R. Sävenhed

Modified stripping technique for the analysis of trace organics in water

Abstract A modification of closed loop stripping analysis that considerably reduces the problem of contamination of the standard system is reported. This modification also makes the system more flexible in regard to stripping temperature and flow-rate of the purging gas. This modification, designated the straight and open system, allows the stripping technique to be utilized without sacrificing sensitivity or capacity, but gives very few blank peaks in the subsequent high resolution gas chromatogram. A case study of trace organics in the Motala river is presented. This river is a raw water source for water works and is a recipient for industries and sewage plants.

Optimization of the open stripping system for the analysis of trace oranics in water

Abstract With the open modification of the system for closed-loop stripping analysis, the stripping conditions can be varied widely. By using stripping temperatures between 30 and 90°C, the technique can be optimized to meet specific analytical demands. In particular, the analysis of trace organics in water can be extended to less volatile and more polar compounds. Desorption of the adsorbent is often the key step in the stripping procedure. Efficiency of extraction from the filter is generally low. This has been investigated, and a solvent mixture not used previously for stripping analysis (carbon disulphide—benzene—methanol, 65:30:5) is recommended.

Systematic approach to adsorption on XAD-2 resin for the concentration and analysis of trace organics in water below the μg/1 level

Abstract The adsorption on XAD-2 resin of trace organics in water has been optimized and evaluated step-by-step at concentration levels below 1 μg/1 and in the presence of organic substances that may interfere with the adsorption. Two solvent sequences, methanol-diethyl ether-water (sample) and methanol-acetone-water (sample), gave satisfactory blank levels without reducing the adsorption capacity. Separate studies of the adsorption, desorption and evaporation steps showed that for a great number of non-polar compounds with different functional groups the recovery was mainly limited by losses in the evaporation step. For polar compounds such as certain alcohols and phenols the adsorption efficiency was the most critical factor. Losses during the desorption step could be made negligible except for naphthalene and anthracene. A study of interaction effects between humic substances in the water sample and the low-molecular-weight compounds to be analysed by gas chromatography did not give any evidence of a decrease in recovery or increase in breakthrough for any of the surface-water samples. Comparisons with dichloromethane extraction and stripping enrichment showed that adsorption on XAD-2 can give blank levels and recoveries which are in some respects superior. Furthermore, the XAD-2 technique and dichloromethane extraction were less sensitive to interaction effects from humic substances and less sensitive than the stripping technique.

Stripping analysis and chromatographic sniffing for the source identification of odorous compounds in drinking water

Abstract Chemical and sensory methods have been combined into an improved technique for the source identification of odorous compounds in drinking water. A simple device for gas chromatographic sniffing, in which the capillary column is lead to the odour observer via heated copper tubing, has been developed. This system is highly sensitive and highly accurate for the determination of retention times. A stripping technique that permits high stripping temperatures without technical problems has also been developed, and it has been shown to increase significantly the number of odorous compounds detected by column sniffing. The design of the stripping system gives a very low blank level that results in almost no compounds detected on column sniffing of extracts from odour-free water.

Removal of individual off-flavour compounds in water during artificial groundwater recharge and during treatment by alum coagulation/sand filtration

Abstract The removal of individual off-flavour compounds during artificial groundwater recharge has been compared to the removal of such compounds during conventional alum coagulation/sand filtration. By using an evaluation technique based on gas chromatography with both instrumental and sensory detection (“column sniffing”) it was shown that alum coagulation/sand filtration had no significant effect on any of the off-flavour compounds that could be detected in the raw water samples (geosmin, 2-methylisoborneol, 2-isopropyl-3-methoxypyrazine, 2,4,6-trichloroanisole, 1-octen-3-one, 1-nonen-3-one, dimethyl trisulphide and a number of unidentified muddy or musty odours). During artificial groundwater recharge in sand and gravel ridges, however, the concentrations of all these compounds were substantially reduced, thus proving that artificial groundwater recharge is not only a suitable method for water storage but can also be an effective method for removing muddy and musty odours. The successful use of the column-sniffing technique for evaluating water treatment methods has shown the potential of this technique in resolving some of the present disagreements concerning the effectiveness of different treatment methods for removing tastes and odours from water.

Isolation of off-flavour compounds in water by chromatographic sniffing and preparative gas chromatography

Abstract A procedure for the isolation and identification of off-flavour compounds in water was developed. Odorous volatile compounds were enriched by stripping and dichloromethane extraction. The extracts obtained were analysed by chromatographic sniffing and preparative gas chromatography, followed by sensory evaluation of different fractions dissolved in odourless water. The chromatographic sniffing technique was found to be sensitive enough to detect known odorous compounds in concentrations far below their threshold odour concentrations in water. However, in order to quantify the contribution of specific compounds to the off-flavour of the water, preparative gas chromatography and sensory evaluation of dissolved extracts were indispensable. One of the case studies performed showed that the origin of off-flavours in water can be very complex, with contributions from several so far unidentified compounds.

Odour Control by Artificial Groundwater Recharge

The removal of odorous compounds during artificial groundwater recharge in sand and gravel ridges (“eskers”) has been evaluated by gas chromatography with both instrumental and sensory detection (“chromatographic sniffing”). Seven Swedish water works were included in the study. It was shown that the off-flavour compounds in the raw water samples (geosmin, 2-methylisoborneol, 2-isopropyl-3-methoxy-pyrazine, 2, 4, 6-trichloroanisole, 1-octen-3-one, dimethyl trisulphide, and a number of unidentified muddy or musty odours) were all effectively removed during infiltration, thus proving that artificial groundwater recharge is not only a suitable method for water storage but can also be an effective method for removing odorous compounds.