X-Ray Fluorescence Method for Determining Iodide in Photographic Processing Solutions Iodide Concentration Technique DANIEL OWERBACH, RAYMOND F. HOEFLER, and HERBERT J. KLEM Color Technology Division, Easfman Kodak Co., Rochester 4,
,An x-ray fluorescence spectrometer can be used for the rapid determination of iodide in photographic processing solutions if the iodide is concentrated before analysis. The iodide is precipitated with a slight excess of silver nitrate, filtered off, and dried, and the precipitate analyzed against a known standard. Concentrations as low as 1 mg. per liter can be determined with a standard deviation of a bout 4%.
S
variations in the potassium iodide concentration of photographic developing solutions have large effects on the speed and fogging potential of the process and a fast precise method for its control is desirable. Generally, photographic processing solutions contain very small concentrations of iodide. The chemical methods available consist of potentiometric titrations with silver nitrate (3) or oxidation techniques which attempt to separate the iodide from the other halides (1). The reliability of a modified version of the latter is very poor. The method (1) was modified so that the final solution was treated with potassium iodide and starch and titrated with sodium thiosulfate rather than analyzed polarographically. The potentiometric technique is generally not satisfactory because the ratio of bromide to iodide in the solutions analyzed may be as high as lo3 to lo4to l. Although the concentrating technique presented can also be used to improve the precision of a potentiometric method, the speed and convenience of obtaining the results by x-ray are preferred by the authors. The x-ray technique for iodide is reliable and simple, although the 60-kv. Norelco x-ray spectrometer is not sensitive enough to detect the few milligrams of potassium iodide per liter by a direct reading of the solution. This paper describes a concentrating technique in which iodide is precipitated with a slight excess of silver nitrate. The mixed silver halide precipitate is analyzed for iodide on the x-ray specMALL
N. Y.
trometer. The effects of varying bromide concentrations a t different iodide levels and some possible interferences in using an x-ray technique are set forth, as well as the reasons for using the 984H filter to collect the silver halide precipitate. APPARATUS A N D REAGENTS
Norelco x-ray spectrograph with lithium fluoride analyzing crystal (North America Philips Co., Inc.). 984H Ultra filter glass paper, 4.25 cm. (H. Reeve Angel & Co., Inc.). Millipore filter holder, Pyrex, Catalog No. XX 10 047 00 (Corning Glass Works). Foamex (Glyco Products Co., Inc.). Krylon crystal clear spray coating No. 1303 (Krylon Inc.). Conditions for Norelco Spectrometer X-ray tube Tungsten target Operating power 56 kv., 40 ma. Operating
Analyzing crystal
Lithium fluoride 2d spacing 4.0276 A.
Detector Photomultiplier voltage
Scintillation counter 900 volts
X 0.435A.
Instrument Settings and Counting Rates. The goniometer settings are
12.90' for the background and approximately 12.40' for the KCYpeak of iodine (Figure 1). The net count rate is the difference between these two count rates. The counting rate (counts per second) found on samples analyzed (1 to 20 mg. per liter) is between 180 and 230 for the background and 250 and 2000 for the KCY iodine peak. The total counts are in the range 6400 to 12,800 for the background and 12,800 t o 51,200 for the KCYiodine peak. PROCEDURE
A 250-ml. sample of photographic developer is measured into a MO-ml. beaker and acidified with 50 ml. of 18N sulfuric acid in an exhaust hood. A drop or two of Foamex is added where excess foaming occurs, as in color developers. I n the AI&-type developers foaming is minimized by using 5 ml. of water-saturated ethyl acetate.
If a precipitate forins on acidification (color developers), it should be reniovecl by filtratioi (paper filter) using a filter aid. Tiyo hundred and fifty milliliters filtrate are collected and added t o a GOOml. beaker. The acidified sample (300 ml. if unfiltered, or 250 filtered) is stirred rap dly on a magnetic miser. Fifty milliliters of 0 001N silver nitrate are added slowly (20 seconds) to the beaker, and the mixture is stirred for an additional 5 minutes, and filtered through a 994H Ultra Filter in a UlLpore filter holder. The precioitate is rinsed with a small amount of acetone to dry it. The sample is removed from the filter holder, and qx-ayed with a light coating of a plastic like Krylon, to keep the dry precipilzite from flaking off the filter. The 984H Ultra Filter containing the precipitate is placed in a standard Norelco sample holder, the instrument i s set as described, and the net count r2,te determined. This netcount rate is converted to milligrams per liter fron an appropriate calibration curve. CA.IBRATION CURVES
Calibration curves are prepared by analyzing three aliquots of a solution to which are :tdded different amounts of potassium iodide. d fourth solution containing ncs potassium iodide is also run. I n analyzing unknown samples the instrummt amperage-voltage is first readjusted on the basis of a standard patch. Standard M v e r Iodide-Silver Bromide Precipitate (Standard Patch).
A standard patch is prepared from a standard dewloping solution to check the instrument each time a set of samples is ar alyzed. This standard patch may be used to readjust the amperage on the tube to give the correct value for the standard patch, or the instrument can be left unadjusted and I correction applied to the iodide results based on the result of the standard patch. Once such a patch is prepared it may be re-used until physically damaged as shown by the following experiment. A test patch was prepared from a developer solution and analyzed on 9 VOL. 31, NO. 4, APRIL 1959
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Table 1. Varying Silver Content Net Counts per Second Ag.NO1, I Br Meq. 4 Mg. of 111per Liter 484 470
10,907 21,424
0.025 0.05
Figure 1. Partial scan of silver iodide-silver bromide precipitate on x-ray fluorescence spectrometer
10 Mg. of IC1 per Liter 1211 18,587 0.05 1130 36,693 0.10 2521 2408
20 Mg. of IC1 per Liter 10,788 0.05 31,108 0.10
different days over a 2-week period A fresh test patch was also prepared each day from the same developer solution. The information from the daily test patches is discussed below in the Reliability of Method section. The results on the two test patches mere corrected on the basis of results obtained on the standard patch then in use. The patch prepared daily not only provided reliability data, but also was a check on whether or not the reused patch was slowly decomposing. The observed standard deviation (no subgrouping) for the re-used patches was 0.8% of the total value for the color developer and 0.2'% for the RfQtype developer. The MQ-type developer standard deviation is substantially lower than the statistical estimate of instrument variability would indicate. Each set of counts (background and peak) used in the calculations are based on averages of two counting measurements. Several patches from one sample were prepared and stored over a 2-
I 13" Degrees 2 B
14'
n-eek period and :unalyzed periodically. Each patch was irradiated only once and remained statfle over this period. A Millipore filter can be used in place of the 984H Ultrt Filter, but has disadvantages. Fi1t::itions are much slower through Clie Millipore filter with samples that contain gelatin. Some photograph c developing solutions slowly build up in gelatin content with use, and some m i y contain the gelatin as part of the 'ormula. The use of Foamex, to minimize foaming during the acidification step, dissolves the Millipore filter.
Table II. Effect of Varying Bromide Concentrations a t Different Iodide Levels NaBr, Grams per Liter 1.o
0
2.5
5.0
10.0
566
I Br
1276
501 21,9iO
508 22,933
10 Mg. of III per Liter 1125 1125 17,833 16,906
,165 22,'>55
395 23,169
1116 18,131
1044 19,230
Br, Grams per Liter 0
I Br
2357
1.0
2.5
5.0
20 blg. of IC1 per Liter 2,325 2,232 10,464 9, s35
2 1167 11 348
10.0 2,135 12,655
Table 111. Typical Calibration Datu Color Developer A Color Developer B KI, mg. per liter Net counts per second
580
5.0
10.0
15.0
20.0
4.0
8.0
12.0
16.0
640 638
1266 1211
1899 1892
2554 2523
472 458
1028 990
1521 1480
2030 1979
ANALYTICAL CHEMISTRY
I
DlSCUSSlON
Some of the basic problems considered in developing this method were the effect of different amounts of silver and bromide, in the precipitates, on the count rate of the iodine Iia wave length (absorption), the effect of varying concentrations of bromide a t different iodide levels on the iodide concentration in the precipitate, and the effect of silver halide solvents, such as thiocyanates, and amines, present in some developer solutions. Mass absorption coefficients for various elements (2) plotted against x-ray wave lengths (Angstrom units) show that silver has a large absorption and bromide a smaller but still significant absorption at the iodine Ka! wave length of 0.435 A. (20 of 12.40')
(4).
Net Counts per Second 4.0 N g . of I C 1 per Liter I Br
I
The absorption due to silver will not be of consequence, because a constant amount of silver nitrate (0.05 meq.) is used in the method. The concentration of potassium iodide involved is rarely greater than 20 mg. per liter or 0.03 meq. for the 250-ml. sample used. Solutions containing more than 30 mg. of potassium iodide per liter require a smaller sample size. As long as the sample contains no less than 0.021 gram of sodium bromide per liter (0.05 meq.), essentially all the silver will be precipitated even if there is no iodide in the sample. Table I shows the effect of the silver halide precipitate on the iodide counts when the silver content is increased twofold. The data were obtained on precipitates from water solutions containing 2.50 grams of sodium bromide per liter and concentrations of
potassium iodide varying from 4 to 20 mg. per liter. The bromide count rates were also obtained by counting at the bromine K a wave length to observe the corresponding bromide changes in the precipitate. The effect of a tenfold increase in silver content in the precipitate, produced from a production sample containing 4.7 mg. of potassium iodide per liter is shown b y the following data: with 0.05, 0.10, and 0.50 meq. of silver nitrate, the iodide net counts per second were 580, 531, and 326, respectively. Variations in the bromide level of a solution will change the bromide content of the silver halide precipitate somewhat. However, even large changes in the amount of bromide in the developer solution-i.e., 1 gram per liter-have no significant effect on the iodide result, as shown by the iodide counts in Table 11. Precipitates from water solutions containing different ratios of sodium bromide to potassium iodide were analyzed for potassium iodide and the results expressed in Table I1 in terms of net counts per second. The precipitates were also examined for bromide a t the bromine 28 angle and are included in Table I1 as an indication of bromide increases in the precipitate itself. The samples containing no bromide are assumed to have iodide 100% precipitated, and will have substantially less silver in the precipitate than the precipitates of the samples containing bromide. Developer solutions in which the iodide varies (bromide constant) will also introduce differences in the amount of bromide in the precipitate but these are not significant. This is shown by the fact that calibration curves made from
the analyses of a t least three mixes analyzed in duplicate, are essentially straight lines. Typical calibration data from two developer solutions are shown in Table 111. The calculations from the solubility products are used to estimate the percentage of potassium iodide expected to precipitate from samples of different bromide-iodide ratios as shown in Table IV. The data in Table I1 do not agree with this theoretical estimate. No positive explanation is available to the authors; however, the conditions of the method may be such that the system does not reach equilibrium. Additional mixes mere prepared and analyzed as a check on the data in Table I1 rind the results shown were verified. I n spite of this apparent discrepancy between the practical and theoretical data, this method has been used successfully on a routine basis for approximately 1 year, with no apparent difficulties. Silver halide solvents, such as thiocyanate and various amines present in small amounts in some solutions, appear to have no significant effect on the analysis.
Table IV. Estimate of Per Cent Potassium Iodide Expected to Precipitate
KI, h!ig./L. 5 10 20
- NaBr, Grams per Liter 1.0 2 . 5 5 . 0 10.0 90 75 50 Essentially0 80 60 9G 90 80 95 90 98
potassium iodide per liter and the MQ-type c eveloper approximately 5 mg. per liter. The results on fresh samples are accurate t y definition, because a calibration cu:ve is prepared. There is no reason to suspect complications with samples of used solutions. On the basis of the 4% standard deviation discussed above and the 0.2 to 0.8:G standard deviation due to variability of patch readings discussed previously, i t is obvious that most of the variability occurs in preparing the patches.
RELIABILITY OF METHOD
Data on precision were obtained by analyzing a developing solution 10 different times over a 2-1veek period. Samples of color developer, which form a precipitate on acidification, and of an ill&-type developer, which does not were thus analyzed. The standard deviation (no subgrouping) corresponds to approximately 4% of the total potassium iodide in either sample. The color’ developer contained approximately 19 mg. of
LITERATURE CITED
(I) Evans, R. M., Hanson, W. T., ENQ.CIIEM.,ASAL. Glasoe, 1’. K., IND. ED. 14, E 14 (1942). (2) “Handbook of Chemistry and Physics,” pp. 2183-90, 33rd ed., Chemical Rubber Pub., Cleveland, Ohio, 1951-52.
(3) Kolthoif, I. &I Furman, ., N. H., “Potentiometric Titrations,” pp. 16470, 199-203, Wiley, New Yorlr, 1926. (4) Victoreen, J. A., J . A p p l . P h y . 2 0 , 1141 (1949).
RECEIVEDfor review July 31, 1958. Accepted Pl’ovember 6, 1958. This paper is for inforination only and no statement herein should be considered as in inducement or recommendation for use of any process, substances, or apparatus which infringes any patent.
Determination of Nitrite in Quaternary Ammonium Nitrites J. V. KILLHEFFER, Jr., and ERIC JUNGERMANN Armour Chemical Division, 7 355 West 31sf St., Chicago
bA
method for the estimation of the nitrite ion in commercial quaternary ammonium nitrites has been developed using excess Chloramine-T to oxidize nitrite to nitrate, then iodometric determination of unreacted oxidant. The aqueous system used for inorganic materials was not suitable for the organic quaternary ammonium nitrites, but the technique was rendered practicable by the substitution of N,Ndimethylformamide as solvent.
I
9, 111.
other work in progress in this laboratory, it became necessary to determine nitrite ion in commercial quaternary ammonium nitrites containing one or two long-chain alkyl groups derived from fatty acids. For convenience, a volumetric technique was sought. A search of the literature indicated that no methods had been published for the analysis of organic quaternary nitrites. Techniques for analyzing inorganic N CONNECTION WITH
nitrites, uiilizing a large number of oxidizing agents ( 2 4 , mere reported, but their application was questionable because of the presence of possibly interfering components of the products, such as chloride ion, alcohols, and unsaturation. A procedure which appeared promising mas one described by Vogel (6): The nitrite ion is oxidized by excess Chloramine-T (sodium salt of N chloro-p-toluenesulfonamide), and the VOL. 31, NO. 4, APRIL 1959
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