Repeat Samples

Cone. Calibration Samples Spiked Samples Repeatability... 

Based on samples that can be obtained nonlethally and noninvasively, and that can be sampled repeatedly in the same individual... 

Benzene chemisorption on platinum-alumina in the range 26°-470°C has been measured in a flow system by Pitkethly and Goble (7). A small dose of benzene was injected into a stream of inert carrier gas and transported to the reactor the effluent was then sampled repeatedly and analyzed by gas-liquid chromatography. Information concerning the adsorption and desorption of benzene was obtained from the shape of the subsequent benzene concentration versus time curves. Evidence was obtained for four types of adsorption of benzene ... 

Repeat samples provide a less formal check than conventional QC samples. Within an analytical process, samples may be analysed singly, in duplicate, in triplicate, etc. Normally, the repeat sample is a conventional sample, repeated later in the batch of samples, or perhaps in a different batch. The variation between the two sets of results is studied to ensure that the variation is within the acceptable limits (see Chapter 4, Section 4.6.2). Higher than expected variation (for example, variation greater than the stated repeatability for the method) provides an indication that there is a possible fault in the analytical system. The analyst is normally aware when repeat samples are used. 

Difficult to wash out samples Out of specification samples repeated... 

The major advantage of this dramatic time reduction lies in the ability to scan the sample repeatedly, combine the relaxation-decay patterns collected from each scan, and then perform a Fourier transform upon the final composite relaxation-decay pattern. This technique, in essence, increases the spectral sensitivity by allowing the NMR signals acquired from each scan to be constructively added to each other while the noise cancels itself de-con structively. This approach greatly increases the sensitivity of the instrument and allows NMR experiments to be performed on samples that have low concentrations of the desired nucleus (i.e., for 31P, 20 mg of P/L is a feasible concentration with instrument time of hours to a few days). 

Aqueous samples repeatedly extracted with methylene chloride extracts combined and concentrated by evaporation of methylene chloride solvent exchanged to hexane florisil cleanup (for removal of interferences) extract analyzed on GC-ECD or GC/MS. 

To collect another sample, repeat steps 5 through 12. 

It has already been mentioned that all rhodium-containing samples repeatedly showed a regain of activity when finally heated to 650 °C during the experimental protocol. The reversible adsorption of monoatomic carbon species might be an explanation for this observation [52]. 

Acceptance criteria. Two-thirds (67 %) of the ISR samples repeat values must be within 20 % of the mean of original and ISR values. 

Step 5. Fasten disk to center of planchet with double-sided tape at the back of the disk. Count sample. Repeat with 2 other samples and blank with proportional counter. 

D. Other Film Samples. Repeat these tests with other samples of film that are available. Record your observations and compare results with different kinds of films. 

In paper chromatography the stationary phase is the cellulose of the paper, and the spot of sample is added to the paper. A suitable solvent, say water or alcohol, is called the mobile or moving phase. This is added to push the materials across the paper or a thin layer of powder as it soaks across. Each material in the mixture to be separated will have a different solubility in the solvent and also a different degree of adsorption (sticking) to the paper. As the solvent soaks along the paper, the sample repeatedly becomes dissolved in the solvent and adsorbed and desorbed to and from the paper. These variables make the time it takes for a material to move along unique for each material in the mixture. 

Figure 4.10 Representation of two procedures used to obtain multiple samples for analysis. (A) Several identical reaction mixtures are prepared, and the enzyme will be added to each to start the reaction. Each tube is sampled only once during the incubation. (B) Only one reaction mixture is prepared, and the enzyme is added to start the reaction. The incubation mixture is sampled repeatedly during the course of the reaction. Note that the volume of the reaction mixture in arrangement (B) is usually greater than in arrangement (A).

Imagine that there exists a population of permeabilities consisting of a very large number of datum. The population has a knowii V p. Let us draw a certain number N from this population and calculate an estimated from this sample. Repeating the procedure several times will generate a probability distribution function (p.d.f.) for the estimate V. This function that illustrates the difficulties in estimating V p. 

Count the sample repeatedly for 0.5 minutes, increasing the coarse gain control one step each time until more than 20 counts are accumulated in 0.5 minutes. 

Fig. 4 The relationship between the I, distance and the pumping time, r, for graphite intercalated by AsFj (and F2) C -f- AsFg(n),C + AsFg repeated treatments (O), C + AsFj + F2 (A). For those samples repeatedly treated with AsFg, the pumping time is measured from the last cycle...

Chute splitter Subsampler A series of chutes split sample repeatedly Large Can be repeated until the desired sample size is achieved If segregation occurs, the result can be misleading Prone to operator bias... 

Wjg = r, flag = 2 Otherwise, take another sample, repeat the above process until flag = 2. Step 5. Let corresponding trial assigmnent after above perturbation be Wj. Calculate the... 

Since radioactive decay follows Poisson statistics, a lower limit to the precision of an analysis can be obtained by a single measurement. In practice, counting statistics generally is the limiting uncertainty, since chi-squared tests often show that the single-measurement precision is an excellent predictor of sample-to-sample repeatability. 

Place the bracket containing the film in the instrument and obtain a transmission spectrum of the sample. Repeat for all samples to be tested. 

Bioanalytical study reports should describe the reason of repetition for each repeated sample. A table that lists each type of repeat is useful and facilitates straightforward and clear reporting. The table should include the original, repeat, and accepted result for use in pharmacokinetic calculations. To facilitate an understanding of the repeats as part of the overall study conduct, it is desirable to include the source of each result by listing the run ID for both the original and repeat results. Samples repeated in error (e.g., the analyst did not intend to repeat the sample) should also be reported. Furthermore, if no samples are repeated, the bioanalytical study report should include a statement in this regard. 

If the refractive indices indicate that you are now distilling absolute ethanol, then shut off the transformer. If not, then distill for 5 to 10 minutes more and collect another sample. Repeat as necessary until you are satisfied with the result. 

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