Experimental design approaches to optimize ultrasound-assisted simultaneous-silylation dispersive liquid-liquid microextraction for the rapid determination of parabens in water samples.

This work describes a rapid solvent-minimized process to effectively determine four common paraben preservatives (methyl-, ethyl-, propyl- and butyl-paraben) in surface water samples. The method involved the use of a combination of a novel ultrasound-assisted simultaneous-silylation within dispersive liquid-liquid microextraction (UASS-DLLME) with detection by gas chromatography-tandem mass spectrometry (GC-MS/MS). To overcome the challenges related to the different experimental conditions, multivariate experimental design approaches conducted by means of a multilevel categorical design and a Box-Behnken design were utilized to screen and optimize parameters that have significant influences on the efficiency of silylation and extraction. The method was then validated and shown to provide low limits of quantitation (LOQs; 1-5 ng L-1), high precision (3-11%), and satisfactory mean spiked recoveries (accuracy; 79-101%). Upon analyzing samples of surface water obtained from the field, we found that, in total, there was a relatively high concentration of the target parabens ranging from 200 to 1389 ng L-1. The sources of the elevated levels of these parabens may be from the release of untreated municipal wastewater in this region, and also due to the widespread application of parabens in personal care and food products.

Determination of benzotriazole and benzothiazole derivatives in marketed fish by double-vortex-ultrasonic assisted matrix solid-phase dispersion and ultrahigh-performance liquid chromatography-high resolution mass spectrometry.

Benzotriazoles (BTRs) and benzothiazoles (BTs) are two groups of emerging concern and high production volume contaminants. Via the biomagnification of the food web, they could jeopardize human health. In this work, rapid determining the presence of five BTRs and two BTs in marketed fish was performed by a novel double-vortex-ultrasonic assisted matrix solid-phase dispersion (DVUA-MSPD) and UHPLC-electrospray ionization (+)-quadrupole time-of-flight mass spectrometry detection. Unlike traditional MSPD, we simplified the method without the use of mortar/pestle and SPE-column procedures. The DVUA-MSPD factors were screened by a multilevel categorical design, and then optimized by Box-Behnken Design plus with response surface methodology. The limits of quantification were 0.15-2 ng g-1 (dry weight). The satisfactory average recovery ranged from 70% to 93% with RSDs less than 9%. The developed method was successfully applied for the rapid determination of selected BTRs and BTs in fish samples at trace-level.

Optimization of double-vortex-assisted matrix solid-phase dispersion for the rapid determination of paraben preservative residues in leafy vegetables.

The extensive use of preservatives during the growth, transport and storage of vegetables has been a concern because of their known or suspected toxicity that jeopardizes human health. This paper reports the development of a technique that rapidly determines the presence of five paraben preservative residues in leafy vegetables using double-vortex-assisted matrix solid-phase dispersion (DVA-MSPD) and UHPLC-electrospray ionization(-)-quadrupole time-of-flight mass spectrometry detection. We simplified the original MSPD technique by eliminating the use of mortar/pestle and SPE-column procedures. The DVA-MSPD factors were screened by a multilevel categorical design, and then optimized by Box-Behnken Design plus response surface methodology. The limits of quantification were 1.2-1.8 ng g-1 (dry weight). The satisfactory average recoveries were 85-104% with RSDs less than 10%. The developed method was successfully employed for the rapid determination of selected paraben residues at trace-level in leafy vegetable samples.

Dual-vortex-assisted matrix solid-phase dispersion coupled with isotope-dilution ultrahigh-performance liquid chromatography-high resolution mass spectrometry for the rapid determination of parabens in indoor dust samples.

A reliable and straightforward method was developed for the rapid determination of nine parabens (methyl-, ethyl-, propyl-, butyl-, isopropyl-, isobutyl-, pentyl-, hexyl-, and benzyl-parabens) in indoor dust by a mortar/pestle-free and column-free dual-vortex-assisted matrix solid-phase dispersion (DVA-MSPD) technique. After that, they were determined by isotope-dilution ultrahigh-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-qTOF-MS, or called UHPLC-HRMS) and operating in negative electrospray ionization mode. Optimization of the DVA-MSPD was done using Box-Behnken Design along with response surface methodology. Validation was done by measuring and calculating selectivity, limits of detection (LOD), limits of quantitation (LOQs), precision and trueness (accuracy) of intra- and inter-day analysis. The LOQs of the method ranged from 0.9 to 2.8 ng/g. High precisions for both intra- and inter-day analysis were obtained ranging from 1 to 8%. Excellent trueness (or mean extraction recovery) varied from 93 to 104%. The DVA-MSPD combined with isotope-dilution UHPLC-qTOF-MS was successfully applied to determine parabens in indoor dust samples from office rooms and private houses, and the total concentrations ranged from 55 to 686 ng/g.

Ultrasound-assisted emulsification microextraction for rapid determination of unmetabolized synthetic polycyclic and nitro-aromatic musks in human urine.

An effective method to rapidly determine the presence of seven unmetabolized synthetic musks in human urine samples is developed. The target musks are five synthetic polycyclic musks (i.e., celestolide (ADBI), phantolide (AHMI), traseolide (ATII), galaxolide (HHCB), tonalide (AHTN)), and two nitro-aromatic musks (i.e., musk xylene (MX) and musk ketone (MK)). The method involved an ultrasound-assisted emulsification microextraction (USAEME) coupled with gas chromatography-mass spectrometry (GC-MS). The factors that affect USAEME efficiency were optimized in detail, and the optimized procedure involved the rapid injection of 50 µL of carbon tetrachloride into 1.0 mL of urine sample (contained 0.1-g of sodium chloride) in a conical bottom glass tube. After 1.0 min ultrasonication and 3 min centrifugation (at 7000 rpm), the sedimented extract 10 µL was directly injected into the GC-MS system. The limits of quantitation (LOQs) varied from 0.1 to 0.5 ng/mL. The precisions for both repeatability and reproducibility were <8%. The trueness varied from 79 to 96% with the RSD ranging from 2 to 8%. The total concentrations of the seven unmetabolized target musks in collected human urine samples were in the range from 0.93 to 3.74 ng/mL. HHCB and AHTN were detected in all the collected samples, and the daily excretion doses were evaluated.

Vortex-assisted liquid-liquid microextraction for the rapid screening of short-chain chlorinated paraffins in water.

The rapid screening of trace levels of short-chain chlorinated paraffins in various aqueous samples was performed by a simple and reliable procedure based on vortex-assisted liquid-liquid microextraction combined with gas chromatography and electron capture negative ionization mass spectrometry. The optimal vortex-assisted liquid-liquid microextraction conditions for 20 mL water sample were as follows: extractant 400 µL of dichloromethane; vortex extraction time of 1 min at 2500 × g; centrifugation of 3 min at 5000 × g; and no ionic strength adjustment. Under the optimum conditions, the limit of quantitation was 0.05 µg/L. Precision, as indicated by relative standard deviations, was less than 9% for both intra- and inter-day analysis. Accuracy, expressed as the mean extraction recovery, was above 91%. The vortex-assisted liquid-liquid microextraction with gas chromatography and electron capture negative ionization mass spectrometry method was successfully applied to quantitatively extract short-chain chlorinated paraffins from samples of river water and the effluent of a wastewater treatment plant, and the concentrations ranged from 0.8 to 1.6 µg/L.

Optimization of dispersive micro solid-phase extraction for the rapid determination of benzophenone-type ultraviolet absorbers in aqueous samples.

A solvent-free method for the rapid analysis of six benzophenone-type UV absorbers in water samples is described. The method involves the use of dispersive micro solid-phase extraction (DmSPE) followed by the simultaneous silylation and thermal desorption (SSTD) gas chromatography-mass spectrometry (GC-MS) operating in the selected-ion-storage (SIS) mode. A Plackett-Burman design was used for screening and a central composite design (CCD) for optimizing the significant factors was applied. The optimal experimental conditions involved immersing 1.5mg of the Oasis HLB adsorbent in a 10mL portion of water sample. After vigorous shaking for 1min, the adsorbents were transferred to a micro-vial, and were dried at 122°C for 3.5min, after cooling, 2µL of the BSTFA silylating reagent was added. For SSTD, the injection-port temperature was held at 70°C for 2.5min for derivatization, and the temperature was then rapidly increased to 340°C to allow the thermal desorption of the TMS-derivatives into the GC for 5.7min. The limits of quantitation (LOQs) were determined to be 1.5-5.0ng/L. Precision, as indicated by relative standard deviations (RSDs), was equal or less than 11% for both intra- and inter-day analysis. Accuracy, expressed as the mean extraction recovery, was between 87% and 95%. A preliminary analysis of the municipal wastewater treatment plant (MWTP) effluent and river water samples revealed that 2-hydroxy-4-methoxybenzophenone (BP-3) was the most common benzophenone-type UV absorber present. Using a standard addition method, the total concentrations of these compounds ranged from 5.1 to 74.8ng/L.

Dispersive micro solid-phase extraction for the rapid analysis of synthetic polycyclic musks using thermal desorption gas chromatography-mass spectrometry.

A simple and solvent-free method for the rapid analysis of five synthetic polycyclic musks in water samples is described. The method involves the use of dispersive micro solid-phase extraction (D-µ-SPE) coupled with direct thermal desorption (TD) gas chromatography-mass spectrometry (GC-MS) operating in the selected-ion-storage (SIS) mode. The parameters affecting the extraction efficiency of the target analytes from water sample and the thermal desorption conditions in the GC injection-port were optimized using a central composite design method. The optimal extraction conditions involved immersing 3.2mg of a typical octadecyl (C18) bonded silica adsorbent (i.e., ENVI-18) in a 10mL water sample. After extraction by vigorously shaking for 1.0min, the adsorbents were collected and dried on a filter. The adsorbents were transferred to a micro-vial, which was directly inserted into GC temperature-programmed injector, and the extracted target analytes were then thermally desorbed in the GC injection-port at 337°C for 3.8min. The limits of quantitation (LOQs) were determined to be 1.2-3.0ng/L. Precision, as indicated by relative standard deviations (RSDs), was less than 9% for both intra- and inter-day analysis. Accuracy, expressed as the mean extraction recovery, was between 74 and 90%. A preliminary analysis of the river water samples revealed that galaxolide (HHCB) and tonalide (AHTN) were the two most common synthetic polycyclic musks present. Using a standard addition method, their concentrations were determined to in the range from 11 to 140ng/L.