Samples spiked

Illustration showing an alternative form of the method of standard additions. In this case a sample containing the analyte is spiked with a known volume of a standard solution of analyte without further diluting either the sample or the spiked sample. 

A spike recovery for the analysis of chloride in well water was performed by adding 5.00 mb of a 25,000-ppm solution of Ck to a 500-mL volumetric flask and diluting to volume with the sample. Analysis of the sample and the spiked sample resulted in chloride concentrations of 183 ppm and 409 ppm, respectively. Determine the percent recovery of the spike. 

The use of several QA/QC methods is described in this article, including control charts for monitoring the concentration of solutions of thiosulfate that have been prepared and stored with and without proper preservation the use of method blanks and standard samples to determine the presence of determinate error and to establish single-operator characteristics and the use of spiked samples and recoveries to identify the presence of determinate errors associated with collecting and analyzing samples. 

Moreover recovery studies on commercial spiked samples were developed in order to asses the no contribution of the matrix and evaluate the accuracy of the proposed procedure. 

The only recourse is to modify the recovery experiments above in the sense that the sample to be tested itself is used as a kind of blank, to which further analyte is spiked. This results in at least two measurements, namely untreated sample and spiked sample, which can then be used to establish a calibration line from which the amount of analyte in the untreated sample... 

Cone. Calibration Samples Spiked Samples f-Tests... 

The back-calculated results (99.9 0.9%) for both calibration and spiked samples are acceptable. 

There is no systematic difference between calibration and spiked samples. (Cf. Fig. 3.2.)... 

This process shonld be considered in the light of the preceding comments on association. Many experiments on the recoverability, persistence, and toxicity of xenobiotics have used spiked samples that do not take into acconnt the cardinal issne of alterations in the contaminant that have taken place after deposition. This is termed aging, and shonld be evalnated critically in determining persistence. Some examples are given below as illnstration for both terrestrial and aquatic systems ... 

In case of reduced availability of an impurity a possible approach is to prepare a spiked sample , i.e. a known amount of impurity is added to the CRS and may serve in a system suitability test as well as for the control of the level of this impurity. An example is given in the monograph for chlorprothixene hydrochloride (Monograph 0815 1999) where the content of the E-isomer is controlled to a level of not more than 2 per cent, Figure 5.5. 

For the mixtures described under (3) it is sufficient to determine the chromatographic profile of the CRS and to demonstrate that all impurities are well separated according to the monograph description. When the spiked sample is also used in the purity control, then the content of the impurity in the CRS material must be determined by appropriate chromatographic methods and a value assigned to the material. 

Method accuracy is defined as fhe agreemenf befween fhe measured value and fhe frue value and is usually determined by measuring fhe percenfage recovery of spiked samples. Recovery values of 70-110% are usually desired, allhough fhe EDA and the EU allow for wider ranges for analyses at low concentration levels. 

Urine Spiked sample clean-up by co-precipitation, purified by TRU-spec column and electrodeposition a -Spectrometry 0.016 pCi/800 cm3 95% at 0.1-100 pCi/sample Goldstein et al. 1991... 

Soft tissue Spiked sample wet ashed, treated with HN03/H202, purified by A-CU column, anion exchange, TRU-spec column, and electrodeposition a -Spectrometry No data 53% Qu et al. 1998... 

In isotope dilution inductively coupled plasma-mass spectrometry (ID-ICP-MS) the spike, the unspiked and a spiked sample are measured by ICP-MS in order to determine the isotope ratio. Using this technique, more precise and accurate results can be obtained than by using a calibration graph or by standard addition. This is due to elimination of various systematic errors. Isotopes behave identically in most chemical and physical processes. Signal suppression and enhancement due to the matrix in ICP-MS affects both isotopes equally. The same holds for most long-term instrumental fluctuations and drift. Accuracy and precision obtained with ID-ICP-QMS are better than with other ICP-QMS calibration... 

In the lab, the same primary sample types were used, and samples were also done to verify that the recovery from the coveralls alone was similar to that for the combined underwear plus coveralls patch and to verify that recovery from the individual types of cotton matrix was adequate. The results showed that recovery for the underwear was reduced by the large size of the garment compared to the patches used for the primary field and lab spiked samples. Recovery from the spiked cotton swabs was lower than expected but was still considered adequate (see Table 1). 

Table 1 Recovery and Standard Deviation from Spiked Samples...

Matrix Lab-spiked samples Percent recovery (S.D.) Number of samples... 

Results from experiments using the protocol above27 have shown that anti-Salmonella immunomagnetic beads could be used to unambiguously determine the presence of Salmonella choleraesuis from suspensions of bacterial mixtures. This target organism was also positively identified from spiked samples of river water, human urine, chicken blood, and 1 % milk. For the river water and urine samples, no cross-reactivity was observed and only protein... 

The analytical results for each sample can again be pooled into a table of precision and accuracy estimates for all values reported for any individual sample. The pooled results for Tables 34-7 and 34-8 are calculated using equations 34-1 and 34-2 where precision is the root mean square deviation of all replicate analyses for any particular sample, and where accuracy is determined as the root mean square deviation between individual results and the Grand Mean of all the individual sample results (Table 34-7) or as the root mean square deviation between individual results and the True (Spiked) value for all the individual sample results (Table 34-8). The use of spiked samples allows a better comparison of precision to accuracy, as the spiked samples include the effects of systematic errors, whereas use of the Grand Mean averages the systematic errors across methods and shifts the apparent true value to include the systematic error. Table 34-8 yields a better estimate of the true precision and accuracy for the methods tested. 

Table 35-3 illustrates the ANOVA results comparing laboratories (i.e., different locations) performing the same METHOD A for analysis. This statistical test indicates that for the mid-level concentration spiked samples (i.e. 4 and 4 at 3.40 and 3.61% levels, respectively) difference in reported average values occurred. However, this trend did not continue for the highest concentration sample (i.e., Sample No. 6) with a concentration of 3.80%. The Lab 1 was slightly lower in reported value for Samples 4 and 5. There is no significant systematic error observed between laboratories using the METHOD A. 

The first result in Table 2.2 is the value found directly. The next set of three results shows that recovery of fluoride after deliberate addition to the spiked samples is excellent. The fifth result is that obtained from an acidified sample. The sixth, seventh, eighth, and ninth sets of data show that the expected fluoride concentration is still obtained after deliberate addition of aluminium or iron in the form of their alums. Aluminium (III) and iron (III) form very strong fluoride complexes [70] and, provided that sufficient time is allowed for equilibration (as noted by Baumann [64] for very low fluoride concentrations), total flu-... 

Matrix-matched Certified Reference Materials or spiked samples should be used to determine the linearity of a method. 

Spiked sample A sample prepared by adding a known quantity of analyte to a matrix which is as close to or identical to that of the sample of interest. 

For the 87Rb(spiked) sample, the 87Rb peak in the mass spectrum is 1.12 times as tall as the... 

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