Static extraction

The effect of different pai ameters such as temperature, pressure, modifier volume, dynamic and static extraction time on the SFE of the plant were investigated. The orthogonal array experimental design method was chosen to determine experimental plan, (5 ). In this design the effect of five parameters and each at five levels were investigated on the extraction efficiency and selectivity [4]. 

SFE can be carried out in three different ways. In a static extraction (no flow-rate), the extraction vessel is pressurised to the desired pressure with the extracting fluid and then simply left for a certain length of time. The main benefit of this method is that the fluid has time to penetrate the matrix. It is most applicable when the analyte has a high affinity for the solvent and a low affinity for the matrix and also when the solubility limit of the analyte in the fluid is much higher than the actual level reached during the extraction [89]. This method was popular in early SFE experiments but has declined in favour of dynamic SFE. Here, fresh SCF is continuously passed over the sample, extracting soluble compounds and depositing them in a suitable solvent or on a solid trap. The dynamic mode is particularly useful when the concentration of the solute... 

Kreisselmeier and Diirbeck [28] extracted alkylphenols, NPEO and OPEO by SFE using methanol as a modifier. The extraction pressure had to be set as high as possible (>450 atm), with a dynamic extraction time of 30 min. Neither an elevation of the temperature from 100 to 150°C nor an extension of the static extraction time improved the recovery. Comparable results were even obtained at 30°C while omitting the static extraction step. The modifier proved again to be quite important, as the recoveries increased by 20% with the addition of 27.5% methanol. Problems arose with the extraction of aged samples, for which the extractability was reduced by 40% for NPEO and NP, and 22% for OPEO. 

Shang et al. [5] used ASE for the extraction of NP and NPEO from estuarine sediments. A sample of 15-25 g was extracted three times using hexane/acetone at 100°C and 103 atm. This was followed by a clean-up step using CN-SPE. A blank sample was extracted between all samples to avoid contamination. Hexane/acetone was also used in the ASE method for alkylphenols and NPEO by Heemken et al. [12]. Extraction conditions for samples of 0.5-1 g were 100°C, 150 atm, with a static extraction step of 15 min, and a rinse step with 20 mL solvent. After a clean-up by HPLC, the analytes were derivatised with heptafluorobutyric acid anhydride for GC analysis. 

Extractions can be carried out in dynamic, static, or combination modes. In the dynamic mode, the supercritical fluid continuously flows through the sample in the extraction vessel and out the restrictor to the trapping vessel. In the static mode, the supercritical fluid circulates in a loop containing the extraction vessel for some period of time before being released through the restrictor to the trapping vessel. In the combination mode, a static extraction is performed for some period of time, followed by a dynamic extraction. 

Low-volatizing, nonaqueous solvent e.g., propylene glycol (for static extraction) Liquid nitrogen or other cryogenic liquid... 

If the peak area is too small for detection or for reasonable calculations (i.e., <10% of the peak area from sample analysis), the static extraction analysis should be repeated with a more concentrated solution. 

If another GC peak resulting from SPME of the sample or other extractions is larger than the peak observed, the fiber is not saturated. Saturation can be tested (see Critical Parameters). If the fiber is saturated, or if the GC peak is flat at the top or exceeds the detector limits, the static extraction and SPME analysis should be repeated with a less concentrated solution. 

With the 12-vessel extractor, the 1/8" valve receives the extraction effluent from the vessels in tandem column selectors 1 and 2 (TCS-1 and TCS-2) into two separate ports 1 and 4 as shown in Figure 7. During the static mode, the counter-current valves, i.e. modifier pump valves (MP-3 and MP-4) are closed. Pressure build-up for static extraction then follows. Valves MP-3 and MP-4 are mounted close to the ports so that no accumulation of extract occurs. The valves are connected via a stainless steel tee (T2), to the modifier pump which is also used for flushing the lines after the extractions have been conducted. In the dynamic mode, extract flows from the unblocked ports of 1 and 4 to ports 5 and 6 then through to the delivery nozzles. 

Step 4 is the introduction of the modifier for the second static extraction Step 5 is a second static extraction. 

Step 1 is a dynamic flush of the first static extraction at 300 atm modifier (methanol/water) was added before the initial extraction began. 

When the experiments were performed at the same pressure, temperature, and moisture content but with toluene as modifier and with a static extraction time of 15 or 30 min prior to the dynamic extraction step, then recovery was most affected by moisture content (sum of ranks 88) followed by pressure (sum of ranks 70) and the toluene volume (sum of ranks 68). The fourth variable to influence was the static extraction time (sum of ranks 57). Temperature, volume of collection solvent, and the presence/absence of glass beads were the least important. Figure 6 shows the relative changes in recovery for each compound and for each of the seven variables investigated in Test 2. 

Figure 6. Relative change in percent recovery (when going from low to high) for the 15 target compounds identified in Table IX (test 2). The variables are identified as follows pressure (P), temperature (D), volume of toluene as modifier (F), volume of collection solvent (G), moisture (M), glass beads (B) and static extraction time (E). The 15 compounds are those listed in Table DC...

Figure 3. Static extraction apparatus (A) pressurization mode and (B) equilibration mode...

Quantitative analysis is best performed on liquid samples or on solutions prepared from solid samples. This approach is not possible when a suitable solvent cannot be found. Multiple static extractions can be conducted in these situations. 

Multiple static extractions can be conducted until the sample is exhaustively extracted. The result is the sum of the individual extractions. This, however, can be a time-consuming process. 

The use of SCCO2 in extraction and chromatography has recently been reviewed. Equipment is commercially available for both processes, on a large and small scale, and the two techniques can be hyphenated. Essentially, for static extractions, a pressure vessel and carbon dioxide pump are required, but most extractions are performed under flow conditions that require an additional back-pressure regulator and flow meter. It should be noted that... 

For a 10 ml vessel with a flow of 3 ml/min and a 3/8 inch diameter at a CO2 pressure of 350 atm., the Reynolds number is 73, and the Schmidt number is 6.6. Substituting these values into Eq. 4 yields a mass transfer rate six times greater for viscous flow versus static extraction. 

Assuming that the rate of mass transfer is proportional to the concentration difference over the membrane according to Equation 12.1 and noting that in static extraction, the concentration in the donor phase Cd decreases as analyte is transferred over the membrane. We get the following differential equation ... 

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