Recovery technique summary table

Table II. Summary of Recovery Data (M icroextr action-Deri vatization Techniques)...

As an extraction technique, SFE proved to give comparable recoveries to those of Soxhlet extraction. In all cases, SFE dramatically shortened extraction times and minimized most environmental hazards, solvent concentration steps, and waste disposal costs. A summary of this comparison is included as Table XII and is a projected cost comparison of SFE to Soxhlet extraction, based on our experiences with the SFE system used in these studies (Isco SFE System 1200). The projected cost per extraction was determined to be 15.85(SFE) vs. 22.60(Soxhlet). 

ED appears to be an inefficient method to recover free citric acid because of its low electric conductivity (Novalic et al., 1995). As it is converted into the monovalent (at pH ca. 3), divalent (at pH ca. 5), or trivalent (at pH about 7) citrate anion, there is a significant increase in the electric conductivity (%), the latter increasing from 0.95 to 2.18 and to 3.9 S/m, respectively, in the case of an aqueous solution containing 50 kg/m3 of citric acid equivalent (Moresi and Sappino, 1998). By increasing the pH from 3 to 7, e reduced about eight times, the solute flux (JB) practically doubled, while the overall water transport (/w) increased 3-4 times. The latter partly counterbalanced the greater effectiveness of the electrodialytic concentration of citric acid at pH 7 with respect to that at pH 3. Table XV presents a summary of the effect of current density ( j) on the main performance indicators of the electrodialytic recovery of the monovalent, divalent, or trivalent ionic fractions of citric acid (Moresi and Sappino, 1998). All the mean values or empirical correlations of the earlier indicators were useful to evaluate the economic feasibility of this separation technique (Moresi and Sappino, 2000). 

A summary of Georgia Tech and G-P formaldehyde chamber recoveries in Table V indicates good agreement between chambers, and there appears to be no major formaldehyde losses within the chambers considering experimental error of the techniques used. 

Table 7.7 A summary of solvent recovery and disposal techniques...

Chromatographic techniques require various procedures to isolate the drugs from biological matrices. In the reviewed methods, two distinct approaches are applied liquid-liquid extraction and direct injection into a chromatographic system. Diethyl ether and ethyl acetate,chloroform,toluene, benzene, methyl r-butyl ether, and n-butyl chloride are used as solvents to obtain recoveries well over 80% for all considered compounds. However, manual sample preparation can be labor and time intensive. Therefore, direct injection is used as a highly automated methodol-ogy. The direct injection of complex samples, however, may lead to contamination of columns, thereby impairing their performance. Contamination often persists, even when a precolumn is used to protect the analytical column. A summary of these chromatographic methods for determination of sulfonylureas is presented in Table 1. 

Limitations of this technique include the extended length of time required for analysis, the lack of automation capability, and its relatively poor repeatability compared with other techniques, all of which limit its usefulness for routine analysis. Because of sample pipetting uncertainties and variation in the sample vaporization step, the relative precision (10—15% RSD) of this technique is not as good as that achieved by solution nebulization methods. Table 5.3 shows a summary of precision and the percent recovery of various analyte elements for a 1 p.g/L standard solution. 

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