Furthermore, an “LCGC Troubleshooting” article, published soon after the ASTM A967 dossier, described the passivation and practical recommendations to keep a well-passivated high performance liquid chromatography (HPLC) instrument by using a 50% nitric acid solution as the last resource when stainless steel parts replacement is not a viable option (1). ASTM A967 also describes several tests to confirm the effectiveness of passivation, particularly concerning the removal of free iron. The American Society for Testing and Materials International (ASTM International) official standard A967 has been the official protocol since 1996 describing the chemical treatment for stainless steel parts via nitric acid, citric acid, and electrochemical treatment. However, 316 stainless steel is still subject to corrosion and rust under certain conditions. Specifically, 316 stainless steel, which contains up to 3% molybdenum, has been implemented in instrument and column hardware due to its superior resistance to chemical corrodents, such as brine solutions and sulphuric acid. Stainless steel has been the preferred material to manufacture HPLC columns due to its ease of fabrication and mechanical resistance to pressure. This article explores these solutions in more detail, particularly the recent adaptation and benefits of coated metal surfaces in LC. Such solutions encompass swapping stainless steel components for non-reactive polymers, “biocompatible” metals or alloys, the addition of additives into the mobile phase, pretreating the system with large amounts of sample or strong acids, and the use of coated stainless steel materials. As a result, many solutions that circumvent and mitigate this type of secondary interaction have been published or commercialized in the last few years. NSA represents a chromatographic challenge since it may lead to poor peak shape, low recovery, and poor performance from the high performance liquid chromatography (HPLC) system. Metal-analyte interaction is a type of nonspecific adsorption (NSA) that occurs mainly between acidic analytes and active adsorptive sites present in the metal surfaces of the fluidic path of any chromatographic system.
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