1190
ANALYTICAL CHEMISTRY
recovered. Amounts found are calculated as parts per million based on the weight of the fresh fruit samples: Milligrams in total sample x 1000 = p.p.m. of K-6451 grams of fruit in sample NOTES ON PROCEDURE
TOensure a uniform blank among a given series of fruit samples, the entire washing process and every step in the subsequent analytical procedure should be rigidly standardized. Controls on untreated fruit should be run with the samples and the final results then corrected for any blank found. Care must be exercised when evaporating the stripping solutions to prevent loss of the compound by volatilization. Only the bottom of the flask should be exposed to the heat, and the sample should be removed from the steam bath as soon as evaporation is complete. Although 5 minutes is generally sufficient for samples to reach full color with 4-aminoantipyrine, it is advisable to check each different type of sample to determine the shortest length of time necessary for maximum color development. INTERFERENCES
I n addition to the interference or “blank,” the nature of which is unknown, any phenolic compound, volatile with steam, which forms a colored product with 4-aminoantipyrine under the conditions employed, will obviously interfere. Any p-chlorophenol formed by previous hydrolysis would be determined along with
the p-chlorophenyl p-chlorobenzenesulfonate. There is no supporting evidence for such hydrolysis. RECOVERY OF p-CHLOROPHENYL p-CHLOROBENZENESULFONATE ADDED TO FRUIT STRIPPINGS
To check the recovery by the procedure proposed, known quantities were added to 100-mI. samples of stripping solutions from control fruits and 10-ml. aliquots of the final solution, after steam distillation, were analyzed. Results, showing recoveries ranging from 94.5 to loo%, are listed in Table I. TYPICAL SPRAY RESIDUE DATA
Table I1 shows the results of analyses of surface residues on apples, peaches, and prune plums, obtained by the procedure given. Reasonable correlation between residues found and corresponding spray schedules is apparent. LITERATURE CITED
(1) Gottlieb, Sidney, and hlarsh, P. B., IND. ENQ.CHEM.,ANAL.ED., 18, 16 (1946). (2) Metcalf, R.L., J . Econ. Enlomol., 41, 875 (1948). (3) Stgnger, V. A., private communication, The Dow Chemical Co.,
Midland, hlich. RECEIVED for review April 30, 1961. Accepted March 27, 1952. Presented before the Division of Agricultural a n d Food Chemistry, Symposium on Methods of Bnalysis for Micro Quantities of Pesticides, a t the 119th MeetSOCIETY, Boston, Maas. ing of the . ~ M E R I C A N CHEYICAL
Improved Machine Method for Calculation of Mass Spectrometer Analyses E. C. DAIGLE AND H. A. YOUNG Re$ning Division, Magnolia Petroleum Co., Beaumont, Tex. ASS spectrometers are now used extensively for the analysis of gaseous mixtures that do not lend themselves readily to analysis by other means. This is particularly true in the petroleum industry, where samples may contain many hydrocarbon components. While the mass spectrum of a sample usually may be obtained very rapidly, the computation may be more difficult. It depends upon the proportionality of galvanometer deflections caused by the various charged molecules or fragments to the partial pressure of the contributing molecule and upon the additive nature of these deflections. I n general, then, systems of simultaneous equations must be solved involving as many equations as there are components. Thus the time consumed in calculating results is a major portion of the total time required for an analy6is. Electric analog computers are available, but their use is limited by the high initial expense and the relatively few equations handled. The method of Crout ( 1 ) has been viidely used and more recently rapid methods which are particularly suitable for use with desk calculators have been described by Milne ( 3 )and by Daigle and Lee ( 2 ) . This paper describes an improved calculating machine method which permits the reduction of a 24-componglt matrix in as little as 2 hours to a form suitable for repeated use with the same calibration coefficients. Using the reduced matrix, 24-component mixtures may be evaluated in about 30 minutes. The procedure may be considered a variation of the method of Daigle and Lee ($), in which the diagonal terms of the reduced matrix are made unity by the technique of solving for multiples of the unknowns corresponding to the coefficients of the diagonal terms and correcting the final solution by multiplying by the reciprocals of the respective diagonal terms.
M
DESCRIPTION OF PROCEDURE
Reduction. While the present method is applicable to any number of equations, it may be illustrated for mass spectrometry by assuming the following three equations: a1121 a2121 a3121
+++
a1222 a2222
a3222
adz3 = A1 +f+ a23za = A2 = a3323
A3
where the x ’ s are unknown quantities, the a’s are the calibration data a t selected masses, and the A’s are the corresponding mixture data. In practice, the calibration data only would be arranged in matrix form as follows:
The arrangement of the equations should be such that as many as possible of the terms below the diagonal formed by all, a22, and a33 are zero and the other prediagonal terms are as small as possible. This is accomplished by arranging the data in the order of ascending molecular weights with branched isomers appearing before the normal compounds and nonhydrocarbons appearing before hydrocarbons of nearly the same molecular weight. Such an arrangement greatly reduces the amount of labor involved and the probability of errors in the calculations. From Matrix I, intermediate Matrix I1 and final Matrix 111, below, are calculated as subsequently described.
V O L U M E 24, NO. 7, J U L Y 1 9 5 2
1191
m N
* * *
* *
*
@??h - m m
- 3
* * *
*
*
3hOC
* * *
& a
* m
?
m
C? ; -d 5
m. e .2 0. N - o
h 5;
N h 31 c
*
d 0 w
*
h
-2 m
e
,
3 *
*
nr-31
01
o
*
* * * N a ? h
. . .
-1 L?
% h O -h
* * *
*
*
*
*
w w
m - 3
I
* *
I
???
* * *
*
i
* 4 d
3
* * *
*
* * *
*
I
u3
. . .
*
w-r,
L a N
i
*
1
i
*i*
h LS LY
* * *
h
* k
N
I-
c -
* * *
I
ml w
a .? w.
3
ia
0 3 m
*
*
I
*
*
I
?)"? - 9 2 m
* * *
7 4
'0
5 m
. . Rrn %**
T a m
a?
*
h
c m 51 occc
* * *
L a
m
*
'2 -F.t
* * * -2 *
*
. . . $3 . m i m c * * G I I * *
m
d ' r C
*
I?
*
0
I*
3 m L a
h.
*
h m
a?
m
li
1
d
LY c? n
m
L1
m
h 3
+
%
*
21-
, *1 * d
*I
*
e
? h
'9
*
N
*
*
il
1192
ANALYTICAL CHEMISTRY bz3 =
-
a23
(7)
c?1 b13
b33 = a33 - e31613 - wb23 In order t o allow for adjustment of the diagonal terms to unity, caomputations are carried down the columns through Matrix I11 hefore proceeding to the next column of Matrix 11. Column 1 of Matrix I will remain unchanged in Matrix I1 and will be converted to pattern form in Matrix I11 by the following formulas, where j = 1, 2, 3: =
b,l
b,n. =
Ujk
- cjibiic -
b,z =
aj2
(3) - cjlbl? ( j = 2, 3)
(4)
and corrected to pattern form in Matrix I11 by the formula: C ~ Z= b72
( l l b z z ) ( j = 1, 21 3)
(5)
I n like manner the third columns are calculated by the formulas: =
bi3
(6
ai3
-
cj.b?k
. .
......
--
-Cjk-ibj-ik
= bjk ( l l b k k )
(10) (11)
The reduction step may be checked as t,hecalculation progresses by successively substit,uting the calibration ooefficients for the mixture data, in which caw the solution will show 100% of the components whose coefficients were substituted. Because the calculat,ions must be made columnwise while only square matrices arc checked in this fashion, the checks will lag behind the calculations somewhat until the reduction is complete. .$e a practical matter, hon-ever, experienced operators will need to do little checking. Sunierical examples of these niat,rices involving 24 components are shown in Tables I, 11, and 111. I n Table I11 the reciprocals 1 / b , , , l / b Z z ,etc., are recorded a t the bottom of their respectivc
Column 2 in Matrix I1 is calculated by the formulas: a12
(9)
I n the development of Matrix I1 and Matrix I11 for n equations, the j t h term in kth column may be calculat,ed by the following formulas:
cjk
biz =
( j = 1, 2, 3)
cj? = bj, ( l / b r a )
(1)
a,l
(8)
Table 111. Matrices Involving 24 Components 2 16
Ha
C1
1.0000 -
0.0021
co
N2
- 1.0000
1.0000
28
0.0783
12 26 30 32 34 39 44 29 48 54 56 43 58 62 64
0.1653 7.7003 1.0000 0,0089 0.0173
0 2
0.0152 0.0365 4.3149 0.0860 1,0480
0,0858
1.0000
~
0.0003
Cl
C* = 0.0042 0.0106 1.5349
0.1342
1.0000
-0,0016
-0,0100 0.0008 0.0002 1 E O 0.0045
HzS
C J=
0,0015 0.0012 0.0024 0.0004 0,0008 0.0080 0.4317 LOO00
0.0053 0.0035 0.0386 0.0411 0,1589 0.0019
CO?
1 . 0000 __ 0.0080
0.0635
0.0190
0.8670
0,0004
0.0046 0.0106
-0.0034
0.0960 0.2176 0,1560 -0,0011 -0,0023 0.0254 0.0002 0,0007 1 .oooo __
CiSH
C& 0.0021 0.0030 0.6000 0,0083 0.0973 0.0231
0.1882 0,2540
-0.0070
0.0043 0.0035 0 0078 0 0578 0.0018 - 0.0005 0 0818 0.0339. 0 0099 0 1277 0 0125 1 0000
-
0.0447
0.0014
0.2136
0.0203
0.001062
0.000711
0.000590
0.000866
io 57 72
71/86 85/100 97/112
0.001418
0,000799
0.000694
0.005249
0.001084
0.002666
0.000902
0,000589
1,3=C4=
C4c's
Ieo-ca
n-C4
CBH
so2
Cs='s
0.0057 0,0013 0.5398 0,0477 0 3140 -0,0002
0.0066 0.0076 0.6540 0,0303 0.2307 0,0133
0.0012 0.0034 0.0315 0.0056 0.0271 0,0015
0.0166 0.0166 3.8070 0,0359 0.8123 0.1183 0.0172
0.0048 0.0513 0.4294 0.0174 0.2320 0.0244 0.0604
0,0002
0.0108 0.0011 0.1763 0.0113 0.1663 0.0185
0.0032 0.0068 0.1386 0.0038 0.0920 0.0212 0.0024
0.0117
1.1954 0,0034 0.0065 0.0212 1.0000
0.9681 0,0041 0.2746 0,0088 0.0654 1,0000 -0,0933 0.0009
0.1906 0,0336 0.0582 0.0007 0.0011 0,0041 g 0 0 0.0215
1.6515 0,3882 5,0649 0.0102 0.0262 0,0928 10,4189 1,0000
0.0210 0,0224 0.9930 0.0272 0.0007 0.0218 -0,1707 0.1112
1 1082
0.0021 0.6941
0.4728 0.0621 0.8465
2.7713 0.5432 4.0333
0.0674 0.1023 -0.0720 0.0023 0.0208 0.0021 1.0000 __0.0062 0.0016 0,0539
0.0100 0.3015 1.7368 0.0087 0.0031 0.0005 0,0022 1.0000 0.0883 0.0332
0.0574 0.3794 16.2443 -0.2613 0.0297 0.0028 0.0228 1.5909
0.0807 2,6045 3.7408 0 02.59 0.0108 0.0020 0.3164 2.4639 - 0 171%
.-
0,0076
-0
0369
n n~fin
0.0531 0,0107
-- 0 , 0 0 3 1 0,0013 0.0005 0.1226 0.0061
0.0038 0.0021 0,0028 n - . iRR5 0.0004 0,0028
-0.0083 0 0006
1.0000 ~~~~
0,0300
-0,0241
0.0442
1
0.0996
0.0013
3
n-Cs
CS'S
(2,'5
C8'8
0,0214 0.0228 1.1196 0.0263 0.6565 0.0981
0.0077 0,0137 0.4725 0.0057 0.2074 0,0479
0,0192 0.0113 0.3724 0.0158 0.1287 0.0288
0.0100
0.0135 0.0161 0.7766 0.0062 0.2578 0,0712 0.0114
2 16 28 12 26 30 32
1.3192 0.1889 1.9084
2,0449 0.1876 2,7019
1.0987 0.0739 1.1342
39
Iso-Ca
n " . _nnnx I__
____
n I. n n x
~
1
-
z
0.0359
0,2630 0.1185 4.9864 1.1704 5.8041 2.1816 0.00% -0,0130 0,0254 0.0156 0.0113 0.0052 1.0276 2.8823 1,1540 2.5850 -0 0751 -0 1388 0.4774 loo00 1 6'348 0.3899 0 0593 1 .0000 0,0322 1~~ 0.002883 0.005198 0.005643 ~
0.000942
0.001354
0.000389
0.005362
0.001055
0.000792
0.001637 0.001197
0.006911
8-1
44 29
J. R.
54 56
43 58 62
64 70 57
72 71/86 85/100 97/112
V O L U M E 24, NO. 7, J U L Y 1 9 5 2
1193
columns. Table I1 has numerous terms (indicated by an *)in common with Table I, and in pract.ice this table is prepared by drawing lines through the affected terms of Table I and writing in the new values. It is also convenient, to prepare Table I (and t,hus Table 11) as a series of colunins on separate pages. I n the use of Table I11 in evaluating problems the signs may be transposed, the diagnonal terms omitted, and the reciprocals multiplied by 100, so that t,he resulting x values will be in terms of mole per cent inptead of mole fraction. Evaluation. The solution of problems using Matrix I11 is carried out in three steps, calculating first a set of intermediate B values according t o the following formulas:
R, = AI B? = A? B3
=
-18
-
(12)
B,
c.1 ~
g
(13)
-~
Bl l
a B? ?
-
CB
Table I\'. 26
12
-0.002i 649.0 540 0
- 0.0783 -0 0003
Cy -
~ 1 2
21: =
ck ( l / b k s )
63.0 0.1418 8.9 __ H2
643.4 0.0799 51.4
- 0,0057
-0,0013 -0.5398 -0,0477 -0.3110 0.0002 -1 -0 -0 -0 0 -0
n
19% 0034 0065 0212 6 0076
o m
0080
Bi, = -in. -
102 0 -0.0042
-0.1653 - 7.7003 13.2 - 0.0089 -0,0173
-0,0105 -1.5349 -0,0858 101.7 0 0016
-0,0076 -0.6540 -0,0303 -0,2307 -0.0133 -0 9681 -0 0041
-0 2746 -0
0088 0654 8 3 o 0933 - 0 0009
-n
3 . 4 0.5249
~~
1 . 8
-0 -0 -0 -0 -0 -0
0012 0034 0316 0056 0271 001.5
-0.19oe - 0.0336 - 0.0682
- 0.0007 -0.0011 -0.0041 33.9 -0 021.5
-0
-0,0190
35 3 0 1084 3 8
~
7
39.8 8.3 -___ ____ - 0.0066
-0.0635
C0
43
36
(17)
(18)
Ck1Bi
-
..
Ck?Zj? ........ ( k = 1 , 2 , 3, . . . . . n )
.
(I!))
- -
-Ckk-iBk--~
C values are next obtained as follows:
C, = B, Ci, = BI; -
Cki,+iC'a+i
from 1%hich
values ale calculated according to the formula:
(20)
.
+OCk--P - . . .. _ _ - C k ki k = 1, 2, 3 , . . . . n - 1)
5
.
..
( k = 1, 2, 3, . . . . , . .
=:Ck ( I / h A L )
XI
-
(21)
Ck,~c,,
. . . . . 12)
(22)
Sample Evaluation
30
-6 4 . 0
187 7 0 0694 13 0
CI--1
54
C3
( k = 1, 2, 3)
32
.;9.4 -0.0152 -0,0365 - 4 3149 -0,0850 -1.0180 .59 3
44
39
34
0.0 -0 0015 -0.0012 -0.0024 -0.0004 -0.0008 -0 0080 -0 4317 0 0
-0,1342 0 0100
-0.0008 -0 0002
OR00
C
62
58
2.0 -0.0166 -0.0166 -3.8070 -0 03.59 -0,8123 -0 I153 -0 0172 -1
-0
6513 3882
-3,0649 - 0 . 0 102
- 0 0232 -0,0928 -10.4189 1.3
0 0241
1 3 0 5362 0 7 -~ n-C?
7
-0,0048 -0.0513 -0.4294 - 0,0174 -0,2320 -0.0244 -0.0604 -0.2560 -0.0210 - 0.0224 - 0.9930 -0.0272 - 0.0007 - n ,0218 0,1707 -0.1112 0.0 -0,0442 - 0,0996
0.0 __ 0 1055 __ 0
CiSH
0
-0.0004
-0.8670
58 7_ _
10 7 ___
1 % C?=
0
0
64 0.0 -0 0002 -0 0531 -0 0107 0 0031 -0 0013 -0 0005 -0 1226 -0 0051 -0 0038 -0 0021 -0 0028 -0 5885 -0 0004 -0 0028 0 0085 -0 0006
n v -0.0013
00.-
00792 0 . 0
so2
6
0.0034
0
O O s o q 1 0
- 0.0053 -0.0035 - 0.0386 -0,0411 -0,1589 -0.0019
-0.1882 -0.2840 26.6
-0.0447
-0.0014
-0.2136
-
2__ .9 0 2 0 . 3 c3 =
0
57
3 0
3 3 0 4 iso-cs
0 0 0z6 00. CtGH
85/100
97/112
1.2 - 0.0077 -0.0137 -0,4725 -0.0057 - 0.2074 - 0.0479 -0.0100
-0.0135 -0.0161 -0,7766 -0.0062 -0.2578 -0.0712 -0,0114
-0,0192 -0.01 13 -0.3724 -0.Olj8 -0,1287 -0.0288
-1.3192 -0.1389 -1.9084
- 2.0449
- 1.0987 -0.0739 -1.1342
- 0.0807 - 2.6045
-0.2630 -4.9864 -5,8041 0,0130 -0 01S6 -0 0035' -2 8823 -2.5850 0 1388 -1.6348
-0.1185 -1,1704 -2.1816 -0 0036 -0.0254
-2.7713 - 0.3432 -4.0333 -0.0035 -0 0374 -0.3794 -16,2443 0.2543 - 0.0297 -0.0028 -0.0228 - 1.3909 0.0 - n. 0339
~~~
11 .5 0.0590 0.7 Ca
7 1/86
L728 0621 84Gi 008 -0.0674 0100 -0.1023 3015 0.0710 7368 -0.0023 0087 - 0.0208 -0 0031 -0 0005 -0.0021 2 ._ 4 _ -0 0022 _ - 0.0052 5.8 -0.0016 - 0.0883 -0,0539 -0 0332
-0 -0 -0 -0 -0 -0 -1 0
0.7
GO2
-0 0203
72 - 0.0214 -0.0228 - 1.1196 -0.0263 - 0.6568 -0.0981 -0,0117
-1.1082 -0 0021 -0.6941
9.2
0.0711
-0 0043 -0 0035 -0 0078 -0 0578 -0 0018 0 0005 -0 0818 -0 0359 -0 0099 -0 1277 -0 0125 0 0 -__-
0~.~ .5
8 0032 0068 1386 0038 0920 0212 0024
-0 0108 -0 0041 -0 1763 -0 0113 -0 1663 -0 018.5
6 -0 -0 -0 -0 -0 -0 -0
-0.0021 -0.0030 - 0.6000 - 0.0083 -0.0973 -0.0231
-0.0046 -0.0106
0 0 H?S
70
48
-0.0960 -0,2176 -0,1560 0.0011 0.0023 - 0.0254 -0.0002 0.0007 13.4 0.0070
0 x 9
2
29 85.2 ___
13.5
18.8 -__
~
CIS
In the solution of problems involving n unknowns the intermediate B values are calculated hy the formula:
11 0 -0,0045
-0
(16)
~~
28 65.9
C1 = Bi -
(15)
Cp = B3
B, -
from which .z values are calculated according to the formula:
(14)
C values arc next obtained as follows:
=
Cj
-3.7408 -0 02.57 - 0.0108 -0 0020 -0.3164 -2.4639 0.1712 _ _ 0~ . _9 - 0.0593
0
9
0.2893
-0,1876 -2.7019
-0,0113
- l.O27C,
-1,1540 0.07,jl -0 47i4 -~ -0 3899 -0.0332 ~
0
0.2_ p -
CR'i
Cs's
2
""5. Total
1194
ANALYTICAL CHEMISTRY
A sample evaluation is shown in Table IV. Because of normal variations in sample size and instrument sensitivity, the total of the components determined may vary from 100%. Provided that the difference is not too great, i t is common practice t o normalize the results t o 100%. This normalizing can be kept t o a minimum by the use of an automatic sample metering system t o secure reproducibility of sample size and installation of amplifier feedback control t o permit adjustment of instrument sensitivity. OBTAINING INVERSE MATRIX
It is sometimes advantageous to be able to determine one z value independently of the others. To accomplish this end, the above reduction may be followed until Matrix I11 is obtained and the inversion completed by use of the Crout method. This is followed by reconversion of the diagonals to unity by multiplying each row by the reciprocal of its respective diagonal and multiplying the factors 1,611, l / b 2 2 , and l / b 3 3 of Matrix I11 by the re-
spective diagonals. Any x value may be calculated independently, then, in terms of mole per cent, by the usual cumulative multiplications followed by multiplying by the corresponding corrected factor. While obtaining the inverse matrix is much more time-consuming than the reduction step of the principal procedure described herein, its use may be justified where repeated determinations for one component (say 50 or more) are required. Conversion of the diagonals t o unity results in a more rapid procedure, which is less subject t o error than the procedure generally used. ’
LITERATURE CITED
(1) Crout, P. D., Am. Inst. Elec. Engrs. Trans., 60, 123540 (1941). (2) Daigle, E. C., and Lee, J. H., Petroleum Refiner, 27, S o . 9, 492-5 (1948). (3) Milne, IT. E., “Xumerical Calculus,” pp. 15-25, Princeton, N. J., Princeton University Press, 1949. RECEIVED for review December 17, 1951. Accepted March 17, 1952.
Determination of Insecticide Residues Analysis of Flour f r o m Pyrethrum-Treated Cotton Bags ALBERT A. SCHREIBER AND DONALD B. MCCLELLAN McLaughEin Gormley King Co., Inc., Minneapolis, Minn.
HE protective treatment of cotton flour bags achieved by ‘weaving the cloth from a warp treated with a pyrethrum extract size ($) left open the question of whether a n y of the pyrethrins would migrate into the flour and could be detected there after storage. Even though pyrethrum extract is considered as one of the insecticides least harmful to warm-hlooded beings ( 7 ) , definite information was needed. Samples of wheat flour in cambric and Osnaburg bags had been drawn from a flour layer about 0.5 inch thick nearest to the fabric. An equal number of samples was available from untreated bags (group C ) and experimental bags, the warp of which had been treated so that the fabric contained originally 5 mg. (group B) and 10 mg. (group A) of pyrethrins per square foot. All the filled bags of three groups from the same source had been stored in a flat position in the same location. Upon inspection of the groups of samples received in tin cans with airtight lids from mills in three different states, the flour from untreated bags was found t o contain up t o 7 live specimens of confused flour beetle per pound of flour. None was found in the flour from the treated bags. About 3 months later the number of live insects had increased t o about 30 and about 20 larvae were found in the same infested samples; very few, if any were found in the samples from treated bags, confirming Cotton’s and other experiments demonstrating the effectiveness of the treatment. The flour samples were then examined chemically for pyrethrins, after having been sifted t o avoid contamination of the extractives by the body fat of the insects, which might interfere with the determination. Sixty-gram portions of the flour samples were extracted with 200 ml. of low boiling petroleum ether, first by shaking a t room temperature and then by refluxing for 3 hours. The combined extracts were filtered after cooling and then evaporated on the water bath (about 75” C.), The concentrates Jvere subjected t o the usual analysis of pyrethrum extract by the Seil method, which allows separate determination of pyrethrins I (pyrethrolone and cinerolone esters of chrysanthemum monocarboxylic acid) and pyrethrins I1 (equivalent esters of chrysanthemum dicarboxylic acid). No pyrethrins I could be detected but, in all cases, small values were found for “pyrethrins 11”(Table I). ils the latter are present in most commercial pyrethrum extracts t o the extent of approximately 80 t o 90% of the pyrethrins I and never in the complete
absence of pyrethrins I, the values shown in Table I must be attributable t o constituents of the flour which had been extracted and interfered with the normal analytical procedure by reacting as pyrethrins I1 would do. It could be suspected that unsaturated fatty acids in flour (8, 9 ) , such as linoleic acid, ivhich occur in pyrethrum extract in a small proportion (j), might give more soluble barium salts than saturated fatty acids and thus be washed out of the pyrethrins I fraction t o appear in the fraction not volatile with steam in the Sei1 procedure-i.e., that containing the chrysanthemum dicarboxylic acid of pyrethrins 11. Hence, a comparative material of vegetable origin was examined t o determine if such an explanation were possible. I n place of an extended check on the solubility of barium salts of unsaturated fatty acids, samples of linseed oil rvere saponified and then subjected t o the Sei1 procedure. T o obtain comparable data, the quantities of linseed oil were chosen to have as closely as possible the same acid and ester content as the u-beat berry and flour (8, 9 ) . I n each case values for pyrethrins I1 obtained from the pyrethrum-free linseed oil were practically identical r i t h those obtained from the equivalent quantities of flour from treated as n-ell as untreated bags. It appears that the Seil procedure, without modification, is not strictly applicable to the determination of very small amounts of pyrethrins in the pres-
Table I.
Seil .-inalysis of 60 Grams of Flour from Bags of Cotton Fabric Pyrethrins I hlg. %
Group A Cambric 4 Osnahurg Cambric B Group B Cambric A Osnahurg Cambric B Group C Cambric 4 Osnaburg Cambric B 0 . 8 4 g. linseed oil Saponified by hydrogenolysis By AOAC method (6th ed.)
Pyrethrins I1 Mg. 7%
0
3.37 0 2.24
0 0056
0
0 0 0
0
5,60
0.0093 0.00375 0.0037
0 0 0
0 0 0
2.26
0.00376 0.0044 0.0031 0.68 0.37
0 0
... ...
18.5
0
0
0 0
... ...
2.2
Group A , 10 mg. pyrethrins per square foot Group B. 6 mg. Group C, none.
2.25 2.24 2.62 1.87 5.7 3.13
0
0.0037
...
