Development of a dispersive liquid-liquid microextraction method for the determination of plastic additives in seawater.

A method using dispersive liquid-liquid microextraction (DLLME) prior to high performance liquid chromatography-diode array detection (HPLC-DAD) was developed to determine seven additives from the plastics industry (butylated hydroxytoluene, diisodecyl phthalate, irgafos 168, lawsone, quercetin, triclosan and vitamin E) in seawater samples. These compounds can reach seawater due to direct discharge from wastewater treatment plants and leaching from plastics and microplastics. The extraction was performed using 25 mL of seawater, 500 µL of 1-octanol (extraction solvent) and a stirring step instead of dispersive solvent. Additive concentrations were determined by LC-DAD on a C18 column with a mobile phase of acetonitrile and phosphoric acid aqueous solution (pH 3.5) by gradient elution. The analytical recoveries ranged from 82 to 93% for all compounds, except for lawsone (60%). Repeatability and intermediate precision were adequate with RSD < calculated values following the Horwitz equation at the concentration levels evaluated (0.06 and 0.24 mg L-1). All additives exhibited linear matrix calibration curves (R2 > 0.99). Detection limits ranged from 0.009 to 0.028 mg L-1 and quantification limits ranged from 0.027 to 0.084 mg L-1. Finally, the application of the method to real samples verified the method as accurate and applicable to seawater.

Mixed-mode chromatography of mixed functionalized analytes as the homologues of benzalkonium chloride. Application to pharmaceutical formulations.

In this work, a retention behavior based on mixed-mode reversed-phase (RP)/hydrophilic interaction liquid chromatography (HILIC) was observed for benzalkonium chloride (BAK) using a core-shell column functionalized with biphenyl groups. Although in the literature, the U-shaped retention was reported for polar compounds in mixed functionalized phases, in the present work, the behavior was dependent upon the chemical structure of the analyte with mixed functionality (ammonium group, a benzyl group and an alkyl chain) and on the high selectivity of the chromatographic column. The bimodal retention was observed for the four BAK homologues using a content of acetonitrile from 65 to 95% in the mobile phase. The data were adjusted to polynomial equations which allow for modeling and predicting the U-shaped retention. The salt concentration (50 and 100 mM), anion (formate and acetate) and cation (ammonium and triethylammonium) of the salt, pH (4 and 5) in the mobile phase were studied in order to understand their influence on the two retention modes. Significant electrostatic interactions were involved in the two retention modes, especially with a content of acetonitrile higher that 90%. Linear relationships between the retention factors of the four homologues were found in a wide range of %acetonitrile when the salt and triethylamine concentration, pH and nature of salt were changed. The differences found on the retention of the homologues, when increasing the alkyl chain length, were more significant in the RP mode due to predominant hydrophobic interactions. A pH decrease and a salt concentration increase caused a retention decrease for both modes. A decrease on of the retention was observed when acetate anion was replaced by formate anion. The different order of the polynomial equations according to the used mobile phase confirmed its relevant role in the interactions with the analytes and stationary phase. A mobile phase was selected (85% acetonitrile, pH 4 and 100 mM ammonium formate) for the BAK determination in cutaneous, otic and ophthalmic formulations with different active pharmaceutical ingredients and excipients. Low sample volume (500 µL) and short analysis time (<5 min) were some of the advantages of the proposed method. In addition, good analytical performance (R2 > 0.999, % RSD <4.5% for intra-day precision and <5.8% for inter-day precision, and recoveries in the 92-105% range) was obtained.

A Simple Method for the Determination of Triazines from Seawater in Accordance with the Directive 2013/39/EU.

Since the Directive 2013/39/EU included terbutryn to the list of priority substances of all water bodies, a previous method based on dispersive liquid-liquid micro-extraction (DLLME) for the determination of triazines in seawater has been modified. The main change consisted on the use of tandem mass spectrometry instead of diode array as detection technique. Due to the higher sensitivity of mass detector, sample volume was reduced and extraction solvent volume was optimized. The optimum extraction conditions were 5 mL of sample, 50 µL of 1-octanol and an agitation step instead of disperser solvent. The obtained analytical recoveries (73%-101% with relative standard deviations below 4%) meeting the requirements. The limits of quantification (between 0.016 and 0.021 µg L-1) were more than 10 times lower than the limit set by the European Directive 2013/39/EU for terbutryn (0.34 µg L-1). The proposed method was applied to the determination of the target compounds in seawater samples from A Coruña (Galicia, NW of Spain).

Application of a developed method for the extraction of triazines in surface waters and storage prior to analysis to seawaters of Galicia (northwest Spain).

A simple method based on solid-phase extraction combined with liquid chromatography for simultaneous determination of nine triazine herbicides (ametryn, atrazine, cyanazine, prometryn, propazine, simazine, simetryn, terbuthylazine, and terbutryn) in surface water samples was developed and validated. Under optimized conditions, 50 mL of water sample was pumped through the Oasis HLB cartridge, and triazines were eluted with 3 mL acetone. Finally the extract was concentrated to dryness, reconstituted with 1 mL methanol : water (1 : 1) and injected into the HPLC-DAD system. The stability of the herbicides on the cartridges at -18 and 4°C was also evaluated, and the recoveries obtained after three weeks of storage were satisfactory for all compounds. The analytical features of the proposed method were satisfactory: repeatability and intermediate precision were <10% and recoveries in spiked river water and seawater samples were higher than 93% for all compounds studied. Limits of quantification (varied from 0.46 to 0.98 µg L⁻¹) were adequately allowing the determination of these compounds at the levels requested by the 2008/105/EC Directive. Finally, this method was applied to the analysis of 50 seawater samples from Galicia (northwest Spain).

Sample preparation based on matrix solid-phase dispersion and solid-phase extraction cleanup for the determination of organochlorine pesticides in fish.

A method based on matrix solid-phase dispersion (MSPD) and SPE to determine 20 organochlorine pesticides (OCPs) in fish tissues (muscle and liver) was optimized in terms of the sorbents and elution solvents used for the analysis. The following analytical components were evaluated: ENVI-CarbTM and ENVI-18 as dispersing agents, Florisil and Florisil over alumina as cleanup adsorbents, and hexane and hexane-ethyl acetate (80 + 20) as elution solvents. The pesticides were determined by GC with electron capture detection. The best results were obtained with ENVI-Carb as a dispersing agent and an ENVI-Florisil co-column using 40 mL hexane-ethyl acetate (80 + 20) as the elution solvent. Analytical recoveries ranged between 75 and 130% except for beta-HCH in fish liver, and the RSD values were < 15% for most of the pesticides studied. Furthermore, sensitivity was sufficient (LOD of < 300 microg/kg) for all OCPs under study, in compliance with the tolerance limits of the U.S. Food and Drug Administration for OCPs in fish. The results were compared with those obtained by microwave-assisted extraction (MAE) and pressurized liquid extraction (PLE) in order to evaluate the performance of the MSPD procedure. The MPSD methodology was shown to be easy to use and fast, with a clear advantage relative to cost, because it does not need the expensive equipment required for MAE and PLE.