Non-Metals
159
under a nitrogen stream, and the condensate trapped at -80°C. Hexane extracts of the
condensate were then concentrated to 100-200 1Jl, and analysed by gas chromatography. Concentrations as low as 5 ng methylisoborneol per g of fish were detectable.
About 80 % of the organoleptically off-flavoured fish had elevated 2-methylisoborneol concentrations (5.0-815.5 ng 2-methylisoborneol g-I), but other musty odorants
(geosmin, pyrazine isomers) were not detected. On average 2-methylisoborneollevels
in channel catfish from off-flavour ponds were approximately 34 and 28 times higher
than those in mud and water, respectively.
Lovell et al. [484] showed in a survey that a high proportion of catfish samples
taken in ponds in Alabama had an off flavour due to the presence of geosmin. Persson
[485] investigated threshold odour concentrations of geosmin and 2-methylisoborneol in fish.
7.3.20
~~a-Trifluoro-4-nitro-m-cresol
This pesticide has been determined gas chromatographically in fish in amounts down
to 0.01 mg kg- I [486]. The fish sample is homogenized with hexane-ethyl ether (7:3).
The phenol is extracted into 0.1 mol I-I sodium hydroxide, back-extracted into hexane-ether (7:3) after acidification, and methylated with diazomethane. The product
formed is analysed by gas chromatography at 140°C with the use of a glass column
(1.8 m x 4 mm) packed with 3 % of OV-l on 80 to 100-mesh Chromo sorb W, with
nitrogen as carrier gas (60 ml min-I) and electron capture detection.
7.3.21
8 2 Vitamins
A sensitive method has been described [487] for the determination of riboflavin,
flavin mononucleotide, and flavin adenine dinucleotide in serum of different fish
using reversed-phase high-performance liquid chromatography with fluorimetric detection. Trichloroacetic acid was used to isolate B2 vitamins from the serum, and an
aliquot of this solution was analysed by high performance liquid chromatography
using a Zorbax-NH 2 column with methanol-0.2 mol I-I phosphate buffer (1 + 9) as the
mobile phase. The detection limits of riboflavin, flavin mononucleotide, and flavin
adenine dinucleotide in the serum were 4.89, 9.13 and 73.1 ng ml- I respectively.
Samples were prepared for analysis either by acid hydrolysis in 1 N hydrochloric
acid at 120°C for 1 h or by enzyme hydrolysis at pH 4.2. Proteins were then precipitated with trichloroacetic acid to provide a solution ready for high performance liquid
chromatography. Typical concentrations in fish sera were: riboflavin 0.31-0.37 f,lg
ml- I , flavin mononucleotide LD 0.05 flg ml- I , and flavin adenine dinucleotide 0.250.44 flg ml- I . Recoveries were in the range 92 to 97 %.
7.3.22
Vitamin E (Tocopherol)
Schulz [489] has described a high performance liquid chromatographic method using
fluorimetric detection, which permitted the simultaneous determination of four toco-
159
under a nitrogen stream, and the condensate trapped at -80°C. Hexane extracts of the
condensate were then concentrated to 100-200 1Jl, and analysed by gas chromatography. Concentrations as low as 5 ng methylisoborneol per g of fish were detectable.
About 80 % of the organoleptically off-flavoured fish had elevated 2-methylisoborneol concentrations (5.0-815.5 ng 2-methylisoborneol g-I), but other musty odorants
(geosmin, pyrazine isomers) were not detected. On average 2-methylisoborneollevels
in channel catfish from off-flavour ponds were approximately 34 and 28 times higher
than those in mud and water, respectively.
Lovell et al. [484] showed in a survey that a high proportion of catfish samples
taken in ponds in Alabama had an off flavour due to the presence of geosmin. Persson
[485] investigated threshold odour concentrations of geosmin and 2-methylisoborneol in fish.
7.3.20
~~a-Trifluoro-4-nitro-m-cresol
This pesticide has been determined gas chromatographically in fish in amounts down
to 0.01 mg kg- I [486]. The fish sample is homogenized with hexane-ethyl ether (7:3).
The phenol is extracted into 0.1 mol I-I sodium hydroxide, back-extracted into hexane-ether (7:3) after acidification, and methylated with diazomethane. The product
formed is analysed by gas chromatography at 140°C with the use of a glass column
(1.8 m x 4 mm) packed with 3 % of OV-l on 80 to 100-mesh Chromo sorb W, with
nitrogen as carrier gas (60 ml min-I) and electron capture detection.
7.3.21
8 2 Vitamins
A sensitive method has been described [487] for the determination of riboflavin,
flavin mononucleotide, and flavin adenine dinucleotide in serum of different fish
using reversed-phase high-performance liquid chromatography with fluorimetric detection. Trichloroacetic acid was used to isolate B2 vitamins from the serum, and an
aliquot of this solution was analysed by high performance liquid chromatography
using a Zorbax-NH 2 column with methanol-0.2 mol I-I phosphate buffer (1 + 9) as the
mobile phase. The detection limits of riboflavin, flavin mononucleotide, and flavin
adenine dinucleotide in the serum were 4.89, 9.13 and 73.1 ng ml- I respectively.
Samples were prepared for analysis either by acid hydrolysis in 1 N hydrochloric
acid at 120°C for 1 h or by enzyme hydrolysis at pH 4.2. Proteins were then precipitated with trichloroacetic acid to provide a solution ready for high performance liquid
chromatography. Typical concentrations in fish sera were: riboflavin 0.31-0.37 f,lg
ml- I , flavin mononucleotide LD 0.05 flg ml- I , and flavin adenine dinucleotide 0.250.44 flg ml- I . Recoveries were in the range 92 to 97 %.
7.3.22
Vitamin E (Tocopherol)
Schulz [489] has described a high performance liquid chromatographic method using
fluorimetric detection, which permitted the simultaneous determination of four toco-