Capabilities of laboratories to determine melamine in food—results of an international proficiency test

A proficiency test to assess the capabilities of laboratories to determine melamine in a milk powder and a baking mix, representing starch-containing foods like bread and biscuits, was carried out in January 2009. The need for such an interlaboratory comparison arose from a health scare in China about melamine-tainted powdered milk in the second half of 2008. Laboratories in 31 countries, including Australia, China, India, Japan, New Zealand and the USA, and 21 of the 27 Member States of the European Union participated and reported back 114 results for the milk powder and 112 for the baking mix test materials. The reported results were compared to reference values determined by exact-matching double isotope dilution mass spectrometry. The so-determined assigned values were 10.0 ± 0.6 mg/kg melamine in the milk powder and 3.18 ± 0.17 mg/kg melamine in the baking mix. A coverage factor k of 2 was applied to calculate the expanded uncertainties. Three quarters of all reported results for both materials had associated z scores which were satisfactory (z ≤ |2|). Of the reported results, 90% was accompanied by a measurement uncertainty statement, and the majority of the measurement uncertainty ranges were reasonable. A number of laboratories were found to underestimate their measurement uncertainties. Methods that involved the use of stable-isotope-labelled melamine were shown to be clearly advantageous with regard to the accuracy of the results. However, no significant influence by other method parameters could be identified.     

Accuracy and reliability of radiometric measurements – results of a laboratory proficiency test with labelled sediment

 In 1995, a laboratory proficiency test was carried out in Germany with labelled sediment which was analyzed by 40 participants (operators of nuclear power plants, officially authorized institutions of the German Federal States, and laboratories of research centers). Preparation and certification of the labelled material were described in detail. The deviations of the laboratory means from the corresponding certified reference values of ten radionuclides were determined. Outliers of type 2 were recognized by means of the Grubbs test and eliminated. The consistency of laboratory means and reference values was tested by a modified t test. To describe the reliability of the measurements performed, a radioanalytical quality index which has been defined elsewhere was used. By use of this index, the radioanalytical quality of laboratory means and the means of laboratory means could be evaluated and a very realistic picture of the "state-of-the-practice" of the participating laboratories obtained. In some cases, it was possible to identify systematic errors and to explain their causes by physical phenomena. Received: 11 June 1996 Accepted: 14 September 1996     

Production of spiked vegetation samples containing γ-emitting radionuclides for proficiency testing

Journal of Radioanalytical and Nuclear Chemistry - The production of environmental reference materials such as soil, sediment, water and vegetation containing radionuclides for interlaboratory...     

Adsorption of mercury species on river sediments — effects of selected abiotic parameters

Abiotic parameters (pH, temperature, current velocity, mercury species concentration, and sediment and aqueous media composition) influence mercury species (MeHg⁺, EtHg⁺, PhHg⁺ and inorganic Hg²⁺) adsorption on river sediments. The highest amount of adsorbed MeHg⁺ and EtHg⁺ (82–93% and 85–91% for static and agitated system, respectively) occurred at pH 3–4. For PhHg⁺ the maximum adsorption (90% and 95% for static and agitated systems) was located over the broad 3–10 pH range, while for Hg²⁺ (94% and 97% for static and agitated systems) it was at pH ∼ 3. Temperature (4.5–60°C) influenced the adsorption rate but not the quantity. Both rate and quantity increased in the order: static < agitated ≤ stirred systems. The aqueous medium composition affected both rate and quantity. Sulfate caused the largest adsorption decrease for organomercury species (15–25% decrease); sulfide reduced Hg²⁺ adsorption about 67%. Cations at pH 5.2 reduced either the adsorption rate (Ca²⁺, Al³⁺) or the total adsorption (Zn²⁺, Fe³⁺). Positive correlations were found between sediment C, N, S content as well as cation exchange capacity (CEC) with mercury adsorption (R = 0.45–0.66, 0.56–0.89, 0.45–0.61 and 0.55–0.73, respectively) while negative correlations were observed with Fe and Al (R = −0.63 to −0.90 and −0.65 to −0.86, respectively).     

Determination of ziram in vegetable samples by square wave voltammetry

The electrochemical behaviour and electrode reaction mechanism of ziram （zinc-dimethyl dithiocarbamate） on a hanging mercury drop electrode were investigated in Britton-Robinson （B-R） buffer by using cyclic and square wave voltammetry （SWV）. Based on these studies a voltammetric method for determination of ziram wasdeveloped and applied to determine the ziram in synthetic and spiked vegetable samples, satisfactory results were obtained in both cases.     

Determination of selected β-receptor antagonists in biological samples by solid-phase extraction with cholesterolic phase and LC/MS

A new method is presented for the determination of five selected β-receptor antagonists by HPLC, which emphasizes sample preparation via retention on a new type of silica gel sorbent used for solid-phase extraction (SPE). Sorbents of this type were obtained by the chemical modification of silica gels of various porosities by cholesterol ligands. The cholesterol-based packing material was investigated by spectroscopic methods and elemental analysis. The recoveries obtained with the extraction procedure were optimum over a relatively broad sample pH range (3.08–7.50). Analytical factors such as the sample loading, the washing step and elution conditions, the concentration of β-receptor antagonists to be extracted, and the type of sorbent were found to play significant roles in the sample preparation procedure and would therefore need to be controlled to achieve optimum recoveries of the analytes. Under optimum conditions, the recoveries of nadolol, acebutolol, esmolol, oxprenolol and propranolol from spiked buffers, blood and urine were reproducible and dependent on the polarity or hydrophilicity of the compounds. The above analytes were determined by reverse-phase high-performance liquid chromatography (HPLC) with UV and ESI-ion trap mass spectrometry (MS) detection. The described method was found to be suitable for the routine measurement of compounds that are both polar and basic, and can be applied for the analysis of biological samples such as urine and blood in clinical, toxicological or forensic laboratories. The recovery measurements were performed on spiked human urine and serum, and on real samples of mouse blood serum.     

Determination of aniline in environmental water samples by alternating-current oscillopolarographic titration

A new method for the determination of aniline in environmental water based on oscillopolarographic titration was presented in this paper. Several factors including the kind, concentration, and volume of acid, the dosage of potassium bromide, the temperature and concentration of concomitant substances were investigated in detail. The experimental results indicated that this method was simple, rapid, and sensitive. The linear range was 8.367×10-4 to 2.789×10-2 mol L-1, the relative standard deviation (R.S.D.) was lower than 0.96%, and the spiked recoveries of aniline in environmental water samples were in the range of 99.4-106.9% under the optimal conditions. The results indicated that the present method could be used as an alternative method for aniline determination in realworld water samples.     

Determination of the standard deviation for proficiency assessment from past participant’s performances

The ??uncertainty function?? introduced by Thompson et al. estimates the reproducibility standard deviation as a function of concentration or mass fraction. This model was successfully applied to data derived from three proficiency testing schemes aiming at the quantification of cadmium, lead and mercury in blood and urine. This model allows the estimation of standard deviation for the performance assessment for proficiency testing rounds.     

Determination of sub—ppm levels of boron in ground water samples by laser induced breakdown spectroscopy

Laser induced breakdown spectroscopy (LIBS) was applied to the determination of sub-ppm levels of boron in ground water samples using spectroscopically pure graphite planchets as solid support. The data obtained by LIBS agreed well with those from ICP-AES. No spectral interference due to the possibly interfering elements Fe, Cr, Al and Mo was observed. The detection limit was 0.01 µg.g^?1 for boron using the B(I) 249.773 nm emission line. The method is considered to be promising for the rapid determination of boron, with an acceptable degree of accuracy and without the need for elaborate sample treatment, preconcentration and purification steps.     

Determination of phosphorus in small amounts of protein samples by ICP–MS

Inductively coupled plasma mass spectrometry (ICP-MS) is used for phosphorus determination in protein samples. A small amount of solid protein sample (down to 1 micro g) or digest (1-10 micro L) protein solution was denatured in nitric acid and hydrogen peroxide by closed-microvessel microwave digestion. Phosphorus determination was performed with an optimized analytical method using a double-focusing sector field inductively coupled plasma mass spectrometer (ICP-SFMS) and quadrupole-based ICP-MS (ICP-QMS). For quality control of phosphorus determination a certified reference material (CRM), single cell proteins (BCR 273) with a high phosphorus content of 26.8+/-0.4 mg g(-1), was analyzed. For studies on phosphorus determination in proteins while reducing the sample amount as low as possible the homogeneity of CRM BCR 273 was investigated. Relative standard deviation and measurement accuracy in ICP-QMS was within 2%, 3.5%, 11% and 12% when using CRM BCR 273 sample weights of 40 mg, 5 mg, 1 mg and 0.3 mg, respectively. The lowest possible sample weight for an accurate phosphorus analysis in protein samples by ICP-MS is discussed. The analytical method developed was applied for the analysis of homogeneous protein samples in very low amounts [1-100 micro g of solid protein sample, e.g. beta-casein or down to 1 micro L of protein or digest in solution (e.g., tau protein)]. A further reduction of the diluted protein solution volume was achieved by the application of flow injection in ICP-SFMS, which is discussed with reference to real protein digests after protein separation using 2D gel electrophoresis.The detection limits for phosphorus in biological samples were determined by ICP-SFMS down to the ng g(-1) level. The present work discusses the figure of merit for the determination of phosphorus in a small amount of protein sample with ICP-SFMS in comparison to ICP-QMS.     

Determination of γ-hexachlorocyclohexane and its metabolites in biological samples from rat

We have determined γ-hexachlorocyclohexane (lindane) and its metabolites in urine, serum and feces samples from rats using HPLC-UV-Vis and confirmation of mass with matrix assisted laser desorption/ ionization-time of flight (MALDI-TOF) analysis. Samples were collected from rats treated orally with lindane (17.6 mg/kg; 1/5 of LD₅₀) or vehicle for 2 weeks. Lindane and metabolites were extracted from samples with hexane and analyzed. The HPLC–MALDI-TOF is highly sensitive to the point of detecting very low level (5 ppm) of lindane and metabolites. The HPLC-UV-Vis analysis confirmed the presence of lindane in urine (386–1652 ppm), serum (207–371 ppm) and feces (5–74 ppm). Control samples had no peak corresponding to lindane. MALDI-TOF analysis of urine and serum samples showed a major peak at 293 m/z, whereas feces showed a minor peak at 292–293 m/z, which were consistent with the peak obtained for standard lindane (293 m/z). Our data indicates that HPLC-UV-Vis–MALDI-TOF combo method is sensitive for detecting and quantifying lindane and its metabolites in serum, urine and feces. Our results further showed that minor quantities of lindane and metabolites were excreted through feces confirming that the main pathway for excretion of lindane and metabolites is through urine.     

Determination of hydroxylated metabolites of polycyclic aromatic hydrocarbons in sediment samples by combining subcritical water extraction and dispersive liquid–liquid microextraction with derivatization

A sample preparation method for the determination of hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) in sediment samples was developed using gas chromatography–mass spectrometry (GC–MS). Dispersive liquid–liquid microextraction (DLLME) with derivatization was performed following the subcritical water extraction (SWE) that provided which was provided by accelerated solvent extraction (ASE). Several important parameters that affected both SWE extraction and DLLME, such as the selection of organic modifier, its volume, extraction temperature, extraction pressure and extraction time were also investigated. High sensitivity of the hydroxylated PAHs derivatives by N-(tert-butyldimethylsilyl)-N-methyl-trifluoroacetamide (MTBSTFA) could be achieved with the limits of detection (LODs) ranging from 0.0139 (2-OH-nap) to 0.2334 μg kg⁻¹ (3-OH-fluo) and the relative standard deviations (RSDs) between 2.81% (2-OH-phe) and 11.07% (1-OH-pyr). Moreover, the proposed method was compared with SWE coupled with solid phase extraction (SPE), and the results showed that ASE–DLLME was more promising with recoveries ranging from 57.63% to 91.07%. The proposed method was then applied to determine the hydroxylated metabolites of phenanthrene in contaminated sediments produced during the degradation by two PAH-degraders isolated from mangrove sediments.     

Molecularly imprinted polymers for simultaneous determination of antiepileptics in river water samples by liquid chromatography–tandem mass spectrometry

A restricted access media–molecularly imprinted polymer (RAM–MIP) for cyclobarbital has been developed for selective extraction of antiepileptics in river water samples. The RAM–MIP was prepared using 4-vinylpyridine and ethylene glycol dimethacrylate as a functional monomer and cross-linker, respectively, by a multi-step swelling and polymerization method followed by a surface modification technique. The RAM–MIP for cyclobarbital showed molecular recognition abilities for phenobarbital, amobarbital and phenytoin as well as cyclobarbital. Thus, selective analysis of antiepileptics in river water samples was attained with RAM–MIP extraction followed by column-switching liquid chromatography–tandem mass spectrometry. The concentrations of phenobarbital and phenytoin in river water samples were about 15 and 4 ng/L, respectively, while that of amobarbital was below the limit of quantitation.     

The risk of altering soil and sediment samples upon extract preparation for analytical and bio-analytical investigations—a review

Organic total extracts play an important role in soil and sediment risk assessment. Beside a routine application in analytical chemistry, they are used in bio-analytical investigations as a “worst-case scenario” or, e.g., in order to simulate chronic intoxication, and as samples for effect-directed analysis. While theoretically providing highly reliable data and good reproducibility, the whole process of sample handling and extract preparation can lead to extracts that might fail to accurately represent a toxic potential of their corresponding sampling site. This review identifies and discusses the most important possible alterations that have the potential to lead to over and, more often, underestimation of the effectiveness of extracts. Since incorrect data will compromise soil and sediment risk assessment as a whole, results from analytical and bio-analytical investigations of extracts demand cautious interpretation. Reliability of extract testing grows with reproducibility; experiments should therefore be repeated with independent extraction replicates. New or optimized extraction procedures should circumvent the issues mentioned here while being suitable for routine application.     

Determination of priority pollutants in aqueous samples by dispersive liquid–liquid microextraction

A dispersive liquid–liquid microextraction (DLLME) method followed by high-performance liquid chromatography–triple quadrupole mass spectrometry has been developed for the simultaneous determination of linear alkylbenzene sulfonates (LAS C₁₀, C₁₁, C₁₂, and C₁₃), nonylphenol (NP), nonylphenol mono- and diethoxylates (NP₁EO and NP₂EO), and di-(2-ethylhexyl)phthalate (DEHP). The applicability of the method has been tested by the determination of the above mentioned organic pollutants in tap water and wastewater. Several parameters affecting DLLME, such as, the type and volume of the extraction and disperser solvents, sample pH, ionic strength and number of extractions, have been evaluated. Methanol (1.5 mL) was selected among the six disperser solvent tested. Dichlorobenzene (50 μL) was selected among the four extraction solvent tested. Enrichment factor achieved was 80. Linear ranges in samples were 0.01–3.42 μg L⁻¹ for LAS C₁₀–₁₃ and NP₂EO, 0.09–5.17 μg L⁻¹ for NP₁EO, 0.17–9.19 μg L⁻¹ for NP and 0.40–17.9 μg L⁻¹ for DEHP. Coefficients of correlation were higher than 0.997. Limits of quantitation in tap water and wastewater were in the ranges 0.009–0.019 μg L⁻¹ for LAS, 0.009–0.091 μg L⁻¹ for NP, NP₁EO and NP₂EO and 0.201–0.224 μg L⁻¹ for DEHP. Extraction recoveries were in the range from 57 to 80%, except for LAS C₁₀ (30–36%). The method was successfully applied to the determination of these pollutants in tap water and effluent wastewater from Seville (South of Spain). The DLLME method developed is fast, easy to perform, requires low solvent volumes and allows the determination of the priority hazardous substances NP and DEHP (Directive 2008/105/EC).     

Evaluation of Argentation TLC—Densitometry for the Determination of trans Fatty Acids in Butterfat

JPC – Journal of Planar Chromatography – Modern TLC - A stand-alone argentation TLC (Ag-TLC) procedure has been established for rapid estimation of the authenticity and densitometric...     

Determination of cadmium, chromium and copper in high salt samples by LA-ICP-OES after electrodeposition—preliminary study

A novel method is presented for determination of heavy metal ions in a high-saline matrix. It is based on the electrodeposition of the ions and subsequent laser ablation coupled to inductively coupled plasma optical emission spectrometry (LA-ICP-OES). Three arrangements for electrodeposition were worked out, two of them with stationary working electrodes. Materials for use in the working electrodes, and conditions for electrodeposition of Cd, Cr and Cu (pH, deposition current, time of electrolysis) were studied. Nickel was found to be the best electrode material. The metals accumulate on the surface of electrode and were then evaporated/ablated with a Nd:YAG laser focused into the ICP-OES spectrometer. The detection limits are 0.13 mg?L^?1 for Cd, 0.15 mg?L^?1 for Cu, and 1.9 mg?L^?1 for Cr in case of a stationary bottom working electrode, and 0.25 mg?L^?1 for Cd, 0.05 mg?L^?1 for Cu, 0.8 mg?L^?1 for Cr when using a rotating electrode. The relative standard deviation is in range from 3.8 to 10.3%. Waste water was analyzed in this way by the standard addition method.     

Determination of butyltin compounds in environmental samples by isotope-dilution GC–ICP–MS

Isotope-dilution analysis in combination with GC-ICP-MS detection has been applied to the determination of butyltin species in environmental samples. Different spikes containing the isotopically labeled butyltin species have been synthesized in the laboratory after optimization of the reaction conditions. The isotopic compositions of the tin species in the different spike solutions were determined by GC-ICP-MS after derivatization by aqueous ethylation with sodium tetraethylborate. Reverse isotope-dilution analysis was used for quantitation of the spike solutions by means of natural MBT, DBT, and TBT standards. The mixed spikes were used for simultaneous analysis of MBT, DBT and TBT in the certified reference materials, PACS-2, CRM 462, and CRM 646, with satisfactory results. The excellent agreement of the different speciation results obtained by use of the different spikes is a good indicator of the precision, accuracy, and reliability which can be achieved by using isotope-dilution analysis for trace metal speciation.Application of a double spike containing (119)Sn-enriched MBT (79.7 At%), (118)Sn-enriched DBT (86.7 At%), and (119)Sn-enriched TBT (83.1 At%) also enabled evaluation of the conditions resulting in quantitative extraction of the species from the solid matrix, in combination with possible alterations depending on the different extraction procedures used (mechanical shaking, ultrasounds, and microwaves). Mathematical equations used for this purpose computed the correct species concentrations directly and, additionally, the decomposition factors (from TBT to DBT and from DBT to MBT) after precise measurement of the (119)Sn/(120)Sn and (118)Sn/(120)Sn ratios for all butyltin species by GC-ICP-MS.     

Spectrofluorometric method for determination of the total mercury content in environmental samples — Waste waters

A highly selective spectrofluorometric method for the determination of total mercury (Hg) in waste waters is described. Fluorescence quenching of rhodamine B with Hg(II) in the presence of iodide, after a concentration step, is the basis of this sensitive method. All forms of mercury, including organic compounds, are pre-oxidized to ionic mercury by acidic potassium permanganate. The final and complete oxidation is achieved by adding potassium persulphate and heating. Hg(II) was reduced by tin(II) chloride and Hg vapour driven by an air stream into an absorption solution containing potassium permanganate and sulphuric acid, using a closed, recirculating air stream. In this solution fluorescence quenching of rhodamine B at an excitation wavelength of 485 nm and emission wavelength of 586 nm was measured. The recoveries were done by adding 3.0 g Hg/100 ml to each sample before the digestion. It was indicated that the recoveries for determining mercury in waste waters were 98.3%–102.7%. The method gives reliable results down to a concentration of 10 ng Hg/ml waste water.     

Determination of selected polycyclic aromatic hydrocarbons and oxygenated polycyclic aromatic hydrocarbons in aerosol samples by high-performance liquid chromatography and liquid chromatography–tandem mass spectrometry

Fine and ultrafine particles are probably responsible for numerous health effects, but it is still unclear whether and to what extent the particle itself or organic compounds adsorbed or condensed on the particle are responsible for the effects observed. One important class of particle-bound substances are the polycyclic aromatic hydrocarbons (PAH) and their oxygenated derivatives. To improve the tools used for chemical characterization of particulate matter analytical methods for the determination of PAH and oxygenated PAH in aerosol samples of different origin have been developed and optimized. PAH on high-volume filters and on soot aerosols were analyzed by using accelerated solvent extraction for extraction and high-performance liquid chromatography with fluorescence detection for separation and quantification. Total PAH concentrations were in the range 0.3–9.3 ng m^–3. For analysis of selected oxygenated PAH on high-volume filters a liquid chromatography–tandem mass spectrometric method was developed and optimized. Preliminary investigations showed that oxygenated PAH at pg m^–3 concentrations can be determined.