间接竞争酶联免疫法检测水样中的重金属镉

利用重金属镉多克隆抗体,建立一种低仪器成本的检测水样中重金属镉的间接竞争酶联免疫法,其检测限(IC15)为0.76μg/L,灵敏度(IC50)为11.33μg/L。交叉反应结果表明,该抗体除与汞螯合物的交叉反应率为10.9%,与其他金属(锰,铬,镁,铁,铅,镍,银和铜)螯合物的交叉反应率均低于1.32%。自来水和河水样品中镉的添加回收率为93.95%～107.40%,变异系数为3.97%～14.69%。     

Verifiable metamodels for nitrate losses to drains and groundwater in the Corn Belt, USA

Nitrate leaching in the unsaturated zone poses a risk to groundwater, whereas nitrate in tile drainage is conveyed directly to streams. We developed metamodels (MMs) consisting of artificial neural networks to simplify and upscale mechanistic fate and transport models for prediction of nitrate losses by drains and leaching in the Corn Belt, USA. The two final MMs predicted nitrate concentration and flux, respectively, in the shallow subsurface. Because each MM considered both tile drainage and leaching, they represent an integrated approach to vulnerability assessment. The MMs used readily available data comprising farm fertilizer nitrogen (N), weather data, and soil properties as inputs; therefore, they were well suited for regional extrapolation. The MMs effectively related the outputs of the underlying mechanistic model (Root Zone Water Quality Model) to the inputs (R(2) = 0.986 for the nitrate concentration MM). Predicted nitrate concentration was compared with measured nitrate in 38 samples of recently recharged groundwater, yielding a Pearson's r of 0.466 (p = 0.003). Predicted nitrate generally was higher than that measured in groundwater, possibly as a result of the time-lag for modern recharge to reach well screens, denitrification in groundwater, or interception of recharge by tile drains. In a qualitative comparison, predicted nitrate concentration also compared favorably with results from a previous regression model that predicted total N in streams.     

原子荧光光谱法测定饮用天然矿泉水中的镉

将氢化物发生-原予荧光光谱法应用在盐酸介质中,以钴离子-硫脲体系为增感剂,测定饮用天然矿泉水中的镉并优化了仪器条件。该方法灵敏度高,线性范围宽,准确度高,操作简单。检出限为0．00027mg／L,相对标准偏差小于7．9％,适用于饮用天然矿泉水中镉的测定。     

Selective cloud point extraction for the determination of cadmium in food samples by flame atomic absorption spectrometry

A new cloud point extraction (CPE) procedure for preconcentration of cadmium prior to the determination by flame atomic absorption spectrometry (FAAS) was developed. The method is based on the fact that cadmium could form hydrophobic ion-associated complex in the presence of iodide and methyl green (MG), and the hydrophobic ion-associated complex could be extracted into surfactant-rich phase. The main factors affecting CPE procedure, such as pH, concentration of KI, MG and surfactant, equilibrium temperature and incubation time, sample volume were investigated. Potential interference from co-existing ions was largely eliminated as most of co-existing ions can not form extractable ion-associated complex with iodide and MG. Under the optimum conditions, the limit of detection (3σ) and limit of quantity (10σ) were 0.90 ng mL⁻¹ and 3.0 ng mL⁻¹ for cadmium, respectively, and relative standard deviation was 4.2% (c = 50 ng mL⁻¹, n = 7). The proposed method was successfully applied to determination of cadmium in the certified reference rice sample (GBW08510) and food samples with satisfactory results.     

Foliar analysis as a diagnostic technique in cocoa nutrition. II.—Errors during the preparation phase prior to analysis of leaf samples

Errors arising from the preparative phase of storing the fresh harvested cocoa leaves during transit to the laboratory, washing, drying, grinding and storage of the ground material before analysis have been studied. A procedure aimed at reducing such errors is recommended.     

A highly sensitive method for simultaneous determination of ultra trace levels of copper and cadmium in food and water samples with luminol as a chelating agent by adsorptive stripping voltammetry

In the present study a selective method is presented for the simultaneous determination of copper and cadmium in food samples by adsorptive stripping voltammetry. In preliminary studies, it has been proven that the copper and cadmium react with 3-aminophthalhydrazide (luminol), giving rise to the formation of these complexes. These complexes have adsorptive characteristics on hanging mercury drop electrode (HMDE) and can be reduced in a reduction step. In this study the optimum reaction parameters and conditions studies are investigated. The calibration graphs were linear in the concentration range of 0.5–105.0 and 0.8–70.0 ng/ml for copper and cadmium, respectively. The limit of detection of the method was 0.04 ng/ml for Cu²⁺ and 0.02 ng/ml for Cd²⁺. The interference of some common ions was studied and it was concluded that application of this method for the determination of copper (II) and cadmium in food and water samples led to satisfactory results.     

The oral nitrate and nitrite intake in The Netherlands: evaluation of the results obtained by HPIC analysis of duplicate 24-hour diet samples collected in 1994.

In spring and autumn of 1994 duplicates of 24-h diets were collected from 123 respondents. One of the goals of this study was to determine the amount of nitrite and nitrate in the duplicates of 24-h diets to establish the oral daily intake of these analytes. For this purpose an HPIC/UV method for the determination of nitrate and nitrite in duplicate diets was developed and validated. The sample preparation procedure was derived from the in-house method used for the determination of nitrate and nitrite in human blood plasma. The sample is diluted with water, deproteinized with Carrez reagent, followed by chromatographic clean-up on an SPE C18-column. Both the nitrate and the nitrite results are quantitative. The recovery for nitrite was on average 104% (n = 21, spiking levels: 0.84-95 mg/kg) and for nitrate on average 103% (N = 21, spiking levels: 1.8-404 mg/kg). Samples of duplicates of 24-h diets were analysed according to the method developed. The median intake of nitrite calculated from the samples collected in spring 1994 was 0.6 mg/person day (range < 0.1-6.1 mg/person/day). For the samples collected in autumn 1994 these figures were < 0.2 mg/person/day (range < 0.1-16 mg/person/day). The mean intake of nitrate was 73 mg/person/day (range 7-322 mg/person/day) in spring 1994 and 87 mg/person/day (range 1-310 mg/person/day) in autumn 1994. The overall mean intake of nitrate in 1994 was 80 mg/person/day. The daily intake for nitrate was higher than that found in the duplicate diet study carried out in 1984/1985, when an average daily intake of 52 mg/person was measured. The intake of nitrite was also higher than found in the duplicate diets collected in 1984/1985. The findings of the study are discussed in the context of the ADI for nitrate and nitrite as well as the outcome of other recent European intake studies.     

Solid phase extraction of large volume of water and beverage samples to improve detection limits for GC-MS analysis of bisphenol A and four other bisphenols

Solid phase extraction (SPE) of large volumes of water and beverage products was investigated for the GC-MS analysis of bisphenol A (BPA), bisphenol AF (BPAF), bisphenol F (BPF), bisphenol E (BPE), and bisphenol B (BPB). While absolute recoveries of the method were improved for water and some beverage products (e.g. diet cola, iced tea), breakthrough may also have occurred during SPE of 200 mL of other beverages (e.g. BPF in cola). Improvements in method detection limits were observed with the analysis of large sample volumes for all bisphenols at ppt (pg/g) to sub-ppt levels. This improvement was found to be proportional to sample volumes for water and beverage products with less interferences and noise levels around the analytes. Matrix effects and interferences were observed during SPE of larger volumes (100 and 200 mL) of the beverage products, and affected the accurate analysis of BPF. This improved method was used to analyse bisphenols in various beverage samples, and only BPA was detected, with levels ranging from 0.022 to 0.030 ng/g for products in PET bottles, and 0.085 to 0.32 ng/g for products in cans.     

The effect of bone in meat samples upon analytical results for fat, protein and water by foss Super-Scan type 10600

Investigations have been made into possible spectral interferences at fat, protein and water wavelengths of the Super-Scan (infra-red meat analyser) due to absorbance by phosphorus (a natural constituent of bone) at the carbohydrate wavelength. Instrument calibration for boneless meat resulted in the need for correction factors to results for bone-in meat of × 0·96, × 1·05 and × 0·97 for % fat, % protein and % water, respectively, to bring them in line with those by standard chemical methods. Comparisons between Super-Scan results for boneless meat to which tricalcium phosphate (the major constituent of bone) has been added showed an interference proportional to the amount of phosphate present and varied in size depending on sample fatness. Calibration with bone-in meat controlled interference adequately for % fat and % water, but still required an empirical correction factor of × 0·97 for protein.     

Application of multiwalled carbon nanotubes modified by diphenylcarbazide for selective solid phase extraction of ultra traces Cd(II) in water samples and food products

A novel sorbent for separation of cadmium ions was prepared by functionalizing multiwall carbon nanotubes with diphenylcarbazide and underutilised to develop a solid-phase extraction method to separate and concentrate trace amounts of cadmium ions from some real samples by flame atomic absorption spectrophotometry measurements. The optimum experimental conditions such as pH, flow rates, type and the smallest amount of eluent for elution of cadmium ions, break through volume and effect of coexisting ions on the separation and determination of cadmium ions were evaluated.     

Investigation of test performance of the dual reminder A-Not A (DR A-Not A) in comparison to 3-AFC for discriminating samples of drinking water

Although the relative performance of sensory discrimination methods is well theorized in Thurstonian modeling and signal detection theory (SDT), empirical research is needed to investigate how such theorized models could be validated in complex sensory testing situations of food and beverages. This paper presents a practical procedure to utilize the existing SDT-based A-Not A sensory discrimination model based on a beta-strategy for detecting the off-sensory quality of samples of drinking water and validates the model for effective and efficient sensory quality management of food and beverages. Dual reminder A-Not A (DR A-Not A) using two tastings of the reference stimulus before evaluating every test stimulus is proposed as the optimal test procedure because it uses more sensitive test sequences and facilitates subjects’ familiarization with the standard quality of the reference. To test the performance of DR A-Not A, 3-AFC, which also uses three stimuli and is the recommended method for detecting odor or taste stimuli by ASTM, was used as a control method. In Experiment 1, 98 subjects each performed both DR A-Not A and 3-AFC. Based on these results, only sensitive subjects were selected for the next experiment, in which they were divided into two equally well performing groups. In Experiment 2, each group performed either DR A-Not A or 3-AFC over three repeated sessions. The results confirmed that the A-Not A beta-strategy was adopted for DR A-Not A and that its test performance was improved over replications. These results suggest that although DR A-Not A is an unspecified difference test method and does not use a forced-choice task, embedding the familiarization procedure for the reference renders it an effective sensory difference method for the sensory quality management of drinking water.     

Magnetic graphene oxide nanocomposites as the adsorbent for extraction and pre-concentration of azo dyes in different food samples followed by high-performance liquid chromatography analysis

ABSTRACT

This work presents a method of magnetic solid-phase extraction (MSPE) combined with high-performance liquid chromatography (HPLC) to analyse five synthetic azo dyes (tartrazine, amaranth, carmine, sunset yellow, allura red) in different food samples. The magnetic graphene oxide nanocomposite (GO@Fe₃O₄) was prepared by a one-step solvothermal method and used as the sorbent for extraction and pre-concentration of azo dyes in food samples. The as-prepared GO@Fe₃O₄ nanocomposite was characterised by transmission electron microscope, Fourier transform-infrared spectroscopy, X-ray diffraction, vibrating sample magnetometer, and Brunuer-Emmett-Teller analysis. The extraction and desorption parameters were investigated, including the material amount, extraction time, pH of the solution, desorption temperature, and desorption solvents. Under the optimised conditions, the limits of detection (LODs) were 1.14–2.23, 0.36–0.77 and 0.68–1.26 ng/g for candy, jelly, and plum candy, respectively. The limits of quantification (LOQs) were 4.02–7.73, 1.21–2.50 and 2.31–4.20 ng/g for candy, jelly, and plum candy, respectively. For the analysis of spiked jelly, recoveries were between 73.2% and 107.7%, with RSDs lower than 1.34 %. The developed method was successfully applied to the analysis of real samples including jelly, candy and plum candy.     

Genome-wide association analysis for susceptibility to infection by Mycobacterium avium ssp. paratuberculosis in US Holsteins

Paratuberculosis, or Johne's disease, is a chronic, granulomatous, gastrointestinal tract disease of cattle and other ruminants caused by the bacterium Mycobacterium avium subspecies paratuberculosis (MAP). Control of Johne's disease is based on programs of testing and culling animals positive for infection with MAP and concurrently modifying management to reduce the likelihood of infection. The current study was motivated by the hypothesis that genetic variation in host susceptibility to MAP infection can be dissected and quantifiable associations with genetic markers identified. Two separate GWAS analyses were conducted, the first using 897 genotyped Holstein artificial insemination sires with phenotypes derived from incidence of MAP infection among daughters based on milk ELISA testing records. The second GWAS analysis was a case-control design using US Holstein cows phenotyped for MAP infection by serum ELISA or fecal culture tests. Cases included cows positive for either serum ELISA, fecal culture, or both. Controls consisted of animals negative for all tests conducted. A total of 376 samples (70 cases and 306 controls) from a University of Minnesota Johne's management demonstration project and 184 samples (76 cases and 108 controls) from a Michigan State University study were used. Medium-density (sires) and high-density (cows) genotype data were imputed to full genome sequence for the analyses. Marker-trait associations were analyzed using the single-step (ss)GWAS procedure implemented in the BLUPF90 suite of programs. Evidence of significant genomic contributions for susceptibility to MAP infection were observed on multiple chromosomes. Results were combined across studies in a meta-analysis, and increased support for genomic regions on BTA7 and BTA21 were observed. Gene set enrichment analysis suggested pathways for antigen processing and presentation, antimicrobial peptides and natural killer cell–mediated cytotoxicity are relevant to variation in host susceptibility to MAP infection, among others. Genomic prediction was evaluated using a 5-fold cross-validation, and moderate correlations were observed between genomic breeding value predictions and daughter averages (～0.43 to 0.53) for MAP infection in testing data sets. These results suggest that genomic selection against susceptibility to MAP infection is feasible in Holstein cattle.     

Study of a microwave digestion method for total arsenic determination in marine mussels by electrothermal atomic absorption spectrometry: application to samples from the Ria de Arousa

Arsenic determination in mussel tissue was performed by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman background correction and using iridium as a chemical modifier. Samples were digested by microwave heating using a mixture of nitric and sulphuric acids. This mixture makes possible the destruction of organoarsenic compounds, specifically arsenobetaine, prior to the graphite furnace determination. Optimum pyrolysis and atomization temperatures were 1,100 and 1,800 °C, respectively. The method was precise (with RSD% < 10), accurate (study of a certified reference material: 18.4 ± 1.4 μg As g⁻¹ vs. a certified content: 18.0 ± 1.1 μg As g⁻¹; recoveries between 90 and 104%) and sensitive (LOD 0.21 μg g⁻¹ on a dry weight basis). The method was applied to the determination of arsenic in aquaculture mussels collected in four sampling campaigns from the productive Ría de Arousa (estuary sited in Galicia, NW of Spain).     

Multiclass methods for the analysis of antibiotic residues in milk by liquid chromatography coupled to mass spectrometry: A review

Milk is an important and beneficial food from a nutritional point of view, being an indispensable source of high quality proteins. Furthermore, it is a raw material for many dairy products, such as yoghurt, cheese, cream etc. Before reaching consumers, milk goes through production, processing and circulation. Each step involves potentially unsafe factors, such as chemical contamination that can affect milk quality. Antibiotics are widely used in veterinary medicine for dry cow therapy and mastitis treatment in lactating cows, which can cause the presence of antimicrobial residues in milk. In order to ensure consumers’ safety, milk is analyzed to make sure that the fixed Maximum Residue Limits (MRLs) for antibiotics are not exceeded. Multiclass methods can monitor more drug classes through a single analysis, so they are faster, less time-consuming and cheaper than traditional methods (single-class); this aspect is particularly important for milk, which is a highly perishable food. Nevertheless, multiclass methods for veterinary drug residues in foodstuffs are real analytical challenges. This article reviews the major multiclass methods published for the determination of antibiotic residues in milk by liquid chromatography coupled to mass spectrometry, with a special focus on sample preparation approaches.     

Development and validation of multi-residue analysis for tetracycline antibiotics in feed by high performance liquid chromatography coupled to mass spectrometry

ABSTRACT

A new multi-residue method for the analysis of the tetracycline antibiotics oxytetracycline, tetracycline, chlortetracycline, and doxycycline was developed and validated for animal feed. After extraction with 0.1M Na₂EDTA-McIlvaine buffer (pH 4), the samples were centrifuged, purified by SPE (Strata-X-CW cartridges) and analysed by HPLC-MS. Validation of the method was performed according to the guidelines indicated in European Commission Decision 2002/657/EC. The procedure was validated by spiking feed samples at three different levels (300, 1000, and 5000 µg/kg). Average recoveries for tetracyclines were in the range 79.70–98.8%, with RSD for repeatability and reproducibility in the ranges of 5.0–9.5% and 6.5–11.0%, respectively. The method was successfully validated and proved to be efficient, precise, and useful for quantification of tetracyclines in animal feed. The validated method was successfully applied to 65 suspect feed samples collected from different regions of Poland in 2015–16 and obtained from farms and feed manufactures. Of these 65 purportedly non-medicated feeds, eight (12.3%) were positive for the presence of doxycycline or chlortetracycline.     

An accurate quantitative method for the analysis of terpenes in milk fat by headspace solid-phase microextraction coupled to gas chromatography–mass spectrometry

HS-SPME analysis of terpenes does usually have inherent quantification problems when working with complex samples, especially due to the matrix effect of the substrate or the calibration solution. Three different terpene carrier matrices were compared: methanol, synthetic oil and milk fat obtained by centrifugation from milk cream. Considerable differences in calibration sensitivity parameters were observed depending on the matrix used and on the type of terpene standard analysed. For milk sample quantification purposes internal standard method was preferred using milk fat as calibration matrix. Linearity range, repeatability, recovery and limits of detection and quantification were determined. Validation parameters were different depending on the concentration and molecular structure of each terpene analysed, particularly between mono- and sesquiterpenes. The method was useful to determine in an accurate manner the terpene content in milk samples from pasture fed animals, and it will help to establish objective terpene levels to differentiate milks from specific production systems.     

Development and validation of rapid multiresidue and multi-class analysis for antibiotics and anthelmintics in feed by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry

A new multi-residue method for the analysis of veterinary drugs, namely amoxicillin, chlortetracycline, colistins A and B, doxycycline, fenbendazole, flubendazole, ivermectin, lincomycin, oxytetracycline, sulfadiazine, tiamulin, tilmicosin and trimethoprim, was developed and validated for feed. After acidic extraction, the samples were centrifuged, purified by SPE and analysed by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry. Quantitative validation was done in accordance with the guidelines laid down in European Commission Decision 2002/657/CE. Matrix-matched calibration with internal standards was used to reduce matrix effects. The target level was set at the authorised carryover level (1%) and validation levels were set at 0.5%, 1% and 1.5%. Method performances were evaluated by the following parameters: linearity (0.986 < R² < 0.999), precision (repeatability < 12.4% and reproducibility < 14.0%), accuracy (89% < recovery < 107%), sensitivity, decision limit (CCα), detection capability (CCβ), selectivity and expanded measurement uncertainty (k = 2).This method has been used successfully for three years for routine monitoring of antibiotic residues in feeds during which period 20% of samples were found to exceed the 1% authorised carryover limit and were deemed non-compliant.     

Multiresidue method for simultaneous analysis of aflatoxin M1, avermectins,organophosphate pesticides and milbemycin in milk by ultra-performance liquid chromatography coupled to tandem mass spectrometry

A method developed for the simultaneous analysis of aflatoxin M₁, abamectin, doramectin, eprinomectin, ivermectin, moxidectin, acephate, azinphos-ethyl, azinphos-methyl, diazinon, methamidophos, methidathion, mevinphos, pirimiphos-ethyl and pirimiphos-methyl in whole raw milk, based on the QuEChERS method for extraction and clean-up, with detection and quantification by ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) is described. The method was validated according to parameters of the Analytical Quality Assurance Manual from the Brazilian Ministry of Agriculture and Commission Decision 2002/657/EC, and proved suitable for analysis of these analytes within the proposed working range, with recovery values between 77% and 110%, a standard deviation lower than 20%, limits of detection between 0.05 and 0.99 µg l^?1, and limits of quantification between 0.15 and 1.98 µg l^?1. Samples from animals treated with abamectin, doramectin, ivermectin and diazinon were analysed by the validated method. Residues of aflatoxin M₁ were also found in field samples at levels below the established maximum residue limit.