Preparation techniques buffers

Sample preparation techniques vary depending on the analyte and the matrix. An advantage of immunoassays is that less sample preparation is often needed prior to analysis. Because the ELISA is conducted in an aqueous system, aqueous samples such as groundwater may be analyzed directly in the immunoassay or following dilution in a buffer solution. For soil, plant material or complex water samples (e.g., sewage effluent), the analyte must be extracted from the matrix. The extraction method must meet performance criteria such as recovery, reproducibility and ruggedness, and ultimately the analyte must be in a solution that is aqueous or in a water-miscible solvent. For chemical analytes such as pesticides, a simple extraction with methanol may be suitable. At the other extreme, multiple extractions, column cleanup and finally solvent exchange may be necessary to extract the analyte into a solution that is free of matrix interference. 

A number of developments have increased the importance of capillary electrophoretic methods relative to pumped column methods in analysis. Interactions of analytes with the capillary wall are better understood, inspiring the development of means to minimize wall effects. Capillary electrophoresis (CE) has been standardized to the point of being useful as a routine technique. Incremental improvements in column coating techniques, buffer preparation, and injection techniques, combined with substantive advances in miniaturization and detection have potentiated rugged operation and high capacity massive parallelism in analysis. 

In the separation of biomolecules, sample preparation almost always involves the use of one or more pretreatment techniques. With high-performance liquid chromatography (HPLC), no one sample preparation technique can be appHed to all biological samples. Several techiques may be used to prepare the sample for injection. For example, complex samples require some form of preffactionation before analysis, samples that are too dilute for detection require concentration before analysis, samples in an inappropriate or incompatible solvent require buffer exchange before analysis, and samples that contain particulates require filtration before injection into the analytical instrument. 

The sample-preparation technique may depend on a number of variables, for example the molecular weight of sample and interferences, the sample volume and analyte concentration, buffer salt (anion and cation) content and metal concentration and type. Other than filtration for particulate removal, most of the approaches are based on the use of chromatographic media for cleaning up samples before analysis. 

Liquid-liquid extraction is an important sample preparation technique from both historical and practical perspectives.18,19 LLE has been in use for many decades as an analytical sample pretreatment to remove unwanted matrix components20 or to selectively extract components of interest from a mixture, thereby purifying and concentrating them for further workup. It is based on the principles of differential solubility and partitioning equilibrium of analyte molecules between two immiscible phases, usually aqueous and organic. Depicted in Figure 2, LLE initially involves pH adjustment of the original (aqueous) sample with an appropriate buffer. This pH adjustment is... 

The following protocol, which is derived from the one-step liposome preparation technique, originally described in (12) is suited. A slurry is made from a single phospholipid or a freeze-dried cake of lipid-blend and buffer (drug/marker solution). The slurry is processed using an APV MicronLab 40 lab-scale homogenizers. A micro-fluidizer Ml 10 may be used as well. 

The easiest method to assess the quality of two-dimensional crystals is by electron diffraction (10). Special preparation techniques may be necessary to preserve the order of two-dimensional crystals in the electron microscope. For LHC-II, washing with a dilute (0.5 %), buffered (pH 6.0) solution of tannin has proved most successful (9). Cooling the crystals to a temperature below -100 °C is essential to reduce the effect of radiation damage which is severe at room temperature. 

A. Tissue Slice Technique. B. Tissue Homogenates. C. Fractionation of Cellular Components. D. Methods of Extraction of Enzymes. E. Protein Fractionation. F. Preparation of Buffers. 

Brunkhorst R, Fromm S, Wronger E, Berke A, Petersen R, Riede G, Westphale J, Zamore E, Ledebo 1.1998. Automated peritoneal dialysis with on-line -prepared bicarbonate-buffered dialysate Technique and first clinical experience. Nephrol Dial Transplant 13(12) 3189-3192. 

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