Single level calibration

Single level calibration Linear through zero and response factor... 

In the calibration routine, peak data of the unknowns are related to those of the calibration standards. From several calibration functions the most suitable for the task can be chosen. Single-level calibration (not to be mistaken for single-standard calibration) is the method of choice when the expected concentration in the unknowns is a fixed value, e.g. in content uniformity tests. It allows the use of a maximum ratio of unknowns to calibration standards with favorable error propagation. Only the results of unknowns within a narrow, user selectable range are accepted for calculations. The width of the range is defined by linearity and slope of the calibration function as established during method validation. 

Quantitation is performed by the single-point calibration technique. The calibration standard should be at a level similar to the expected residues and should be injected after every 3 samples throughout the sample batch. The mean response of the calibration standards which bracket the sample should be used for the residue calculation. 

This definition also implies the duality between the hierarchical establishing of traceability and the corresponding cumulative effect of the uncertainties referring to the single levels of the calibration chain [7]. 

Demonstration of linear response enables the use of single point calibration techniques, which can offer considerable cost savings regarding the number of calibration materials that must be maintained and the time it takes to calibrate the on-line analyzer. A 2000 ppmw standard was made with 7.88 g of pure dibutyl sulfide diluted in 1 L of toluene. This standard was further diluted sequentially 1 1 nine times until the expected sulfur concentration in the sample was down to 3.91 mg/kg. Each of these 10 samples were injected multiple times in a 6000 series analyzer that was set for a 2500 ppmw full scale range and calibrated with the 2000 ppmw sample (see Figs. 8 and 9). Data from the results of the 16.13 ppmw sample were lost due to a data acquisition problem. The data, shown in Table 3, indicate a % RSD of better than 1 % in the sulfur range 62-2000 mg/kg. At lower sulfur levels of 4-31 mg/kg, the %RSD is 11-2 %. 

It should be emphasized that this graph represents a single-element calibration. However, because ICP-MS is usually used for multielement analysis, multielement standards are typically used to generate calibration data. For that reason, it is absolutely essential to use multielement standards that have been manufactured specifically for ICP-MS. Single-element AA standards are not suitable, because they usually have only been certified for the analyte element and not for any others. The purity of the standard cannot be guaranteed for any other element and as a result cannot be used to make up multielement standards for use with ICP-MS. For the same reason, ICP-OES multielement standards are not advisable either, because they are only certified for a group of elements and could contain other elements at higher levels, which will affect the ICP-MS multielement calibration. 

A single-point calibration was used at a level of 10 ng/L. The concentration is calculated on the actual levels in the water sample. The result shown in Figure 4.36 demonstrates the method capability to reach 0.05 ng/L of organotins in the water sample and below. The actual amount injected on column was 0.2 pg for each organotin compound. Calculations were performed using tripropyltin as internal standard. 

Individual Working Standards (Tier 2-Quantitation)—Working standards are typically prepared in isooctane at concentrations of 0.02 ug/mL, 0.05 ug/mL, 0.1 u/mL, 0.3 Ug/mL and 0.5 ug/mL for Aroclors 1016 and 1260. All other Aroclors are prepared at the mid level concentration (0.1 Ug/mL) for the single point calibration. An alternative calibration range may be used as long as the criteria for linearity of the calibration range is documented. 

Prepare a single multicomponent working standard from the stock standards by making appropriate dilutions with methanol. Concentrations in the working standards should be at such a level that a 20- xL sample added to 100 mL of water gives a calibration standard whose response for each trihalomethane is within 25% of that for the samples to be analyzed. 

The MSF model (NUREG/CR-3837) is used principally to determine the level of dependence between safety systems introduced by maintenance, testing, and calibration activities. It is a mathematical model which modifies the independent failure probability of any single component by considering that a component with which it is redundant has already failed. This allows the conditional failure probabilities of redundant components to be calculated to determine the overall system failure probability. Documentation requirements are given in Table 4.5-6. 

Determinarion of MW and MWD by SEC using commercial narrow molecular weight distribution polystyrene as calibration standards is an ASTM-D5296 standard method for polystyrene (11). However, no data on precision are included in the 1997 edition of the ASTM method. In the ASTM-D3536 method for gel-permeation chromatography from seven replicates, the M of a polystyrene is 263,000 30,000 (11.4%) for a single determination within the 95% confidence level (12). A relative standard deviation of 3.9% was reported for a cooperative determination of of polystyrene by SEC (7). In another cooperative study, a 11.3% relative standard deviation in M, of polystyrene by GPC was reported (13). 

For solution-based analyses, it is normal to make up a set of synthetic standards from commercial calibration solutions (normally supplied as 1000 ppm stock solutions, e.g., from Aldrich, BDH, Fisons, or ROMIL). These are available to different degrees of purity, and it is necessary to use the level of purity commensurate with the sensitivity of the analytical technique to be used it is, however, better not to use the highest purity in all circumstances, since these are very expensive. Ideally each element to be determined in the sample should be calibrated against a standard solution containing that element, although interpolation is sometimes possible between adjacent elements in the periodic table, if some elements are missing. For most techniques, it is better to mix up a single standard solution... 

The introduction of EU directives on Waste Electrical and Electronic Equipment and Reduction of Hazardous Substances has highlighted the need for precise and repeatable elemental analysis of heavy metals in the plastics production process. X-ray fluorescence (XRF) spectroscopy has emerged as the most economical and effective analytical tool for achieving this. A set of certified standards, known as TOXEL, is now available to facilitate XRF analyses in PE. Calibration with TOXEL standards is simplified by the fact that XRF is a multi-element technique. Therefore a single set of the new standards can be used to calibrate several heavy elements, covering concentrations from trace level to several hundred ppm. This case study is the analysis of heavy metals in PE using an Epsilon 5 XRF spectrometer. 

A SIMCA model is actually an assembly of J class-specific PCA models, each of which is built using only the calibration samples of a single class. At that point, confidence levels for the Hotelling P and Q values (recall Equations 12.21 and 12.22) for each class can be determined independently. A SIMCA model is applied to an unknown sample by applying its analytical profile to each of the J PCA models, which leads to the generation of J sets of Hotelling P and Q statistics for that sample. At this point, separate assessments of the unknown sample s membership to each class can be made, based on the P and Q values for that sample, and the previously determined confidence levels. 

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