Blind spikes

Table 4.7 HPLC-cold vapour ICP of blind spiked distilled water...

Method transfers are typically done between laboratories, where a method has been validated at one laboratory and is being transferred to another laboratory. This requires at least a partial validation that is documented and agreed upon by both parties. It is highly recommended that blinded spiked samples as well as incurred samples be tested during a method transfer to compare the performance of both laboratories. Method transfer studies should employ appropriate statistical design and data analysis. 

In a blind spiking experiment, (XI) was added to plasma at concentrations 50, 200, 600 and 750 ng/ml and (XII) at concentrations 300, 500, 1500 and 2000 ng/ml and the analytical operator asked to estimate concentration in these samples according to preconstructed calibration graphs. The results are given in Table 2. 

In order to validate, in part, this newer approach, both sample workup and GC-FPD/DCP detection, we have performed several separate, single blind spiking studies with different levels of TBT. Table 9.1 summarizes some of this data, wherein two flounder (fish) and one whiting (fish) sample were separately spiked by one analyst, at the levels indicated, and these were then analyzed by GC-FPD a second... 

SINGLE-BLIND, SPIKED RESULTS FOR TRIBUTYLTIN IN FISH BY GC-FPD. SUMMARY OF TRIBUTYLTIN PRESENT IN FISH AND SHELLFISH BY GC-FPD AND GC-DCP DETECTION, SEPARATELY ON THE SAME SAMPLE... 

Single blind, spiked sample, no tributyltin incurred. GC-FPD recoveiy = 98.6%, GC-DCP recovery = 98.9%. 

Internal QC inclndes the nse of blanks, chemical calibrants, spiked samples, blind samples, replicate analysis, and QC samples. QC samples shotrld be homogeneous and stable. They shotrld be available in sufficient quantities. The use of control charts is recommended (see chapter 13). 

Two aspects are important for IQC (1) the analysis of control materials such as reference materials or spiked samples to monitor trueness and (2) replication of analysis to monitor precision. Of high value in IQC are also blank samples and blind samples. Both IQC aspects form a part of statistical control, a tool for monitoring the accuracy of an analytical system. In a control chart, such as a Shewhart control chart, measured values of repeated analyses of a reference material are plotted against the run number. Based on the data in a control chart, a method is defined either as an analytical system under control or as an analytical system out of control. This interpretation is possible by drawing horizontal lines on the chart x(mean value), x + s (SD) and x - s, x + 2s (upper warning limit) and x-2s (lower warning limit), and x + 3s (upper action or control limit) and x- 3s (lower action or control limit). An analytical system is under control if no more than 5% of the measured values exceed the warning limits [2,6, 85]. 

The data user may assess laboratory performance through analysis of singleblind and double-blind PE samples for project-specific analytes. Single-blind samples are clearly identified as PE samples, whereas double-blind samples are disguised as field samples. Certified blind PE samples may be obtained from several manufacturers in the USA. They are prepared as water and soil samples spiked with a variety of common contaminants. The manufacturer collects the interlaboratory recovery data for these samples and calculates acceptance criteria that are available to the PE sample purchaser. 

It is important to point out that the quality of analytical results is not immediate it can only be achieved if an extensive set of measures are adopted and complied with. Therefore, in parallel to the development of the QA concept, QC systems were introduced as an important tool supporting the QA of chemical measurements. The QC process of examination of laboratory performance in time should always follow QA. QC thus comprises a set of operational techniques and activities used to check whether the requirements for quality are fulfilled. In practice, QC in an analytical chemistry laboratory implies operations carried out daily during the collection, preparation, and analysis of samples, which are designed to ensure that the laboratory can provide accurate and precise results. QC procedures are intended to ensure the quality of results for specific samples or batches of samples and include the analysis of reference materials (RMs), blind samples, blanks, spiked samples, duplicate, and other control samples.2... 

Glutamate release from synaptic terminals of photoreceptor and bipolar cells is regulated by calcium influx through L-type calcium channels (Heidelberger et al., 2005). The use of F-type channels at ribbon synapses contrasts with the reliance on N, P, and Q type channels for neurotransmission at conventional synapses of spiking neurons. A retina-specific L-type channel, alpha IF (CaVl.4), is localized to rod terminals. Mutations in this channel produce a congenital stationary night blindness (Bech-Hansen et al., 1998). 

Camfield PR, Camfield CS, Dooley JM, Gordon K, JoUymore S, Weaver DF. Aspartame exacerbates EEG spike-wave discharge in children with generalized absence epilepsy a double-blind controlled study. Neurology 1992 42(5) 1000-3. 

Rating D, Wolf C, Bast T. Sulthiame as monotherapy in children with benign childhood epilepsy with centrotemporal spikes a 6-month randomized, double-blind, placebo-controlled study. Sulthiame Study Group. Epilepsia 2000 41(10) 1284-8. 

There are several concepts and terms that are essential to discussions about QA, even the concept itself. While at a very detailed level any definition can be challenged as being too narrow or too broad, the definitions presented below are useful (20). It should be noted that these terms are quite recent in definition and are not usually given in statistics books. Other terms like pollution have evolved over hundreds of years (21). Some key terms used in the field like reproducibility, standard deviation, standard error, replicate analysis, blanks, spiked samples and blind samples are self-explanatory. 

At the same time, internal quality control must be carried out to verify the performance stability of the limited-scope performance of the method. Triply redundant verification methods are carried out with regard to control of first, second and/or third line, each set of methods applied to a particular type of test. The first line of verification involves pro forma repetition of all the steps of the test, in order to establish repeatability or reproducibility for quantitative tests, and to verify the range of sensitivity or detection for qualitative tests. This verification is performed by the experimenter himself, as part of the proper performance of the test. A second line of verification is put into operation by administrative decision, and includes testing with blind samples, repetition of samples, internal audit procedures, etc. If necessary, a third line of verification can be set up by the use of certified reference materials (or spiking materials), or through collaborative trials. These procedures are based on external cooperation. External audit procedures and complaints handling procedures are also part of this third line of verification. 

Samples must be homogeneous and tested for homogeneity, and should be coded at random, including the two or more blind replicates. A blank or negative control, and, if available, reference materials should be provided. Spiked materials are recommended for recovery study, incurred materials for residues study. 

The underlying concept of the validation experiments is to provide a prediction of the performance to be expected over an extended period in routine use, and a minimal dataset will not satisfy this expectation. Therefore, a typical validation design will include the six different sources of matrix, usually at each of three concentrations bracketing the MRL, repeated as analyst spikes in three or four analytical runs, followed by one or two additional runs where the materials are provided as unknowns (blind) to the analyst. The design is usually repeated for each required matrix (e.g., each species-tissue combination) for the initial target species and may be also be required when the method is applied routinely to other species. However, when there are obvious commonalities (such as tissues from different ruminants), method extension may require only a reduced dataset, based on experience with the method. 

Control charts can be plotted in the same way using the results from blind control samples that is, blank (or previously analyzed) samples spiked at an appropriate level, unknown to the analyst, by a third party. The use of blind control samples gives an additional degree of quality control, since any bias (intentional or non-intentional) on the part of the analyst is precluded because the analyst is not aware of the expected result. Blind control samples are being used increasingly and are required in some official testing laboratories in the USA. Many laboratories in the UK routinely use blind controls for confirmatory analyses, and in some instances for screening as well. 

Blind traceable reference material To evaluate the accuracy of the analyst. Sufficient spike is added for precise measurement. 

All but the fourth QC sample type are inserted in batches of routine samples. Although inserting these QC samples without the knowledge of the operator ( blind ) ensures that they are not treated with special care, this may not be possible in small laboratories, where the analyst may recognize the QC samples. Distinctive features are their radionuclide concentration (i.e., radionuclide concentrations are zero in blank samples and elevated in spiked samples), salt content (blank samples may have none), or the manner of their insertion into the sample flow. The last of the above types also is used for external QC in the form of interlaboratory comparison samples (see Section 11.2.11). 

TWen -three collaborators received 18 coded sanples, vAiidi included six sets of blind dv licates of spiked and naturally ccxitaminated com, wheat, and feed (Table I). All collaborators... 

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