Using calibration approaches to compensate for remaining matrix effects in quantitative liquid chromatography/electrospray ionization multistage mass spectrometric analysis of phytoestrogens in aqueous environmental samples

Rapid Mass Spectrometric Calibration and Standard Addition Using Hydrophobic/Hydrophilic Patterned Surfaces and Discontinuous Dewetting

The rapid calibration chip (RCC) is a device that uses the fast and reproducible wetting behavior of hydrophilic/hydrophobic patterned surfaces to confine a series of differently sized droplets on a substrate to obtain a calibration curve. Multiple series of droplets can be formed within seconds by dipping an RCC into a calibration solution. No pipetting, sequential droplet deposition, or advanced equipment is required. The performance and reproducibility of RCCs were evaluated with an electrospray ionization triple-quadrupole mass spectrometer equipped with a liquid microjunction-surface sampling probe (LMJ-SSP) that allows for fast sampling of surfaces. Using circular hydrophilic areas with diameters ranging from 0.25 to 2.00 mm, liquid volumes of 4.6-70.6 nL could be deposited. Furthermore, the use of a second hydrophobic/hydrophilic patterned transfer chip can be used to add internal standard solutions to each calibration spot of the RCC, allowing to transfer a liquid volume of 22.5 nL.

On-column internal standardisation as an alternative calibration strategy for speciation analysis: feasibility demonstration through analysis of inorganic As in rice

Species-specific isotope dilution mass spectrometry (SS-IDMS) has been the calibration method of choice for high accuracy speciation analysis because it can correct for detector sensitivity drifts, matrix effects, and analyte loss during sample preparation and analysis. However, in many cases SS-IDMS calibration is either not applicable (e.g. for monoisotopic elements) or not feasible (e.g. limited by the cost and availability of like-for-like isotopically enriched species). The work presented here demonstrates the potential of a novel on-column species-specific internal calibration approach, which is based on the chromatographic injection of the same species of the analyte as the internal standard (IS), after the sample injection. It can compensate for on-column analyte losses and signal drift and can be applied with any detector capable of recording time-resolved data, provided that enough species resolution can be achieved. The feasibility of this novel calibration strategy for accurate quantitative elemental speciation in complex matrices is demonstrated here through the analysis of inorganic arsenic in rice. An expanded uncertainty (k = 2) of <10% was obtained for a mass fraction range of 60 to 300 μg kg^-1 inorganic-As (i-As) in dry rice products. The method is currently used for the certification of i-As in baby food matrices to support Commission Regulation (EU) 2015/1006 in regard to the maximum levels of i-As in foodstuffs.

Benefits and Pitfalls of HPLC Coupled to Diode-Array, Charged Aerosol, and Coulometric Detections: Effect of Detection on Screening of Bioactive Compounds in Apples

The new screening method for rapid evaluation of major phenolic compounds in apples has been developed. Suitability of coupling HPLC/UHPLC separation with the diode-array detection and universal charged aerosol detection with respect to the presence of interfering substances was tested. Characteristics of both detection techniques were compared and method linearity, limits of detection and quantitation, and selectivity of them determined. Student t-test based on slopes of calibration plots was applied for the detailed comparison. The diode-array detection provided the best results regarding sensitivity and selectivity of the developed method in terms of evaluation of phenolics profiles. The response of the charged aerosol detector was negatively affected by co-eluting substances during rapid-screening analyses. Coulometric detection was used for advanced characterization of extracts in terms of antioxidant content and strength to obtain more complex information concerning sample composition. This detection also allowed evaluation of unidentified compounds with antioxidant activity. HPLC/UHPLC separation using a combination of diode-array and coulometric detectors thus represented the best approach enabling quick, yet complex characterization of bioactive compounds in apples.

Simultaneous measurement of free and conjugated estrogens in surface water using capillary liquid chromatography tandem mass spectrometry

Given detrimental impacts induced by estrogens at trace level, determination of them is significant but challenging due to their low content in environmental samples and inherent weak ionisation. A modified derivatisation-based methodology was applied for the first time to detect estrogen in free and conjugated forms including some isomers simultaneously using liquid chromatography tandem mass spectrometry (LC-MSn). Derivatisation reaction with previously used 1,2-dimethyl-1H-imidazole-5-sulphonyl chloride allowed significant increase of mass spectrometric signal of analytes and also provided distinctive fragmentation for their confirmation even in complicated matrix. Then satisfactory recovery (>75%) for the majority of analytes was achieved following optimisation of solid phase extraction (SPE) factors. The linearity was validated over a wide concentration with the correlation coefficient around 0.995. The repeatability of this methodology was also confirmed via the intra-day and inter-day precision and was less than 11.73%. Validation of method quantification limits (MQLs) for all chosen estrogens was conducted using 1000 mL surface water, ranging from 7.0 to 132.3 pg L-1. The established methodology was applied to profile presence of targeted estrogens in natural surface water samples. Out of the ten compounds of interest, three free estrogens (E1, E2, E3) and two sulphate estrogens (E1-3S and E2-3S) were found over their MQLs, being in the range of 0.05-0.32 ng L-1.

Simultaneous quantification of 18 different phytocannabinoids in serum using a highly sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method

The potential therapeutic effects of various phytocannabinoids and the availability of multiple cannabis-based medicines make it desirable to have an analytical method that simultaneously quantifies a wide range of cannabinoids in blood, beyond delta-9-tetrahydrocannabinol and its metabolites. A liquid chromatography tandem mass spectrometry (LC-MS/MS) method for quantification of 18 phytocannabinoids and cannabinoid metabolites in serum was developed and validated. The method enables simultaneous detection of delta-9-tetrahydrocannabinol, cannabidiol, cannabinol, cannabigerol, cannabichromene, cannabicyclol, tetrahydrocannabivarin and cannabidivarin and their acidic precursors tetrahydocannabinolic acid A, cannabidiolic acid, cannabinolic acid, cannabigerolic acid, cannabichromenic acid, cannabicyclolic acid, tetrahydrocannabivarinic acid and cannabidivarinic acid as well as the delta-9-tetrahydrocannabinol metabolites 11-hydroxy-tetrahydrocannabinol and 11-nor-9-carboxy-tetrahydrocannabinol. Limits of detection ranged from 0.0004 to 1 ng/mL and limits of quantification ranged from 0.004 to 2 ng/mL. Calibration curves of all analytes were linear over the whole calibration range. Recovery rates of 52 to 86% were obtained for all analytes except for cannabicyclol (49%), 11-nor-9-carboxy-tetrahydrocannabinol (46%), cannabichromenic acid (44%) and cannabidivarinic acid (36%). Acceptable bias and precision data were demonstrated for all analytes. The method was successfully applied to 55 forensic serum samples, obtained from the Institute of Legal Medicine Mainz.

Optimized multimatrix calibration concept for liquid chromatography mass spectrometry-based bioanalysis methods

In this paper, a calibration procedure for LC/MS-based bioanalysis methods, termed "A/B fortification", is proposed. The concept relies on the post-extraction fortification (B-spike) of an aliquot of the injection-ready sample extract for the determination and compensation of specific signal suppression or enhancement effects compared to matrix-free extract prepared in buffer or mobile phase. Conventional analyte recovery, observed due to the incomplete extraction of analytes from the sample or losses during a cleanup, is determined by the conventional pre-extraction fortification (A-spike) of a blank sample that belongs to the same type of matrix as the sample with the unknown analyte concentration. This approach permits a higher throughput than conventional sample fortification strategies. The results obtained by utilizing the A/B fortification concept were extensively compared against conventional methods (representative bank matrix fortification, sample fortification and internal standard). The proposed concept (based on the pre-fortification of a reference matrix and post-fortification of the sample) was found to be significantly less biased than internal standard-based techniques. The A/B fortification indicated a better accuracy than the sample fortification or representative blank matrix fortification approach and, most importantly, produced significantly fewer outliers. This was linked to the fact that in the case of the A/B fortification, the uncertainty of the subtraction of two peak areas (fortified minus unfortified sample) is reduced, because fortifications are not made prior to the extraction step but are made into the final injection-ready sample extract. Fortification into an injection-ready aliquot eliminates all sample processing-related differences (procedural errors), which can affect conventional sample fortification-based quantifications.

Compensate for or Minimize Matrix Effects? Strategies for Overcoming Matrix Effects in Liquid Chromatography-Mass Spectrometry Technique: A Tutorial Review

In recent decades, mass spectrometry techniques, particularly when combined with separation methods such as high-performance liquid chromatography, have become increasingly important in pharmaceutical, bio-analytical, environmental, and food science applications because they afford high selectivity and sensitivity. However, mass spectrometry has limitations due to the matrix effects (ME), which can be particularly marked in complex mixes, when the analyte co-elutes together with other molecules, altering analysis results quantitatively. This may be detrimental during method validation, negatively affecting reproducibility, linearity, selectivity, accuracy, and sensitivity. Starting from literature and own experience, this review intends to provide a simple guideline for selecting the best operative conditions to overcome matrix effects in LC-MS techniques, to obtain the best result in the shortest time. The proposed methodology can be of benefit in different sectors, such as pharmaceutical, bio-analytical, environmental, and food sciences. Depending on the required sensitivity, analysts may minimize or compensate for ME. When sensitivity is crucial, analysis must try to minimize ME by adjusting MS parameters, chromatographic conditions, or optimizing clean-up. On the contrary, to compensate for ME analysts should have recourse to calibration approaches depending on the availability of blank matrix. When blank matrices are available, calibration can occur through isotope labeled internal standards and matrix matched calibration standards; conversely, when blank matrices are not available, calibration can be performed through isotope labeled internal standards, background subtraction, or surrogate matrices. In any case, an adjusting of MS parameters, chromatographic conditions, or a clean-up are necessary.

Ultrafast enzymatic digestion of proteins by microdroplet mass spectrometry

Enzymatic digestion for protein sequencing usually requires much time, and does not always result in high sequence coverage. Here we report the use of aqueous microdroplets to accelerate enzymatic reactions and, in particular, to improve protein sequencing. When a room temperature aqueous solution containing 10 µM myoglobin and 5 µg mL⁻¹ trypsin is electrosonically sprayed (−3 kV) from a homemade setup to produce tiny (∼9 µm) microdroplets, we obtain 100% sequence coverage in less than 1 ms of digestion time, in sharp contrast to 60% coverage achieved by incubating the same solution at 37 °C for 14 h followed by analysis with a commercial electrospray ionization source that produces larger (∼60 µm) droplets. We also confirm the sequence of the therapeutic antibody trastuzumab (∼148 kDa), with a sequence coverage of 100% for light chains and 85% for heavy chains, demonstrating the practical utility of microdroplets in drug development.

Mass spectrometry (MS)-based protein sequencing usually relies on in-solution proteolytic digestion, which is time-consuming and inefficient for certain proteins. Here, the authors achieve full protein sequence coverage in less than 1 ms by subjecting protein-protease mixtures to electrosonic spray ionization-MS.

Evaluation of Matrix Effects in Quantifying Microbial Secondary Metabolites in Indoor Dust Using Ultraperformance Liquid Chromatograph-Tandem Mass Spectrometer

Background

Liquid chromatography-tandem mass spectrometry (LC-MSMS) for simultaneous analysis of multiple microbial secondary metabolites (MSMs) is potentially subject to interference by matrix components.

Methods

We examined potential matrix effects (MEs) in analyses of 31 MSMs using ultraperformance LC-MSMS. Twenty-one dust aliquots from three buildings (seven aliquots/building) were spiked with seven concentrations of each of the MSMs (6.2 pg/μl-900 pg/μl) and then extracted. Another set of 21 aliquots were first extracted and then, the extract was spiked with the same concentrations. We added deepoxy-deoxynivalenol (DOM) to all aliquots as a universal internal standard. Ten microliters of the extract was injected into the ultraperformance LC-MSMS. ME was calculated by subtracting the percentage of the response of analyte in spiked extract to that in neat standard from 100. Spiked extract results were used to create a matrix-matched calibration (MMC) curve for estimating MSM concentration in dust spiked before extraction.

Results

Analysis of variance was used to examine effects of compound (MSM), building and concentration on response. MEs (range: 63.4%-99.97%) significantly differed by MSM (p < 0.01) and building (p < 0.05). Mean percent recoveries adjusted with DOM and the MMC method were 246.3% (SD = 226.0) and 86.3% (SD = 70.7), respectively.

Conclusion

We found that dust MEs resulted in substantial underestimation in quantifying MSMs and that DOM was not an optimal universal internal standard for the adjustment but that the MMC method resulted in more accurate and precise recovery compared with DOM. More research on adjustment methods for dust MEs in the simultaneous analyses of multiple MSMs using LC-MSMS is warranted.

Characterization of membrane-bound sulfane reductase: A missing link in the evolution of modern day respiratory complexes

Hyperthermophilic archaea contain a hydrogen gas-evolving,respiratory membrane-bound NiFe-hydrogenase (MBH) that is very closely related to the aerobic respiratory complex I. During growth on elemental sulfur (S°), these microorganisms also produce a homologous membrane-bound complex (MBX), which generates H₂S. MBX evolutionarily links MBH to complex I, but its catalytic function is unknown. Herein, we show that MBX reduces the sulfane sulfur of polysulfides by using ferredoxin (Fd) as the electron donor, and we rename it membrane-bound sulfane reductase (MBS). Two forms of affinity-tagged MBS were purified from genetically engineered Pyrococcus furiosus (a hyperthermophilic archaea species): the 13-subunit holoenzyme (S-MBS) and a cytoplasmic 4-subunit catalytic subcomplex (C-MBS). S-MBS and C-MBS reduced dimethyl trisulfide (DMTS) with comparable K_m (∼490 μm) and V _max values (12 μmol/min/mg). The MBS catalytic subunit (MbsL), but not that of complex I (NuoD), retains two of four NiFe-coordinating cysteine residues of MBH. However, these cysteine residues were not involved in MBS catalysis because a mutant P. furiosus strain (MbsLC85A/C385A) grew normally with S°. The products of the DMTS reduction and properties of polysulfides indicated that in the physiological reaction, MBS uses Fd (E _o' = -480 mV) to reduce sulfane sulfur (E _o' -260 mV) and cleave organic (RS _n R, n ≥ 3) and anionic polysulfides (S _n ^2-, n ≥ 4) but that it does not produce H₂S. Based on homology to MBH, MBS also creates an ion gradient for ATP synthesis. This work establishes the electrochemical reaction catalyzed by MBS that is intermediate in the evolution from proton- to quinone-reducing respiratory complexes.

Comparison of different calibration approaches for chloramphenicol quantification in chicken muscle by ultra-high pressure liquid chromatography tandem mass spectrometry

Matrix-dependent signal suppression often occurs in quantitative analysis by ultra-high pressure liquid chromatography tandem mass spectrometry (UPLC-MS/MS).

European Bioanalysis Forum: recommendation on dealing with hemolyzed and hyperlipidemic matrices

Recent guidelines on bioanalytical method validation have recommended to investigate matrix effects in special matrices such as hemolytic and hyperlipidemic plasma. However, these guidelines were not clear on how to implement these recommendations. The European Bioanalysis Forum has discussed this topic in depth and has asked for feedback from member companies. Those discussions have resulted in more specific guidance on how to define hemolytic and hyperlipidemic plasma, how to validate bioanalytical methods for these matrices and how to deal with hemolytic and hyperlipidemic study samples. These recommendations are presented in this manuscript.

Analysis of 118 pesticides in tobacco after extraction with the modified QuEChRS method by LC-MS-MS

A liquid chromatography-tandem quadrupole mass spectrometry (LC-MS-MS) multi-residue method for the simultaneous target analysis of a wide range of pesticides in tobacco has been developed. Gradient elution has been used in conjunction with positive mode electrospray ionization tandem mass spectrometry to detect up to 118 pesticides in tobacco. The recoveries obtained for each pesticide ranged between 70 and 118% at two spiked concentration levels. Good linear relationships were observed with correlation coefficients r(2) > 0.992 for all analytes. The established method was successfully applied to the determination of pesticide residues in real tobacco samples in order to validate the suitability for routine analysis.

Measuring free, conjugated, and halogenated estrogens in secondary treated wastewater effluent

Steroidal estrogens are potent endocrine-disrupting chemicals that enter natural waters through the discharge of treated and raw sewage. Because estrogens are detrimental to aquatic organisms at sub-nanogram per liter concentrations, many studies have measured so-called "free" estrogen concentrations in wastewater effluents, rivers, and lakes. Other forms of estrogens are also of potential concern because conjugated estrogens can be easily converted to potent free estrogens by bacteria in wastewater treatment plants and receiving waters and halogenated estrogens are likely produced during wastewater disinfection. However, to the best of our knowledge, no studies have concurrently characterized free, conjugated, and halogenated estrogens. We have developed a method that is capable of simultaneously quantifying free, conjugated, and halogenated estrogens in treated wastewater effluent, in which detection limits were 0.13-1.3 ng L(-1) (free), 0.11-1.0 ng L(-1) (conjugated), and 0.18-18 ng L(-1) (halogenated). An aqueous phase additive, ammonium fluoride, was used to increase the electrospray (negative mode) ionization efficiency of free and halogenated estrogens by factors of 20 and 2.6, respectively. The method was validated using treated effluent from the greater Boston metropolitan area, where conjugated and halogenated estrogens made up 60-70% of the steroidal estrogen load on a molar basis.

Development and validation of an UHPLC-LTQ-Orbitrap MS method for non-anthocyanin flavonoids quantification in Euterpe oleracea juice

Euterpe oleracea fruits have gained much attention because of their phenolic constituents that have shown potential health benefits. The aim of this work was to quantify the major non-anthocyanin flavonoids (NAF) in the fruit juice by an accurate method coupling ultra-high pressure liquid chromatography with a linear ion trap-high resolution Orbitrap mass spectrometry system (UHPLC-LTQ-Orbitrap MS). Fruits were processed to juice, and then the juice was lyophilized and defatted. The residue was then extracted in the presence of methanol by sonication. The extraction time was optimized and recovery rates of the extraction were >90%. The extracts were dried and solubilized again in 40% MeOH, which showed the best compromise for MS detection. For the UHPLC quantification, a HSS C18 column (1.8 μm) was used with a gradient elution of methanol and water both with 0.1% formic acid. Total error and accuracy profiles were used as validation criteria. Seven compounds and their isomers were successfully separated, including the major NAF. Calibration in the matrix was found to be more accurate than calibration without matrix. Trueness (<15% relative bias), repeatability, and intermediate precision (<13% RSD), selectivity, response function, linearity, LOD (ranged from 0.04 to 0.81 μg/mL) and LOQ (0.15-5.78 μg/mL) for 12 compounds were evaluated and the quantification method was validated. Its applicability was demonstrated on real samples from different suppliers. Their qualitative and quantitative profiles were similar and some compounds were for the first time quantified. In addition, eriodictyol was identified for the first time in this fruit along with five other flavonoids for which possible structures were proposed.

Beware of Pseudo Matrix-Matched Standard Calibration Curve due to Matrix Effect on Sulfonamide Residue in Honey

Honey was a particular matrix with a variety of composition and origin, which lead to different degree of matrix effect on analytes. As a rule, the matrix-matched calibration curve from blank honey was adopted to quantifying analyte in a batch. This paper investigated matrix effect on sulfonamide in four honey samples by high-performance liquid chromatography hyphenated with mass spectrometry detection. The main goal was to check whether matrix-matched calibration curve obtained from a random blank honey could match the real samples in character within current recommended acceptance criteria. It was found that analyte recovery from true matrix-matched standard calibration curve ranged 87.7-117.3%, whereas recovery from surrogate matrix-matched calibration curves gave a very wide range from 54.3 to 150.2%, far beyond the acceptance criteria. So it was perhaps not feasible to use a surrogated blank sample to prepare matrix-matched calibration curve for quantifying analyte, particularly for largely diverse honey samples in a batch. To reduce error from inter-sample matrix effect, the best solution seemed to use internal standard or standard addition.

Matrix effect in high-performance liquid chromatography-tandem mass spectrometry analysis of antibiotics in environmental water samples

This paper describes the matrix effect during the analysis of ten antibiotic compounds in water by SPE followed by HPLC-ESI-MS/MS. The target analytes were tetracycline, oxytetracycline (tetracyclines), sulfathiazole, sulfamethazine, sulfadiazine (sulfonamides), erythromycin-H(2)O, roxithromycine, spiramycin (macrolides), ofloxacin, and norfloxacin (quinolones). The matrix effect was examined for internal standards and the target analytes in five different water matrixes, with signal suppression being increased in the order: ultrapure water, tap water, river water, sewage effluent, and sewage influent. A combined application of the internal standards and matrix-matched extract calibration was shown to be successful in compensating the matrix effect for the analytes. The procedural recovery of the target compounds in sewage effluents and influents was higher than in river water samples, which was further enhanced by sample acidification to pH 2. The validity of the internal standard based matrix-matched calibration approach was verified by the standard addition method.

Effect of methanol quality on the ionisation of herbicides, insecticides and fungicides using gradient elution liquid chromatography

This paper explores the changes in the electrospray signal response of 39 structurally different compounds caused by the quality of the methanol, when used as a component in a gradient elution mobile phase. When three batches of LC-MS grade methanol from one manufacturer were evaluated, the largest variation in the electrospray signal responses of the 39 compounds examined was 18%. However, significant enhancement of the electrospray signals of up to 106% were observed among different brands of LC-MS grade methanol from different manufacturers. The effect of methanol quality on signal response was found to be compound dependent. This study also demonstrated that the senescence of the methanol was important. Using an expired batch of LC-MS grade methanol, electrospray signals were suppressed by as much as 95% for all compounds measured using positive mode electrospray. Conversely, the negative mode electrospray signals of compounds such as 4-octyl benzoic acid showed an enhancement of up to 96% when using the same batch of methanol. Linuron was used as a model compound to examine the change in the electrospray response, during gradient elution, when the proportion of an expired batch of methanol was varied. An infusion experiment showed that the linuron signal intensity decreased as the proportion of expired methanol increased in the mobile phase, which was in direct contrast to the increase in linuron signal observed with a non-expired batch of methanol. A series of isocratic experiments also showed that the linuron signal decreased as the proportion of expired methanol increased in the mobile phase. The ion ratios of several of the compounds studied changed significantly when using the expired batch of LC-MS methanol. The change in the ion ratios accentuates the difficulty of identifying compounds from in-source spectral libraries. A protocol is recommended for assessing the quality of methanol for LC-MS applications.

Evaluation of carbamazepine uptake and metabolization by Typha spp., a plant with potential use in phytotreatment

Phytoremediation technologies such as constructed wetlands have shown higher efficiencies in removal of pharmaceuticals from wastewaters than conventional wastewater treatment processes, and plants seem to have an important role in the removal of some of those compounds. In this context, a study was conducted to assess tolerance, uptake, and metabolism of the epilepsy drug, carbamazepine, by the macrophyte Typha spp. This evaluation was conducted in hydroponic solutions with 0.5-2.0mg/L of this pharmaceutical for a maximum period of 21 days. The removal of carbamazepine from nutrient solutions by the plants reached values of 82% of the initial contents. Furthermore, a metabolite (10,11-dihydro-10,11-epoxycarbamazepine) was detected in leaf tissues indicating carbamazepine translocation and metabolism inside plants. Activities of antioxidant enzymes catalase, superoxide dismutase, and guaiacol peroxidase generally increase (after some mild initial inhibition in the case of the latter enzyme) as result of the abiotic stress caused by the exposure to carbamazepine, but ultimately Typha seemed able to cope with its toxicity. The results obtained in this study suggest the ability of Typha spp., to actively participate in the removal of carbamazepine from water when used in phytotreatment systems.

An overview of matrix effects in liquid chromatography-mass spectrometry

Matrix-dependent signal suppression or enhancement represents a major drawback in quantitative analysis with liquid chromatography coupled to atmospheric pressure ionization mass spectrometry (LC-API-MS). Because matrix effects (ME) might exert a detrimental impact on important method parameters (limit of detection, limit of quantification, linearity, accuracy, and precision), they have to be tested and evaluated during validation procedure. This review gives a detailed description on when these phenomena might be expected, and how they can be evaluated. The major sources of ME are discussed and illustrated with examples from bioanalytical, pharmaceutical, environmental, and food analysis. Because there is no universal solution for ME, the main strategies to overcome these phenomena are described in detail. Special emphasis is devoted to the sample-preparation procedures as well as to the recent improvements on chromatographic and mass spectrometric conditions. An overview of the main calibration techniques to compensate for ME is also presented. All these solutions can be used alone or in combination to retrieve the performance of the LC-MS for a particular matrix-analyte combination.

Liquid chromatography coupled with tandem mass spectrometry method for thirty-three pesticides in natural water and comparison of performance between classical solid phase extraction and passive sampling approaches

The aim of this study is to propose an analytical method for determining different classes of pesticides in water using LC-ESI-MS/MS. Two techniques of field-sampling and analyte extraction were used: solid phase extraction (SPE) of water samples from active sampling and field exposure of Polar Organic Chemical Integrative Samplers (POCIS). We have worked with thirty-three molecules representing eight pesticide classes: carbamates, chloroacetanilides, dicarboximides, morpholines, organophosphorous, phenylureas, strobilurines and triazines. First, liquid chromatography separation protocols and the optimization of the ESI-MS/MS parameters were developed. Then, the SPE step was optimized to obtain acceptable levels of recovery for the various classes of molecules. The matrix effect that may significantly lower the ionization efficiency with ESI interfaces was evaluated and minimized. The performances (limits of quantification, accuracy and precision) of the SPE and POCIS techniques were evaluated, and a comparison between the active and passive sampling techniques was carried out with a field application.

Assessing the matrix effects of hemolyzed samples in bioanalysis

Nicola Hughes obtained her PhD in 1992 in Biochemistry at the University of London, UK, where she studied the covalent binding of carcinogenic polyaromatic hydrocarbons to DNA in mouse tissues using the 32P-postlabelling technique. She did her postdoctoral fellowship at the Hospital for Sick Children in Toronto. She specialized in the development of phenotyping and genotyping methods to investigate the pharmacogenetic variations in the N-acetyl transferases in relation to bladder cancer susceptibility and exposure to aromatic amines. She has been at Biovail Contract Research since 1997, when she first joined the Bioanalytical Laboratory as a Senior Scientist in the Method Development Group and is currently the Director of the Bioanalytical Laboratory. Over the years, Nicola has been responsible for providing leadership in the development and application of novel and highly sensitive LC–MS/MS bioanalytical methods and has improved the method validation process at Biovail Contract Research. Nicola is a member of the American Society of Mass Spectrometry and American Society of Pharmaceutical Scientists. She has published more than 20 articles in peer-reviewed journals and presented more than 60 posters and oral presentations at scientific meetings.

Validation of LC–MS/MS assays includes an assessment of matrix effects. Hemolysis effect, a special type of matrix effect, can also have an impact on analyte quantitation. In situations where the hemolysis effect is marginal, this can be resolved simply by dilution of hemolyzed samples with plasma prior to analysis. However, in some cases, the impact can be so dramatic that analytes are completely immeasurable. In such situations, modification to the bioanalytical method will be required, including, but not limited to, adjusting the chromatographic conditions to separate interferences present in hemolyzed samples; additional sample clean-up techniques such as protein precipitation in combination with SPE or a change in extraction technique such as from SPE to a liquid–liquid extraction method. Here, we report examples from four bioanalytical methods, where the presence of hemolyzed blood in plasma was found to have an impact on analyte quantitation and a description of the solutions adopted to resolve this are provided.

Overcoming matrix effects in liquid chromatography-mass spectrometry

A major limitation in quantitative analysis with electrospray ionization mass spectrometry (ESI-MS) is represented by the so-called matrix effects in which the matrix coextracted with the analytes can alter the signal response, causing either suppression or enhancement, resulting in poor analytical accuracy, linearity, and reproducibility. In the direct electron ionization liquid chromatography-mass spectrometry (direct-EI LC-MS) interface the ionization process is based on electron impact ionization, and it occurs in the gas phase and is not influenced by coeluted matrix compounds. In this work we quantitatively evaluated matrix effects on enriched environmental and biological samples, with different extraction procedures, using ESI and direct-EI LC-MS. As expected, the samples analyzed with direct-EI were not affected by matrix composition, whereas with ESI we observed either signal suppression or enhancement, depending on the sample nature.

Occurrence of phytoestrogens in municipal wastewater and surface waters

Phytoestrogens (isoflavones, enterolignans and coumestrol) in wastewater samples and surface water samples have been analysed by LC-ESI-MS(n). In wastewater samples, high levels of enterolactone (581-2111 ng/L), daidzein (341-1688 ng/L) and enterodiol (60-834 ng/L) were detected in raw sewage, but the vast majority of the analysed phytoestrogens were removed effectively in the treatment process. The removal rates of the analysed phytoestrogens in the two advanced tertiary treatment plants were >99%; a case study in one of the treatment plants showed that most of the residual phytoestrogens were removed by biological treatment using activated sludge. In surface water samples, daidzein was found at concentrations ranging from 2 ng/L to 33 ng/L in samples from two creeks, and up to 120 ng/L in surface water (pond) on a dairy farm. The analytical results suggest that direct excretions of livestock discharged from farmyards can be another potential source of phytoestrogen contamination in the aquatic environment.

Plasma free fatty acid profiling in a fish oil human intervention study using ultra-performance liquid chromatography/electrospray ionization tandem mass spectrometry

A rapid method was developed for the simultaneous profiling of 29 free fatty acids in plasma using ultra-performance liquid chromatography/electrospray ionization tandem mass spectrometry (UPLC/ESI-MS/MS). Barium acetate was used as the cationization agent in the positive ion mode for sensitive multiple reaction monitoring (MRM) experiments. The cis- and trans-C18:1 and -C18:2 isomers were baseline-separated using two tandem reversed-phase C18 UPLC columns, while identification of two pairs of positional isomers of C18:3 and C20:3 required isomer-specific product ions, as the analytes were not chromatographically resolved. The assay linearity was greater than three orders of magnitude and correlation coefficients were >0.99; the limits of detections were typically less than 0.2 microM. The method was successfully applied to plasma free fatty acid profiling of samples from volunteers who participated in a randomized crossover study involving the administration of either placebo or fish oil capsules. The results clearly indicate the ability to measure the time profiles of the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in plasma for the volunteers given fish oil capsules while the concentrations of the other free fatty acids and the total free fatty acid concentration in plasma remained virtually constant.