Sample recovery rates

In the method described, the procedural blank determination is essential for the analytical procedure since it allows the estimation of all kinds of contaminations. To assess the matrix effect for each sample, recovery rates were determined. The checking of the half range of the calibration graph for each 10 runs of samples allowed the evaluation of calibration graph deviation. 

Obtaining realistic errors is one of the most difficult, yet most crucial problems in all flux estimates. Such errors can be approximated through an independent error analysis for several factors that are involved in estimating fresh and altered rock composition. There are uncertainties arising from petrographic observations, in the choices of representative samples, recovery rate biases, and analytical errors. In most cases analytical errors are a relatively minor source of uncertainty, and they are typically rather well documented. Probably the most crucial analytical uncertainty is in acurately determining the titanium concentration that is used as a normalizing factor to account for open-system behavior. This uncertainty directly relates to an error in the fluxes, and thus fluxes are difficult to constrain to better than 1 % of the whole rock abundance of a particular element. 

Sample stability becomes increasingly important as the time between sampling and analysis increases. Effects of temperature, trace contaminants, and chemical reactions can cause the collected species to be lost from the collection medium or to undergo a transformation that will prevent its recovery. Nearly 100% recovery is also required because a variable recovery rate will prevent quantification of the analysis. Interference should be minimal and, if present, well understood. 

For many proteins, especially glycoproteins, the physical characteristics, particularly the hydrophilic nature of Toyopearl HW resins, improve mass and activity recovery rates. Toyopearl HW media do not adsorb proteins, as conventional gels can, and thus do not interfere with sample recovery (39). 

Almost all fiber and partial titanium dioxide can be recovered from white water by DAF under full flow pressurization mode43 with chemical addition. On June 10, 1982, at Mead Corporation, pulp was prepared with 40% cotton fiber and 60% wood fiber. The loading of titanium dioxide was about 50% (i.e., 273 kg Ti02 per 600 kg total pulp). The white water from No. 2 machine was fed to a DAF cell (diameter = 3 m) at 15.8 L/s (250gal/min) under full flow pressurization mode. Turkey red oil (TRO) was dosed as a flotation aid at 80mL/min. The influent white water (before TRO addition), DAF effluent, and floated scum were sampled for analysis. The DAF influent had 98 mg/L of TSS, and 650 NTU of turbidity at pH 9.27. The DAF effluent had 15 mg/L TSS and 550 NTU of turbidity at pH 9.25. Although TSS (fiber and titanium dioxide) recovery rate was 85%, the ash content (titanium dioxide) of the recovered TSS was very low. Therefore, using a DAF clarifier under full flow pressurization mode and TREO, the majority of fibers in white water but only about half of titanium dioxide can be recovered. 

In another example, urine samples were extracted with MIP phases imprinted with clenbuterol in order to determine the concentration of this (3-agonist, which is known to be misused in animal breeding and thus is occasionally found as a food contaminant. Recovery rates of up to 75% were observed for spiked samples when extracting the clenbuterol. However, in subsequent control experiments clenbuterol was detected also in non-spiked blank urine samples, and further experiments lead to the conclusion that the clenbuterol used as template permanently bled from the Mi-polymer. Consequently, the authors decided to use in the future a structural analogue as template instead of clenbuterol in order to avoid this problem [44]. 

It is required for quantitative purity assays, and it must be established across the specified range of the analytical procedure. This can be done, by establishing the recovery rate over the range of the method. Alternatively, a method comparison between a validated method and a new method can be performed. Accuracy can be determined by spiking degraded, aggregated, pure or impure material into a known amount of sample. A theoretical recovery would then be calculated and the spike material analyzed using the chosen method. The actual recovery should then be compared to the theoretical recovery to calculate the accuracy of the method. Accuracy in this case would be reported as percent recovery. 

The Recovery Rate Chart reflects the influence of the sample matrix. Values from the analysis of a spiked and non-spiked sample are used. 

Real samples that are analysed with and without a spike are used for the Recovery Rate Chart. It is necessary to consider, whether the sample used for control has a representative matrix and whether the spike is boimd to the matrix in the same way as the analytes in the sample. 

System (4) has been described for the analysis of corticosteroids in human adrenal tissues [152]. Prior to the HPLC analysis, the corticosteroids were extracted from adrenal tissues by acetone. The permissible columns were 20 cm X 2.4 mm, consisting of Zorbax-SIL (for more polar compounds) or Zorbax-CN (for less polar compounds). The mobile phase was 9 4 1 cyclohexane-dichloromethane-ethanol or aqueous methanol, and eluted at a flow rate of 0.4 mL/min. Using a UV detection wavelength of 254 nm, sample recoveries were 78.5-99.5%, and the relative standard deviation was 2-5%. 

Accuracy. In the quantitative method that is used to measure the heavy metal quantity in the drug substance, the accuracy is usually represented by the recovery rate obtained from a spiked recovery test where lead is added to the samples. Since the heavy metals limit test specified in monograph specifications is a test where the intensity of coloring of the samples with sodium sulfide is compared with that of the control solution, it is necessary to confirm that heavy metal components can be detected fully in the process of test solution preparation. The Heavy Metals Limit Test in JP specifies four preparation methods for the test solutions. An appropriate method will be selected and used for further testing. The test method that gives the best recovery rate is to be adopted. The procedure is as follows ... 

Treat the three-level lead-spiked drug substance samples according to methods 1 to 4 to prepare the test solutions and the control solution. Separately, designate a solution prepared according to the same preparation method as the control solution. Using this control solution, determine the absorbance of the test solutions and calculate the recovery rate at each amount added. 

A typical example of accuracy (recovery rate) is shown in Table 7.2. The samples were prepared by adding a standard lead solution corresponding to 2, 5, 10, and 15 ppm to 2.0 g of a compound. Results of the recovery were determined from the absorbance at 400 nm. 

Qualitative evidence of the possible influence of pressure drop can be seen by comparing recoveries of carbonaceous material, as carbon, while varying filter sampling flow rates. For example, samplers operating at a face velocity (i.e., flow rate per unit area of the macroscopic filter surface) of 11 cm/s yielded an average of 30% greater total carbon, in xg/m3, compared to a standard high-volume sampler operated at 50 cm/s (67). 

Many different sample preparation procedures have been employed, ranging from simple filtration of juice products to solvent extraction, and extraction by SPE using C, 8, Sephadex LH-20 (49,50,52), and Amberlite XAD-2 (51,54,57). The Amberlite XAD-2 cleaning step has been used for many phenolic extracts, especially for fruit purees, to remove the sugars and other polar compounds. However, due to the low recovery rate with Amberlite XAD-2 for certain phenol glycosides, a modified sample preparation technique is needed, especially for quantification of ar-butin in pear juice and blends (54). Figure 6 describes the fractionation procedure for phenolics using a Sephadex LH-20 column (58). 

However, due to the artifacts resulting from oxidation, hydrolysis of esters or ethers, or isomerization of phenolics during pretreatment of wines, as well as due to the low recovery rates of some phenolics, analysis of wine phenolics via direct injection of the filtered wine into the chromatographic column is often selected (80,82-84). For the red wine and musts (80), which were injected directly into the HPLC without sample preparation, a ternary-gradient system was often employed for phenolic compounds. Twenty-two phenolic compounds, including 10 anthocyanins, were analyzed from red wine. The separation of cinnamic acid derivatives (313 nm),... 

Using separation-optimized SI with 0.05 M HN03 as the eluent and 1-octanol saturated solutions, 90Sr recoveries were 96%, and carryover from one sample into a subsequent blank run was typically 1-2% 47 Blank runs or column clean-up procedures can be used to reduce or eliminate carryover between samples. Recoveries were not sensitive to elution flow rates, and columns could be used repeatedly. There were no significant performance differences between Sr-Resin materials with 20-50... 

Cone and plate sensor systems are useful when a constant shear rate across the gap is required, when sample sizes must be very small, and when sensor cleaning or sample recovery are problematic. They are less well suited to the study of suspensions of moderately-sized particles which may bridge the gap, causing erroneous readings, and cause wear to the cone and plate surfaces. 

OV-17. Just prior to extraction, all samples were fortified with o,//-DDE to evaluate the integrity of the analysis. The recovery rates of o,//-DDE in all tests were greater than 89%, indicating no significant loss during analyses. 

The measured recovery of added 90Sr tracer in the QC sample is then taken to be the yield for all samples in a batch. If the 90Sr tracer is from a standard solution, then the QC sample measurements provide the combined yield and counting efficiency. (Note This is described in the alpha-particle spectral analysis in Experiment 15.) The 90Sr activity in each sample is its net count rate multiplied by the ratio of the QC sample activity (in Bq or pCi) to the average QC sample count rate. 

Once the analytical parameters have been determined from the method development and the method has proven suitable for routine measurements, internal quality control (IQC) procedures must be established to maintain the validity of the analytical scheme and to better monitor potential sources of errors. The IQC used includes pre- and post-digestion controls, blank determination, half range of the calibration graph checking, and recovery rate of the samples. The stability of the recovery rate with time (Fig. 1.4) shows that the method is robust after using... 

For foodstuff matrices, the use of PFA labware and H2O2 reagent improved the conventional analytical parameters (LoDs, level of blanks, stability, recovery rate, and also the speed of analyses. The quantification of lead at low concentration was possible down to 9 pig kg-1, whereas in the recent past the LoD in the same laboratory was at about 35 pig kg-1, thus making participation in the previous FAPAS S7R40 PT impossible. Thanks to the improved procedure, more parameters of quality control could be integrated in the program, that is, recovery rate is calculated for each run of sample and this without lengthening analysis time. 

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