Fraction 30 samples, analytical

FIGURE 6.58 External standard curve obtained by FIA of fractionated samples (error bars represent + one standard deviation). Concentration values represent analyte concentrations injected onto MS system for FIA. 

Recovery is defined as the fraction of analyte detected, compared with what was added to a test sample (fortified or spiked sample) prior to analysis. 

Vl = volume fraction of analyte 7], = refractive index of pure analyte 172 = refractive index of pure solvent j] = refractive index of solution in sample cell... 

The analytical procedures for determining organic compounds in water samples usually involve a number of steps, such as solvent extraction, chemical fractionation, sample cleanup, and solvent reduction, before the final analysis is undertaken. Regardless of the complexity of the analytical procedure, however, almost all water samples are stored in a container for some time between... 

For LLE the liquid sample is mixed with a larger volume of a non-polar organic solvent to induce a partition equilibrium of the analyte between the aqueous and organic layer. Typically, the latter one contains the major fraction of analytes and is further processed for LC-MS analysis. In contrast to protein precipitation, LLE thus requires a subsequent drying step by evaporation or with a gentle stream of nitrogen... 

The simplest analytical information that can be obtained with the aid of FFF is the homogeneity of the sample or evidence for the presence of a compound of interest in the fractionated sample by the appearance of a peak in the expected interval of retention volume. In some cases, comparison of the retention volume and the peak shape of the investigated component with the peak shape of a reference sample can provide sufficient qualitative analytical information on sample purity and homogeneity. The peak areas in the fractogram can be used to evaluate quantitatively concentrations of the detected components provided that the relationship between detector response and concentration or quantity of the detected component is known. This relationship is usually determined by a calibration procedure. However some sample is lost in the void peak so that it is not possible to relate the detected concentration to that of the original sample consequently, concentration determinations can more advantageously serve to compare the relative concentrations of the fractionated components. 

Another important technique in lAC is the use of immobilized antibody columns to perform chromatographic (or flow-injection) immunoassays. One way this can be done is in a competitive binding format. The simplest approach to a competitive binding scheme is to mix the sample and a labeled analyte analog (the label) and apply these simultaneously to the lAC column this is a method known as a simultaneous injection competitive binding immunoassay. If the sample is applied to the lAC column and followed later by a separate injection of the label, then the technique is called a sequential injection competitive binding immunoassay. In both formats, an indirect measure of the sample analyte is obtained by examining the amount of label that elutes in either the nonretained or retained lAC fractions. 

X—weight fraction of liquid retained in the marc z—acceptable sample analytical error... 

The migration rate of a sample anion will be proportional to the ratio of [A-] [P- A-]. The fraction of sample anion present as the free anion (A ) will migrate rapidly toward the anode, while the fraction associated with the ion exchanger (P+A ) will move but slowly in the opposite direction. These equations show that salt concentration in the BGE (CE in the example) will have a major effect on sample analyte migration as well as the polymer ion concentration and the equilibrium constant, K. 

Water samples may contain appreciable amounts of particulate matter, dissolved organic carbon, or colloidal material and all of these may form associations with the analytes and affect their recoverability. For these reasons, discrepancies may arise between the concentrations of analytes determined by liquid extraction and those obtained by sorption on polyurethane or XAD resins (Gomez-Belinchon et al. 1988). Empirical procedures have been developed (Landrum et al. 1984) for fractionating samples to assess the relative contribution of the associations of xenobiotics with the various organic components, while sediment traps for collection of particulate matter have been extensively used in investigations in the Baltic Sea where appreciably turbid water may be present (Nat et al. 1992). 

With the array of extremely sensitive instruments now available, the analytical chemist can identify materials of odour interest that are present at very low levels in natural materials. However, we still rely on traditional techniques and laboratory skills to fractionate samples and isolate new materials for identification. 

Note that this computation is a summary of the individual calculation steps taken to arrive at the fraction of analyte in the sample using proper dimensional analysis. You should use it in that sense rather than simply memorizing a formula. 

Mester, Z., C. Cresmisini, E. Ghiara R. Morabito, 1998. Comparison of two sequential extraction procedures for metal fractionation in sediment samples. Analyt. Chim. Acta 359 133-142. 

In spite of the reduction in complexity that can be achieved by cellular fractionation, an analytical separation is frequently required to separate one or more components from the cellular milieu. As evidenced throughout this book, capillary electrophoresis (CE) provides high resolution and separation efficiency, both of which are necessary for subcellular analysis. In addition, CE is advantageous because it requires very little sample volume, typically less than a nanoliter, and generally very little sample preparation. Hence, capillaries have been used to directly sample subcellular compartments within neurons, oocytes, and muscle tissue sections. They have also been used to analyze individual organelles from a single cell following on-column lysis." ... 

Let Co represent the concentration of a particular analyte of interest after being extracted into an organic solvent whose volume is Vq from an aqueous sample whose volume is Faq. Assume also that the concentration of analyte that remains in the aqueous phase after extraction is Caq. Let us define the fraction of analyte extracted E by... 

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