Determination of oxalate in beer by zone electrophoresis on a chip with conductivity detection

The use of a poly(methylmethacrylate) capillary electrophoresis chip, provided with a high sample load capacity separation system (a 8500 nL separation channel combined with a 500 nL sample injection channel) and a pair of on‐chip conductivity detectors, for zone electrophoresis (ZE) determination of oxalate in beer was studied. Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the chip were suppressed and electrophoresis was a dominant transport process in the separations performed on the chip. A low pH of the carrier electrolyte (3.8), implemented by aspartic acid and bis‐tris propane, provided an adequate selectivity in the separation of oxalate from anionic beer constituents and, at the same time, also a sufficient sensitivity in its conductivity detection. Under our working conditions, this anion could be detected at a 0.5 μmol/L concentration also in samples containing chloride (a major anionic constituent of beer) at a 1800 higher concentration. Such a favorable analyte/matrix concentration ratio made possible accurate and reproducible [typically, 2–5% relative standard deviation (RSD) values of the peak areas of the analyte in dependence on its concentration in the sample] determination of oxalate in 500 nL volumes of 20–50‐fold diluted beer samples. Short analysis times (about 200 s), minimum sample preparation, and reproducible migration times of this analyte (0.5–1.0% RSD values) were characteristic for ZE on the chip.     

Determination of oxalate in urine by zone electrophoresis on a chip with conductivity detection

The use of a poly(methylmethacrylate) capillary electrophoresis chip, provided with a high sample load capacity separation system (a 8500 nL separation channel coupled to a 500 nL sample injection channel) and a pair of on-chip conductivity detectors, for zone electrophoresis (ZE) determination of oxalate in urine was studied. Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the chip were suppressed and electrophoresis was a dominant transport process in the separations performed on the chip. A low pH of the carrier electrolyte (4.0) provided an adequate selectivity in the separation of oxalate from anionic urine constituents and, at the same time, also a sufficient sensitivity in its conductivity detection. Under our working conditions, this anion could be detected at a 8 x 10(-8) mol/L concentration also in samples containing chloride (a major anionic constituent of urine) at 3.5 x 10(-3) mol/L concentrations. Such a favorable analyte/matrix concentration ratio (in part, attributable to a transient isotachophoresis stacking in the initial phase of the separation) made possible accurate and reproducible (typically, 2-5% relative standard deviation (RSD) values of the peak areas of the analyte in dependence on its concentration in the sample) determination of oxalate in 500 nL volumes of 20-100-fold diluted urine samples. Short analysis times (about 280 s), no sample pretreatment (not considering urine dilution) and reproducible migration times of this analyte (0.5-1.0% RSD values) were characteristic for ZE on the chip. This work indicates general potentialities of the present chip design in rapid ZE analysis of samples containing the analyte(s) at high ionic matrix/analyte concentration ratios.     

On‐line coupled capillary isotachophoresis‐capillary zone electrophoresis in hydrodynamically closed separation system hyphenated with laser induced fluorescence detection

An analytical method, based on a column coupling capillary ITP and CZE in a hydrodynamically closed separation mode hyphenated with the detection in the modular arrangement, was developed in this work. Analytical possibilities of this approach are demonstrated on the direct and ultrasensitive quantitative determination of quinine (QUI) in diluted real multicomponent ionic matrices (beverages, urine). The detection cell interface, with the rectangular arrangement of the optical channels inside, connected the separation capillary with the LIF detector via optical fibers in the on‐column detection arrangement. ITP enabled the direct large volume (30 μL) injections of the diluted real matrices with an on‐line sample pretreatment (preseparation, preconcentration) so that no external sample preparation (except for the dilution) was necessary for the separation of the analyte in the multicomponent ionic matrices. Due to the ITP sample preconcentration and intrinsic sensitivity of the LIF detection, very low concentration LOD (as low as 77 pg/mL), were reached at the same time. This was ca. two orders lower than the corresponding LOD achieved by the same 2D separation system with UV absorbance detection. Compared to the single column CE‐LIF methods applied for this model analyte and matrix, this method was found to be superior in terms of concentration LOD, with acceptable selectivity and benefits of the on‐line sample preparation. A food control and bioanalytical application clearly illustrates great practical possibilities and routine use of the proposed modular ITP–CZE–LIF technique.     

Determination of free sulfite in wine by zone electrophoresis with isotachophoresis sample pretreatment on a column-coupling chip

This work deals with the determination of free sulfite in wine by zone electrophoresis (ZE) with on-line isotachophoresis (ITP) sample pretreatment on a column-coupling (CC) chip with conductivity detection. A rapid pre-column conversion of sulfite to hydroxymethanesulfonate (HMS), to minimize oxidation losses of the analyte, was included into the developed analytical procedure, while ITP and ZE were responsible for specific analytical tasks in the separations performed on the CC chip. ITP, for example, eliminated the sample matrix from the separation compartment and, at the same time, provided a selective concentration of HMS before its transfer to the ZE stage of the separation. On the other hand, ZE served as a final separation (destacking) method and it was used under the separating conditions favoring a sensitive conductivity detection of HMS. In this way, ITP and ZE cooperatively contributed to a 900 microg/l concentration detectability for sulfite as attained for a 60 nl load of wine (a 15-fold wine dilution and the use of a 0.9 microl sample injection channel of the chip) and, consequently, to the determination of free sulfite when this was present in wine at the concentrations as low as 3 mg/l. The separations were carried out in a closed separation compartment of the chip with suppressed hydrodynamic and electroosmotic flows. Such transport conditions, minimizing fluctuations of the migration velocities of the separated constituents, made a frame for precise migration and quantitation data as achieved for HMS in both the model and wine samples. Ninety percent recoveries, as typically obtained for free sulfite in wine samples, indicate promising potentialities of the present method as far as the accuracies of the provided analytical results are concerned.     

Scaling behavior in on‐chip field‐amplified sample stacking

Field amplified sample stacking (FASS) uses differential electrophoretic velocity of analyte ions in the high‐conductivity background electrolyte zone and low conductivity sample zone for increasing the analyte concentration. The stacking rate of analyte ions in FASS is limited by molecular diffusion and convective dispersion due to nonuniform electroosmotic flow (EOF). We present a theoretical scaling analysis of stacking dynamics in FASS and its validation with a large set of on‐chip sample stacking experiments and numerical simulations. Through scaling analysis, we have identified two stacking regimes that are relevant for on‐chip FASS, depending upon whether the broadening of the stacked peak is dominated by axial diffusion or convective dispersion. We show that these two regimes are characterized by distinct length and time scales, based on which we obtain simplified nondimensional relations for the temporal growth of peak concentration and width in FASS. We first verify the theoretical scaling behavior in diffusion‐ and convection‐dominated regimes using numerical simulations. Thereafter, we show that the experimental data of temporal growth of peak concentration and width at varying electric fields, conductivity gradients, and EOF exhibit the theoretically predicted scaling behavior. The scaling behavior described in this work provides insights into the effect of varying experimental parameters, such as electric field, conductivity gradient, electroosmotic mobility, and electrophoretic mobility of the analyte on the dynamics of on‐chip FASS.     

Separation of proteins by zone electrophoresis on-line coupled with isotachophoresis on a column-coupling chip with conductivity detection

This feasibility study deals with the separations of proteins by an on-line combination of zone electrophoresis (ZE) with isotachophoresis (ITP) on a poly(methylmethacrylate) column-coupling (CC) chip with integrated conductivity detection. ITP and ZE provided specific analytical functions while performing the cationic mode of the separation. ITP served, mainly, for concentrations of proteins and its concentrating power was beneficial in reaching a low dispersion transfer (injection) of the proteinous constituents, loaded on the CC chip in a 960 nL volume, into the ZE separation stage. This was complemented by an electrophoretically driven removal of the sample constituents migrating in front of the focused proteins from the separation system before the ZE separation. On the other hand, ZE served as a final separation (destacking) method and it was used under the separating conditions providing the resolutions and sensitive conductivity detections of the test proteins. In this way, ITP and ZE cooperatively contributed to low- or sub-microg/mL concentration detectabilities of proteins and their quantitations at 1-5 microg/mL concentrations. However, a full benefit in concentration detectabilities of proteins, expected from the use of the ITP-ZE combination, was not reached in this work. Small adsorption losses of proteins and detection disturbances in the ZE stage of separation, very likely due to trace constituents concentrated by ITP, appear to set limits in the detection of proteins in our experiments. The ITP-ZE separations were carried out in a hydrodynamically closed separation compartment of the chip with suppressed hydrodynamic and electroosmotic flows of the electrolyte solutions. Such transport conditions, minimizing fluctuations of the migration velocities of the separated constituents, undoubtedly contributed to highly reproducible migrations of the separated proteins (fluctuations of the migration time of a particular protein were typically 0.5% RSD in repeated ITP-ZE runs).     

Separation of Enantiomers by On‐Line Capillary Isotachophoresis‐Capillary Zone Electrophoresis

The ability of capillary zone electrophoresis (CZE) coupled on‐line with capillary isotachophoresis (ITP) sample pretreatment in the column‐coupling capillary electrophoresis equipment to separate trace enantiomers present in samples of complex ionic matrices and enantiomers present in their mixtures at significantly differing concentrations has been studied. Enantiomers of 2,4‐dinitrophenyl labeled norleucine (DNP‐Nleu) and tryptophan enantiomers were employed as model analytes in this work while urine and mixtures of tryptophan enantiomers of differing concentrations served as model samples. Experiments performed with urine samples spiked with the DNP‐Nleu racemate at sub‐μmol/L concentrations demonstrated excellent sample pretreatment capabilities of ITP (concentration of the analytes, in‐column and post‐column sample clean up) when coupled on‐line with chiral CZE separations. In the CZE separations of enantiomers present in the samples at trace concentrations the sample pretreatment could be performed in both achiral and chiral ITP electrolyte systems. The use of a chiral electrolyte system was found to be essential in the ITP pretreatment of the samples containing the enantiomers at very differing concentrations. For example, a 2×10^–7 mol/L concentration of L‐tryptophan could be detected in the CZE separation stage of the ITP‐CZE combination in samples containing about a 10⁴ excess of D‐tryptophan only when the ITP pretreatment was carried out in the electrolyte system providing the resolution of enantiomers (α‐cyclodextrin served for this purpose in the present work). A post‐column ITP sample clean up was found effective in enhancing the destacking rate of the trace enantiomer in the CZE stage when the migration configuration of the enantiomers was less favorable (the trace constituent migrating behind the major enantiomer).     

Lab‐on‐a‐Chip Sensor with Evaporated Bismuth Film Electrode for Anodic Stripping Voltammetry of Zinc

In this work, we report on the development of a lab‐on‐a‐chip electrochemical sensor that uses an evaporated bismuth electrode to detect zinc using square wave anodic stripping voltammetry. The microscale electrochemical cell consists of a bismuth working electrode, an integrated silver/silver chloride reference electrode, and a gold auxiliary electrode. The sensor exhibits a linear response in 0.1 M acetate buffer at pH 6 with zinc concentrations in the 1–30 μM range and a calculated detection limit of 60 nM. The sensor successfully detected zinc in a bovine serum extract and the results were corfirmed by independent AAS measurements. Our results demonstrate the advantageous qualities of this lab‐on‐a‐chip electrochemical sensor for clinical applications, which include small sample volume (µL scale), reduced cost, short response time and high accuracy at low concentrations of analyte.     

Sample pre-concentration by isotachophoresis in microfluidic devices

We have designed microfluidic devices with the aim of coupling isotachophoresis (ITP) with zone electrophoresis (ZE) as a method to increase the concentration limit of detection in microfluidic devices. We used plastic multi-channel chips, designed with long sample injection channel segments, to increase the sample loading. The chip was designed to allow stacking of the sample into a narrow band by discontinuous ITP buffers and subsequent separation in the ZE mode. In the ITP-ZE mode, with a 2-cm long sample injection plug, sensitivity was increased by 400-fold over chip ZE and we found that the separation performance after the ITP stacking was comparable to that of regular chip ZE. We report sub-picomolar limits of detection of fluorescently labeled ACLARA eTag reporter molecules electrokinetically injected from cell lysate sample matrixes containing moderate salt concentrations. We evaluated sample injections from buffers with varied ionic strengths and found that efficient stacking and separations were obtained in both low and high conductivity buffers, including physiological buffer with at least 140 mM salt. We applied ITP-ZE to the analysis of a cell surface protease (ADAM 17) which used live intact cells in physiological buffers with detection limits below 10 cells/assay.     

Trace analysis of glyphosate in water by capillary electrophoresis on a chip with high sample volume loadability

A new method for the determination of trace glyphosate (GLYP), non-selective pesticide, by CZE with online ITP pre-treatment of drinking waters on a column-coupling (CC) chip has been developed. CC chip was equipped with two injection channels of 0.9 and 9.9 μL volumes, two separation channels of 9.3 μL total volume and a pair of conductivity detectors. A very effective ITP sample clean-up performed in the first channel at low pH (3.2) was introduced for quick CZE resolution and detection of GLYP carried out at higher pH (6.1) in the second channel on the CC chip. The LOD for GLYP was estimated at 2.5 μg/L (15 nmol/L) using a 9.9 |mL volume of the injection channel. ITP-CZE analyses of model and real samples have provided very favorable intra-day (0.1-1.2% RSD) and inter-day (2.9% RSD) repeatabilities of the migration time for GLYP while 0.2-6.9% RSD values were typical for the peak area data. Recoveries of GLYP in spiked drinking water varied in the range of 99-109%. A minimum pre-treatment of drinking water (degassing and dilution) and a short analysis time (ca. 10 min) were distinctive features of ITP-CZE determinations of GLYP on the CC chip with high sample volume loaded, as well.     

Quantification of acyclovir in dermal interstitial fluid and human serum by ultra‐high‐performance liquid–high‐resolution tandem mass spectrometry for topical bioequivalence evaluation

Time–concentration curves for the topical anti‐viral drug acyclovir can provide valuable information for drug development. Open flow microperfusion is used for continuous sampling of dermal interstitial fluid but it requires validated methods for subsequent sample analysis. Therefore, we developed a sensitive, selective and high‐throughput ultra‐high‐performance liquid chromatography–high‐resolution tandem mass spectrometry method to determine acyclovir in human dermal interstitial fluid and serum. We validated the method over a concentration range of 0.1–25 ng/mL for a sample volume of just 20 μL and employed cation‐exchange solid‐phase extraction in a fully automated sample treatment procedure. Short‐ and long‐term sample stability data and the analysis of 5000 samples from a clinical trial demonstrate the successful application of our method.     

Rapid quantification of quinine by multi‐stacking in a portable microchip electrophoresis system

A new multi‐stacking pre‐concentration procedure based on field‐enhanced sample injection (FESI), field‐amplified sample stacking, and transient isotachophoresis was developed and implemented in a compact microchip electrophoresis (MCE) with a double T‐junction glass chip, coupled with an on‐chip capacitively coupled contactless conductivity detection (C⁴D) system. A mixture of the cationic target analyte and the terminating electrolyte (TE) from the two sample reservoirs was injected under FESI conditions within the two sample‐loading channels. At the double T‐junction, the stacked analyte zones were further concentrated under field‐amplified stacking conditions and then subsequently focused by transient‐isotachophoresis and separated along the separation channels. The proposed multi‐stacking strategy was verified under a Universal Serial Bus (USB) fluorescence microscope employing Rhodamine 6G as the model analyte. This developed approach was subsequently used to monitor the target quinine present in human plasma samples. The total analysis time for quinine was approximately 200 s with a sensitivity enhancement factor of approximately 61 when compared to the typical gated injection. The detection and quantification limits of the developed approach for quinine were 3.0 μg/mL and 10 μg/mL, respectively, with intraday and interday repeatability (%RSDs, n = 5) of 3.6 and 4.4%. Recoveries in spiked human plasma were 98.1–99.8%.     

Preconcentration and separation of double-stranded DNA fragments by electrophoresis in plastic microfluidic devices

We have evaluated double-stranded DNA separations in microfluidic devices which were designed to couple a sample preconcentration step based on isotachophoresis (ITP) with a zone electrophoretic (ZE) separation step as a method to increase the concentration limit of detection in microfluidic devices. Developed at ACLARA BioSciences, these LabCard trade mark devices are plastic 32 channel chips, designed with a long sample injection channel segment to increase the sample loading. These chips were designed to allow stacking of the sample into a narrow band using discontinuous ITP buffers, and subsequent separation in the ZE mode in sieving polymer solutions. Compared to chip ZE, the sensitivity was increased by 40-fold and we showed baseline resolution of all fragments in the PhiX174/HaeIII DNA digest. The total analysis time was 3 min/sample, or less than 100 min per LabCard device. The resolution for multiplexed PCR samples was the same as obtained in chip ZE. The limit of detection was 9 fg/microL of DNA in 0.1xpolymerase chain reaction (PCR) buffers using confocal fluorescence detection following 488 nm laser excitation with thiazole orange as the fluorescent intercalating dye.     

Determination of total sulfite in wine. Zone electrophoresis-isotachophoresis quantitation of sulfate on a chip after an in-sample oxidation of total sulfite

This work deals with the determination of total sulfite in wine. The determination combines an in-sample hydrogen peroxide oxidation of total sulfite in alkalized wine to sulfate with the separation and quantitation of the latter anion by zone electrophoresis (ZE) on-line coupled with isotachophoresis (ITP) on a column-coupling chip. Sample clean up, integrated into the ITP-ZE separation, eliminated wine matrix in an extent comparable to that provided by a highly selective distillation isolation of sulfite. At the same time, conductivity detection, employed to the detection of sulfate in the ZE stage of the ITP-ZE combination, provided for sulfate the concentration limit of detection corresponding to a 90 microg/l concentration of sulfite in the loaded sample (0.9 microl). Such a detectability allowed a reproducible quantitation of total sulfite when its concentration in wine was 15 mg/l. Formaldehyde binding of free sulfite in wine, included into the pre-column sample preparation, prevented an uncontrolled oxidation of this sulfite form. This step contributed to an unbiased determination of sulfate present in the original wine sample (this determination corrected for the concentration of sulfate determined in the sample after the peroxide oxidation of sulfite to the value equivalent to the total sulfite). The 99-101% recoveries of sulfite, determined for appropriately spiked wine samples, indicate a very good accuracy of the present method. Such a statement also supports excellent agreements of the results of quantitation based on the in-sample peroxide oxidation of the total sulfite (bound sulfite released at a high pH) with those in which this analyte was isolated from wine by distillation (bound sulfite released at a very low pH).     

Column switching in zone electrophoresis on a chip

This feasibility study deals with column switching in zone electrophoresis (ZE) separations on a column coupling (CC) chip. The column switching implemented into the ZE separations an on-chip sample clean up applicable for both the multicomponent and high salinity samples. In addition, complemented by different separation mechanisms in the coupled columns (channels), it provided benefits of two-dimensional separations. Properly timed column switching gave column-to-column transfers of the analytes, characterized by 99-102% recoveries, delivered to the second separation stage on the chip the analyte containing fractions contaminated only with minimum amounts of the matrix constituents. A diffusion driven transport of the matrix constituents to the second channel of the chip (due to direct contacts of the electrolyte solutions in the bifurcation region), representing 0.1-0.2% of the loaded sample constituents, was found to accompany the sample clean up performed on the CC chip. This source of potential disturbances to the separation in the second channel, however, is not detectable in a majority of practical situations. With respect to a 900 nl volume of the sample channel on the CC chip, the electric field and isotachophoresis (ITP) stackings were employed to minimize the injection dispersion in the separations and concentrate the analytes. Here, the column switching, removing a major part of the stacker from the separation system, provided a tool effective in a control of the destacking of analytes. Highly reproducible ZE separations as attained in this work also for the chip-to-chip and equipment-to-equipment frames can be ascribed, at least in part, to suppressions of electroosmotic and hydrodynamic flows of the solutions in which the separations were performed.     

Isotachophoresis of proteins in a networked microfluidic chip: experiment and 2-D simulation

This paper reports both the experimental application and 2-D simulation of ITP of proteins in a networked microfluidic chip. Experiments demonstrate that a mixture of three fluorescent proteins can be concentrated and stacked into adjacent zones of pure protein under a constant voltage of 100 V over a 2 cm long microchannel. Measurements of the isotachophoretic velocity of the moving zones demonstrates that, during ITP under a constant voltage, the zone velocity decreases as more of the channel is occupied by the terminating electrolyte. A 2-D ITP model based on the Nernst-Planck equations illustrates the stacking and separation features of ITP using simulations of three virtual proteins. The self-sharpening behavior of ITP zones dispersed by a T-junction is clearly demonstrated both by experiment and by simulation. Comparison of 2-D simulations of ITP and zone electrophoresis (ZE) confirms that ZE lacks the ability to resharpen protein zones after they pass through a T-junction.     

Determination of bromate in drinking water by zone electrophoresis-isotachophoresis on a column-coupling chip with conductivity detection

The use of capillary zone electrophoresis (CZE) on-line coupled with isotachophoresis (ITP) sample pretreatment (ITP-CZE) on a poly(methylmethacrylate) chip, provided with two separation channels in the column-coupling (CC) arrangement and on-column conductivity detection sensors, to the determination of bromate in drinking water was investigated. Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the chip were suppressed and electrophoresis was a dominant transport process in the ITP-CZE separations. A high sample load capacity, linked with the use of ITP in this combination, made possible loading of the samples by a 9.2 microL sample injection channel of the chip. In addition, bromate was concentrated by a factor of 10(3) or more in the ITP stage of the separation and, therefore, its transfer to the CZE stage characterized negligible injection dispersion. This, along with a favorable electric conductivity of the carrier electrolyte solution, contributed to a 20 nmol/L (2.5 ppb) limit of detection for bromate in the CZE stage. Sample cleanup, integrated into the ITP stage, effectively complemented such a detection sensitivity and bromate could be quantified in drinking water matrices when its concentration was 80 nmol/L (10 ppb) or slightly less while the concentrations of anionic macroconstituent (chloride, sulfate, nitrate) in the loaded sample corresponding to a 2 mmol/L (70 ppm) concentration of chloride were still tolerable. The samples containing macroconstituents at higher concentrations required appropriate dilutions and, consequently, bromate in these samples could be directly determined only at proportionally higher concentrations.     

Supported liquid extraction in combination with LC‐MS/MS for high‐throughput quantitative analysis of hydrocortisone in mouse serum

A high‐throughput LC–MS/MS bioanalytical method was developed and validated for the determination of hydrocortisone in mouse serum via supported liquid extraction (SLE) in a 96‐well plate format. Although sample extracts from SLE result in similar matrix effects compared with conventional liquid–liquid extraction (LLE), greater analyte extraction recovery and much higher analysis throughput for the quantitative analysis of hydrocortisone in mouse serum were obtained. The current LC‐MS/MS method was validated for a concentration range of 2.00–2000 ng/mL for hydrocortisone using a 0.100 mL volume of mouse serum. The intra‐ and inter‐day precision and accuracy of the quality control samples at low, medium and high concentration levels showed ≤12.9% CV and ?3.4–6.2% bias for the analyte in mouse serum. Copyright © 2009 John Wiley & Sons, Ltd.     

Capacitance‐to‐digital: The upgrades of single chip detector

The capacitance‐to‐digital single chip detector was upgraded. The paper discusses hardware issues and benefits of the designed/upgraded detector. The device can be operated from rechargeable lithium‐ion battery as stand‐alone, portable system and is capable of transmitting real‐time data wirelessly. The detector and additional modules (battery, battery holder, microcontroller board, wireless module) weight is less than 85 g. Electrophoretic separation in low conductivity 20 mM MES/L‐His buffer, pH 6.1, was performed in order to evaluate detection parameters. The system is capable of quantification of potassium ions down to 0.31 μM. Investigation of differential signal acquisition configuration showed improved performance regarding external noise and temperature fluctuations. The system can be a solution for stand‐alone, field‐portable capillary format separation detector.     

Toxicological screening of human plasma by on‐line SPE‐HPLC‐DAD: identification and quantification of basic drugs and metabolites

An automated multi‐analyte screening method for the identification and quantification of 92 drugs and metabolites based on on‐line solid‐phase extraction–high‐performance liquid chromatography–diode array detection technique was developed and successfully validated. In addition, a database with 870 entries including UV‐spectra, relative/retention times and response factors of toxicologically relevant compounds was created. Plasma samples (0.2 mL) were treated with methanol, diluted with buffer and on‐line extracted (Strata X, 20 ×2 mm, 25 µm) at pH 9. Analytical separation was carried out on a Gemini NX column (150 ×4.6 mm, 3 µm) using gradient elution with acetonitrile–water (90:10,v/v) and 0.05 m potassium dihydrogen phosphate buffer (pH 2.3). Linear calibration curves with correlation coefficients ≥0.9950 were obtained for 78 analytes. As an additional benefit, the newly developed method allows the quantification of 42 analytes (e.g. antidepressants, neuroleptics and anticonvulsants) in a concentration range suitable for therapeutic drug monitoring. Limits of quantitation ranged from 0.02 mg/L (chlordiazepoxide) to 3.4 mg/L (mexiletine). Inter‐ and intra‐day precisions of quality control samples (low/high) were better than 15% (zolpidem) and accuracy (bias) ranged from ?11% (opipramol, venlafaxine) to 11% (venlafaxine, trazodone). Tests for carry‐over and sample stability under different storage conditions were also performed and stability was adequate. Four cases of poisoning analysis are presented. Copyright © 2014 John Wiley & Sons, Ltd.