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Comparison of Conventional Solid Phase Extraction (SPE), Automated-online SPE and Large Volume Injection (LVI) for Analysis of Emerging Organic Contaminants in Water
Oral Presentation
Prepared by T. Anumol, S. Snyder
University of Arizona, 1657 E Helen Street, BIO5 Institute, Office: 0400A22, Tucson, AZ, 85719, United States
Contact Information: tanumol@email.arizona.edu; 412-656-0490
ABSTRACT
Emerging Organic contaminants (EOCs) are ubiquitous and have been detected in surface and ground waters throughout the globe. These compounds are difficult to attenuate in conventional water treatment plants and hence can result in contamination of potable waters. EOCs have been shown to impact aquatic wildlife at concentrations occurring in wastewater, while the potential synergistic effects of low dose exposure to these compounds on humans are currently unknown. Thus, the monitoring of these compounds is of great significance. When dealing with matrices as varied as raw sewage to reverse osmosis treated water and with the continual advancement of analytical equipment, it can often be a struggle for even experienced analysts to choose the best form of sample clean-up and extraction step to get robust and sensitive data. Traditionally, labor intensive and time-consuming extraction techniques like SPE and LLE have been used for concentration of these samples so as to achieve required detection limits of these compounds. These methods require large amounts of sample (100-2000 ml) and solvents for extraction. Recently, the development of automated online SPE systems have given rise to the possibility of achieving similar detection limits with the use of just 1-10 ml of sample while significantly reducing cost, labor and time of analysis. With increase in sensitivity of modern mass spectrometers, large volume injection of the sample with no or minimal pretreatment has been mooted as a possibility for analysis of these contaminants. This paper will compare all three techniques while considering factors like method reporting limits and issue with ion suppression. Further, the type of water matrix, cost and time of analysis will also be discussed with regards to analysis of EOCs.
In this study, a single LC analytical method for the analysis of over 25 EOCs (both in ESI- and ESI+) using on-line SPE coupled to a tandem mass spectrometer, were compared to direct large volume injection of sample and offline-SPE followed by LC/MS/MS analysis will be shown. The offline extraction method with a 1000 fold concentration provided comparable detection limits to the automated online SPE method, and lower than the LVI method in ultrapure water. However, in dirtier water matrixes like surface water and wastewater effluent, a 1000 fold concentration provided significant ion suppression due to concentration of a large amount of natural organic matter too. As a result, the true detection limits for this method were higher than the online SPE method and comparable to LVI for most compounds. Even when a smaller concentration factor was used (250 fold), the ion suppression was much more for the conventional SPE method compared to the other two. The direct injection method had least ion suppression and maybe the most suitable technique for wastewater analysis where higher concentrations of EOCs are seen. LVI though adversely affects the life of an analytical column while failing to remove possible interference in the matrix due to a lack of sample clean-up. Trace enrichment or on-line SPE eliminates all these difficulties while providing sample clean-up and reduces interferences which LVI cannot do. Further, it can be completely automated to reduce labor while increasing reproducibility of results. In conclusion, each method has its own merits and disadvantages. This paper will provide quantitative data of all these techniques with special focus on method detection limits, ion suppression effects, sample cycle time and cost of analysis.
Oral Presentation
Prepared by T. Anumol, S. Snyder
University of Arizona, 1657 E Helen Street, BIO5 Institute, Office: 0400A22, Tucson, AZ, 85719, United States
Contact Information: tanumol@email.arizona.edu; 412-656-0490
ABSTRACT
Emerging Organic contaminants (EOCs) are ubiquitous and have been detected in surface and ground waters throughout the globe. These compounds are difficult to attenuate in conventional water treatment plants and hence can result in contamination of potable waters. EOCs have been shown to impact aquatic wildlife at concentrations occurring in wastewater, while the potential synergistic effects of low dose exposure to these compounds on humans are currently unknown. Thus, the monitoring of these compounds is of great significance. When dealing with matrices as varied as raw sewage to reverse osmosis treated water and with the continual advancement of analytical equipment, it can often be a struggle for even experienced analysts to choose the best form of sample clean-up and extraction step to get robust and sensitive data. Traditionally, labor intensive and time-consuming extraction techniques like SPE and LLE have been used for concentration of these samples so as to achieve required detection limits of these compounds. These methods require large amounts of sample (100-2000 ml) and solvents for extraction. Recently, the development of automated online SPE systems have given rise to the possibility of achieving similar detection limits with the use of just 1-10 ml of sample while significantly reducing cost, labor and time of analysis. With increase in sensitivity of modern mass spectrometers, large volume injection of the sample with no or minimal pretreatment has been mooted as a possibility for analysis of these contaminants. This paper will compare all three techniques while considering factors like method reporting limits and issue with ion suppression. Further, the type of water matrix, cost and time of analysis will also be discussed with regards to analysis of EOCs.
In this study, a single LC analytical method for the analysis of over 25 EOCs (both in ESI- and ESI+) using on-line SPE coupled to a tandem mass spectrometer, were compared to direct large volume injection of sample and offline-SPE followed by LC/MS/MS analysis will be shown. The offline extraction method with a 1000 fold concentration provided comparable detection limits to the automated online SPE method, and lower than the LVI method in ultrapure water. However, in dirtier water matrixes like surface water and wastewater effluent, a 1000 fold concentration provided significant ion suppression due to concentration of a large amount of natural organic matter too. As a result, the true detection limits for this method were higher than the online SPE method and comparable to LVI for most compounds. Even when a smaller concentration factor was used (250 fold), the ion suppression was much more for the conventional SPE method compared to the other two. The direct injection method had least ion suppression and maybe the most suitable technique for wastewater analysis where higher concentrations of EOCs are seen. LVI though adversely affects the life of an analytical column while failing to remove possible interference in the matrix due to a lack of sample clean-up. Trace enrichment or on-line SPE eliminates all these difficulties while providing sample clean-up and reduces interferences which LVI cannot do. Further, it can be completely automated to reduce labor while increasing reproducibility of results. In conclusion, each method has its own merits and disadvantages. This paper will provide quantitative data of all these techniques with special focus on method detection limits, ion suppression effects, sample cycle time and cost of analysis.