Haloacetic acids are an important class of disinfection byproducts that are being regulated. We have developed novel instrumentation for continuous monitoring of the nine haloacetic acids. Hollow fiber liquid-liquid membrane extraction (LLME) and supported liquid membrane extraction (SLME) followed by on-line HPLC-UV detection were studied. With continuous LLME, seven halo-acetic acids could be analyzed and enrichment factor (EF) was around 50. All the nine acids could be extracted and quantified by continuous SLME. Experiments with laboratory standards demonstrated that EF and extraction efficiency could be as high as 500 and 54% respectively. Relative standard deviations based on seven replicates were between 3.3 and 10.3 %, and the MDLs were at sub-ppb levels.
References:
1. “Continuous on-line monitoring of haloacetic acids via membrane extraction”. X. Wang and Somenath Mitra. J. of . Chromatogr. A. 1089, 39-44 (2005).
2. “Microfluidic supported liquid membrane extraction”. X. Wang and S. Mitra. Analytica. Chimica. Acta. 543, 92-98, (2005).
Figure 1: Schematic diagram of the system used for the continuous monitoring of haloacetic acids in water.
Figure 2. Chromatogram of continuous SLME of reagent water spiked with 80 ng/mL (ppb) nine HAAs. The donor flow rate was 4 ml/min. The acceptor was 0.05 M tris buffer (PH 8.7) with a flow rate of 0.005 ml/min. Injections were made every 15 min. The numbered peaks in the chromatogram are: 1: MCAA; 2: DCAA; 3: MBAA; 4: BCAA; 5: DBAA; 6: TCAA; 7: BDCAA; 8: CDBAA; and 9: TBAA.
Fig. 3 Microfluidic chip made of polycarbonate material into which microchannels have been machined.
Prior to the development of a continuous monitoring system, supported liquid membrane microextraction (SLMME) had been developed for the extraction, preconcentration, and determination of all the nine haloacetic acids (HAAs) in water. The HAAs are extracted into a supported liquid membrane, and then back-extracted into few microliters of an acceptor solution. Enrichment factors, as high as 4000, and low to sub-ppb detection limits were obtained in a 60 minute extraction. The extract was directly analyzed within ten minutes by flow programmed HPLC-UV. The detection limits were at ng/L (ppt) levels, and RSDs were between 2 and 12%. The parameters that affected analyte enrichment were studied. This approach offers an attractive alternative to the current standard EPA methods for HAAs, which require complex sample preparation and derivatization prior to GC analysis. SLMME can be used in conjunction with other detection schemes, such as, ion chromatography and capillary electrophoresis.
References:
1. “Development of supported liquid membrane microextraction for the trace determination of haloacetic acids”. D. Kou and S. Mitra, J. of Chromatogr. A, 1055, 63-69 (2004).
2. Microfluidic supported liquid membrane extraction”. X. Wang and S. Mitra. Analytica. Chimica. Acta. 543, 92-98, (2005).