Extraction conditions and analysis

Barnes, S., Kirk, M., and Coward, L., Isoflavones and their conjugates in soy foods extraction conditions and analysis by HPLC-mass spectrometry, J. Agric. Food Chem., 42, 2466, 1994. 

Once the proper HPLC conditions were achieved for VI, a study was conducted to determine which pH and extraction solvent would be optimum. For this study 100 ng of VI was added to 1 ml of plasma taken from laboratory workers known to be free of marijuana. Each plasma was run in triplicate using pH and extraction conditions shown in Table VII. As a result of these studies, a pH of 4 and benzene containing 1.5% isopropanol was used as the extracting conditions for analysis of VI since this pH gave consistently better appearing chromatograms than did pH 2.5. 

The optimised HS-SPME extraction conditions and other parameters finally selected for use in sample preparation prior to GC-MS analysis are given in Table 3. 

A method for the determination of silica in seawater using solvent extraction is described. EtOAc extraction was used in the determination of molybdosilicic acid 3 M H2SO4 was chosen as the extraction condition, and the absorbance measurements were made at 3350 A. At this acid concentration the interference by phosphate was small. The solvent extraction method was quick and eliminated the necessity for filtering turbid waters before analysis. 

In bioanalytical studies it is always necessary to collect appropriate blank samples. These blank samples are the matrices that have no measurable amount of the analyte of interest. The ideal blank will be collected from the same source as the samples, but will be free of analyte. All the conditions related to the collection of the blank sample—storage, pretreatment, extraction, concentration, and analysis— have to be the same as for the actual samples. Such an ideal blank sample is not always available, so often a compromise is necessary. For example, when an... 

To determine secondary alkanesulfonates in sewage wastewaters, solid phase extraction (SPE) and a single-step procedure which combines elution and injection port derivatization for analysis with GC-MS were developed [36]. Again a tetrabutylammonium ion pair reagent was employed both to elute the secondary alkanesulfonates as their ion pairs from CI8-bonded silica disks and to derivatize sulfonate ion pairs under GC injection port conditions. Secondary alkanesulfonates were effectively recovered from samples of raw sewage (>92%) and from primary (>98%) and secondary (>85%) effluents. No... 

Topal, U. et al.. Extraction of lycopene from tomato skin with supercritical carbon dioxide effect of operating conditions and solubility analysis, J. Agric. Food Chem., 54, 5604, 2006. 

Supercritical fluid extraction (SFE) is generally used for the extraction of selected analytes from solid sample matrices, but applications have been reported for aqueous samples. In one study, recoveries of 87-100% were obtained for simazine, propazine, and trietazine at the 0.05 ug mL concentration level using methanol-modified CO2 (10%, v/v) to extract the analytes, previously preconcentrated on a C-18 Empore extraction disk. The analysis was performed using LC/UV detection. Freeze-dried water samples were subjected to SFE for atrazine and simazine, and the optimum recoveries were obtained using the mildest conditions studied (50 °C, 20 MPa, and 30 mL of CO2). In some cases when using LEE and LC analysis, co-extracted humic substances created interference for the more polar metabolites when compared with SFE for the preparation of the same water sample. ... 

For an individual pesticide (e.g., carbendazim) or a limited class of pesticides (e.g., carbamates, benzoylphenylureas, pyrethroids ), it may be possible to optimize the SPE conditions so that the pesticide(s) are selectively retained on the cartridge. A wash step can be introduced to elute the matrix selectively, thus producing an extremely clean extract. For example, when cleaning up sample extracts for carbendazim analysis, a cation-exchange (SCX) cartridge may be used and the pH carefully controlled to retain the carbendazim firmly, whilst the co-extractives are washed to waste. The carbendazim residues can then be eluted from the column by adjusting the pH. 

Principles and Characteristics A first step in additive analysis is the identification of the matrix. In this respect the objective for most polymer analyses for R D purposes is merely the definition of the most appropriate extraction conditions (solvent choice), whereas in rubber or coatings analysis usually the simultaneous characterisation of the polymeric components and the additives is at stake. In fact, one of the most basic tests to carry out on a rubber sample is to determine the base polymer. Figure 2.1 shows the broad variety of additive containing polymeric matrices. 

Brandt [200] has extracted tri(nonylphenyl) phosphite (TNPP) from a styrene-butadiene polymer using iso-octane. Brown [211] has reported US extraction of acrylic acid monomer from polyacrylates. Ultrasonication was also shown to be a fast and efficient extraction method for organophosphate ester flame retardants and plasticisers [212]. Greenpeace [213] has recently reported the concentration of phthalate esters in 72 toys (mostly made in China) using shaking and sonication extraction methods. Extraction and analytical procedures were carefully quality controlled. QC procedures and acceptance criteria were based on USEPA method 606 for the analysis of phthalates in water samples [214]. Extraction efficiency was tested by spiking blank matrix and by standard addition to phthalate-containing samples. For removal of fatty acids from the surface of EVA pellets a lmin ultrasonic bath treatment in isopropanol is sufficient [215]. It has been noticed that the experimental ultrasonic extraction conditions are often ill defined and do not allow independent verification. 

Modifiers can be used very effectively in on-line SFE-GC to determine the concentration levels of the respective analytes. This presents an advantage in terms of the use of modifiers in SFE, since they appear as solvent peaks in GC separations and do not interfere with the target analyte determination. Although online SFE-GC is a simple technique, its applicability to real-life samples is limited compared to off-line SFE-GC. As a result, on-line SFE-GC requires suitable sample selection and appropriate setting of extraction conditions. If the goal is to determine the profile or matrix composition of a sample, it is required to use the fluid at the maximum solubility. For trace analysis it is best to choose a condition that separates the analytes from the matrix without interference. However, present SFE-GC techniques are not useful for samples... 

---