Table 111. Comparison of Iodine Values of Vegetable Oils Determined by Br, in PC and IC1 Methods Iodine valueb Oila
"
I
I
I
I
Volume
I
I
I
I
I
L
0.5 M Br, in PC
Flgure 2. Titration of unsaturation in vegetable oils with bromine in 70% PC-3OYo CHCls
tion with nitrogen prior to titration gave slightly higher results, but the effect was small, and although oxygen was removed in all the titrations reported here, this step does not appear necessary in routine work. Vegetable oils contain a variety of fatty acids. Of the unsaturated acids, oleic and linoleic are the most common. Iodine values for a number of oils by direct bromination and by indirect iodine monochloride determination are compared in Table 111. The general shape of the bromine titration curves is shown in Figure 2; those oils with higher percentages of molecules containing two or more double bonds show evidence for two potential breaks. The results for the bromine method tend to be higher than for the IC1 method by about 5 to 10%. However, iodine numbers are useful primarily for relative comparisons among various oils and, for this purpose, a direct titration is more rapid and convenient.
LITERATURE CITED (1) A. Polgar and J. L. Jungnickel, in "Organic Analysis", Vol. 111, J. Mitchell, Ed., Interscience, New York. 1956, pp 206-255. (2) K. Uhrig and H. Levin, lnd. Eng. Chem., Anal. Ed., 13, 90 (1941). (3) P. C.Mcllhiney, J. Am. Chem. SOC., 16, 275 (1894). (4) A. W. Francis, lnd. Eng. Chem., 16, 821 (1926). (5) H. P.Kaufmann and E. Hansen-Schmidt, Arch. Pharm. (Weinheim), 263, 32 (1925).
Br, in PC method
IC1 method
Corn 145 131 Cottonseed 124 119 Linseed 168 168 Olive 91 87 Peanut 103 97 Rapeseed 125 118 (low erucic acid variety) Soybean 123 112 Safflower 143 139 a Commercial oils used as received. b Calculated as equivalent number of grams of iodine that would have been consumed by 100 g of oil. All values are the average of two titrations.
(6) F. A. Leiseyand J. F. Grutch, Anal. Chem., 28, 1553(1956). (7) F. Baumann and D. D. Gilbert, Anal. Chem., 35, 1133 (1963). (8) J. W. Miller and D. D. DeFord, Anal. Chem.. 29, 475 (1957). (9) W. Walisch and M. R . F. Ashworth. Mikrochim. Acta, 1959, 497. (10) T. Williams, J. Krudener, and J. McFarland, Anal. Chim. Acta, 30, 155 (1964). (11) I. M. Kolthoff and F. A. Bovey. Anal. Chem., 19,498 (1947). (12) B. Braae, Anal. Chem., 21, 1461 (1949). (13) H. D. DuBois and D. A. Skoog, Anal. Chem., 20, 624 (1948). (14) P. 8. Sweetser and C. E. Bricker. Anal. Chem., 24, 1107 (1952). (15) "United States Pharmacopeia", 18th Revision, Mack Publishing Co., Easton, Pa., 1970, p 905. (16) "The British Pharmacopoeia", The Pharmaceutical Press, London, 1968, pp 1266-1267. (17) F. Said, M. M. Amer, A. K. S. Ahmed, and A. A. Said, J. Pharm. Pharmacob, 16, 210 (1964). (18) R. D. Krause and B. Kratochvil, Anal. Chem., 45, 844 (1973). (19) J. Bloeseken and E. T. Gelber, Rec. Trav. Chim., 46, 158 (1927); Chem. Abstr., 21, 1628 (1927). (20) C. F. Van Duin, Rec. Trav. Chim., 45, 345 (1926); Chem. Abstr., 20, 2441 (1926).
RECEIVEDfor review August 19, 1975. Accepted December 8, 1975. Financial support by the National Research Council of Canada and by the University of Alberta is gratefully acknowledged.
Removal of Copper and Iron Prior to Water Hardness Titration James S. Fritz' and Jeffrey N. King
Ames Laboratory, ERDA, and Department of Chemistry, lowa State University, Ames, lowa 500 7 I
Silica gel was reacted with 3-aminopropyitriethoxysiiane or with the N-methyl derivative of the same reagent to produce a material with an amino silyl functional group. If a water sample in the pH range of 5.0 to 7.5 is passed through a short column of this material, iron(l1) and copper(11) are completely retained, while calcium(l1) and magnesium(il) pass through. This permits an accurate water hardness titration without adding any cyanide.
In the determination of water hardness by the EDTA titration method, several metal ions interfere by blocking the indicator ( I ) . In natural water supplies, the chief interfering ions are iron(I1) and copper(I1). Interference from these ions can be avoided by masking with cyanide, although re570
ANALYTICAL CHEMISTRY, VOL. 48,
NO. 3,
MARCH 1976
action of cyanide with iron is sometimes incomplete and the end point of the titration is not as sharp as when iron is absent. Cyanide is extremely poisonous and thus its use may be hazardous, especially when large numbers of samples are being analyzed. The purpose of this study was to develop a quick, simple method for removing iron and copper from water so that water hardness titrations could be performed without the use of cyanide. Various workers have incorporated amine functional groups in silica material by reaction with different alkoxy silanes which contain an amine group. Thus, Leyden and co-workers (2-4) have shown that silica gel containing a chemically bonded organic amine or diamine will quantitatively retain metal ions such as mercury(II), copper(II), zinc(II), and manganese(I1). Dingman et al. ( 5 ) prepared
polyamine-polyurea resins and showed that those resins with free amine groups would effectively retain several divalent metal ions. Two resins were prepared and studied in the present work. One was prepared by reacting silica gel with 3-aminopropyltriethoxysilane, and the other by reaction of silica gel with the N-methyl derivative of the same organic reagent. Assuming complete reaction with the hydroxyl groups on the silica gel surface, the resins would have the following structure.
I
I1
I t is more likely t h a t the organic reagent reacts with only one or two silica gel hydroxyls, in which case remaining ethoxy groups on the organic silane would hydrolyze giving a resin of the following structure. I
I
OH
OH I11
Both of the resins proved to be effective in removing iron and copper from hard water. After passing a water sample rapidly through a short column of the resin, the total water hardness can be titrated accurately without using any cyanide.
EXPERIMENTAL Silica gel, 100-200 mesh, was activated by refluxing in concd hydrochloric acid for 4 h as described by Aue and Hastings (6). This was washed until neutral with distilled water and dried in a vacuum desiccator. The activated silica gel was then refluxed in a 10% solution of either 3-aminopropyltriethoxysilane (APTSI) or N methyl APTSI in toluene for 4 h as described by Weetall (7). The silylated resin was washed with toluene and acetone and then dried overnight at 80 OC. The resin used in this work had a capacity of 1.05 mequiv/g. All of the resins used in this work were prepared and furnished by Richard Courtney (8). The column consisted of a 1 2 X 2.2 cm glass tube attached to a 50-ml buret at about the 27-ml mark. A flow rate of 16-18 ml/min was achieved with a 2-cm resin bed and 9 lb/in2 pressure on the column. All hardness titrations were carried out using EDTA ( I ) . The copper(I1) and iron(I1) concentrations were determined colorimetrically with bis(2-hydroxyethy1)dithiocarbamate (9) and 1 , l O phenanthroline (IO),respectively. A stock solution of hard water equivalent to 118.9 mg/l. of calcium carbonate was made using equimolar quantities of MgS04 and CaC03. Stock metal ion solutions containing 0.968 mg/l. iron(I1) and 0.925 mg/l. copper(I1) were prepared from their ammonium sulfate and chloride salts, respectively. The ability of the resin t o extract calcium(I1) and magnesium(11) was determined by passing 25.0-ml samples of the stock hardness solution through the resin. The effluent was then titrated for hardness by the standard method using cyanide. In a similar manner, 50.0-ml samples of the stock metal ion solutions were passed through the resin, collected, and analyzed for iron(I1) and copper(11) colorimetrically. The effective pH range of the resins was determined by repeating the above procedure with solutions of various pH values. Several natural water samples were passed through the column and titrated for hardness without using cyanide. These results were then compared to those obtained by the standard method of analysis with cyanide added. The following procedure was used for analysis of natural water samples.
Table I. Extraction Ability of Resin I Component
detns
Before column, ppm
column, ppm
Hardness Cu(11) Fe(I1)
7 3 3
118.9 0.925 0.968
117.7 0.000 0.000
No. of
After
-
Table 11. Results of Comparison between Standard Method and the New Method Using Resin I Hardness Standard method APTSI resin
Source of sample
Fe(II), PPm
Cu(II), ppm
Iowa State University Ames, Iowa (raw) Squaw Creek, Ames, Iowa Slater, Iowa
0.127
0.235
310.7
309.7
6.47
0.246
291.0
289.1
0.991
0.193
221.7
221.1
0.274
1.27
109.1
109.7
(1)Adjust pH of the water sample to between 5 and 7.5 using 0.1 M NaOH or 0.1 M HC1. (2) Pass the sample through a column containing the amino resin at a convenient flow rate (16-18 ml/min for example). Discard the first 10 ml of effluent, then collect the subsequent effluent for titration. (3) Titrate an aliquot of the column effluent with EDTA using the standard procedure ( I ) except for the addition of cyanide. (4)When needed, regenerate APTSI resin by washing with 0.1 M HC1, then 0.1 M NaOH, then distilled water until neutral. (Do not allow the resin to stand in contact with NaOH.)
RESULTS AND DISCUSSION In the p H range of 5.0 to 7.5, both iron(I1) and copper(I1) are completely retained by a short column of either resin I or 11, while the calcium(I1) and magnesium(I1) pass quantitatively through the column. Results are given in Table I. Below p H 5.0, the ability of the resin to extract copper and iron decreases rapidly and, a t p H 4.0, no extraction was observed. Above pH 7 . 5 , both resins begin to extract calcium and magnesium from solution. This is interesting in that Dingman e t al. specifically stated that their resin did not retain calcium or magnesium (5). The N-methyl resin (resin 11) binds metal ions more strongly than resin I. This was evident from the fact that 0.1 M hydrochloric acid was sufficient t o elute copper and iron rapidly from resin I; while, with resin 11, extended washing with 1.0 M hydrochloric acid was required to remove the sorbed metal ions. For this reason, resin I was used in all subsequent work. At the end of each run, blue and orange bands could be seen a t the top of the resin bed. The blue band was from the formation of the copper amine complex. T h e orange band is thought t o be from oxidation of Fe(I1) to Fe(II1) and then precipitation as Fen03 onto the resin. The formation of these bands did not appear to have any effect upon the flow rate of the column. A column can be used for several samples before regeneration is required. Using natural water samples, we compared our procedure with the standard method ( I ) . The results of this study are given in Table 11. As shown in Table 11, even with a high iron(I1) content of 6.47 ppm, the resin method gave results to within 0.65% of the standard method. This method appears to be a viable alternative to using cyanide in water hardness titrations. T h e column procedure adds no more than 2-3 minutes to the total analysis time. A 2-cm resin column can be used for more t h a n 500 ml of water samples, depending upon iron and copper content. ANALYTICAL CHEMISTRY, VOL. 48, NO. 3, MARCH 1976
571
(5)J. Dingman, Jr., S. Siggia. C. Barton, and K. B. Hitchcock. Anal. Chem., 44, 1351 (1972). (6)W. A. Aue and C. R. Hastings, J. Chromatogr..42, 319 (1969). (7)H. H. Weetall. Biochim. Biophys. Acta, 212, 1, (1970).
ACKNOWLEDGMENT Special thanks are given to Richard Cortney, Ames Laboratory summer trainee, for preparing the resins used.
LITERATURE CITED (1)"Standard Methods for the Examination of Water and Wastewater", 13th ed.,1971,p 179. (2)G. B. Harper, Anal. Chem., 47, 348 (1975). (3)D . E. Leyden and G. H. Luttrell, Anal. Chem., 47, 1612 (1975). (4)D . E. Leyden, G. H. Luttrell, and T . A. Patterson, Anal. Lett., 8, 51 (1975).
(8) R.
E. Courtney, Ames Laboratory ERDA. Ames Iowa, unpublished work,
1975. (9)Ref. 1. p 164. (IO)Ref. 1, p 189.
RECEIVEDfor review October 24, 1975. Accepted December 1, 1975.
Lead Determination in Airborne Particulate Matter by Proton Activation Analysis Georges Desaedeleer,' Claude Ronneau, and Desire Apers Universite de Louvain, Laboratoire de Chimie lnorganique et Nucleaire, 2,chemin du Cyclotron, B- 13~8-Louvain-la-Neuve,Belgique
Proton activation analysis has been applied to determine lead concentrations in airborne particulate matter collected on filter papers. 204Biradioactivity, produced by 40-50 MeV proton activation via 208Pb(p,3n), 207Pb(p,4n), 208Pb(p,5n) reactions, is used to identify and measure trace amounts of lead. Up to 40 samples are bombarded simultaneously for a half-hour period. The 374-KeV y ray is usually used to identify lead; however, y rays above the annihilation radiation, as the 899 KeV, are sometimes more suitable. Counting times range from 5 to 50 min per sample. Under reasonable irradiation and counting conditions, and without chemical separations, sensitivities of less than 1 ng/cm2 are currently obtained.
Lead in air is globally due to automotive emissions (1-4). Locally, other sources may also be prevalent (4-6). The physical and chemical properties of leaded aerosol are defined through their emission sources. These physical and chemical properties, as well as the total concentrations, should be taken into account to determine the potential toxicity of the aerosol ( I , 7). I t should be noted that there is still a lack of agreement concerning the toxicity of continuous low exposure to leaded aerosol. This is in part due to the variations with time and location in both total concentration and size distribution (8). In order to study the toxicity of leaded aerosol, one should have the best information on the exposure of humans to airborne lead and therefore take into account all these variations (9). This, however, requires a knowledge of the occurrence of lead in air that can be analyzed over short periods of time. Such analyses require high sensitivity techniques. Irradiation techniques using accelerator beams are very suitable for these high sensitivities. Furthermore, the sensitivity reached also allows considerable simplification of the air sampling devices, and therefore better air monitoring can be achieved (10). Lead analysis in atmospheric particulate matter is currently performed by flame and flameless atomic absorption (11-13), anodic stripping voltametry (14), mass spectrometry ( 1 5 ) ,x-ray fluorescence ( 1 6 ) ,and particle-induced x-ray emission (17, 18). 3He activation analysis has also recently been applied (19).Other activation techniques were used to determine lead in various materials, e.g. thermal and fast 572
ANALYTICAL CHEMISTRY, VOL. 48,
NO. 3,
MARCH 1976
neutron activation (20, 21 ), photon activation (22), protons and deuteron activation (23,24), and 4He activation (25). Low energy, 20 MeV, proton activation allows lead determination down to the nanogram levels (23).206Pb(p,n)and 207Pb(p,2n) reactions induce 206Biradioactivity. However, these levels are reached only under prolonged irradiation and counting conditions, and only after chemical separation of the radioisotopes. On the contrary, in the method presented here, irradiations are performed with more energetic protons. These protons produce 204Biradioactivity by means of *OGPb(p,3n), 207Pb(p,4n),and 208Pb(p,5n) reactions, all having a cross section close to 1 barn (28). Because of its shorter half-life (Table I), 204Biis much more suitable for the evaluation of minute amounts of lead. Also this half-life is long enough so that a large number of samples-up to 40-can be irradiated simultaneously, and subsequent counting may be achieved, making the method readily carried out on a routine basis.
EXPERIMENTAL Target. Standards are made a) of thin aluminum foils (2.7 mg/ cm2)covered by a lead film ( 2 mg/cm2) by evaporation in vacuum or b) of Whatman 41 cellulose filter paper and Sartorius membrane filters (SM11302) (3-5 mg/cm2) uniformly impregnated with a lead nitrate solution (1pg/cm2). Typical samples consist of 1-10 pg/cm2 of aerosol collected on Whatman or Sartorius filter paper. Irradiations. Irradiations are performed at the cyclotron of Louvain-la-Neuve. In a preliminary step, different sets of standards, each standard being sandwiched between aluminum degrader foils, are irradiated at different energies, 60, 55, 50, and 45 MeV. In the routine procedure, targets are covered on both sides by high-purity thin aluminum foils (1 mg/ cm2) and sandwiched between aluminum rings. In these rings, a hole is drilled, allowing helium circulation to cool the targets. They are maintained and aligned by means of two brass rods which are driven through the holes A (Figure l ) , allowing easy dismounting. Irradiations are done with 50-MeV protons and 1-MAintensity, for 30 min. Together with each set of three samples, several standards interleaved with the samples are irradiated. Counting. Radionuclides are identified by y spectrometry by means of an 80-cm3 Ge(Li) detector and a Northern 4096 channel analyzer coupled with a PDP 11-20 computer. Data acquisition is made in two steps: a) first, on-line with the analyzer, the PDP computer allows a simple treatment of the spectrum and stores it on magnetic tape, and b) second, the magnetic tape is treated by SAMPO (26) on an IBM 370 computer for peak location and area calculation. Samples are counted, without chemical separations, after at least 6-h cooling time in order to reduce the annihilation
