Eastern Regional Research Laboratory, Philadelphia, Pennsylvania
**One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, United States Department of Agriculture.
Brooks A. Brice and Margaret L. Swain, "Ultraviolet Absorption Method for the Determination of Polyunsaturated Constituents in Fatty Materials*," J. Opt. Soc. Am. 35, 532-544 (1945)
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Ultraviolet absorption data for purified fatty acids and esters: observed or reported values for wave-length λmax and specific extinction coefficient k at absorption maximum used; values tentatively adopted as standard in analysis for conjugated fatty acid constituents; and ratio of k value at λmax to average value of k at λmax+6 mμ and λmax−6 mμ, i.e., k/Δk.
Conjugated.
Data obtained by comparator measurements on Fig. 1 of reference 6.
From reference 12.
See footnote 13.
No maxima or inflections observed at this wave-length.
Table II
Absorption and reproducibility for 1.30N KOH-ethylene glycol and 11 percent KOH-glycerol solutions heated in the presence of air for 25 minutes at 180°C. Spectral densities for 10 percent solutions in absolute ethanol, 1 cm at 260 mμ, 5 cm at 316 mμ (i.e., thicknesses and concentrations commonly used for analysis of animal fats) vs. equal layers of absolute ethanol. Each group of six samples was run simultaneously in the constant temperature bath.
Spectral density
KOH-ethylene glycol
KOH-glycerol
260 mμ
316 mμ
260 mμ
316 mμ
1.13
2.79
.359
.585
1.18
2.91
.362
.590
1.02
2.69
.377
.600
1.09
2.71
.377
.605
1.22
2.88
.377
.605
0.96
2.51
.370
.595
Mean
1.10
2.75
.370
.597
Standard deviation
±0.10
±0.15
±.008
±.008
Table III
Specific extinction coefficients for alkali-isomerized pure polyunsaturated fatty acids.
Observed values, in glycerol 30 minutes at 180°C.
Values used for analysis, in glycerol 30 minutes at 180°C: observed values adjusted to 100 percent purity of acid; arachidonic acid coefficients assumed valid for these conditions.
Values reported by Beadle and Kraybill (see reference 2) in ethylene glycol 25 minutes at 180°C.
At 234 mμ.
Table IV
Specific extinction coefficients in ethanol, and wave-lengths of absorption maxima for conjugated fatty materials before (k) and after (k′) heating for 30 minutes at 180°C in KOH-glycerol solution. The ratio k′/k gives approximately the proportion of conjugated material undestroyed by the treatment.
Before
After
Sample No.
Material
λ
k
λ′
k′
k′/k
1
10,12 linoleic acid
231
117
231
110
.94
9
β-eleostearic acid
268
200
268
161
.81
10
Pseudo-eleostearic acid
267.5
193
267.5
156
.81
11
α-eleostearic acid
270
171
269
131
.77
12
Tung oil
270
140
269
118
.84
Table V
Analysis of tallow 15 for polyunsaturated fatty acids by different methods. [(a), (b), (c) were isomerized in KOH-glycerol; (d) was isomerized in KOH-ethylene glycol (no corrections made).]
(a)
(b)
(c)
(d)
(e)
(f)
(g)
Acid
Proposed method, percent
Correction for conjugation neglected, percent
Corrections for background and conjugation neglected, percent
See reference 1.
See reference 2.
See reference 3.
See reference 7.
See reference 8.
Table VI
Analysis of miscellaneous fatty materials for polyunsaturated constituents. Effect of variations in isomerization medium, size of sample, and temperature; reproducibility of results; and analysis of known mixtures.
Thiocyanometric method, assuming the presence of saturated, oleic, and linoleic acids only.
Thiocyanometric method: linoleic acid, 14.7 percent; linolenic acid, 65.2 percent.
Standard.
Tables (6)
Table I
Ultraviolet absorption data for purified fatty acids and esters: observed or reported values for wave-length λmax and specific extinction coefficient k at absorption maximum used; values tentatively adopted as standard in analysis for conjugated fatty acid constituents; and ratio of k value at λmax to average value of k at λmax+6 mμ and λmax−6 mμ, i.e., k/Δk.
Conjugated.
Data obtained by comparator measurements on Fig. 1 of reference 6.
From reference 12.
See footnote 13.
No maxima or inflections observed at this wave-length.
Table II
Absorption and reproducibility for 1.30N KOH-ethylene glycol and 11 percent KOH-glycerol solutions heated in the presence of air for 25 minutes at 180°C. Spectral densities for 10 percent solutions in absolute ethanol, 1 cm at 260 mμ, 5 cm at 316 mμ (i.e., thicknesses and concentrations commonly used for analysis of animal fats) vs. equal layers of absolute ethanol. Each group of six samples was run simultaneously in the constant temperature bath.
Spectral density
KOH-ethylene glycol
KOH-glycerol
260 mμ
316 mμ
260 mμ
316 mμ
1.13
2.79
.359
.585
1.18
2.91
.362
.590
1.02
2.69
.377
.600
1.09
2.71
.377
.605
1.22
2.88
.377
.605
0.96
2.51
.370
.595
Mean
1.10
2.75
.370
.597
Standard deviation
±0.10
±0.15
±.008
±.008
Table III
Specific extinction coefficients for alkali-isomerized pure polyunsaturated fatty acids.
Observed values, in glycerol 30 minutes at 180°C.
Values used for analysis, in glycerol 30 minutes at 180°C: observed values adjusted to 100 percent purity of acid; arachidonic acid coefficients assumed valid for these conditions.
Values reported by Beadle and Kraybill (see reference 2) in ethylene glycol 25 minutes at 180°C.
At 234 mμ.
Table IV
Specific extinction coefficients in ethanol, and wave-lengths of absorption maxima for conjugated fatty materials before (k) and after (k′) heating for 30 minutes at 180°C in KOH-glycerol solution. The ratio k′/k gives approximately the proportion of conjugated material undestroyed by the treatment.
Before
After
Sample No.
Material
λ
k
λ′
k′
k′/k
1
10,12 linoleic acid
231
117
231
110
.94
9
β-eleostearic acid
268
200
268
161
.81
10
Pseudo-eleostearic acid
267.5
193
267.5
156
.81
11
α-eleostearic acid
270
171
269
131
.77
12
Tung oil
270
140
269
118
.84
Table V
Analysis of tallow 15 for polyunsaturated fatty acids by different methods. [(a), (b), (c) were isomerized in KOH-glycerol; (d) was isomerized in KOH-ethylene glycol (no corrections made).]
(a)
(b)
(c)
(d)
(e)
(f)
(g)
Acid
Proposed method, percent
Correction for conjugation neglected, percent
Corrections for background and conjugation neglected, percent
See reference 1.
See reference 2.
See reference 3.
See reference 7.
See reference 8.
Table VI
Analysis of miscellaneous fatty materials for polyunsaturated constituents. Effect of variations in isomerization medium, size of sample, and temperature; reproducibility of results; and analysis of known mixtures.