Control blank value

Different Control Charts Blank Value Chart... 

We can convert all types of classical control chart (X-chart, blank value, recovery, range control chart etc.) into target control charts. 

There is no normal dstribution ofthe values fom the control sample due to persisting out of control situations (e.g. blank values)... 

To obtain blank values it is not suflScient to treat a duplicate incubation mixture with so-called diazo-blank reagent (NaN02 omitted from the diazo reagent), as is common practice in assaying serum or bile (H12). Contributions (b)-(d) would be obtained with the test, not with the control mixture. A control incubation mixture, treated with diazo reagent in parallel with the text mixture, will adequately measure contributions (b)-(f). Whether endogenous conjugate formation in the incubation control (contribution a) is suppressed completely or not, must depend on the preference of the reader (Sections 3.1.4 and 3.2). 

Second Control Run. The second run is compared to the first. Improved slope, smaller blank values, and smaller standard deviations are desir-... 

Three calibration blank standards should be analyzed to establish a representative blank level, after which the calibration standards are analyzed. After calibration, the quality control standard should be analyzed to verify the calibration. The sample introduction system is flushed with rinse blank, and the blank solution is analyzed to check for carry-over and the blank level. If the blank level is acceptable, the samples can be analyzed. If the blank values are too high, the flushing of the sample introduction system and analysis of the blank solution should be repeated until an acceptable blank level is reached. The calibration blank value, which is the same as the absolute value of the instrument response, must be lower than the method s detection limit. 

Method A. The rationale of method A is that HDL and LDL are separated by selective precipitation of LDL by dextran sulfate and Mg2+ after the reaction between LDL and reconstituted HDL containing radiolabeled CE by CETP. The method was originally described by Kato et al. [77], The assay mixtures consist of reconstituted [14C]CE-HDL as the donor for CE, LDL as the acceptor, 5,5 -dithiobis-2-nitrobenzoic acid, bovine serum albumin (BSA), partially purified CETP, and a test sample in Eppendorf tubes (1.5 ml). After a 30-min incubation at 37°C, the reaction is terminated by the addition of an LDL-precipitation solution. After standing for 20 min in an ice bath, the assay mixtures are centrifuged, and the supernatant solution containing [14C]CE-HDL is analyzed for radioactivity. Furthermore, the [14C]CE-LDL precipitate is also analyzed for radioactivity if necessary. Usually the blank and control transfer values are about 6% and 34% of initial [14C]CE-HDL added under the assay conditions, respectively. 

The quality control procedures, recovery experiments and blank values were examined. It was decided to reject all data obtained with the following recovery values less than 70%,... 

The quality control procedures, recovery experiments and blank values were examined. It was decided to reject all data obtained with recovery values exceeding lOO V o by more than the standard deviation. Some of the data were withdrawn, the reasons including bad peak shapes, doubts about calibration, insufficient chromatographic separation, doubts about peak purity incorrect peak assignment. 

The usage of quality control charts in the field of quality assurance is based on the assumption that the determined results are distributed normally. Typical control charts used in a LIMS for routine analysis are, for example, the Shewhart charts for mean and blank value control, the retrieval frequency control chart, and the range and single-value control chart [19]. Quality regulation charts can be displayed graphically in the system or exported to spreadsheet programs. 

Due to the widespread use phthalates can be found everywhere, not only in soil but also in the laboratory environment, in the usual packing materials for samples and also in solvents. Controlling and reducing the blank values therefore is the main problem in the determination of phthalates. 

Interpreting the results of phthalate determinations in soil may be rather difficult. Even if blank values are really under control, phthalate contents, especially DEHP, may be caused by some artefacts, even the presence of pieces of plastics in the sample. If large samples have been pre-treated by milling, such an artefact may be difficult to recognise. Therefore, a different strategy should be considered and taking a number of small size samples that can be visually inspected may be a better choice. In any case the analyst should have a close look at the contents of the sample container in taking the required portion for... 

The EPA Contract Laboratory Program under Superfund (CERCLA) provides another example of how blanks and detection limits are treated.(17)(18) With respect to blanks, the statements of work specify that the laboratory should not blank correct sample responses. In the case of organics analyses, the EPA evaluator and/or data auditor has the authority to blank correct sample responses. In practice this Is never done. For both organics and Inorganics, the absolute blank level Is primarily used as a control to determine If samples need to be reanalyzed. Detection limits are based on replicate analyses of a standard at 3-5 times the required detection limit concentration. The Instrument detection limit Is calculated as being equal to 3 times the standard deviation of the measured value. Since blank correction is not permitted or not done, sample results will all be biased high by an amount equal to the blank response. The absolute blank value (actually usually a multiple of 5 or 10 times the blank value) rather than... 

Operation of a recovery control chart, when systematic errors from matrix interferences are expected Measurement of two blank solutions at the beginning and at the end of a batch in order to identify contamination of reagents, of the measurement system and instrumental faults and documentation of the blank values on a blank control chart... 

Here, Q is the initial solution concentration and Cf is the final solution concentration. Comparison of the k values for the imprinted and control blank gels can show the effect of imprinting on the metal-ion selectivity for a given material. A measure of the increase in selectivity due to molecular imprinting can be defined by the ratio of the selectivity coefficients of the imprinted (MIP) and nonimprinted (NP) materials ... 

Princi (1947), Smith et al. (1955), Smith and Kench (1957), and Tsuchiya (1967) used colorimetric procedures similar to those described in the CDB section above to estimate CDU concentrations. In these methods, urine (50 ml) is reduced to dryness by heating in a sand bath and digested (wet ashed) with mineral acids. Cadmium then is complexed with dithiazone, extracted with chloroform and quantified by spectrophotometry. These early studies typically report reagent blank values equivalent to 0.3 pg Cd/I, and CDU concentrations among nonexposed control groups at maximum levels of 10 pg Cd/I—erroneously high values when compared to more recent surveys of cadmium concentrations in the general population. 

The blank value control card represents a special application form of the mean value control card and gives direction as to the reagents and the measuring system to be used. Because it would be too expensive to determine the blank value for every analysis, it is reasonable to carry out two blank value determinations for every analysis series, one at the beginning and one at the end of the analysis series. Such a procedure has the advantage of an additional drift control in addition to the precise determination of the blank value. 

The reagent and system blanks must be recorded at specified intervals. These intervals may be related to the number of samples processed or may be fixed periods of time. Changes in the analytical system, including replacement of parts of the detector and new sets of reagents, should always be followed by blank controls. The blank values should be monitored using control charts. 

Some years ago, a microprocessor-controlled flow-stream system was introduced for the determination of ultratrace levels of easily reducible mercury in water samples (Stockwell et. al., 1989). The system is based on an autosampler, reduction unit, gas-liquid separator, gold trap and APS monitor and allows processing of 8 samples per hour. For sample volumes of 4S mL, a detection limit (3 s of the blank values) of 0.1 ng/L was found with an analytical precision of 5 % (Cossa et al., 1995). 

A stock of sub-boiled and blank-controlled acids is prepared and a dilution of a metal standard solution e.g., 100mg/L of gallium). Several separation procedures are performed to clean the Teflon bombs (refer to next section), until the blank values are constant and low. 

Mean value control card (and blank value control card)... 

The detection limit differs from laboratory to laboratory and is situated between 10 and 40 Mg/g. Using pressure digestion and the micro Kjeldahl method concentrations as low as 1 ug/g can however be determined. The essential conditions for obtaining accurate analytical results in the Kjeldahl process are complete control of the blank value and rigid exclusion of contamination from the atmosphere of the laboratory. It is therefore advisable to determine the blank value by the use of very pure aluminium, and to carry out the determination in a separate room in an atmosphere free from ammonia and nitric acid". 

The detection limits were different for each laboratory and are situated between 10 and 40 Mg/g of nitrogen. In the micro-Kjeldahl method the detection limit is however as low as 1 Mg/g. To obtain accurate results using the Kjeldahl method it proved however to be necessary to control the blank value in a correct way and to avoid contamination from the laboratory environment. It was therefore recommended to determine the blank value with ultra pure aluminium and to carry out the analyses in a clean room with an atmosphere free of ammonia and nitric acid (64). These good results were confirmed in certification analyses carried out within BCR on candidate reference materials for nitrogen in titanium metal and TiA16V4 alloy (Table VI-12). 

Bachmann, H. J. (1996). Special aspects in automatic analysis of environmental samples (soil extracts, fertilizers, plant material) with ICP-MS Blank values, quality control, retrospective analysis. Analusis 24(9-10), 32. 

Control or blank experiments have frequently to be employed in organic estimations. Their value is twofold ... 

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