ISO 14502-1:2005 pdf download.Determination of substances Usual laboratory apparatus and, in particular, the following.
5.1 Analytical balance, capable of weighing to an accuracy of ± 0001 g.
5.2 Water bath, capable of being maintained at 70 °C ± 1 °C.
5.3 Dispenser. for methanol/water extraction mixture (4.4), and set at 5,0 ml.
5.4 Centrifuge, capable of 2 000 Relative Centrifugal Force (R.C.F.) (typically 3 500 r/min).
5.5 Spectrophotometer, set at 765 nm and able to accommodate 10 mm path length cells, preferably in an automatic flow cell assembly.
5.6 Pipettes, glass or automatic, to cover the volume range for standard and sample extract dilutions.
5.7 One-mark volumetric flasks, of capacities 100 ml, 200 ml, 500 ml, and 1 litre.
5.8 Vortex mixer, for efficient mixing during extraction.
5.9 Extraction tubes, glass, of 10 ml capacity, stoppered and able to withstand being centrifuged.
5.10 Graduated tubes, glass, of 10 ml capacity with 0,1 ml graduations.
As the assay is sensitive to traces of organic impurities, extraction tubes (5.9) and graduated tubes (5.10) should all be taken through an additional cleaning procedure of washing in approx. 15 % (volume fraction) nitric acid, followed by rinsing thoroughly in water and drying in an air oven at 100 °C. The use of disposable plastic tubes as an alternative to the graduated tubes in the final colorimetic assay is recommended, as additional cleaning has not been found necessary.
6 Sampling
A representative sample should have been sent to the laboratory. It should not have been damaged or changed during transport or storage.
Sampling is not part of the method specified in this part of ISO 14502. A recommended sampling method is given in
— ISO 1839 for leaf tea, and ISO 7516 for instant tea.
7 Preparation of test samples
To ensure homogeneity, grind the sample of leaf tea in accordance with ISO 1572 and store samples in wellsealed containers protected from light.
5.2 Water bath, capable of being maintained at 70 °C ± 1 °C.
5.3 Dispenser. for methanol/water extraction mixture (4.4), and set at 5,0 ml.
5.4 Centrifuge, capable of 2 000 Relative Centrifugal Force (R.C.F.) (typically 3 500 r/min).
5.5 Spectrophotometer, set at 765 nm and able to accommodate 10 mm path length cells, preferably in an automatic flow cell assembly.
5.6 Pipettes, glass or automatic, to cover the volume range for standard and sample extract dilutions.
5.7 One-mark volumetric flasks, of capacities 100 ml, 200 ml, 500 ml, and 1 litre.
5.8 Vortex mixer, for efficient mixing during extraction.
5.9 Extraction tubes, glass, of 10 ml capacity, stoppered and able to withstand being centrifuged.
5.10 Graduated tubes, glass, of 10 ml capacity with 0,1 ml graduations.
As the assay is sensitive to traces of organic impurities, extraction tubes (5.9) and graduated tubes (5.10) should all be taken through an additional cleaning procedure of washing in approx. 15 % (volume fraction) nitric acid, followed by rinsing thoroughly in water and drying in an air oven at 100 °C. The use of disposable plastic tubes as an alternative to the graduated tubes in the final colorimetic assay is recommended, as additional cleaning has not been found necessary.
6 Sampling
A representative sample should have been sent to the laboratory. It should not have been damaged or changed during transport or storage.
Sampling is not part of the method specified in this part of ISO 14502. A recommended sampling method is given in
— ISO 1839 for leaf tea, and ISO 7516 for instant tea.
7 Preparation of test samples
To ensure homogeneity, grind the sample of leaf tea in accordance with ISO 1572 and store samples in wellsealed containers protected from light.
Grinding of instant tea is only required on samples of a coarse granular structure.characteristic of green and black tea —Part 1: Content of total polyphenols in tea —Colorimetric method using Folin-Ciocalteu reagent.
