Solid phase extraction loading

It is noteworthy that trifluoroacetic acid was introduced as the most appropriate acidifler for column chromatography and solid phase extraction techniques, i.e., low boiling point due to its high acidity, requiring low amounts to reach the respective pH. Also, its high volatility allows easy evaporation thus minimizing the thermal load and acidification during concentration. 

Application of SPE to sample clean-up started in 1977 with the introduction of disposable cartridges packed with silica-based bonded phase sorbents. The solid phase extraction term was devised in 1982. The most commonly cited advantages of SPE over liquid-liquid extraction (LLE) as practiced on a macroscale include the reduced time and labor requirements, use of much lower volumes of solvents, minimal risk of emulsion formation, selectivity achievable when desired, wide choices of sorbents, and amenability to automation. The principle of operation consists of four steps (1) conditioning of the sorbent with a solvent and water or buffer, (2) loading of the sample in an aqueous or aqueous low organic medium, (3) washing away unwanted components with a suitable combination of solvents, and (4) elution of the desired compound with an appropriate organic solvent. 

Initial Fractionation. The most effective method found for the initial fractionation of the complex enzyme mixtures present in wood-culture extracts was anion exchange chromato phy eluting with salt gradients (9,74,75). This permitted further sample concentration by functioning as a solid phase extractant during loading. It also showed higher sample capacity and better separations than other methods. 

Figure 13.11 Electropherogram of a solid-phase extraction sample in acetonitrile/ methanol [87.5/12.5 (v/v)] containing 2.5 mM NaOH and 1.0 mM SDS, derived from a seawater sample spiked with 0.5 [tg/L of TNT, TNB, and tetryl. Applied separation field strength, —506 V/cm, using a 10-s floating load. (Reprinted from [38] with permission from Elsevier.)...

Typically solid phase extraction is based on the type of system shown in Figure 15.5. The volume of sample which can be loaded onto this small column can be increased using a column with a larger sample reservoir. The sample is usually aspirated through the column under vacuum. 

Fig. 18.1 Systems used to absorb aroma compounds from samples for analytical purposes, a Traps loaded with various adsorbents [4]. b Solid-phase extraction (disk in a holder assembly) [5]. c Solid-phase microextraction (coated needle inserted in sample) [5]. d Twister (1 -cm length) [4]. (Courtesy of GERSTEL GmbH and Co. KG)...

Solid-phase extraction for milk, urine, and feces samples is carried out by washing the loaded Cig cartridge successively with 5 ml water, 5 ml acetone/ water (20 80), 5 ml methanol/water (20 80), 5 ml dichloromethane/hexane (20 80), and 5 ml ethyl acetate/hexane (10 90). The corticosteroids are eluted with 3 ml ethyl acetate. The eluate is evaporated, and the residual is reconstituted in 0.5 ml ethanol and 5 ml phosphate-buffered saline, pending subsequent immunoaffinity column cleanup. The solid-phase extraction procedure differs for liver samples. In that case, washing of the cartridge is performed with 5 ml water, 5... 

Solid-phase extraction was also evaluated for its potential to achieve the desired cleanup. Either Cig or Cg cartridges were loaded with defatted and deproteinized milk extracts, washed with water or water-methanol, and elution of the analytes was performed with methanol (553). The recoveries in this case were also poor. These results of poor recovery for solid-phase extraction and both acidic and basic extractions are consistent with those reported in the literature (553, 557). 

The solid-phase extractant will become colored. Stop loading sample if excessive color is passing through the cartridge (see Critical Parameters and Troubleshooting, discussion of anthocyanin purification). 

Solid phase extraction applicable to extracts of carrot, orange juice, peach, tomato, vegetable soup. Load hexane extracts onto alumina N Sep-Pak cartridge. Elute a- and /3-carotene with hexane/acetone, 96.5 3.5 and /3-cryp-toxanthin with acetone... 

The analyte binding efficiency is matrix dependent. Some matrices, such as urine and tissue extracts, can be directly loaded onto the column, other matrices such as milk may need sample processing prior to loading onto an immunoaffinity column. The simplest sample preparation method is dilution this method has been applied to serum, liver, and kidney extracts after removal of particulates. Sometimes dilution alone is not sufficient to eliminate the matrix effect and classical sample preparation techniques (solvent/solvent extraction, solid phase extraction, etc.) will be necessary prior to immunoaffinity chromatography. We found milk often needs this type of treatment. 

The DNPH derivatives may also be extracted by solid-phase extraction (liquid-solid extraction). The sorbent cartridge is conditioned with 10 mL of dilute 1 M citrate buffer solution (1 25 dilution) and 10 mL of saturated NaCl solution. The cartridge is then loaded with the extract and the derivatives eluted with acetonitrile. 

Figure 3.23. Steps in solid-phase extraction (a) column conditioning, (b) sample loading, (c) column rinsing, and (d) elution. (Adapted from Ref. 62 with permission.)...

The IS concentration should not be so high as to cause issues of solubility or exceed the loading capacity of solid-phase extraction (SPE) cartridges or similar products. 

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