ISO 8655-7 pdf download – Piston-operated volumetric apparatus —Part 7: Non-gravimetric methods for the assessment of equipment performance

ISO 8655-7 pdf download – Piston-operated volumetric apparatus —Part 7: Non-gravimetric methods for the assessment of equipment performance.
ISO 8655-1, Piston-operated volumetric apparatus — Part 1: Terminology, general requirements and user recommendations
ISO 8655-2, Piston-operated volumetnc apparatus — Part 2: Piston pipettes
ISO 8655-3:2002, Piston-operated volumetric apparatus — Part 3: Piston burettes ISO 8655-4, Piston-operated volumetric apparatus — Part 4: Dilutors
ISO 8655-5, Piston-operated volumetric apparatus — Part 5: DIspensers
ISO 8655-6:2002, Piston-operated volumetric apparatus — Part 6: Gravimetnc methods for the determination of measurement ermr
3 Terms and definitions
For the purposes of this part of ISO 8655, the terms and definitions given in ISO 8655-1 apply.
4 Principle
4.1 Photometric method
The photometric method of testing piston-operated volumetric apparatus relies upon the relationship between the concentration of a chromopi’iore in solution and its absorbance of light at a specified wavelength, as descrted by the Beer-Lambert law. The method can use one of two procedures, depending on the needs of the calibration. In both methods, the test volume of liquid to be measured is delivered by the piston-operated volumetric apparatus under test into a known volume of liquid, and the degree of dilution is calculated from photometric measurements.
The first method is suitable for test volumes :. 20 % of the total volume, The total volume depends on the size of the photometric measuring cell and shall be large enough to adequately fill the cell in the UVNIS photometer. In this method a known volume of solution is prepared having an abso.’bance near the upper end of the working range of the photometer and its absorbance is measured. The piston-operated volumetric apparatus being tested is used to add an unknown volume of diluent. e.g. water or buffer. The resulting solution is mixed well and its absorbance is measured. The unknown volume delivered can be calculated from the decrease in absorbance,
The second method is suitable for test volumes <20 % of the total volume. In this method a known volume of dduent is prepared. The piston-operated volumetric apparatus being tested is used to add an unknown volume of a sample solution of chromophore having known absorbance, The resulting solution is mixed well and s absorbance is measured. The unknown volume delivered is then calculated from the increase in absorbance. Annex A and Annex B give examples for test procedure and calculation. Other photometric methods can be used, the suitability of which has been validated for the intended purpose. 4.2 Titrimetnc method The titrimetnc test method Is suitable for testing volumes of piston-operated volumetric apparatus 500 lii. In general, any titration can be used, the suitability of which has been validated for the intended purpose, For example, a potassium chloride (KCI) solution can be used as test liquid to be dispensed by the device under test into an acidified receiver liquid. The resulting test solution is titrated with silver nitrate (A9NO3) solution. The equivalence point is determined by potentiometric detection, e.g. with a silver electrode. If the device under test is a piston burette, known concentrations of potassium chloride in a receiver vessel can be titrated potentiometncally with silver nitrate using the piston burette under test Annex C gives an example for Ifue test procedure. 5.1.3 Reagent system The reagent system, consisting of chromophore, diluent, preservative (if needed) and buffer (if needed) shallbe chosen with the following criteria in mind. In all cases the uncertainty of measurement due to the variouscontributions, e.g. uncertainty of pH, shall be estimated and included in the uncertainty budget. The concentration against absorbance relationship for the reagent system shall be well documented inliterature or shall be determined by the user. The wavelength chosen for absorbance measurement shall be ator near an absorbance maximum of the reagent system to minimize the effect of wavelength errors on results.The reagent system shall either be independent of pH or be buffered to limit pH change to an acceptablerange established in the uncertainty budget. The reagent system shall either be independent of temperature or the results shall be characterized andcompensated for temperature.