Experimental methods water column

Ribeyre F. 1991. Experimental ecosystems - comparative study of two methods of contamination of the water column by mercury compounds in relation to bioaccumulation of the metal by rooted macrophytes (ludwigia-natans). Environ Technol 12(6) 503-518. 

HPLC Experiments. The liquid chromatograph model ALC 202 of Waters Associates fitted with a differential refractometer was used in this work. The method of column preparation and the general experimental technique used were the same as those reported earlier (2). All experiments were carried out at the laljoratory temperature (23-25°C). The solvent (water) flow rate... 

Mo is removed from sulfidic waters by sorption of thiomolybdate ions on sinking particles. Rather, they postulated that Mo is incorporated into an Fe-Mo sulfide mineral phase that precipitates in euxinic waters below the depth where FeS becomes supersaturated and that solubility of this phase controls the Mo concentration in the sulfidic water column. This may be the same Fe-Mo phase that was experimentally precipitated by Flelz et al. [35] and was shown by EXAFS analysis to contain Mo tetrahedrally coordinated by S, as appears to be the case in some samples of black shale. To understand better the conditions in which Mo might precipitate as an Fe-Mo sulfide, Helz et al. [17] used thermodynamic methods to calculate the solubility of the putative sulfide phase as a function of pH, [Mo], and [H2S]. Their calculations predicted that only a narrow range of pH-[Mo]-[H2S] conditions will result in complete insolubility of Mo. Their model succeeded in predicting the Mo concentrations in deep waters in several other modern anoxic and euxinic areas. Helz et al. [17] concluded that the complete removal of Mo from the water column in the Black Sea is not representative of the general behavior of Mo in euxinic basins over time, but is instead the exception to the rule. 

For the experimental investigation of compressibility of superheated and saturated vapors, the method of the constant-volume nonballasted piezometer was employed. The fundamental variables (pressure, temperature, and mass of the substance) were measured with instruments of the same class as those used in the work of MEI. The distinguishing feature of the piezometric rig was the use of a membrane zero indicator of pressure of the electrocontact type. The sensitivity of this instrument reached 1 mm water column, but the zero point drifted by 10 mm water column. The authors in Refs. [2.19, 2.21] evaluated the scatter of experimental points on the saturation curve as 0.4% for pressure, and the repeatability of presssure during the forward and reverse tracing along the constant-volume lines was 0.15%. 

The recovery of gold by the carbon-in-pulp (CIP) method utilizes the strong adsorption of [Au(CN)2 ] onto the surface of activated carbon in alkaline (pH >11) regimes (Adams Fleming 1989 Adams 1993). The same mechanisms can be utilized to adsorb contaminants from a water column. At the present time only experimental studies have been carried out (Hegenberger et al. 1987 McEnamey 1988 van der Merwe van Deventer 1988). The technique has also been applied to volatile and dense organic solvents (Pankow Cherry 1996). 

A thin film of water spreads up the inside walls of the capillary because of strong adhesive forces between water and glass (water wets glass). The pressure below the meniscus falls slightly. Atmospheric pressure then pushes a column of water up the tube to eliminate the pressure difference. The smaller the diameter of the capillary, the higherthe liquid rises. Because its magnitude is also directly proportional to surface tension, capillary rise provides a simple experimental method of determining surface tension, described in Exercise 122. 

One of the first examples of the application of reverse-phase liquid chromatography-gas chromatography for this type of analysis was applied to atrazine (98). This method used a loop-type interface. The mobile phase was the most important parameter because retention in the LC column must be sufficient (there must be a high percentage of water), although a low percentage of water is only possible when the loop-type interface is used to transfer the LC fraction. The authors solved this problem by using methanol/water (60 40) with 5% 1-propanol and a precolumn. The experimental conditions employed are shown in Table 13.2. 

The experimental approaches are similar to those for solubility, i.e., employing shake flask or generator-column techniques. Concentrations in both the water and octanol phases may be determined after equilibration. Both phases can then be analyzed by the instrumental methods discussed above and the partition coefficient is calculated from the concentration ratio Q/Cw. This is actually the ratio of solute concentration in octanol saturated with water to that in water saturated with octanol. 

In order to preclude this problem and the necessary frequent regeneration of the anion system s suppressor column, an ion chromatography exclusion scheme was utilized. Samples collected in a mine environment were reliably concentrated by freeze-drying and then analyzed on an ICE system with dilute hydrochloric acid eluent. The precision of the ICE method was experimentally determined to be 2.5% in a concentration range of 1 to 10 yg/mL. The accuracy was not independently determined but good precision and recovery yield confidence that measured values are within 5% of the true value. No interferences were observed in the ICE system due to strong acids, carbonic acid or other water soluble species present in mine air subject to diesel emissions. 

In this case, we use two methods to make single measurements on several different samples. No measurement has been duplicated. Do the two methods give the same answer within experimental error Figure 4-7 shows measurements of aluminum in 11 samples of drinking water. Results for Method 1 are in column B and results for Method 2 are in column C. For each sample, the two results are similar, but not identical. 

Ultimately, the usefulness of tracer methods will partially depend upon how readily they can be incorporated into a field study. Methods that can be applied to filtered water samples are less labor intensive than those requiring some type of fractionation, such as the use of small-volume XAD-8 columns or ultrafiltration. However, column or ultrafiltration fractionation can be streamlined to make them practical for field studies, and the better resolution of DOM chemistry may make the extra effort worthwhile. If fulvic acid or high molecular weight fractions are isolated in a study, these can be saved for potential subsequent analysis of trace moieties as motivated by initial results. Finally, the overall question being addressed in a particular experimental or field study will determine which tracer methods, if any, are included. 

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