Trends in sample preparation and separation methods for the analysis of very polar and ionic compounds in environmental water and biota samples

Abstract

Recent years showed a boost in knowledge about the presence and fate of micropollutants in the environment. Instrumental and methodological developments mainly in liquid chromatography coupled to mass spectrometry hold a large share in this success story. These techniques soon complemented gas chromatography and enabled the analysis of more polar compounds including pesticides but also household chemicals, food additives, and pharmaceuticals often present as traces in surface waters. In parallel, sample preparation techniques evolved to extract and enrich these compounds from biota and water samples. This review article looks at very polar and ionic compounds using the criterion log P ≤ 1. Considering about 240 compounds, we show that (simulated) log D values are often even lower than the corresponding log P values due to ionization of the compounds at our reference pH of 7.4. High polarity and charge are still challenging characteristics in the analysis of micropollutants and these compounds are hardly covered in current monitoring strategies of water samples. The situation is even more challenging in biota analysis given the large number of matrix constituents with similar properties. Currently, a large number of sample preparation and separation approaches are developed to meet the challenges of the analysis of very polar and ionic compounds. In addition to reviewing them, we discuss some trends: for sample preparation, preconcentration and purification efforts by SPE will continue, possibly using upcoming mixed-mode stationary phases and mixed beds in order to increase comprehensiveness in monitoring applications. For biota analysis, miniaturization and parallelization are aspects of future research. For ionic or ionizable compounds, we see electromembrane extraction as a method of choice with a high potential to increase throughput by automation. For separation, predominantly coupled to mass spectrometry, hydrophilic interaction liquid chromatography applications will increase as the polarity range ideally complements reversed phase liquid chromatography, and instrumentation and expertise are available in most laboratories. Two-dimensional applications have not yet reached maturity in liquid-phase separations to be applied in higher throughput. Possibly, the development and commercial availability of mixed-mode stationary phases make 2D applications obsolete in semi-targeted applications. An interesting alternative will enter routine analysis soon: supercritical fluid chromatography demonstrated an impressive analyte coverage but also the possibility to tailor selectivity for targeted approaches. For ionic and ionizable micropollutants, ion chromatography and capillary electrophoresis are amenable but may be used only for specialized applications such as the analysis of halogenated acids when aspects like desalting and preconcentration are solved and the key advantages are fully elaborated by further research.

Sample Preparation to Determine Pharmaceutical and Personal Care Products in an All-Water Matrix: Solid Phase Extraction

“…Generally, compounds with polar characteristics are more suitable for LC, and those with non-polar properties are more amenable to GC; most PPCPs are polar or moderately polar [24]. Surprisingly, some contemporary review articles either cover broader aspects of environmental analysis [25][26][27], or focus on a particular type of extraction process (e.g., microextraction, use of nanomaterials, magnetic, ultrasonic, etc.) [28][29][30] but do not cover the entire sample preparation.…”

Isolation of three polyoxins by reversed‐phase liquid chromatography with pure aqueous mobile phase

“…In recent years, HILIC has been widely used for the separation of highly polar compounds both at analytical [1][2][3][4][5] and preparative [6][7][8] scales. However, a solubility issue in a high proportion of organic solvent is still a problem that has to be faced when water-soluble samples are analyzed, and this problem becomes particularly prominent at the preparative scale: Large injection volume of sample solution into the mobile phase can easily cause peak distortions.…”

Miniaturization of an extraction protocol for the monitoring of pesticides and polar transformation products in biotic matrices

“…The QuEChERS (quick, easy, cheap, effective, rugged, and safe) method (Anastassiades et al 2003) is one of the most universal extraction approach for multi-residue analysis of pesticides, including polar pesticides. It usually ensures good extraction rates (ERs) for a large number of substances (Knoll et al 2020). This method was successfully applied to solid matrices with different levels of complexity such as fruit and vegetables (Lehotay et al 2010;Koesukwiwat et al 2010), meat and fish (Lazartigues et al 2011;Lichtmannegger et al 2015;Oliveira et al 2018), or food from animal origin (Giroud et al 2013;Golge et al 2018;Song et al 2019).…”

“…Another disadvantage of most current extraction methods is the use of high sample masses, usually greater than 1 g, that can be very difficult to obtain for many environmental matrices. This hinders the study of PPP transfers in food webs for two reasons: (1) it may not be possible to collect enough biomass to analyze pesticides in smaller organisms such as insects or small fish (Knoll et al 2020); or (2) individuals must be pooled, which may lead to less accurate results (Roche et al 2009). This is typically the case for MIs (e.g., insect or crustacean larvae), which have small individual masses but play a key role in trophic chains by ingesting plant matter and then being consumed by predators (Four et al 2019).…”