ISO_NWIPs-for-Ballot

ISO/NP

use NMR tubes with high levels of circular symmetry, and no distortion. If the NMR tube is not selected 571 with adequate care, it may not be possible to obtain good quality spectra. 572 6.2 Samples and reference material preparation with a balance 573 6.2.1 General 574 With 1 H qNMR the quantification values are determined using Formula (8) (see 4.2). This formula 575 suggests that it is extremely important to weight the amount of sample and reference material 576 accurately in order to obtain reliable results. If the sample/analyte is hygroscopic or volatile, 577 appropriate measures shall be taken to ensure that the properties of the sample/analyte do not cause 578 deviations in the weighing results. 579 6.2.2 Weighing 580 When a sample or a reference standard for qNMR is prepared using a balance, the weighing accuracy 581 that is required should be defined. For achieving a very high degree of accuracy, a value of 0.10 % is 582 quite common. In order to achieve the required weighing accuracy, the mass of the sample or the 583 reference material shall exceed the respective minimum weight. The minimum weight is calculated 584 from the measurement uncertainty of the balance derived during calibration [see ref. 9]. The relative 585 measurement uncertainty becomes larger when smaller amounts of sample are weighed. When the 586 weight of the sample corresponds to the minimum weight, the relative measurement uncertainty of this 587 weighment equals the required relative weighing accuracy. Weighing smaller amounts of sample results 588 in a relative measurement uncertainty that exceeds the required relative weighing accuracy, while 589 weighing larger amounts of sample results in a measurement uncertainty that is smaller than the 590 required relative weighing accuracy. For analytical, micro- and ultra microbalances, the dominant 591 factor contributing to measurement uncertainty comes from repeatability. A simplified approach to 592 calculating minimum weight is presented in [see ref. 5]. 593 NOTE The measurement uncertainty and the minimum weight are derived during calibration of the balance [see 594 ref. 9]. 595 6.2.3 Preparation of the balance 596 The following procedure shall be followed before weighing a sample or a reference standard for qNMR . 597 a) Properly clean, maintain and prepare the tools used for weighing. 598 b) Adjust the sensitivity of the balance. This is usually done by means of the built-in adjustment 599 weights. 600 Since the sensitivity of the balance is affected by environmental conditions (mainly temperature 601 changes), and a sensitivity drift might occur over time, it is recommended to perform a sensitivity 602 adjustment periodically. 603 To ensure performance qualification, routine testing of the balance should be performed. A balance 604 check using external weights helps ensure that the balance meets weighing tolerance requirements. The 605 balance check is performed at appropriate intervals based on applicable standard operating procedures. 606 The frequency of the balance check depends on the risk of the application and the required weighing 607 accuracy. Checks with external weights can be replaced partially using automatic or manually triggered 608 adjustment by means of built-in weights. Prepare standard operating procedures for weighing out 609 materials, including the content of the routine checks by the operator (including the standard weights 610 used for the check). 611 A typical balance check recommends the use of standard weights with certified SI traceability, and 612 verification and recording of the results for the following two factors (see ref 4, 5, and 7): 613

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