Range and precision

The molar absorptivity of the partly reduced heteropoly acid is 22700 at 880 nm, which means that the net absorbance for a l.O/xmol/L phosphate sample is 0.227 measured in a 10 cm cuvette. With a good spectrophotometer an absorbance of 0.002 can be read, and the smallest concentration of phosphate-phosphorus that can be determined directly thus is 0.01 /imol/L. The absorbances are a linear function of the concentrations up to 28 /imol/L, equal to a net absorbance of approximately 0.630 in a 1 cm cell. 

A spectrophotometer wavelength of 660-700 nm can be used for the determination of high phosphate concentrations, or if required by the spectrophotometer design (e.g., an LED photometer). This results in a loss of sensitivity of about 30 % (see Section 10.3.4.4, Fig. 10-24). 

In the report of the ICES/SCOR nutrient calibration, Koroleff and Palmork (1977) give a relative precision for phosphate of 15 % at the low level (0.2 /unol/L), at the medium level (0.9pimol/L) +5% and at the high level (2.8/imol/L) 2%. At the Baltic Intercalibration Workshop (Kiel, 1977) nearly identical results were obtained with natural samples having salinities of from 5 to 34. The Fifth ICES Intercomparison Exercise (Aminot and Kirkwood, 

1995) confinned these results. Standard deviations of 0.03-0.09/iinol/L were found for phosphate concentrations up to 3 pmol/L. This is considerably higher than the reproducibility in the laboratory of 0.02-0.03 pmol/L Riley et aL, 1972 Strickland and Parsons, 1968). 

---

Balances and measuring equipment of an appropriate range and precision should be available for production and control operations. Measuring, weighing, recording, and control equipment should be calibrated and checked at predetermined intervals by appropriate methods. Adequate records of such tests should be maintained [10]. 

The performance of analytical methods based on atomic spectrometry is characterized by Pgures of merit, such as LoDs and limits of quantiPcation (LoQs), linear dynamic range, and precision and accuracy of measurements. 

In addition to the usual evaluation parameters for analytical methods (Chapter 16), the sensitivity, detection limit, dynamic range, and precision profile, biosensors are also characterized with respect to the rapidity of their response and recovery. This... 

Hydride generation can also be used for sample introduction into a helium, argon or neon discharge and depending on the pressure and current more molecular ions or atomic species are found. The technique has excellent sensitivity and a fairly good dynamic range and precision [660],... 

Brauner, N. and Shacham, M. (1998) Role of range and precision of the independent variable in regression of data. AIChE, 44, 603-611. 

The values of A0 computed in this way from Shedlovsky s measurements are given in the last column of Table I. It will be seen that the values are constant within a small limit of error up to a concentration, c, of about 0.0014 mol per liter, above which there is a definite deviation. The range and precision of the agreement between the theory and the measurements is also shown in Fig. 3, based on Sliedlovsky s investiga-... 

Balances and measuring equipment of an appropriate range and precision should be available for production and control operations. 

The instruments, meters, weighing and measuring equipment of an appropriate range and precision shall be available for production and quality control. Their status shall be clearly labeled and their checking schedule shall be defined. Heat sterilization equipment, equipment for filling aseptic or sterilized products and sterile filters shall be validated after installation and their revaiidation schedule shall be defined. 

TXRF has been applied for certification of lAEA-SRM lichen 336. The concentrations of Ca, Cu, Fe, Mn, Pb, Rb, Sr and Zn have been determined after acid digestion. The concentration of determined elements is in the mg/kg range, and precision varies between 3.5 and 7%. All the results are within the range of accepted values (Schmelling et al., 1997b). 

Chemists use models to interpret and systematize information and to extrapolate from the known to the unknown. A good model is simple, has a wide validity range, and precise predictive power. However, since they all represent simplifications of a more complex reality, they will all fail in some instances. In this book we describe these models in parallel with the molecular structures for which they are most successful. The aim has been to provide a clear description of their physical basis, and to delineate the limits of their applicability. 

Age ranges and precision vary with uranium content of each sample, but in general the method can cover a period between 1000 and 100 000 years bp to error limits of +1 % of age. 

For the determination of phosphate in the presence of arsenic, the arsenate ion is reduced with thiosulphate to arsenite which does not form complexes with molybdate. Arsenate up to 3 timoVL is quantitatively reduced within 15 min. The blue phosphomolybdic complex is developed using the reagents given in Section 10.2.5.4. Calibration must be performed as described because thiosulphate reduces the colour of the blue phosphorus complex by ca. 10 %. Range and precision are the same as for the main procedure. 

Electrochemical detection in HPLC has become established for some, more specialized, applications such as catecholamine analysis though it can be exploited for a far wider range of compounds. The work in this paper has attempted to investigate some of the basic properties of an electrochemical detection system and some more difficult applications. The detector has a linear dynamic range and precision that are comparable with those of other detectors for HPLC. It is, however, more dependent on temperature than, for example, the UV absorption detector and must be operated in a temperature controlled environment to obtain the lowest detection limits. For many electroactive compounds with moderate oxidation potentials, the electrochemical detector can yield sub-nanogram detection limits. 

---