Calibration controlling

A pH electrode is normally standardized using two buffers one near a pH of 7 and one that is more acidic or basic depending on the sample s expected pH. The pH electrode is immersed in the first buffer, and the standardize or calibrate control is adjusted until the meter reads the correct pH. The electrode is placed in the second buffer, and the slope or temperature control is adjusted to the-buffer s pH. Some pH meters are equipped with a temperature compensation feature, allowing the pH meter to correct the measured pH for any change in temperature. In this case a thermistor is placed in the sample and connected to the pH meter. The temperature control is set to the solution s temperature, and the pH meter is calibrated using the calibrate and slope controls. If a change in the sample s temperature is indicated by the thermistor, the pH meter adjusts the slope of the calibration based on an assumed Nerstian response of 2.303RT/F. 

A second reason for using reference materials in clinical chemistry is to ensure values obtained are traceable to those in a recognized, authoritative reference material (Johnson et al. 1996). As a result, the assignment of values of secondary and tertiary reference materials, calibrants, controls, and proficiency samples shordd be performed as precisely as possible (Johnson et al. 1996). Surprisingly there is still debate on this topic, and on the need for clinical chemistry to incorporate the principals of analytical quality assurance (Dybkaer et al. 1999). 

Pankey et al.21 described a rapid, reliable, and specific enzyme multiplied immunoassay technique (EMIT ) for amitriptyline, nortriptyline, imipramine, and desipramine in sera. To overcome crossreactivity, solid phase extraction was included in sample pretreatment. Disposable 1 mL columns packed with covalently labeled silica gel were conditioned with HPLC-grade methanol (1 mL) and then with de-ionized or distilled water (1 mL). Serum (calibrator, control, or patient sample, 500 L) was applied onto the column, eluted to waste, washed with 900 /uL of wash solution containing acetonitrile (236.1 g/L) and ion-pairing reagent in acetate buffer, pH 4.2, washed with 500 fiL of mobile phase solution containing acetonitrile (393.5 g/L) in methanolic phosphate buffer, pH 7.0,... 

Blank, calibrator, control, and patient whole-blood samples (50 /iL) were transferred into 1.5 mL conical test tubes, mixed with 100 /xL of the IS, vortexed for 10 sec, and centrifuged at 13,000 g for 5 min. Twenty-five microliters of supernatant were injected onto a Cohesive Technologies Cyclone polymeric turbulent flow column (50 x 1 mm, 50 /flushed with a mixture of methanol and water (10 90 v/v) at a flow of 5 mL/min. Column switching from the TFC to HPLC systems was via a Cohesive Technologies system. The analytical column was a Phenomenex Phenyl-Hexyl-RP (50 x 2.1 mm, 5 /.mi). The mobile phase consisted of methanol and ammonium acetate buffer (97 3 v/v). The buffer was 10mM ammonium acetate containing 0.1% v/v acetic acid. The flow rate was 0.6 mL/min. 

Even once a method is standardized, erroneous results can still be generated. As a result, it is critical to have robust quality control procedures in place. Here, careful attention should be paid to identify opportunity for in-process control measures such as internal standards, calibration, control plates, replicates and so on as opposed to post-processing data review steps. Inline QC approaches allow sources of error to be identified and remedied much more rapidly and help limit costly re-tests, or the possibility of erroneous data leaving the laboratory. 

Do the records include details of calibration controls, environmental data, designated error limits, and information necessary to establish traceability ... 

Calibration control standards (CCSs) are used to check calibration. The CCS is the first sample analyzed after calibration. Its concentration may or may not be known, but it is used for successive comparisons. A CCS may be analyzed periodically or after a specified number of samples (say, 20). The CCS value can be plotted on a control chart to monitor statistical control. 

Transfer a 25.0-mL aliquot of the distillate into a 250-mL plastic beaker, and dilute to 100 mL with the Buffer Solution. Place the fluoride ion and reference electrodes (or a combination fluoride electrode) of a suitable ion-selective electrode apparatus in the solution. Adjust the calibration control until the indicator needle points to the center on the logarithmic concentration scale, allowing sufficient time for equilibration (about 20 min), and stirring constantly during the equilibration period and throughout the remainder of the procedure. Pipet... 

Figure 20.15. Digital image of bread obtained by automated image analysis (C-Cell, Calibre Controls).

Fig. 7.3 The relationship between electrical potential and pH. The solid line shows the response of a calibrated electrode while the other plots are for instruments requiring calibration 1 has the correct slope but incorrect isopotential point (calibration control adjustment is needed) 2 has the correct isopotential point but incorrect slope (slope control adjustment is needed).

Lyophilization (freeze drying) is used in laboratory medicine for the preparation of calibrators, control materials, reagents, and to a lesser extent individual specimens for analysis. Lyophilization first entails freezing a material at -40 °C or less and then subjecting it to a high vacuum. Very low temperatures cause the ice to sublime solid nonsub-limable material, initially locked in an ice matrix, remains behind in a dried state. 

For compendial purposes, pH is defined as the value given by a suitable, properly standardized, potentiometric instrument (pH meter) capable of reproducing pH values to 0.02 pH unit using an indicator electrode sensitive to hydrogen ion activity, the glass electrode, and a suitable reference electrode. The instrument should be capable of sensing the potential across the electrode pair and, for pH sfandardization purposes, applying an adjustable potential to the circuit by manipulation of "standardization," "zero," asymmetry, or "calibration" control. 

To standardize the pH meter, select two buffer solutions for standardization whose difference in pH does not exceed 4 units, and such that the expected pH of the material under test falls between them. Fill the cell with one of the buffer solutions for standardization at the temperature at which the test material is to be measured. Set the control "temperature" at the temperature of the solution, and adjust the calibration control to make the observed pH value identical with that tabulated. Rinse the electrodes and the cell with several portions of the second buffer solution for standardization, then fill the cell with it, at the same temperature as the material to be measured. The pH of the second buffer solution is within +0.07 pH emit of the tabulated value. If a larger deviation is noted, examine the electrodes and, if they are faulty, replace them. Adjust the "slope" or "temperature" control to make the observed pH value identical with that tabulated. Repeat the standardization tmtil both buffer solutions for standardization give observed pH values within 0.02 pH unit of the tabulated value without further adjustment of the control. When the system functions satisfactorily, rinse the electrodes and cell several times with a few portions of the test material, fill the cell with the test material, and read the pH value. Use carbon dioxide-free water for solution or dilution of test material in pH determinations. In all pH measurements, allow a sufficient time for stabilization. 

Calibrate the instrument set the meter to pH mode, if appropriate, and then place the electrode assembly in a standard solution of known pH, usually pH 7.00. This solution may be supplied as a liquid, or may be prepared by dissolving a measured amount of a calibration standard in water calibration standards are often provided in tablet form, to be dissolved in water to give a particular volume of solution. Adjust the calibration control to give the correct reading. Remember that your calibration standards will only give the specified pH at a particular temperature, usually either 20 C or 25 C. If you are working at a different temperature, you must establish the actual pH of your calibration standards, either from the supplier, or from literature information. 

Calibration should be traceable to national or international standards through an unbroken chain of comparisons. For instrumentation affecting sterility control in aseptic manufacturing facilities this usually involves comparison of values measured with the item of equipment under test, say a particle counter or a pressure differential gauge, with values measured with a standardized device. In many cases this may mean the use of external contract calibration services, with all that this implies in relation to assuring that the contractor s calibration control systems are themselves under good control. 

National Conference of Standards Laboratories (1986). Recommended Practice, Medical Products and Pharmaceutical Industry Calibration Control System,... 

Analytical sensitivity may be significantly improved for samples from preclinical toxicology studies where samples are analyzed in batches with concurrent controls, in comparison with samples submitted for individual animals. This batch analysis reduces interassay variation due to differences in reagents, calibrators, controls, analyzers, and analysts. 

MRP 11 or ERP systems provide functionality for not only production planning and manufacturing but also ordering, receiving, warehouses, shipping and so on. These systems support supply chain management and may include related functions such as maintenance, calibration control and human resource information. 

The electrodes are normally stored in distilled or deionized water and should be rinsed with deionized water before use. The electrodes can be dried by draining the excess water off onto a tissue. The electrode must be standardized by immersion in buffer solutions whose pH are well separated. The procedure is to immerse the electrodes in the buffer solution for a period of 1 min with continuous stirring and observe the value which is then adjusted to the buffer value by the pH or calibration control. The electrode is then rinsed and dried and immersed in the second buffer solution and allowed to equilibrate for 1 min with stirring and the second buffer value is read. If this differs from that which is expected then the slope control of the pH meter should be altered. This whole procedure is then repeated until the values obtained in the buffer solutions at each end of the pH range agree with those of the known buffer solution. 

In the first set of experiments, the uramum concentration was varied, kee ng the side and end reflector 2 to 3 ft thick. For each concentration several pseudo-cylinders were constructed with slightly different core cross-sectional areas, and their excess reactivities determined by calibrated control rods. Cores of difierent cross section but equivalent cross-scctional area were found to have the same reactivity within five cents. Therefore, the critical diameter for each concentration can be reported. 

Tlie siiecial elements used in the reactivity worth measurements consisted of graphite compacts containing the isotopes U, and Np loaded Into sealed aluminum tubes. These elements were substituted in place of a special all-graphite element at the central location and the change in reactivity measured using calibrated control rods. Measurements were also made on a series of boron- and gold-loaded special elements that were used as standards. 

Mercury D (2007) GMPT Approach to After-treatment Calibration Control. Proceedings of the SAE TopTec Optimizing Powertrain Future Improvements through Control Symposium , Turin June 12-14, 2007... 

Propose a general rule for how long the reactor must be level before the control element is moved and how long one should wait after element motion has ceased to get period or doubling time measurements accurate to 1%. Identify sources of error in control element worth curves and estimate the accuracy of the reactivity of the calibrated control element. Be sure to use the repeated measurement you made in step 9 of rising period measurement. 

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