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发表于 2006-7-12 13:55:51
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IEC62321! u }; e8 e; G
9.7.2 Boiling-water-extraction procedure
* a$ G2 H; x4 T! \# Y; t; ga) 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 E% h. S, F( R6 E/ C
get the total required surface area of (50±5) cm2.0 t# `: g* Q4 f6 |1 L5 N! `: ?
b) Heat in a suitable beaker (with volume graduation) 50ml of DI water to boiling and totally
! Z0 L. o+ a# n, V8 Nimmerse the sample(s) inside the beaker. Leach for exactly 5 minutes while the water7 t/ `; J5 R- A. @ `# m
continues to boil. Remove the sample(s), and cool the beaker and its content to room
" N, k( O" b% l1 ?+ X- atemperature. Fill up with DI water to 50ml if some water evaporated. If the solution is milky: H) A! x, ]: o# n& l, w
or has a precipitate, filter it through a paper filter (0.45μm pore size) into a dry beaker- S3 l! h4 W# {8 `/ N; I1 s
Add 1ml of orthophosphoric acid solution (9.5 e) and mix well. Pour half the solution into! X" W) w! M# ]1 o# k: L# k
another dry beaker. Add 1ml test solution (9.7.1. a) to one of the two beakers, mix and
( z( A* k1 P& Jobserve the color against the other beaker which serves as the blank. A red color) P* @5 @7 Z0 L: N* A% U- n7 D
indicates the presence of Cr (VI
" Q! E, G" J, i. I8 X/ V( lc) If the color developed during the test is difficult for the analyst to judge, transfer a portion( K" w; x9 b( }% m0 }& J
of the solution to an absorption cell. After a reaction time of 2 minutes, measure thebbs/ a% E6 y+ B x7 `* t* k3 L" ?
absorbance in a colorimetric equipment against the blank.! `8 e! t9 H; V% X# d
d) Dilute 1ml of 1mg/kg K2Cr2O7 standard solution (9.5 b) to 50ml with DI water. Add 1ml of9 h0 s H" j5 P6 n/ S) u7 F- Y+ ?
orthophosphoric acid solution (9.5 e) and mix well. Add 2ml test solution (9.7.1 a), mix and1 Q% Z" M; N1 v) G8 X( y# P
measure the absorbance as above.6 d, m! n9 ~9 i# [
e) If the absorbance value obtained in 9.7.2 c) is equal to, or greater than that obtained in( ~; L0 b; |$ R6 U
9.7.2 d), the sample is considered to have a hexavalent chromium coating. If not, the testbbs: A/ W F$ y5 t6 u; l- h
result is negative. The detection limit for the boiling-water-extraction test is 0.02mg/kg F" |! p3 I$ i/ X1 `% o4 n
with 50cm2 sample surface area used. |
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发表于 2006-7-11 09:49:34
