【讨论】-浓缩果汁中甲胺磷的气相色谱法检测

楼主，你好！这里有一份日本肯定列表中的方法，您可以参考一下；此外您也可以参考一下相关的标准方法。


乙酰甲胺磷和甲胺磷检测方法

1．分析目标化合物
农药等成分物质 分析目标化合物
乙酰甲胺磷 乙酰甲胺磷
甲胺磷 甲胺磷

2．仪器设备
带火焰光度检测器（磷干涉片、波长526 nm ）的气相色谱仪及气相色谱-质谱仪。
3．试剂
使用附录2所列试剂。
4．标准品
乙酰甲胺磷：含乙酰甲胺磷纯度99％以上，熔点为90℃～91℃
甲胺磷：含甲胺磷纯度99％以上，熔点为：44.5℃
5．试验溶液的制备
a 提取方法
① 谷类、豆类、水果、蔬菜、种子类、末茶和啤酒花
谷类、豆类及种子类：将样品粉碎，通过420μm标准网筛后，称取其20.0g，加入20mL水，放置2小时。
水果和蔬菜：准确称取约1kg样品，必要时定量加入适量的水，搅碎混合均匀后，称取相当于20.0g样品的量。
末茶：称取5.00g样品，加入20mL水，放置2小时。
啤酒花：样品粉碎后，称取其5.00g，加入20mL水，放置2小时。
加入150mL乙酸乙酯及150g无水硫酸钠，搅拌5分钟后，用涂布1cm厚硅藻土的滤纸，抽滤于磨口减压浓缩器中。再用40mL乙酸乙酯洗涤滤纸上的残留物，反复操作三次，合并洗液于上述减压浓缩器，40℃以下浓缩为约10mL。
② 末茶以外的茶
将9.00g样品浸泡于540mL 100℃水中，室温下放置5分钟，过滤，取60mL冷却后的滤液。加入150mL乙酸乙酯和200g无水硫酸钠，搅拌5分钟后，用涂布1cm厚硅藻土的滤纸抽滤于磨口减压浓缩器中。再用40mL乙酸乙酯洗涤滤纸上的残留物，反复操作三次，合并洗液于上述减压浓缩器，40℃以下浓缩为约10mL。
b 净化方法
在内径15mm、长300mm 的色谱管中注入10g悬浮于乙酸乙酯中的柱色谱用硅胶(粒径63～200μm)，其上再装入约5g无水硫酸钠，放出乙酸乙酯至柱上端留有少量乙酸乙酯。柱中注入a 提取方法所得溶液，注入100mL乙酸乙酯，弃去流出液。再注入100mL丙酮，收集流出液于减压浓缩器中，40℃以下除去大部分丙酮。残留物中加入丙酮溶解，准确至5mL（茶为2mL），此为试验溶液。
6．操作方法
a 定性试验
按下述操作条件进行试验，试验结果必须与标准品一致。
操作条件
柱： 内径0.53mm，长15m的石英毛细管，涂有1.0μm 厚的气相色谱用50%三氟丙基--甲基硅酮，老化。
柱温：100℃保持1分钟，此后以毎分钟升温10℃，达到180℃后保持5分钟。
进样器温度：220℃
检测器温度：250℃
气体流量：以氦气作载气。调整流速使乙酰甲胺磷约7分钟流出。调整空气和氢气的流量至适当条件。
b 定量试验
根据与a 定性试验相同的操作条件下所得试验结果，峰高法或峰面积法定量。
c 确证试验
按照与a 定性试验相同的操作条件下，用气相色谱--质谱仪测定。试验结果必须与标准品的一致。此外，必要时用峰高法或峰面积法进行定量。
7．定量限
乙酰甲胺磷：0.01 mg/kg（茶：0.1 mg/kg）
甲胺磷：0.01 mg/kg（啤酒花：0.05 mg/kg）

我现在很奇怪的就是，我做标样回收，就是不加样品，只加标样进行实验，回收还是上不来，什么原因？很是奇怪。

很简单，提取率低，你可以看我国405种农药多残留测定，也是用乙腈提取，就是没有甲胺磷。

好像是因为甲胺磷比较易溶于水吧，所以可以考虑在加乙腈提取时加适量的无水硫酸钠一起进行提取，这样好像回收率会比较好。

甲胺磷太易溶于水了，一般用有机溶剂液液萃取回收率很低的，考虑用合适的固相萃取小柱做。

同意楼上的看法，用极性固相萃取吸附剂萃取应该能好一些。如果是水样中的甲胺磷，也可以用液相色谱直接进样分析的。

这里有几篇文献的摘要都是用SPE做的甲胺磷：
Determination and load of organophosphorus and organochlorine pesticides at water from Jiulong River Estuary, China
Zhang Zulin, Hong Huasheng, Wang Xinhong, Lin Jianqing, Chen Weiqi and Xu Li
Marine Pollution Bulletin
Volume 45, Issues 1-12, September 2002, Pages 397-402
Abstract
Seventeen organic phosphorus pesticides (OPs) and 18 organic chlorine pesticides (OCs) at water from Jiulong River Estuary (JLRE) are determined by SPE–GC–(FPD and μECD). The contents of the total OPs (17) ranged from 134.8 to 354.6 ng/l (the mean is 227.2 ng/l). Total OCs concentrations varied from 115.4 to 414.7 ng/l in water (mean 237.7 ng/l). The levels of total hexachlorocyclohexane in water varied from 31.95 to 129.8 ng/l (mean 62.51 ng/l), and those of total DDTs were in the range 19.24–96.64 ng/l (mean 48.69 ng/l). The distribution and behavior characteristics of OPs indicate that five main OPs (methamidophos, dichlorvos, malathion, omethoate and dimethoate) occupied the most part of the total OPs, in addition, the sources of the OPs (mainly from current usage) are not stable. While the OCs mainly came from early application and were more stable. The OPs did not have obvious correlation with the dissoved organic carbon and suspended particulate matter at water from JLRE. It maybe due to the complicated hydrological kinetics in the estuary, and the higher water solubility and weak absorption (with organic matter) action of OPs. When compared with other areas, the OPs and OCs level in JLRE are some moderate.

Determination of acephate and its degradation product methamidophos in soil and water by solid-phase extraction (SPE) and GC-MS
Annick D. St-Amand; Louise Girard
International Journal of Environmental Analytical Chemistry, Volume 84, Issue 10 August 2004 , pages 739 - 748
Abstract
Acephate and its metabolite, methamidophos, are both highly polar organophosphorus pesticides (OPs) and are therefore highly soluble in water, which leads to difficulties when traditional methods of extraction, such as LLE (liquid-liquid extraction), are used. Solid-phase extraction (SPE) is a relatively new, highly versatile method, which has proven successful in many cases that were considered problematic in the past. In this study, several adsorbents (polymeric and silica based) and parameters are considered and modified to obtain maximum recovery. Maximum recoveries for acephate and methamidophos were found to be 90-95% and 85-90% respectively with Oasis HLB cartridges and methylene chloride as the elution solvent. In order to establish applicability and reliability, the matrix effect of several real water and solid (compost and soil) samples was evaluated. A 20-30% diminution of recovery is noted for some samples with a complex matrix containing a high amount of dissolved organic matter.

就是水中溶解度的问题，调整乙腈和水的比例在3：1左右，就可以解决了。

8楼的意见明天做实验一下，主要是样品太多，不想过柱子，每天要做几十个样品，
应该是甲胺磷的极性比较大，由于水的极性比乙腈的极性大，所以在水中的溶解度要大于乙腈中的，
我用乙腈提取样品时回收率好歹也在30%左右，而只作标样，也就等于做水中的甲胺磷时回收只有2%。
今天尝试了一下，先加水稀释，然后乙腈提取，再加无水硫酸镁吸水，看怎么样，明天把结果告诉大家。