A New Way to Extract Off-Flavor Compounds in the Aquatic Environment. Stir Bar Sorptive Extraction (SBSE)

Transcription

1 A New Way to Extract Off-Flavor Compounds in the Aquatic Environment Stir Bar Sorptive Extraction (SBSE) Young In Scientific Co., Ltd Content Introduction Purpose Experimental Results Experimental mass spectra of target compounds SIM chromatogram of target compounds Influence of extraction time Influence of sample volume on recovery Influence of sample volume on quantity extracted Influence of storage after extraction Method Validation Application to Real Water Sample Conclusion 34-2

2 Introduction Complants received by water companies are most often due to bad taste and odors in drinking water The presence of these unpleasant tasting but otherwise harmless compounds can be taken as unsafe water by the consumer In most cases, complaints concern chlorine and earthy/musty smelling compounds, which was commonly accepted those were associated with the presence of geosmin, MIB* and/or haloanisoles *MIB - Mithylisoborneol 34-3 Characteristics of target compounds MIB woody or camphor odor detectable at a threshold, 5 to 10ng/L actinomycetes or their metabolic products, cyanobacteria and fungi Geosmin characteristic earthy odor detectable at a threshold, 1 to 10ng/L actinomycetes or their metabolic products, cyanobacteria and fungi Haloanisoles musty odor at a low threshold, 2,4,6-TCA detectable at ng/L caused by microbiological methylation of halophenols during water treatment or transport through the distribution system 34-4

3 Identification of target compounds Have a real analytical problem because they are odorous at very low concetrations Closed Loop Stripping Analysis(CLSA) - based on adsorption - same as Purge and Trap - is very useful for concentratoin levels above 100ng/L - because these stripping techniques were not efficient enough for less volatile and/or more polar compounds SBSE( alternative choice to conventional stripping method) - Based on sorption - Novel extraction technique, sensitive, simple and fast - Magnetic stirring eliminates sample matrix effaction 34-5 Purpose To analysze six odorous organic compounds in water with the SBSE technique To quantified at the subnanogram/l level, under or close to target compounds odor threshold 34-6

4 Analyzed Odorous Compounds Name Abbreviation Taste Odor Thresh, CAS No. ng/l 2-methylisoborneol MIB Earthy 5-10 N/A 2,4,6-trichloroanisole 2,4,6-TCA Musty ,3,6-trichloroanisole 2,3,6-TCA Musty Geosmin Geosmin Camphor ,3,4-trichloroanisole 2,3,4-TCA Musty ,4,6-tribromoanisole 2,4,6-TBA Musty Experimental Agilent 6890N GC Agilent 5973 MSD Gerstel Twister desorption unit, TDU Cooled injection system, CIS4 Olfactory Detection Port, ODP2 Twister, 20mm long and 0.5mm layer of PDMS 34-8

5 Experimental mass spectra of target compounds For monitoring ions in the SIM mode MIB: 95, 108 Geosmin: 112, 125 2,4,6-TBA: 346, Experimental mass spectra of target compounds For monitoring ions in the SIM mode Three TCA: 210,

6 SIM chromatogram of target compounds Influence of extraction time 2ng/L of each compound was analyzed after extraction times ranging from 15min to 300 min on PDMS 34-12

7 Influence of extraction time For routine analysis with high sample throughput, an extraction time of 120 minutes was chosen Influence of sample volume on recovery 1ng/L, 2 hours A: experimental recoveries B: theoretical recoveries (by calculated Ko/w) C: theoretical recoveries (by experimental recoveries) 34-14

8 Influence of sample volume on recovery The difference between experimental and expected values increased when the sample volume increased Influence of sample volume on quantity extracted In order to achieve concentrations more close to the odor threshold, use two 100ml aliquots of each sample and two Twisters, which were desorbed together 34-16

9 Influence of storage after extraction These results show that no compound loss occurs during 1 week of storage Method Validation Was validated according to the AFNOR regulation XP T The linearity is studied over seven concentration levels, from 0.1 to 10ng/L, replicated five times The *LOQ is validated when the *RSD of 10 replicate samples, spiked with supposed LOQ, is under 20% The repeatability is expressed as %RSD and is calculated on the basis of three replicates of eight different water samples. It must be under 20% The trueness is expressed as the percent recovery of spiked real water samples and must be between 80% and 120% The reproducibility is expressed as a %RSD of a check calibration standard(2ng/l). It must be under 20% *AFNOR: Association Francaise de Normalization *LOQ: Limit of Quantification *RSD: Relative Standard Deviation 34-18

10 Validation Results for Target Compounds Name R LOQ, Repeatability trueness Reproducibility ng/l % % % MIB ,4,6-TCA ,3,6-TCA Geosmin ,3,4-TCA ,4,6-TBA The validation criteria were achieved for all target compounds Calibration curves for investigated compounds 34-20

11 CASE 1 Two samples (A and B) were collected at the consumer s home. Sample A gave a very pronounced musty odor and sample B gave a soft musty odor and a pronounced metallic odor Concentration of Target Compounds in Sample A and B Sample A, ng/l Sample B, ng/l MIB <1 <1 2,4,6-TCA ,3,6-TCA <0.1 <0.1 Geosmin 5.2 <0.5 2,3,4-TCA <0.2 <0.2 2,4,6-TBA CASE 1 conti. SIM chromatograms for samples A and B 34-22

12 CASE 1 conti. However, the concentration levels found in both samples can not certainly explain the musty odor. Those must be contain OTHER odorous compounds!! The GC with olfactometric detection showed a pronounced musty odor but also a medicinal one in sample A. For sample B, the olfactometric detection gave a mild musty odor and also a medicinal one CASE 1 conti. The medicinal odor was dibromoiodomethane at 8 min, and the other solvent odor was tetrachlorobenzene around 8 min 34-24

13 CASE 2 An off-flavor episode occurred in a tank. Drinking water stored in this tank is produced from ground water, which first undergoes aeration and sand filtration for iron removal (sample A) and then the water is chlorinated just prior to entering the tank (sample B) Concentration of Target Compounds in Sample A and B Sample A, ng/l Sample B, ng/l MIB <1 <1 2,4,6-TCA <0.1 <0.1 2,3,6-TCA <0.1 <0.1 Geosmin <0.5 <0.5 2,3,4-TCA <0.2 <0.2 2,4,6-TBA < CASE 2 conti. EIC(m/z:346) of chlorinated and filtered water 34-26

14 CASE 2 conti. The presence of 2,4,6-TBA can easily explain the significant musty taste imparted to the water However, Those must be contain OTHER odorous compounds!! GC with olfactometric gave a significant musty odor in addition to different phenolic odors at around 8, 14, 17 min CASE 2 conti. The phenolic odors were phenol and its derivatives, 2,4,6- trichlorophenol and 2,4,6-tribromophenol. 2,4,6-TBA was synthesized by living organisms present at the surface of the coating

15 CASE 3 This case consisted in network distribution system. Two samples were taken sample A at the outlet of the treatment plant and sample B at the consumer s home at the end of the network. A gave only a chlorine odor, B gave musty, swampy, earthy odors. Concentration of Target Compounds in Sample A and B Sample A, ng/l Sample B, ng/l MIB <1 <1 2,4,6-TCA <0.1 <0.1 2,3,6-TCA <0.1 <0.1 Geosmin <0.5 <0.5 2,3,4-TCA < ,4,6-TBA < CASE 3 conti. However, these concentrations cannot explain the significant taste and odor impairment in sample B Those must be contain OTHER odorous compounds!! Olfactometry allowed the detection of seven different odors 34-30

16 CASE 2 conti. Odors generated during the chromatographic run time Tr (min) Odor Qualification 7 Sweaty Phenylacetaldehyde 7.8 Swampy Dimethyltrisulfide 10.7 Citrus Decanal 12 Flower Undecanal 12.8 Sweaty Not Qualified 12.9 to 15.2 Musty Alkylbromobenzene isomers Rancid Isopropyldodecanoate 16.8 to 17.4 Tar Diisopropylnaphthalene Tar Dodecahydrophenanthrene A musty odor was smelled from 13 to 15 min. of which the major component was 2-methyl-4-isopropylbromobenzene CASE 3 conti. Comparison of TIC of each compound between sample A and B 34-32

17 Conclusions Rapid SBSE-TD-GC/MS-Olfactometry method for the determination of MIB, geosmin, and haloanisol compounds in water samples was developed. The combination of TD- GC/MS and the SBSE made it possible to quantify all of the odorous components at levels close to or under their odor threshold limit The influence of extraction time, sample volume, and storage time were studied in order to optimize the method s sensitivity. The final method was validated according to the AFNOR regulation and satisfied Conclusions - conti. Storage time for Twsiters is for at least 7 days after extraction without loss of the extracted compounds When applied to real odorous water samples, SBSE showed a good response. In addition to the target compounds, it was possible to identify unknown odorous compounds at very low levels far more rapidly than possible using conventional techniques 34-34