Determination of perfluorocarboxylic acids in water by ion-pair dispersive liquid–liquid microextraction and gas chromatography–tandem mass spectrometry with injection port derivatization

An overview on human exposure, toxicity, solid-phase microextraction and adsorptive removal of perfluoroalkyl carboxylic acids (PFCAs) from water matrices

Perfluoroalkyl carboxylic acids (PFCAs) are sub-class of perfluoroalkyl substances commonly detected in water matrices. They are persistent in the environment, hence highly toxic to living organisms. Their occurrence at trace amount, complex nature and prone to matrix interference make their extraction and detection a challenge. This study consolidates current advancements in solid-phase extraction (SPE) techniques for the trace-level analysis of PFCAs from water matrices. The advantages of the methods in terms of ease of applications, low-cost, robustness, low solvents consumption, high pre-concentration factors, better extraction efficiency, good selectivity and recovery of the analytes have been emphasized. The article also demonstrated effectiveness of some porous materials for the adsorptive removal of the PFCAs from the water matrices. Mechanisms of the SPE/adsorption techniques have been discussed. The success and limitations of the processes have been elucidated.

A Rapid Derivatization for Quantitation of Perfluorinated Carboxylic Acids from Aqueous Matrices by Gas Chromatography-Mass Spectrometry

Ultrashort-chain perfluorinated carboxylic acids (PFCAs) are receiving more attention due to their ever-increasing presence in the environment. Methods have been established for the analysis of short- and long-chain PFCAs, while robust quantitation of ultrashort-chain species is scarce. Here, we develop a novel derivatization method using diphenyl diazomethane for quantitation of C2-C14 PFCAs in aqueous matrices. The method is highlighted by rapid completion of derivatization (<1 min) and retention and separation of ultrashort-chain (C2/C3) PFCA derivatives using H₂ carrier gas (R > 1.5). A weak anion exchange solid-phase extraction procedure for analyte recovery from representative aqueous samples was developed and validated by spike and recovery from ultrapure water, synthetic ocean water, and simulated denuder extracts used for collecting gaseous PFCAs. Recoveries for PFCAs ranged from 83 to 130% for the majority of analytes and matrices. The instrument detection limits (IDLs) range from 8 to 220 fg per injection, and method detection limits (MDLs) range from 0.06 to 14.6 pg/mL for 500 mL aqueous samples, which are within an order of magnitude to conventional LC-MS/MS methods. The method was applied to the analysis of real samples of tap water, rainwater, ocean water, and annular denuder extracts. The overall method provides a cost-effective alternative to conventional LC-MS/MS methods, overcoming the typical GC-MS drawbacks of high detection limits and long sample preparation times while being able to simultaneously analyze the complete spectrum of environmentally relevant PFCAs.

Analytical derivatizations in environmental analysis

Analytical derivatization is a technique that alters the structure of an analyte and produces a product more suitable for analysis. While this process can be time-consuming and add reagents to the procedure, it can also facilitate the isolation of the analyte(s), enhance analytes' stability, improve separation and sensitivity, and reduce matrix interferences. Since derivatization is a functional group analysis, it improves selectivity by separating reactive from neutral compounds during sample preparation. This technique introduces detector-orientated tags into analytes that lack suitable physicochemical properties for detection at low concentrations. Notably, many regulatory bodies, especially those in the environmental field, require these characteristics in analytical methods. This review focuses on note-worthy analytical derivatization methods employed in environmental analyses with functional groups, phenol, carboxylic acid, aldehyde, ketone, and thiol in aqueous, soil, and atmospheric sample matrices. Both advantages and disadvantages of analytical derivatization techniques are discussed. In addition, we discuss the future directions of analytical derivatization methods in environmental analysis and the potential challenges.

Gas chromatography-mass spectrometric determination of organic acids in fruit juices by multiwalled carbon nanotube-based ion-pair dispersive solid-phase extraction and in situ butylation

RATIONALE

Fruit juices are naturally acidic, and the acidity is due to the formation of various organic acids formed in several metabolic processes. The content of acids varies due to various processing parameters during the preparation of fruit juices and their packaging for commercialization. Quantitative determination of organic acids provides the necessary information leading to changes occurred during processing.

METHODS

The organic acids were extracted by ion-pair dispersive solid-phase extraction by multiwalled carbon nanotubes and analyzed using gas chromatography-mass spectrometry (GC-MS) and in situ butylation.

RESULTS

The developed analytical method was validated, and the obtained results showed a linearity in the range of 0.5-5000 μg/L levels of the analytes with limit of detection and quantification values of 2-10 and 5-20 μg/L, respectively. The inter- and intra-day reproducibilities are less than 15% with 80%-98% recoveries and less than 20% matrix effect. The developed method was used for the quantitative determination of organic acids present in fresh and packaged apple, grape, orange, and pomegranate juice samples. The content of organic acids was observed in the range of 0.26-3793 μg/L. Pimelic acid was not detected in any of the analyzed fruit juices. Fumaric acid (FA) was observed to be a major organic diacid present in the natural fruit juices. The results indicated that the processing of fruit juices for packaging decreases the content of organic acids in fruits.

CONCLUSIONS

The developed GC-MS-based analytical method for the analysis of organic acids has good sensitivity and reproducibility for the quantitative determination of various organic acids in fruit juices. FA was observed to be the major carboxylic acid present in fruits. The processed juice samples possess the lowest concentration of organic acids, suggesting that processing has a significant effect on the concentration of organic acids in fruits.

Simultaneous determination of seven perfluoroalkyl carboxylic acids in water samples by 2,3,4,5,6-pentafluorobenzyl bromide derivatization and gas chromatography-mass spectrometry

A new derivatization reagent, 2,3,4,5,6-pentafluorobenzyl bromide (PFBBr), was employed to determine seven perfluoroalkyl carboxylic acids (PFCAs) simultaneously in tap water with gas chromatography-mass spectrometry (GC-MS) technique in this study. Firstly, seven PFCAs were derivatized to their corresponding esters under alkaline condition. The derivatization conditions including the amount of PFBBr and K₂CO₃, derivatization temperature and time were optimized to increase the derivatization efficiency. The 14 tap water samples collected from different places of China were enriched and purified through solid phase extraction pretreatment. The limits of detection (LODs) and the limits of quantitation (LOQs) ranged from 0.1 ng/L to 0.28 ng/L and from 0.3 ng/L to 0.84 ng/L, respectively. The new method offers a linear relationship in the range from 2 ng/L to 2000 ng/L, and the correlation coefficients ranged from 0.9938 to 0.9994. The results showed that GC-MS combined with pre-column derivatization is a reliable method for the analysis of PFCAs in the aqueous environment.

Structural investigation of perfluorocarboxylic acid derivatives formed in the reaction with N,N-dimethylformamide dialkylacetals

A structural investigation of perfluorocarboxylic acid derivatives formed in the reaction with N,N-dimethylformamide dialkylacetals employing several techniques of mass spectrometry (MS) is described. Two derivatizing reagents, dimethylformamide dimethyl acetal (DMF-DMA) and dimethylformamide diethylacetal (DMF-DEA) were used. In contrast to carboxylic acids, perfluorocarboxylic acids are not able to form alkyl esters as the main product in this reaction. We found that perfluorooctanoic acid (PFOA) forms a salt with N,N-dimethylformamide dialkylacetals. This salt undergoes a further reaction inside the injection block of a gas chromatograph (GC) by loss of CO₂ and then forms 1,1-perfluorooctane-(N,N,N,N-tetramethyl)-diamine. The GC-MS experiments using both electron ionization (EI) and positive-ion chemical ionization (PCI) revealed that the same reaction products are formed with either derivatizing reagent. Subjecting the perfluorocarboxylic acid derivative to electrospray ionization (ESI) and direct analysis in real time (DART), both positive- and negative-ion modes indicated that cluster ions are formed. In the positive-ion mode, this cluster ion consists of two iminium cations and one PFOA anion, while in the negative-ion mode, it comprises two PFOA anions and one cation. The salt structure was further confirmed by liquid injection field desorption/ionization (LIFDI) as well as infrared (IR) spectroscopy. We propose a simple mechanism of N,N,N',N'-tetramethylformamidinium cation formation. The structure elucidation is supported by specific fragment ions as obtained by GC-EI-MS and GC-PCI-MS analyses.

Method for the determination of carboxylic acids in industrial effluents using dispersive liquid-liquid microextraction with injection port derivatization gas chromatography-mass spectrometry

The paper presents a new method for the determination of 15 carboxylic acids in samples of postoxidative effluents from the production of petroleum bitumens using ion-pair dispersive liquid-liquid microextraction and gas chromatography coupled to mass spectrometry with injection port derivatization. Several parameters related to the extraction and derivatization efficiency were optimized. Under optimized experimental conditions, the obtained limit of detection and quantification ranged from 0.0069 to 1.12μg/mL and 0.014 to 2.24μg/mL, respectively. The precision (RSD ranged 1.29-6.42%) and recovery (69.43-125.79%) were satisfactory. Nine carboxylic acids at concentrations ranging from 0.10μg/mL to 15.06μg/mL were determined in the raw wastewater and in samples of effluents treated by various oxidation methods. The studies revealed a substantial increase of concentration of benzoic acids, in samples of wastewater after treatment, which confirms the need of carboxylic acids monitoring during industrial effluent treatment processes.

Paired-ion electrospray ionization--triple quadrupole tandem mass spectrometry for quantification of anionic surfactants in waters

A new paired ion electrospray ionization tandem mass spectrometry method for determination of anionic surfactants in water samples was developed. In this method, dicationic ion-pairing reagents were complexed with monoanionic analytes to facilitate analyte detection in positive mode electrospray ionization - mass spectrometry. Single ion monitoring and selected reaction monitoring on a triple quadrupole instrument were performed and compared. Four dicationic reagents were tested for the determination of perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), sodium dodecyl sulfate (SDS), dodecylbenzene sulfonic acid (DBS), and stearic acid (SA), among other common anions. The obtained limits of detection were compared with those from previous literature. Solid phase extraction using a C18 cartridge was performed in order to eliminate matrix interferences. A literature review was compiled for the methods published between 2010 and 2015 for determination of anionic surfactants. The optimized method was more sensitive than previously developed methods with LOD values of 2.35, 35.4, 37.0, 1.68, and 0.675 pg for SDS, SA, DBS, PFOS, and PFOA, respectively. The developed method was effectively applied for the determination of anionic surfactants in different water samples such as bottled drinking water, cooking water, tap water, and wastewater.

Simultaneous determination of 11 related impurities in propofol by gas chromatography/tandem mass spectrometry coupled with pulsed splitless injection technique

A variety of related impurities, including starting materials, process impurities, and degradation products, can be detected in propofol. In this article, a sensitive and selective GC-MS/MS method using pulsed splitless injection technique for the determination of 11 main related impurities in propofol in one chromatogram is investigated. This method is extensively validated for its linearity, recovery, precision, LOD, and LOQ, and is able to detect trace-level related impurities (LOD = 0.2-5.6 μg/g) in propofol bulk drug. Stressed tests proposed that oxidative degradation, photolytic degradation, and heat are the main causes for the formation of degradation products in propofol.

In situ aqueous derivatization as sample preparation technique for gas chromatographic determinations

The use of derivatization reactions is a common practice in analytical laboratories. Although in many cases it is tedious and time-consuming, it does offer a good alternative for the determination of analytes not compatible to gas chromatography. Many of the reactions reported in the literature occur in organic medium. However, in situ aqueous derivatization reactions, which can be performed directly in aqueous medium, offer important advantages over those mentioned above, such as no need of a previous extraction step and easy automation. Here we review the most recent developments and applications of in situ aqueous derivatization. The discussion focuses on the derivatization reactions used for the determination of alcohols and phenols, carboxylic acids, aldehydes and ketones, nitrogen-containing compounds and thiols in different aqueous matrices, such as environmental, biological and food samples. Several reactions are described for each functional group (acylation, alkylation, esterification, among others) and, in some cases, the same reagents can be used for several functional groups, such that there is an unavoidable overlap between sections. Finally, attention is also focused on the techniques used for the introduction of the derivatives formed in the aqueous medium into the chromatographic system. The implementation of in situ aqueous derivatization coupled to preconcentration techniques has permitted the enhancement of recoveries and improvements in the separation, selectivity and sensitivity of the analytical methods.

Environmental mass spectrometry

Environmental mass spectrometry is an important branch of science because it provides many of the data that underlie policy decisions that can directly influence the health of people and ecosystems. Environmental mass spectrometry is currently undergoing rapid development. Among the most relevant directions are a significant broadening of the lists of formally targeted compounds; a parallel interest in nontarget chemicals; an increase in the reliability of analyses involving accurate mass measurements, tandem mass spectrometry, and isotopically labeled standards; and a shift toward faster high-throughput analysis, with minimal sample preparation, involving various approaches, including ambient ionization techniques and miniature instruments. A real revolution in analytical chemistry could be triggered with the appearance of robust, simple, and sensitive portable mass spectrometers that can utilize ambient ionization techniques. If the cost of such instruments is reduced to a reasonable level, mass spectrometers could become valuable household devices.

Analysis of losartan and carvedilol in urine and plasma samples using a dispersive liquid–liquid microextraction isocratic HPLC–UV method

Background: A simple, precise and sensitive HPLC method has been developed for simultaneous determination of carvedilol and losartan in human plasma and urine samples. The analytes were extracted by a dispersive liquid–liquid microextraction method. A mobile phase of 15 mM sodium dihydrogen phosphate buffer (pH 4.0)/acetonitrile/2-propanol (70/27.5/2.5, v/v/v) was used to separate the drugs using a Waters® ODS column (250 × 4.6 mm) and detected by a UV detector at 222 nm. Results: The developed method is selective for studied drugs possessing a linearity range of 0.1–1.0 and 0.05–0.75 µg/ml, respectively, for losartan and carvedilol with precision <15%. The accuracy is better than 15% and the mean recovery of carvedilol and losartan was 98.9 and 100.2% for plasma and 100.7 and 100.5% for urine samples, respectively. Conclusion: The developed method is applicable for therapeutic drug monitoring and PK analyses.