ISO_NWIPs-for-Ballot

ISO/NP

c) Ensure the auto-zero function of the balance is switched on and confirm that a value of zero is 689 displayed. This function compensates a long-term drift of the zero indication based on variations in 690 the sensor. 691 d) Place the empty container onto the weighing pan. 692 e) Use the tare function of the balance to set the displayed value to zero (0) before weighing samples. 693 After taring, the displayed value will then be the pure mass of the sample not including the mass of 694 the container. 695 f) Exercise the balance by repeat weighings of the empty container to confirm the tare and the balance 696 repeatability. 697 g) Place the sample (or standard reference material for qNMR) into the container; Record the 698 displayed value after the display becomes stable. 699 h) Take the container with the sample from the weighing pan. After weighing a sample or standard 700 reference material for qNMR, again record the relevant environmental conditions surrounding the 701 balance. 702 N OTE 1 Changes in the relevant environmental conditions surrounding the balance can cause deviations in the 703 sensitivity or the repeatability of the balance that result in weighing errors. For example, when handling 704 containers or samples that are susceptible to becoming charged, or when the relative humidity in the workroom is 705 ≤40 %, the displayed value is likely to shift upward or downward, or to be unstable due to the effects of the charge 706 force on the balance. This can introduce errors in the weighed values. 707 NOTE 2 See OIML R76-1 [see ref. 1] for details regarding the tare function of a balance. 708 NOTE3 In order to avoid spilling onto the weighing pan, weighing by difference can be applied. When applying 709 this method, step d) The displayed value shall be recorded after the value becomes stable, and step e) shall be 710 omitted. For step f) the container is taken out of the balance and set again onto the centre of the weighing pan 711 after the sample is placed into the container. The applied sample mass is calculated by taking the difference 712 between record f) and record d). As the net sample mass is derived by two weighments and its value calculated by 713 difference, the measurement uncertainty of the net sample mass and the minimum weight are a factor of square 714 root of two higher than for a single weighment. In order to achieve the same target accuracy for the weighing 715 process, the amount of sample to be weighed shall be a factor of square root of two higher than if a single 716 weighment is applied. 717 NOTE4 Sample and standard preparation can be carried out using a weighing instrument that performs 718 automated dosing of the material to a target value without the intervention of the operator, with subsequent 719 automated dosing of the solution to achieve the target concentration, based on weight by weight. This weighing 720 process increases the accuracy of sample or standard preparation and reduces weighing errors introduced by the 721 operator or the environment. It also allows reducing the exposure of the operator to harmful substances. 722 Furthermore this procedure avoids spilling of the sample. 723 724 6.8 Sample solution preparation 725 If particular conditions for 1 H qNMR of sample preparation and/or sampling method are stipulated, 726 those should be followed. However, for the purposes of this document, a sample solution for qNMR is 727 normally prepared as follows. 728 a) Verify that the conditions of the sampling environment, such as temperature and humidity, are 729 suitable for handling of the sample and the reference materials for qNMR. 730

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