Automated preconcentration water

Uza M, Hunsinger R, Thompson T, et al. 1990. Validation studies of an automated preconcentration water sampler APS for chlorinated dibenzo-p-dioxins and dibenzofurans. Chemosphere 20 1349-1354. 

The choice of the system to be used for collecting particulate matter depends on the water volume to be sampled and the expected particle concentration therein. Borosilicate glass microfiber filters proved to be appropriate to separate the suspended material from the aqueous solution for a sample size up to 300 L [14]. A limiting factor may be represented by filter plugging, as demonstrated in a validation study conducted by Uza and coworkers to test the efficiency of an automated preconcentration water sampler (APS) for PCDDs and PCDFs [21]. The APS system is composed of a two-stage particulate filtering unit with coarse and fine filters, and an Amberlite XAD-2 resin column to trap dissolved hydrophobic compoimds. Various filter combinations were tested and, in all runs, filter plugging was observed. 

Figure 11. Diagram of system used to carry out automated preconcentration and analysis of water samples. Detection accomplished with UV absorption and photochemical dehalogenation with subsequent fluorescence detection of the photochemical reaction products. (Reproduced with permission from reference 50. Copyright 1982 Vieweg.)...

Winge et al. [730] have investigated the determination of twenty or more trace elements in saline waters by the inductively coupled plasma technique. They give details of experimental procedures, detection limits, and precision and accuracy data. The technique when applied directly to the sample is not sufficiently sensitive for the determination of many of the elements at the low concentrations at which they occur in seawater, and for these samples preconcentration techniques are required. However, it has the advantages of being amenable to automation and capable of analyzing several elements simultaneously. 

Riu et al. [542] has reported the determination of linear ethyl benzane-sulfates in coastal waters using automated solid-phase extraction followed by capillary electrophoresis with ultraviolet detection, and confirmed by capillary electrophoresis-mass spectrometry. The detection limits were 1 pg/1 when 250 ml of coastal water was preconcentrated. 

Sample preconcentration was performed by means of an automated on-line SPE sample processor Prospekt-2 (Spark Holland, Emmen, The Netherlands). Oasis HLB cartridges (Waters, Barcelona, Spain) were used to preconcentrate cannabi-noids present in the water samples whereas isolation of the rest of the compounds was done in PLRPs cartridges (Spark Holland). Before extraction, influent samples were diluted with HPLC water (1 9, v/v) to reduce matrix interferences and to fit some analyte concentrations, e.g., cocaine (CO) and benzoylecgonine (BE), within the linear calibration range. A sample volume of 5 mL was spiked with the internal standard mixture (at 20 ng/L) in order to correct for potential losses during the analytical procedure, as well as for matrix effects. Elution of the analytes to the LC system was done with the chromatographic mobile phase. 

Automated online SPE LC systems are used extensively for environmental assays. Trays of SPE cartridges and autosampler can be used in the field. Water samples are preconcentrated trays of SPE cartridges loaded with analytes are brought to the laboratory and mounted onto an online SPE LC/ MS/MS system for analysis. Prospekt and Symbiosis systems were used for monitoring herbicides and transformation products (Hogenboom et al. 1998,1999a and b Lopez-Roldan et al. 2004 Kato et al. 2003 Lacorte and Barcelo 1995 Ferrer and Barcelo 1999,2001 Riediker et al. 2002), phenols... 

In 1994, Dadfarnia and McLeod described the analysis of uranium in surface waters and sea water using a simple FI system with an alumina column for preconcentration.77 Species eluted from this column were delivered to an ICP-MS as the detector. Also in 1994, Hollenbach et al. described the automation of extraction chromatographic methods based on TRU-Resin and TEVA-Resin to separate and preconcentrate U, Th, and Tc from soil samples, using ICP-MS for detection.49125 In 1996, Aldstadt et al. described the use of FI and extraction chromatography using TRU-Resin to determine U in environmental samples by ICP-MS.78... 

Figure 13.14 LC-diode-array detection (DAD) chromatogram (at 220 nm) obtained after preconcentration of 50 ml of ground water sample spiked with various pollutants at levels of 3 p.g l-1 passed through (a) a PLRP-S cartridge and (b) an anti-isoproturon cartridge. Peak identification is as follows 1, chlortoluron 2, isoproturon plus diuron 3, linuron 4, diben-zuron , water matrix. Reprinted from Journal of Chromatography, A 777, I. Ferrer et al. Automated sample preparation with extraction columns by means of anti-isoproturon immunosorbents for the determination of phenylurea herbicides in water followed by liquid chromatography diode array detection and liquid chromatography-atmospheric pressure chemical ionization mass spectrometry , pp. 91-98, copyright 1997, with permission from Elsevier Science.

In the 1980s, an analytical technique was developed for the study of chromium speciation in natural waters based on the atomization of electrodeposited species on graphite tubes.79 Two independent automated platforms consisting of an ultraviolet (UV) on-line unit and a chelation/preconcentration/... 

Katarina, R.K., N. Lenghor, and S. Motomizu. 2007. On-line preconcentration method for the determination of trace metals in water samples using a fully automated pretreatment system coupled with ICP-AES. Anal. Sci. 23 343-350. 

In some cases, ultrasonic nebulization or preconcentration is used to enhance detection limits. As, Se, and Sb were measured in cloud water detection limits were 20, 100, and 20 pg/mL, respectively, using pneumatic nebulization and four to five times lower using ultrasonic nebulization [311]. In another study [312], activated charcoal from a 1-L sample volume was used to preconcentrate Pd and Pt in fresh waters. Detection limits were 0.3-0.8 ng/L. An automated online preconcentration system based on a cationic resin (AG50W-X8) was used to measure Cd, Pb, Ni, Cu, and Zn. A preconcentration factor of 30 was obtained even with a sample throughput of 20 samples per hour [313]. 

Guedes da Mota, M. M., Rdmer, F. G., Griepink, B. Automated separation and preconcentration of copper II from natural waters using a column treatment. Z. Anal Chem. 287, 19(1977)... 

Generally, preconcentration of pollutants from water samples and sample preparation steps are accomplished by extraction techniques based on enrichment of liquid phase (liquid/liquid extraction) or solid phase (solid/liquid extraction) ". Historically, liq-uid/liquid extraction (LEE) was used exclusively to enrich phenols from water samples. LEE is still used as a preconcentration step . However, there is an increasing tendency to replace LEE by solid phase extraction (SPE) and solid phase microextraction (SPME). Among the reasons for replacing LEE are foam formation, the large volume of organic solvents needed, the length of the analysis time and difficulties in the automation of LEE procedures. On the other hand, SPE requires incomparable smaller amounts of solvents (SPME requires no solvent at all) and can be easily automated . Finally, SPE and SPME are cheaper in comparison with LEE. 

Marvin, C. H., Brindle, I. D., Hall, C. D., and Chiba, M., Development of an automated high-performance liquid chromatographic method for the online preconcentration and determination of trace concentrations of pesticides in drinking water, J. Chromatogr., 503, 167-176, 1990. 

Brossa et al. developed an automated SPE-GC-MS method for the determination of endocrine disrupting compounds including six phthalate esters. The interface device was a programmed temperature vaporizer (PTV), whose liner was packed with Tenax. The samples were spiked with 50% of methanol and 15 ml of this mixture were preconcentrated. Before elution, the precolumn was dried with nitrogen. The analytes were desorbed in the backflush mode with three ethyl acetate fractions of 100 /rl and online transferred to the GC system. The performance of the method was tested with several environmental water samples. The recoveries achieved were satisfactory and the detection limits were between 1 to 36 ng/1. 

The sampling of water for the determination of traces of organic pollutants requires a preconcentration step. The use of sorptive pre-columns Is a representative example of the Inability to separate sample collection and treatment, which are carried out In a single step. This analytical methodology Is described In greater detail in Chapter 11, dealing with the automation of chromatographic processes. 

A more recent development is the use of formed plastics, especially opencell type resilient polyurethanes, for the separation and/or preconcentration of trace species from water samples. The main advantages of these materials are a quasimembrane structure which allows rapid solid/liquid or solid/gas contact in column operation and the ability to immobilize a variety of reagents as collectors and so act as a highly versatile solid phase support. The resilience of these foams permit their use in special modes such as automated batch pressure or pulsating column operation [10]. 

Since the optimum detection limit of the automated method for the determination of mercury in natural waters used in this work is at or close to the level of mercury in natural waters, some improvements in the method are necessary before it can be used on a routine basis for monitoring the mercury concentrations in natural waters. Fortunately, the FAA technique is flexible enough to allow greater sensitivity in a number of ways. The two principal methods of improving the sensitivity have involved preconcentration (27) and the maximization of the physical parameters in the aeration-atomic absorption system (25). 

---