Bioanalytical chromatographic method validation according to current regulations, with a special focus on the non-well defined parameters limit of quantification, robustness and matrix effect

Method validation is a mandatory step in bioanalysis, to evaluate the ability of developed methods in providing reliable results for their routine application. Even if some organisations have developed guidelines to define the different parameters to be included in method validation (FDA, EMA); there are still some ambiguous concepts in validation criteria and methodology that need to be clarified. The methodology to calculate fundamental parameters such as the limit of quantification has been defined in several ways without reaching a harmonised definition, which can lead to very different values depending on the applied criterion. Other parameters such as robustness or ruggedness are usually omitted and when defined there is not an established approach to evaluate them. Especially significant is the case of the matrix effect evaluation which is one of the most critical points to be studied in LC-MS methods but has been traditionally overlooked. Due to the increasing importance of bioanalysis this scenario is no longer acceptable and harmonised criteria involving all the concerned parties should be arisen. The objective of this review is thus to discuss and highlight several essential aspects of method validation, focused in bioanalysis. The overall validation process including common validation parameters (selectivity, linearity range, precision, accuracy, stability…) will be reviewed. Furthermore, the most controversial parameters (limit of quantification, robustness and matrix effect) will be carefully studied and the definitions and methodology proposed by the different regulatory bodies will be compared. This review aims to clarify the methodology to be followed in bioanalytical method validation, facilitating this time consuming step.

Simultaneous determination of aflatoxin M1, ochratoxin A, zearalenone and α-zearalenol in milk by UHPLC-MS/MS

In this study, a sensitive and rapid method has been developed for the simultaneous determination of aflatoxin M1, ochratoxin A, zearalenone and α-zearalenol in milk by ultra high performance liquid chromatography combined with electrospray ionisation triple quadrupole tandem mass spectrometry (UHPLC-ESI-MS/MS). The milk samples were purified using Oasis HLB cartridge. The matrix effects were evaluated by determining the signal suppression-enhancement (SSE) and corrected by external matrix-matched calibration. The limits of quantity (LOQ) of the mycotoxins were in the range of 0.003-0.015μgkg(-1). The high correlation coefficients (R(2)⩾0.996) were obtained in the range of 0.01-1.00μgkg(-1) of the mycotoxins, along with good recovery (87.0-109%), repeatability (3.4-9.9%) and intra-laboratory reproducibility (4.0-9.9%) at the concentrations of 0.025, 0.1 and 0.5μgkg(-1). The detected rates of the mycotoxins were from 16.7% to 96.7% in raw milk, liquid milk and milk powder samples collected from the dairy farms and supermarkets in Beijing. The method proposed is suitable for the simultaneous determination of aflatoxin M1, ochratoxin A, zearalenone, and α-zearalenol, and could be performed for analysing the mycotoxins in milk.

Rapid HPLC analysis of amino acids and biogenic amines in wines during fermentation and evaluation of matrix effect

A rapid HPLC method has been developed for the simultaneous determination of 23 amino acids, 10 biogenic amines and the ammonium ion in wine. Samples were pre-column derivatised with diethyl ethoxymethylenemalonate and separated using reversed-phase HPLC within 30 min. The matrix effect was evaluated when measuring samples taken from different stages of fermentation. Most compounds showed no obvious matrix effect, whereas proline, ethanolamine and spermine had remarkably different responses to variable concentrations of sugar. High concentrations of sugar affected the pH of the derivatisation reaction system; proline, ethanolamine and spermine derivatives were sensitive to this effect. Matrix-matched calibration was used for the quantification of these compounds. Validation of the method showed that it was accurate, reproducible and efficient for the simultaneous determination of amino acids and biogenic amines in wines during fermentation. As a specific application of the method, red wine samples taken from different stages of fermentation were analysed.

Are Physicochemical Properties Shaping the Allergenic Potency of Plant Allergens?

This review searched for published evidence that could explain how different physicochemical properties impact on the allergenicity of food proteins and if their effects would follow specific patterns among distinct protein families. Owing to the amount and complexity of the collected information, this literature overview was divided in two articles, the current one dedicated to protein families of plant allergens and a second one focused on animal allergens. Our extensive analysis of the available literature revealed that physicochemical characteristics had consistent effects on protein allergenicity for allergens belonging to the same protein family. For example, protein aggregation contributes to increased allergenicity of 2S albumins, while for legumins and cereal prolamins, the same phenomenon leads to a reduction. Molecular stability, related to structural resistance to heat and proteolysis, was identified as the most common feature promoting plant protein allergenicity, although it fails to explain the potency of some unstable allergens (e.g. pollen-related food allergens). Furthermore, data on physicochemical characteristics translating into clinical effects are limited, mainly because most studies are focused on in vitro IgE binding. Clinical data assessing how these parameters affect the development and clinical manifestation of allergies is minimal, with only few reports evaluating the sensitising capacity of modified proteins (addressing different physicochemical properties) in murine allergy models. In vivo testing of modified pure proteins by SPT or DBPCFC is scarce. At this stage, a systematic approach to link the physicochemical properties with clinical plant allergenicity in real-life scenarios is still missing.

Dispersive solid-phase extraction using microporous metal-organic framework UiO-66: Improving the matrix compounds removal for assaying pesticide residues in organic and conventional vegetables

An efficient dispersive solid-phase extraction method was developed to trace pesticide residues in commonly consumed vegetables. In this method, UiO-66 with uniform micropores was used as sorbent, and gas chromatography-mass spectrometry was applied to detect the pesticides. Thanks to the size sieving action of uniform micropores, UiO-66 directly extracted the target pesticides from vegetable matrices and excluded the relatively large matrix compounds. This well eliminated the matrix effect. The important experimental conditions were evaluated by orthogonal array experimental design. In optimized conditions, good linearity (R² ≥ 0.99), detection limits (0.4-2.0 ng/g), recoveries (60.9-117.5%) and precision (relativestandarddeviations < 14.6%) were achieved. Moreover, the sorbent UiO-66 can be reused more than 20 times. These demonstrate a simple, reliable and robust method to screen the pesticide residues in vegetables. Furthermore, the validated method was applied to detect the pesticides in various organic and conventional vegetables.

Validation of lipidomic analysis of human plasma and serum by supercritical fluid chromatography-mass spectrometry and hydrophilic interaction liquid chromatography-mass spectrometry

Ultrahigh-performance supercritical fluid chromatography-mass spectrometry (UHPSFC/MS) has a great potential for the high-throughput lipidomic quantitation of biological samples; therefore, the full optimization and method validation of UHPSFC/MS is compared here with ultrahigh-performance liquid chromatography-mass spectrometry (UHPLC/MS) in hydrophilic interaction liquid chromatography (HILIC) mode as the second powerful technique for the lipid class separation. First, the performance of six common extraction protocols is investigated, where the Folch procedure yields the best results with regard to recovery rate, matrix effect, and precision. Then, the full optimization and analytical validation for eight lipid classes using UHPSFC/MS and HILIC-UHPLC/MS methods are performed for the same sample set and applied for the lipidomic characterization of pooled samples of human plasma, human serum, and NIST SRM 1950 human plasma. The choice of appropriate internal standards (IS) for individual lipid classes has a key importance for reliable quantitative workflows illustrated by the selectivity while validation and the calculation of the quantitation error using multiple internal standards per lipid class. Validation results confirm the applicability of both methods, but UHPSFC/MS provides some distinct advantages, such as the successful separation of both non-polar and polar lipid classes unlike to HILIC-UHPLC/MS, shorter total run times (8 vs. 10.5 min), and slightly higher robustness. Various types of correlations between methods (UHPSFC/MS and HILIC-UHPLC/MS), biological material (plasma and serum), IS (laboratory and commercially mixtures), and literature data on the standard reference material show the intra- and inter-laboratory comparison in the quantitation of lipid species from eight lipid classes, the concentration differences in serum and plasma as well as the applicability of non-commercially available internal standard mixtures for lipid quantitation.

Three approaches to minimize matrix effects in residue analysis of multiclass pesticides in dried complex matrices using gas chromatography tandem mass spectrometry

This paper discusses one of the major concerns in pesticide residue analysis: the matrix effect related to gas chromatography (GC), which can adversely affect quantification. In this study, a comparison of approaches for dealing with the matrix effect was investigated for 236 pesticides in complex matrices, including dried herbs (Centaurea cyanus L., Matricaria chamomilla L., Thymus vulgaris L.) and dried fruit (currants, chokeberry), using a modified QuEChERS method and GC-MS/MS analysis. Three approaches were evaluated: (i) using matrix-matched calibration, (ii) adding a mixture of analyte protectants (APs) to every extract or (iii) injection prior to GC-MS/MS analysis. Finally, minimization of the matrix effect to the acceptable levels of -20 to 20% for over 80% of investigated pesticides was found when APs mixture was injected at the beginning of the sequence. In this approach, the matrix effects were significantly weaker for some pesticides than when matrix-matched calibration was used.

Sorption of norfloxacin in soils: analytical method, kinetics and Freundlich isotherms

Fluoroquinolones are potent antibacterial agents that are active against a wide range of pathogenic organisms and are widely used in veterinary medicine. Fluoroquinolones and their metabolites may reach the soil through animal excreta or manure and may contaminate water and soils. The degree of sorption of these antimicrobials to soils varies widely, as does the mobility of these drugs. In the present study, sorption of norfloxacin in four soils of the state of São Paulo was investigated with batch equilibrium experiments. A strong matrix effect on the chromatographic determination of norfloxacin was verified. Sorption kinetics were best fit by a pseudo second-order model (r>0.99), and sorption/desorption isotherms were well fit by the Freundlich model in log form (r>0.97). Norfloxacin showed high affinity for soil particles, with KF sorption values ranging from 643 to 2410 μg(1-1/n)(cm(3))(1/n)g(-1) and KF desorption values ranging from 686 to 2468 μg(1-1/n)(cm(3))(1/n)g(-1). The high desorption KF values indicate that norfloxacin is highly immobile in the evaluated soils.

Ion mobility-derived collision cross section database: Application to mycotoxin analysis

The recent hyphenation of ion mobility spectrometry (IMS) with high resolution mass spectrometry (HRMS) has risen as a powerful technique for both targeted and non-targeted screening, reducing background noise and allowing separation of isomeric and isobaric compounds. Nevertheless, such an approach remains largely unexplored in food safety applications, such as mycotoxin analysis. To implement ion mobility in routinely MS-based mycotoxin workflows, searchable databases with collusion cross section (CCS) values and accurate mass-values are required. This paper provides for the first time a traveling-wave IMS (TWIMS)-derived CCS database for mycotoxins, including more than 100 CCS values. The measurements showed high reproducibility (RSD < 2%) across different instrumental conditions as well as several complex cereal matrices, showing a mean inter-matrix precision of RSD <0.9%. As a proof of concept, the database was applied to the analysis of several spiked as well as naturally incurred cereal-based samples. In addition, the effect of adducts on the drift time was studied in a series of mycotoxins in order to understand potential deviations from expected drift time behaviors. Overall, our study confirmed that CCS values represent a physicochemical property that can be used alongside the traditional molecular identifiers of precursor ion accurate mass, fragment ions, isotopic pattern, and retention time.

Evaluation of the impact of matrix effect on quantification of pesticides in foods by gas chromatography-mass spectrometry using isotope-labeled internal standards

The impact of the matrix effect in GC-MS quantification of pesticides in food using the corresponding isotope-labeled internal standards was evaluated. A spike-and-recovery study of nine target pesticides was first conducted using paste samples of corn, green soybean, carrot, and pumpkin. The observed analytical values using isotope-labeled internal standards were more accurate for most target pesticides than that obtained using the external calibration method, but were still biased from the spiked concentrations when a matrix-free calibration solution was used for calibration. The respective calibration curves for each target pesticide were also prepared using matrix-free calibration solutions and matrix-matched calibration solutions with blank soybean extract. The intensity ratio of the peaks of most target pesticides to that of the corresponding isotope-labeled internal standards was influenced by the presence of the matrix in the calibration solution; therefore, the observed slope varied. The ratio was also influenced by the type of injection method (splitless or on-column). These results indicated that matrix-matching of the calibration solution is required for very accurate quantification, even if isotope-labeled internal standards were used for calibration.

Postmortem distribution of α-pyrrolidinobutiophenone in body fluids and solid tissues of a human cadaver

We experienced an autopsy case of a 21-year-old male Caucasian, in which the direct cause of his death was judged as subarachnoid hemorrhage. There was cerebral arteriovenous malformation, which seemed related to the subarachnoid hemorrhage. The postmortem interval was estimated to be about 2days. By our drug screening test using gas chromatography-mass spectrometry, we could identify α-pyrrolidinobutiophenone (α-PBP) in his urine specimen, which led us to investigate the postmortem distribution of α-PBP in this deceased. The specimens dealt with were right heart blood, left heart blood, femoral vein blood, cerebrospinal fluid, urine, stomach contents and five solid tissues. The extraction of α-PBP and α-pyrrolidinovalerophenone (α-PVP, internal standard) was performed by a modified QuEChERS (quick, easy, cheap, effective, rugged and safe) method, followed by the analysis by liquid chromatography-tandem mass spectrometry. Because this study included various kinds of human matrices, we used the standard addition method to overcome the matrix effects. The highest concentration was found in urine, followed by stomach contents, the kidney, lung, spleen, pancreas and liver. The blood concentrations were about halves of those of the solid tissues. The high concentrations of α-PBP in urine and the kidney suggest that the drug tends to be rapidly excreted into urine via the kidney after its absorption into the blood stream. The urine specimen is of the best choice for analysis. This is the first report describing the postmortem distribution of α-PBP in a human to our knowledge.

Significant role of supercritical fluid chromatography - mass spectrometry in improving the matrix effect and analytical efficiency during multi-pesticides residue analysis of complex chrysanthemum samples

As an important "food and drug dual-use" product, chrysanthemums are widely used in both botanical medicine and food applications. However, the misuse of pesticides during chrysanthemum cultivation makes pesticide residue monitoring crucial. The aim of the present work was to address this practical demand for the simultaneous determination of multiple pesticide residues in various species of chrysanthemums. Both the sample pre-treatment and instrumental methods were systematically investigated. Seven chrysanthemum samples were extracted using acetonitrile and purified by dispersive solid-phase extraction with amino-modified multi-walled carbon nanotubes (MWCNTs-NH₂) and C18 as the cleanup co-adsorbents. After optimizing the amounts of MWCNTs-NH₂ and C18, matrix effects could not be avoided during LC-MS/MS analysis of 112 pesticides, although satisfactory recoveries were obtained. The use of SFC-MS/MS was evaluated, which demonstrated the significant positive role of SFC-MS/MS in reducing the matrix effects during pesticide residue analysis. In addition, the use of SFC-MS/MS permitted a shorter run time and afforded greater analytical efficiency. Method validation was further performed to evaluate the linearity, sensitivity, recovery, and precision of the developed method. Good linearity was observed for 92% of the analytes in the concentration range of 2-250 μg L^-1 for all seven of the chrysanthemum samples. The LODs of the 112 pesticides ranged from 0.01 to 31.41 μg L^-1, depending on the sample, while the mean recoveries of all of the spiked pesticides ranged from 81.8% to 102% for concentrations of 20, 50, and 200 μg kg^-1. These results clearly demonstrate the applicability of the developed method for the simultaneous determination of multi-pesticides in various chrysanthemum samples.

Cu(II) adsorption from copper mine water by chitosan films and the matrix effects

Adsorption of copper ions onto chitosan films was studied, and the matrix effect was evaluated using a synthetic solution and a real effluent from closed copper mine. Chitosan films were prepared by casting technique and characterized. The adsorption study was carried out by equilibrium isotherms, thermodynamics, and kinetics. The thermodynamic parameters indicated that the copper adsorption onto chitosan film was favorable, spontaneous, and exothermic, suggesting an increased randomness at the solid/solution interface. The matrix effect was evaluated in kinetic assays, where a synthetic solution and a real system were carried out at different stirring rates. The highest values of adsorption capacity reached in all stirring rates were about 20% lower in the real effluent, and this reduction in the competitiveness was due to the presence of other ions in the matrix of the real effluent. The maximum adsorption capacity of copper ions onto chitosan films for the synthetic solution was of 450 mg g^-1, and the removal percentage was in the range from 78 to 96%, and these values for the real effluent were of 360 mg g^-1 and removal ranging from 62 to 76%. The mapping done of ions present in the water adsorbed of the mine in the films showed that the same was homogeneously distributed in the films' surfaces.

Evaluation of matrix effect on the determination of rare earth elements and As, Bi, Cd, Pb, Se and In in honey and pollen of native Brazilian bees (Tetragonisca angustula - Jataí) by Q-ICP-MS

Bees are considered the main pollinators in natural and agricultural environments. Chemical elements from honey and pollen have been used for monitoring the environment, the health of bees and the quality of their products. Nevertheless, there are not many studies on honey and pollen of native Brazilian bees. The goal of this work was to determine important chemical elements (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Lu and Yb) along with As, Bi, Cd, Pb, Se and In, in honey and pollen of native Brazilian bees, assessing analytical interferences from the matrix. A proposed analytical method was developed for these elements by quadrupole ICP-MS. Matrix effect was verified in honey matrix in the quantification of As, Bi and Dy; and in pollen matrix for Bi, Cd, Ce, Gd, La, Pb and Sc. The quality of the method was considered satisfactory taking into consideration the recovery rate of each element in the spiked solutions: honey matrix (91.6-103.9%) and pollen matrix (94.1-115.6%). The quantification limits of the method ranged between 0.00041 and 10.3μgL^-1 for honey and 0.00041-0.095μgL^-1 for pollen. The results demonstrate that the method is accurate, precise and suitable.

Comparison of new approach of GC-HRMS (Q-Orbitrap) to GC-MS/MS (triple-quadrupole) in analyzing the pesticide residues and contaminants in complex food matrices

Performances of multiresidue analysis of one hundred of pesticides and contaminants, using GC-Q-Orbitrap method in full scan mode were compared to those obtained with GC-triple-quadrupole method in multiple reaction monitoring mode. In terms of sensitivity, 86% of molecules exhibited lower limit of detection values using GC-Q-Orbitrap than using GC-triple-quadrupole. For the GC-Q-Orbitrap method, more than 85% of the pesticides and contaminants showed good recovery [70-120%] in wheat samples, with relative standard deviation values < 20%. GC-Q-Orbitrap method appeared the most sensitive for most pesticides studied in wheat with limit of quantification values ranged between 0.1 µg/kg and 4 µg/kg. Moreover, the matrix effect was acceptable in wheat extracts for 84 molecules but strong suppression of the chromatographic signal was observed for 16 molecules for the GC-Q-Orbitrap method. The injection of unpurified wheat extracts spiked at 10 µg/kg proved the potential of the GC-Q-Orbitrap method for use in performing high-throughput pesticide screening.

Study of matrix effects for liquid chromatography-electrospray ionization tandem mass spectrometric analysis of 4 aminoglycosides residues in milk

Matrix effect (ME) is always a major issue for the development of LC-MS/MS method. ME resulting from co-eluting residual matrix components can affect the ionization efficiency of target analytes, leading to quantification errors of the analytes of interest. The present work evaluates MEs of milk samples on simultaneous analysis of four aminoglycosides residues via LC-ESI/MS/MS including streptomycin, dihydrostreptomycin, spectinomycin and kanamycin. Approaches to reduce MEs were examined: optimization of the sample preparation, sample dilution and lower flow rate used. Three commercial sorbents were tested including Oasis MCX, Oasis HLB and Oasis WCX. WCX behaved better for all analytes, but high MEs (80.8-134.9%) were obtained. Therefore, a consecutive SPE of tC18-WCX was found to effectively reduce ME. Milk samples from different manufacturers were analyzed and low MEs (85.6-112.9%) were obtained.

Aqueous acetonitrile extraction for pesticide residue analysis in agricultural products with HPLC-DAD

To reduce hazardous organic solvent consumption during sample preparation procedures as much as possible, an extraction method of smallest feasible sample volume (5g) using aqueous acetonitrile (MeCN) was developed to extract pesticide residues from agricultural samples prior to HPLC-DAD determination. Extraction with MeCN/water (1:1, v/v), and adjustment of the MeCN concentration by diluting with water after extraction recovered successfully most pesticides showing various physicochemical properties. The matrix effects of tested samples on the proposed method developed herein were generally negligibly-small. The average recoveries were in the range 70-120% for all pesticides with the coefficient of variation values below 20%. The reduction rate of organic solvents used for the proposed sample preparation method was up to approximately 60% compared with the Japanese authorised official method for pesticide residue analyses. These results demonstrate the feasibility of the proposed method for pesticides with diverse properties.

Applicability of Supercritical fluid chromatography-Mass spectrometry to metabolomics. II-Assessment of a comprehensive library of metabolites and evaluation of biological matrices

In this work, the impact of biological matrices, such as plasma and urine, was evaluated under SFCHRMS in the field of metabolomics. For this purpose, a representative set of 49 metabolites were selected. The assessment of the matrix effects (ME), the impact of biological fluids on the quality of MS/MS spectra and the robustness of the SFCHRMS method were each taken into consideration. The results have highlighted a limited presence of ME in both plasma and urine, with 30% of the metabolites suffering from ME in plasma and 25% in urine, demonstrating a limited sensitivity loss in the presence of matrices. Subsequently, the MS/MS spectra evaluation was performed for further peak annotation. Their analyses have highlighted three different scenarios: 63% of the tested metabolites did not suffer from any interference regardless of the matrix; 21% were negatively impacted in only one matrix and the remaining 16% showed the presence of matrix-belonging compounds interfering in both urine and plasma. Finally, the assessment of retention times stability in the biological samples, has brought into evidence a remarkable robustness of the SFCHRMS method. Average RSD (%) values of retention times for spiked metabolites were equal or below 0.5%, in the two biological fluids over a period of three weeks. In the second part of the work, the evaluation of the Sigma Mass Spectrometry Metabolite Library of Standards containing 597 metabolites, under SFCHRMS conditions was performed. A total detectability of the commercial library up to 66% was reached. Among the families of detected metabolites, large percentages were met for some of them. Highly polar metabolites such as amino acids (87%), nucleosides (85%) and carbohydrates (71%) have demonstrated important success rates, equally for hydrophobic analytes such as steroids (78%) and lipids (71%). On the negative side, very poor performance was found for phosphorylated metabolites, namely phosphate-containing compounds (14%) and nucleotides (31%).

Determination of Sudan dyes in chili products by micellar electrokinetic chromatography-MS/MS using a volatile surfactant

A new MEKC-MS/MS method was developed for the determination of four Sudan dyes in chili products. The separation and MS detection conditions were optimized to achieve fast, efficient, selective, and sensitive determination of Sudan I, Sudan II, Sudan III, and Sudan IV dyes. The target compounds were extracted from chili samples with acetonitrile and cleaned by freeze-out. This two-step sample preparation led to excellent extraction efficiency and minimal matrix effect. The analytical performance of the method was very good, with r² ≥ 0.9914 and limits of quantification lower than 22 μg kg^-1. The precision was below 15.7%. The recovery for spiked samples ranged from 84.4 to 99.6%, with relative standard deviations less than 8.0%. For all evaluated samples, the matrix effects did not exceed ± 10%. The applicability of the proposed method was demonstrated with 20 chili products, two of which were found to contain Sudan I and IV residues.

Determination of selected cardiovascular active compounds in environmental aquatic samples--Methods and results, a review of global publications from the last 10 years

In recent years cardiovascular diseases were the second most common cause of death worldwide. Therefore, the consumption of cardiovascular drugs is high, which might result in an increase of them in the environment. The major source of aquatic environmental contamination is still effluents of wastewater treatment plants (WWTPs). Unfortunately removal of cardiovascular active compounds and/or their metabolites in WWTP is still unsatisfactory. Among microbial and abiotic degradation of these compounds during wastewater processes, photolysis and photodegradation of cardiovascular drugs also play an important role. New formed compounds may be more toxic or retain the properties of parent compounds. Thus the main goal of this paper was to provide a detailed and comprehensive review of used analytical methods, coupled to liquid chromatography-tandem mass spectrometry, to determine the presence of cardiovascular compounds in surface waters as well as WTTPs effluents and influents. Exhaustive preparation for mass spectrometry detection and quantitation including samples pre-treatment, and the common problem of the matrix effect are thoroughly explored in this paper. Additionally, the article provides some hints in respect of recently noted problematic issue related to the availability of specific standards for the analysis of drug's metabolites. Furthermore, information concerning the metabolism of cardiovascular active compounds including differences in metabolism within enantiomers is described. This article also touches on the problems associated with environmental risk assessment due to the presence of cardiovasculars in the environment. The paper also tries to explain differences in concentrations among cardiovascular compounds between countries worldwide.

Role of calcium ions on the removal of haloacetic acids from swimming pool water by nanofiltration: mechanisms and implications

We investigated the removal of haloacetic acids (HAAs) from swimming pool waters (SPWs) by two nanofiltration membranes NF270 and NF90. The strong matrix effect (particularly by Ca²⁺) on membrane rejection prompts us to systematically investigate the mechanistic role of Ca²⁺ in HAA rejection. At typical SPW pH of 7.5, NF90 maintained consistently high rejection of HAAs (>95%) with little influence by Ca²⁺, thanks to the dominance of size exclusion effect for this tight membrane (pore radius ∼ 0.31 nm). In contrast, the rejections of both inorganic ions (e.g., Na⁺ and Cl^-) and HAA anions were decreased at higher Ca²⁺ concentration for NF270 (pore radius ∼ 0.40 nm). Further tests show that the rejection of neutral hydrophilic molecular probes and the membrane pore size were not affected by Ca²⁺. Although Ca²⁺ is unable to form strong complex with HAAs, we observed the binding of Ca²⁺ to NF270 together with a reduction in its surface charge. Therefore, the formation of membrane-Ca²⁺ complex, which weakens charge interaction effect, was responsible for the reduced HAA rejection. The current study reveals important mechanistic insights of the matrix effect on trace contaminant rejection, which is critical for a better understanding of their fate and removal in membrane-based treatment.

Method validation using weighted linear regression models for quantification of UV filters in water samples

This paper describes the validation of a method consisting of solid-phase extraction followed by gas chromatography-tandem mass spectrometry for the analysis of the ultraviolet (UV) filters benzophenone-3, ethylhexyl salicylate, ethylhexyl methoxycinnamate and octocrylene. The method validation criteria included evaluation of selectivity, analytical curve, trueness, precision, limits of detection and limits of quantification. The non-weighted linear regression model has traditionally been used for calibration, but it is not necessarily the optimal model in all cases. Because the assumption of homoscedasticity was not met for the analytical data in this work, a weighted least squares linear regression was used for the calibration method. The evaluated analytical parameters were satisfactory for the analytes and showed recoveries at four fortification levels between 62% and 107%, with relative standard deviations less than 14%. The detection limits ranged from 7.6 to 24.1 ng L(-1). The proposed method was used to determine the amount of UV filters in water samples from water treatment plants in Araraquara and Jau in São Paulo, Brazil.

Evaluation of the matrix effect of different sample matrices for 33 pharmaceuticals by post-column infusion

Matrix effects that occur during quantitative measurement by liquid chromatography mass spectrometry specifically when using electrospray ionization are a widely recognized phenomenon. Sample matrix compounds affect the ionization process of the target analytes, lead to a low signal response, and flawed analytical results. How these matrix compounds directly influence the ionization process has not yet been completely understood. In the present study, we determined the matrix effect for 33 pharmaceutical substances in sample extracts of urine, plasma and wastewater. Most of the investigated substances were subject to a signal suppression effect. Only for a small subset of the compounds we detected a signal enhancement effect. We investigated the matrix effect profiles in detail to disentangle the influence of different matrices and to correlate the impact of specific components and groups of the analyzed extract in suppressing or enhancing effects in the profile. Most signal suppression effects were detected in the first half of the chromatographic run-time for the matrix extracts of urine and wastewater. The observed effects are caused by high mass flow of salts and other diverse matrix components that were contained in high concentrations in those biological matrices. We also found signal suppression in the matrix effect profile of plasma samples over a wide time range during the chromatographic separation that were associated with a high content of triglycerides of diverse carbohydrate chain lengths. Here, we provide a broader picture of how 33 substances were influenced during analysis. Our results imply that a high number of the investigated substances had comparable effects of matrix compounds, despite differences in their chemical structure.

Bioanalytical insights into mediator lipidomics

The importance of lipids in health and disease has been widely acknowledged. Lipids are well known to undergo enzymatic and/or non-enzymatic conversions to lipid mediators (LMs), which demonstrate potent actions in various biological events, such as the regulation of cellular signaling pathways and the promotion and resolution of inflammation. LMs activate G-protein-coupled receptors (GPCRs) to exert various functions. Monitoring these mediators in disease is essential to uncover the mechanisms of pathogenesis for many diseases, such as asthma, rheumatoid arthritis, Alzheimer's disease, and cancer. Along with technical developments in mass spectrometry, highly sensitive and multiplexed analyses of LMs in the human periphery and other tissues have become available. These advancements enable the temporal and spatial profiling of LMs; therefore, the findings obtained from LM profiling are expected to decode pathology. As trace amounts of LMs can exert functions, the development of a highly sensitive, accurate, and robust analytical method is necessary. Although not mandatory, mediator lipidomics validation is becoming popular and remains challenging. Because LMs already exist in biological matrices, evaluations of the matrix effect and extraction efficiencies are important issues. Thus, more careful analyses are required. In this review, we focus on mediator lipidomics, including polyunsaturated fatty acids (PUFAs), such as omega-3 and omega-6 fatty acids, and LMs derived from PUFAs, such as eicosanoids, lipoxins and resolvins. In addition to the recent progress in human mediator lipidomics, bioanalytical insights derived from this field (i.e., effective sample preparation from biological matrices and evaluation of the matrix effect) are described herein.

Evaluation of the matrix effect on gas chromatography--mass spectrometry with carrier gas containing ethylene glycol as an analyte protectant

The consequences of matrix effects in GC are a major issue of concern in pesticide residue analysis. The aim of this study was to evaluate the applicability of an analyte protectant generator in pesticide residue analysis using a GC-MS system. The technique is based on continuous introduction of ethylene glycol into the carrier gas. Ethylene glycol as an analyte protectant effectively compensated the matrix effects in agricultural product extracts. All peak intensities were increased by this technique without affecting the GC-MS performance. Calibration curves for ethylene glycol in the GC-MS system with various degrees of pollution were compared and similar response enhancements were observed. This result suggests a convenient multi-residue GC-MS method using an analyte protectant generator instead of the conventional compensation method for matrix-induced response enhancement adding the mixture of analyte protectants into both neat and sample solutions.