protein) applied to our analyzer (PE ABI model 420H). The standard is hydrolyzed and analyzed routinely and protein concentration values falling within 10% of the expected value and compositional errors <=10% are considered satisfactory. Values falling outside of this range indicate that caution should be used in data interpretation from unknowns and alert us to the possibility of problems with the analysis/hydrolysis system. The stability of the BSA solution so far is good; the same dilution stored at 4 C has been used over the past 12 months with no change in concentration.
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