Liquid-chromatographic determination of sulfadimidine in milk and eggs

A method for the determination/identification of residual sulfadimidine (SDD) in milk and eggs by high-performance liquid chromatography (HPLC) with a photo-diode array detector was developed. The sample preparation was performed by shaking with a mixture of 20% (w/v) trichloroacetic acid-methanol (4:1, v/v) followed by ultra-filtration using Molcut II^?. A LiChrospher^? 100 RP-8 (e) column and a mobile phase of 4% (v/v) acetic acid solution-acetonitrile (6:4, v/v) were used. The average recoveries from spiked SDD samples were 80.8–88.0% with coefficients of variation of 2.8–5.5%. The limits of detection in milk and eggs were 0.01 μg/mL and 0.01 μg/g, respectively. The total time required for the analysis of one sample was less than 20 min. Received: 7 October 1998 / Revised: 29 December 1998 / Accepted: 30 December 1998     

Determination of molybdenum in biological samples by flame atomic spectrometry after preconcentration on activated carbon

Abstract  

Molybdenum is well known for its toxic effects, although it is also essential for N₂-fixing cyanobacteria and several enzymes. This study proposes a simple and accurate procedure for separation, preconcentration, and determination of trace amounts of molybdenum in biological samples by flame atomic absorption spectrometry. It is based on complexation of Mo by cupferron and sorption onto activated carbon. Effects of parameters such as pH, stirring time, and amounts of activated carbon and cupferron on recovery were examined. The results demonstrated that Mo at pH range of 2.5–3.5 was quantitatively sorbed onto activated carbon as its cupferron complex. The optimum stirring time was found to be 30 min. The relative standard deviation was found to be 12% for 200 cm³ 50 ng/cm³ Mo using 10 replicate preconcentration procedures. The limits of detection and quantification were found to be 1.0 and 3 ng/cm³, respectively, by preconcentration of 200 cm³ initial sample to 2 cm³ final volume. As a result, an enrichment factor of 100-fold was achieved. The proposed preconcentration procedure was applied to determine Mo in biological samples such as vegetables, milk, and animal liver. The molybdenum concentrations were found (as μg/dm³ or μg/kg) in the range of 70–5,500 for plants, 3–124 for milk and milk powder, and 960 for liver samples.     

Immuno-affinity columns versus conventional clean-up: a method-comparison study for the determination of zearalenone in corn

The efficiency of a modern analytical method employing immuno-affinity columns (IACs) is compared to a well established traditional technique with respect to the determination of zearalenone (ZON) in corn in the μg/kg range. Despite of a constant error of about 4 μg/kg in the examined working range of 10–200 μg/kg, analytical data obtained from the analysis of spiked and naturally contaminated samples showed good correspondence for the compared methods. The performance characteristics of immuno-affinity-chromatography as a new clean-up technique for the determination of ZON in corn is reported for the first time and compared to a conventional clean-up procedure Received: 25 March 1997 / Revised: 5 May 1997 / Accepted: 12 May 1997     

Determination of L-arginine in amniotic fluid by capillary zone electrophoresis

Conditions for the determination of L-arginine in a biological fluid using capillary zone electrophoresis were optimized. The effects of the pH of a running buffer, the time of sample injection into a capillary, the operating voltage, the temperature, and the wavelength on the results of the determination were studied. The procedure made it possible to evaluate the concentration of L-arginine over a range of 6–1000 μg/mL (c = 3 μg/mL; RSD = 2%). The duration of analysis including sample preparation was no longer than 30 min. The analysis of amniotic fluid samples in the cases of physiological pregnancy and pregnancy complicated by placental insufficiency demonstrated that the arginine content of amniotic fluid increased in the case of placental insufficiency, as compared to normal values.     

Determination of trace amounts of lead in mussels by flow-injection flame atomic-absorption spectrometry coupled with on-line minicolumn preconcentration

A minicolumn packed with poly(aminophosphonic acid) chelating resin incorporated in an on-line preconcentration system for flame atomic-absorption spectrometry was used to determine ultratrace amounts of lead in mussel samples at μg L^–1 level. The preconcentrated lead was eluted with hydrochloric acid and injected directly into the nebulizer for atomization in an air-acetylene flame for measurement. The performance characteristics of the determination of lead were: preconcentration factor 26.8 for 1 min preconcentration time, detection limit (3σ) in the sample digest was 0.25 μg g^–1 (dry weight) for a sample volume of 3.5 mL and 0.2 g sample (preconcentration time 1 min), precision (RSD) 2.3% for 25 μg L^–1 and 2.0% for 50 μg L^–1. The sampling frequency was 45 h^–1. The method was highly tolerant of interferences, and the results obtained for the determination of lead in a reference material testify to the applicability of the proposed procedure to the determination of lead at ultratrace level in biological materials such as mussel samples. Received: 1 November 2000 / Revised: 8 January 2001/ Accepted: 11 January 2001     

Development of a colloidal gold-based lateral-flow immunoassay for the rapid simultaneous detection of zearalenone and deoxynivalenol

A multianalyte lateral-flow technique using colloidal gold-labeled monoclonal antibodies was developed for the rapid simultaneous detection of deoxynivalenol (DON) and zearalenone (ZEA). The results of this qualitative one-step test were interpreted visually. A very simple and fast sample preparation was used, and the assay procedure could be accomplished within 10 min. When applied to spiked wheat samples, the technique gave accurate and reproducible results. Cut-off levels of 1500 and 100 μg kg⁻¹ for DON and ZEA, respectively, were observed. The described multianalyte format can be used as a reliable, rapid and cost-effective on-site screening technique for the simultaneous determination of mycotoxins in grain samples.     

Direct copper determination in whole milk, non-fat milk and whey milk by electrothermal atomic absorption spectrometry

A method for the direct determination of copper in samples of whole milk, non-fat milk and whey milk by electrothermal atomic spectrometry (ETAAS) was studied. The fat separation by centrifugation at 3200 rpm and the separation of casein mycelles to obtain the whey milk by ultracentrifugation at 31 000 g were investigated. In all cases Mg(NO₃)₂ was used as chemical modifier and Triton X-100 (0.2% w/v) as emulsifying agent. The optimum pyrolysis temperature was 1500° C. The detection limit was 0.4 μg/l of copper. The precision was studied for the whole milk and the coefficients of variation (CV) were 5.7, 4.0, 2.4 and 2.8% for 0, 5, 10 and 20 μg/l of copper added. The accuracy was determined by using the Reference Material Milk A-11 (IAEA) with a certified content of 378.4 ± 24 ng Cu/g; 359 ± 16 ng/g were found. The method was applied to ten cow milk samples, the levels of copper being determined for whole milk, non-fat milk and whey milk. A statistical study was applied and it was concluded that the majority of copper is in the non-fat milk. Received: 29 February 1996 / Revised: 19 April 1996 / Accepted: 28 April 1996     

Determination of selected pesticides by GC with simultaneous detection by MS (NCI) and μ-ECD in fruit and vegetable matrices

A gas chromatography–mass spectrometry method in negative chemical ionization mode has been developed incorporating simultaneous detection using a micro-electron capture detector (μ-ECD) for the determination of pesticides in fruits and vegetables. This instrument configuration uses a three-way splitter device which divides the effluent from the analytical column between the two detectors with the split ratio 1:0.1 (MSD/μ-ECD) in each run. The μ-ECD was used for confirmation purposes. Validation of the method was performed on three matrices: tomato, apple, and orange. The ethyl acetate method was assayed; recovery studies were performed at 10 and 100 μg/kg. Recoveries between 70% and 120% were achieved and relative standard deviations lower than 20% (n = 5) were obtained for all pesticides and matrices studied. Limits of quantification lower than 10 μg/kg were obtained for 100% of pesticides in all of the matrices. Limits of quantification lower than 2.5 μg/kg were achieved for 77.8% of pesticides in the tomato and apple matrices, and for 72.2% of pesticides in the orange matrix. The method showed linear response in the concentration range tested (2.5–500 μg/kg) with correlation coefficients >0.99. Good repeatability and reproducibility results were obtained in all cases, with relative standard deviations lower than 16.7% and 20%, respectively. Finally, 20 incurred samples were analyzed using the proposed method. The simultaneous use of the two detectors was satisfactory for the analysis of these real samples. The total number of pesticides identified was 25. The number of samples which contained at least one pesticide was 15—this represented 75% of the total number of samples studied.     

On the certification of cadmium at trace and ultratrace levels in standard reference materials using ID ICP-MS

Analytical methods used for the isotope dilution inductively coupled plasma mass spectrometric (ID-ICP-MS) measurement of Cd at μg kg⁻¹ and sub-μg kg⁻¹ levels are described and applied to the certification of new dietary supplement, blood, and serum Standard Reference Materials (SRMs). The materials are: SRM 3240 Ephedra sinica Stapf Aerial Parts, SRM 3241 Ephedra sinica Stapf Native Extract, SRM 3243 Ephedra-Containing Solid Oral Dosage Form, SRM 3244 Ephedra-Containing Protein Powder, SRM 966 Toxic Metals in Bovine Blood, Level 1 (L1) and Level 2 (L2), and SRM 1598a Animal Serum. The concentration of Cd in the materials ranges from 120 μg kg⁻¹ down to 0.03 μg kg⁻¹. At these levels, the factors that most influence the accuracy of the ICP-MS data are the procedure blank and spectral and nonspectral interferences. Nonspectral interference, caused by the high concentration of dissolved solids in the matrices investigated, resulted in signal suppression. Matrix separation was used to enhance signal intensity and to reduce spectral interference for the accurate determination of Cd in SRM 1598a and SRM 3244. Chromatographic separation procedures using Chelex for SRM 1598a and anion exchange for SRM 3244 were optimized to achieve the desired separation characteristics without substantially increasing the procedure blank. Sensitivity for the determination of Cd in serum was additionally enhanced through the use of desolvation nebulization. We determined that separations were not required for the accurate ICP-MS determination of Cd in SRM 3240, SRM 3241, SRM 3243, and SRM 966 L2 under optimized analysis conditions. These samples were diluted to a minimum volume and introduced to the ICP-MS via low flow (40–100 μL/min) microconcentric nebulizers. SRM 966 L1 was also analyzed directly, but results were highly variable. The ID-ICP-MS sample preparation and ratio measurement protocols described here resulted in total expanded uncertainties of less than 1% for the determination of 90.85 μg kg⁻¹ Cd in SRM 3240, and less than 10% total expanded uncertainty for the determination of 0.0468 μg kg⁻¹ Cd in SRM 1598a.     

Flame atomic absorption spectrometric determination of trace amounts of palladium,gold and nickel after cloud point extraction

In this article, a sensitive cloud point extraction procedure for the preconcentration of trace amounts of palladium, gold and nickel prior to their determination by flame atomic absorption spectrometry has been developed. The cloud point extraction method is based on the complexation of Pd(II), Au(II), and Ni(II) ions with 1-(2-pyridylazo)-2-naphthol and entrapping in non-ionic surfactant Triton X-114. The main factors affecting cloud point extraction efficiency, such as pH of sample solution, concentration of 1-(2-pyridylazo)-2-naphthol and Triton X-114, equilibration temperature and time, were investigated in detail. Under the optimized conditions, calibration curves were constructed for the determination of palladium, gold and nickel according to the general procedure. Linearity was maintained from 0.01 to 1.0 μg/mL for palladium, 10.0 μg/mL to 1.5 μg/mL for gold, and 10.0 μg/mL to 0.5 μg/mL for nickel. Detection limits based on three times the standard deviation of the blank divided by the slope of analytical curve (3Sb/m) for Pd(II), Au(III), and Ni(11) ions were 3.4, 3.9, and 2.4 μg/mL, respectively. Seven replicate determination of a mixture of 0.5 μg/mL palladium and gold and 0.2 μg/mL nickel gave a mean absorbance of 0.174, 0.150, and 0.201 with relative standard deviation ±1.5, ±1.3, and ±1.8%, respectively. The high efficiency of cloud point extraction to carry out the determination of analytes in complex matrices was demonstrated. The proposed method has been applied for determination of trace amount of palladium, gold and nickel in certified reference material and water samples with satisfactory results.     

Proficiency testing as a tool for implementing internal quality control: the case of ochratoxin A in cocoa powder

This paper describes the interlaboratory study aimed at assessing the performance of 18 laboratories (14 national and 4 European) for Ochratoxin A (OTA) determination in cocoa powder samples. The study was tested at three levels of OTA covering the range in which presumably European regulatory limits could fall in the near future. For the extraction step, almost all laboratories used an aqueous solution of sodium hydrogen carbonate with the exception of one laboratory using dichloromethane consistently with the ELISA procedure adopted in the study. The clean-up step was performed by utilizing the immunoaffinity columns by the two main manufacturers (R-Biopharm Rhone and VICAM) and for the quantitative analysis, HPLC was used by all the participants except one using ELISA. From the output of the study, it can be concluded that at low level (0.19 μg/kg) 10 out of 18 (56%), at medium level (0.45 μg/kg) 11 out of 18 (61%), and at high level (1.45 μg/kg) 12 out of 18 (67%) results fell within the satisfactory ranges. This interlaboratory study provides an estimate of the performance of national and European laboratories involved in OTA determination in cocoa powder samples, which sounds extremely valuable in view of potential future legislation by the European Commission.     

Interlaboratory comparison study for the determination of the Fusarium mycotoxins deoxynivalenol in wheat and zearalenone in maize using different methods

Seventeen laboratories from six different countries, using their usual in-house methods, participated in an interlaboratory comparison test for the determination of the Fusarium mycotoxins deoxynivalenol (DON) in wheat and zearalenone (ZON) in maize. The toxins generally were extracted from maize and wheat employing mixtures of water, acidified water with an organic solvent or even pure water (for DON). While participants who used enzyme linked immuno sorbent assays (ELISA) for the determination of DON did not perform any clean-up, various techniques were applied for the purification of raw extracts (e.g. liquid/liquid extraction, solid phase extraction (SPE), immuno affinity chromatography (IAC)). For the final separation/quantification step either high performance liquid chromatography (HPLC) (mostly for ZON), gas chromatography (GC) (for DON) or ELISA were employed by participants. The aim of this study was to obtain information about the state of the art of mycotoxin analysis in cereals and to support a knowledge and experience exchange between the participating laboratories in the field of mycotoxin analysis. For each mycotoxin 5 different sample types were distributed, standard solutions (10.10 μg/ml ZON in methanol, 10.09 μg/ml DON in ethyl acetate), blank materials, spiked samples (75.1 μg/kg and 378.3 μg/kg ZON in maize, 126.2 μg/kg and 2519 μg/kg DON in wheat) and naturally contaminated maize and wheat. Coefficients of variation (CV) between laboratory mean results (outliers excluded) ranged from 6.2 to 27.7% for ZON and from 18.9 to 30.0% for DON. Except for the maize samples spiked at 75.1 μg/kg ZON the overall means (outliers rejected) statistically could not be distinguished from the respective target values. Average recoveries of the reported results ranged from 87.7 to 96.2% for ZON and from 94.2 to 108.5% for DON. Received: 2 December 1996 / Revised: 17 February 1997 / Accepted: 18 February 1997     

Environmental monitoring of phenolic pollutants in water by cloud point extraction prior to micellar electrokinetic chromatography

Many aromatic compounds can be found in the environment as a result of anthropogenic activities and some of them are highly toxic. The need to determine low concentrations of pollutants requires analytical methods with high sensitivity, selectivity, and resolution for application to soil, sediment, water, and other environmental samples. Complex sample preparation involving analyte isolation and enrichment is generally necessary before the final analysis. The present paper outlines a novel, simple, low-cost, and environmentally friendly method for the simultaneous determination of p-nitrophenol (PNP), p-aminophenol (PAP), and hydroquinone (HQ) by micellar electrokinetic capillary chromatography after preconcentration by cloud point extraction. Enrichment factors of 180 to 200 were achieved. The limits of detection of the analytes for the preconcentration of 50-ml sample volume were 0.10 μg L⁻¹ for PNP, 0.20 μg L⁻¹ for PAP, and 0.16 μg L⁻¹ for HQ. The optimized procedure was applied to the determination of phenolic pollutants in natural waters from San Luis, Argentina. Figure Schematic representation of the cloud point extraction process.     

Determination of uranium and thorium in natural waters by ICP-OES after on-line solid phase extraction and preconcentration in the presence of 2,3-dihydro-9,10-dihydroxy-1,4-antracenedion

An on-line solid phase extraction method, linked to inductively coupled plasma optical emission spectrometry (ICP-OES), has been examined using octadecyl-bonded silica cartridge for determination of low levels of uranium and thorium in aqueous samples. 2,3-dihydro-9,10-dihydroxy-1,4-anthracenedion forms a hydrophobic complex with cations and the resulted complex was retained on SPE. The retained complex was eluted using an acidic solution and introduced into ICP for determination. Various effective parameters and chemical variables such as sample pH, amount of ligand (as a complexing agent), sampling and eluting flow rates and concentration of the eluent were optimized. Under optimal conditions, calibration curves with dynamic linear ranges of 1–200 μg/L (r ₂ = 0.9999) and 1–500 μg/L (r ₂ = 0.9994) for U and Th were obtained, respectively. Detection limits based on three times of standard deviations of blank by 6 replicates were 0.69 μg/L and 0.84 μg/L for U and Th, respectively. Sample throughput was 10 samples/h. The interference effects of several metal ions on percentage of recovery of U and Th were also studied. The method was applied to the recovery and sequential determination of these actinide elements in different water samples.     

Trace determination of sulfonylurea herbicides in water and grape samples by capillary zone electrophoresis using large volume sample stacking

A sensitive and reliable method using capillary zone electrophoresis with UV-diode array detection has been developed and validated for trace determination of residues of sulfonylurea herbicides in environmental water samples and grapes from different origins. The analytes included are triasulfuron, rimsulfuron, flazasulfuron, metsulfuron-methyl, and chlorsulfuron. Optimum separation has been achieved on a 48.5-cm × 50-μm (effective length 40 cm) bubble cell capillary using 90 mM ammonium acetate buffer, pH 4.8, by applying a voltage of 20 kV at 25 °C and using p-aminobenzoic acid as the internal standard. In order to increase sensitivity, large volume sample stacking with polarity switching has been applied as on-line preconcentration methodology. For water samples, a solid-phase extraction (SPE) procedure based on the use of Oasis HLB cartridges was applied for off-line preconcentration and cleanup. For grape samples, the SPE procedure was achieved with C₁₈ sorbent, after extraction of the compounds with MeOH:H₂O (1:1) by sonication. The limits of detection for the studied compounds were between 0.04 and 0.12 μg/L for water samples and 0.97 and 8.30 μg/kg in the case of grape samples, lower in all cases than the maximum residue limits permitted by the EU for this kind of food. The developed methodology has demonstrated its suitability for the monitoring of these residues in environmental water and grape samples with high sensitivity, precision, and satisfactory recoveries.     

Sample preparation procedure for the determination of polycyclic aromatic hydrocarbons in petroleum vacuum residue and bitumen

This paper describes a novel method of sample preparation for the determination of trace concentrations of polycyclic aromatic hydrocarbons (PAHs) in high-boiling petroleum products. Limits of quantitation of the investigated PAHs in materials of this type range from tens of nanograms per kilogram to <20 μg/kg. The studies revealed that in order to separate most of interferences from the analytes without a significant loss of PAHs, it is necessary to use size exclusion chromatography as the first step of sample preparation, followed by adsorption using normal-phase liquid chromatography. The use of orthogonal separation procedure described in the paper allows the isolation of only a group of unsubstituted and substituted aromatic hydrocarbons with a specific range of molar mass. The lower the required limit of quantitation of PAHs, the larger is the scale of preparative liquid chromatography in both steps of sample preparation needed. The use of internal standard allows quantitative results to be corrected for the degree of recovery of PAHs during the sample preparation step. Final determination can be carried out using HPLC-FLD, GC-MS, or HPLC-UV–VIS/DAD. The last technique provides a degree of identification through the acquired UV–VIS spectra.     

液相色谱-串联质谱法测定牛奶中35种四环素类、磺胺类、青霉素类、大环内酯类、氯霉素类抗生素残留

建立了液相色谱-质谱测定牛奶中35种四环素类、磺胺类、青霉素类、大环内酯类、氯霉素类等5类抗生素残留的检测方法。样品经碱性乙腈-Mcllvaine缓冲液超声提取,用Eclipse XDB-C₈色谱柱(150 mm×2.1 mm, 3.5 μm)分离,梯度洗脱,流速0.25 mL/min,进样量10 μL,采用多反应监测正离子或负离子模式,可以一次性对牛奶中的目标化合物进行定性和定量测定。在优化条件下,35种化合物的检出限均低于10.0 μg/kg,方法回收率为70.1%~109.9%,相对标准偏差(RSD)为2.89%~9.99%。结果表明该方法适用于牛奶中抗生素残留的检测。采用所建立的检测方法对市售的50种不同乳品进行了检测,其中一个样品检出氯霉素含量为0.48 μg/kg。检测结果表明,中国市场上销售的乳品氯霉素污染的风险仍然存在。本研究建立的液相色谱-质谱联用方法实现了牛奶中35种四环素类、磺胺类、青霉素类、大环内酯类、氯霉素类等5类抗生素残留的测定。该方法简单、快捷、经济,可实现多种抗生素残留的快速测定。     

Flow-injection spectrofluorimetric determination of ethylenethiourea

A flow-injection configuration is proposed for the fluorimetric determination of ethylenethiourea. The procedure is based on the inhibitory effect of ethylenethiourea on the oxidation of thiamine to thiochrome by mercury(II). A linear calibration graph was obtained between 0.1 and 2.0 μg mL^–1, with a sampling rate of 40 samples per hour and a relative standard deviation of about 1.11%. The usefulness of the method was tested for the determination of ethylenethiourea residues in water, milk, potatoes, pear, grape and apple. Received: 26 January 1998 / Revised: 6 April 1998 / Accepted: 9 April 1998     

Flow-injection spectrofluorimetric determination of ethylenethiourea

A flow-injection configuration is proposed for the fluorimetric determination of ethylenethiourea. The procedure is based on the inhibitory effect of ethylenethiourea on the oxidation of thiamine to thiochrome by mercury(II). A linear calibration graph was obtained between 0.1 and 2.0 μg mL^–1, with a sampling rate of 40 samples per hour and a relative standard deviation of about 1.11%. The usefulness of the method was tested for the determination of ethylenethiourea residues in water, milk, potatoes, pear, grape and apple. Received: 26 January 1998 / Revised: 6 April 1998 / Accepted: 9 April 1998