Direct and simultaneous determination of methionine sulfoxide and pyroglutamic acid impurities in Compound Amino Acid Injection-18 AA by ion-pair reversed-phase HPLC

Determination of Free Amino Acids in Banlangen Granule and its Fractions by Solid Phase Extraction Combined with Ion-pair Hig-h Perfor mance Liquid Chromatography using a Corona-charged Aerosol Detector (SPE-HPLC-CAD)

Background:

Banlangen granules are broad-spectrum effective antiviral drugs, and have a large clinical demand in China. Free amino acid is one of the main antiviral active ingredients of Banlangen granules. The pre-processing of samples by the existing pre-column derivatization reversed- HPLC method is complicated. Therefore, the determination of free amino acids (AAs) by underivatized ion-pair HPLC-CAD is advantageous for simplifying the preparation process and improving sensitivity.

Objective:

To better optimize AAs analysis methods, here a sensitive SPE-HPLC-CAD method with a better resolution was established for the determination of underivatized AAs in Banlangen Granule for the first time.

Method:

The analytes were separated only by HPLC using a Hypercarb column with gradient elution of solvent A (20 mM nonafluorovaleric Acid in water) and solvent B (0.3% trifluoroacetic acid in acetonitrile-0.3% trifluoroacetic acid in water (1:9, v/v)) at a flow rate of 0.15 mL/min. N2 gas pressure and evaporation temperature of CAD were held at a constant 58.6 psi and 60 ℃, respectively.

Results:

This method was linear over the respective concentration range of six amino acids. The precision, accuracy, stability and recovery were satisfactory in all samples examined. And the method was successfully applied to determination of free amino acids in Banlangen granules and its fractions. The total contents of six amino acids in 28 batches of Banlangen Granule were between 1.36 mg/g-11.62 mg/g.

Conclusion:

The proposed method could be a simple, accurate and sensitive alternative approach for the determination of free AAs in Banlangen Granule.

Ion Chromatography and Related Techniques in Carboxylic Acids Analysis

Ion chromatography (IC) is a variant of high-performance liquid chromatography. Its most important applications include the determination of inorganic and some organic ions in different types of liquid samples. The development of new types of stationary phases with various separation mechanisms, sample preparation methods, and detection modes has extended ion chromatography applications to practically all ionic and ionogenic substances, as well as extending sample types to include gaseous and solid matrices. Carboxylic acids and their derivatives are examples of compounds that are becoming more frequently analyzed using ion chromatography and related techniques. Their occurrence in the environment can be natural or anthropogenic in origin and are broadly used in various industries and daily life. This article discusses the applications of ion chromatography and related techniques for the determination of carboxylic acids in different types of liquid, solid, and gaseous matrices. It also presents detailed methodologies and literature data on this subject from the last 15 years.

Quantitation of Methionine Sulfoxide in Milk and Milk-Based Beverages-Minimizing Artificial Oxidation by Anaerobic Enzymatic Hydrolysis

Protein oxidation in milk products may entail flavor changes through reactions at methionine residues. However, little is known about the extent of methionine oxidation in milk and milk products. In the present study, a method for quantitation of methionine, methionine sulfoxide, and methionine sulfone by a stable isotope dilution assay using HILIC-ESI-MS/MS was established. For the quantitation of protein-bound analytes, anaerobic enzymatic hydrolysis was optimized to suppress artificial methionine oxidation. Moreover, the method allowed for monitoring of artificial oxidation by coincubation of the labeled probe [²H₈]methionine. The percentage of oxidized methionine was low in UHT milk (up to 1.6%) and evaporated milk (up to 8.8%), but higher in beverages such as cocoa milk drinks (up to 19.0%) and coffee milk drinks (up to 32.8%), resulting in methionine sulfoxide concentrations of up to 6.7 g/kg protein in the latter. These products are important dietary sources of methionine sulfoxide. Model studies revealed that methionine residues can be oxidized strongly in the presence of phenolic compounds such as catechin, caffeic acid, and gallic acid, which are present in cocoa and coffee and may account for the high extent of oxidation in commercial samples.