Various internal sta,ndards have been suggested to monitor physical losses during sample preparation and amino acid analysis by ion-exchange chromatography
(1,2). Norleucine, though widely used, is qucstionable for basic amino acid corrections in two-column systems. A separate, basic column standard is preferred for accurate corrections.'
Although most physical losses occur while removing the hydrolytic agent, subsequent errors are encountered during sample dilution, aliquot application to the column, and from daily variations within ion-exchange columns. Walsh and Brown suggested applying L-cr-amino-P-guanidinopropionic acid as a daily basic column monitor with the sample (2). Keutmann and Potts, to correct sample preparation errors, added homoarginine. They reported homoarginine stable up to 96 hr at 110ยฐC in pure 6 N HCl (3).
This communication deals with the suitability of the above two basic amino acids and +aminocaproic acid as internal standards for analyses of natural products.
Whole wheat and mature maize endosperm samples were reduced to flours and defatted with hexane in a Soxhlet apparatus. Air drying at room temperature removed excess solvent. All samples were hydrolyzed with 6N HCl for 24 hr at 10~110ยฐC. The wheat flour hydrolyzaten were prepared in sealed glass tubes under vacuum while the maize samples (earlier studies) were refluxed in an excess (4000-fold by weight) of 6 S HCI. The hydrolyzates were dried at less than 47" with a glass-Teflon rot'ary evaporator, solubilized with pH 2.2 citrate buffer, and filtered with 'Contribution