Within-run precision

Thus, there is a distinction between a within-run precision (repeatability) and... 

Because of these complications, regardless of the very high within-run precision attainable via TIMS or ICP-MS, the true precision of the runs (as opposed to the internal or within run precision provided by the TIMS or ICP-MS operating software) can only be reliably established by replicate analyses of natural samples. One useful approach is to establish the external variance of a measurement technique by subtracting the internal variance from the total (= run-to-run) variance from replicate analyses, e.g.. 

In short, there exists a marked and pronounced distinction between a within-run precision (i.e., repeatability) and an in-between-run precision (i.e., reproducibility). 

The precision of this method was evaluated by repeated analysis of the main human faecal BAs (iso-LCA, LCA, iso-DCA, DCA, CDCA, CA, and 12-oxo-DCA). Within-run precision of ten samples amounted to 4-7% for all BAs. The between-run precision was approximately 5-10% of five time-shifted measurements over 1 month of faeces samples. A standard solution of DCA acetate methyl ester with a DCA concentration of 0.875 mg/ml was added to ten faecal samples of the same origin also used for within-run precision. The mean of concentrations amounted to 1.672 mg/ml, corresponding to a recovery of 94.6%. 

The within-run precision of derivatisation and chromatography procedures was assessed in the reported work a single standard solution was analysed in eight replicates. The relative standard deviation values of the peak-height ratios ranged from... 

Ioannou et al. [41] reported the use of terbium sensitized fluorescence to develop a sensitive and simple fluorimetric method for the determination of the anthranilic acid derivative, mefenamic acid. The method makes use of radiative energy transfer from anthranilate to Tb(III) in alkaline methanolic solutions. Optimum conditions for the formation of the anthranilate-Tb(III) complex were investigated. Under optimized conditions, the detection limit was 1.4 x 10-8 mol/L, and the range of application was 2.5 x 10 8 to 5.0 x 10 5 mol/L. The method was successfully applied to the determination of mefenamic acid in serum after extraction of the sample with ethyl acetate, evaporation of the organic layer under a stream of nitrogen at 40°C, and reconstitution of the residue with alkaline methanolic terbium solution prior to instrumental measurement. The mean recovery from serum samples spiked with mefenamic acid (3.0 x 10-6, 9.0 x 10-6, 3.0 x 10-5 mol/L) was 101 5%. The within-run precision (RSD) for the method for the two serum samples varied from 2 to 8%, and the day-to-day precision for two concentration levels varied from 2 to 13%. 

Human specimens. In our laboratory, we first developed a good laboratory practice (GLP)-validated procedure for quantification of intact rafAON in control human plasma. The rafAON assay validation endpoints were standard curve, between-run precision and accuracy, within-run precision and accuracy, effects of dilution and freeze thaw, stability of rafAON at -80° C, and 4°C in plasma for various times, specificity, integrity of rafAON during plasma sample collection and processing, and lipid interference. The reader is referred to a previous citation for further details (17,27). 

Precision of an assay describes how well an assay result can be reproduced. Within-run precision is defined as the precision of the same sample run on several occasions with the same assay under the same assay conditions. Between-run precision is an index of the ability of the assay to reproduce the same result on the same sample at different runs, time moments, by different operators or in different labs. Precision is described by the variance (s ), standard deviation (s) and coefficient of variation (CV). 

To quantitate the ascorbic content of various tissues, a standard curve (3.0-50 /xg/mL ascorbic acid) was prepared in 3% metaphosphoric for each analytical run. A typical standard curve is shown in Figure 4. Correlation coeflBcients of 0.998 or better were consistently obtained for the standard curve. Pooled serum samples were used to measure day-to-day and within-run precision. The coeflBcient of variation for within-run... 

Repeatability closeness of agreement between results of successive measurements carried out under the same conditions (i.e., corresponding to within-run precision). Reproducibility closeness of agreement between results of measurements performed under changed conditions of measurements (e.g., time, operators, calibrators, and reagent lots). Two specifications of reproducibility are often used total or between-run precision in the laboratory, often termed intermediate precision and interlaboratory precision (e.g., as observed m external quality assessment schemes [EQAS]) (see Table 14-2). 

Aiach and co-workers have reported on the adoption of five different substrate assays onto an automated discrete analyzer (A2). They observed excellent within-run precision coefficient of variation (CV) values ranging from 1 to 3%, as well as satisfactory day-to-day precision. Ito and Statland similarly evaluated and compared the DuPont aca and Kabi/CentrifiChem automated method for measuring antithrombin III and plasminogen (13). 

The precision data is shown in Table 1. Three serum samples were assayed in replicates of 2, two separate times per day, for 20 testing days. Within-run precision and Total precision were calculated according to the NCCLS EP5-A protocol. 

Precision. The within-run precision of the assay was determined by assaying three control sera, corresponding to different levels of T4 (mean T4 concentrations of 15, 59.3, and 122 ng/mL), in 12 replicates in a single assay. For the determination of the between-run precision, duplicate measurements of these control sera were performed in 12 different runs. The within-run CVs were 4.5, 5.6, and 4.0% (mean), and the between-run CVs were 5.4, 10.3, and 5.9%, respectively. 

Angerer et al. (1985) developed a GFAAS method for the determination of copper in serum and urine. The samples were directly injected into the graphite tube. The injected volume was 10 for serum and 50 /matrix matched samples. Within run precision for serum with 1 mg/L copper concentration was 2.3%, for urine in the range of 20.8 to 126.6 g/L from 2.3% to 4.1%. Accuracy was tested with reference samples and by the FAAS method developed at the same time (Winter and Schaller, 1985). Under the given conditions the detection limit was 0.015 mg/L for serum and 3 Wg/L for urine. 

The within-run precision (SD ) measures the random error during processing of a single batch of samples analyzed at the same time. 

Overall precision (S ) was calculated by combining within-run precision (Sj) and between-run precision... 

Another important area of terminology is the difference between reproducibility and repeatability. We can illustrate this by an extension of our previous experiment. In the normal way student A (for example) would do the five replicate titrations in rapid succession very probably the whole exercise would not take more than an hour or so. The same set of solutions and the same glassware would be used throughout, the same preparation of indicator would be added to each titration flask, and the temperature, humidity and other laboratory conditions would remain much the same. In such circumstances the precision measured would be the within-run precision this is called the repeatability. Suppose, however, that for some reason the... 

A method is required to analyse noise and reproducibility in biomedical vibrational spectroscopy. If spectra are compared at a single wavenumber only, the nomenclature and calculation procedures could readily follow the univariate methods used to evaluate single parameter measurements in standard analytical chemistry. The concepts of precision and bias are frequently introduced in analytical chemistry in order to distinguish between the random noise and the systematic error. While precision evaluates the deviation among repeated measurements and is therefore meant to address the random errors in the quantification of analytes, the bias enumerates the difference between the mean of the average results of repeated measurements and the reference value. Finally, the term accuracy covers both the precision and the bias and it is defined as the closeness of agreement between a test result and the accepted reference value. In analytical chemistry, another frequent distinction is made between the within-run precision ( repeatability ) and the between-run precision ( reproducibility ). These terms are adequate for a univariate comparison of a measured value with a reference value. 

Precision, which is a measure of the variability or dispersion within a set of replicated values or results obtained under the same prescribed conditions, can be assessed in several ways. The spread or range (i.e. the difference between the highest and lowest value) is sometimes used, but the most popular method is to estimate the standard deviation of the data (vide infra). The precision of results obtained within one working session is known as repeatability or within-run precision. The precision of results obtained over a series of working sessions is known as reproducibility or between-runs precision. It is sometimes necessary to separate the contributions made to the overall precision by within-run and... 

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