Spike concentrations

On the other hand, for the standard addition method, the spiking concentrations are in the range of 50-150% of the label-claimed value, and are made by spiking of known analyte concentrations in matrices such as serum, plasma, etc. 

The results of interlaboratory study II are presented in Fig. 4.5.1. Five sets of results were obtained for the LAS exercise, and four sets for the NPEO exercise. For LAS, the within-laboratory variability ranged between 2 and 8% (RSD) for sample III (distilled water spiked with lmgL-1 LAS), 1 and 13% for sample 112 (wastewater influent), and 3 and 8% for sample 113 (sample 112 spiked with lmgL-1 LAS). Between-laboratory variations (calculated from the mean of laboratory means, MOLM) amounted to RSDs of 15, 30 and 30% for samples III, 112 and 113, respectively. The LAS values reported were in the range of 700—1100 p,g L-1 in sample III, 1100-1800 p,g L-1 in sample 112 and 1900-3000 p,g L-1 in sample 113, indicating that even in the matrix wastewater influent, the spiked concentration of lmgL-1 LAS could be almost quantitatively determined by all laboratories. 

Once the oxidation of the phosphothionate pesticide was optimized, the assay was applied to nine spiked samples resulting in acceptable recovery (Table 29.3). The spiking concentration was 5 mg/kg for all the samples, which correspond to the legal limit settled by the European Union. 

Metal Spiked concentration (pg/L) Found concentration (pg/L) Recovery (%)... 

Sample code Spiked concentration of Aroclor 1248 (pg/kg) BJB0 (%) Classification... 

Sometimes for convenience, and to enable homogeneity testing to be completed in a practical timeframe, one or two representative analytes are selected as markers for homogeneity and undergo full testing as described above. Spiking concentrations of the remaining analytes are checked by duplicate analysis. 

S, the formulated (spiked) concentration (accompanied by measurement uncertainty estimate) traceable to SI through gravimetric preparation using pure substance chemicals of specified purity... 

Experiment. Three analyte levels generally near the low, medium, and high QC concentrations and the internal standard at the working spiking concentration were tested. The response of extracted samples (Preprocess) is compared to the response of samples representing 100 % recovery (Postprocess). 

An in vitro study in human blood showed that chromium(VI) was rapidly cleared from the plasma (Corbett et al. 1998). The reduction capacity appears to be concentration dependent and is overwhelmed at spike concentrations between 2,000 and 10,000 pg/L. High chromium(VI) concentrations (10,000 pg/L spike concentration) resulted in an accumulation of chromium(VI) in the erythrocytes and a lower plasma erythrocyte ratio of total chromium. This study also found that the plasma reduction capacity was enhanced by a recent meal. 

The information which is usually obtained from a ruggedization experiment is limited to the identification of the nonsignificant parameters. However, if the expected experimental precision is independently known, it is possible to determine whether the standard error of the ruggedization experiment is comparable to the expected instrumental precision. The standard error of all the 10 metals except Cr, Mo, and Pd (Table VII) is very close to the expected instrumental deviation at spiked concentration levels of 1.0 to 3.0 yg/ml in solution. This indicated that for Be, Cd, Co, Cu, Mn, Ni, and Pb analysis, the screening experiments did not introduce significant imprecision compared to repetitive analysis of synthetic standard solutions of these metals. One variable uniquely significant (99 per cent) for Cr, Mo, and Pd is the treatment with perchloric acid (variable F). An attempt to explain the... 

This relationship can also be used to establish the accuracy of the Se spike concentration, which Is most conveniently added as a solution. Employing accurately prepared samples of natural selenium (Sen known) spiked with known amounts of the 2se solution, R is then measured and Equation 4 solved for Sega This is basically an inverse Isotope dilution procedure. When performed on the same Instrument to be used for subsequent measurements. It has the added advantage of cancelling out any mass discrimination by the Instrument. 

In practice, measured isotope ratios are reported as mean and standard error. For analyses with stable ion-beam intensities, the within-run statistical errors are typically similar to those predicted by counting statistics. Uncertainties in sample weight, spike weight, spike concentration, chemical blanks, and filament blanks are typically small compared to the analytical uncertainty, but are also included in the error propagation through Eq. (1). 

The PPC, required by the FDA Guideline, is a sample of the test material that contains a concentration of endotoxin that is double the labeled sensitivity of the LAL reagent.The PPC must be tested with each sample in a Limits test or kinetic LAL assay to ensure that a result is valid and free of interference. The most accurate and reliable technique is the hot spike method that requires adding 10 pi of endotoxin standard to the reaction vessel (tube or well) before addition of LAL. The gel clot method requires the addition of 10 pi of 20 A to the reaction mixture. Kinetic methods require the addition of 10 pi of a standard, 10 times greater than the spike concentration, to the wells or tubes designated as PPCs. Only inhibition is seen in gel-clot Limits tests, whereas both inhibition and enhancement are seen in kinetic LAL methods. 

An identical procedure to the rate studies was employed for the adsorption equilibrium studies except that a matrix consisting of different pollutant spike concentrations, as well as different soil masses (except for the p-DCB), was... 

Responses are obtained from replicate analyses (n = 4) of a field blank and the field blank spiked to contain a level of analyte that is close to the LOQ. The means of the obtained responses are tested statistically (with the f-test) to determine whether they are statistically different. If the difference is significant, the variability of the response in the spiked sample is evaluated by taking the ratio of its mean response to the response standard deviation. If the ratio is greater than or equal to 3, then the spiked concentration is taken as the LOQ. 

Analytical Curves. Appropriate spikes of mercmric chloride standards were added to the sample matrix, and the sample determination procedmre was repeated. Three spike additions were usually made. A sample blank is measmred and the mercury concentration determined from an individual calibration curve for each sample. The working calibration curve for a seawater sample is prepared by plotting the gas phase absorption of mercury (arbitrary units) against the mercury spike concentration (ng/1.). Using log-log coordinates, the mercury response is linear over... 

SPIKE CONCENTRATION EALSE POSITIVES RESPONSE TIME -LIMIT OF DETECTION ... 

If the spike is added as a solution, it will also dilute the existing analyte and so the equation must reflect this. Let the initial volume of analyte be F and an addition be made of V of the spike, concentration x. The original analyte is diluted by F/(F+ V) and the added spike by V/(V+ V). Now the equations are... 

For selectivity determination, individual matrices are tested with and without analyte spiked at one or more concentrations between the LLOQ and LQC levels. A selective method has the targeted analytical recovery (typically within 100 20 25% of the nominal spiking concentration) in >80% of the samples. During the development phase, method selectivity can be evaluated using a small number of individual matrices however, during validation, 30 50 samples should be tested. 

Serum samples from nonsmokers, smokers, and cancer patients (breast, colon, prostate, head, and neck) on cytotoxic and protein therapies. Aliquots of the serum samples were spiked with 6 or 60mU/mL erythropoietin. The unspiked and spiked samples were analyzed using an in house ELISA method. The basal concentration (unspiked) was subtracted from the observed concentration of each individual to obtain the corrected concentration. The % recovery was calculated against the nominal spike concentration of 6 or 60 mU/mL. 

With regard to the concentration levels (concentration jump), it is acceptable to double the concentration of the analyte(s). In many other cases reported in the literature, spike concentrations ten times higher than the concentrations of the native compounds are generally applied. In this case, the risk of overestimation of a recovery is quite high. 

The sample is then gravimetrically spiked with an isotopic analogue of the analyte (this analogue is termed the spike) such that the spike concentration matches the prior estimate of the natural analyte concentration in the sample. To prepare a sample solution blend, extraction (organic analysis) or acid mineralisation (inorganic analysis), followed by any clean-up stages necessary is carried out. 

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