EN 62321-7-2-2017 pdf download.Determination of certain substances in electrotechnical products- Part 7-2: Hexavalent chromium – Determination of hexavalent chromium (Cr(VI)) in polymers and electronics by the colorimetric method (IEC 62321-7-2:2017).
4.2 Reagents
The following reagents shall be used:
a) N-Methyl-pyrrolidone (NMP), analytical reagent grade. Add 10 g activated molecular sieves (4.2 r)) per 100 ml of newly opened NMP, seal the cap tightly, keep In the dark, shake occasionally and maintain over 12 h before first use. Store at 20 C to 25 °C with molecular sieves in a tightly sealed brown glass container and avoid direct light exposure. The suggested maximum storage period is four weeks after the opening time of the container.
b) Nitric acid, volume fraction of 35 %. Dilute 50 ml of reagent grade HNO3 to 100 ml with water (see 4.2 p)) in a volumetric flask (5.2 j)). Store at 20 °C to 25 °C in the dark. Do not use concentrated HNO3 If it has a yellow colour, which is an indication of photoreduction of N03 to NO2. a reducing agent for Cr(Vl).
c) Sodium carbonate: Na2CO3, anhydrous, analytical reagent grade.
d) Sodium hydroxide: NaOH, analytical reagent grade.
e) Magnesium chloride: MgCl2 (anhydrous), analytical reagent grade. A mass of 200 mg MgCI2 is approximately equivalent to 50 mg Mg2.
f) Phosphate buffer. To prepare a buffer solution at pH 7, dissolve 87,09 g K2HPO4 (analytical reagent grade) and 68,04 g KH2PO4 (analytical reagent grade) Into 700 ml of water (4.2 p)). Transfer to a I I volumetric flask (5.2 j)) and dilute to volume. As prepared. the solution will contain 0,5 mol/l K2HPO4 and 0,5 mol/l KH2PO4.
g) Lead chromate: PbCrO4, analytical reagent grade. Store at 20 ‘C to 25 ‘C in a tightly sealed container. This Is the agent used for the matrix spike recovery correction method.
h) Digestion solution. Dissolve 20.0 g ± 0,05 g NaOH and 30,0 g ± 0.05 g Na2CO3 in water (4.2 p)) In a 1 I volumetric flask (5.2 j)) and dilute to the mark. Store the solution in a tightly capped polyethylene bottle at 20 ‘C to 25 ‘C, and prepare fresh monthly. The pH of the digestion solution shall be checked before using. If the pH Is < 11.5 discard the solution and prepare a fresh batch.
I) Toluene, analytical reagent grade.
j) Potassium dichromate stock solution, Dissolve 141,4 mg of dried (105 °C) K2Cr2O7 (analytical reagent grade) in water (4.2 p)) and dilute to 1 I in a volumetric flask (5.2 j)) (1 ml contains 50 ig Cr).
k) Potassium dichromate standard solution. Dilute 10 ml potassium dichromate stock solution (4.2 fl) with water (4.2 p)) to 100 ml In a volumetric flask (5.2 j)) (1 ml contains 5 pg Cr).
I) Sulfuric acid, volume fraction of 10 %. Dilute 10 ml of distilled reagent grade or spectroscopic grade H2S04 to 100 ml with water (4.2 p)) in a volumetric flask (5.2 j)).
m) Diphenylcarbazide solution. Dissolve 250 mg 1,5-diphenylcarbazide in 50 ml acetone (4.2 q)). Store in a brown bottle. Prior to use, check the solution for discoloration. Store for use up to two weeks and if solution becomes discoloured, discard it and prepare a fresh batch.
n) Potassium dichromate, K2Cr2O7, spike solution 1 000 mg/I Cr(VI)). Dissolve 2,829 g of dried (105 °C) K2Cr2O7 in water (4.2 p)) in a I I volumetric flask (5.2 j)), and dilute to the mark. Alternatively, a 1 000 mg/I Cr(Vl)-certified standard solution can be used. Store for use up to six months at 20 °C to 25 °C in a tightly sealed container.
o) Potassium dichromate. K2Cr2O7, matrix spike solution (100 mg/I Cr(Vl)): Add 10.0 ml of the 1 000 mg/i Cr(Vl) solution made from K2Cr2O7 spike solution (4.2 n)) to a 100 ml volumetric flask (5.2 j)) and dilute to volume with water (4.2. p)). Mix well.
p) Water. Grade 3 specified in ISO 3696, which shall be free of interferences.
q) Acetone, analytical reagent grade.
r) Molecular sieves (4A). CAS: 70955-01-0. desiccant.
WARNING — All potential Cr(Vl)-containing samples and reagents used in the method have to be handled with appropriate precautions. Solutions or waste material containing Cr(Vl) have to be disposed of properly. For example, ascorbic acid or some other reducing agents can be used to reduce Cr(Vl) to Cr(lll).
5 Apparatus
5.1 General
All re-usable laboratory ware (glass, quartz, polyethylene, polytetrafluoroethylene (PTFE), etc.) Including the sample containers shall be soaked overnight in laboratory-grade detergent and water, rinsed with water, and soaked for 4 h or more in HNO3 (volume fraction of 20 %) or in a mixture of dilute acids (HNO3:HCI:H20 = 1:2:9 by volume) followed by rinsing with water (4.2 p)), Alternative cleaning procedures are permitted, provided adequate cleanliness can be demonstrated through the analysis of method blanks.
5.2 Apparatus
The following items shall be used for the analysis:
a) Vacuum filtration apparatus.
b) Heating or microwave device capable of maintaining the digestion solution at temperatures between 150 C and 160 °C.
c) Ultrasonic water bath, capable of maintaining the temperature between 60 C and 65 C.
d) Calibrated pH meter to read pH in a range of 0 to 14 with an accuracy of ±0,03 pH units.
e) Analytical balance capable of measurement to 0,1 mg.EN 62321-7-2-2017 pdf download.