Determination of purity values of amino acid reference materials by mass balance method: an approach to the quantificati
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Determination of purity values of amino acid reference materials by mass balance method: an approach to the quantification of related structure impurities Hong Liu 1 & Pui Sze Cheow 1 & Sharon Yong 1 & Yizhao Chen 1 & Qinde Liu 1
&
Tang Lin Teo 1 & Tong Kooi Lee 1
Received: 15 July 2020 / Revised: 26 August 2020 / Accepted: 2 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract A systematic procedure for the determination of purity values of amino acid reference materials was developed by use of mass balance method where four categories of impurities (related structure impurities (RSIs), water, organic solvent residue (OSR), and non-volatile residue (NVR)) were quantified separately. The amount of RSIs was determined using a combination of three quantification methods. To ensure metrological traceability in the determination of RSIs, at least one such impurity in each candidate amino acid reference material was quantified using liquid chromatography–isotope dilution tandem mass spectrometry (LC-IDMS/MS). Other RSIs were determined using external calibration liquid chromatography–tandem mass spectrometry (LCMS/MS) or o-phthaldialdehyde (OPA) derivatization, followed by liquid chromatography–ultraviolet (LC-UV) measurement. As the UV absorption of most RSIs came basically from the same chromophore after OPA derivatization, a relative peak area approach was used in the LC-UV method to quantify the amount of RSIs by comparing their peak areas with that of a reference RSI. The reference RSI was pre-selected and the amount determined by LC-IDMS/MS separately. The absence of D-amino acids was confirmed using Marfey’s reagent derivatization, followed by LC-UV analysis. The amounts of water, OSR, and NVR were measured using Karl Fischer coulometry, gas chromatography–mass spectrometry (GC-MS) and thermogravimetry, respectively. By using this procedure, four amino acid (L-valine, L-leucine, L-isoleucine, and L-phenylalanine) certified reference materials (CRMs) were developed from the candidate materials. The homogeneity and stability of the CRMs were demonstrated by use of LC-IDMS/MS or OPA-LC-UV method, following the principles in ISO 17034 and ISO Guide 35. Keywords Amino acids . Isotope dilution mass spectrometry . Mass balance method . OPA derivatization . Protein analysis . Related structure impurity
Introduction In the past decades, the importance of proteins in the areas of clinical chemistry and research, especially those for therapeutic and diagnostic purposes, has led to an increasing interest and demand in the accurate determination of these materials
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00216-020-02936-7) contains supplementary material, which is available to authorized users. * Qinde Liu [email protected] 1
Chemical Metrology Division, Applied Sciences Group, Health Sciences Authority, 1 Science Park Road, #01-05/06, The Capricorn, Singapore Science Park II, Singapore 117528, Singapore
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