Surface waters analytical methods

This analytical method determines levels of major oxanilate and sulfonate soil metabolites of acetochlor, alachlor, and metolachlor in groundwater and surface water. The method consists of analysis of environmental samples by direct aqueous injection reversed-phase LC/MS/MS. 

FurtmannK. 1994. Phthalates in surface water—a method for routine trace level analysis. Fresenius Journal of Analytical Chemistry 348(4) 291-296. 

Triazine herbicides represent another class of herbicides that are found widely in groundwater and surface water. This method uses the automated analysis of 10-mL water samples by SPE followed by analysis directly by GC/MS (Brinkman, 1995). The method uses innovative technology to interface the SDU of the PROSPEKT with a precolumn in the GC. The GC is modified such that the sample may be injected onto a precolumn, which is essentially a retention gap column of uncoated deactivated fused-silica capillary that is several meters in length, with the analytical column off-line (see Fig. 10.20). Then the GC may be turned on and analyze the sample automatically. Because the retention-gap column is uncoated, there is refocusing of the analyte on the retaining precolumn, even with large injection volumes of up to 100 pL. 

In the case of surface water, the LOQ must not exceed a concentration which has an impact on nontarget organisms deemed to be unacceptable according to the requirements of Annex VI. At present, no harmonized limits for surface water exist. Therefore, provisions in Annex VI of Directive 91/414/EEC will be used to calculate guidance limits for analytical methods for surface water. In SANCO/825/00 the limits given in Table 6 are established [the relevant concentrations (the lowest will always be taken into consideration) depend on the species as indicated and can be taken from toxicity tests]. 

The method using GC/MS with selected ion monitoring (SIM) in the electron ionization (El) mode can determine concentrations of alachlor, acetochlor, and metolachlor and other major corn herbicides in raw and finished surface water and groundwater samples. This GC/MS method eliminates interferences and provides similar sensitivity and superior specificity compared with conventional methods such as GC/ECD or GC/NPD, eliminating the need for a confirmatory method by collection of data on numerous ions simultaneously. If there are interferences with the quantitation ion, a confirmation ion is substituted for quantitation purposes. Deuterated analogs of each analyte may be used as internal standards, which compensate for matrix effects and allow for the correction of losses that occur during the analytical procedure. A known amount of the deuterium-labeled compound, which is an ideal internal standard because its chemical and physical properties are essentially identical with those of the unlabeled compound, is carried through the analytical procedure. SPE is required to concentrate the water samples before analysis to determine concentrations reliably at or below 0.05 qg (ppb) and to recover/extract the various analytes from the water samples into a suitable solvent for GC analysis. 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

The following is a general method for ground and surface water samples. Interferences in particular samples may require modification of this method. The analytical sample size is 200 mL, but the volume may be varied depending on the concentration of analytes in the sample. 

Method validation determined the limit of detection (LOD) to be 1 ngL (ppt) for isoxaflutole, 1 ngL for RPA 202248 and 3 ngL for RPA 203328. However, after experience with a number of surface waters with high levels of matrix components, the method LOD was increased to 3 ng L for all three analytes. RPA 202248 also proved to be particularly sticky and prone to carry over. Over time, this produced abackground level, which also prevented determinations below the 3ngL method LOD. 

Even before a method is developed for detecting the presence of a pesticide or pesticides in the environment, the level of sensitivity in the method that will be needed for fate and monitoring studies to adequately portray the behavior of the analytes in the environment must be assessed. For example, in surface water monitoring programs. 

As more sensitive analytical methods for pesticides are developed, greater care must be taken to avoid sample contamination and misidentification of residues. For example, in pesticide leaching or field dissipation studies, small amounts of surface soil coming in contact with soil core or soil pore water samples taken from further below the ground surface can sometimes lead to wildly inaccurate analytical results. This is probably the cause of isolated, high-level detections of pesticides in the lower part of the vadose zone or in groundwater in samples taken soon after application when other data (weather, soil permeability determinations and other pesticide or tracer analytical results) imply that such results are highly improbable. 

An analytical procedure that quantifies the total AE concentration resolved by alkyl chain length for various environmental matrices (influent, effluent, and river water) was developed by Di Corcia et al. [41]. The method utilises a reverse-phase column to extract and concentrate AE from surface waters and wastewaters and utilises strong anionic and cationic exchange columns to remove potential interferences. Samples are passed through the RP extraction column (Ci). AE and potential anionic and cationic interferences are eluted from the Ci column and passed directly through the SAX and SCX. The SAX and SCX columns retain anionic and cationic materials while non-ionic AE are not retained. Recovery of AE from influent, treatment plant effluent, and river water is quantitative (65—102%) over a range of concentrations for all matrices. 

To put things into perspective, we. can broadly classify these analytical methods into bulk, dry surface, and in situ interfacial techniques. This chapter focuses on the last category, illustrating two in situ techniques used to study anion binding at the goethite (a-FeOOH)-water interface titration calorimetry and cylindrical internal reflection-Fourier transform infrared (CIR-FTIR) spectroscopy. In fact, CIR-FTIR could prove to be extremely powerful, since it allows direct spectroscopic observation of ions adsorbed at the mineral-water interface. 

Many of the analytes of interest for solid phase chemical reference materials are the same as those in seawater, but the need for and the preparation of reference materials for suspended particulate matter and sediments is quite different. The low concentrations of many seawater species and the presence of the salt matrix create particular difficulties for seawater analyses. However while sediments frequently have higher component concentrations than seawater, they also have more complicated matrices that may require unique analytical methods. A number of particulate inorganic and organic materials are employed as paleoceano-graphic proxies, tracers of terrestrial and marine input to the sea, measures of carbon export from the surface waters to the deep sea, and tracers of food-web processes. Some of the most important analytes are discussed below as they relate to important oceanographic research questions. 

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