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The determination of fluorides in food products

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The determination of fluorides in food products

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Content THE DBTERMI If AT I OH OF FLUORIDES
Iff FOOD PRODUCTS
A Thesis
Presented to
the Faculty of the Department of Chemistry
University of Southern California
In Partial Fulfillment
of the Requirements for the Degree
Master of Solenoe
by
Joseph Marlon Sanohis
June 1935
UMI Number: EP41473
All rights reserved
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UMI
D i s S i f M h n P j b l i s h ns£f
UMI EP41473
Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author.
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This thesis, written under the direction of the
candidate's Faculty Committee and approved by
all its members, has been presented to and ac
cepted by the Council on Graduate Study and
Research in partial fulfillment of the require
ments for the degree of
z--' .
.1 " , 4
Master of Science
Date. June , . . . 1935.
Faculty Committee
ACMOWLEGMEKTS
The author wishes to acknowledge hie Indebted
ness to Professor Paul H* ii.-P. Brinton for his
valuable suggestions in outlining the investigation
as well as in the performance of the experimental
work* Acknowledgments are also due to Professors
1* B* Roberts and Leroy S* Weatherby for their will
ing cooperation in securing some of the equipment
and materials used in this study*
Special thanks are due l£r* H. A* Van Borman,
Chief Engineer, and Mr. R. P« Goudey, Sanitary
Engineer, Bureau of Water Works and Supply, City
of Los Angeles, for their kind permission to use
equipment and materials needed In the colorimetric
determination of fluorides*
TABLE OF CONTENTS
CHAPTER PACE
I. THE PROBLEM................................ 1
Statement of the problem ................ 1
Heed for the study . . . .............. 1
II. REVIEW OF THE LITERATURE................... 3
Proposed procedures for the quantitative
estimation of fluorine ................. 3
General review of methods ............ 3
Colorimetric procedures .............. 4
Limitations of available methods . . . • 6
Procedures used for the oxidation of
organic material ....................... 7
Oxidation by oombustion .............. 7
Wet oxidation......................... 9
Other methods used for the extraction of
halogens from organic compounds . . • • 9
III. PROCEDURES SELECTED....................... 11
Outline of procedure . . . • .......... 11
Remarks on experimental technique . . . • IS
Apparatus used......................... . 13
Materials............................... SO
Detailed procedure . .................. SI
iv
CHAPTER PAGE
IV, DATA AND RESULTS........................... 27
Data.................................. . 27
Sample computations ............ 35
Results................................ 55
Discussion of results.................. 57
V. SUMMARY AND CONCLUSIONS................... 39
Summary................................. 39
Conclusions.......... 39
BIBLIOGRAPHY................................... 41
LIST OF TABLES
TABLE PAGE
I. Late Obtained in the Fluorine Recovery Study
by the Alizarin Zirconium Colorimetric
Procedure............................... 88
II• Lata Obtained in the Fluorine Recovery Study
by the Thorium Nitrate Volumetric Pro
cedure . ............ 29
III. Lata Obtained in the Study for the Letermin-
ation of Correction Necessary for Blank . SO
IV. Lata Obtained to Letermine the Effect of
Residual Sodium Peroxide upon the Apparent
Fluorine Content of Unknown ....... SI
V. Lata Obtained from the Letermination of
Fluorine in Commercial Food Products . . . S2
VI. Results Obtained by the Colorimetric and Vol
umetric Procedures in the Fluorine Recov
ery Studies............................. 35
VII. Results Obtained from the Letermination of
Fluorine in Commercial Food Products . . . 36
LISO? OP FIGURES
FIGURE PAGE
1. Thermostatically Controlled Electric Drying
O v e n ..................................... 15
2. Trays Used to Support Material in Drying
Tunnel ....... ..................... 15
5. Drying Tunnel - Side View.................. 16
4. Drying Tunnel - Front View . . ........... 16
5* Standard Parr Calorimeter................ . 17
6. Apparatus Used for the Volatilization of
Fluorine as Hydrofluosilicic Acid........ 17
7. Set of Color Standards and Supporting Rack
Used for the Colorimetric Determination of
Fluorides - Front V i e w ................... 18
8. Standards and Support - Front View (perspec
tive ) ..................................... 18
9. Standards and Support - Rear View........... 19
CHAPTER I
THE PROBLEM
The relationship established recently-*' between the
total amount of fluorides ingested during the period of
formation of the permanent teeth and the production of
mottled tooth enamel has emphasized the need for knowledge
of the amount of this element present in the various articles
consumed in our daily diet.
Statement of the problem. The purpose of this study
was to investigate the possibilities of some of the most
promising methods proposed for the determination of fluor
ine in organic materials in an attempt to simplify them
and, if possible, increase the accuracy with which this
element can be estimated.
Heed for the study. As a result of the demand for
information in regard to the fluorine content of food pro
ducts, considerable interest has been aroused in the de
velopment of methods for the determination of the element.
Although we have now reliable procedures for the deter
mination of fluorine in water, the methods available for
■**Smith and Laverton, Ind. Eng. Ohem., 7, 791-7 (1954).
their estimation in other articles of diet hare not proved
altogether satisfactory.^* ®
2
Boruff and Abbott, Ind. Bng. Chem.. Anal. Bd.. 5,
236-8 (1933).
3Sanohis. J. M.. Ind. Eng. Chem., Anal. Ed., 6, 134-5
(1934). —
CHAPTER II
REVIEW OP THE LITERATURE
A considerable number of methods and modifications
have been suggested from time to time for the quantitative
determination of fluorine. Wagner and Ross4 have present
ed such a complete discussion and bibliography on this sub
ject, that a repetition here seems unnecessary. However,
since the colorimetric procedures are especially adaptable
to the determination of very small amounts of fluorine, such
as those found in water and in food products, and since con
siderable work has been done on these in recent years, it
may be well to review the most promising contributions.
I. PROPOSED PROCEDURES FOR THE QUALITATIVE
ESTIMATION OP FLUORIHE
General review of methods. Wagner and Ross, in
A
their excellent review of fluorine methods in general; group
the various procedures proposed into four classes as follows
Gravimetric methods, in which the fluorine is
weighed as calcium fluoride.
2. Etching methods, in which comparative tests are
4Wagner and Ross, Ind. Eng. Chem.. 9, 1116 (1917).
4
made on the action of hydrofluoric acid on glass
or quartz.
3. Volatilization methods, in which the fluoride is
volatilized as silicon tetrafluoride or hydrofluo-
silicic acid and collected in water.
4. Colorimetric procedures.
To these may he added combinations of 3 and 4 which
makes a convenient procedure when the presence of large
amount of interfering substances makes separation advisable.
Colorimetric procedures. Of the various colorimetric
methods mentioned in the literature, those of Steiger,5 and
6 7
Pe Boer and Basart * deserve consideration.
Steiger's method has been modified recently by both
8 9
Wiohman, and Boissevain. This method is based on the
bleaching action of fluorine upon a peroxidized titanium
chloride solution.
The difficulty with which very small differences
in fluoride concentration oan be detected by this method
5Steiger, G., J. Am. Chem. Soo.. 30, 219 (1908).
5Pe Boer and Basart, Bee. Trav. chim.. 44, 1071 (1925).
?Pe Boer and Basart, Z. anorg. allgem. Chem.. 152,
203, (1926).
%iehmann and Pable, _J. Assoc. Official Agr. Chem..
612 (1933).
^Boissevain, P. H., Colorado Med.. April (1933).
is its most serious disadvantage.
The procedure of De Boert and Basart has heen modi
fied and extended by Pavelka,10 Alimarin,11 Koone, 12
Willard and Winter,13 Armstrong,14 and Kolthoff and Stansby.
In this method, use is made of the fact that in an acid
solution fluorides cause a zirconium alizarin mixture, or
a solution of purpurin (1, 2, 4, trihydroxy&nthraquinone)
to ohange color from pink to yellow. The amount of fluor
ide present can be estimated by the fading of the pink
color or by titration with standard thorium nitrate in a
solution containing ethyl alcohol. The end point of the
titration is the reappearance of the pink color made pos
sible by the precipitation of thorium fluoride, a rather
insoluble compound in an ethyl alcohol solution.
This method and its modifications have been found
satisfactory in many oases for the direct determination
lOpavelka, Miorochem., 6, 149 (1928) •
13*Alimarin, I. P., Z. anal. Chem., 81, 8 (1950).
l^Koone, B., Ohemist-Anal.vst, 20, Wo. 4. 14 (1951).
l&Willard and Winter, Ind. Eng. Chem.. Anal. Ed..
5, 7-10 (1953).
^Armstrong, W. 0., J. Am. Chem. Soo.. 55, 1741
(1933).
15Kolthoff and Stansby, Ind. Eng. Chem.. Anal. Ed.,
6, 118-21 (1934).
6
16 17 18
of soluble fluorides# * * The presence of aluminum,
iront phosphates, borates, silicates, sulphates, and ox
alates in appreciable concentrations have been known to
interfere more or less seriously with these oolorimetric
or volumetric procedures. In solutions of high aoidity,
however, considerably fewer substances interfere, and
often a long separation of the fluoride from Interfering
substances can be eliminated# The distillation of fluor
ine as hydrofluosilioic acid according to the method of
Willard and Winter*^ can be used most conveniently to
separate fluorine from these interfering substances when
necessary.
Limitations of available methods# The previously
mentioned procedures are applicable to the estimation of
fluorides in the absence of appreciable amounts of organic
matter. Therefore, in order to apply these methods to the
determination of fluorine in food products it is necessary
to liberate it by oxidation of the organic material.
^Kolthoff and Stansby, loc. cit.
17Sanehis, J. M., Ind. Eng. Chem., Anal. Ed., 6,
134-5 (1934).
^Thompson and Taylor, Ind. Eng. Chem.. Anal. Ed.,
5, 87-9 (1933).
l^Willard and Winter, Ind. Eng. Chem.. Anal. Ed.,
5, 7-10 (1933).
II. PROCEDURES USED FOR THE OXIDATIOH OP ORGANIC MATERIAL
Oxidation fry combustion. Organic material is common
ly oxidized fry ashing. Winter and Butler,19 reporting
their experiences in the determination of fluorides in plant
materials fry the Willard and Winter volatilization method,
stated that when fluoride is added to the ash from plant
material the fluorine can he recovered quantitatively, and
when the fluoride is added to the plant material and the
material turned at dull redness 89 - 98$ of the fluorine
can he recovered. Identical experience was reported fry
Shuey^0, 251 on the determination of fluoride in foliage
and fruits.
Sharpiess and McCollum22 have summarized the major
sources of error while ashing the organic material as
follows:
a. High temperature
fr. Acid ash
o. Moisture in the sample when it ds placed in the
furnace•
19Winter and Butler, jJ. Assoc. Official Agr. Chem..
16, 105-7 (1933).
2^Shuey, G. A., J. Assoc. Official Agr. Chem.. 16,
153-5 (1933).
^Shuey, 0. A., J. Assoc. Official Agr. Chem., 17,
149-56 (1934).
^Sharpless and MoCollum, J. Hutrition. 6, 163-78 (1933).
8
Their recommendations for avoiding losses of fluor
ides during the ashing process are:
a* Dull red heat not exceeding 500 or 600° C.
b. Treatment of sample before ashing with calcium
acetate or with a mixture of sodium hydroxide
and calcium acetate in case of very aoid ash*
o* Complete drying at 70° C. prior to ashing*
The remark is also made that in boron-containing
samples the presence of sodium carbonate is desirable*
Bockemuller,2^ however, doubts if decomposition at
500 - 650° C* is often really quantitative.
A combustion method which seems to be superior to
the ordinary muffle furnace prooedure, in both the short
ening of the time required for oxidation of the material
and the accuracy of the results obtained, is that involving
a sodium peroxide fusion* This is carried on in an ordin
ary Parr sulfur bomb.
Pringham,24 Parr and Lemp,25 Broderson, 26 Hahn and
Reid,27 and Pflaun and Wenzke28 have shown that the fluoride
23Bockemuller, W*t 2*. anal* Chem*. 91, 81-90 (1932).
2^Pringham, Am. Chem* J*, 31, 386 (1904).
25parr and Lemp, J. Am. Chem. Soc*. 30, 764 (1908).
^Broderson, J. Am.Chem. Soc., 39, 2069 (1917).
27Hahn and Reid, J. Am. Chem. Soc.. 46, 1652 (1924).
9
content of pure organic products, both aliphatic and aro
matic and regardless of the position of the fluorine atoms,
whether on a side chain or a ring, can be satisfactorily
determined by fusion with sodium peroxide*
Wet oxidation. The method of wet oxidation usually
applied to the determination of halogens in organic com
pounds consists in treating the substance with fuming sul
phuric acid alone or in conjunction with chromic acid or a
OQ
persulfate, etc., as oxidizing agent.Alkaline decompo
sition with sodium hydroxide and potassium nitrate or by
sodium peroxide has been used also.
III. OTHER METHODS FOR THE EXTRACTION OF HALOGENS
FROM ORGANIC COMPOUNDS
a. Extraction with alcoholic potassium hydroxide.30
b. Alkali metal treatment.31
o. Decomposition at high temperature (1000° C.) in
the presence of an excess of oxygen and subse-
38Pflaun and Wenzke, Ind. Eng. Chem., Anal. Ed.,
4, 392-3 (1932).
^Thompson and Oakdale, J. Am. Chem. Soc.. 52,
1196 (1930).
30Sohloemar, A*, Miprochem.. 12, 114-16 (1932).
^lvaugh and Nieuwland, Ind. Eng. Chem., Anal. Ed.,
3, 274 (1931).
10
quent absorption of the hydrofluoric acid pro
duced in calcium oxide.
d. Decomposition of the substance in a current of
hydrogen gas, burning the resulting gases and
absorbing the combustion products in a potassium
hydroxide solution.
-------
Boofcemuller, W., Z. anal. Chem.. 91, 81-90 (1932).
SSCadenbach, g## Angew. Chem.. 46, 130 (1933).
CHAPTER III
PROCEDURES SELECTED
After unsuccessful attempts to combine wet oxidation
procedures, using potassium permanganate and manganese di
oxide as oxidants, with distillation of the liberated flu
orine as hydrofluosilicic acid, it was decided to resort
to sodium peroxide fusion followed by volatilization of the
fluorine as the most promising method for the preparation
of the element for its quantitative estimation by either
the Willard and Winter volumetric method or the colori
metric procedure, suggested by the writer,3® usihg the
zirconium-alizarin reaction.
Outline of procedure. The procedure selected in
volves the following steps:
a. Drying of the material at a temperature below 70°C.
b. Pulverizing the dry products.
c. Peroxide fusion.
d. Distillation of fluorine as hydrofluosilicic acid.
e. Volumetric or colorimetric determination of
^Willard and Winter, Ind. Eng. Chem.. Anal. Ed.,
5, 7-10 (1923).
®5Sanchis, J. M., Ind Eng. Chem.. Anal. Ed., 6,
134-5 (1934).
IE
fluorides.
Remarks on experimental technique. The drying of
certain food products such as potatoes, lettuce, beets,
oarrots, etc., was accomplished without difficulty by the
simple procedure of placing very thin slices of the sub
stance on a drying support of close meshed wire screen
material and exposing it to a ourrent of warm air. The
draft may be natural or forced. Good results were obtained
by both methods. The difference was the time required for
drying, the natural draft requiring about four times the
time necessary to dry with forced draft.
Other substances, such as bananas and apples, were
more difficult to obtain in a condition which permitted
grinding. Apples were found to be especially hard to pul
verise due to the fact that the product never became orisp
while in the oven. It was noticed, however, that after re
moving the product from the oven it acquired a certain
degree of rigidity, while cooling, only to become soggy
again after it had stood for a time at room temperature.
By taking advantage of the short period of rigidity it was
possible to obtain a pulverized product which could be ig
nited in a Parr bomb.
The drying process is, therefore, one which will tax
the ingenuity of the analyst. However, there is always
13
some way of accomplishing this, and it is a matter of indi
vidual experiment for eaoh substance to be analyzed* The
things to keep in mind are that the drying must be done at
low temperature and in a neutral or alkaline medium. The
grinding of the dried material was accomplished with the
aid of a glass mortar and pestle*
The conversion of organic to inorganic fluorides
was obtained by fusing the pulverized product with sodium
peroxide. The fusion product was extracted with a small
volume of distilled water*
The inorganic fluorides were separated from the rest
of the substances present in the fusion extract by volatil
ization, as hydrofluosilicic acid, from their acidified
solution in the presence of quartz powder.
The estimation of fluorides in the distillate was
done by two methods for the purpose of comparing their
accuracy and applicability to the determination of very
small amounts of fluorine. One of these methods was a vol
umetric procedure, while the other was a oolorimetrio one*
Apparatus used* The low temperature drying of the
food products was accomplished in two ways: by the use of
an ordinary thermostatically controlled electric drying
oven using natural draft (see Figure 1), and by the use of
a specially designed drying tunnel.
14
The drying tunnel consists of a warm chamber through
which air is constantly driven by means of an electric fan*
This chamber was made from a standard piece of tapering
stove pipe 3 feet long, 6 inches in diameter at one end and
7 inches at the other. A funnel shaped piece of tin was
fastened to the small end of the stove pipe to drive the
air from the fan through the drying chamber* The temper
ature of the tunnel was kept at from 35° C* to 50° C. by
means of a battery of three Fisher burners* This type of
apparatus is illustrated in Figures 3 and 4*
The drying chamber contained the drying racks which
consisted of standard rectangular wire test tube supports,
5 inches wide by 3 inches high by 10 inches long. Figure
2 illustrates the type of drying rack used.
A 2J- inch glass mortar was used for pulverizing the
material*
A standard Parr electrically ignited calorimeter,
shown in Figure 5, was used for the peroxide fusion* It
consisted of a resistance block, combustion cup, and cool
ing chamber*
The set-up shown in Figure 6 was used for the hydro
fluosilicic acid distillation. It consists of a 250 ml.
distilling flask stoppered with a two-holed rubber stopper
through which pass a thermometer and a capillary tube, both
of which extend down to the liquid. A 150 ml. separating
Figure 1
THERMOSTATICALLY CONTROLLED
ELECTRIC DRYING OVEN*
Figure E
TRAYS USED TO SUPPORT MATERIAL
IN DRYING TUNNEL
Figure 3
DRYING TUNNEL - SIDE VIEW
Figure 4
DBYIIIG- TUOTEL - FRONT VIEW
Figure &
STANDARD PARK CALORIMETER
Figure 6
APPARATUS USEE FOR THE VOLATILIZATION OF FLUORINE
AS HYDROFLUOSILICIC ACH>
Figure 8
STANDARDS AND SUPPORT
FRONT VIEW - PERSPECTIVE
1 &l £$r ?*#$♦
mlwSs,
Pg$?3W
„ SET
USED FOR
Figure 7
rvm nnTAR STANDARDS AND SUPPORTING RACK
THE COLORIMETRIC DETERMINATION OF FL0O3IM6
FRONT VIEW
Figure 9
STANDARDS AND SUPPORT
„ REAR VIEW
20
funnel is connected to the capillary tube. An ordinary
Liebig condenser and a glass adapter complete the distilling
equipment.
For the volumetric determination of fluorides a 5 ml.
serological burette was used.
The color comparison, in the colorimetric procedure,
was made with 100 ml., 325 mm., Kessler tubes supported in
a comparison rack designed by the writer and shown in Fig
ures 7, 8, and 9.
A chainomatic balance was used for precision weigh
ings, while a 10 gram torsion balance, sensitive to one-
tenth gram, was used for weighing the food products uBed in
the experiments.
Materials. For the preliminary investigation and
for fluorine recovery studies, a sample of pulverized let
tuce, which had been dried at a temperature below 70° C. in
a forced draft electric drier, and a sample of finely ground
commercial table sugar were used.
The sodium fluoride was a C. P. product of the high
est purity obtainable. The sulfuric acid and sodium per
oxide were also C. P. reagents. The p-fluorobenzoic acid
used was an Eastman Kodak Company product which appeared
to be in an impure condition since the result of two melting
point determinations gave 172° C. and 174° C. as the melt
ing point of the compound, while the theoretical melting
SI
point is 182° C.
Other materials used were lettuce, beets, beet tops,
carrots, apples, bananas, potatoes, and milk. These were
commercial products bought at the market in their natural
condition and prepared for fusion by the methods previous
ly described.
Detailed procedure. If the material was not a pow
der or in a condition which could be readily pulverized, it
was prepared as follows:
A weighed amount of the fresh material was placed in
the oven and dried below 70° C. until it was in a pulveriz-
able oondition. After weighing to determine the loss of
moisture, a representative portion was ground up in a mor
tar to a fine powder. The powdered material was kept in
a desiccator, over caloium chloride, until ready for the
fusion.
from one to one-half gram of the pulverized material
was intimately mixed with 14 grams of sodium peroxide in
the combustion cup of the Parr calorimeter, for the re
covery experiments weighed amounts of sodium fluoride or
p-fluorobenzoic acid were added to the cup prior to mixing
its contents.
The charge was ignited with the aid of pure iron
wire through which a current, of sufficient density to pro
duce the burning of the wire, was passed.
22
After cooling the ignited charge, the combustion cup
was opened and its contents were dissolved in 100 ml. of
distilled water placed in a 250 ml. beaker. The fused mass
was gray with little or no unburned carbon. Solution of
the fused mass was accelerated by heating the water in the
250 ml. beaker to the point where a vigorous effervescence
began to emanate from the cup containing the melt. After
the contents of the bomb had dissolved in the water, the
cup was taken out of the beaker and washed repeatedly with
a minimum amount of water.
The resulting solution was boiled for ten minutes
to decompose all the remaining sodium peroxide.
The contents of the beaker were then made up to
100 ml. with distilled water. 50 ml. of this solution
were then placed in the 250 ml. distilling flask which
contained six glass beads and about 0.05 grams of powdered
quartz. Keeping the distilling flask cool by means of
flowing water from a laboratory tap, 25 ml. of sulfuric
acid were slowly added with constant shaking of the contents
of the flask.
The flask was placed on an asbestos mat which had an
opening sufficiently large for about one-third of the
flask to be exposed to the flame. The stopper carrying
the thermometer and capillary tube was firmly set and connec
tion with the Liebig condenser was made. The distillate
23
was collected in an open container#
The temperature of the contents of the flask was
brought slowly to the boiling point, about 110° C. Then
it was allowed to rise to 130? c# The temperature of the
boiling liquid was maintained between 130 and 140° 0# dur
ing the distillation by adding water from the dropping fun
nel through the capillary tube and adjusting the gas flame.
A set of screw clamps was found very convenient in con
trolling the water and gas flows.
A 150 ml. portion of distillate was collected from
each distillation for the subsequent determination of fluor
ides by both the volqmetrio and the colorimetric methods.
For the volumetric determination, a modification of
the Willard and Winter method was used. A 50 ml# aliquot
of extract was diluted with 50 ml. of distilled water and
made alkaline to phenolphthalein with 5 % sodium hydroxide.
After boiling down to about 50 ml. this solution was render
ed just aoid with dilute hydrochloric acid, transferred to
a 100 ml. volumetric flask and made up to the mark with
water. A 10 ml. aliquot of the resulting solution was
transferred to a 6 inch by 1 inch test tube. After adding
0.15 ml. of a 0.05 $ aqueous solution of sodium alizarine
sulfonate and restoring the pink color by the dropwise
addition of 1 f o sodium hydroxide solution, 10 ml. of 95 %
ethyl alcohol were added. Several drops of 1:50 hydrochlor
24
ic acid were then added to discharge the color and the
resulting solution was titrated, to the reappearance of the
pink color, with 0.01 ff. thorium nitrate. The titration
result was corrected for the indicator blank. The prepar
ation of reagents and standardization of the 0.01 normal
thorium nitrate solution were done in accordance with the
36
directions given in Shuey's report.
For the colorimetric determination a 100 ml. aliquot
was treated as described by the writer previously.*57 A 2 ml.
portion of 3# hydrochloric acid, an equal amount of 3H sul
furic acid, and two ml. of the working zirconium alizarine
solution were added to the unknown and to a set of standards
prepared with a sodium fluoride solution which contained
0.01 mg. fluorine per ml. After bringing the oontents of
the 250 ml. flasks rapidly to the boiling point, the ali
quots were allowed to cool for four hours, and the colors
developed were compared with those of the known standards
by means of Bfessler tubes. A detailed procedure for the
preparation of reagents and performance of the test may be
37
found in the study noted below.
In the first part of the work an effort was made to
36Shuey, G. A., J. Assoc. Official Agr. Chem., 17,
149-56 (1934).
S7Sanchis, J. M., Ind Eng. Chem*. Anal. Ed.. 6, 134-5
(1934).
25
determine the possibility of reoovering small amounts of
fluorine added to a quantity of organic material after the
mixture had been subjected to a sodium peroxide fusion. To
this end, a one gram sample of dried and powdered lettuce
was fused and extracted in the usual manner and the dis
tillates obtained from three separate 50 ml. portions of
extract were analyzed for fluorides by the colorimetric
method. The tests were repeated, adding to a one gram por
tion of lettuce small amounts of fluorine as sodium fluor
ide or as p-fluorobenzoic acid.
The data obtained in these experiments are shown
in Table I.
In order to check the results obtained by the oolor-
metrio procedure, and for the further purpose of determin
ing the applicability of each of these methods to the de
termination of small amounts of fluorine, a set of two
volumetric determinations were made for each aliquot ob
tained in the above hydrofluosilicic acid distillations.
The data obtained by the volumetric procedure are
shown in Table II.
In order to obtain the net amount of fluorine
present in the organic material under investigation, it
was necessary to correct the total fluorine readings
by the blank distillations with distilled water, and on
fused charges with various amounts of powdered sugar and
26
lettuce* The same amount of reagents was used for each
fusion and distillation* The data are shown in Table III.
Attempts were also made to determine the desirabil
ity of destroying the excess sodium peroxide by boiling
for ten minutes prior to the volatilization of fluorine.
Table IV shows the data obtained in this experiment.
Table V shows the data obtained from the determina
tion of fluorine on a number of food products by the adop
ted procedure.
CHAPTER IV
DATA AND RESULTS
In the following tables a summary of the experi
mental information obtained during the course of this
study is presented.
Lata.
TABLE I
LATA OBTAINED IN THE FLUORINE RECOVERY STUDY
BY THE ALIZARIN ZIRCONIUM COLORIMETRIC PROCEDURE
Subatan09 Analyzed Fusion
Extract
ml*
Extract
Distilled
ml.
Volume of
Distillate
ml*
Volume
Analyzed
ml.
Fluorine
in Aliquc
mg.
Sugar (0.5 gram) 160 50 157 100 0.025
Lettuoe (l.O gram) 160 50 160 100 0.125
Lettuce (1.0 gram) 160 50 163 100 0.125
Lettuce (1.0 gram) 145 50 145 100 0.140
Lettuoe (1*0 gram) plus 47*5 mg* NaF 160 50 168 5 0.210
Lettuce (1*0 gram) plus 47*5 mg* NaF 160 50 165 5 0.200
Lettuce (1*0 gram) plus 17.1 mg. NaF 175 50 165 5 0.075
Lettuoe (1*0 gram) plus 17*1 mg* NaF 175 50 170 5 0.070
Sugar (0.50 g.) plus lettuce (0.25 g.)
plus 18*5 mg. NaF 160 50 160 10 0.175
Sugar (0*50 g.) plus lettuce (0*5 g.)
plus 20*0 mg. NaF 154 50 160 10 0.210
Lettuce (1.0 g.) plus 25.5 mg.
p - fluorobenzoio acid 163 50 165 20 0.120
Lettuce (1*0 g.) plus 25*5 mg.
p - fluorobenzoio acid 163 50 165 20 0.115
Lettuce (1*0 g.) plus 45*5 mg.
p - fluorobenzoio acid 165 50 158 10 0.100
Lettuce (1.0 g.) plus 45.5 mg.
p - fluorobenzoio acid 165 50 156 10 0.095
Lettuoe (l.O g.) plus 95*0 mg.
p - fluorobenzoio acid 165 50 170 10 0.190
Lettuoe (1*0 g.) plus 95*0 mg.
p - fluorobenzoic acid 165 50 170 10 0.190
TABLE II
DATA OBTAINED IN THE FLUORINE RECOVERY STUDY
BY THE THORIUM NITRATE VOLUMETRIC PROCEDURE
Substance Analyzed
Fusion
Extract
ml.
Volume of
Distillate
ml.
Dist. taken
for Conoen.
ml.
Made-up
Conoentrate
ml.
Standard
Solution
ml.
Sugar (0.5 g.) 160 157 57 70 0.020
Sugar (0.5 g.) 160 157 57 70 0.020
Lettuoe (1.0 g.) 160 160 60 60 0.035
Lettuoe (1.0 g.) 160 160 60 60 0.075
Lettuoe (1.0 g.) 160 163 63 72 0.050
Lettuce (l.O g.) 160 163 63 72 0.025
Lettuce (1.0 g.) 145 145 45 73 0.045
Lettuoe (1.0 g.) 145 145 45 73 0.040
Lettuce (1.0 g.) plus 47.5 mg. NaF 160 168 100 43 3.635
Lettuoe (1.0 g.) plus 47.5 mg. NaF 160 168 100 43 3.700
Lettuoe (1.0 g.) plus 47.5 mg. NaF 160 165 100 56 2.905
Lettuoe (1.0 g.) plus 47,5 mg. NaF 160 165 100 56 £.815
Lettuce (1.0 g.) plus 17.1 mg. NaF 175 165 100 37 1.450
Lettuoe (1.0 g.) plus 17.1 mg. NaF 175 165 100 37 1.455
Lettuce (1.0 g.) plus 17.1 mg. NaF 175 170 100 45 1.105
Lettuoe (1.0 g.) plus 17.1 mg. NaF 175 170 100 45 1.095
Sugar (0.5 g.) plus lettuoe (0.£5g.i
plus 18.5 mg. NaF 160 160 100 43 1.685
Sugar (0.5 g.) plus lettuoe (0.25g,
plus 18.5 mg. NaF
)
160 160 100 43 1.685
Sugar (0.5 g.) plus lettuoe (0.5 g.
plus 20.0 mg. NaF
)
154 160 100 40 1.935
Sugar (0.5 g.) plus lettuoe (0.5 g.
plus 20.0 mg. NaF
)
154 160 100 40 1.965
Lettuoe (1.0 g.) plus 25*5 mg
p - fluorobenzoio aoid 163 165 145 81 0.345
Lettuoe (1.0 g.) plus 25.5 mg
p - fluorobenzoio aoid 163 165 145 81 0.375
Lettuoe (1.0 g.) plus 25.5 mg
p - fluorobenzoio aoid 163 165 145 65 0.455
Lettuce (1.0 g.) plus 25.5 mg
p - fluorobenzoio aoid 163 165 145 65 0.450
Lettuoe (1.0 g.) plus 45.5 mg
p - fluorobenzoio aoid 165 158 100 56 0.715
Lettuoe (1.0 g.) plus 45.5 mg
p - fluorobenzoio acid 165 158 100 56 0.735
Lettuoe (1.0 g.) plus 45.5 mg
p - fluorobenzoio aoid 165 158 100 39 1.015
Lettuoe (1.0 g.) plus 45.5 mg
p - fluorobenzoio aoid 165 158 100 39 1.028
Lettuoe (1.0 g.) plus 95.0 mg
p - fluorobenzoio aoid 165 170 100 30 2.480
Lettuoe (1.0 g.) plus 95.0 mg
p - fluorobenzoie aoid 165 170
100 35 2.105
Lettuoe (1.0 g.) plus 95.0 mg
p - fluorobenzoio aoid 165 170 100 35 2.035
Remarks: In all oases 50 ml. of extract were taiken
for distillation and 10 ml . Of
mad9-up oonoentrate were taken for titration. One ml. of thorium nitrate solution
was equivalent to from 0.19 to 0.25 mg. of Fluorine, according to the amount of
fluoride titrated.
TABLE XII
BATA OBTAINED IN THE STUDY FOR THE
DETERMINATION OF CORRECTION NECESSARY FOR BLANK
Sub stance Analyzed
Fusion
Extract
ml*
Extract
Distilled
ml*
Volume of
Distillate
ml#
Volume
Analyzed
ml#
F in
Aliquot
mg*
Distilled water - blank #i S O 150 100 0.025
it h i» n
-- 50 150 50 0.012
Distilled water - blank to
mmvmmm
50 150 100 0.020
H ft « tt
*m w >m
50 150 50 0#010
Sugar (0*5 g.) 100 50 150 100 0.035
Tt H
100 50 150 50 0.025
Sugar (1*0 g.) 100 50 155 100 0.035
it ?t
100 50 155 50
0*025
Lettuoe (0*5 g.) 100 50 160 100 0.035
i? it
100 50 160 50 0.025
Lettuce (1*0 g*) 100 50 155 100 0.045
u *t
100 50 155 50 0*035
TABLE IV
DATA OBTAINED TO DETERMINE THE EFFECT Of
RESIDUAL SODIUM PEROXIDE TOON THE
APPARENT FLUORIDE CONTENT OF THE UNKNOWN
Substance Analyzed
Fusion
Extract
ml.
Volume of
Distillate
ml.
Volume
Analyzed
ml.
Fluorine
in Aliquot
mg.
Sodium peroxide solution Straight 150 100 0.080
Sodium peroxide solution - Boiled * * * * * 155 100 0.000
Sugar (1.0 gram) Straight 100 150 100 0.045
Sugar (1.0 gram) Boiled 100 155 100 0.035
Lettuce (1*0 gram) Straight 100 160 100 0.200
Lettuce (1*0 gram) Boiled 100 145 100 0.090
Lettuoe (1.0 gram) plus 45
p - fluorobenzoic acid
•5 mg.
Straight 165 158 10
0.100
Lettuce (1.0 gram) plus 45.5 mg.
p - fluorobenzoio acid - Boiled 165 157 10 0.095
Remark: Fifty ml. of extract were taken for distillation in all cases.
TABLE V
DATA OBTAINED IB THE DETERMIH ATIOB OP
PLUORIBE IB POOD PRODUCTS
Amount Yol. taken Volume Volume P in
Wet Pry taken for Extract for dis of dis- taken for aliquot
Substance Weight Weight
fusion volume tillation tillate analysis analyzed
grams grams grams ml.
ml. ml. ml. mg.
Bananas 87.9 19.0 0.5 100 50 155 50 0.022
Bananas 87.9 19.0 0.5 100 50 155 100 0.045
Bananas 87.9 19.0 1.0 100 50 149 50 0.030
Bananas 87.9 19.0 1.0 10Q 50 149 99
0.055
Beet tops 28.3 3.3 0.8 100 50 160 50
0.032
Beet tops 28.3 3.3 0.8 100 50 160 100 0.060
Beets 30.4 3.5 1.6 100 50 155 50 0.025
Beets 30.4 3.5 1.6 100 50 155 100 0.055
Oarrots 53.7 8.4 1.0 100 50 155 50 0.018
Carrots 53.7 8.4 1.0 100 50 155 100 0.035
Lettuce (sample A) 46.8 6.4 1.0 100 50 152 50 0.030
Lettuce
R
46.8 6.4 1.0 100 50 152 100 0.055
Lettuoe (sample B) 50.2 5.7 1.0 100 50 155 50 0.025
Lettuce
t t
50.2 6.7 1.0 100 50 155 100 0.045
Milk 0*5 g. sug. 132.1 17.7 1.0 100 50 155 50 0.030
Milk " 132.1 17.7 1.0 100 50 155 100 0,055
Milk " 132.1 17.7 1.0 100 50 155 50 0.025
Milk " 132.1 17.7 1.0 100 50 155 100 0.050
Potatoes - 60.2 16.3 1.0 100
50 160 50 0.018
Potatoes 60.2 16.3 1.0 100 50 160 100
0.035
Apple s 47.5 6.7 1.0 100 50 160 50 0.018
Apples 47.5 6.7 1.0 100 50 160 100
0.035
Sugar 1.0 1.0 1.0 100 50 155 50 0.018
Sugar 1.0 1.0 1.0 100 50 155 100 0.035
Sugar 0.5 0.5 0.5 100 50 150 50 0.018
Sugar 0.5 0.5 0.5 100
50 150 100 0.035
Blank ---
— -
— 50 0.018
Blank ——
100 0.035
33
Sample computations. As a matter of convenience It
was decided to express the results in terms of fluorine per
gram of dry material and in parts per million of material as
found in a natural condition*
The factors involved in the computations for the
colorimetric procedure were:
m milligrams of fluorine per gram of dried
©
material.
Pppm m parts per million of fluorine in original
material.
w^ - number of grams of wet material.
W£ * number of grams of material after drying,
wg ? number of. grams of dried material taken for
analysis,
v^ = volume of fusion extract.
v2 s volume of fusion extract taken for distillation.
Vg - volume of distillate collected,
v^ z volume of distillate taken for colorimetric test,
R 5 milligrams of fluorine found in volume tested.
The milligrams of fluorine present in one gram of
dried substance are given by the formula:
P s_LxIixI^xH
6 ' w3 v2 v4
The parts per million in the original material -are
given by the formula:
The faotors involved in the volumetric procedure,
were identical to those given above, down to Tg* In ad
dition, the following terms had to be taken into consider
ation:
vg z volume of distillate taken for concentration,
Vg s total volume after making up concentrate.
v^ 5 volume of made-up concentrate taken for
titration.
T : milliliters of standard thorium nitrate used
in the titration.
K z milligrams of fluorine equivalent to one ml.
of standard thorium nitrate solution.
The milligrams per gram of dry material are given
by the formula:
n Vn v* vA
Fp. ::~-x-=x-~x—2-x T x K:
S w3 v£ Vg v7
The parts per million of fluorine in the original
material are given by the formula:
TABLE VI
RESULTS OBTAINED BY THE COLORIMETRIC AND VOLUMETRIC PROCEDURES
IN THE FLUORINE RECOVERY STUDY
Substanoe Analyzed
Colorimetric
F F Per cent
Added Found Recovery
mg* mg.
Volumetrio
F F Per oent
Added Found Reoovery
mg. mg.
Sugar (0.5 g.) 0 0.126
—
0 0.247
---
n n
—
--- —
0 0.247
---
Lettuoe (1.0 g.) 0 0.640
—
0 0.358
—
n n
—
--- —
0 0.767
---
Lettuce (1.0 g.) 0 0.650
—
0 0.596
---
T t W
—
--- —
0 0.298
---
Lettuoe (l.O g.) 0 0.650
—
0 0.678
---
I f 1 1
—
---
— 0 0.602
---
Lettuoe (1.0 g.) plus 47.5 mg. NaF 21.50 21.95 102 21.50 21.00 98
t » n i f
—
--- ---
21.50 21.40 99.5
Lettuce (l.O g.) plus 47.5 mg. NaF 21.50 20.44 95 21.50 21.40 99.6
t i n * t
--
--- ---
21.50 20.80 97
Lettuoe (1.0 g.) plus 17.1 mg. NaF 7.73 7.99 103 7.73 7.70 105
I T I t T t
—
--- ---
7.73 7.80 101
Lettuoe (1.0 g.) plus 17.1 mg. NaF 7.73 7.69 99.5 7.73 7.80 101
T I I f I I
—
--- ---
7.73 7.73 100
Sugar (0.50 g.) plus lettuoe (0.25
plus IB.5 mg. NaF
g*)
8.38 8.66 103 8.38 9.27 110
Sugar (0*50 g.) plus lettuoe (0.25
plus IB .5 mg. NaF
g*)
— — ---
8.38 9.27 110
Sugar (0*50 g.) plus lettuce (0.50
plus £0.0 mg. NaF
g*)
9.05 9.91 n o 9.05 9.55 105
Sugar (0.50 g.) plus lettuoe (0.50
plus £0.0 mg. NaF
g.)
— ... ---
9.05 9.70 107
Lettuoe (1.0 g.) plus 25.5 mg.
p - fluorobenzoio aoid 3.44 2.58 75 3.44 2.38 69
Lettuoe (1.0 g.) plus 25.5 mg.
p - fluorobenzoio aoid
— ... ---
3.44 2.59 75
Lettuoe (l.O g.) plus 25.5 mg.
p - fluorobenzoio aoid 3.44 2,44 71 3.44 2.52 73
Lettuoe (1.0 g.) plus 25.5 mg.
p - fluorobenzoio aoid
.. --- ---
3.44 2.49 72
Lettuoe (1.0 g.} plus 45.5 mg.
p - fluorobenzoio aoid 6.13 4.57 75 6.13 5.01 82.5
Lettuoe (1.0 g.) plus 45.5 rag.
p - fluorobenzoio aoid
— --- ---
6.13 5.14 84
Lettuoe (1.0 g.) plus 45.5 mg.
p - fluorobenzoio aoid 6.13 4.30 70 6.13 4.95 81
Lettuoe (1.0 g.) plus 45.5 mg.
p - fluorobenzoio aoid
— ... ...
6.13 5.02 82
Lettuoe (1.0 g.) plus 95.0 mg.
p - fluorobenzoio aoid 12.78 10.00 78 12.78 10.40 81
Lettuoe (1.0 g.) plus 95.0 mg.
p - fluorobenzoio aoid — — --
12.78 11.00 86
lettuoe (1.0 g.) plus 95.0 mg.
p - fluorobenzoio aoid 12.78 10.00 78 12.78 10.30 81
Lettuoe (1.0 g.) plus 95.0 rag.
p - fluorobenzoio aoid
... ...
12.78 10.00 78
TABLE VII
RESULTS OP FLUORIDE DETERMINATIONS MADE ON POOD PRODUCTS
Fluorine Fluorine in milli- Fluorine in
in aliquot grqms per gram of parts per
Aliquot Fluorine qorreoted dry substanoe. million.
Substance analyzed in aliquot for blank Individual Indiv.
ml* mg. mg. determination Average deter. Avera^
Apples 50 0*018 0 . 0 0 0 0 0 0 0
Apple s 100 0*035 0 . 0 0 0 0 0 0 0
Bananas 50 0.082 0.004 0.050 11.
Bananas 100 0*045 0.010 0.062
mmm
13.
mmm
Bananas 50 0.030 0*012 0.078
mmmrn
17.
mm m
Bananas 100 0.055 0.020 0.060 0.062 13. 13.5
Beet tops 50 0.032 0.014 0.112 13.
Beet tops 100 0.060 0.025 0.100 0.106 12. 12.5
Beets 50 0.025 0.007 0.027
- - -
3.
mm m
Beets 100 0.055 0.080 0.039 0.033 4. 3.5
Carrot s 50 0.018 0 . 0 0 0 0 0
. . .
Carrots 100 0.035 0 . 0 0 0 0 0 0 0
lettuoe A 50 0.025 0.007 0.043 6.
mm m
Lettuce A 100 0.045 0.010 0.031 0.037 4. 5.
Lettuoe B 50 0.030 0.012 0.073
- - -
8.
Lettuce B 100 0.055 0.020 0.061 0.067 7. 7.5
Milk 0*5 gnu sugar 50 0.030 0.012
0.074
m m m
10.
Milk " 100 0.055 0.020 0.062 0.068 8. 9.
Milk 0*5 gm. sugar 50 0.025 0.007 0.043
mmm
6.
m m *
Milk " 100 0.050 0.015 0.047 0.045 6. 6.
Potatoes 50 0.018 0 . 0 0 0 0
. . .
0
w o *
Potatoes 100 0.035 0 . 0 0 0 0 0 0 0
Sugar 50 0.018 0 . 0 0 0 0
* * * * *
0
Sugar 100 0.035 0 . 0 0 0 0 0 0 0
37
Pisoussion of results. Considering that only or
dinary precautions were taken in the performance of the
experimental work, the results obtained seem to be quite
satisfactory.
Table VI shows unusually good recoveries of fluorine
in the presence of organic matter. The sodium fluoride
recoveries from six independent determinations by the
colorimetric procedure averaged 108$. The lowest recovery
was 95 $ and highest 110$. The average of 12 independent
determinations by the volumetric method was 104$, the range
being between 97$ and 110$.
The recovery of fluorine from p-fluorobensoic acid
was quite consistent by both methods. The average oolor-
imetric recovery was 75$ and ranged from 70$ to 78$. The
average volumetric recovery was 78$ and ranged from 69$ to
84$.
This low recovery was no doubt due to the impure
oondition of the product as indicated by its low melting
point.
The data in this table also show the superiority
of the colorimetric prooedure for very low concentrations
while the volumetric method appears to have a slight ad
vantage with larger amounts.
Table III indicates the difficulty with which fluor
ides in food products may be determined by the adopted pro-
38
cedure when present in concentrations lower than 0*02
milligrams of fluorine per gram of dried material. If we
assume a one to ten loss in weight while drying, the 0*02
milligrams of fluorine will correspond to two parts per
million. This is a satisfactory precision for fluorine
determinations in food products*
The information in this table suggests the desirabil^
ity of making the determination on two separate weights of
the substanoe, e.g., on a one gram and a one-half gram por-*
tion of dried material, and taking the difference as the
fluorine content of the difference in weight. This appears
to be the best method to allow for the over all blank.
Table IV shows that destruction of the excess sodium
peroxide by boiling the extract for ten minutes is desirable.
The results obtained for the sample containing 45.3 mg. of
p-fluorobensoip aoid show that no material loss of fluorine
is produced by this treatment, since recovery was the same
in both cases.
CHAPTER V
SU1SEARY ASD COSTCLUSIOHS
Summary. A method has been suggested which seems
to be applicable to the determination of fluorine in food
products*
The procedure followed involves:
a. drying the material below 70° C.
b* pulverizing the material.
c. fusing two portions, a one gram and a one-half
gram, of material with 14 mg* of sodium peroxide*
d* extracting each melt with 100 ml. of warm water
e* destroying the excess peroxide by boiling the
extract for ten minutes.
f. acidifying cautiously 50 ml of extract, which had
been previously cooled and placed in a 250 ml.
distilling flask containing 0.05 grams of powder
ed quartz and 6 glass beads.
g. distilling over the fluorine as hydrofluosilicic
acid at between ISO and 140° G,
h. determining the fluorine content of a suitable
aliquot, from 50 ml. to 100 ml* depending on the
amount of fluorine present, oolorimetrically.
Conclusions. The relative meagerness of the ex-
40
perimental data obtained should be sufficient warning
against its acceptance without further investigations.
However, the results obtained are sufficiently con
sistent to justify the following conclusions.
1. The method seems to be capable of detecting
fluorides in food products when present in con
centrations higher than two parts per million,
and is, therefore, believed to be suitable for
that purpose.
2. The main advantages of this procedure over others
previously suggested are the great saving in time
required for oxidation of the organic material,,
and the satisfactory recoveries possible by the
sodium peroxide fusion.
3. The disadvantages of the method are the need for
drying and pulverizing the material prior to the
fusion, and the small amount of material which
must be used for analysis in order to obtain a
satisfactory melt.
BIBLIOGRAPHY
Alimarin, I# P., Z. anal. Chem., 81, 8 (1930).
Armstrong, W. 0., J. Am. Chem. Soo., 55, 1741 (1933).
Bockemuller, W., Z. anal; Chem.. 91, 81-90 (1938).
Boer, de & Basart, Reo. trav. ohlm.. 44, 1071 (1935).
Boer, de & Basart, Z. anorg. allgem. Chem.. 158, 303 (1936)
Boissevain, L. H., Colorado Med.. April (1933).
Boruff and Abbott. Ind. Eng. Chem., Anal. Ed.. 5. 836-8
(1933). ~
Brodereon, J. Am. Chem. Soo.. 39, 2069 (1917).
Cadenhaoh, G., Angew. Chem.. 46, 130 (1933).
Hahn and Reid, J. Am. Chem. Soo.. 46, 1652 (1924).
Kolthoff and Stansby. Ind. Eng. Chem.. Anal. Ed.. 6. 118-21
(1934). ~
Eoone, B., Chemist-Analyst. 20, No. 4, 14 (1931).
Parr and Lemp., J. Am. Chem. Soo.. 30, 764 (1908).
Pavelka, Mikroohem.. 6, 149 (1928).
Pflaun and Wenzke. Ind. Eng. Chem., Anal. Ed.. 4. 392-3
(1932). -------------------------
Pringham, Am. Chem. J., 31, 386 (1904).
Sanehis, J. M., Ind. Eng. Chem.. Anal. Ed., 6, 134-5 (1934)
Sohloemer, A., Mlkroohem.. 12, 114-16 (1932).
Shaxpless and MeCollnm., J. Nutrition. 6, 163-78 (1933).
Shuey, G. A., J. Assoo. Official Agr. Chem., 16. 153-5
(1933). "■
42
Shuey, 0. A., J, Assoc* Official Agr* Chem** 17, 149<-56
(1934)*
Smith and haverton, Ind. Eng* Chem*. 7, 7.91-7 (1934).
Steiger, G., J. M, Chem. Soc* * 30, 219 (1908).
Thompson and Oakdale, J. Am* Chem. Soo*. 52, 1196 (1930).
Thompson and Taylor, Ind. Eng* Chem*. Anal* Ed*, 5, 87-9
(1933).
Vangh and Uieuwland, Ind. Eng* Chem** Anal* Ed., 3, 274
(1931).
Wagner and Ross, J. Ind* Eng* Chem** 9, 1116 (1917)*
Wichmann and Dable, j[. Assoc* Offioial Agr* Chem*. 612 (1933).
Willard and Winter, Ind. Eng* Chem*. Anal* Ed.* 5, 7-10
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Winter and Butler, J. Assoo. Offioial Agr* Chem,. 16, 105-7
(1933).

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Asset Metadata

Creator Sanchis, J. M (author)

Core Title The determination of fluorides in food products

Degree Master of Science

Degree Program Chemistry

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

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