Method repeatability

An analytical procedure is often tested on materials of known composition. These materials may be pure substances, standard samples, or materials analyzed by some other more accurate method. Repeated determinations on a known material furnish data for both an estimate of the precision and a test for the presence of a constant error in the results. The standard deviation is found from Equation 12 (with the known composition replacing /x). A calculated value for t (Eq. 14) in excess of the appropriate value in Table 2.27 is interpreted as evidence of the presence of a constant error at the indicated level of significance. 

Product inhomogeneity (F) for replicate samples pulled from the same production lot would show up in sample means that scatter much more than the method repeatability (=A=). 

For early phase methods, the precision tests only include injection repeatability (also referred to as system repeatability) and method repeatability (also referred to as analysis repeatability). The former is demonstrated by repeating injections of a standard solution and the latter by preparing multiple samples over multiple concentration levels (usually at 80%, 100%, and 120% of the nominal concentration) from the same lot of a composite sample of the dosage form. 

For each test it is advised to analyze the samples with replicates (e.g., n=6). The acceptance criteria are based on the method purpose and on the validation characteristics. A recommended approach would be to propose acceptance limits based on the results of the Gage R R study. If this study is not performed the Horwitz equation can be used to relate method repeatability with method reproducibility. Typically the difference in average assay values for DS methods should be within 2.0% and the precision should be less than 1.0% RSD in each laboratory. For DP, these limits are 3.0% and 2.0% for average assay difference and for the precision in each lab, respectively. The impurities are usually considered at a 0.5% level and the typically allowed difference between labs... 

Optical reflection from a monomolecular film must be measured from the interface with a very small amount of material present. Therefore, in these methods, repeated interaction of the light beam with one or more identical films is generally employed. The simplest way to observe a light beam that has passed through several identical monolayers is to transfer portions of the layer to suitable transfer end plates, which are then stacked and examined in a conventional spectrophotometer. This method was used where monolayers of chlorophyll were deposited on glass slides by the LB method. Ferrodoxin and chlorophyll monolayers were investigated by measuring the spectra (550-750 nm) of these films at the interface. 

Repeatability of a method can be determined by multiple replicate preparations of the same sample. This can be done either by multiple sample preparations (n = 6) in the same experiment or by preparing three replicates at three different concentrations. In general, one should evaluate results of individual related substances, total related substances, and the consistency of related substance profiles in all experiments. The percent RSD and confidence level of these results are reported to illustrate the method repeatability. 

The reproducibility standard deviation is typically two to three times as large as that for repeatability. Precision decreases with a decrease in concentration. This dependence has been expressed as RSD = 2° 0 5 exp 108 C), where RSD is expressed as a percentage and C is the concentration of the analyte [38]. For the concentration ranges typically found in pharmaceutical dosage forms (1—10 3), the RSD under conditions of repeatability should be less than 1.0%, and less than 2.0% under conditions of reproducibility [21]. These are similiar to the 1.5% recommendation made for RSD of system repeatability after analyzing a standard solution six times [35]. For method repeatability, which includes sample pretreatment, six replicate assays are made with a representative sample. A RSD no greater than 2% should be obtained. 

A01, N01, Nn. To maximize L(Q) by changing 0, the Newton-Raphson method repeats the following update ... 

Assay Determine as directed under Solidification Point, Appendix IIB, drying a sample over anhydrous sodium sulfate. Transfer 3 g of the dried oil, accurately weighed, into a test tube, and add 2.1 g of melted o-cresol. The o-cresol must be pure and dry and have a solidification point not below 30°. Insert the thermometer, stir, and warm the tube gently until the mixture is completely melted. Continue as directed in the method. Repeat the procedure until two successive readings agree within 0.10°. Compute the percentage of cineole from the table found under Percentage of Cineole, Appendix VI. Acid Value Determine as directed under Acid Value, Appendix VI. 

Kretzoi, following an idea of Hokr (1951), has recently estimated the July mean temperatures that must have prevailed at the time, which he based on the numerical abundance of some vole species of various faunas, and their frequency in our days. V rtes (1965) has also used this method repeatedly. More recently, Kordos (Janossy and Kordos, 1976a) has done similar calculations. Nevertheless, because of the presumed ecological changes through time that I have mentioned above, and due to the evolutionary changes in the various species, this method may be applied only to the periods closest in time to ours, i.e. the Holocene and the Upper Pleistocene. 

No single sampling method repeatedly recovers a known and consistent percentage of all types of organisms ... 

Control charts used for monitoring the reproducibility of methods (repeated analyses of one or several reference materials) may be considered as long-term references for analytical measurements since they allow the monitoring of analytical variation with respect to an anchorage point, i.e. the reference material(s). This concerns reproducibility checking but not necessarily trueness whose evaluation relies on relevant CRM analysis. 

When Sbb cannot be calculated (as MSbetween < MSwuhin in ANOVA results), the uncertainty contribution due to between-bottle heterogeneity is taken from the u hh value given in Equation 5.1.2 (where df are the degrees of freedom). ubb represents the maximum heterogeneity that can be hidden by the method repeatability and it was considered as the minimum uncertainty contribution from heterogeneity in this approach. 

Residual maximum likelihood analysis of the ring-test data also provides an estimate of the underlying repeatability of each test method ( repeatability)- As part of a quality control scheme, this can be compared with variances estimated from the EC/LC50 values derived from a series of repeat tests carried out within a laboratory using the same toxicant (S2) and using a conventional 2 test, as shown below ... 

Take from one vial n sub-samples and measure them with the tested method Repeat the exercise on a second vial ... 

Repeatability is a measure of the ability of the method to generate similar results for multiple preparations of the same homogeneous sample by one analyst using the same instrument in a short time duration (e.g., on the same day). For instance, method repeatability for pharmaceutical assays may be measured by making six sample determinations at 100% concentration, or by preparing three samples at 80,100, and 120% concentration levels each. 

We have defined the precision of a method. Repeatability is the long-term precision over several weeks. Ruggedness refers to the precision of one lab over multiple days. 

SCF method (repeat the calculation with a trial function until getting self-consistent solution) -77.879eV... 

The first group of methods repeats, in principle, the whole variety of organic chemistry, with logical amendments and with due attention paid to isotope effects. It suffices in this connection to refer to the series of articles by Leitch and his collaborators.4... 

LODs 20 to 40 pg//xl all types of sorbent gave recoveries around 100% for most of the studied compounds method repeatability from 2 to 8% in all cases Determination. GC-ECD LOD 0.02 /ag/1 for Milli-Q water 155... 

Determination continuous ultrasound-assisted extraction coupled to on line filtration-SPE-column hquid chromatography—post column derivatisation—fluorescence detection LOD 12 ng/g and LOQ 40 ng/g carbamates at 1 /xg/g spiked level recoveries similar to those provided by the EPA 8318 method repeatability 3.1% reproducibility 7.5%... 

Test Performance Index = Laboratory Standard Deviation / Test Method Repeatability... 

A similar experimental design to assess method repeatability is contained in Decision 2002/657/EC ... 

The terms Ti, T2, T3, Tq, p represent calculations used in ISO 5725-2 to facilitate calculation of estimates of method repeatability and laboratory variability, and are given in the following equations ... 

Obtain one or more soil samples from a hazardous waste site. Alternatively, your instructor may have a series of fortified soils available in the laboratory. An illustration of how a series of laboratory fortified acidic, neutral, and alkaline soils can be prepared and given to students as sample unknowns is shown in Table 5.3. Implement EPA Method 9045C while reviewing its details. Assume that the unknown soil is noncalcareous. Notice the use of flowcharts in helping to understand the procedural aspects of the method. Repeat the pH measurement for the four other samples and record your results in your laboratory notebook. The chemical nature of the contaminated soil samples will be revealed to you after you have completed your pH measurements. Rationalize the observed pH value for each soil based on a knowledge of the chemical used to contaminate the soil. Write your comments into your lab notebook. 

The use of CRMs for validation purposes is, however, not limited to the above intralaboratory verification of trueness (checking the absence of significant systematic errors). They also enable the user to estimate the precision of a method (repeatability and reproducibility), which should actually represent one of the first steps of the method validation. In this respect, the evaluation will have to take into account specific characteristics of the CRM, in particular, possible sources of uncertainties linked to the material heterogeneity which should in principle be considered for the calculation of the uncertainty of the certified values. 

Method Repeatability (%) Limit of detection (g) Sample volume (ml) Time (min) Simultaneous analysis... 

Add 20 mg inactive Bi carrier and repeat BiOCl separation by above method. Repeat precipitation of PbCrO. ... 

Curvilinear-Squares Graphical Method. Repeat Example 4.4-1 but with the... 

Alternative Convective Boundary Condition for Numerical Method. Repeat Ex-... 

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