Calibration Matrix Research Articles

Validation of an LC-MS/MS Method for the Quantification of Caffeine and Theobromine Using Non-Matched Matrix Calibration Curve.

Caffeine is one of the most widely consumed psycho-stimulants. The study of the beneficial effects of caffeine consumption to decrease the risk of developing several neuropsychiatric pathologies is receiving increasing attention. Thus, accurate and sensitive methods have been developed, mainly by LC-MS/MS, in order to quantify caffeine and its metabolites. These quantifications of caffeine and its metabolites by LC-MS/MS require a considerable effort to select or find a surrogate matrix, without the compounds of interest, to be used in the calibration curves. Thus, we evaluated the possibility of using calibration curves prepared in solvent instead of calibration curves prepared in human plasma. Results show that the calibration curves prepared in solvent and in human plasma were similar by comparing their slopes and interceptions, and the accuracy and precision were within the limits of acceptance for both calibration curves. This work demonstrates that, by using internal standards, it is possible to use a calibration curve in solvent instead of a calibration curve in plasma to perform an accurate and precise quantification of caffeine and theobromine.

Rotation Calibration Method for Thrust Based on Force Error Analysis

Accurate measurement of thrust in rocket engine, as a core parameter of attitude control of rocket engine, is an important guarantee for reliable operation of rocket engines. Therefore, it is very important for accurate calibration. In this paper, a novel rotation calibration method for rocket thrust engine is proposed based on piezoelectric force measurement system. Based on the calibration matrix, sensitivity analysis model of calibration accuracy to coupling relationship between axes is established, and error mechanism and offset mechanism of force are studied. Starting from the deviation principle between actual axis of thrust system and theoretical one, an elliptical geometrical distribution law of lateral force caused by main force is obtained. According to the periodicity of ellipse distribution of calibration force, a new calibration method, rotation calibration method, is obtained based on an idea of homogenization error. Finally, vector force verification is designed, and experimental data are calibrated with the rotation calibration method compared with the traditional linear calibration method, verifying feasibility and rationality of the calibration method. The novel calibration can be also used in force measurement in any rotation devices like manipulator in robot,thrust vector engine, manufacturing force, rocket engine,etc.

Simultaneous determination of food colorants in liquid samples by UV‐Visible spectroscopy and multivariate data analysis using a reduced calibration matrix

AbstractColorants are widely used in food industry to improve appearance of edible products. This work present a method for the determination of two colorants, tartrazine and allura red, with UV‐Vis spectrophotometry and MCR‐ALS using only five standards for calibration and the correlation constraint. MCR‐ALS is usually applied in second‐order data but it rarely has been used for first order data, for which is more usual the use of PLS. In this case, MCR‐ALS applied to first order data can show some advantages like interference identification and the use of a reduced calibration matrix. Using this methodology, the relative errors obtained are below 0.28%, correlation coefficients are above 0.99 and the calculated LOD and LOQ are 0.26 and 0.80 mg L‐1 for allura red and 0.70 and 2.11 mg L‐1 for tartrazine respectively. The procedure has been successfully applied to some food dyes and other liquid commercial products and, compared to HPLC analysis, no significant differences were found in the results. Recovery values obtained at two spiked levels were between 92.0% and 106.7% except for a sample.

On Calibration and Direction Finding with Uniform Circular Arrays

Antenna array calibration methods and narrowband direction finding (DF) techniques will be outlined and compared for a uniform circular array. DF is stated as an inverse problem, which solution requires a parametric model of the array itself. Because real arrays suffer from mechanical and electrical imperfections, analytic array models are per se not applicable. Mitigation of such disturbances by a global calibration matrix will be addressed, and methods to estimate this calibration matrix will be recapped from literature. Also, a novel method will be presented, which circumvents the problem of a changed noise statistic due to calibration. Furthermore, local calibration, where array calibration measurements are incorporated in the DF algorithm, is considered as well. Common DF algorithms will be outlined, their assumptions regarding array properties will be addressed, and required preprocessing steps such as the beam-space transformation will be presented. Also, two novel DF techniques will be proposed, based on the Capon beamformer, but with reduced computational effort and higher resolution for bearing estimation. Simulations are used to exemplary compare calibration and DF methods in conjunction with each other. Furthermore, measurements with a single and two coherent sources are considered. It turns out that global calibration enables computational efficient DF algorithms but causes biased estimates. Furthermore, resolution of two coherent sources necessitates array calibration.

Rapid Identification and Determination of N-Nitrosamines in Food Products by Ultra-High-Performance Liquid Chromatography–High Resolution Quadrupole-Time-of-Flight Mass Spectrometry by Exact Masses of Protonated Molecules

A method is proposed for the rapid identification and determination of seven N-nitrosamines in food products by ultra-high-performance liquid chromatography in combination with high-resolution quadrupole-time-of-flight mass spectrometry. The ranges of detectable concentrations of N-nitrosamines are from 0.001–5 to 2–100 ng/mL for liquid (water, beer) and from 2–50 to 4–100 ng/g for solid (meat, fish, mussels, malt, grain, sausage, wieners, and bockwursts) products. The limits of detection are 0.0005–2 ng/mL, 2–5 ng/g for liquid and solid products, respectively. The recovery of analytes is from 62 to 105%. The matrix effect was estimated in determining N-nitrosamines in samples of different nature. The matrix effect is negligible (≤20%) in the determination of N-nitrosamines in water and is significant for beer, meat products, grain, malt, and fish (>20%). A procedure is proposed for the rapid identification and determination of N-nitrosamines by the standard addition method and using matrix calibration. The relative standard deviation of the results of analysis does not exceed 17%. The duration of sample identification is 40 min; the determination of the detected analytes takes 1–1.5 h.

Simultaneous separation and detection chiral fenobucarb enantiomers using UPLC–MS/MS

A reliable and sensitive method was developed and validated for the determination of chiral pesticide fenobucarb enantiomers with UPLC–MS/MS. The fenobucarb enantiomers were baseline separated on Daicel IG-3 chiral column using a mixture of acetonitrile and 0.1% formic acid water (60:40, v/v) as mobile phase. The absolute configuration of fenobucarb enantiomers was confirmed as (R)-(+)-fenobucarb and (S)-(−)-fenobucarb by experimental and calculated electronic circular dichroism spectra. Good linearity (R2 > 0.9962) was obtained for the four matrix calibration curves within the range of 0.5–50 μg mL−1. The limit of detection of the two enantiomers were in the range of 0.07–0.16 μg L−1. The mean recoveries of the two enantiomers ranged from 80.4 to 102% with intra-day relative standard deviations (RSDs) from 1.8 to 6.6% and inter-day RSDs from 3.0 to 5.7% in four matrices. The (R)-(+)-fenobucarb degraded faster than (S)-(−)-isomer in cucumber. The established method can provide additional information for the further research about the enantioselective environmental behaviors of fenobucarb.

Discovering the spatio-temporal impacts of built environment on metro ridership using smart card data

The primary objective of this study is to identify the spatio-temporal relationship between metro ridership and built environment by integrating smart card data with online point of interest (POI) data. This study proposes the geographically weighted regression (GWR) model to address the spatial autocorrelation and nonstationarity of metro ridership at the station level. Different from the Euclidean distance (ED) commonly used in the traditional GWR, the Minkowski distance (MD) metric is introduced into the study to measure geographical distance and improve weighting matrix calibrations. This study provides useful insights in adaptive model settings based on selections of spatial range and distance metric parameters. A case study is conducted in Nanjing, China, by utilizing large-scale metro smart card data and POI data obtained from the Gaode map by a web crawler written in Python. The comparative analysis indicates that MD-GWR achieves better goodness-of-fit than the global ordinary least squares (OLS) and traditional GWR in the case of modeling metro ridership. Finally, this study quantifies the impacts of built environment at both spatial and temporal scales, under the proposed modeling structure. We examine the existence of job-housing separation and corresponding areas in spatio-temporal ridership analysis. Impacts of non-commuting activities and intermodal connection on boarding and alighting ridership differ in spatial and temporal ranges. The proposed modeling structure promotes modeling precision and thus enhances the understanding of the relationship between station-level ridership and surrounding built environment, which can provide useful guidance for planning departments and transit agencies to implement targeted policies and create accessible, livable and vibrant communities.

Micro-Residual Stress Measurement in Nanocomposite Reinforced Polymers

Abstract In the present study, residual stress is measured in fiber-reinforced SWCNT/epoxy at weight fractions of 0.1% and 0.5% with a cross-ply layup on a micro-scale. The mechanical properties of the SWCNT/epoxy composites were determined by tensile testing and the Young's modulus of the epoxy increased moderately with the addition of CNTs. The micro-residual stress of the cross-ply CF/epoxy and CNF-reinforced CF/epoxy laminates were measured using a new experimental approach. The micro-hole was milled by laser beam and the surface displacement was recorded by SEM after milling. In order to determine the residual stress from the recorded strain, the calibration matrix was calculated using the finite element method. The residual stress was obtained at a certain hole depth of specimens. The reliability of this approach was assessed by comparing the residual stress measurements from this method and from the standard hole-drilling method. The experimental results of the present approach confirmed that laser hole drilling SEM-DIC has excellent potential as a reliable method for measuring residual stress in polymer nanocomposites. Generally, CNT agglomerates, especially in high weight fractions, increased the micro-residual stress. An analytical method based on classical theory was used to calculate the residual stress and was compared with the experimental results. Good agreement was found between the results of the analytical methods and the experimental measurement.

Measurement of nutrients in saline and hypersaline waters by discrete analyzer colorimetry without matrix matched calibration standards

Automated, colorimetric analysis of nutrients in samples with high and variable salinity can be time consuming due to the need to matrix match calibration and reference solution matrices with those of samples—particularly when using flow-based analyzers that are prone to detector artifacts caused by optical inhomogeneities, “schlieren,” that form at interfaces between samples and deionized water carrier or wash solutions. Such detector artifacts do not occur in discrete analyzers. Here we report spike recoveries when nitrite plus nitrate, nitrite, ammonia, orthophosphate, and silica were determined in estuarine waters, seawater, and hypersaline surface water samples without calibrator matrix matching using an automated discrete analyzer set up with standard colorimetric methods. Salinities of these samples varied from 0 to 22%. Spike recoveries and precision were excellent for nitrite and nitrite plus nitrate analyses in samples with salinities up to 15%, for ammonia in samples with salinities up to about 1.7%, and for orthophosphate in samples with salinities up to about 3.5%. Orthophosphate spike recoveries were high biased in hypersaline matrices (salinity >3.5%), likely due to an unidentified sample matrix interference. After applying linear correction factors to account for chemistry-related salt effects, spike recoveries were acceptable for ammonia analyses in samples with salinities in the range of 1.7–3.5%, and for silica analyses in samples with salinities in the range of 0–3.5%.

1-kV Wideband Voltage Transducer, a Novel Method for Calibration, and a Voltage Measurement Chain

A new reference resistive-capacitive voltage divider is presented in this paper, operating in dc and ac from 10 to 200 kHz. The ratio error is lower than 0.1% and the phase error is lower than $400~\mu $ rad (1.375’) at 100 kHz. The divider is stable and repeatable. The scale factor (SF) and the phase error repeatability, tested in 24-h continuous measurements repeated during 15 weeks, show an SF variation lower than 80 ppm and a phase error variation lower than 20 $\mu $ rad. This allows one to define a calibration matrix of the device bringing its relative measurement uncertainty lower than $0.5 \cdot 10^{-3}$ . The divider calibration has been obtained with a step-up method, which could improve traceability in many laboratories and is described in this paper. The divider can be embedded in a calibration chain to test the accuracy of voltage transducers in the measurement of the ac voltage ripple, in the presence of a significant dc component, as it occurs in many power electronic systems. The voltage calibration chain is based on the use of the reference divider and a voltage injector, the secondary of which is placed in series with a stable dc source. By means of this calibration system, one of the best commercial voltage transducers on the market has been analyzed. This paper also highlights how the proposed voltage calibration chain could be used in perspective in a phantom power system for the development of a dc plus ac power standard.

Correspondence Between 3D Shapes Based on Improved Functional Map

We propose a shape matching algorithm based on an improved functional map in order to calculate correspondence between two given 3D non-rigid shapes, in which shape correspondence can be represented as a mapping function of mixed transformation matrix B and calibration matrix P of basis functions. First, Laplace matrix is calculated and a new matrix is constructed as basis matrix of function space by using eigenvectors of Laplace matrix after eigen-decomposition. Then, a calibration algorithm based on statistical covariance is proposed to calculate the matrix P that is used to calibrate basis matrices of function space of two shapes. Finally, the matrix B is optimized by an improved ICP(Iterative Closest Point) algorithm in order to calculate shape correspondence with the matrix P. Experimental results show that the proposed algorithm avoids excessive initial conditions, obtains accurate shape correspondence and significantly solves symmetry ambiguities of 3D shapes during matching process.

Application of quadrupole-Orbitrap high-resolution mass spectrometry in rapid screening and identification of synthetic dyes in herbal medicines

In this work, a method combining ultra-high performance liquid chromatography and hybrid quadrupole-Orbitrap high-resolution mass spectrometry (HR-MS) was developed and validated for use in the simultaneous screening, identification, and quantification of 21 synthetic dyes in herbal medicines. To optimize the chromatographic conditions, we used a combined Full mass scan and data-dependent MS/MS (Full MS/dd-MS2) approach in positive and negative ion mode. Under this mode, selected ions with given fragmentation energy were subjected to a dd-MS2 scan following a Full MS scan. The selectivity of this method was effectively improved using 70,000 full width at half maximum mass resolution and narrow mass window (typically 5 ppm), and a single injection was sufficient for simultaneous identification and quantification of 21 synthetic dyes within 10 min. The combined method was fully validated and complies with all criteria for selectivity, sensitivity, calibration curve linearity, accuracy, precision, recovery, matrix effect, and stability. All analytes showed excellent linear relationships as all the coefficients of determination (r2) are greater than 0.9978 over wide ranges of concentrations (e.g. 1.0-500 ng/mL for sunset yellow). The validated method was employed to detect synthetic dyes in herbal medicines and was demonstrated to provide a reliable technical basis for drug regulation and public health protection.

In situ determination of trace elements in melt inclusions using laser ablation inductively coupled plasma sector field mass spectrometry

In situ trace element analysis of melt inclusions by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) provides important geochemistry information. However, the precision and accuracy of this technique are affected by many factors, such as matrix effect, laser conditions, and calibration method. In addition, many previous LA-ICP-MS studies ablated entire melt inclusions along with their host minerals and obtained trace element composition by deconvoluting the mixed ablation signal, which may induce much uncertainty. A 193 nm ArF laser ablation system combined with inductively coupled plasma sector field mass spectrometry (ICP-SF-MS) was used to investigate matrix effect, laser conditions, choice of external calibration standards, and data reduction strategy for in situ analysis of 36 major and trace elements in six common silicate reference glasses. The validity of the protocol presented here was demonstrated by measuring trace elements in olivine-hosted melt inclusions. Instead of ablating entire melt inclusions along with their host minerals, melt inclusions were polished to the surface to avoid laser ablating the mineral host. The calibration lines calculated from the calibration standards should cross the coordinate origin, especially for low-concentration elements (<10 ppm). As the laser crater size increased from 17 to 33 μm, the precision was improved from <20% to <8% (2RSD), and accuracy was improved from ±20% to better than ±10%. Most measured trace elements in Dali melt inclusions are consistent with those in their host rocks. For mobile elements (Ba, Sr, Pb), melt inclusions display much smaller variations than their host rocks. A simple but accurate approach for in situ analysis of trace elements in melt inclusions by LA-ICP-SF-MS has been established, which should greatly facilitate the wider application of in situ trace element geochemistry to melt inclusion studies.

Eigenvector-based SPIRiT Parallel MR Imaging Reconstruction based on ℓp pseudo-norm Joint Total Variation

Parallel Magnetic Resonance (MR) imaging is a well-established acceleration technique based on the spatial sensitivities of array receivers. Eigenvector-based SPIRiT (ESPIRiT) is a new parallel MR imaging reconstruction method that combines the advantages of the SENSE and GRAPPA methods. It estimates multiple sets of the sensitivity maps from the calibration matrix that is constructed from the auto-calibration data. To improve the quality of the reconstructed image, we introduced the Total Variation (TV) and ℓp pseudo-norm Joint TV (ℓpJTV) regularization terms to the ESPIRiT model for parallel MR imaging reconstruction, which were solved by using the Operator Splitting (OS) method. The resulting denoising problems with the TV and ℓpJTV regularization terms were solved by exploiting the Majorization Minimization method. Simulation experiments on two in vivo data sets demonstrated that the proposed OS algorithm with the TV regularization term (OSTV) and OS algorithm with the ℓpJTV regularization term (OSℓpJTV) outperformed the conventional method with the ℓ1 regularization term in terms of SNR and NRMSE. And the OSℓpJTV algorithm was slightly superior to the OSTV algorithm with the TV regularization term.

A simplified and versatile multivariate calibration procedure for multiproduct quantification of pharmaceutical drugs in the presence of interferences using first order data and chemometrics

In the present work, a methodology for multiproduct quantification of paracetamol, caffeine and sodium diclofenac using ultraviolet (UV) detection (first order data) associated with multivariate curve resolution with alternating least squares (MCR-ALS) and Partial Least Squares (PLS), was developed. Generally, for first order data modelling, a high number of samples are required to include all the constituents present in future samples. However, it is possible that interferences impair the use of the calibration model when it comes to multiproduct analyses. We propose a methodology based on the use of individually built calibration curves, one for each analyte, similarly to a univariate calibration, and use chemometrics approaches to accurately quantify the analytes in the presence of interferences. Two strategies were evaluated: 1) the individual curves were grouped in a calibration matrix and 2) only the curve of the analyte of interest was used for calibration. These strategies were applied to two sample sets: 1) a test set prepared with a mixture of the analytes, according to a Central Composite Design and 2) 15 commercial drug products with very different compositions and dosage forms. Partial Least Squares (PLS) and Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) were compared and are discussed regarding first and second order advantages in the two approaches. PLS presented adequate performance using strategy 1 and the test set mixture, indicating that there was no need to prepare mixtures of the analytes for calibration. MCR-ALS achieved accurate results for both strategies and both sample sets, fulfilling the requirements to achieve first and second order advantages, which are related to the capability of providing the analyst with information about the presence of unmodelled compounds in unknown samples, on the one hand, and achieving an accurate quantification in the presence of these unknown compounds, on the other hand. Building a calibration set with standards of pure compounds not only will reduce the number of samples required for calibration, but makes it easier to update the model by simply including new calibration samples for the quantification of new compounds. This is an interesting strategy for pharmaceutical analysis, since the composition of samples is known by the manufacturer.

Determination of some pesticide residues in conventional-grown and IPM-grown tomato by using QuEChERS method

The present study was conducted to determine pesticide (emamectin-benzoate, penconazole and imidacloprid) residues over tomatoes by using QuEChERS method. The method was validated by spiking tomato matrix at 0.1, 1.0, and 10.0 MRL levels of the pesticides. Tomatoes were harvested from two conventional and two Integrated Pest Management-grown fields. Laboratory samples were taken from the bulk samples. Analyses of spiked and real-field tomatoes were performed with QuEChERS procedure. Experimental samples were subjected to LC-MS/MS analysis. As indicated in “CAC/GL 40-1993,” representative sample matrix (apple) calibration was used for quantification. The overall recovery was 107.12% with a relative standard deviation of 17.96% (n = 162). Present values were within the specified recovery ranges (60-140%) and repeatability value of (RSD ≤20%) of SANCO. Analysis of field experiment samples showed that both conventional tomato plots had trace levels (less than MRL) of emamectin-benzoate and imidacloprid, whereas there were not any pesticide residues in both IPM tomato plots

Comparative LC-MS/MS and HPLC-UV Analyses of Meropenem and Piperacillin in Critically Ill Patients

Therapeutic drug monitoring (TDM) of beta-lactam antibiotics has become a valuable tool to guide dosing in critically ill patients. The main goal of the study was to compare two routinely used techniques for beta-lactam TDM in intensive care unit (ICU) patient samples, namely isotope dilution liquid chromatography tandem mass spectrometry (ID-LC-MS/MS) and high-performance liquid chromatography combined with ultra-violet detection (HPLC-UV). A set of 80 sera/plasma samples from ICU patients receiving therapeutic meropenem or piperacillin dosage was investigated. Sample duplicates and quality assessment samples were assayed in parallel with an in-house LC-MS/MS and a commercially available IVD HPLC-UV kit. A pharmacokinetic and pharmacodynamic (PK/PD) target with ≥ 22.5 mg/L for piperacillin and ≥ 8.0 mg/L for meropenem was used for medical assessment of trough sample (n = 40) antibiotic concentrations. There was no difference between serum and Li-heparin plasmas. Concentration deviations were found for 4% of meropenem and 17% of piperacillin samples. Eliminating the influence of the systemic bias of approximately 10% for piperacillin, measurement discrepancies ≥ 25% between LC-MS/MS and HPLC-UV analyses were only observed for ≈ 4 - 6% of all samples. In the same way, identical PK/PD target attainment rates of 50 - 60% could be obtained. After correction of the analytical bias for piperacillin measurements, both methods showed comparable results, also with respect to clinical decision limits. HPLC-UV analysis is an adequate TDM methodology for testing of beta-lactam antibiotics in centers where no special knowledge in LC-MS/MS based TDM is present. However, potential matrix effects, interferences, and calibration issues for both methods must be taken into account.

Determination of 11 sulfonamides in pork by two-step liquid-liquid extraction-solid phase extraction purification coupled with high performance liquid chromatography-tandem mass spectrometry

A method based on two-step liquid-liquid extraction-solid phase extraction purification coupled with high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for the determination of 11 common sulfonamides in pork. The samples were extracted first with ethyl acetate containing 2%(v/v) formic acid and then with acetone for the second step. The supernatant was degreased with n-hexane and cleaned using an Oasis MCX SPE column. Finally, nitrogen was blown over the obtained mixture, and the mixture was filtered for conducting HPLC-MS/MS analysis. The sulfonamides were detected in the multiple reaction monitoring positive ion mode, and quantification was performed by employing the external standard method with matrix calibration curves. All the 11 sulfonamides demonstrated good linearity in the range of 20-400 μg/L, with the correlation coefficient (r2) higher than 0.99. The limits of detection (LODs; S/N=3) and limits of quantification (LOQs; S/N=10) were found to be in the ranges of 0.1-1.0 μg/kg and 0.2-3.0 μg/kg, respectively. Furthermore, the results indicated that the average recoveries of the 11 sulfonamides ranged from 79.3% to 105.5% at three spiked levels of 50, 100, and 200 μg/kg, with the relative standard deviations (RSDs) in the range of 1.3%-11.6% (n=6). This method showed higher extraction efficiency than the one-step liquid-liquid extraction, and the detection sensitivity was highly improved.

Development a monoclonal antibody-based enzyme-linked immunosorbent assay for screening pyrimethanil in fruits and vegetables

ABSTRACTAbuse of pyrimethanil in crops to cause deleterious effects on humans has been of great concern. In this study, functionalized derivatives of pyrimethanil have been synthesized and conjugated to carrier proteins, and highly specific and sensitive monoclonal antibodies (mAb) have been produced. Based on the mAb 1F05, an ic-ELISA was developed and characterized for the analysis of pyrimethanil residues. The standard curves based on the pyrimethanil matrix calibration ranged from 0.03 to 3 ng/mL, with a 50% inhibitory concentration of 0.25 ng/mL. The limits of detection were 0.02–0.04 μg/kg in various matrices. The recoveries for pyrimethanil ranged from 88.6% to 102.3%, with coefficient of variation below 11%. A good correlation (R2 > 0.9825) between the ic-ELISA and HPLC-MS/MS showed the reliability of the developed ic-ELISA. The proposed ic-ELISA was demonstrated to be a simple, rapid, and sensitive tool to monitor the residues of pyrimethanil in fruits and vegetables.

Simultaneous determination of the quaternary ammonium pesticides paraquat, diquat, chlormequat, and mepiquat in barley and wheat using a modified quick polar pesticides method, diluted standard addition calibration and hydrophilic interaction liquid chromatography coupled to tandem mass spectrometry

In this study, a modified Quick Polar Pesticides (QuPPe) method, optimized by a central composite design, was developed to determine quaternary ammonium pesticides (QUATs) residues in barley and wheat by ultra-high-performance liquid chromatographic tandem mass spectrometry (UHPLC-MS/MS) using a hydrophilic interaction chromatography (HILIC) column. Considering the high polarity of these compounds, special conditions of sample preparation and analysis are required. Different mobile phases, extraction procedure and clean-up were evaluated. An isocratic elution with aqueous solution of ammonium formate 60 mmol L−1 (pH 3.7) and acetonitrile, 40:60 (v/v), was selected. Water and acidified methanol as extraction solvent, without heating, and a clean-up with dichloromethane, chitosan and acetonitrile presented good results. The validated method presented satisfactory selectivity, linearity, matrix effect, trueness and precision, providing recoveries from 93 to 110% with RSD < 13% for barley, and 70 to 115% with RSD < 18% for wheat. The complexity of these matrices requires the calibration in matrix and the diluted standard addition calibration (DSAC) procedure has been shown to be an excellent option to compensate for the matrix effect and the losses of the analytes in the extraction. Real samples of barley and wheat were analyzed and 60% presented concentrations of paraquat above the maximum limits allowed by the European Union. The modified QuPPe method combined with DSAC and HILIC-UHPLC-MS/MS demonstrated to be an effective approach to determine QUATs in barley and wheat, and is a good alternative for routine analysis. The use of the biosorbent chitosan is effective, low cost and more ecological when compared to others conventional sorbents.