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 This method (first described and put into use as an automated method in 1953 by Stein, Moore and Spachman) is considered the "Gold Standard" for amino acid analysis. The reproducibility of retention times, run-to-run and column-to-column, is excellent. Since consistency in pH and molarity of the eluents are primary in reproducibility, all reagents are purchased directly from commercial manufacturers rather than being formulated in house. Although within-lot reproducibility of the Ninhydrin coloring reagent is excellent, we periodically recalibrate the peak areas of the amino acids standards for each bottle of Ninhydrin used. We have spent years refining the classical ion-exchange post column Ninhydrin method of amino acid analysis for optimum accuracy, precision, and efficiency. Even though this classical method requires extra time and costly reagents and instrumentation, we have determined that the alternative methods commercially available cannot achieve the level of precision that we demand in serving our clients needs.
Following amino acid analysis and quantification, an Excel spreadsheet is typically created; analysis results are reported in the spreadsheet as the average micromoles/L per amino acid, mg/L, or gm/L depending on client requests. Because various matrices require different amino acid profiles, we offer analysis tailored to a wide variety of materials. |
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Amino acid analysis is performed on Hitachi High-Technologies Model L-8900 dedicated amino acid analyzers. The Hitachi analyzers are under the manufacturer's (Hitachi) service contract for Preventive Maintenance (biyearly) and routine servicing as required. These instruments incorporate 6.0mm ID x 40mm cation exchange columns, multiple sequential lithium-based eluents, and lithium hydroxide for column regeneration. Absorbance is measured at 440 and 570 nm following post-column color development by Ninhydrin reagent at 131 degrees C. Data acquisition and management is accomplished with a computer running EZChrom Elite for Hitachi version 3.1.5b chromatography software. (S)-2-Aminoethyl-1- cysteine (S2AEC) or Glucosaminic acid is added to the sample as the internal standard.
