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饮用水嗅味是用户可以直接感受到的水质指标,关系到人民群众的获得感及对饮用水水质的信任度[1],随着用户对饮用水感官品质的要求升高,新版《生活饮用水卫生标准》 (GB 5749-2022) [2]更加关注了嗅味指标的重要性。一项针对我国55个重点城市自来水厂的水质调查结果显示,80%以上的水源及约40%的出厂水存在一定嗅味问题,主要的嗅味类型包括土霉味、腥臭味、化学品味和草木味等[3][4]。关键的致嗅物质涉及藻、微生物、工业等多种来源,具有不同物质结构与物理化学性质。除广泛报道的2-甲基异莰醇和土臭素等生物来源的土霉味物质,与污染有关的2-甲氧基-3,5-二甲基吡嗪也对土霉味产生贡献,该物质在极低的纳克/升水平即可导致嗅味问题[5-8]。二甲基二硫醚、二甲基三硫醚等硫醚类物质是水中腥臭味的主要来源,也是2007年太湖嗅味事件的主因[9]。藻类代谢物β-环柠檬醛可以导致水中草木味问题。工业化学品及副产物的排放可能导致水中化学品味、溶剂味、塑料味等问题,如2013年杭州饮用水源2-叔丁基苯酚污染导致饮用水塑料味问题[10]。考虑到饮用水中存在多种嗅味类型,开展不同嗅味类型的关键致嗅物质同时分析检测,是阐明我国饮用水嗅味污染特征并提出针对性管控措施的基础,对于进一步提升饮用水水质具有重要的意义。
目前,国内外针对典型土霉味物质2-甲基异莰醇和土臭素及腥臭味物质硫醚的检测方法已经有了较多报道,常采用气相色谱-质谱联用技术,并且已有了相应的标准检测方法。一些突发的致嗅新污染物如2-甲氧基-3,5-二甲基吡嗪、2-叔丁基苯酚等,检测方法鲜有报道,导致水厂应对能力不足。由于致嗅物质种类繁多、物理化学性质各异,但部分嗅阈值极低,可能存在多种低浓度嗅味物质协同致嗅,如何提升复杂样品中痕量致嗅物的分析准确度与精确度,是限制供水行业多种痕量致嗅物同时检测的关键。近年来发展的气相色谱-三重四极杆串联质谱法 (GC-MS/MS) 因其二级碎片的引入可以有效降低噪声干扰,提高分析的灵敏度。此外,在测试中,引入致嗅物的同位素标记物、或结构性质类似物作为内标,将进一步提升分析的准确性。除广泛关注的土霉味、腥臭味外,还选取了我国饮用水中存在的化学品味和草木味等问题的潜在致嗅物质,以二甲基二硫醚-d6为内标,利用顶空固相微萃取结合气相色谱三重四极杆串联质谱建立了一种快速分析水源及自来水中9种致嗅物质的同时定量分析方法。
顶空固相微萃取-气相色谱三重四极杆串联质谱同时测定饮用水中9种嗅味物质
Simultaneous quantification of 9 odorants in drinking water by headspace solid-phase microextraction coupled with gas chromatography-triple quadrupole tandem mass spectrometry
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摘要: 针对新国标背景下饮用水不同异味类型致嗅物的同时检测需求,建立了基于顶空固相微萃取与气相色谱三重四极杆串联质谱联用的内标法同时测定9种关键致嗅物的分析方法。分析了萃取纤维类型、盐浓度、萃取温度、萃取和解析时间等条件对萃取效果的影响,优化后的测试条件为:使用CAR/PDMS-85 μm萃取纤维,氯化钠投加量为3 g,内标浓度为100 ng·L−1,将10 mL水样于65 ℃条件下萃取30 min,250 ℃条件下解析300 s。该方法9种嗅味物质的标准曲线具有良好的线性 (R2 >0.995) ,检出限为0.2~1.5 ng·L−1,在超纯水、自来水和水源水中的加标回收率分别为84.0%~115% (10 ng·L−1) 、80.5%~112% (50 ng·L−1) 、88.8%~111% (250 ng·L−1) ,相对标准偏差小于16%,满足样品定量分析要求。采用优化后的方法测定南方某水库水样,二甲基二硫醚 (12.1~41.6 ng·L−1) 、二甲基三硫醚 (9.9~11.6 ng·L−1) 、β-环柠檬醛 (5.8~13.1 ng·L−1) 、2-甲基异莰醇 (11.1~25.3 ng·L−1) 和土臭素 (5.6~8.7 ng·L−1) 均有检出。
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关键词:
- 饮用水 /
- 嗅味 /
- 顶空固相微萃取 /
- 气相色谱三重四极杆串联质谱
Abstract: In response to the implementation of the new national drinking water quality standard in China, an internal standard method based on headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS) was developed for the simultaneous determination of nine typical odorants in water, including 2-methylisoborneol, and dimethyl disulfide. The effects of extraction fiber type, salt concentration, extraction temperature, extraction and resolution time on the extraction efficiencies were analyzed. The optimized HS-SPME procedures were as follows: CAR/PDMS-85 μm fiber was used to extract odorants. After adding 3 g NaCl, the extraction of 10 mL water sample with 100 ng·L−1 internal standard was carried out at 65 ℃ for 30 min, and the resolution was carried out at 250 ℃ for 300 s. The standard curves of nine odorants had good linearity (R2 >0.995) under the optimized conditions, and the detection limits ranged from 0.2 to 1.5 ng·L−1. The spiked recoveries in ultrapure water, tap water, and source water were 84.0%~115% (10 ng·L−1), 80.5%~112% (50 ng·L−1), and 88.8%~111% (250 ng·L−1), respectively, with relative standard deviations (RSD) less than 16%, which meeted the requirements of quantitative analysis of water samples. The optimized method was used to determine odorant concentration in water samples collected from a reservoir in southern China. Dimethyl disulfide (12.1~41.6 ng·L−1), dimethyl trisulfide (9.9~11.6 ng·L−1), β-cyclocitral (5.8~13.1 ng·L−1), 2-methylisocamphol (11.1~25.3 ng·L−1) and geosmin (5.6~8.7 ng·L−1) were detected. -
表 1 9种嗅味物质多离子反应监测质谱参数
Table 1. Mass parameters of multiple reaction monitoring of 9 odorants
嗅味类型 物质名称 保留时间/
min定量离子/
(m·z−1)Ch1/
(CE·eV−1)参考离子1/
(m·z−1)Ch2/
(CE·eV−1)参考离子2/
(m·z−1)Ch3/
(CE·eV−1)腥臭味 二甲基二硫醚 13.027 94.00>79.00 15 94.00>61.00 9 94.00>64.00 27 二甲基三硫醚 18.026 126.00>79.00 18 79.00>64.00 18 126.00>61.10 6 异丙基丙基硫醚 14.788 118.00>76.10 9 103.00>61.00 6 118.00>103.10 9 草木味 β-环柠檬醛 22.477 137.00>109.20 6 152.00>137.20 9 152.00>123.10 6 土霉味 2,4,6-三氯苯甲醚 23.926 195.00>166.90 18 197.00>169.00 18 210.00>194.90 12 2-甲基异莰醇 21.985 95.00>67.10 15 95.00>55.10 18 108.00>93.10 12 土臭素 25.595 112.00>97.10 12 112.00>83.10 12 112.00>69.10 21 2-甲氧基-3,5-二甲基吡嗪 18.735 138.00>120.10 6 138.00>109.10 9 120.00>52.10 21 化学品味 2-叔丁基苯酚 23.309 135.00>107.10 12 107.00>77.10 18 150.00>135.10 9 — 二甲基二硫醚-d6 12.915 100.00>82.00 12 82.00>64.00 12 100.00>66.00 9 注:MRM参数引自课题组前期研究[11];Ch表示通路,CE表示相应通路的碰撞能量。 表 2 9种物质的标准曲线和检出限
Table 2. Standard curves and detection limits of 9 odorants
嗅味类型 物质名称 拟合方程 R2 线性范围/ (ng·L−1) 本研究检出限/ (ng·L−1) 文献报道检出限/ (ng·L−1) 腥臭味 二甲基二硫醚 y=8.98×10−3x-1.59×10−2 0.999 5~250 1.3 0.6[17]、2.0[18] 二甲基三硫醚 y=3.80×10−3x-1.19×10−2 0.997 5~250 0.9 0.6~2.5[17,19-21] 异丙基丙基硫醚 y=6.35×10−3x-1.93×10−2 0.999 5~250 0.3 1.5[22] 草木味 β-环柠檬醛 y=1.27×10−3x+1.84×10−3 0.996 5~250 1.1 0.3~4.4[17,21,23-26] 土霉味 2,4,6-三氯苯甲醚 y=3.73×10−3x+1.26×10−2 0.998 5~250 1.5 1.4~3.8[19,21,24-28] 2-甲基异莰醇 y=5.08×10−3x+2.32×10−2 0.996 5~250 0.2 0.3~2.7[17,24,25,28-30] 土臭素 y=1.37×10−2x+8.85×10−3 0.997 5~250 0.2 0.9~2.2[17,23-25 ,30] 2-甲氧基-3,5-二甲基吡嗪 y=1.12×10−3x+4.99×10−3 0.997 5~250 1.2 — 化学品味 2-叔丁基苯酚 y=7.22×10−3x+3.36×10−2 0.997 5~250 1.4 1.0[27]、7.2[31] 表 3 9种物质的加标回收率和相对标准偏差
Table 3. Recoveries and relative standard deviation of 9 odorants
嗅味物质 加标浓度/ (ng·L−1) 超纯水 自来水 水源水 回收率/% RSD/% 回收率/% RSD/% 回收率/% RSD/% 二甲基二硫醚 10 86.7 6.2 85.7 5.3 93.3 13.5 50 88.9 10.1 89.3 6.9 98.8 9.0 250 97.1 5.5 106 5.2 97.4 7.0 二甲基三硫醚 10 102 2.9 107 2.5 103 7.6 50 98.5 7.5 80.5 7.8 100 6.4 250 107 7.6 99.6 4.0 96.8 6.5 异丙基丙基硫醚 10 97.3 2.3 101 1.4 97.3 13.3 50 99.6 9.6 94.4 8.3 91.4 7.9 250 102 7.8 111 4.6 88.8 6.7 β-环柠檬醛 10 112 3.2 115 1.9 98.2 14.1 50 100 7.4 87.9 2.8 102 5.9 250 104 7.2 93.6 6.5 89.7 6.5 2,4,6-三氯苯甲醚 10 100 2.8 103 2.7 103 9.5 50 102 10.2 93.6 6.5 83.2 6.5 250 104 8.1 108 4.5 98.7 5.5 2-甲基异莰醇 10 106 3.2 101 2.2 115 9.9 50 96.7 8.0 93.2 2.2 112 6.8 250 108 7.4 98.9 6.0 96.1 6.5 土臭素 10 102 1.5 100 1.4 101 9.5 50 98.9 9.2 85.7 3.6 111 6.0 250 104 5.7 91.5 5.4 93.3 6.8 2-叔丁基苯酚 10 85.2 5.6 90.8 12.7 85.7 14.1 50 100 9.2 84.6 3.5 111 6.6 250 105 11.0 97.4 6.3 96.7 8.8 2-甲氧基-3,5-二甲基吡嗪 10 105 15.6 105 3.6 84.0 14.9 50 106 8.3 87.6 5.5 106 7.7 250 107 11.1 99.4 6.2 93.5 7.2 -
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