Determination of methyl bromide residues in stored foods using automated headspace gas chromatography

An automated gas chromatographic headspace method capable of detecting methyl bromide (MB) down to 0.01 mg kg^?1 has been developed and evaluated. The method is suitable for analysing cereals, nuts, seeds and dried fruit. Commodities are extracted with solvent and MB present is derivatised to methyl iodide (MI) which is determined by automated headspace gas chromatography. Results from the method described are compared with those using an established solvent extraction method and show good quantitative agreement. The analytical conditions recommended are likely to be suitable for examination of other commodities for MB residues.     

顶空气相色谱法测定小麦中熏蒸剂氰及其代谢物氰化氢的残留量

采用溶剂顶空毛细管气相色谱-氮磷检测器(NPD)建立了熏蒸剂氰(C2N2)及其代谢物氰化氢(HCN)在小麦中残留的分析方法。在气相与液相体积比(β)为4时,采用GS-Q大孔毛细管色谱柱和进样60 μL顶空气体,可提高C2N2和HCN的分离效果和灵敏度。以质量分数为50%的磷酸作溶剂,在25 ℃下平衡4 h,C2N2和HCN在液相与气相间的分配系数(k)分别为0.44和48.82。平衡温度和基质对C2N2和HCN挥发的影响存在差异,而盐化效应的影响较小。用50% 的磷酸提取熏蒸过的小麦72 h,释放至顶空的C2N2和HCN的量最大,用添加标准品的小麦作标准可评价熏蒸小麦中C2N2和HCN的残留量。C2N2和HCN标准曲线的线性范围分别在质量浓度为1.0~500 μg/L和1.2~500 μg/L之间,相关系数(R2)分别为0.999 7和0.999 8,相对标准偏差分别为4.6%和7.4%,检出限(LOD)分别为0.032和0.145 mg/kg,定量限(LOQ)分别为0.107和0.483 mg/kg。方法操作简单、灵敏度高、干扰少,适用于小麦中C2N2和HCN残留量的检测。     

Extraction of allyl isothiocyanate from horseradish (Armoracia rusticana) and its fumigant insecticidal activity on four stored‐product pests of paddy

BACKGROUND: Isothiocyanates (ITCs) extracted from Armoracia rusticana Gaertn., May & Scherb. have been shown previously to have insecticidal activity. Allyl isothiocyanate (AITC), a major component of ITCs with high volatility, was therefore extracted using different methods and tested as a fumigant against four major pest species of stored products, maize weevil Sitophilus zeamais (Motsch.), lesser grain borer Rhizopertha dominica (F.), Tribolium ferrugineum (F.) and book louse Liposcelis entomophila (Enderlein). RESULTS: Whereas there was no significant difference between hydrodistillation and supercritical carbon dioxide fluid extraction in extraction rate for AITC from A. rusticana, both methods resulted in higher extraction efficiency than water extraction. AITC fumigation showed strong toxicity to the four species of stored‐product pests. Adult mortality of 100% of all four pest species, recorded after 72 h exposure to AITC fumes at an atmospheric concentration of 3 µg mL^?1, showed no significant difference from that of insects exposed to phosphine at 5 µg mL^?1, the recommended dose for phosphine. CONCLUSIONS: The results suggest good insecticidal efficacy of AITC against the four stored‐product pests, with non‐gaseous residuals on stored products. AITC obtained from A. rusticana may be an alternative to phosphine and methyl bromide against the four pest species. Copyright © 2009 Society of Chemical Industry     

Ethyl formate,formic acid and ethanol in air,wheat, barley and sultanas: analysis of natural levels and fumigant residues

Ethyl formate and ethanol in air, eg in fumigant studies, were readily detected by gas chromatography (GC) (flame ionisation). Residues in wheat, barley and sultanas were analysed by GC, after extraction in polar solvents (eg methanol, aqueous propanol). Both natural levels and levels resulting from fumigation with ethyl formate were measured. Formic acid was extracted from commodities with polar solvents (eg methanol, water) and analysed by GC after esterification. Solvent extracts of commodities were concentrated after addition of disodium hydrogen orthophosphate, and an aliquot added to acidified alcohols (several combinations of acids and alcohols were tested) in a sealed container. Formic acid esters were determined by GC, from headspace sampling over the esterification solvent. Esterification was faster with strong acids than with boric acid. However, esterification with boric acid/butanol gave the least interference of all tested methods. Product identity was confirmed by GC/mass spectrometry. High natural levels of formic acid, and low natural levels of ethyl formate and ethanol, presented problems in identifying residues arising from fumigation. These natural levels are relevant to food regulations for ethyl formate, especially those based on ‘total formic acid, free and combined’. Polar columns (eg FFAP, carbowax) were useful for measurement of formic acid esters, which eluted before the alcohols used for esterification or extraction, whereas elution followed the molecular mass on non-polar columns, such as GS-Q or DB-624. © 1999 Society of Chemical Industry     

HPLC determination of fenoxaprop and fenoxaprop-ethyl in different soils

This paper describes a method for the determination of fenoxaprop ethyl and fenoxaprop residues in four soil types using two extraction procedures: extraction with 0.1 M hydrochloric acid/methanol, partitioning with dichloromethane and extraction with ethyl acetate. The extracts were purified on florisil or alumina cartridge. The analyses were performed by reverse phase HPLC with UV detection at 280 nm. The best results in terms of recovery, clean-up efficiency and independence of soil characteristics were obtained with the combination ethyl acetate extraction alumina clean-up. Under these conditions, the recoveries were higher than 70 % and the detection limit was 0.02 mg kg^?1 soil.     

气相色谱-串联质谱法快速检测当归中102种农药残留

建立了当归中102种农药残留的快速检测方法。样品采用优化的QuEChERS前处理方法，利用气相色谱-串联质谱 (GC-MS/MS) 检测，动态多反应监测 (dMRM) 模式，基质匹配外标法定量。结果表明:在样品前处理过程中，经对提取溶剂、提取体系、净化体系的组成和用量进行筛选优化后，样品采用乙腈、1.0 g氯化钠、4.0 g无水硫酸镁、1.0 g柠檬酸钠和0.5 g柠檬酸二钠盐提取，无水硫酸镁800 mg、PSA 150 mg、C₁₈ 150 mg净化，通过基质匹配外标法校正，当归中基质效应对目标化合物的定性、定量影响明显减弱。在0.02~0.64 mg/kg范围内，102种农药的质量浓度与对应的峰面积间呈良好的线性关系，R2均大于0.99，检出限为0.002 5~0.025 mg/kg，定量限为0.005~0.05 mg/kg；在0.04、0.08和0.32 mg/kg 3个添加水平下，102种农药的平均回收率为52 %~128%，RSD为1.0%~10 %。该方法快速简便、耗时短，具有良好的灵敏度、正确度和精密度，为提高当归中农药安全水平，降低健康风险提供了一种快速、高效、可靠的分析手段。     

Ethyl formate plus methyl isothiocyanate--a potential liquid fumigant for stored grains

BACKGROUND: Methyl bromide is being phased out for use on stored commodities, as it is listed as an ozone‐depleting substance, and phosphine is the fumigant widely used on grains. However, phosphine resistance occurs worldwide, and phosphine fumigation requires a long exposure period and temperatures of > 15 °C. There is an urgent requirement for the development of a fumigant that kills insects quickly and for phosphine resistance management. This paper reports on a new fumigant formulation of 95% ethyl formate plus 5% methyl isothiocyanate as an alternative fumigant for stored grains. RESULTS: The formulation is stable for at least 4 months of storage at 45 °C. A laboratory bioassay with the formulation showed that it controlled all stages of Sitophilus oryzae (L.), Sitophilus granarius (L.), Tribolium castaneum (Herbst), Rhyzopertha dominica (F.), Trogoderma variabile Ballion and Callosobruchus maculatus (Fabricius) in infested wheat, barley, oats and peas at 80 mg L^?1 for 5 days, and in canola at both 40 mg L^?1 for 5 days and 80 mg L^?1 for 2 days at 25 ± 2 °C. After an 8–14 day holding period, residues of ethyl formate and methyl isothiocyanate in wheat, barley, peas and canola were below the experimental permit levels of 1.0 and 0.1 mg kg^?1. However, fumigated oats needed an 18 day holding period. CONCLUSIONS: The findings suggest that the ethyl formate plus methyl isothiocyanate formulation has potential as a fumigant for the control of stored‐grain insect pests in various commodities. Copyright © 2011 Society of Chemical Industry     

Comparison of extraction procedures for detection of Xanthomonas axonopodis pv. phaseoli in common bean seed

Xanthomonas axonopodis pv. phaseoli (Xap) is an important seedborne pathogen of Phaseolus vulgaris. Accurate seed health testing methods are critical to protect seed quality and meet phytosanitary requirements. Currently employed selective media‐based methods include several variations in extraction procedures. In order to optimize pathogen extraction from seeds, the influence of different extraction steps on the sensitivity of Xap detection was assessed. Seeds were inoculated by vacuum infiltration with Xap to achieve inoculum levels from 10¹ to 10⁵ CFU per seed; one contaminated seed was mixed into 1000‐seed subsamples of uncontaminated P. vulgaris seeds. Thirty subsamples of 1000 seeds were tested using each different extraction procedure. These included soaking whole seeds in sterilized saline phosphate buffer, either overnight at 4°C or for 3 h at room temperature, with or without vacuum extraction, and either with or without concentrating the seed extract by centrifuging. Seed extract dilutions were cultured on semiselective agar media MT and XCP1. The percentages of positive subsamples were compared to measure the effects of each extraction step on detection sensitivity. Vacuum extraction and centrifugation of seed extracts increased sensitivity; the highest sensitivity was obtained with the 3 h vacuum extraction followed by centrifugation. These results were confirmed with naturally infested seeds; Xap was detected in 48 of 70 samples using the 3 h vacuum extraction with centrifugation, whereas only 35 of 70 field samples tested positive using overnight soaking, a significant difference. The results suggest that these steps would be valuable modifications to the current method approved by the International Seed Testing Association (ISTA).     

Evaluation of methyl iodide as a soil fumigant in container and small field plot studies

Methyl iodide was evaluated as a soil fumigant as a potential replacement for the widely used soil fumigant methyl bromide. In container trials, methyl iodide was significantly more effective than methyl bromide against the plant parasitic nematodes Meloidogyne incognita, Heterodera schachtii and Tylenchulus semipenetrans and the plant pathogenic fungus Rhizoctonia solani. In small field plots, soil populations of root-knot nematodes were no longer detected after methyl iodide fumigation at an application rate of 112 kg ha^-1. However, after growing a susceptible lima bean host for two months, substantial root-knot galling occurred, while Rhizobium nodulation was absent. At 168 kg ha^-1 of methyl iodide, root-knot galling was reduced to less than 1%, and no Pythium propagules were recovered on selective detection media. These efficacy data support the conclusion that methyl iodide is a likely candidate for replacing methyl bromide as a soil fumigant. © 1998 SCI.     

毛细管电泳定量测定稻田土壤中痕量磺酰脲类除草剂残留

研究了提取浓缩和毛细管电泳相结合测定稻田土壤中低剂量多个磺酰脲类除草剂混合残留的分析方法。结果表明: 毛细管电泳可有效分离和定量测定稻田土壤中甲磺隆、氯磺隆和氯嘧磺隆混合残留。通过定量补偿甲磺隆、氯磺隆和氯嘧磺隆可使残留检测限达到ng/kg级,回收率>87%。表明毛细管电泳具有定量测定土壤中ng/kg级磺酰脲类除草剂残留的能力。     

几种有机氯杀虫剂防治小麦吸浆虫成虫研究

施用药剂杀灭小(?)吸浆虫成虫,是防治吸浆虫重要方法之一。以几种有机氯杀虫剂进行室内、田间杀虫作用和药效等研究,证明γ 666、艾氏剂、狄氏剂和DDT 均具有强大的触杀作用,其中以γ 666毒效最怏,DDT 最慢。γ 666及艾氏剂还具有相当强的熏蒸杀虫作用。田间试验结果也说明γ 666粉剂浓度虽低至0.1%,仍能杀虫95%以上。0.25% γ 666粉剂效果与0.5%的相若,试验也证明,不同浓度的γ 666粉剂兑土稀释为0.25%药粉,稀释土的种类,对杀虫效果均无影响,并在全国不少地区推广应用均证明效果显著,解决了药剂供应问题,扩大了防治面积。田间残效试验证明,不同浓度的666粉剂,在羽化盛期前2天施用,均能毒杀羽化盛期的成虫;但如在前5天施用,除1%粉剂效果较好外,0.25%及0.5%粉剂浓度的防治效果均不理想。     

The significance of response time in the detection and measurement of fumigant resistance in insects with special reference to phosphine

The significance of the time of assessment in measurements of fumigant toxicity was examined, using the response of adults of Tribolium castaneum to phosphine. When assessments were made before end-point was reached, large differences were obtained in mortality levels and in parameters of probit lines fitted to the data. These differences reflected the concentration- and dosage-dependent nature of the speed of action, observed previously with this fumigant. The implications of this in the measurement of resistance were examined. In this instance, comparisons at the same concentration were not greatly affected if seven days or longer had elapsed after exposure. However, it was clear that if different concentrations were used for the susceptible strain and the resistant strain, comparisons made before the end-point for acute mortality response was reached could be grossly misleading. This is further discussed in the context of some recent reports of phosphine resistance. The results of this study are of significance in assessing the effect of any poison, drug or other stimulus applied to a group of organisms when the time to respond is likely to vary among individuals.     

A multiresidue analytical method for determining organochlorine,organophosphorus, dinitrophenyl and carbamate pesticides in apples

A multiresidue analytical method for the simultaneous extraction of organochlorine, organophosphorus, dinitrophenyl and carbamate pesticides from apples is presented. Extraction is performed with a mixture of toluene and hexane. After clean-up on a Florisil column, and in some cases conversion to derivatives, quantitative determination is performed by electron-capture gas chromatography. Qualitative verification is performed by thin-layer chromatography or gas chromatography-mass spectrometry.     

Methyl isothiocyanate volatilization from fields treated with metam‐sodium

Emission of methyl isothiocyanate (MITC) from fields treated with metam‐sodium (sodium N‐methyldithiocarbamate) is a potential environmental and human safety hazard. Concentrations of MITC at three heights above four arable fields were measured following the application of metam‐sodium at a rate of 480 litre ha⁻¹ (166 kg AI ha⁻¹). Two of these fields were treated by injection into a center‐pivot irrigation system (chemigation), while in the other two fields the fumigant was applied through injection directly into the soil. Generally, higher MITC air concentrations were observed above chemigated than above injected fields. Maximum MITC air concentrations were 11.2 and 7.4 µg m⁻³ recorded 10 cm above ground 6–8 h following application and the minimum concentrations were 0.7 and 0.2 µg m⁻³ observed at 200 cm 30–35 h after application above chemigated and injected fields, respectively. The estimated MITC respiratory exposure a worker might encounter during the re‐entry period ranged between 1.37 and 0.03 mg day⁻¹ in chemigated fields and between 0.35 and 0.02 mg day⁻¹ in the injected fields. These results suggest that application of the fumigant through injection reduced MITC volatilization losses in comparison with the chemigation method, thus posing a relatively lower risk of exposure to MITC emissions. © 2000 Society of Chemical Industry     

Efficacy of vaporised ethyl formate/carbon dioxide formulation against stored‐grain insects: effect of fumigant concentration,exposure time and two grain temperatures

BACKGROUND: The ethyl formate/carbon dioxide (CO₂) formulation Vapormate? is a rapid‐acting fumigant being developed for the control of stored‐grain insects. The effects have been investigated of concentration, exposure times of 1, 3, 24 and 72 h and two grain temperatures, 15 and 25 °C, on its efficacy against mixed‐stage cultures of Sitophilus oryzae (L.) Tribolium castaneum (Herbst) and strongly phosphine‐resistant Rhyzopertha dominica (F.) strain QRD569. RESULTS: High mortalities (≥92%) of mixed‐stage cultures of all three species were obtained when grain was fumigated with the formulation (193 g m^?3 ethyl formate) for 1 h. Complete control of R. dominica QRD569 and T. castaneum was achieved with 63 and 76 g m^?3 ethyl formate respectively, with exposure for 24 h, whereas mean mortality of S. oryzae was 86% under the same conditions. Mortalities of S. oryzae juvenile stages were significantly lower than adults under the conditions tested, which was due to pronounced tolerance of mid‐stage pupae to the fumigant. Reducing grain temperature from 25 to 15 °C had no effect on insect mortality. CONCLUSION: Ethyl formate/CO₂ formulation is highly effective against stored‐grain insects over a range of concentrations and exposure times. Efficacious fumigations were conducted in as little as 1 h, and a strongly phosphine‐resistant R. dominica strain was readily controlled with the fumigant. Copyright © 2009 CSIRO, Australia. Published by John Wiley & Sons, Ltd     

改进的QuEChERS-高效液相色谱-串联质谱法同时测定蔬菜水果中百菌清及其代谢物残留

建立了同时检测蔬菜水果中百菌清及其代谢物4-羟基百菌清的高效液相色谱-串联质谱分析方法.样品经酸化乙腈提取后,采用配备大气压化学电离源的三重四极杆串联质谱仪测定.结果表明:百菌清及其代谢物4-羟基百菌清在0.005～0.2 mg/L范围内峰面积与质量浓度的线性关系良好,决定系数(R2)大于0.99;方法定量限为0.01...     

Fumigant bioactivity of five Citrus essential oils against Tribolium confusum

During the past decades, the huge use of pesticides caused several environmental problems, so research investigations moved to find a series of compounds with selective toxicity, of a biodegradable and environment-friendly nature, maintaining a positive action in crop and stored products protection. In this perspective, interesting results in the control of pests and fungal pathogens were obtained using essential oils, which are compounds produced by many species of plants as secondary metabolites. The purpose of this research was to evaluate the fumigant activity of five Citrus essential oils against the confused flour beetle Tribolium confusum Du Val, planning a possible employment in the mill industry. The fumigant effectiveness was evaluated 24, 48, 72 hours and 7 days after the start of exposure and each essential oil was analyzed by means of GC and GC/MS. Further evaluations about the toxicity of these compounds were made by partially filling the glass vials with food matrix, in order to assess the possible interference of this matter on the active compounds. The data obtained indicated that, at a low level of fumigant concentration, essential oils can effectively control stored product pests; in the presence of debris, like flour, the efficacy decreased. Plant extracts caused also increased mortality levels after the end of fumigation. The results obtained from this experimentation confirm the efficacy of essential oils in pest control and, in particular, against stored product pests.     

顶空气相色谱法测定土壤中氯化苦残留

建立了一种快速测定土壤中氯化苦残留的方法。用石油醚室温下浸提土壤30 min后漩涡振荡,离心后取上清液直接采用顶空气相色谱法测定。结果显示,在质量浓度0.005 ~4 mg/L范围内,线性相关系数R2=0.999。氯化苦的添加水平在0.012 5 ~1.25 mg/kg范围内,5次重复的平均添加回收率在82.7% ~109.9%之间,相对标准偏差(RSD)在8.4% ~9.5%之间,检测限为0.008 8 mg/kg,定量限为0.029 mg/kg 。该方法可以满足土壤中氯化苦残留测定的要求。     

Contact and fumigant toxicity of plant essential oils and efficacy of spray formulations containing the oils against B‐ and Q‐biotypes of Bemisia tabaci

BACKGROUND: The contact + fumigant toxicity of 92 plant essential oils and control efficacy of 18 experimental spray formulations containing nine selected essential oils (0.5 and 0.1% sprays) and six commercial insecticides to females from B‐ and Q‐biotypes of Bemisia tabaci were evaluated using vapour‐phase mortality and spray bioassays. RESULTS: Garlic and oregano (LC₅₀, 0.15 mL cm^?3) were the most toxic oils against B‐ and Q‐biotype females. Strong fumigant toxicity to both biotype females was also obtained from catnip, cinnamon bark, clove bud, clove leaf, davana, savory and vetiver Haiti oils (LC₅₀, 0.17–0.48 mL cm^?3). The 0.5% sprays of these oils (except for thyme red oil) resulted in 90–100% mortality against both biotype females. Only garlic applied as 0.1% spray provided 100% mortality. Spinosad 100 g L^?1 suspension concentrate (SC) treatment resulted in 92 and 95% mortality against both biotype females, whereas acetamiprid 80 g L^?1 wettable powder (WP), imidacloprid 80 g L^?1 SC, thiamethoxam 100 g L^?1 water‐dispersible granule (WDG) and pyridaben 200 g L^?1 WP treatments resulted in 89–100% mortality against B‐biotype females only. CONCLUSION: In the light of global efforts to reduce the level of highly toxic synthetic insecticides in the agricultural environment, the essential oils described, particularly garlic, cinnamon bark and vetiver Haiti, merit further study as potential insecticides for the control of B. tabaci populations as fumigants with contact action. Copyright © 2011 Society of Chemical Industry     

Application of Solid Phase Micro‐Extraction (SPME) to the analysis of pesticide residues in vegetables

Solid Phase Micro‐Extraction (SPME) is a new analytical technique, based on capturing the analytes by adsorption onto an organic phase coating a glass fibre, and subsequent direct desorption into the injector of a gas chromatograph. This technique has been successfully applied in the analysis of organic contaminants in water, giving linear responses and, in some cases, high sensitivities. The present paper reports data about the application of SPME to the analysis of pesticide residues in a vegetable matrix, testing over nearly one hundred active compounds, with two types of adsorbent phase (polydimethylsiloxane and Carbowax/divinylbenzene). A vegetable matrix spiked with pesticides was analyzed by SPME and by a traditional multi‐residue method; recoveries were determined and compared for the two cases. The behaviour of the analytical response by SPME was studied in the range 0.01–1 mg kg⁻¹ by adding increasing amounts of given pesticide mixtures to the vegetable matrix. The procedure was further tested by analyzing real samples, and gave some difficulties in recovering the whole amount of some of the residues present (in comparison with the traditional method). The SPME method was then improved by pre‐extracting with acetone and sonicating before the extraction/adsorption step. The results obtained were satisfactory (some certified matrices were also tested) with good accordance between the two methods. Nevertheless some active compounds showed very low responses or remained undetectable by SPME in our experimental conditions. © 2000 Society of Chemical Industry