Blank analysis, quality control

Each laboratory should have a quality assurance program which should be well understood and used by individuals as well as by laboratory organizations to prevent, detect, and correct problems. The purpose is to ensure that the results have a high probability of being of acceptable quality. Ongoing activities may include preventative instrument maintenance, performance verification and calibration, system suitability testing, analysis of blanks and quality control samples, and ensuring system security. A plan should be set up to... 

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. 

Brandt [200] has extracted tri(nonylphenyl) phosphite (TNPP) from a styrene-butadiene polymer using iso-octane. Brown [211] has reported US extraction of acrylic acid monomer from polyacrylates. Ultrasonication was also shown to be a fast and efficient extraction method for organophosphate ester flame retardants and plasticisers [212]. Greenpeace [213] has recently reported the concentration of phthalate esters in 72 toys (mostly made in China) using shaking and sonication extraction methods. Extraction and analytical procedures were carefully quality controlled. QC procedures and acceptance criteria were based on USEPA method 606 for the analysis of phthalates in water samples [214]. Extraction efficiency was tested by spiking blank matrix and by standard addition to phthalate-containing samples. For removal of fatty acids from the surface of EVA pellets a lmin ultrasonic bath treatment in isopropanol is sufficient [215]. It has been noticed that the experimental ultrasonic extraction conditions are often ill defined and do not allow independent verification. 

Data verification, also called quality control (QC), to verify the results before reporting, including statistical analysis of duplicates, standards, and blanks. 

Quality controls are single procednres that are performed in conjnnction with an analysis to help assess the snccess of the analysis in a qnantitative manner. Examples of qnality controls are blanks, calibration, calibration verification. 

An added elution step was used in this experiment to check the completeness of elution and the cleanliness of the resin. After sampling and elution of the resin (200 mL, 2 X 150 mL) with ethyl ether, the resin column was eluted with an additional 200 mL of ether, which was then concentrated to 1 mL for broad spectrum GC analysis. This fourth elution was a quality control blank for the subsequent reuse of the resin (Figure 2, top chromatogram). 

The laboratory quality control program has several components documentation of standard operating procedures for all analytical methods, periodic determination of method detection levels for the analytes, preparation of standard calibration curves and daily check of calibration standards, analysis of reagent blank, instrument performance check, determination of precision and accuracy of analysis, and preparation of control charts. Determination of precision and accuracy of analysis and method detection limits are described under separate subheadings in the following sections. The other components of the quality control plan are briefly discussed below. 

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. 

Quality control procedures are generally established to provide checks on the data that have been collected to evaluate whether in fact the quality assurance procedures were followed and whether the data meet agreed-upon norms. Otherwise, it is difficult for the user to judge the integrity of a data set per se, because there may be few ways to tell that procedures were not followed or values properly recorded. Quality control measures can be linked to the quality assurance procedures. In the example given above for use of field blanks, spikes and duplicate samples, laboratories must provide evidence that their analysis of these samples meets acceptable statistical guidelines for accuracy and precision. Quality control can also simply involve careful analysis of a data set to determine whether it is internally consistent. 

For foodstuff matrices, the use of PFA labware and H2O2 reagent improved the conventional analytical parameters (LoDs, level of blanks, stability, recovery rate, and also the speed of analyses. The quantification of lead at low concentration was possible down to 9 pig kg-1, whereas in the recent past the LoD in the same laboratory was at about 35 pig kg-1, thus making participation in the previous FAPAS S7R40 PT impossible. Thanks to the improved procedure, more parameters of quality control could be integrated in the program, that is, recovery rate is calculated for each run of sample and this without lengthening analysis time. 

At least 10 % of the samples should be quality control samples. Blank sampling cartridges should be taken to the field and returned to the laboratory for analysis however, they should not be exposed to the air. Spiked sampling media may also be similarly transported as field controls. 

Once sampling is completed, sampling media should be placed immediately in appropriate clean, sealed containers and placed on ice or dry ice for return or shipment to the laboratory. The sealed containers should be placed in a freezer maintained at -20 °C or lower until extracted. Media should not be stored for more than about two weeks. Frozen extracts may be safely stored for 90d or more. At least 10% of the samples shonld be quality control samples. Blank media should be taken to the field, briefly removed from the containers to air, and then retnmed to the laboratory for analysis. 

The term quality control (QC) is applied to procedures used to provide evidence of quality and confidence in the analytical results. It includes use of blanks, replication, analysing reference materials or other well-defined samples and participation in Proficiency Testing schemes. Several other features of analysis forming part of QC are control of reagents and instrumentation, equipment maintenance and calibration, and procedures for checking calculations and data transfer. It should be noted that what is referred to as quality assurance in the UK is known as quality control in Japan. 

Control samples should have a high degree of similarity to the actual samples analyzed otherwise, one cannot draw reliable conclusions on the measurement system s performance. Control samples must be so homogeneous and stable that individual increments measured at various times will have less variability than the measurement process itself. Quality Control samples are prepared by adding known amounts of analytes to blank specimens. They can be purchased as certified reference material (CRM) or may be prepared in-house. In the latter case, sufficient quantities should be prepared to allow the same samples to be used over a longer period of time. Their stability over time should be proven and their accuracy verified, preferably through interlaboratory tests or by other analysis methods. 

Standard quality control procedures were followed. These Included a) careful washing of all glassware In strong oxidizing solutions and with Type I water b) frequent analyses of glassware and reagent blanks c) analyses of procedural blanks with each batch of samples and d) calibration of Instruments before each set of analyses by analyzing standard solutions. Analytical proficiency In the analysis of biota and sediment samples have been demonstrated by participation In round-robin type Interlaboratory calibration exercises (2 ). 

Approximately one liter of rainfall-runoff solution was collected from each of three experimental racks following rainfall events. Limestone and marble reference rocks were in two of the racks a third rack without a rock was used as a control (hereinafter referred to as a blank sample). Runoff volume, specific conductance, and pH measurements were determined at the exposure site as soon as possible after collection, typically within a few hours. Samples then were filtered through a 0.45-micrometer pore size membrane filter, placed in a clean polyethlyene bottle, and sent to the U.S. Geological Survey laboratory in Denver, Colorado, for chemical analysis. Sample preparation, analytical procedures, and laboratory quality-control protocols are described by Skougstad et al. (6). 

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. 

Quality control procedures should include blanks to indicate contamination. Replicate sample analysis indicates random contamination and precision. Accuracy can be assessed by quantitative recovery of added Al, including use of CRMs that are similar in nature to the samples, utilization of more than one procedure such as standard additions and comparison to aqueous standard curve, comparison to another analytical technique and/or participation in inter-laboratory comparison programs. 

Analysis It involves several steps, including, calibration, replication, the use of quality control (QC), and quality assurance (QA) measures, and the experimental design should also address the use of suitable blanks and control samples. The measurements are obtained using specialized analytical instrumentation. 

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