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发表于 2006-7-12 13:55:51
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来自： 中国
IEC623212 @* e* \+ h( g+ h* `1 Y9 |
9.7.2 Boiling-water-extraction procedure
$ c: }/ F( i# [( E0 `* L& Q7 e3 |a) The sample to be tested shall have a surface area of (50±5) cm2. For small parts, such asfasteners, or samples with irregular surface shapes, use a suitable number of samples to7 j ]. C$ K9 |0 `
get the total required surface area of (50±5) cm2.2 {* x8 r( d! L7 t. k5 u3 h/ c
b) Heat in a suitable beaker (with volume graduation) 50ml of DI water to boiling and totally, B+ s* D3 |' h9 Q2 |+ {) t
immerse the sample(s) inside the beaker. Leach for exactly 5 minutes while the water
i0 G! F, z; E6 d0 v) ~continues to boil. Remove the sample(s), and cool the beaker and its content to room& \, e6 G g5 J1 I, c* f) S( P
temperature. Fill up with DI water to 50ml if some water evaporated. If the solution is milky
0 h) D! C8 | Hor has a precipitate, filter it through a paper filter (0.45μm pore size) into a dry beaker' y7 e! D; q; A8 N$ i5 g" c& j: j7 H
Add 1ml of orthophosphoric acid solution (9.5 e) and mix well. Pour half the solution into5 [, L" A: C. q+ K
another dry beaker. Add 1ml test solution (9.7.1. a) to one of the two beakers, mix and6 ]- N/ {+ @# a- x3 ~
observe the color against the other beaker which serves as the blank. A red color( x5 L1 u. ?" z2 H
indicates the presence of Cr (VI
& f, g% E0 u( W! vc) If the color developed during the test is difficult for the analyst to judge, transfer a portion
$ v/ x; U* l1 O- j: y! J' n) Zof the solution to an absorption cell. After a reaction time of 2 minutes, measure thebbs u! ^# q5 Y' F
absorbance in a colorimetric equipment against the blank.
& R/ k0 e, S1 x! Md) Dilute 1ml of 1mg/kg K2Cr2O7 standard solution (9.5 b) to 50ml with DI water. Add 1ml of7 i$ c6 P( C) p
orthophosphoric acid solution (9.5 e) and mix well. Add 2ml test solution (9.7.1 a), mix and
" b9 j; R! w% e5 Mmeasure the absorbance as above.
# ^( i/ M3 i5 {2 ?+ V2 d& V3 a Oe) If the absorbance value obtained in 9.7.2 c) is equal to, or greater than that obtained in' @" ?; K! k- m! N) {, p8 i/ V% F
9.7.2 d), the sample is considered to have a hexavalent chromium coating. If not, the testbbs `, Z2 @% @0 E
result is negative. The detection limit for the boiling-water-extraction test is 0.02mg/kg
* L2 S# \" F* Z" \4 X3 Uwith 50cm2 sample surface area used. |
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发表于 2006-7-11 09:49:34
