166
Fish
Table 7.16 Determination of total mercury in tuna: collaborative tests (from [499])
All Figures are concentrations of mercury in mg kg-I, corrected for the blank
Laboratory By method of Appendix I
Mean By other method d
Mean
Blank
1
0.53,0.56
0.55
0.02
2
0.49, 0.52, 0.51, 0.62,
0.61
(b) 0.56, 0.52, 0.54
0.54
0.62, 0.71, 0.75, 0.60,
0.66
4
0.54
0.54
6
(c) 0.51, 0.51, 0.53, 0.50,
0.50
< O.oI
0.47, 0.53, 0.46
7
(d) 0.56, 0.58, 0.59, 0.60,
0.59
0.61,0.62
8
0.41,0.45
0.43
0.01
9
0.49,0.47
0.48
<0.02
10
0.55, 0.57, 0.56, 0.55
(e) 0.56, 0.56, 0.54, 0.57
0.55
< O.oI
0.57, 0.58, 0.56
0.56
0.53,0.54
11
(f) 0.54, 0.54, 0.54
0.54
Mean
0.56
0.54
Standard deviation ....
± 0.08
± 0.04
a = Method employed:
b = Oxidation as in [1], but with smaller pear-shaped digestion flask. Determination by cold-vapour
atomic-absorption spectrometry
c = Sample digested with nitric acid and sulphuric acid under an air condenser. Potassium persulphate was added and digestion continued until temperature exceeded 140 ·C. Determination by
cold-vapour atomic-absorption spectrophotometry
d = A different apparatus from that described above having a smaller flask and liquid nitrogen
condenser. Method essentially the same
e = Method of Holden. [520]
f = Method of Magos. [499]
Determination of methylmecury in tuna:
second round of collaborative tests
All results are concentrations of mercury in mg kg-I, corrected for the blank
Laboratory
By method of Appendix II
By other method
2
4
8
9
0,49,0.48
0.44, 0.45, 0.43
0.48,0.52
0.39,0.42
0.47,0.48
11
Mean
.. .. .. .. 0.46
Standard deviation
a Method employed:
b Method of Hoiden S20
c Method of Magos 499
.... ±0.04
b 0.59, 0.55
c 0.51, 0.46, 0.49
hydrobromic acid are then added (i. e. 2 N acid concentration in the total volume).
Then 50 ml of toluene are added and the tube is shaken for 5 min. After centrifuging,
25 ml of the organic phase are transferred into another 100-ml test-tube; 6 ml of the
1 % cysteine solution are added and the solution is shaken for 2 min and then