A simplified X-ray fluorescence (XRF) procedure for the determination of sulphur in graminaceous materials

An automated, rapid and much simplified XRF procedure for assessing total sulphur in graminaceous plant materials is described. Sample preparation has been refined and microprocessor control incorporated to provide considerable savings in analytical time. The procedure has been tested using samples from two grass-silage cuts, taken from an ADAS (Agricultural Development and Advisory Service) trial studying responses, under intensive grassland management, to sulphur and nitrogen applications. Good correlation between XRF and wet chemical analysis was achieved, and sample turnround was markedly increased. The method produced accurate results for both cuts with high precision and reproducibility where careful attention was paid to sample homogeneity and disc preparation. The potential for wider application of XRF techniques to elemental analysis of agricultural materials is discussed.     

Determination of methoxyphenols in ambient atmospheric particulate matter: tracers for wood combustion

Combustion of wood and other biomass fuels produces source-specific organic compounds arising from pyrolysis of lignin, including substantial amounts of 4-substituted methoxylated phenolic compounds (methoxyphenols). These compounds have been used as atmospheric markers to determine the contribution of wood smoke to ambient atmospheric fine particulate matter (PM). However, reliable quantification of methoxyphenols represents an analytical challenge because these compounds are polar, semi-volatile, and somewhat reactive. We reportherein an improved gas chromatographic-mass spectrometric (GC/MS) method for the sensitive and reliable determination of methoxyphenols in low-volume ambient PM samples. Deuterated standard compounds are added to the environmental samples prior to extraction to determine analyte recoveries in each sample. Analytical figures of merit for the assay, as applied to ambient PM2.5 and PM10 samples are as follows: recovery = 63-100%; precision = 2-6%; analytical limit of detection (S/N 2) = 0.002 microg/mL; limit of quantitation = 0.07-0.45 ng/m3 (assuming a 14 m3 sample). The improved method was applied to ambient PM samples collected between 1999 and 2000 in Seattle, WA. Particle-bound methoxyphenol concentrations in the range <0.1 to 22 ng/m3 were observed and the methoxyphenols were present almost exclusively in the fine (PM2.5) size fraction. We also demonstrated that XRF analysis of samples of atmospheric PM collected on Teflon filters significantly reduced the levels of methoxyphenols measured in the PM samples in subsequent assay of the same filters. Therefore, XRF analysis of filters, commonly undertaken to obtain trace element concentrations for use in source apportionment analyses, would preclude the subsequent analysis of those filters for methoxyphenols and other similarly semivolatile or reactive organic chemicals.     

Methods for determining pesticides and polychlorinated biphenyls in food samples--problems and challenges

Determination of residual amounts of pesticides and polychlorinated biphenyls (PCBs) in food samples requires the use of specific techniques regarding sample preparation as well as instrumental analysis which should be characterized by a very low detection limit. A problem associated with the use of pesticides and PCBs is the need for controlling their residues in the environment, particularly in food, as these chemicals show a propensity to accumulate. The analysis of food samples for the presence of pesticides and PCBs brings on many difficulties because of the specificity of sample preparation consisting of multistep purification procedures of samples that contain trace amounts of an analyte. Concentration determinations of pollutants that easily dissolve in complex matrices, particularly in the presence of a large apportionment of interfering substances, pose a big challenge. Therefore, the basic step in food analysis for the presence of pesticides and PCBs is sample preparation which mainly consists of analyte enrichment and the removal of interfering substances. But all steps of the analytical procedure that include sample collection and preparation, extraction of analytes from matrix, extract purification, and final determination, are very significant; their precision and correct application have a decisive effect on the final result.     

Sample comminution for mycotoxin analysis: Dry milling or slurry mixing?

A comparison was made between dry milling and slurry mixing as a comminuting step preceding mycotoxin analysis. Sample schemes of up to 30 kg are mandated by European Commission legislation. Cocoa, green coffee, almonds and pistachio samples of 10 kg were milled by a Romer analytical sampling mill and all three subsamples were analysed for aflatoxin B₁ or ochratoxin A content. The homogenization process was evaluated in terms of the analytical results, coefficients of variation for different mills and particle size distributions. Coefficients of variation for the comminuting step were higher for dry milling than for slurry mixing. This difference was explained based on measured particle size distributions for both milling types. Measurements also showed slight differences in mycotoxin content of samples based on milling procedures. This might lead to lots being wrongly accepted or rejected based on an erroneous subsample result. It was concluded that sample comminution was best performed by slurry mixing, which produced smaller particles and, consequently, homogeneous samples with lowest coefficients of variation. Additional data are given on analytical results in 10-kg subsamples that originate from the aggregate 30-kg sample as described in Commission Directive 98/53/EC.     

Analytical chromatography for recovery of small amounts of staphylococcal enterotoxins from food

Sample preparation is an important element in the detection of toxins in food samples. In this work, a simple analytical sample preparation method for recovery of small amount of staphylococcal enterotoxin B (SEB) and staphylococcal enterotoxin A (SEA) in food samples was developed. Cation exchanger carboxymethylcellulose (CM) was used for small-scale batch chromatography isolation of SEB from infant formula and from mushrooms spiked with SEB. The resulting materials were analyzed for SEB by Western immunoblotting. Nearly all of the extraneous substances in the sample were removed by this procedure with no significant loss of the toxin. Using this method, even small amounts of SE (0.75 ng/g) can be recovered and immunologically analyzed by Western blotting or by ELISA with a very low background. Because this method is effective, rapid, simple and inexpensive, it has the potential to be a general method for the preparation of samples used for analysis of SEs.     

大米表面颜色与碾削程度的相关性分析

以两优6393、蓉优3号、益禾8号3种稻谷为试验材料,研究大米表面颜色与糙出白率的关系。垄谷后,对每种糙米进行15、30、45、60和90 s的碾削,得到不同碾削程度的大米样本,测定出每个样本的糙出白率、明度(L)、红绿色调(a)和黄蓝色调(b)值,分析大米颜色特征随碾削时间的变化关系,通过回归分析的方法,分别建立大米表面明度(L)值、红绿色调(a)值和黄蓝色调(b)值与糙出白率关系的模型。结果显示,随着碾削时间的延长,大米的糙出白率显著降低,大米的表面明度明显增大,而红绿色调和黄蓝色调则逐渐减小;随着糙出白率的减少,大米表面的明度线性增大,红绿色调值和黄蓝色调值则线性降低;大米表面的L、a和b值与糙出白率的关系可以描述为简单的线性函数式。     

Determination of antibiotics in meat samples using analytical methodologies: A review

Antibiotics are widely used to prevent or treat some diseases in human and veterinary medicine and also as animal growth promoters. The presence of these compounds in foods derived from food-producing animals can be a risk for human health. Consequently, regulatory agencies have set maximum residue limits for antibiotics in food samples. Therefore, the development of novel methodologies for its determination in food samples is required. Specifically, the analysis and quantification of these substances in meat tissues is a challenge for the analytical chemistry research community. This is due to the complexity of the matrix and the low detection limits required by the regulatory agencies. In this sense, a comprehensive review on the development of new sample preparation treatments involving extraction, cleanup, and enrichment steps of antibiotics in meat samples in combination with sensitive and sophisticated determination techniques that have been carry out in the last years is necessary. Therefore, the aim of this work is to summarize the published methodologies for the determination of antibiotics from 2016 until the beginning of the second semester of 2020. The first part of this review includes an introduction about antibiotic families, followed by sample preparation and determination techniques applied to the different families. Finally, a detailed discussion of the current trends and the future possible perspectives in this field are also included.     

利用气质联用仪分析检测白酒中的甜蜜素

采用气质联用仪对白酒进行了检测,并发现经过样品前处理后反应生成了两种物质,并对这两种物质进行了方法学考证,证明此两种物质存在此消彼长的关系,为选择定量方法提供了依据。证明该方法标准曲线的线性好,方法准确度和精确度高,可应用于白酒中甜蜜素的检测。     

The effect of the number of sample units tested on the precision of microbial colony counts

Studies on the precision of chemical methods of analysis, and the associated ‘sampling uncertainty’, suggest that analysis of eight replicate sample units (the sample size) is required to ensure adequate analytical precision. The primary purpose of this work was to assess whether these findings are equally applicable in microbiological examination of foods. We examined the effect of sample size on the analytical precision of microbiological data by iteratively ‘re-sampling without replacement’ (SNR). Using both theoretical data sets and colony counts from foods we demonstrate that SNR provides an effective and efficient guide to (a) choosing the number of samples to be examined in order to optimise precision and (b) deciding whether logarithmic transformation of the raw data is appropriate. We also discuss theoretical aspects of the procedure and their impact on the results obtained.     

Test method for lead in metal utensils for food contact use

We compared test methods for measurement of lead in metal utensils using flame-atomic absorption spectroscopy (AAS), graphite furnace-AAS (GFAA), inductively coupled plasma atomic emission spectrometry (ICP) and X-ray fluorescence analysis (XRF). The procedure for preparation of the test solution was improved. A 100 mg of sample was dissolved in 2.5 mL of HCl and HNO(3) (3 : 1) mixture (in the case of titanium sample, dissolved in HCl). Stock solution was prepared by diluting to 50 mL with water. The test solution was prepared by diluting with 0.1 mol/L HNO(3). The recoveries of lead added to various kinds of metal reagent at the level of 0.1% were 90-118%. When standard materials which contained lead at the level of 0.0098-0.11% were measured, the measured values were in close agreement with the standard values. These procedures are applicable to aluminum, iron, stainless steel, copper, tin and titanium products. The AAS method, GFAA method and ICP method were suitable as the lead test methods. Moreover, the XRF method was useful as a screening method or a simple determination method. The ICP method was used to determine the lead contents in 22 kinds of commercial metal utensils, and 0.011-0.040% of lead were detected in 6 samples.     

Assessment of the solubility and bioaccessibility of barium and aluminum in soils affected by mine dust deposition

Barium is a heavy metal to which human and animal receptors may be exposed in various settings--for example, in mineral extraction industries where the mining and milling of ores occurs. Aluminum is also an element abundant in soil and dust to which human and animal receptors may be exposed in association with such industries. This study investigated the solubility and bioaccessibility of barium and aluminum in simulated gastric fluids using an in vitro test method previously validated for lead. Soil samples were collected from the vicinity of a mine and transport road that generated fugitive dust containing barium as barite (BaSO4). It was found that barium bioaccessibility in different tundra soil and fugitive dust source materials varied greatly, between 0.07 and 66.0%, depending on sample location, grain size, solid-to-fluid ratio used in the in vitro experiments, and the analytical method selected for determining total barium concentrations in the sample substrates. For X-ray fluorescence spectrometry (XRF) analytical methods and a solid-to-fluid ratio of 1:100, barium bioaccessibility from the barite-rich mine waste rock and gyro crusher ore dust source materials was very low (0.07-0.36%). By contrast, the bioaccessibility of barium in tundra soil samples affected by fugitive dust deposition ranged from 3.8 to 19.5%. The relative solubility of barium measured in the simulated gastric fluids of this study is consistent with time-dependent dissolution of barite in mine waste rock and ore dust, and the presence of more soluble chemical forms in tundra soil. Laboratory XRF analysis was the only analytical method used in this study that accurately characterized total barium concentrations for all sample substrates. Aluminum bioaccessibility was distinguished from barium bioaccessibility by its generally lower values and smaller dependence on grain size and solid-to-fluid ratios. The range of aluminum bioaccessibility values (0.31-4.0%) is consistent with the predominance of aluminum in relatively insoluble aluminosilicate minerals.     

利用大体积进样技术与质谱技术联合分析中国白酒中的微量香味成分

中国白酒中含有大量的香味成分和滋味成分,其中很多物质的含量极其稀少,这就给这些物质的分析工作造成了很大的困难。通常情况下为了分析这些极微量的物质,人们需要对白酒样品进行浓缩前处理,然后再利用气相色谱对浓缩样品进行分析。样品的浓缩过程是一项非常耗时耗力的工作,并且浓缩样品中含有大量的溶剂,这些物质在色谱分析中可能引起严重的分析误差,损坏色谱柱或者检测器。而大体积进样技术(LVI)则有效地避免了这些缺点。大体积进样技术可以在短时间内对分析样品进行浓缩,并且排除掉绝大多数的溶剂,从而大大提高了分析的灵敏度。将大体积进样技术和质谱分析技术联合应用,可以大大提高对白酒中极微量成分分析工作的准确性。     

Development and application of an LC-MS method to determine possible migration of mercaptobenzothiazole,benzothiazole and related vulcanization residues from rubber used in contact with food and drink

A method was developed for the analysis of food and drink for residues of specific vulcanization accelerators used to cross-link rubber. The method was applied to the analysis of 236 samples of selected retail foodstuffs that may have been in contact with rubber during their manufacture, transport and storage. The method of analysis involved extraction of the food using acidified solvent and analysis by liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (LC-APcI-MS). The detection limit depended on the sample type and was in the range 0.005-0.043 mg kg -1 for 2-mercaptobenzothiazole (MBT) and benzothiazole (BT). The average analytical recovery rate was 82% for MBT and 87% for BT. The analytical method was validated using a blind check sample exercise. For MBT and BT at seven different concentrations in the range 0.1-0.2 mg kg -1 , the laboratory found a mean of 91 and 90% of the expected concentrations, respectively. No trace of MBT or BT was found in any of the retail samples. It is also concluded that no sample contained significant 2-mercaptobenzothiazyl disulphide (MBTS) or N- cyclohexyl-2-benzothiazole sulphenamide (CBS). Both MBTS and CBS are important accelerators used to vulcanize rubber and they break down in foodstuffs to form MBT and BT. The absence of MBT and BT in the foodstuffs therefore also provides proof of the absence of MBTS and CBS.     

Mineral composition of apples X.—A rapid method for preparing samples of fruit for analysis

Samples of apples can be prepared for sub-sampling for analysis by blending them with an equal mass of water for 2 min at 17,000 rev/min. If seeds are present, or if the suspension of apple is to be fed into an automated analytical system an extra 2 min in a homogeniser fitted with a fine mesh is necessary. Analytical results are reproducible and in agreement, within the limits of variation due to the ashing and analytical methods and the number of apples chosen to make the sample, with those for samples prepared by freezing and grating. The results for magnesium indicate that about 5 % may be lost in the process of freezing and grating.     

Comparison of extraction methods for the determination of soluble and total oxalate in foods by HPLC-enzyme-reactor

Food oxalate analysis in foods is problematic due to the wide range of interfering substances. To prevent oxalate generation during sample preparation mild and rapid extraction methods were evaluated. Soluble oxalate was extracted with distilled water and total oxalate was extracted with 2 N hydrochloric acid. Filtrates were analysed using the HPLC enzyme reactor method. Evaluation yielded a high level of precision and recovery. Glyoxylic acid, d/l malic acid, isocitric acid, oxaloacetic acid, pyruvate, mesoxalic acid, ascorbic acid, d(+) glucose, d(−) fructose, chlorogenic acid, caffeic acid could be excluded as a source of oxalate generation during extraction with hot acids. The soluble and total oxalate content of about 150 food samples were investigated.     

Screening of plant toxins in food, feed and botanicals using full-scan high-resolution (Orbitrap) mass spectrometry

A generic method based on LC with full-scan high-resolution (Orbitrap) mass spectrometry (MS) was systematically investigated for the simultaneous detection of a wide range of plant toxins in a variety of food and feed matrices. For a selection of 150 substances, representing various chemical classes, the limit of detection was established using fixed LC-MS conditions. Ion suppression effects and selectivity were evaluated using generic extracts from representative and relevant matrices (food supplement, honey, silage, compound feed). The majority of the substances could be measured as positive ions after electrospray ionisation (ESI(+)). Using a mass resolving power of 100,000 a reliable high mass accuracy was obtained despite the high abundance of co-extractants in the sample extracts. This enabled the use of ±5?ppm mass extraction windows, which in turn resulted in a high degree of selectivity. On the other hand, except for honey, strong ion suppression effects were frequently observed which adversely affected the detection limits. Nevertheless, for the majority of the substances the detection limits were in the range 0.01-0.05?mg?kg(-1). Since non-selective sample preparation and non-targeted data acquisition were performed, the presence of plant toxins initially not targeted for during data review can be subsequently investigated, which is a very useful option because for many known toxins no analytical reference standards are yet available. The applicability of the method was demonstrated by analysis of a variety of real-life samples purchased on the market or from cases of intoxication. These included honey, herbal tea, food supplements, poppy seeds, traditional Chinese medicines, compound feed, silage and herb-based feed additives. Plant toxins that were detected included various pyrrolizidine alkaloids, grayanotoxins, opium alkaloids, strychnine, ricinine (a marker for ricin), aconitine, aristolochic acid and cardiac glycosides (e.g. digitoxin, digoxin).     

农产品中转基因检测抽样研究-第3部分: 从实验室样品到分析样品

目的针对农产品中转基因检测抽样过程,研究从实验室样品中采取和制备分析样品过程中各参数对最终结果准确性的影响。方法通过5%控制RSD,计算各粒度下的实验室样品、中间样品和分析样品的最小留样量;并通过计算对各相关参数进行考察。结果得到缩分设计及缩分引起的方差;合成制样方差、合成实验室样品总估计方差并对其进行了最终进行实验确认。结论综合考虑检验要求、分析过程和制样过程,得出从实验室样品到分析结果全过程(实验室内过程)中各个参数的优化方案。     

基质辅助激光解吸电离质谱成像技术及其在食品分析中的应用

基质辅助激光解吸电离质谱成像（matrix-assisted laser desorption ionization mass spectrometry imaging, MALDI-MSI）技术是一种新型的分析技术,具有无需提取、分离、纯化待测样品,操作简便、灵敏度高等优点, 广泛应用于生物、医学等领域。虽然其在食品领域还未建立完善的测定方法,但由于该技术可对食品中的化合物进 行空间成像分析,故其在食品领域中也将具有广阔的应用前景。本文在介绍MALDI-MSI技术成像原理的基础上, 综述了该技术的样品制备和在食品成分分析中的应用,并对其应用前景进行了展望,以期为MALDI-MSI技术在食 品研究中的应用和推广提供借鉴。     

Measuring the trace elemental composition of size-resolved airborne particles

A new method to measure the trace elemental composition of size-resolved airborne particles that uses acetone extraction followed by ICPMS analysis is compared to three other established methods: copper anode XRF, molybdenum anode XRF, and an ICPMS method that uses HF digestion. The method detection limit (MDL), accuracy, and precision of each method is studied through the analysis of ambient samples collected in California. The MDLs of the new acetone-ICPMS method are similar to MDLs for the established HF-ICPMS method. Both sets of ICPMS MDLs are 1-3 orders of magnitude lower than XRF MDLs for approximately 50 elements other than the light crustal elements such as silicon, sulfur, calcium, and zinc. The accuracy of the acetone-ICPMS method was verified by comparison to measurements made using ion chromatography and the HF-ICPMS method. The acetone-ICPMS analysis method was more precise than the conventional HF-ICPMS method for collocated measurements. Both ICPMS methods were more precise than XRF for most elements. The size distribution of 21 elements contained in ambient particles collected with cascade impactors could be measured with good precision using the new acetone-ICPMS analysis method: lithium, sulfur, potassium, titanium, vanadium, manganese, iron, gallium, germanium, arsenic, selenium, bromine, rubidium, strontium, cadmium, tin, antimony, barium, thallium, lead, and bismuth. It is likely that the size distribution of an additional 9 elements could also be measured when concentrations are sufficiently high: phosphorus, molybdenum, niobium, palladium, cesium, europium, holmium, platinum, and uranium. None of the conventional methods were able to measure the size distribution of these elements with acceptable precision under the conditions studied. The new acetone-ICPMS method should provide useful data for the study of the health effects of airborne particles.     

A review of methodology for the analysis of pyrethrin and pyrethroid residues in food of animal origin

Pyrethrin and pyrethroid pesticides are commonly used in crop protection and animal health, to control pests. As a result, they can potentially transfer into food if good agricultural practice is not followed or even due to accidental contamination. The analysis of these compounds has been widely reported in crops and the environment. However, the analysis of pyrethrin and pyrethroids has not been reported frequently in foods of animal origin, particularly animal tissues. The focus of this review is to report on pyrethrin and pyrethroid analysis including key aspects such as chemistry, choice of target matrix, sample preparation, chemical analysis, legislation and method validation. This review shows that most methodologies for the analysis of these compounds are based on gas chromatography with the trend in recent years to move towards GC-MS or GC-MS/MS based platforms. This review shows that these compounds can also be satisfactorily analysed by LC-MS/MS, which can be advantageous because of shorter chromatographic run times. A wide range of sample preparation procedures have been applied in analytical methods and more complex protocols are required for GC applications, whereas more crudely prepared extracts can be analysed by LC-MS/MS. This review demonstrates that pyrethrin and pyrethroid residues should be included as analytes in multi-class analytical methods for pesticides and veterinary drug residues in animal derived foods.