Analytical Aspects of Photoelectron Spectroscopy

Photoelectron spectroscopy is a new technique for experimentally measuring the binding energies of electrons in molecules. The basic principles of the method are outlined and simple guidelines for the interpretation of u.v.-excited photoelectron spectra are laid down. The analytical potential and possible development of the method are briefly surveyed.     

顶空固相微萃取-气相色谱-质谱联用测定饮用水中的2-甲基异莰醇和土臭素

2-甲基异莰醇(2-methylisoborneol, 2-MIB)和土臭素(geosmin, GSM)在水源水中大量分泌排放是造成饮用水土霉异味突发事件、引发居民用水恐慌的重用因素之一。使用顶空固相微萃取(HS-SPME)与气相色谱-质谱联用技术(GC-MS)建立了水库水、水库附近土壤、居民自来水中2-MIB和GSM的测定方法。结合正交分析优化了加盐量、萃取温度、萃取时间条件,在电子轰击(EI)-选择离子扫描(SIM)模式下进行了目标物的定性定量分析。结果表明:在5~1000 ng/L范围内,2-MIB和GSM的色谱峰面积与其质量浓度的线性关系良好(r²≥0.998), 2-MIB与GSM的检出限分别为0.72 ng/L和0.34 ng/L,定量限分别为2.40 ng/L和1.13 ng/L;目标物加标水平为10~600 ng/L时,平均回收率为93.6%~107.7%,相对标准偏差(RSD)≤6.1%(n=6)。基于上述方法,对辽宁省某地区水库水、水库附近土壤、居民自来水中的目标物进行检测,结果表明:水库水目标物质量浓度范围为3.0~3.6 ng/L,水库附近土壤中提取的2-MIB为8.1 ng/L、提取的GSM为17.8 ng/L,居民自来水中的目标物未检出。该方法操作简便、准确可靠,灵敏度高,无需有机溶剂,适合于饮用水中2-MIB和GSM的分析检测。     

Development and validation of an SPE-GC-MS/MS taste and odour method for analysis in surface water

The goal of this research was to develop a robust method for taste and odour compounds that can be implemented by laboratories with mass spectrometers lacking chemical ionisation capabilities or specialised sample introduction hardware that are commonly used for taste and odour methods. Development, optimisation, and validation of a solid-phase extraction method using liquid injection and gas chromatography – tandem mass spectrometry detection with electron impact ionisation are described. Camphor was used as an internal standard, and through method development and robustness testing it was shown to extract similarly to other taste and odour compounds, making it a cost-effective alternative to deuterated analogs. The instrumental parameters and extraction procedure were fully optimised prior to assessing the method’s linearity, precision, and accuracy. Using a 2000-fold enrichment factor, method recoveries for priority compounds geosmin (GSM) and 2-methylisoborneol (2-MIB) were >90%. Excellent linearity was obtained from the reportable detection limits up to 200 ng L^?1 and precision %relative standard deviations were 8.5% and 10.9% for GSM and 2-MIB, respectively. Detection limits of 0.9 and 5.5 ng L^?1 for GSM and 2-MIB respectively were deemed fit-for-purpose in comparison to their odour thresholds. Validation data were also obtained for other commonly analysed taste and odour compounds, including 2,4,6-trichloroanisole, 2-isopropyl-3-methoxypyrazine, and 2-isobutyl-3-methoxypyrazine. The validated method was used to screen surface waters in Nova Scotia, Canada for presence of taste and odour compounds, highlighting the presence of GSM on the east coast of Canada.     

Electrospun nanofibers versus drop casting films for designing an electronic tongue: comparison of performance for monitoring geosmin and 2‐methylisoborneol in water samples

Geosmin (GSM) and 2‐Methylisoborneol (MIB) are substances commonly found in river water and arise due to eutrophication process. Such contaminants affect the organoleptic properties of water, hampering its consumption, and use in beverage industries. As the human perception threshold for these compounds is low, the devices aimed at their detection must be sensitive enough to detect concentrations as low as a few nanogram per liter in order to guarantee the water quality parameters. Due to the experimental simplicity, fast analysis, portability, and capability for on‐site analysis, the use of electronic tongues and electronic noses employing hybrid and composite materials are potential for GSM and MIB determination. In this work, two distinct electronic tongues were applied in the electrical determination of GSM and MIB in pure and river water. The difference between them consisted in the type of polymer processing used in the fabrication of sensing units. The thin films deposited onto gold IDEs were based on polyamide 6, polypirrole, and polyaniline, but fabricated by drop‐casting and electrospinning. The differences in the electronic tongue performances were correlated to the distinct morphologies of the sensitive layers. Both devices were able to discriminate pure water from solutions tainted with GSM and MIB in concentration as low as 25 ng L^?1, with high data correlation and a good reproducibility.     

HS-SPME–GC–MS法测定水中2-甲基异冰片及土臭素

采用顶空固相微萃取–气质联用(HS-SPME–GC–MS)的方法对地表水中2-甲基异冰片(2-MIB)和土臭素(GSM)进行分析测定。通过试验确定了HS-SPME的最佳萃取条件:萃取头为DVB/CAR/PDMS,萃取时间为30 min,萃取温度为70℃,NaCl的加入量为30%(质量分数),萃取纤维在GC上的解吸温度为250℃。用内标法进行定量,2-MIB,GSM的质量浓度在5~100 ng/L范围内与色谱峰面积呈良好的线性关系,线性相关系数(r2)分别为0.999 7,0.997 0,检出限分别为0.8,1.7 ng/L。采用该法对水样进行测定,2-MIB,GSM测定结果的相对标准偏差为2.6%~6.3%(n=6),加标回收率为92%~112%。该方法能简单、快速地测定水中痕量嗅味物质。     

Determination of 2-methylisoborneol and geosmin in aqueous samples by static headspace-gas chromatography-mass spectrometry with ramped inlet pressure

A method for determining the earthy and musty odors 2-methylisoborneol (2-MIB) and geosmin in drinking water using static headspace-GC-MS is described. To achieve lower detection limits, split ratio was optimized with ramped inlet pressure for large headspace sampling volume. The ramped inlet pressure, which held higher pressure (higher column flow rate) only during injection, allowed us to inject 3-mL volume to GC with very low split ratio (2:1). Although sequential analysis with a stainless steel ion source often changed the mass spectrum of 2-MIB, this spectral change was eliminated by using an inert ion source with a 6 mm drawout plate. The detection limits of this method were 0.36 and 0.14 ng/L, respectively, for 2-MIB and geosmin. The repeatabilities (n = 30) were 6.6 and 4.8%, respectively, at 1 ng/L for 2-MIB and geosmin.