Effect of liquid chromatography separation of complex matrices on liquid chromatography-tandem mass spectrometry signal suppression

General method for detecting acrylamide in foods and comprehensive survey of acrylamide in foods sold in Southeast China

This study aimed to investigate the distribution of acrylamide (AA) in food by developing a universal method for detecting AA in various foods and analyzing the levels of AA in 437 food samples collected from Southeast China. The developed method was simple, rapid, and widely applicable, with an average recovery rate range of 81.7-94.2% and a relative standard deviation range of 1.7-8.2%. The limit of detection (LOD, 2.0-3.4 µg kg-1) and limit of quantitation (LOQ, 6.0-10 µg kg-1) were also determined. AA was detected in all types of food, with a total detection rate of 76%, and the levels ranged from LOQ to 6020 µg kg-1. Potato chips had the highest level of AA (mean value of 504 µg kg-1), whereas pastries had the lowest level (mean value < 6.0 µg kg-1). Kruskal-Wallis analysis revealed significant differences in AA levels among different foods (H = 229.8, p < 0.05). The AA safety limit intake recommendations suggested that the intake of high-AA foods should be strictly controlled to reduce the risk of potential carcinogenic effects. The developed method provides a useful tool for monitoring AA levels in food.

Rapid determination of plasma vigabatrin by LC-ESI-MS/MS supporting therapeutic drug monitoring in children with infantile spasms

Vigabatrin is one of the second-generation anti-seizure medications (ASMs) designated orphan drugs by the FDA for monotherapy for pediatric patients with infantile spasms from 1 month to 2 years of age. Vigabatrin is also indicated as the adjunctive therapy for adults and pediatric patients 10 years of age and older with refractory complex partial seizures. Ideally, the vigabatrin treatment entails achieving complete seizure freedom without significant adverse effects, and the therapeutic drug monitoring (TDM) will make a significant contribution to this aim, which provides a pragmatic approach to such epilepsy care in that the dose tailoring can be undertaken for uncontrollable seizures and in cases of clinical toxicity guided by the drug concentrations. Thus, reliable assays are mandatory for TDM to be valuable, and blood, plasma, or serum are the matrixes of choice. In this study, a simple, rapid, and sensitive LC-ESI-MS/MS method for the measurement of plasma vigabatrin was developed and validated. The sample clean-up was performed by an easy-to-use method, i.e., protein precipitation using acetonitrile (ACN). Chromatographic separation of vigabatrin and vigabatrin-¹³C,d₂ (internal standard) was achieved on the Waters symmetry C18 column (4.6 mm × 50 mm, 3.5 μm) with isocratic elution at a flow rate of 0.35 mL min^-1. The target analyte was completely separated by elution with a highly aqueous mobile phase for 5 min, without any endogenous interference. The method showed good linearity over the 0.010-50.0 μg mL^-1 concentration range with a correlation coefficient r² = 0.9982. The intra-batch and inter-batch precision and accuracy, recovery, and stability of the method were all within the acceptable parameters. Moreover, the method was successfully used in pediatric patients treated with vigabatrin and also provided valuable information for clinicians by monitoring plasma vigabatrin levels in our hospital.

Current Developments of Analytical Methodologies for Aflatoxins' Determination in Food during the Last Decade (2013-2022), with a Particular Focus on Nuts and Nut Products

This review aims to provide a clear overview of the most important analytical development in aflatoxins analysis during the last decade (2013-2022) with a particular focus on nuts and nuts-related products. Aflatoxins (AFs), a group of mycotoxins produced mainly by certain strains of the genus Aspergillus fungi, are known to impose a serious threat to human health. Indeed, AFs are considered carcinogenic to humans, group 1, by the International Agency for Research on Cancer (IARC). Since these toxins can be found in different food commodities, food control organizations worldwide impose maximum levels of AFs for commodities affected by this threat. Thus, they represent a cumbersome issue in terms of quality control, analytical result reliability, and economical losses. It is, therefore, mandatory for food industries to perform analysis on potentially contaminated commodities before the trade. A full perspective of the whole analytical workflow, considering each crucial step during AFs investigation, namely sampling, sample preparation, separation, and detection, will be presented to the reader, focusing on the main challenges related to the topic. A discussion will be primarily held regarding sample preparation methodologies such as partitioning, solid phase extraction (SPE), and immunoaffinity (IA) related methods. This will be followed by an overview of the leading analytical techniques for the detection of aflatoxins, in particular liquid chromatography (LC) coupled to a fluorescence detector (FLD) and/or mass spectrometry (MS). Moreover, the focus on the analytical procedure will not be specific only to traditional methodologies, such as LC, but also to new direct approaches based on imaging and the ability to detect AFs, reducing the need for sample preparation and separative techniques.

Review of the Use of Liquid Chromatography-Tandem Mass Spectrometry in Clinical Laboratories: Part I-Development

The process of method development for a diagnostic assay based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) involves several disparate technologies and specialties. Additionally, method development details are typically not disclosed in journal publications. Method developers may need to search widely for pertinent information on their assay(s). This review summarizes the current practices and procedures in method development. Additionally, it probes aspects of method development that are generally not discussed, such as how exactly to calibrate an assay or where to place quality controls, using examples from the literature. This review intends to provide a comprehensive resource and induce critical thinking around the experiments for and execution of developing a clinically meaningful LC-MS/MS assay.

Simultaneous determination of pesticides from soils: a comparison between QuEChERS extraction and Dutch mini-Luke extraction methods

The expanding nature of the agricultural sector has fuelled the intensification of plant protection products usage, including pesticides. These pesticides may persist in soils, necessitating their accurate determination in a variety of soil types. However, due to their complex nature, the effective extraction of pesticide residues from soil matrices can present challenges to pesticide detection and quantification. This research compared two well-known extraction methods, QuEChERS and Dutch mini-Luke, by assessing their specificity, sensitivity, accuracy, precision and reproducibility in extracting seven distinct pesticides with a range of chemico-physical characteristics from Irish soils. The HPLC-UV conditions were optimised to separate the seven pesticides, and it was shown that both extraction methods successfully extracted neonicotinoids with recovery values ranging between 85 and 115%. Fluroxypyr and prothioconazole could not be efficiently extracted using QuEChERS, however, the recovery values of both the analytes ranged between 59 and 117% using Dutch mini-Luke. Furthermore, with the exception of prothioconazole using Dutch mini-Luke, both extraction methods resulted in reproducibility and precision values below or equal to 20%. Lastly, Dutch mini-Luke is noted to have a lower matrix effect than QuEChERS, except for prothioconazole. The comparison results showed that Dutch mini-Luke resulted in superior method sensitivity, better recovery, and lower matrix effect towards most investigated analytes and was the only extraction technique that successfully extracted all pesticides analysed in soil matrices.

Application of Dried Blood Spot Cards combined with liquid chromatography-tandem mass spectrometry to determine eight fat-soluble micronutrients in human blood

The analysis of the fat-soluble vitamins A and E and lipid micronutrients in blood, such as carotenoids, is an important parameter to monitor the micronutrient status in humans. Although the potential of dried blood spot (DBS) cards, the use of this technique for blood sampling and subsequent analysis of these fat-soluble micronutrients has been poorly or not studied. An analytical method based on DBS cards (FTA® DMPK-A) combined with liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) has been developed and validated for the determination of carotenoids (lutein, zeaxanthin, β-cryptoxanthin and β-carotene), tocopherols (α-tocopherol, γ-tocopherol and δ-tocopherol) and all-trans-retinol in human blood. Under optimum DBS card extraction conditions, the extraction recoveries of the studied compounds were higher than 72%, the sample matrix effect lower than 17%, and the detection limits at hundred nM concentration levels. The developed method was applied to the analysis of human blood, and the concentration ranges obtained fell within the expected ranges previously reported in healthy adults. Moreover, the influence of hematocrit effect was investigated in a range of 25-55% in order to compare the obtained results to those reported in the literature for the analysis of plasma samples. This method represents an improvement over current techniques reported in the literature due to the use of a non-invasive blood collection method, and moreover, this methodology was for the first time 1) validated for the analysis of all-trans-retinol, tocopherols and carotenoids, and 2) applied for the determination of tocopherols in human blood samples.

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.

Simultaneous determination of pesticides, mycotoxins, and metabolites as well as other contaminants in cereals by LC-LC-MS/MS

A 2D LC-MS/MS method for the simultaneous determination of 350 pesticides, 16 mycotoxins as well as the growth regulators Chlormequat and Mepiquat was developed. The method is applicable to cereals and products thereof. Attention should be paid to the simultaneous analysis of the cereal-relevant mycotoxins aflatoxin B1, B2, G1 and G2, ochratoxin A, deoxynivalenol and zearalenone. Moreover, the tropane alkaloids atropine/scopolamine could be integrated into the final method. The samples were extracted with a mixture of acetonitrile/water (80:20), diluted with acetonitrile and injected into an LC-LC-MS/MS system. There were no further manual clean-up steps. The automatic online clean-up took place during the HILIC-separation in the first dimension (YMC-Pack Diol; 2.1 × 100 mm; 5 μm, 120 Å). Here, polar matrix compounds were retained, while the majority of the analyte scope eluted in a fraction at the beginning of the analytical run. This fraction was transferred to the second dimension by a packed loop interface (Agilent Zorbax SB-C8; 4.6 × 12.5 mm; 5 μm; 80 Å). On the second column (Phenomenex Synergi Fusion RP C18; 2 × 100 mm; 2.5 μm; 100 Å), the majority of the scope was separated by a typical RP-gradient. Only some of the polar pesticides could not be transferred to the second column. They eluted directly after the transfer step from the HILIC-column to the MS/MS. The final method was sensitive enough to meet all the regulated maximum levels for pesticides in cereals according to EU Regulation 396/2005 and those for contaminants according to EU Regulation 1881/2006. Above all, the method was so robust and accurate that nearly 90% of the pesticides and all the tested mycotoxins, growth regulators and tropane alkaloids fulfilled the validation criteria of the SANTE guideline document, although the demanding criteria are only applicable to pesticides. For the verification, eight proficiency tests were passed successfully: three for the pesticide analysis, three for the mycotoxin analysis, and two for the analysis of the tropane alkaloids. In addition to the already mentioned contaminants, the six most important ergot alkaloids (e.g. ergotamine/ergotaminine) and two modified mycotoxins (deoxynivalenol-3-glucoside and zearalenone-sulfate, also known as masked mycotoxins) were detected during the routine analysis of rye and corn samples.

Matrix effect management in liquid chromatography mass spectrometry: the internal standard normalized matrix effect

LC-MS is becoming a standard for many applications, thanks to high sensitivity and selectivity; nevertheless, some issues are still present, particularly due to matrix effect (ME). Considering this, the use of optimal internal standards (ISs, usually stable-isotope labeled) is important, but not always possible because of cost or availability. Therefore, a deep investigation of the inter-lot variability of the ME and of the correcting power of the chosen IS (isotope-labeled or not) is mandatory. While the adoption of isotopically labeled ISs considered as a 'gold standard' to mitigate ME impact on analytical results, there is not consensus about the standard technique to evaluate it during method validation. In this paper, currently available techniques to evaluate, reduce or counterbalance ME are presented and discussed. Finally, these techniques were summarized in a flowchart for a robust management of ME, particularly considering the concept of 'internal standard normalized ME'.

NMR-based plasma metabolomic discrimination for male fertility assessment of rats treated with Eurycoma longifolia extracts

Male infertility is one of the leading causes of infertility which affects many couples worldwide. Semen analysis is a routine examination of male fertility status which is usually performed on semen samples obtained through masturbation that may be inconvenient to patients. Eurycoma longifolia (Tongkat Ali, TA), native to Malaysia, has been traditionally used as a remedy to boost male fertility. In our recent studies in rats, upon the administration of high-quassinoid content extracts of TA including TA water (TAW), quassinoid-rich TA (TAQR) extracts, and a low-quassinoid content extract including quassinoid-poor TA (TAQP) extract, sperm count (SC) increased in TAW- and TAQR-treated rats when compared to the TAQP-treated and control groups. Consequently, the rats were divided into normal- (control and TAQP-treated) and high- (TAW- and TAQR-treated) SC groups [Ebrahimi et al. 2016]. Post-treatment rat plasma was collected. An optimized plasma sample preparation method was developed with respect to the internal standards sodium 3- (trimethylsilyl) propionate- 2,2,3,3- d4 (TSP) and deuterated 4-dimethyl-4-silapentane-1-ammonium trifluoroacetate (DSA). Carr-Purcell-Meibum-Gill (CPMG) experiments combined with orthogonal partial least squares discriminant analysis (OPLS-DA) was employed to evaluate plasma metabolomic changes in normal- and high-SC rats. The potential biomarkers associated with SC increase were investigated to assess fertility by capturing the metabolomic profile of plasma. DSA was selected as the optimized internal standard for plasma analysis due to its significantly smaller half-height line width (W _h/2) compared to that of TSP. The validated OPLS-DA model clearly discriminated the CPMG profiles in regard to the SC level. Plasma profiles of the high-SC group contained higher levels of alanine, lactate, and histidine, while ethanol concentration was significantly higher in the normal-SC group. This approach might be a new alternative applicable to the fertility assessment in humans through the quantitative metabolomic analysis of plasma without requiring semen.

ABBREVIATIONS

TA: Tongkat Ali; LOD: limit of detection; LOQ: limit of quantification; HPLC-UV: high performance liquid chromatography-ultrviolet; PDA: photodiode array; NMR: nuclear magnetic resonance; FID: free induction decay; LC-MS: liquid chromatography-mass spectrometry; GC-MS: gas chromatography-mass spectrometry; HSQC: heteronuclear single quantum coherence; CPMG: Carr-Purcell-Meibum-Gill; VLDL: very low density lipoprotein; HDL: high density lipoprotein; EDTA: ethylenediaminetetraacetic acid; ANOVA: analysis of variance; AMIX: analysis of mixtures; SIMCA: soft independent modeling of class analogy; PCA: principal components analysis; OPLS-DA: orthogonal partial least-squares discriminant analysis; VIP: variable importance plot; AUROC: area under the receiver operating characteristic; TSP: sodium 3-(trimethylsilyl) propionate- 2,2,3,3- d4; DSA: deuterated 4-dimethyl-4-silapentane-1-ammonium trifluoroacetate; ESI: electrospray ionization; TCA: trichloroacetic acid; ACN: acetonitrile; dd H₂O: distilled deionized water; FSH: follicle-stimulating hormone; LH: luteinizing hormone; OECD: Organisation for Economic Co-operation and Development.

Mass spectrometry as a quantitative tool in plant metabolomics

Metabolomics is a research field used to acquire comprehensive information on the composition of a metabolite pool to provide a functional screen of the cellular state. Studies of the plant metabolome include the analysis of a wide range of chemical species with very diverse physico-chemical properties, and therefore powerful analytical tools are required for the separation, characterization and quantification of this vast compound diversity present in plant matrices. In this review, challenges in the use of mass spectrometry (MS) as a quantitative tool in plant metabolomics experiments are discussed, and important criteria for the development and validation of MS-based analytical methods provided.This article is part of the themed issue 'Quantitative mass spectrometry'.

Mass spectrometry-based plant metabolomics: Metabolite responses to abiotic stress

Metabolomics is one omics approach that can be used to acquire comprehensive information on the composition of a metabolite pool to provide a functional screen of the cellular state. Studies of the plant metabolome include analysis of a wide range of chemical species with diverse physical properties, from ionic inorganic compounds to biochemically derived hydrophilic carbohydrates, organic and amino acids, and a range of hydrophobic lipid-related compounds. This complexitiy brings huge challenges to the analytical technologies employed in current plant metabolomics programs, and powerful analytical tools are required for the separation and characterization of this extremely high compound diversity present in biological sample matrices. The use of mass spectrometry (MS)-based analytical platforms to profile stress-responsive metabolites that allow some plants to adapt to adverse environmental conditions is fundamental in current plant biotechnology research programs for the understanding and development of stress-tolerant plants. In this review, we describe recent applications of metabolomics and emphasize its increasing application to study plant responses to environmental (stress-) factors, including drought, salt, low oxygen caused by waterlogging or flooding of the soil, temperature, light and oxidative stress (or a combination of them). Advances in understanding the global changes occurring in plant metabolism under specific abiotic stress conditions are fundamental to enhance plant fitness and increase stress tolerance. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 35:620-649, 2016.

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.

An Economical Online Solid-Phase Extraction LC-MS/MS Method for Quantifying Methylprednisolone

An economical, reproducible and automated online solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry method was developed to quantify methylprednisolone in human plasma. The method was validated in terms of selectivity, precision/accuracy, process efficiency, stability, cartridge reproducibility and carryover studies. Sample pretreatment was performed by protein precipitation and elimination using methanol followed by water dilution. Then, the mixture was passed onto the HySphere C8 EC-SE online solid-phase extraction cartridge followed by the separation of the analytes on an Agilent Eclipse XDB column. Electrospray ionization in positive ion mode and multiple reaction monitoring were used to monitor the ion transitions at m/z 375.4/160.8 for methylprednisolone, and m/z 361.2/147.0 for prednisolone. The calibration curve ranged from 5.25 to 525 ng/mL. Meanwhile both the intra-day and inter-day precision values (relative standard deviation) were within 4.45%. The method which turns out to be less laborious, faster and lower consumable cost per sample has already been successfully applied to a pharmacokinetic study in which the oral administration of 16 mg methylprednisolone was conducted in Chinese volunteers.

Validation of a LC-MS/MS method for quantifying urinary nicotine, six nicotine metabolites and the minor tobacco alkaloids--anatabine and anabasine--in smokers' urine

Tobacco use is a major contributor to premature morbidity and mortality. The measurement of nicotine and its metabolites in urine is a valuable tool for evaluating nicotine exposure and for nicotine metabolic profiling--i.e., metabolite ratios. In addition, the minor tobacco alkaloids--anabasine and anatabine--can be useful for monitoring compliance in smoking cessation programs that use nicotine replacement therapy. Because of an increasing demand for the measurement of urinary nicotine metabolites, we developed a rapid, low-cost method that uses isotope dilution liquid chromatography-tandem mass spectrometry (LC-MS/MS) for simultaneously quantifying nicotine, six nicotine metabolites, and two minor tobacco alkaloids in smokers' urine. This method enzymatically hydrolyzes conjugated nicotine (primarily glucuronides) and its metabolites. We then use acetone pretreatment to precipitate matrix components (endogenous proteins, salts, phospholipids, and exogenous enzyme) that may interfere with LC-MS/MS analysis. Subsequently, analytes (nicotine, cotinine, hydroxycotinine, norcotinine, nornicotine, cotinine N-oxide, nicotine 1'-N-oxide, anatabine, and anabasine) are chromatographically resolved within a cycle time of 13.5 minutes. The optimized assay produces linear responses across the analyte concentrations typically found in urine collected from daily smokers. Because matrix ion suppression may influence accuracy, we include a discussion of conventions employed in this procedure to minimize matrix interferences. Simplicity, low cost, low maintenance combined with high mean metabolite recovery (76-99%), specificity, accuracy (0-10% bias) and reproducibility (2-9% C.V.) make this method ideal for large high through-put studies.

Water-based extraction and liquid chromatography-tandem mass spectrometry analysis of neonicotinoid insecticides and their metabolites in green pepper/tomato samples

This paper proposes an environmentally friendly method involving water-based extraction of the samples, cleanup of the extracts by solid-phase extraction, and subsequent liquid chromatography coupled with tandem mass spectrometry, which was used for simultaneous determination of seven hydrophilic neonicotinoid insecticides as well as their metabolites in agricultural samples. The effects of sample matrix on detection of the target compounds were negligibly small. Mean recoveries obtained at spiked concentrations between 0.01 and 1.00 mg/kg were 71.2-122.3% with relative standard deviations of ≤ 7.5%. When the method was applied to crop samples sprayed with commercial formulations of the target compounds, the residual concentrations of the compounds determined by the proposed method (0.015-0.27 mg/kg in green peppers and 0.017-0.31 mg/kg in tomatoes) were equivalent to those determined by the official Japanese method (0.017-0.26 mg/kg in green peppers and 0.013-0.30 mg/kg in tomatoes).

Bioanalysis for plasma protein binding studies in drug discovery and drug development: views and recommendations of the European Bioanalysis Forum

Plasma protein binding (PPB) is an important parameter for a drug’s efficacy and safety that needs to be investigated during each drug-development program. Even though regulatory guidance exists to study the extent of PPB before initiating clinical studies, there are no detailed instructions on how to perform and validate such studies. To explore how PPB studies involving bioanalysis are currently executed in the industry, the European Bioanalysis Forum (EBF) has conducted three surveys among their member companies: PPB studies in drug discovery (Part I); in vitro PPB studies in drug development (Part II); and in vivo PPB studies in drug development. This paper reflects the outcome of the three surveys, which, together with the team discussions, formed the basis of the EBF recommendation. The EBF recommends a tiered approach to the design of PPB studies and the bioanalysis of PPB samples: ‘PPB screening’ experiments in (early) drug discovery versus qualified/validated procedures in drug development.

Automated determination of phenolic compounds in wine, berry, and grape samples using 96-blade solid phase microextraction system coupled with liquid chromatography-tandem mass spectrometry

An automated 96-thin-film solid phase microextraction system was optimized for high throughput analysis of phenolic compounds in wine, berry, and grape samples. Liquid chromatography and tandem mass spectrometry methods were optimized and applied for separation and detection of compounds. Evaluation of five different stationary phases showed that polystyrene-divinylbenzene-polyacrylonitrile (PS-DVB-PAN) is the optimum extraction phase for the extraction of phenolic compounds under study. The thin-film PS-DVB-PAN SPME coating provided almost exhaustive extraction recovery for all phenolics compounds under study, except for naringenin with 80% recovery. Extraction efficiency, inter- and intra-day reproducibility, sensitivity, linearity, limit of detection and quantitation, and matrix effect were evaluated. Intra-day and inter-day reproducibility were in the respective range of 4-8 and 7-13% relative standard deviation (RSD) for all eight phenolic compounds. Limits of detection and quantitation of the proposed SPME-LC-MS/MS system for the analysis of analytes under study were found in the range of 0.2-3 and 0.5-10 ng/mL, respectively. Standard addition calibration was applied for the quantitative determination of unknown phenolic compounds from wine, berry, and grape samples. The assessment of matrix effect showed significant reduction of ion suppression/enhancement using SPME method in comparison with that of solvent extraction technique.

Is SPE necessary for environmental analysis? A quantitative comparison of matrix effects from large-volume injection and solid-phase extraction based methods

Environmental analysis by large-volume injection (LVI) was compared to solid-phase extraction (SPE) based methods using matrix effects as a quantitative indicator of analytical signal quality. LVI was performed by the direct injection of 900 μL of wastewater onto a high-performance liquid chromatography (HPLC) column while SPE-based methods utilized octadecyl silane (C18) and hydrophobic-lypophilic balance (HLB) solid phases to preconcentrate wastewater prior to analysis. Model analytes from three classes of environmental contaminants were selected for study including four estrogens (estrone, estradiol, estriol, and ethinylestradiol), eight perfluoroalkyl carboxylates (C4-C11), and five perfluoroalkyl sulfonates (C4, C6-C8, and C10). The matrix effects on analytes were assessed by two approaches (quantitatively by calculating percent matrix effects and qualitatively with postcolumn infusions) and compared across LVI- and SPE-based methods at constant (high and low) analyte-to-matrix mass ratios. The results from this study demonstrated that the LVI-based method produced analytical signals of quality similar to the two SPE-based methods. Furthermore, LVI presented a clear advantage over SPE because it was performed at lower cost, required fewer materials, involved less labor and eliminated the analyte loss associated with SPE.

A solvation-based screening approach for metabolite arrays

This paper explores a new method for screening metabolites in an array format based on relative polarity using selective solvent dissolution. A synthetic cocktail of metabolites was spotted onto a hydrophobic silicon surface, and solubilised with solvents of varying polarity. The metabolites retained on the silicon surface after the solvent treatments were detected using time-of-flight static secondary ion mass spectrometry (ToF-sSIMS). Solvent-specific metabolite retention was clearly evident on multivariate analysis of the dataset, using principal component analysis. Selective removal of metabolites was observed when solvents with different polarity were used, with the metabolite retention or removal in most cases correlating to the polarity of the solvent used, although consideration of other forces in operation may be needed to arrive at fully predictable behaviours. This approach provides the basis for development of a technique to separate complex metabolites into simpler constituents in a metabolite array prior to identification and quantification using mass spectrometry. It is an analytical approach that is intermediate between the more rapid but less informative direct analysis methods (such as DIMS) that do not involve any analyte separations and the more comprehensive but time consuming methods (such as GC- and LC-MS) that involve chromatographic or electrophoretic separations. The approach has the potential to be successfully developed for rapid, yet informative screening of metabolomes.

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.

Simultaneous determination of 23 amino acids and 7 biogenic amines in fermented food samples by liquid chromatography/quadrupole time-of-flight mass spectrometry

A novel liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (LC-Q-TOFMS) method was developed for the simultaneous determination of 23 amino acids and 7 biogenic amines in food samples. These analytes were pre-column derivatized with dansyl chloride and then separated in an Acquity column (1.7 μm; 2.1 mm × 100 mm). The separation of 31 compounds including an internal standard was achieved within 25 min at a flow rate of 0.2 mL/min. The method linearity for each amino acid and biogenic amine had a relatively wide range with r(2)>0.99. The intra- and inter-day precision, expressed as relative standard deviation (RSD), ranged from 1.1 to 4.6% and from 2.0 to 11.2%, respectively. The limit of detection was between 0.005 and 0.4 μg/mL. With a simple dilution, recoveries of around 80-120% were obtained for most of the compounds. No significant matrix effect was observed, and the developed method was successfully applied to the analysis of amino acids and biogenic amines in beer, cheese and sausage samples.

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.

Metabolomic applications of HILIC-LC-MS

Hydrophilic interaction liquid chromatography (HILIC), although not a new technique, has enjoyed a recent renaissance with the introduction of robust and reproducible stationary phases. It is consequently finding application in metabolomics studies, which have traditionally relied on the stability of reversed phases (RPs), since the biofluids analyzed are predominantly aqueous and thus contain many polar analytes. HILIC's retention of those polar compounds and use of solvents readily compatible with mass spectrometry have seen its increasing adoption in studies of complex aqueous metabolomes. This review describes the stationary phases and their features, surveys HILIC-LC-MS's role in metabolomics experiments, discusses approaches to data extraction and analysis including multivariate analysis, and reviews the literature on HILIC-MS applications in metabolomics.

Compensation of matrix effects by postcolumn infusion of a monitor substance in multiresidue analysis with LC-MS/MS

This study systematically compares matrix effects in liquid chromatography (LC) coupled by electrospray ionization (ESI) in the positive mode with tandem mass spectrometry (MS/MS) for 129 pesticides in 20 plant matrixes. In total, 2388 analyte/matrix combinations were evaluated. Permanent postcolumn infusion (PCI) of analyte standards was used to quantify matrix effects over the whole chromatographic run time. This allowed the analyte signal suppression or enhancement, by different coeluting matrix components, to be assessed throughout the duration of an entire chromatographic run, i.e., independent of a specific retention time. Matrix effects occurring at a certain retention time in one matrix were surprisingly similar for different analytes with diverse physicochemical properties. On the basis of this finding, a new approach for matrix effect compensation in multiresidue analysis was developed in which one single monitor substance is permanently added postcolumn. Signal intensities of all analytes obtained by LC-MS/MS analysis of sample extracts are then corrected for the matrix effect recorded by the monitor substance. With the use of this approach, strong matrix effects could be reduced and apparent recoveries increased from 45% to 85% on average. With dependence on the particular sample matrix, between 69% and 100% of the analytes showed recoveries between 60% and 140% after correction. Thus this approach may significantly reduce the number of cases in which standard addition is required to confirm violations of maximum residue levels.