Enrichment and quantification of 18 polycyclic aromatic hydrocarbons from intermediates for plastics production by a generic liquid chromatography column switching.

The polycyclic aromatic hydrocarbon concentration in plastic products is regulated in (European Union) No. 1272/2013. However, this only covers the end products and not intermediate substances. Therefore, a generic method was developed to analyze the polycyclic aromatic hydrocarbons listed by the Environmental Protection Agency and the European Union. This method is based on direct large volume injection from solutions of plastic additives followed by liquid chromatography coupled to fluorescence detection. The additives Irganox 1010, ureido methacrylate, and cetyl methacrylate 1618F were used as examples for method development. Two serially coupled columns allowed the matrix to be removed on the first column and the analytes to be separated on the second column. The columns were connected by an intermediate valve. The valve allowed the matrix to be diverted after the first column and water to be dosed upstream of the second column via an additional pump. This allowed samples in aqueous or organic media to be focused at the column head. An injection volume of 100 µl and online aqueous dilution of 1:3 led to a limit of detection below 1 ng/ml for 15 polycyclic aromatic hydrocarbons. Moreover, concentrations between 1.6 and 10.3 ng/ml were found in the three plastic additives.

Applicability and Limitations of a Capillary-LC Column-Switching System Using Hybrid Graphene-Based Stationary Phases.

Graphene oxide sheets fixed over silica particles (SiGO) and their modification functionalized with C18 and endcapped (SiGO-C18ec) have been reported as sorbents for extraction and analytical columns in LC. In this study, a SiGO column was selected as the extraction column and a SiGO-C18ec as the analytical column to study the applicability and limitations of a column-switching system composed exclusively of columns packed with graphene-based sorbents. Pyriproxyfen and abamectin B1a were selected as the analytes, and orange-flavored carbonated soft drinks as the matrix. The proposed system could be successfully applied to the pyriproxyfen analysis in a concentration range between 0.5 to 25 µg/mL presenting a linearity of R2 = 0.9931 and an intra-day and inter-day accuracy of 82.2-111.4% (RSD < 13.3%) and 95.5-99.8% (RSD < 12.7%), respectively. Furthermore, the matrix composition affected the area observed for the pyriproxyfen: the higher the concentration of orange juice in the soft drink, the higher the pyriproxyfen the signal observed. Additionally, the SiGO extraction column presented a life use of 120 injections for this matrix. In contrast, the proposed system could not apply to the analysis of abamectin B1a, and the SiGO-C18ec analytical column presented significant tailing compared to a similar approach with a C18 analytical column.

Determination of Phenolic Compounds in Beverages by Three-Flow Channel Isocratic HPLC with Electrochemical Detections Using a Column-Switching Technique.

For the quantitative analysis of phenolic compounds in beverage samples, a three-flow channel isocratic HPLC with electrochemical detection (3LC-ECD) system was devised using a column-switching technique. Phenolic compounds with significantly different hydrophobicity (the range of calculated log P: -0.77 to 3.02) were simultaneously measured to draw three chromatograms by the 3LC-ECD; the peaks of gallic acid (GA), protocatechuic acid (PCA), and gallocatechin (GC) were observed at electrochemical detector 1 (D1) within 42 min, the peaks of procyanidin B3 (B3), epigallocatechin (EGC), catechin (C), epicatechin (EC), procyanidin B2 (B2), ethyl gallate (Eg), and epigallocatechin gallate (EGCg) were observed at D2 within 50 min, and the peaks of epicatechin gallate (ECg), gallocatechin gallate (GCg), catechin gallate (Cg), propyl gallate (Pg), and resveratrol (RVT) were observed at D3 within 70 min. The relationships between the phenolic compound concentrations and their chromatographic peak heights gave good linearity with correlation coefficients of more than 0.998. The detection limits of the phenolic compounds by the 3LC-ECD ranged from 0.6 to 3.0 µg/L. Further, the phenolic compound concentrations of commercially available teas and wines were determined with a relative standard deviation (RSD) of less than 4.9% (n = 6), and their recoveries ranged from 91 to 109%. These results indicate that the 3LC-ECD system provided an accurate, precise, and specific determination of the phenolic compounds in beverages without affecting the matrices derived from these samples.

Robust analysis of angiotensin peptides in human plasma: Column switching-parallel LC/ESI-SRM/MS without adsorption or enzymatic decomposition.

Angiotensin (Ang) peptides are the main effectors of the renin-angiotensin system (RAS) regulating diverse physiological conditions and are involved in renal and vascular diseases. Currently, quantitative analyses of Ang peptides in human plasma mainly rely on radioimmunoassay-based methods whose reported levels are quite divergent. Analyses are further complicated by the potential of Ang peptides to bind to solid surfaces, to be enzymatically decomposed during sample preparation, and to undergo post-translational modifications. A column switching-parallel LC/ESI-SRM/MS method has been developed for seven Ang peptides (Ang I, Ang II, Ang III, Ang IV, Ang 1-9, Ang 1-7, and Ang A) in human plasma. Aqueous acetonitrile (5%) containing 50 mM arginine (Arg) as a dissolving solution and a combination of protease inhibitors with formic acid were used to prevent adsorption and enzymatic degradation, respectively. Plasma samples were simply deproteinized with acetonitrile followed by clean-up with an on-line trap column via column-switching. Stable isotope dilution with [13C5,15N1-Val]-Ang peptides as internal standards was employed for quantitative analysis. The current methodology has been successfully applied to determine the plasma levels of Ang peptides in healthy participants, suggesting future applicability to studies of various diseases related to RAS.

Determination of monosaccharides hydrolyzed from polysaccharides in activated sludge by ion chromatography-mass spectrometry with online pretreatment of column switching technique.

The simultaneous determination of monosaccharides present in the activated sludge would be crucial to understand the water treatment mechanism. Herein, an ion chromatography-mass spectrometry (IC-MS) with online pretreatment of column switching technique was proposed to analyze monosaccharides hydrolyzed from extracellular polysaccharides in the activated sludge. When the matrix was eliminated in the first dimension, monosaccharides were immediately identified by IC-MS. The improved ionization efficiency was achieved with the addition of T-joint prior to MS. During the performance test, our established method showed excellent detection limits ranging from 0.34 to 2.15 µg/L for all sugar targets. Great linearity (R ≥ 0.9955) was also achieved using this method in the range from 0.01 to 5 mg/L. Furthermore, the average recoveries were obtained between 84.82 and 113.46%. RSDs for peak areas and retention times were determined as 3.76% and 0.27%, respectively. Finally, this approach provided a rapid, convenient, and practical determination of monosaccharides in the activated sludge, which would be helpful for the analysis of monosaccharides derived from other biological samples.

Polycaprolactone nanofibers functionalized with a dopamine coating for on-line solid phase extraction of bisphenols, betablockers, nonsteroidal drugs, and phenolic acids.

Polycaprolactone composite nanofibers coated with a polydopamine layer are introduced as a new type of absorption material for on-line solid phase extraction (SPE) in chromatographic system. A hybrid technology combining the electrospinning and melt blowing was used for the preparation of 3D-structured microfiber/nanofibrous polycaprolactone composite. The dopamine coating was then applied to functionalize the micro/nanofibers. Polydopamine-coated polycaprolactone fibers were tested as an extraction phase in on-line SPE prior to HPLC separation and UV detection. Four groups of biologically active substances including bisphenols (Bisphenol S, Bisphenol AF, Bisphenol A, Bisphenol C, Bisphenol AP, Bisphenol Z, Bisphenol BP, and Bisphenol M), betablockers (Timolol, Metoprolol, Labetalol, and Propranolol), nonsteroidal antiphlogistic drugs (Salicylic acid, Ketoprofen, Naproxen, Indomethacin, Diclofenac, Ibuprophen, and Meclofenamic acid), and phenolic acids (Chlorogenic acid, Caffeic acid, Sinapic acid, m-Coumaric acid, Benzoic acid, and Cinnamic acid) were used as the model analytes. Neat and coated fibers were compared and applied as sorbents for the on-line extraction set-up. Both materials produced good extraction potential for the determination of bisphenols and nonsteroidal drugs in model biological and environmental samples including river water, human urine, and blood serum. However, the polydopamine layer significantly increased the extraction efficiency of polar drugs. Typical repeatability of on-line extraction procedure on polydopamine coated fibers was in the range 0.12-4.11% for bisphenols, 0.55-1.41% for antiphlogistic drugs, 0.59-2.52% for phenolic acids, and 1.01-1.65% for betablockers. Graphical abstract Schematic representation of polycaprolactone composite nanofibers coated with a polydopamine layer as an advanced absorption material for on-line solid phase extraction in chromatography.

Environmental Metallomics.

Metallomics is the new paradigm about the metallobiomolecules related to living organisms, considering the interactions between toxic and essential metals, transport through biological fluids, passing across biological membranes and interfaces, synergic and antagonist actions among metal species, and alterations in metabolic pathways triggered by overexpression or inhibition of these metallobiomolecules. These challenging studies require the development of new analytical approaches in order to get suitable information of these species close to their native environment which has promoted the application of new tools based in mass spectrometry under the double focus of elemental (ICP-MS) and molecular (Qq-TOF-MS) mass spectrometry, generally arranged with chromatography in multidimensional platforms. The driving force for the design of these new analytical instrumental arrangements is the analyst imagination who adapts the new metallomic methodology to the new problems. In this work the most recent metallomic approaches proposed have been considered, deepening their application to the most frequent problems related to metal toxicity in environmental issues, such as exposure experiments of mice to toxic metals, interactions and homeostasis of metals, metal imaging, metabolic alterations caused by metallobiomolecules over- or down-expressed, and more interestingly real-life consequences of metal species expression in environmental field studies. In this way, the application of two-dimensional chromatographic approaches with ICP-MS detection, the use of multidimensional chromatography-column-switching-ICP-MS devices, metal imaging with LA-ICP-MS, combined application of metallomics and metabolomics for environmental toxicological appraisal, and the application of these metallomic techniques in environmental field studies have been reviewed.

Simple determination of betaine, l-carnitine and choline in human urine using self-packed column and column-switching ion chromatography with nonsuppressed conductivity detection.

A sequential online extraction, clean-up and separation system for the determination of betaine, l-carnitine and choline in human urine using column-switching ion chromatography with nonsuppressed conductivity detection was developed in this work. A self-packed pretreatment column (50 × 4.6 mm, i.d.) was used for the extraction and clean-up of betaine, l-carnitine and choline. The separation was achieved using self-packed cationic exchange column (150 × 4.6 mm, i.d.), followed by nonsuppressed conductivity detection. Under optimized experimental conditions, the developed method presented good analytical performance, with excellent linearity in the range of 0.60-100 µg mL-1 for betaine, 0.75-100 µg mL-1 for l-carnitine and 0.50-100 µg mL-1 for choline, with all correlation coefficients (R2 ) >0.99 in urine. The limits of detection were 0.15 µg mL-1 for betaine, 0.20 µg mL-1 for l-carnitine and 0.09 µg mL-1 for choline. The intra- and inter-day accuracy and precision for all quality controls were within ±10.32 and ±9.05%, respectively. Satisfactory recovery was observed between 92.8 and 102.0%. The validated method was successfully applied to the detection of urinary samples from 10 healthy people. The values detected in human urine using the proposed method showed good agreement with the measurement reported previously.

Simultaneous detection of reduced and oxidized forms of coenzyme Q10 in human cerebral spinal fluid as a potential marker of oxidative stress.

The redox balance of coenzyme Q10 in human plasma is a good marker of oxidative stress because the reduced form of coenzyme Q10 (ubiquinol-10) is very sensitive to oxidation and is quantitatively converted to its oxidized form (ubiquinone-10). Here we describe an HPLC method for simultaneous detection of ubiquinol-10 and ubiquinone-10 in human cerebral spinal fluid to meet a recent demand for measuring local oxidative stress. Since the levels of coenzyme Q10 in human cerebral spinal fluid are less than 1/500 of those in human plasma, cerebral spinal fluid extracted with 2-propanol requires concentration for electrochemical detection. Using human plasma diluted 500-fold with physiological saline as a pseudo-cerebral spinal fluid, we found that addition of tert-butylhydroquinone was effective in preventing the oxidation of ubiquinol-10. The optimized tert-butylhydroquinone concentration in the extraction solvent was 20 µM. The addition of 20 µM ascorbic acid or co-addition of tert-butylhydroquinone and ascorbic acid (20 µM each) were also effective in preventing the oxidation of ubiquinol-10, but ascorbic acid alone gave poor reproducibility. Good within day reproducibility was observed, and day-to-day analytical variance was excellent.

A column switching ultrahigh-performance liquid chromatography-tandem mass spectrometry method to determine anandamide and 2-arachidonoylglycerol in plasma samples.

This study reports a fast, sensitive, and selective column switching ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method to determine the endocannabinoids (eCBs), anandamide (AEA), and 2-arachidonoylglycerol (2-AG) in plasma samples. This bidimensional system used a restricted access media column (RP-8 ADS, 25 mm × 4 mm × 25 µM) in the first dimension and a core-shell Kinetex C18 (100 mm × 2, 1.7 mm × 1 µM) column in the second dimension, followed by detection in a mass spectrometer triple quadrupole (multiple reactions monitoring mode) operating in the positive mode. RP-8 ADS was used for trace enrichment of eCBs (reverse phase partitioning) and macromolecular matrix size exclusion; the core-shell column was used for the chromatographic separation. The column switching UHPLC-MS/MS method presented a linear range spanning from 0.1 ng mL-1 (LOQ) to 6 ng mL-1 for AEA and from 0.04 ng mL-1 (LOQ) to 10 ng mL-1 for 2-AG. Excluding the LLOQ values, the precision assays provided coefficients of variation lower than 8% and accuracy with relative standard error values lower than 14%. Neither carryover nor matrix effects were detected. This high-throughput column switching method compared to conventional methods is time saving as it involves fewer steps, consumes less solvent, and presents lower LLOQ. The column switching UHPLC-MS/MS method was successfully applied to determine AEA and 2-AG in plasma samples obtained from Alzheimer's disease patients. Graphical abstract A column switching ultra high-performance liquid chromatography-tandem mass spectrometry method using RP-8 ADS column and core shell column to determine endocannabinoids in plasma samples.

Accelerated quantification of amphetamine enantiomers in human urine using chiral liquid chromatography and on-line column-switching coupled with tandem mass spectrometry.

Amphetamine (AM) is a powerful psychostimulant existing in two enantiomeric forms. Stereoselective analysis of AM in biosamples can assist clinicians and forensic experts in differentiating between abuse of illicitly synthesized racemic AM and ingestion of pharmaceutical AM formulations containing either S-AM or different proportions of the S- and R-enantiomers. Therefore, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantifying AM enantiomers in urine was newly developed. The method comprised dilution with water, followed by injection of the diluted sample onto an achiral C18 trapping column for purification and subsequent backflush elution to a chiral Lux 3 µm AMP LC column by means of a switching valve. An isocratic mobile phase of 25 % acetonitrile in 0.1 M aqueous ammonia was used for enantiomeric separation. Injection, cleanup, and backflush of the next sample were performed before the previous sample had eluted from the analytical column, thus enabling simultaneous enantioseparation of up to three samples within the analytical column. This novel chromatographic concept allowed for increased sample throughput by accelerating both the sample preparation and the LC analysis. Analyte detection was accomplished by electrospray ionization in positive ion mode and selected reaction monitoring using a triple-stage quadrupole mass spectrometer. The method was successfully validated through assessment of its linearity, lower limit of quantification, accuracy and precision, selectivity, matrix effect, carry-over, dilution integrity, and re-injection reproducibility. Linearity ranged from 0.05 to 25 mg/L for both enantiomers. Proof of the method included analysis of urine samples obtained from drug abusers and patients receiving an S-AM prodrug. Graphical Abstract Enantioselective determination of amphetamine in human urine using liquid chromatography with achiral-chiral column-switching and tandem mass spectrometry.

Determination of betaine, l-carnitine, and choline in human urine using a self-packed column and column-switching ion chromatography with nonsuppressed conductivity detection.

A simple method for the determination of betaine, l-carnitine, and choline in human urine was developed based on column-switching ion chromatography coupled with nonsuppressed conductivity detection by using a self-packed column. A pretreatment column (50 mm × 4.6 mm, id) packed with poly(glycidyl methacrylate-divinylbenzene) microspheres was used for the extraction and cleanup of analytes. Chromatographic separation was achieved within 10 min on a cationic exchange column (150 mm × 4.6 mm, id) using maleic anhydride modified poly(glycidyl methacrylate-divinylbenzene) as the particles for packing. The detection was performed by ion chromatography with nonsuppressed conductivity detection. Parameters including column-switching time, eluent type, flow rates of eluent, and interfering effects were optimized. Linearity (r2 ≥ 0.99) was obtained for the concentration range of 0.50-100, 0.75-100, and 0.25-100 µg/mL for betaine, l-carnitine, and choline, respectively. Detection limits were 0.12, 0.20, and 0.05 µg/mL for betaine, l-carnitine, and choline, respectively. The intra- and interday accuracy and precision for all quality controls were within ±10.11%. Satisfactory recovery was observed between 92.5 and 105.0%. The validated method was successfully applied for the determination of betaine, l-carnitine, and choline in urine samples from healthy people.

Identification of l-carnitine and its impurities in food supplement formulations by online column-switching liquid chromatography coupled with linear ion trap mass spectrometry.

The identification of impurities in l-carnitine by mass spectrometry is difficult because derivative reagents or ion pair reagents are usually used to separate and increase the retention of l-carnitine on the reversed-phase column. In this study, four impurities including 3-chloro-2-hydroxy-N,N,N-trimethylpropan-1-aminium, 3-cyano-2-hydroxy-N,N,N-trimethylpropan-1-aminium, 3-carboxy-N,N,N-trimethylprop-2-en-1-aminium, and 4-chloro-2,3,4-trihydroxy-N,N,N-trimethylbutan-1-aminium were identified in l-carnitine and its tablets by using two-dimensional column-switching high-performance liquid chromatography coupled with linear ion trap mass spectrometry. The first column was a C8 column at a flow rate of 0.15 mL/min; the detection wavelength was 220 nm. The second column was an Acclaim Q1 column using a gradient elution program with aqueous 30 mM ammonium acetate (pH 5.0) and acetonitrile as the mobile phase at a flow rate of 0.5 mL/min. The mass fragmentation patterns and structural assignments of impurities were studied, and the quantitative validation of three impurities was further investigated. The linearity (r2 ) was found to be >0.99, with ranges from 0.2 to 50 ng/mL and 0.1 to 10 ng/mL. The method was used successfully for determination of impurities in five samples of l-carnitine and tablets.

Critical comparison of the on-line and off-line molecularly imprinted solid-phase extraction of patulin coupled with liquid chromatography.

Reaching trace amounts of mycotoxin contamination requires sensitive and selective analytical tools for their determination. Improving the selectivity of sample pretreatment steps covering new and modern extraction techniques is one way to achieve it. Molecularly imprinted polymers as selective sorbent for extraction undoubtedly meet these criteria. The presented work is focused on the hyphenation of on-line molecularly imprinted solid-phase extraction with a chromatography system using a column-switching approach. Making a critical comparison with a simultaneously developed off-line extraction procedure, evaluation of pros and cons of each method, and determining the reliability of both methods on a real sample analysis were carried out. Both high-performance liquid chromatography methods, using off-line extraction on molecularly imprinted polymer and an on-line column-switching approach, were validated, and the validation results were compared against each other. Although automation leads to significant time savings, fewer human errors, and required no handling of toxic solvents, it reached worse detection limits (15 versus 6 µg/L), worse recovery values (68.3-123.5 versus 81.2-109.9%), and worse efficiency throughout the entire clean-up process in comparison with the off-line extraction method. The difficulties encountered, the compromises made during the optimization of on-line coupling and their critical evaluation are presented in detail.

Development and validation of an HPLC-UV method for the simultaneous determination of the antipsychotics clozapine, olanzapine and quetiapine, several beta-blockers and their metabolites.

A simple, accurate and selective column-switching high-performance liquid chromatography (HPLC) method was developed and validated for simultaneous quantification of six beta-blockers (metoprolol, timolol, bisoprolol, propranolol, carvedilol and nebivolol), three of their metabolites (α-hydroxy metoprolol, N-desisopropyl propranolol and 4'-hydroxy carvedilol 4-HCAR), three antipsychotics (olanzapine, clozapine and quetiapine) and three of their metabolites (N-desmethyl olanzapine, N-desmethyl clozapine and N-desalkyl quetiapine) in human serum. After pretreatment on a Merck LiChrospher RP-4 ADS column (25 µm), drugs were separated on a Phenomenex Gemini Phenyl Hexyl 110 A column (250 × 4.6 mm, 5 µm) using a gradient mixture of acetonitrile and potassium dihydrogen phosphate buffer pH 3.1 (containing 10% methanol) as a mobile phase at a flow rate of 1 mL/min. The total analysis time was 40 min. For detection of the analytes, four different UV wavelengths were used: 215, 226, 242 and 299 nm. The method was validated according to the guidelines of the Society of Toxicology and Forensic Chemistry in terms of selectivity, linearity, accuracy, precision and stability and successfully applied for the analysis of the 15 described analytes in human serum.

An overview of multidimensional liquid phase separations in food analysis.

Food safety is a priority public health concern that demands analytical methods capable to detect low concentration level of contaminants (e.g. pesticides and antibiotics) in different food matrices. Due to the high complexity of these matrices, a sample preparation step is in most cases mandatory to achieve satisfactory results being usually tedious, lengthy, and prone to the introduction of errors. For this reason, many research groups have focused efforts on the development of online systems capable to do the cleanup, concentration, and separation steps at once through multidimensional separation techniques (MDS). Among several possible setups, the most popular are the multidimensional chromatographic techniques (MDC) that consist in combining more than one mobile and/or stationary phase to provide a satisfactory separation. In the present review, we selected a variety of multidimensional separation systems used for food contaminant analysis in order to discuss the instrumentation aspects, the concept of orthogonality, column approaches used in these systems, and new materials that can be used in these columns. Selected classes of contaminants present in food matrices are introduced and discussed as example of the potential applications of multidimensional liquid phase separation techniques in food safety.

Development of a rapid column-switching LC-MS/MS method for the quantification of THCCOOH and THCCOOH-glucuronide in whole blood for assessing cannabis consumption frequency.

The concentration of 11-nor-9-carboxy-Δ(9)-tetrahydrocannabinol (THCCOOH) in whole blood is used as a parameter for assessing the consumption behavior of cannabis consumers. The blood level of THCCOOH-glucuronide might provide additional information about the frequency of cannabis use. To verify this assumption, a column-switching liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the rapid and direct quantification of free and glucuronidated THCCOOH in human whole blood was newly developed. The method comprised protein precipitation, followed by injection of the processed sample onto a trapping column and subsequent gradient elution to an analytical column for separation and detection. The total LC run time was 4.5 min. Detection of the analytes was accomplished by electrospray ionization in positive ion mode and selected reaction monitoring using a triple-stage quadrupole mass spectrometer. The method was fully validated by evaluating the following parameters: linearity, lower limit of quantification, accuracy and imprecision, selectivity, extraction efficiency, matrix effect, carry-over, dilution integrity, analyte stability, and re-injection reproducibility. All acceptance criteria were analyzed and the predefined criteria met. Linearity ranged from 5.0 to 500 µg/L for both analytes. The method was successfully applied to whole blood samples from a large collective of cannabis consumers, demonstrating its applicability in the forensic field.

Automated screening of reversed-phase stationary phases for small-molecule separations using liquid chromatography with mass spectrometry.

There are various reversed-phase stationary phases that offer significant differences in selectivity and retention. To investigate different reversed-phase stationary phases (aqueous stable C18 , biphenyl, pentafluorophenyl propyl, and polar-embedded alkyl) in an automated fashion, commercial software and associated hardware for mobile phase and column selection were used in conjunction with liquid chromatography and a triple quadrupole mass spectrometer detector. A model analyte mixture was prepared using a combination of standards from varying classes of analytes (including drugs, drugs of abuse, amino acids, nicotine, and nicotine-like compounds). Chromatographic results revealed diverse variations in selectivity and peak shape. Differences in the elution order of analytes on the polar-embedded alkyl phase for several analytes showed distinct selectivity differences compared to the aqueous C18 phase. The electron-rich pentafluorophenyl propyl phase showed unique selectivity toward protonated amines. The biphenyl phase provided further changes in selectivity relative to C18 with a methanolic phase, but it behaved very similarly to a C18 when an acetonitrile-based mobile phase was evaluated. This study shows the value of rapid column screening as an alternative to excessive mobile phase variation to obtain suitable chromatographic settings for analyte separation.

Rapid determination of 12 antibiotics and caffeine in sewage and bioreactor effluent by online column-switching liquid chromatography/tandem mass spectrometry.

This study presents a column-switching solid-phase extraction online-coupled to a liquid chromatography/tandem mass spectrometry (SPE-LC-MS/MS) method for simultaneous analysis of 12 antibiotics (7 sulfonamides and 5 fluoroquinolones) and caffeine detected in the sewage and effluent of a pilot anaerobic reactor used in sewage treatment. After acidification and filtration, the samples were directly injected into a simple and conventional LC system. Backflush and foreflush modes were compared based on the theoretical plates and peak asymmetry observed. The method was tested in terms of detection (MDL) and quantification limit (MQL), linearity, relative recovery, and precision intra- and inter-day in lab-made sewage samples. The method presented suitable figures of merit in terms of detection, varying from 8.00 × 10(-5) to 6.00 × 10(-2) ng (0.800 up to 600 ng L(-1); caffeine) with direct injection volume of only 100 µL and 13 min of total analysis time (sample preparation and chromatographic run). When the method was applied in the analysis of sewage and effluent of the anaerobic reactor (n = 15), six antibiotics and caffeine were detected in concentrations ranging from 0.018 to 1097 µg L(-1). To guarantee a reliable quantification, standard addition was used to overcome the matrix effect.

Analysis of hydroxamate siderophores in soil solution using liquid chromatography with mass spectrometry and tandem mass spectrometry with on-line sample preconcentration.

A liquid chromatography with electrospray ionization mass spectrometry method was developed to quantitatively and qualitatively analyze 13 hydroxamate siderophores (ferrichrome, ferrirubin, ferrirhodin, ferrichrysin, ferricrocin, ferrioxamine B, D1 , E and G, neocoprogen I and II, coprogen and triacetylfusarinine C). Samples were preconcentrated on-line by a switch-valve setup prior to analyte separation on a Kinetex C18 column. Gradient elution was performed using a mixture of an ammonium formate buffer and acetonitrile. Total analysis time including column conditioning was 20.5 min. Analytes were fragmented by applying collision-induced dissociation, enabling structural identification by tandem mass spectrometry. Limit of detection values for the selected ion monitoring method ranged from 71 pM to 1.5 nM with corresponding values of two to nine times higher for the multiple reaction monitoring method. The liquid chromatography with mass spectrometry method resulted in a robust and sensitive quantification of hydroxamate siderophores as indicated by retention time stability, linearity, sensitivity, precision and recovery. The analytical error of the methods, assessed through random-order, duplicate analysis of soil samples extracted with a mixture of 10 mM phosphate buffer and methanol, appears negligible in relation to between-sample variations.