Table 111. Comparison of Results from Determination of Iodine. Concentration in ppm Determination Present method after leaching Neutron with melting with NaOH Sample activation extraction and HzO A
0.41 0.34
B
1.58 1.72 1.49 1 43
C
0 . 3 5 0.38 0.35 0.35 1.65 1 . 8 4 1.72 1.48 1.53 1 . 4 1 1 . 5 1 1.68
0 . 3 6 0.38 1.83 1.71 1.58 1.37
where
E = the potentials Nernst factor a = the activity coefficient A = weight of sample v o = volume of dilution v 1 = volume taken for the measuring c2 = volume of added standard C = concentration of added standard
s =
RESULTS AND DISCUSSION
Calculation of results. The results are calculated from
I
X . A
E,
=
Eo -.
s log CY
fi2
=
Eo
is log a [."UflA
-.
---
-
uo
+
I'
v 2 01 '
Sensitivity. The limit of detection is 0.05 pprn for iodine and 0.1 ppm for fluorine, but sample weight and volume of dilution can be altered. Accuracy. The accuracy of the determination of iodine was tested by analysis of sample mixtures, in different proportions, of iodine-doped selenium and high purity selenium and with results of neutron activation analyses from Institutt for Atomenergi, Kjeller, Norway (Table 111). The accuracy of the determination of fluorine has only been tested by adding fluorine as N a F solution to high purity selenium. RECEIVED October 30, 1970. Accepted March 23, 1971
Determination of Polysorbates in Food Products by Reaction Gas Chromatography Gary Lundquistl and Clifton E. Meloan Department of Chemistry, Kansas State University, Manhattan, Kan. 66502
-.
POLYSORBATES such as the spans and tweens are used as emulsifiers and thickening agents (0.1 0 . 7 x ) in such items as cake icings, vegetable oil toppings, and whipped creams. Because they are food additives, their content in these foods is regulated. Briefly, the official method (1) consists of several extractions, removal of glycerides on a silica column, a saponification, removal of fatty acids, purification of the remaining polyols and glycerol by non-ionic exclusion chromatography, and finally the column effluent is collected, K2Cr2Q added, and the color which develops (18 hours) is used to estimate the original polysorbate. The entire process takes about three weeks, and if a check analysis is to be made also, another three weeks. These polysorbates are esters of the general type shown below.
Direct gas chromatographic separation of these materials has not been successful. It was our idea to do the minimum extractive clean up and then to saponify the ester on the column, the acid salt being retained and the poly01 being separated and determined. Ester
OH-
0
1 I
+
HO OH Separated
Na+-O
&(CH2)&H3 / Retained
This was found to work and a complete analysis could be done in about 2.5 hours. EXPERIMENTAL
Ho-AOT1 Span-60 (sorbitan monostearate) OH Present address, Bethel College, Lindsborg, Kan. (1) "Food Additives Analytical Manual--Sorbitan Monostearate," Food and Drug Administration, 1965.
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ANALY'T'ICAL CHEMISTRY, VOL. 43, NO. 8, JULY 1971
Apparatus. A Wilkens-Aerograph Model 350-B gas chromatograph with TC detector was used. The column was 6-ft, Cu, in. 0.d. packed with 15% carbowax 20 M on silanized Chromosorb-T. The column temperature was 120 "C with the injection port and detector at 190 "C. Helium flow rate was 38 ml/min. The reactive column, a 12-in. selection of C u tubing, 1/4-in. 0.d. was filled with 30 mesh soda-lime beads and placed in front of the carbowax column. It was found that ordinary NaOH pellets would not work and if they were ground and
sieved it still tended t o plug up the column. The reactive selection was changed every 10-12 samples. Samples of 1 p1 were injected. Chemicals. The following were used : Span-60, sorbitan monostearate; Tween-60, sorbitan monostearate polyoxyalkylene ; Tween-80, sorhitan monoleate polyoxyalkylene: soda-lime beads, 30 mesh : Carbowax 20 M ; Chrotnosorb-T; and Itstant Whip. Procedure. A can of whipped cream was placed in a n acetone-dry ice bath. The g2s in the can was released through the nozzle after 30 minutes. The top of the can was then removed and 25 grams. of sample were placed in a 500-ml separatory funnel. Twenty-five milliliters of H20 and 50 ml of absolute alcohol were added and mixed thoroughly. One hundred twenty-five milliliters of ether were added with shaking for one minute. One hundred twenty-five milliliters of petroleum ether were added and shaking repeated for one minute. The aqueous alcohol layer was discarded. The ether layer (containing polysorbates) was washed with 25-ml portions of 1 :1 water-alcohol. ‘ f i e washings were discarded. ’The ether phase was transferred to a 400-ml beaker, evaporated to 10--15 ml, nnd made t o volume in a 25-ml volumetric flask. RESULTS AND DISCUSSION
Extracted polysorbates were saponified in the normal maniier and the saponification mixture was injected into the
chromatograph with a nonreactive column. In all cases, three peaks were obtained, which were the same as those obtained by hjecting tlie polysorbate directly onto the reactive column. A real sample, whipped crcam, was treated by the official method and then .injected into the chromatograph. The same peaks were presun!. but had retention times about 10 seconds longer because of the additicnal time in going through the reactiw c.olamn. The first peak to emerge was tile solvent---ether. The second peak was glyierol, whish is fornied when the glycerides are saponifid. The third peak was the polyol. Polysorbates are mixtures of the polyols of sorbitol and it was expected that these would also be separated. This was not the case. This has the advantage qf making the determination easier to quantitate bst t.he disdvantage oE not being able to identify each c o m p m a ? t . It is possible that the polyols are further converted to sorbitol since the retention time of sorbitol is the same as the polyol peak: our attempts to prove this hRve thus far failed. It was found that the soda-lime beads had to be replaced after about 10 injections.
RECEIVEDfor review April 9, 1970. Resubmitted and accepted April 2, 1971. This work was supported by a grant from the National Science Foundation.
Stoichiometry in the Neutral lodometric Procedure fer Ozone by Gas-Phase Titration with Nitric Oxide J. A. Hodgeson, R. E. Baumgardner, B. E. Martin, and K. A. Rehme Environmental Protection Agency, Air Pollution Control Ofice, Divisiort of Chemisf r y iind Physics, P.O. Box 12055, Research Triangle Park, N . C., 27709
A RECENT ARTICLE by Boyd et al. ( I ) questioned the stoichiometry in the one per cent neutral buffered potassium iodide procedure for the determination of ozone. By making simultaneous ultraviolet absorption measurements of a b solute ozone, Boyd found that the molar ratio between iodine released and ozone absorbed was 1.5. The stoichiometry that has been used for several years in air pollution measurements is 1 : l . This ratio is apparently based on the earlier report by Byers and Saltzman ( 2 ) of a laboratory study of the neutral K I procedure. The neutral buffered potassium iodide procedure with the 1 :1 stoichiometry has recently been adopted by the Environmental Protection Agency’s Air Pollution Control Office (APCO) as the reference technique for oxidant measurernents in the Federal criteria document on photochemical oxidants (3). If the factor of 1.5 is correct, then past ambient oxidant measurements have been high by 33 per cent. Because of present confusion (1) A. W. Boyd, C. Willis, and R . Cyr, ANAL. CHEM.,42, 670 (1970).
(2) D. H. Ryers and B. E. Saltzman, Aduan. Chem.Ser.,21,93--101 (1959). (3) “Air Quality Criteria for Photochemical Oxidants,” USDPIEW-
PHS, National Air Pollution Control Administration, Publication No. AP-63, Washington, D. C., March 1970.
over the issue, a n independent confirmation of the stoichiometry was urgently needed. We have utilized the fast reaction between nitric oxide and ozone in a dynamic gas-phase titration apparatus to provide an independent measure of absolute ozone concentration, along with simultaneous neutral K I measurements. A gasphase chemiluminescent-ozone detector first described by Nederbragt ( 4 , s ) provided a rapid determination of the titration curve and the end point. Comparison of absolute ozone determined in this manner with neutral K I measurements indicates thst the stoichiometry is 1.O, within experimental error. The details of our experiments are given below. EXPERIhIENTAL
A flow schematic of the titration apparatus is shown in Figure 1. The reactor wm a flow tube, 100 cm long by 4 cm
i.d., containing four sampling ports for sampling at different residence times. T’ne (>,zone source consisted of a n 8-in. Pen-Ray lamp (Ultraviolet Products, In:.), which irradiated purified air flowing through a qu:.rtz tube, 30 cm long hy (4) G. W. Nederbragt. A. Van Der Horst, and J. Van Duijn, Nufur?, 206, 87 (1965). ( 9 G. J. Werren and G . Babcock, Rei.. Sei. Zristrurn., 41, 280 (1970). A N A L Y T I X L CHEMISTRY, VOL. 43, NO. 8, JULY 1971
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