Sample Matrix Constituents Research Articles

Matrix Effect Evaluation in GC/MS-MS Analysis of Multiple Pesticide Residues in Selected Food Matrices

Multi-analyte methods based on QuEChERS sample preparation and chromatography/mass spectrometry determination are indispensable in monitoring pesticide residues in the feed and food chain. QuEChERS method, even though perceived as convenient and generic, can contribute to sample matrix constituents’ introduction to the measuring system and possibly affect analytical results. In this study, matrix effects (ME) were investigated in four food matrices of plant origin (apples, grapes, spelt kernels, and sunflower seeds) during GC-MS/MS analysis of >200 pesticide residues using QuEChERS sample preparation. Data analysis revealed considerable analyte signal enhancement and suppression: strong enhancement was observed for the majority of analytes in two matrices within the commodity groups with high water content—apples, and high acid and water content—grapes (73.9% MES and 72.5% MEA, and 77.7% MES and 74.9% MEA, respectively), while strong suppression was observed for matrices within the commodity groups with high starch/protein content and low water and fat content—spelt kernels, and high oil content and very low water content—sunflower seeds (82.1% MES and 82.6% MEA, and 65.2% MES and 70.0% MEA, respectively). Although strong matrix effects were the most common for all investigated matrices, the use of matrix-matched calibration for each sample type enabled satisfactory method performance, i.e., recoveries for the majority of analytes (up to roughly 90%, depending on the fortification level and matrix type), which was also externally confirmed through participation in proficiency testing schemes for relevant food commodity groups with the achieved z-scores within acceptable range ≤ |2|.

Rapid and simple determination of As in bottled birch saps by hydride generation inductively coupled plasma optical emission spectrometry

ABSTRACT A strategy was developed for the determination of total As in birch saps (BSs) by hydride generation (HG) coupled with inductively coupled plasma optical emission spectrometry (ICP-OES). We proposed and validated a simple and robust HG-ICP-OES method with no need for tedious and long sample preparation before measurements. Corresponding As hydride was generated in reaction with NaBH4 (1.0%) in acidic conditions (10 mol L−1 HCl) after pre-reduction of As(V) to As(III) in a KI (0.5%)-ascorbic acid (2.0%)-HCl (3 mol L−1) mixture. Several different sample preparation procedures, including digestive and non-digestive approaches, were tested in order to improve the detectability of As using HG-ICP-OES. Reactivity of As towards HG under conditions of a real sample was investigated to check potential interfering effects coming from undecomposed sample matrix constituents. The proposed method included the direct analysis of untreated samples (only pre-reduction prior to HG) and precision (<6% as relative standard deviation), accuracy (94.7–108.7% as recoveries) and sensitivity (limit of detection at 0.26 ng mL−1) that was suitable for trace analysis. An absence of matrix effects allowed external calibration for quantification of As. Applicability of the method was demonstrated by determination of As in several commercially available bottled BSs.

Novel rapid oxidizing fusion method to determine Polonium-210 in air filters

A rapid method for the determination of polonium-210 in air filters has been developed for use following a radiological event and for routine environmental monitoring. Air filter samples, including cellulose and glass fiber, are fused with a sodium or potassium nitrate/sodium hydroxide flux material. The alkaline matrix minimizes polonium volatility during sample digestion steps, while efficiently dissolving the air filter and inorganic matter implanted on the filter. The addition of nitrate to the flux destroys organic material which can decrease Polonium recovery during precipitation, extraction and source preparation steps. Polonium is concentrated and separated from the sample matrix using an iron hydroxide precipitation and extraction chromatography with DGA Resin. Polonium-210 is subsequently measured by alpha spectrometry following rapid microprecipitation with bismuth phosphate. The new method employs extraction chromatographic purification to remove alpha emitting interferences and sample matrix constituents which can interfere with 210Po measurements using alpha spectrometry. The novel blend of sodium hydroxide and alkali metal nitrate digests the air filters quickly and effectively.

Fully Automated Electric-Field-Driven Liquid Phase Microextraction System with Renewable Organic Membrane As a Front End to High Performance Liquid Chromatography.

This article reports for the first time a programmable-flow-based mesofluidic platform that accommodates electric-field-driven liquid phase microextraction (μ-EME) in a fully automated mode. The miniaturized system is composed of a computer-controlled microsyringe pump and a multiposition rotary valve for handling aqueous and organic solutions at a low microliter volume and acts as a front-end to online liquid chromatographic separation. The organic membrane is automatically renewed and disposed of in every analytical cycle, thus minimizing analyte carry-over effects while avoiding analyst intervention. The proof-of-concept applicability of the automated mesofluidic device is demonstrated by the liquid chromatographic determination of nonsteriodal anti-inflammatory drugs in μ-EME processed complex samples (such as urine and influent wastewater) using online heart-cut approaches. Using 5 μL of 1-octanol, 7.5 μL of untreated sample and 7.5 μL of acceptor solution (25 mM NaOH), and 250 V for only 10 min in a stopped-flow mode, the extraction recoveries for the μ-EME of ibuprofen, ketoprofen, naproxen, and diclofenac exceed 40% in real samples. The flow-through system features moderately selective extraction regardless of the sample matrix constituents with repeatability values better than 13%.

Comparison of different methodologies for the 90Sr determination in environmental samples

The paper describes different isolation/separation and detection procedures for 90Sr determination in the environmental samples which are routinely used in Laboratories A and B. In this context, four different methods for strontium isolation and two methods for detection were tested and compared by 90Sr determination in proficiency test samples (water, soil, vegetation) and animal bone samples. The chromatographic isolation of Sr on Sr resin, AnaLig®Sr01 resin gel, strong base anion exchange resins in nitrate form and combination of strong base anion exchange and Sr resin were used for the examination of the impact of sample matrix constituents on efficiency of strontium isolation (chemical yield), while Cherenkov counting of 90Y and counting of 90Sr(90Y) on proportional counter were used for the quantitative 90Sr determination. The chemical yields obtained with different isolation methods were compared with the emphasis on its influence on reliability of the 90Sr determination in different kinds of samples. The results show that the efficiency of strontium isolation depends on type of sample and separation methodology. The strontium yield on Sr resin column decreases with the increase of Sr, Ca and Na concentration. In the presence of 1 g of Ca and 1 g of Na, the yield of 85% was obtained for 5 mg of Sr carrier and dropped below 50% with further increase of Sr and other elements. However, the yield can be increased to 75% if Na and part of Ca are separated from Sr on the anion exchange column with alcoholic solution of nitric acid and by final separation of Ca from Sr on the Sr resin column. In the presence of large amounts of Ca, Na and other elements, isolation efficiency on the Sr resin column significantly decreases in comparison with other methods. The average yield for isolation from vegetation samples on the Sr resin column is only 21%. For the soil samples the highest average yield (78%) is obtained for the isolation in the combination of anion exchange and Sr resin columns. For the isolation from bone samples the average yields over 80% are on AnaLig®Sr01 and anion exchange resins columns, while Sr resin was not used for separation due to high content of Ca in samples. The results of the 90Sr determination in proficiency testing (PT) samples show that the accuracy of the determination does not depend on high chemical yield but depends on accuracy of yield determination. The analysis of z-values shows that 96% of obtained z-values range from 0 to ±2 while 77% of z-values range between 0 and ± 1. Ninety percent of obtained results of 90Sr determination deviate less than 20% from assigned values in PT provider reports. The results of 90Sr determination in animal bone samples using different methods are in good agreement. The results obtained by Cherenkov counting in both laboratories vary from −3.1–14.5% while results obtained by determination via 90Y and counting on i-Matic vary between −10.0 and −2.9%. These deviations are in accordance with deviations obtained with PT samples. Activity concentrations of 90Sr in wild boar bone samples range from 4 to 30 Bq kg−1 while in deer bone samples from 2 to 8 Bq kg−1.

Two-Dimensional Capillary Electrophoresis with On-Line Sample Preparation and Cyclodextrin Separation Environment for Direct Determination of Serotonin in Human Urine.

An advanced two-dimensional capillary electrophoresis method, based on on-line combination of capillary isotachophoresis and capillary zone electrophoresis with cyclodextrin additive in background electrolyte, was developed for effective determination of serotonin in human urine. Hydrodynamically closed separation system and large bore capillaries (300–800 µm) were chosen for the possibility to enhance the sample load capacity, and, by that, to decrease limit of detection. Isotachophoresis served for the sample preseparation, defined elimination of sample matrix constituents (sample clean up), and preconcentration of the analyte. Cyclodextrin separation environment enhanced separation selectivity of capillary zone electrophoresis. In this way, serotonin could be successfully separated from the rest of the sample matrix constituents migrating in capillary zone electrophoresis step so that human urine could be directly (i.e., without any external sample preparation) injected into the analyzer. The proposed method was successfully validated, showing favorable parameters of sensitivity (limit of detection for serotonin was 2.32 ng·mL−1), linearity (regression coefficient higher than 0.99), precision (repeatability of the migration time and peak area were in the range of 0.02–1.17% and 5.25–7.88%, respectively), and recovery (ranging in the interval of 90.0–93.6%). The developed method was applied for the assay of the human urine samples obtained from healthy volunteers. The determined concentrations of serotonin in such samples were in the range of 12.4–491.2 ng·mL−1 that was in good agreement with literature data. This advanced method represents a highly effective, reliable, and low-cost alternative for the routine determination of serotonin as a biomarker in human urine.

Reliable Determination of Cyanide in Treated Water

Reliable determination of cyanide in water samples is important for both wastewater and drinking water treatment plant operators and regulatory agencies. However, as a result of cyanide's diverse chemistry, obtaining reliable results has been challenging because several chemical mechanisms can form or destroy cyanide—and some of these can occur within the sample container or during laboratory pretreatment and analysis, leading to biased results. Also, sample matrix constituents or preservation chemicals can interfere with the analytical determination. The US Environmental Protection Agency acknowledged this difficulty for wastewater samples in the 2012 Methods Update Rule by revising the footnote for cyanide preservation to indicate that some interferences may not be mitigated and any technique for removal or suppression of interferences can be used as long as quality control measures are used to demonstrate that the technique worked. Many of the same concerns inherent in testing wastewater apply to testing drinking water. In this study, the effects of holding time, preservation, and on‐line digestion and distillation on cyanide results for wastewater and drinking water were examined, including the use of field dilution as a treatment for interferences and field spikes as a means to gauge whether sample integrity was maintained.

Ultrasound- and microwave-assisted extractions followed by hydride generation inductively coupled plasma optical emission spectrometry for lead determination in geological samples

Followed the current idea of simplified sample pretratmet before analysis we evaluated the procedure for the determination of Pb in calcium-rich materials such as dolomites after ultrasound- or microwave- assisted extraction with diluted acids using hydride generation inductively coupled plasma optical emission spectrometry (HG-ICP-OES). Corresponding Pb hydride was generated in the reaction of an acidified sample solution with NaBH4 after pre-oxidation of Pb(II) to Pb(IV) by K3[Fe(CN)6]. Several chemical (acidic media: HCl, HNO3 or CH3COOH, concentration of the reductant as well as type and concentration of oxidazing agents) and physical (reagents flow rates, reaction coil length) parameters affecting the efficiency of plumbane formation were optimized in order to improve the detectability of Pb using HG-ICP-OES. Limitation of the method derived from the matrix effects was pointed out. Employing Pb separation by HG technique allows the significant reduction of interferences caused by sample matrix constituents (mainly Ca and Mg), nevertheless they could not be overcame at all, hence calibration based on the standard addition method was recommended for Pb quantification in dolomites. Under the selected conditions, i.e. 0.3molL−1 HCl, HNO3 or CH3COOH, 1.5% NaBH4 and 3.0% K3[Fe(CN)6] the limits of detection (LODs) between 2.3–5.6μgL−1 (3.4–6.8μgL−1 considering matrix effects) and the precision below 5% were achieved. The accuracy of the procedure was verified by analysis of certified reference materials (NCS DC70308 (Carbonate Rock) and NIST 14000 (Bone Ash)) and recovery test with satisfactory results of Pb recoveries ranging between 94–108% (CRMs analysis) and 92–114% (standard addition method). The applicability of the proposed method was demonstrated by the determination of Pb in dolomites used by different fertiliser factories.

Chemometric extraction of analyte‐specific chromatograms in on‐line gradient LC‐infrared spectrometry

This work exploits the possibilities offered by the recently developed multivariate method named Science-Based Calibration (SBC), for the extraction of 'analyte-specific' chromatograms in on-line gradient reversed phase LC-infrared spectrometry (IR) in the presence of a high spectral and chromatographic overlapping between the analyte of interest, co-eluting sample matrix constituents and the mobile phase components. The SBC method uses an experimentally measured single response spectrum of the analyte of interest and representative noise to calculate an optimum regression vector (b(opt(1))). Then, the b(opt(1)) vector is used to predict the concentration of the analyte of interest in the spectra of the LC-IR sample chromatograms. To evaluate the advantages and pitfalls of the proposed approach, two different situations were analysed on real LC-IR data sets obtained from the injection of a series of standard solutions of four nitrophenols (p-nitrophenol, 3-methyl-4-nitrophenol, 2,4-dinitrophenol and 4-nitrophenol) in a reversed phase system under gradient conditions. In the first situation, the extraction of the 'analyte-specific' chromatogram was carried out without previous knowledge of the spectral features of other interferents present in the sample matrix. In a second situation evaluated, data obtained from the LC injection of a sample blank is available. Results show the potential applicability of this technique in a variety of situations and evidenced that the proposed chemometric approach improves the selectivity and sensitivity of the LC-IR hyphenation.

Possibilities of column coupling electrophoresis provided with a fiber-based diode array detection in enantioselective analysis of drugs in pharmaceutical and clinical samples

The present work illustrated possibilities of column coupling electrophoresis combined with ionizable chiral selector and diode array detection (DAD) for the enantioselective analysis of trace drugs (pheniramine and its analogs) in pharmaceutical and clinical samples. Isotachophoresis (ITP), on-line coupled with capillary zone electrophoresis (CZE), served as an ideal injection technique (high sample load capacity, narrow and sharp drugs zones) of on-line pretreated samples (preseparation, purification and preconcentration of drugs) for the CZE stage. Enhanced (enantio)separation selectivity of CZE with ionizable chiral selector (carboxyethyl-β-cyclodextrin recognized between drugs enantiomers on one hand as well as between drugs and sample matrix constituents on the other hand) enabled to obtain pure zones of the drugs enantiomers, suitable for their detection and quantitation. DAD in comparison with single wavelength UV detection enhanced value of analytical information verifying purity of drugs enantiomers zones (indicating interferents with different spectra to those of drugs). Obtained results indicated pure zones of interest confirming effective ITP–CZE (enantio)separation process. Distinguishing the trace analytes signals superposed on the baseline noise was provided with sufficient reliability (for this purpose the background correction and smoothing procedure had to be applied to the raw DAD spectra). The proposed ITP–CZE–DAD methods were characterized by favorable performance parameters (sensitivity, linearity, precision, recovery, accuracy, robustness, selectivity) and successfully applied for (i) enantiomeric purity testing of dexbrompheniramine in commercial pharmaceutical tablets and (ii) enantioselective metabolic study of pheniramine in human urine.

Enantioselective analysis of pheniramine in urine by charged CD‐mediated CZE provided with a fiber‐based DAD and an on‐line sample pretreatment by capillary ITP

Application potentialities of CZE on-line coupled with capillary ITP and DAD to the identification and determination of trace concentration levels (microg/L) of pheniramine (PHM) enantiomers and their metabolites present in complex ionic matrices of biological origin (urine) are shown. An enhanced (enantio)selectivity of the CZE separation system obtained by the addition of carboxyethyl-beta-CD (CE-beta-CD) to the carrier electrolyte provided CZE conditions for a reliable identification of similar/identical DAD spectra of structurally related compounds (PHM enantiomers and their metabolites) in clinical urine samples differing in qualitative and quantitative composition of sample matrix constituents. A high sample loadability (a 30 microL sample injection volume), partial sample clean-up (removing macroconstituents from the sample), and preconcentration of the analytes in ITP stage resulted in the decrease of concentration LOD for PHM enantiomers in urine to 5.2 and 6.8 microg/L (2.2 x 10(-8) and 2.8 x 10(-8) mol/L), without using any sample pretreatment technique. The background correction and smoothing procedure applied to the raw DAD spectra provided analytically relevant DAD spectra of PHM enantiomers and their metabolites also when they were present in urine sample (30 microL injection volumes of ten-times diluted urine sample) at a 9 x 10(-) (8) mol/L concentration. DAD spectra of PHM enantiomers present in urine samples matched their reference spectra with reasonable certainties. DAD spectra of PHM metabolites were compared with the reference spectra of PHM enantiomers and a good match was found which indicates the similarities in the structures of enantiomers and their metabolites detected in the urine samples. This fact allows performing the quantitative analyses of PHM metabolites in the urine samples by applying the calibration parameters of PHM enantiomers also for PHM metabolites and the results show the possibilities of using the ITP-CZE-DAD combination for the direct analysis of PHM enantiomers and/or their metabolites in urine without any sample pretreatment. ITP-CZE-DAD method with oppositely charged selector is suggested to use in clinical research as it provides favorable performance parameters including sensitivity, linearity, precision, recovery, and robustness with minimal demands on sample preparation.

Analysis of enantiomers in biological matrices by charged cyclodextrin-mediated capillary zone electrophoresis in column-coupling arrangement with capillary isotachophoresis

The possibility to apply charged chiral selector as buffer additive in capillary zone electrophoresis (CZE) on-line coupled with capillary isotachophoresis (CITP) was studied. Enantioseparations and determinations of trace (ng/ml) antihistaminic drugs [pheniramine (PHM), dimethindene (DIM), dioxopromethazine (DIO)] present in samples of complex ionic matrices (urine) served as model examples. A negatively charged carboxyethyl-β-cyclodextrin (CE-β-CD) was used as a chiral selector in analytical CZE stage following upon a sample pretreatment by CITP (preconcentration of the analytes from 5 to 20-times diluted urine samples, partial sample clean up removing macroconstituents from the sample matrices). A high recognition capability of the oppositely charged CE-β-CD was demonstrated by enantioselective retardation of the drugs in presence of micro-and semi-macroconstituents migrating in CZE stage and detectable by UV detector. In this way, enantiomers of the drugs could be easily separated and determined. Due to lack of interferences between the drugs and sample-matrix constituents in presence of charged CE-β-CD, demands on both spacers in CITP step and multiple column-switching were minimized. CITP-CZE method with charged selector appeared to be a useful analytical approach for the trace enantiomers in complex ionic matrices as it combined enhanced separation selectivity and sample loadabitlity with high separation efficiency and provided favorable performance parameters including sensitivity, linearity, precision, accuracy/recovery and robustness with minimal demands on sample preparation. Analysis of urine sample taken from a patient treated by PHM, showing concentration profile of PHM enantiomers and their metabolites, illustrated potentialities of the method in clinical research.

Biochemical analysis with microfluidic systems.

Microfluidic systems are capillary networks of varying complexity fabricated originally in silicon, but nowadays in glass and polymeric substrates. Flow of liquid is mainly controlled by use of electroosmotic effects, i.e. application of electric fields, in addition to pressurized flow, i.e. application of pressure or vacuum. Because electroosmotic flow rates depend on the charge densities on the walls of capillaries, they are influenced by substrate material, fabrication processes, surface pretreatment procedures, and buffer additives. Microfluidic systems combine the properties of capillary electrophoretic systems and flow-through analytical systems, and thus biochemical analytical assays have been developed utilizing and integrating both aspects. Proteins, peptides, and nucleic acids can be separated because of their different electrophoretic mobility; detection is achieved with fluorescence detectors. For protein analysis, in particular, interfaces between microfluidic chips and mass spectrometers were developed. Further levels of integration of required sample-treatment steps were achieved by integration of protein digestion by immobilized trypsin and amplification of nucleic acids by the polymerase chain reaction. Kinetic constants of enzyme reactions were determined by adjusting different degrees of dilution of enzyme substrates or inhibitors within a single chip utilizing mainly the properties of controlled dosing and mixing liquids within a chip. For analysis of kinase reactions, however, a combination of a reaction step (enzyme with substrate and inhibitor) and a separation step (enzyme substrate and reaction product) was required. Microfluidic chips also enable separation of analytes from sample matrix constituents, which can interfere with quantitative determination, if they have different electrophoretic mobilities. In addition to analysis of nucleic acids and enzymes, immunoassays are the third group of analytical assays performed in microfluidic chips. They utilize either affinity capillary electrophoresis as a homogeneous assay format, or immobilized antigens or antibodies in heterogeneous assays with serial supply of reagents and washing solutions.

The effect of sample matrix quenching on the measurement of trace uranium concentrations in aqueous solutions using kinetic phosphorimetry

Laser-induced kinetic phosphorimetry is an accurate, sensitive and rapid alternative to radiometric determination of natural and depleted uranium in aqueous solutions. This method offers detection limits below 10 ng/l U (2.5·10−4 Bq/l natural U) and a broad analytical range to 5 mg/l U (130 Bq/l natural U). For many samples, dilution is the only sample preparation required. However, because this technique infers uranyl concentrations from time-resolved phosphorescence intensities, results are dependent upon sample matrix constituents that affect the phosphorescence of the uranyl cation. This study examines the influence of cations, anions and ligands common to natural water, process and bioassay samples on the quenching of uranyl phosphorescence and the consequences for lower limits of detection and accuracy of measurements.

ACID DEPENDENCY OF THE EXTRACTION OF SELECTED METAL IONS BY A STRONTIUM.SELECTIVE EXTRACTlON CHROMATOGRAPHIC RESIN: CALCULATEDVS.EXPERIMENTAL CURVES*

ABSTRACT The extraction of selected divalent (Ca+2, Sr+2, Ba+2, Ra+2, Pb+2, UO2 +2) and monovalent (Na+, K+, Rb+, CS+, TI+) metal cations at tracer concentration level by a recently introduced strontium-selective extraction chromatographic resin has been studied as function of the nitric acid concentration in the range − 0.1-7 M. The data have been explained by combining the metal extraction, the acid extraction, and the aqueous phase metal complication equilibria. Conditional metal extraction equilibrium constants have been estimated by using calculated activity coefficients of the metal nitrate salts in the nitric acid solutions. The extraction constants have been used to predict the effect of macroconcentrations of sample matrix constituents on the extraction of Sr+2 or Pb+2 by the strontium-selective resin.

Computer-assisted choice of electrolyte systems and spacing constituents for two-dimensional capillary isotachophoresis

Equations enabling interferences due to sample matrix constituents in two-dimensional isotachophoretic analysis using the spike method to be estimated were derived. A computer program and a procedure based on these equations were developed for searching for optimum and less time consuming electrolyte systems and spacing constituents. The procedure, intended mainly for the trace analysis of the constituents present in complex ionic matrices, was examined in experiments with benzoate as a trace analyte. A model mixture of 50 arbitrarily chosen anionically migrating UV light-absorbing constituents simulated the sample matrix. A reasonable agreement in ordering the electrolyte systems according to interfering contributions of the sample matrix was obtained between the experimental and calculated data. Some discrepancies found in the examination of the proposed procedure are discussed.