Aqueous liquid samples

SC 6 Recommended operating procedure for taking aqueous liquid samples... 

CWC-related chemicals in aqueous liquid samples (water samples) are usually recovered by extraction with an organic solvent. Modem methods such as SPE and solid phase micro extraction (SPME) have also been presented 04 24). Organic extractions and these modem methods mainly recover nonpolar CWC-related chemicals, but leave behind the water-soluble and nonvolatile chemicals. These must also be recovered, however, because the agents tend to decompose (hydrolyze) rapidly under conditions in the environment. In the past few years, techniques such as CE and LC, relying on element specific or mass spectrometric detection, have been intensively developed to provide easy and effective ways of recovering these chemicals from water samples with only minor sample preparation (2S 44,1. For GC/MS analysis, the water must be displaced and the analytes derivatized. 

Figure 1. Schematic presentation of the recommended operating procedure for aqueous liquid sample preparation...

In addition, an appropriate portion of the aqueous liquid sample is filtered through an HPLC filter and the filtiate is analyzed by LC/MS and CE (Figure 1, fraction 6), and another portion is prepared for NMR analysis (fraction 7). 

Alternatively, an HPLC filter unit may be used for the filtration. The sample vessel is rinsed with a suitable amount of (deuterated) solvent and the rinsing solutions are added to the sample in the NMR tube. The pH of the aqueous liquid sample is determined, and can be adjusted with DC1 and NaOD solution. For measurements carried out in a standard 5-mm (o.d.) NMR tube, about 0.6-0.8 mL of solvent is required, and for 10-mm tubes, about 3-4mL. If considered necessary, some of the extractions can be performed with deuterated solvents, which will simplify the sample preparation procedure. Related practical sample preparations can be found in the literature (10 12 14 29). 

Ultrasound-assisted emulsification in aqueous samples is the basis for the so-called liquid membrane process (LMP). This has been used mostly for the concentration and separation of metallic elements or other species such as weak acids and bases, hydrocarbons, gas mixtures and biologically important compounds such as amino acids [61-64]. LMP has aroused much interest as an alternative to conventional LLE. An LMP involves the previous preparation of the emulsion and its addition to the aqueous liquid sample. In this way, the continuous phase acts as a membrane between both the aqueous phases viz. those constituting the droplets and the sample). The separation principle is the diffusion of the target analytes from the sample to the droplets of the dispersed phase through the continuous phase. In comparison to conventional LLE, the emulsion-based method always affords easier, faster extraction and separation of the extract — which is sometimes mandatory in order to remove interferences from the organic solvents prior to detection. The formation and destruction of o/w or w/o emulsions by sonication have proved an effective method for extracting target species. 

You are a chemist in a private analytical laboratory, and your specialty is determining ions in aqueous liquid samples such as mineral waters or pond water and the added ions in low acid foods. You are prepared to handle any of these samples. You have been given one of these by your boss as a quality control sample. 

Direct immersion headspace solid phase micro extraction, the SPME fibre is exposed directly into an (aqueous) liquid sample for collection of analytes. 

P 24] Aqueous NaOH solutions of 0.1,1.0 and 2.0 M were used, fed by pumps to the micro devices [5]. Carbon dioxide was supplied as a mixture with nitrogen, the flow rate being set by a mass-flow controller, liquid samples were taken and subjected to carbonate analysis (see original citation in [5]). 

Di Corcia, A., Marchetti, M., Samperi, R., and Marcomini, A., Liquid chromatographic determination of linear alkylbenzenesulfonates in aqueous environmental samples, Anal. Chem., 63, 1179, 1991. 

Liquid samples, in particular aqueous in nature, are the most frequently encountered (waste water, food and beverages, biological fluids, soil and agricultural samples). SPE is a well-established technique, which is... 

Liquid-liquid extraction Analyte extracted from liquid sample into an immiscible solvent Organic compounds in aqueous samples (e.g. pesticides in river water)... 

SPE) a flowing liquid sample by retention on a solid sorbent, followed by elution with a solvent aqueous samples (e.g. PAHs in waste water)... 

The simplest technique is the use of the 96-well collection plate format (analogous to the format used in SPE) in conjunction with a liquid handling robotic system it follows the same principle as bulk scale LLE. However, immobilization of the aqueous plasma sample on an inert solid support medium packed in a cartridge or in the individual wells of a 96-well plate and percolating a water-immiscible organic solvent to extract the analyte from this medium evoked significant enthusiasm from the pharmaceutical industry. 

Following the extraction, the undissolved solid material is then filtered out and the filtrate analyzed. Examples of this would be soil samples to be analyzed for metals, such as potassium or iron, and polymer him or insulation samples to be analyzed for formaldehyde residue. The extracting liquid may or may not be aqueous. Soil samples being analyzed for metals, for example, utilize aqueous solutions of appropriate... 

The complex composition of aqueous environmental sample matrices, especially sewage and marine water samples, and the low concentrations in which the surfactants are generally found, have made it necessary to perform an initial stage of concentration and purification of the analytes prior to its analysis. Traditionally, such steps were carried out off-line with procedures based on liquid—liquid extraction (LLE), sublation or steam distillation, followed by chromatographic clean-up steps. 

Many pesticides degrade to polar products that form organic anions in a water matrix. These are sometimes missed due to the difficulty in extracting trace amounts of the ionic material from a water matrix. A recently developed anion exchange procedure for isolating acidic compounds from dilute aqueous solutions (10-12) was used for recovering the anionic material from liquid samples collected from the two pits. 

Stepnowski, R, Solid-phase extraction of room temperature imidazolium ionic liquids from aqueous environmental samples. Anal. Bioanal. Chem., 381, 189, 2005. 

Before the extraction procedure may commence, the sample must be prepared in such a way that it is in a condition for extraction of the analyte(s). For analyzing sulfonamide residues in liquid samples such as milk, a pretreatment dilution step with water prior to direct fluorometric detection may be required (207). Dilution of milk with aqueous buffer (208) or sodium chloride solution (209) prior to sample cleanup has also been reported. For the analysis of honey a simple dissolution of the sample in water (210, 211) or aqueous buffer (212) is generally required. Semisolid samples such as muscle, kidney, and liver, require, however, more intensive sample pretreatment. The analyte(s) must be exposed to extracting solvents to ensure maximum extraction. The most popular approach for tissue break-up is through use of a mincing and/or homogenizing apparatus. Lyophilization (freeze-drying) of swine kidney has been carried out prior to supercritical-fluid extraction of trimethoprim residues (213). 

---