Supplementary Material for: Screening for More than 1,000 Pesticides and Environmental Contaminants in Cannabis by GC/Q-TOF

A method has been developed to screen cannabis extracts for more than 1,000 pesticides and environmental pollutants using a gas chromatograph coupled to a high-resolution accurate mass quadrupole time-of-flight mass spectrometer (GC/Q-TOF). An extraction procedure was developed using acetonitrile with solid phase extraction cleanup. Before analysis, extracts were diluted 125:1 with solvent. Two data mining approaches were used together with a retention-time-locked Personal Compound Database and Library (PCDL) containing high-resolution accurate mass spectra for pesticides and other environmental pollutants. (1) A Find-by-Fragments (FbF) software tool extracts several characteristic exact mass ions within a small retention time window where the compound elutes. For each compound in the PCDL, the software evaluates the peak shape and retention time of each ion as well as the monoisotopic exact mass, ion ratios, and other factors to decide if the compound is present or not. (2) A separate approach used Unknowns Analysis (UA) software with a peak-finding algorithm called SureMass to deconvolute peaks in the chromatogram. The accurate mass spectra were searched against the PCDL using spectral matching and retention time as filters. A subset PCDL was generated containing only pesticides that are most likely to be found on foods in the US. With about 250 compounds in the smaller PCDL, there were fewer hits for non-pesticides, and data review was much faster. Organically grown cannabis was used for method development. Twenty-one confiscated cannabis samples were analyzed and ten were found to have no detectable pesticides. The remaining 11 samples had at least one pesticide and one sample had seven detectable residues. Quantitative analysis was run on the confiscated samples for a subset of the pesticides found by screening. Two cannabis samples had residues of carbaryl and malathion that were estimated to be about 10 times greater than the highest US Environmental Protection Agency tolerance set for food and about 4,000 times greater than the Canadian maximum residue limits for dried cannabis flower.

本研究开发了一种筛查方法，可利用气相色谱-高分辨精确质量四极杆飞行时间质谱仪（GC/Q-TOF）对大麻提取物中的1000余种农药与环境污染物进行检测。研发了以乙腈为萃取溶剂、辅以固相萃取净化的前处理流程；分析前，将提取物以125:1的体积比用溶剂进行稀释。本方法结合两种数据挖掘策略，以及一套保留时间锁定的个人化合物数据库与谱库（Personal Compound Database and Library，PCDL），该库收录了农药及其他环境污染物的高分辨精确质量质谱数据。
（1）碎片搜索（Find-by-Fragments，FbF）软件工具：可在化合物洗脱的小保留时间窗口内提取若干特征精确质量离子。针对该谱库中的每一种化合物，软件会逐一评估各离子的峰形、保留时间，以及单同位素精确质量、离子比例等多项指标，以此判断目标化合物是否存在于样品中。
（2）未知物分析（Unknowns Analysis，UA）软件：搭配名为SureMass的峰识别算法对色谱图中的峰进行解卷积。通过谱库匹配与保留时间过滤，将获取的精确质量质谱数据与个人化合物数据库与谱库进行比对检索。
研究人员构建了一套精简版个人化合物数据库与谱库，仅收录美国食品中最易检出的农药品类，该精简库包含约250种化合物，可有效减少非农药类的假阳性命中，大幅提升数据审阅效率。
本方法以有机种植大麻作为方法开发的基质样品。研究共分析21份缴获大麻样本，其中10份未检出任何农药残留；剩余11份样本均检出至少一种农药残留，另有1份样本检出7种可检测残留。
研究针对筛查中检出的部分农药，对缴获样本开展了定量分析。结果显示，2份大麻样本中检出的甲萘威（carbaryl）与马拉硫磷（malathion）残留量，约为美国环境保护署（US Environmental Protection Agency，EPA）规定的食品中最高耐受限量的10倍，同时约为加拿大针对干燥大麻花制定的最大残留限量的4000倍。