Flame Photometric Determination of Calcium in Furnace Slag G. W. STANDEN
and
C. 6. TENNANT
Research Department, The N e w Jersey Zinc Co. (of Pa.), Palmerton, Pa.
A flame photometer method was developed for a rapid determination of calcium in the range of 30% by weight in furnace slag. The method gives results comparable in reproducibility with a rapid chemical method presiously employed. Total elapsed time required for the flame analysis is 2 hours. Previously the elapsed time rising the chemical method w a s 21 hours.
HE routine determination of calcium in furnace slag by wet chemical analysis requires several hours. The method hereafter referred to as t>he “slow” chemical method consisted of solution of the sample in aqua regia, a conventional silica determination which resulted in silica removal, a fusion step on a n y insoluble, double ammonia treatment to remove RaOs metals, and a calcium determination after double precipitation. T h e elapsed time required for this procedure was a t least 48 hours. The method referred t o as the “fast” chemical method consisted of the following steps: solution of the sample with hydrochloric, nitric, sulfuric, and hydrofluoric acids; evaporation to dryness; a single ammonia separation; and a calcium determination after a single precipitation. The elapsed time requked for this method was a minimum of 6 hours. I n practice, though, this normally resulted ill a n elapsed time of 24 hours before results could be reported, because work was interrupted overnight’. I t was desirable to increase the speed of determination so that the results might be available in time to serve more effect,ively in the controlling of &ual furnace operation. h flame photometer method has been developed for this purpose. Othrrs (1-3, 6) have recently reported investigations of flame analysis for calcium, This work illustrates the successful applicatiou of the flame method t,o a complex material of high calcium content. Others may find the technique useful when time is more important than high precision. The time required for the determination is ahout 2 hours and the reproducibility is comparahle to that obtained by a routine vhemical method requiring about 24 hours. An adciitionnl 20 minutes per sample is reqiiired 1)y the flame nirthod when run in lots of t,wo or more.
to avoid any possible removal of calcium by silica or iron osides as they are separated. T e n milliliters of the filtered solution is transferred to a 100-nil. volumetric flask; 25 ml. of distilled water and 1 drop of methyl orange are added. The solution is then adjusted to the end point with 10% ammonium hydroxide solution. T h e flask is placed on a hot plate for 10 to 15 minutes, cooled, diluted to 100 ml. with distilled water, and filtered through Whatman S o . 42 filter paper to remove iron. A 25-ml. portion of the filtrate from the removal of iron is placed in a 50-ml. volumetric flask, and 0.1 ml. (2 drops) of 9.5% hydrochloric acid solution is added. T h e solution is made up to 50 ml. with distilled water. This solution, which contains 0.025 gram of sample per liter, is used for the calcium determination. In this work each sample was run in triplicate and the average of the three values obtained was reported. Preparation of Standards. BASE SOLUTIOS -1. h calcium carbonate sample weighing 2.1974 grams is placed in a 250-ml. beaker and 15 inl. of distilled n.ater added. The beaker is covered m-ith a watch glass, then I0 mi. of concentrated hydrochloric arid is added slowly through the beaker lip. K h e n solution is complete, 2 ml. of concentrated nitric acid is added and the solution is evaporated to dryness. The sample is then cooled and redissolved with heating in 15 nil. of distilled water and 10 ml. of concentrated hydrochloric acid. The solution is again cooled and transferred to a 1-liter volumetric flask, diluted to volume with distilled water, and filtered through a Whatman KO. 42 filter paper. This solution contains 1000 p.p.m. of calcium. Two analyses of the calcium carbonate and one of thP actual standard base solution gave 55.5% calcium oside. Calcium carbonate is 56y0 calcium oxide by theory. BASESOLUTION B. Twenty-five milliliters of Base Soliition A is transferred to a 250-ml. volumetric flask, 2 drops methyl orange added, and the solution is adjusted t o the end point with 10% ammonium hydroxide. The solution is diluted to volume with distilled water and filtered through Whatman S o . 42 filter paper. This solution contains 100 p . p m of calcium. Ten milliliters of Solution l 3 is transC.~I,CIUM STANDARDS. ferred to a 100-ml. volitmetric flask. Two drops (0.1 ml.) of 9,5y0 hydrochloric acid solution is added, and the solution is diluted to volume with distilled n.:iter. Tliis standard contains 10 p.p.m. of calcium. For the 5-p.p.m. c:ilciuni st:indard, 5 nil. of Soltition B is
Table I.
Per C,ent Calcium Oxide in Daily Slag Samples _____._ Cliemical Methods -
Sarnple
Flanie :34.7 33,G
so.
SH-34
EXPERIIIENTAL
34.7
Preparation of Sample Solutions. I n the preparation of samples for analysis, three steps are required: (1) dissolution of sample, (2) removal of iron, and (3) dilution to bring the calcium content of the solution within the limits of the calcium standards, and adjustment of pH. A 0.250-gram portion of the sample, preferably ground to pass 200 mesh, is placed in a quartz dish (Vitreosil opaque fused silica dish, 75-ml. capacity, 38/a inches in diameter, 11/16 inch deep, flat bottomed, glazed; Geo. D. Feidt & Co., Philadelphia, Pa.). Fifteen milliliters of water is added to wet the sample, followed by 10 ml. of concentrated hydrochloric acid. The dish is placed on a hot plate (medium setting) and the sample stirred with a glass rod t o keep i t from sticking to the surface of the dish. When solution is complete, 2 ml. of concentrated nitric acid is added to ensure oxidation of iron. T h e solution is then evaporated to dryness; this requires about 45 minutes. The sample is cooled and redissolved with heating (for about 1 minute) in 15 ml. of distilled water and 10 ml. of concentrated hydrochloric acid. T h e solution is then transferred to a 500-ml. volumetric flask, the dish is thoroughly rinsed, and the solution plus washings are made u p to volume with distilled water. After the solution is thoroughly mixed, about 25 ml. are filtered through two sheets of Whatman No. 42 filter paper. I n this and the next step, the large dilutions were established
Rapid 33.1 33 1
33 0
34 9
33.5
SIUW
.lv. 3 4 3
Check A\..
SIC-30
Std. d e r . % std. dev. (for mean CaO value of 30%) Number of multiple determinations
858
32 5 32.5 33.0 32.7
3.5 3
0 43
0.86
0.21
1.43
2.87
0 70
7
8
8
V O L U M E 28, NO. 5, M A Y 1 9 5 6
859 solutions prepared for the daily sample, average results, and the chemical analysis results performed by each of the two methods outlined above. The multiple determinations u-ere entirely different preparations run on different days. One duplicate pair for the rapid chemical method checked very poorly and, in the small group of dupiicates available, had a large effect on the standard deviation determination. K i t h the flame procedure described, the error in scale i,raitling on tlie Beckman instrument is equivalent t o 0.5Yc calcium o d e . This is of the same order as the standard deviation (0.43('i), and indicates that, the present limits of the method are determined t o a considerable extent by the instrnmrnt chai,actvristics, over which there is no control.
7H4j w I-
I
DISCUSSION OF RESULTS
Irispertion of the above results indicates that Imth the r:ipid cliemic~almethod and the flame method gi-JP highpr results t h i the slow chemical method, whic-h is I-)elievetl to he the most accurate and has been used for reference throughout this ~ v o r k . T h r sourc'e of this constant ei'i'or in the flame results is unkno~vn. I
20
25
I
30
PERCENT CAO
- 35 SLOW
I
1
45 METHOD
40
Figure 1. Correction curve for flame method z's. slow chemical method
treated as above; for the 3-p.11.m. and 1-p.p.ni. standards, 3 ml. and 1 ml., respectively, of Solution I3 are used. Stan:l:Lrds are stored in polyethylene hottles. T h e sample and standard solutions are prepared as just d r srrihed t o ensure the removal of iron and t o maintain a const:int acidity of t h e final solut,ion. Both of these conditions are essential brcause tests have indicated t h a t lon- results are caused l)y the presence of iron and t h a t decreasing values are obtainetl from increasing acidity. Examples of each are noted below. Spectrophotometer. A Beckman Model DG spectrophotonieter equipped with a photomultiplier tube and the Model 9200 flame attachment with oxyhydrogen flame was used for measuring calcium emission intensity. Although the original xvorl; on this method was done with the blue-sensiti7.e photocell and the osyacetylene flame, the final tests and all of the comparative anal>.ses were made using the photomultiplier tube and oxyhydro:;en flame. It is likely t h a t t h e added sensitivity of the photomultiplier W:LR vital t o t h e successful development of this analytical method. Measurement Procedure. T h e instrument settings 1vhii.h w r e used in this method are as follows: oxygen pressure, 20 pounds per square inch; hydrogen pressure, 5 pounds per square inch: photomultiplier detector cell; wave length setting, 554 nip: slit width, 0.1 min.; selector range, 0.1; sensitivity setting, full counterclockwise; resistor, 22 megohms. Plots of t h e flame emission curves for most common elements have beeii published (4). These have been found useful in predetermining possible interference. For t h e 10-p.p.m. calcium standard, the instrument is adjusted for a reading of 100% emission b y a small adjustment of the sensitivity control in a clockn-isc direction. Less than one complete turn of the knob was found sufficient t o accomplish this. \Vith this setting t h e corresponding emission readings arc. obtained for t h e 5 , 3-, and 1-p.p.m. calcium standards nnd for distilled water. Emission readings are then taken for t h r sample solutions. Corrected emission readings are obtained by subtracting t h e twckground reading for distilled water from the readings for t h e standards and sample solutions. These corrected values for t h e standards are used in preparing a n analytical curve. D a t a are plotted as per cent emission against parts per million of calcium. T h e corrected values obtained for the sample solutions are referred t o this curve t o determine cdcium concentration, R E S U L T S OY D i I L Y S 4 3 I P L E S
Using the method described above, a test was carried out in which daily samples a-ere analyzed over a period of 19 days. I n Table I, representative results of this test and d a t a on precision are listeJ showing values obtained for each of the three
Table 11.
Effect of Iron % C'nlciiirn Oxidi. ~~
Sain))lp No. 26 389
SB-6
SB-3.5 SB-39
~~
Iron rexiloved
Original solution 11 3
7 20 30 37
.
19.6 14.i 2.3. 33.i
8
z
5 3 9
41.4
-2 studj- of the 7.-ariation i n malysis of calciuni with v u h tioii in concaentration of other element? present, inrluding zinc. zulfur, failed to establish :in>. lead! iron, c*:idniium, silicon, :d corre!:it ion. If it is desirable to correct the accwracy of the flanic result; to correspond t o those of the sloa- method, a correction curve like that shown in Figme 1 is satisfactory, where i,esults from the flame photometer method are plotted against the slow rhemicd method. The straight line which fits the points as calcu1:itetl by a least, squares method. T h e line goes through the origin a t OTc calcium oxide. ( S o t e t h a t the plot starts a t 2051.) To correc't i i n experimental flame determination, the point coIresponding to the per cent analyzed is located on the vertical asis and cwrected by going to the straight line plot and down to tlie horizontal asis t o obtain t h e corresponding corrected loTver v d u c . For erample, corrected values are shown below for the five i.Cx.dtJ li+ted i n T:il)le I.
REPRESENTATIVE SLAG ANALYSIS
Iiep1,esentative weight percentages of some materials occurring in the slag samples of interest in this work are as follows:
72 Silica Calcium oxide Iron Zinc Magnesium oxide Sulfur Lead
33 32 10 3 3 2 0.4
860
ANALYTICAL CHEMISTRY ConcLusIox
Table 111. Effect of Acidity Solution
B”C
D E
Hydrochloric Acid Added, RI1.
Acid Concn. of S o h , 7c
%
Calcium Oxide
1 2
5 10 15
The reproducibility of the flame method is better than t h a t of the rapid chemical method, as indicated by the check analysis. Because the rapid chemical method has been used for furnace control work, it appears that the flame method is a satisfactory substitute from the point of view of reproducibility. Furthermore, it offers a rapidity of determination not previously available. ACKNOWLEDGMENT
EFFECT OF IRON
Several samples which were taken to solution a t different times during this investigation were analyzed for calcium, using both the original solution and the same solution after removal of iron by precipitation with ammonium hydroxide. The results are listed in Table 11. EFFECT O F ACIDITY
For this test a sample was used which had been carried through the solution preparation pmcedure t o include the removal of iron, but not the final dilution. Five 26-ml. aliquots were evaporated to a volume which permitted the addition of varying amounts of hydrochloric acid before adjusting the volume to 25 ml. The results of this test are shown in Table 111.
The authors are pleased to acknowledge the valuable assistance received from P. A. Henry and S. S.Roeder throughout the course of this work. LITERATURE CITED
(1) Baker, G. L., Johnson, L. H., .LN.~L.CHEM.26, 465-8 (1954). (2) Chow, T. J., Thompson, T. G., Ibid., 27, 910-13 (1955). (3) Curtis, G. UT.,Knauer, H. E., Hunter, L. E., Am. Soc. Testing Materials, Symposium on Flame Photometry, Spec. Tech. Pub. 116 (1952). 14) Gilbert. P. T.. Jr.. I n d . Laboratories. u. 41 (Auaust 1952) (5) Hinsvark, 0. S . , Wittwer, S. H., Seil, H. ;Ll.,-hzra~.CHEM.25, 320-2 (1953).
RECEITED for review Sovember 19, 1955.
Accepted February 27. 1956.
Absorptiometric Study of Certain Organic Fluorine Compounds FREDERICK KINGDON’ with M. G. MELLON Department o f Chemistry, Pordue University, Lafayette, Ind.
Fluorinated 1,3-diones can be applied to the absorptiometric determination of some metal ions, in limited concentration range. A method for iron using thenoyltrifluoroacetone is developed in detail. Advantages are speed, simplicity, and a stable color reaction. Disadvantages are relatively low sensitivity and many interferences. Of the common methods used for determining acetone, only the 2,&dinitrophenylhydrazine reagent is applicable to halogenated acetones. XIethods for bromo-, chloro-, 1,3-dichloro-, and l,l,l-trifluoroacetone are given. Absorption curves for the derivatives are presented.
T?E
substitution of fluorine into organic compounds has melded a great variety of new products, some of which have properties of possible analytical interest. I n general, these properties may be related to the high electronegativity of the fluorine. Thus, in aliphatic compounds several fluorine substituents will deactivate neighboring groups, such as hydrogen or another halogen. A nitro group is stabilized. Complete fluorination of an aliphatic chain gives the very inert fluorocarbons I n contrast, fluorine increases the acidity of some groups and thus may enhance reactivity. Fluorinated nitriles are more easily hydrolyzed than simple nitriles. Acid strengths of organic acids, of compounds such as 1,3-diones, and of alcohols are increased. A carbonyl or an alcohol group near a perfluoroalkyl group forms a hydrate readily. T h e chelate compounds of 1,3diones are more stable, more volatile, and lower melting when fluorine is present. 1 Present address, Experiment Station, Hercules Powder Co., Wilmington, Del.
This research aimed to examine some of these neir conipounds for their usefulness in analysis. .4n incidental and less practical objective was to extend generalizations on the effect of fluorine in organic analytical reagents. -4literature survey was made in order to find, if possible, good examples of organic fluorine compounds of the general kinds of organic analytical reagents listed by Welcher (6) 11 ith the types of applications summarized by Yoe and Sarver (8) and to locate any known analytical methods which involved use or determination of fluorine compounds. Of the vast number of fluorine compounds now k n o m , many have little or no present analytical interest because of their high volatility, insolubility, or low reactivity. Of those of possible anal) tical usefulness, few have been examined, For present purposes, attention was diiected only to compounds of possible absorptiometric interest. This interest finally centered on 1,3-diones and on halogenated acetones. As possible analytical reagents, the 1,3-diones offered a wide field for study of chelate systems. Functioning as weak acids, they form salts with most metal ions. Possibly because of the large number of colored compounds, and consequently many possibilities for interference, they have not been used extensively in absorptiometric analysis. Pulsifer in 1904 ( 5 ) recommended acetylacetone as a reagent for iron(II1). Though the sensitivity (0.003 mg.) compared favorably with that for the thiocyanate method, the latter has become a standard method while the former is seldom mentioned. Recently Cefola ( 3 ) suggested a new dione, thenoyltrifluoroacetone (TTA), as a sensitive reagent for the detection of iron(II1) The red color formed in benzene served to detect 10 p.p,m. of iron(II1). Other previous uses of the 1,3-diones are in the determination of microgram quantities of beryllium (1) by acetylacetone, using the ultraviolet spectrum of the complex and the determination of uranium by dibenzoylmethane ( 7 , 9 ) .
