1. Field Methods of Monitoring Aquatic Systems Unit 11 – Organics Copyright © 2006 by DBS

2. Organic Trace Pollutants Include Naturally occurring compounds from decomposition of OM Anthropogenic pollutants Degradation and inter-reaction products of pollutants Substances derived from sewage treatment Typical analysis: Individual compounds or groups of compounds Total analysis of all organic components Field screening for specific pollutants prior to lab analysis Qualitative identification of trade products in spills and discharges

3. Question Compounds causing widespread environmental problems include toxicity, resistance to biodegradation and bioaccumulation. List the types of organic compounds which fall under these catagories Pesticides, chlorinated solvents, PCBs. dioxins, edochrine disruptors

4. Techniques GC Gas Chromatography – organic compounds have significant volatility HPLC High Performance Liquid Chromatography – increasing in use UV-Vis Spec Ultraviolet-Visible Spectrometry – useful for groups of compounds since absorptivities vary little between similar compounds

5. Storage Considerations (a)Volatility – containers should be completely filled and kept at sub-ambient temperatures (b)Microbial degradation – store at < 0 °C to lower further (c)Photolysis – store in the dark (e.g. organochlorines) (d)Contamination – glass should be used (no plastics) (e)Adsorption – analyze ASAP (low-solubility organics)

6. Volume Considerations Depends on concentration of analyte Analysis may require microliters But…sample may need several extractions

7. Precautions - Eliminating Contamination (i)Perform analysis in lab free from analyte (ii)Solvents should be kept away from work area (iii)Samples and standards should be kept well away from stock solvents (iv)Pesticide-free grade solvents should be used for analysis (v)Glassware must be cleaned thoroughly

8. Extraction Methods for GC Extract into organic solvent Separates unwanted components Separates minor components which may interfere Concentrates the components of interest Method depends on: (i) Properties of compounds determined and potential interference (ii) Choice of GC or LC as separation method (iii) Possibility of solvent-free methods (no contamination/health effects/waste) (iv) No. of samples (v) Field extractions

9. Extraction Methods (a) Solvent extraction, (b) solid-phase extraction – cartridge, (c) solid-phase extraction – disc, (d) head-space analysis, (e) purge and trap, (f) solid-phase microextraction – direct, (g) solid-phase microextraction – head-space

10. (a) Solvent Extraction (liquid-liquid) Sample is shaken with immiscible organic solvent Hexane or petroleum ether (most common) pH may be altered to favor acidic or basic components RNH 2 + HClRNH 3 + Cl - amine (soluble in np solvent)amine hydrochloride (less soluble in np solvent) RCO 2 H + NaOHRCO 2 - Na + carboxylic acid (soluble np solvent)carboxylic acid salt (less soluble np solvent)

11. (b + c) Solid-phase Extraction Disposable column 100-500 mg adsorbent material (e.g. Florisil) –Column first conditioned with methanol –Sample gravity or vacuum filtered through column –Wash with water etc. to remove interfering compounds –Dry by passing air through column –Elute with a few mLs of suitable organic solvent (concentrates x 100) e.g. hexane used for non-polar pestcides

12. Question What are the advantages of solid-phase extraction over liquid- liquid extraction? Rapid process High concentration factors Less solvent used May have problems with high solid content or OM content which block the column

13. (d) Head-space Analysis Water sample in container with septum seal Air sample with volatile components is injected into GC No solvent interference Favors low molecular-mass neutral species (e) Purge and Trap Volatile organic content are extracted using N 2 gas and collected in a tube of adsorbent material (TENAX resin) Trap tube is flash-heated releasing organics May be second liquid N 2 trap

14. (f + g) Solid-Phase Microextraction (SPME) Fused silica fiber coated in non-volatile polymeric coating (polydimethylsiloxane or polyacrylate) Dissolved components partition onto fiber Fiber retracts into syringe for storage Thermally desorbed into GC Useful technique for polar organics (e.g. phenols) Pros: –100-700 x lower detection limits –Solvent free Cons: –Equilibration texhnique –Each compound extracts differently –Changes in sample composition may affect extraction equilibria Source: http://www.science.uwaterloo.ca/chemistry/pawliszyn/Research/SPME/spme.html

15. SPME http://www.sigmaaldrich.com/Brands/Supelco_Home/Spotlights/SPME_central.html#spmeanim

16. Gas Chromatography Chromatographic separation by differential partition of components between stationary phase (liquid adsorbed or bonded to a solid) and mobile phase (gas) High separation efficiency Highly sensitive detectors

17. Detectors DetectorApplications Thermal ConductivityUniversal detector for organics Flame IonizationUniversal detector for organics Electron CaptureSpecific to atoms with high e - affinity e.g. Cl e.g. chlorinated pesticides, PCBs Hall electrolytic conductivitySpecific for halogens, N and S e.g. pesticides, trihalomethanes ThermionicElement-specific for compounds containing N and P e.g. pesticides Flame photometricElement-specific for compounds containing NS and P e.g. pesticides Photo-ionizationSpecific tocompounds containing aromatic rings or double bons e.g. solvents Mass spectrometricAll organic compounds

18. Columns and Stationary Phases Narrow-bore Capillary Columns Wide-bore Capillary columns Packed Columns Compounds of interest have high M and low volatilities, require high temperatures Best separation when stationary phase has same polarity as analyte –Fuel oils on non-polar columns –Pesticides and chlorinated solvents on medium-polarity columns –Dioxins on highly polar columns Decreasing separation efficiency

19. Question How would you confirm that a peak is due to a single component rather than two components with identical retention times? Chromatogram should be made on two columns of differing polarities Many procedures specifiy the use of a second confirmational column

20. Example Procedures Most involve extraction prior to analysis –Separate interferences –Concentrates –GC would get blocked if injected with water For analysi of individual components expected at low concentrations (e.g. pesticides) further pre-treatment may be necessary

21. e.g. DDT DDT is a mixture Environmental scamples would also contain metabolic breakdown products Multi-component mixture even without other species expected in water!!! Possible interference from PCBs, similar pesticides etc. p,p’-DDD 1-4 % o, p’-DDT 15-20 % p,p’-DDT 70-80% o,p’-DDD p, p’-DDD p, p’-DDE

22. DDT - Pretreatment Hexane extraction into 3 aliquots of 30 mL of solvent Drying extract in a 5 g column Na 2 SO 4 Concentration to 1 mL using an evaporator Clean-up of extract by colum chromatography –Al 2 O 3 (removes polar components) –AgNO 3 (retains unsaturated C compounds) –Na 2 SO 4 Concentration to 1 mL using an evaporator Overall C.F. x 100detection limit ng L -1

23. Question Clean-up of the extract simplifies the chromatogram. What is a further advantage? Protection of the column and detector from contamination

24. Quantification External standards –Compare the peak area of unknown with areas of a series of solutions used to form a calibration curve (library) –Not ideal as injection volumes may be different Internal standards –Produces peak close to but resolved from unknown species –Variation in volume shows up as change in peak area of internal standard –Results are normalized to internal standard peak area –Also useful to quantify losses during pretreatment and calculate %-age recovery

25. HPLC Fluorescence detection of PAHs Typical extracts would contain up to 70 PAH’s ~ 1 μg L -1 Require preconcentation via solid-phase extraction Some pestcides may be analyzed via post-column derivatization Pestcides may be detcted via less sensitive UV

26. Text Books Rump, H.H. (2000) Laboratory Manual for the Examination of Water, Waste Water and Soil. Wiley-VCH. Nollet, L.M. and Nollet, M.L. (2000) Handbook of Water Analysis. Marcel Dekker. Keith, L.H. and Keith, K.H. (1996) Compilation of Epa's Sampling and Analysis Methods. CRC Press. Van der Leeden, F., Troise, F.L., and Todd, D.K. (1991) The Water Encyclopedia. Lewis Publishers. Kegley, S.E. and Andrews, J. (1998) The Chemistry of Water. University Science Books. Narayanan, P. (2003) Analysis of environmental pollutants : principles and quantitative methods. Taylor & Francis. Reeve, R.N. (2002) Introduction to environmental analysis. Wiley. Clesceri, L.S., Greenberg, A.E., and Eaton, A.D., eds. (1998) Standard Methods for the Examination of Water and Wastewater, 20th Edition. Published by American Public Health Association, American Water Works Association and Water Environment Federation.