LITERATURE CITED (1) M. H. Kurbatov and C. W. Townlev. J. hora Nuci. Chem.. 18. 19 (1961). (2) D. F. C. Morris and M. A . Khan, i?adiochik Acta, 6, 110 (1966). (3) Y. Kobayashi. J. Inorg. Nucl. Chem., 29, 1374 (1967). ( 4 ) K. F. Fouche. J. G. V. Lessing and P. A. Brink, "Proceedings of Interna.
I
tional Solvent Extraction Conference, Lyon. September 1974," Society for Chemical Radiology, London, 1974, p. 2685. (5) K. Renaan and W. R . Pierson, d. Inorg. Nucl. Chem.. 27, 21 13 (19651.
RECEIVEDfor review May ?, 1974. Accepted August 6, 1974.
Determination of Fluorine Wolfgang J. Kirsten and 2. H. Shah' Department of Chemistry, Agricultural College of Sweden, S-75007 Uppsala 7, Sweden
Though there are several good measuring methods for fluoride ions ( I ) , the determination of fluorine has been a difficult problem because of the interference of phosphate, sulfate, and a large number of metal ions. In the sulfur determination method described by Kirsten ( 2 - 4 ) , phosphate is hydrogenated to phosphine and sulfate to sulfide. It appeared, therefore, that the worst interferences would be eliminated if the same method of sample decomposition could be used for the determination of fluorine. The apparatus shown in Figure 1was tried, together with the spectrophotometric method described by Belcher, Leonard, and West ( 5 ) . The resulting method was almost completely free from interferences and applicable to both organic and inorganic compounds.
EXPERIMENTAL Reagents f o r Combustion-Hydrogenation. 25% Orthophosphoric acid: Dilute 25 ml of concentrated orthophosphoric acid, sp gr 1.71, to 100 ml with water. Flux: Dissolve 14 grams of NaH2P04 H 2 0 in the least possible amount of water, add 3.5 ml of concentrated orthophosphoric acid and dilute to 25 ml with water. Potassium hydroxide solution: Dissolve 100 grams of analytical grade potassium hydroxide, 85%, in 100 ml of water. Keep 25% orthophosphoric acid and flux in syringe burets. Reagents f o r Spectrophotometry. Prepare the reagents as described by Belcher ( 5 ) .Except for the acetone, prepare and keep all reagents in polyethylene or polypropylene vessels and pipet with polypropylene pipets Adjustment of Apparatus. Set up the apparatus as shown in Figures 1 and 2. Turn stopcocks (D) and (H) so that the hydrogen can pass out through stopcock (H) into free air and the connection to tube (I) is closed. This position of (H) is called the starting position. Turn on hydrogen and oxygen and adjust the oxygen flow to 25 ml/min and the hydrogen flow to 80 ml/min. Switch on the electrical current to heat the furnaces. Place spoon (R) 30 that the sample can be introduced into it through opening (Q). Analytical Procedure. Weigh out the sample into a small platinum boat. Add 2 p l of orthophosphoric acid from a syringe buret to the sample and introduce the boat into the spoon through opening (Q), If the sample is inorganic or contains ashes, add flux instead of orthophosphoric acid. Close stopper (Q). Turn stopcock (H) so that the hydrogen passes into chamber (M). Connect flask (21) with 29 ml of water to joint (J) and introduce spoon (R) with the sample quickly into furnace ( N l ) . Weigh out the next sample. After 10 minutes detach flask (Zl), wash the inlet tube with a small volume of water, and take it out. Turn stopcock (H) to the starting position. Add 5.00 ml of complexan, 1.00 ml of buffer, 5.00 ml of lanthanum, and 12.50 ml of acetone. Shake well after each addition. Fill to the mark with water, mix, and let stand for at least 90 minutes in the dark. Read at 620 nm in 50-mm cuvets. Use a reagent solution, mixed in the same way, in the reference cuvet. All reagents must be added with a high precision. e
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Present address, Institute of Chemistry, University of Sind, Sind. Pakistan. 184
Samples should contain 5-17 pg of fluorine. If the fluorine content is higher, make up the volume of the water solution in the absorption flask t o the mark, pipet an aliquot containing 5-17 pg of fluorine into a second flask, and develop the color there. When samples larger than 300 fig of organic material are to be decomposed, push back split type furance (NI), remove spoon (R) and introduce the boat with the sample-preferably placed into a larger platinum boat-through opening (T). Draw furnace ( N l ) over the combustion tube near the side tube and let it pass slowly over the sample. The rates of gas-flow can be considerably increased if desirable. Water is formed from most of the oxygen and hydrogen, and the excess hydrogen is not critical. Simultaneous Determination of Fluorine a n d Sulfur. When starting the apparatus, turn stopcock (D) in such a manner that the hydrogen passes out into free air and the connection to the soda lime tube is closed. First, when the furnaces are hot, turn the stopcock so that all hydrogen passes through the soda lime tube. Keep the combustion furnaces a t 700 "C when ultramicro amounts of sulfur are to be determined, and the hydrogenation furnace a t 1200 "C. Use the absorption train (22).Charge the first flask with 20 ml of water and 1.00 ml of buffer and the second flask with zinc acetate solution and water. Allow a somewhat longer time for combustion-hydrogenation and sweeping-about 20 minutes. After the absorption, first detach the second flask and determine the sulfide with a methylene blue (7, 8 ) or ethylene blue method (8,9). Then detach the first flask and develop the fluoride color a s described above, with the exception that no more buffer is added.
r. /' T
Figure 1. Apparatus for determination of fluorine and sulfur (A) Narrow safety capillaries which prevent breakage of apparatus if gas tanks are opened too quickly. Tubing is blown off before too much gas enters. They also provide for a quiet and steady gas flow. (6) Rotameters. (C) Quartz tubes in furnace (N3) at 950 "C. (D) Three-way stopcock connected to scrubber (E), compare Figure 2. (F) Scrubber, compare Figure 2. (G) Soda lime tubes. (H) Three-way stopcock. (I) Glass capillary connections. (J) Joint for absorption flask, (K) Tygon tubing. (L) Combustion tube, quartz, inner diameter 8 . outer ll mm. (M) Hydrogenation chamber, sealed on combustion tube, inner diameter 9, outer 12 mm. (NI, N2) Split type combustion furnaces, 900 OC, lengths (Nl) 60 mm. (N2) 120 mm. (N4) Hydrogenation furnace, 1200 OC. ( Q ) Side-tube with silicone rubber stopper for introduction of sample into quartz spoon (R), which is provided with magnet (S). (T) Silicone rubber stopper. (U) Capillary, inner diameter 2, length 15 mm.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 1 , J A N U A R Y 1975
Table 11.Determination of Fluorine in Inorganic Compounds Content of fluorine iVei ht of sample, u g
Substance
Calcd, %
Sodium fluoride
Figure 2. Details and accessories (D, E, F) Three-way stopcock, scrubbers, compare Figure 1. Scrubbers are filled with potassium hydroxide solution below orifices of inlet tubes. Their main purpose is to keep the soda lime in tubes (G)moist and active. Evaporated water must be replaced now and then. (21)Volumetric flask of polypropylene, 50 ml, with inlet tube of quartz, inner diameter 1.5 mm. (22)Absorption train for simultaneous determination of fluorine and sulfur. Head with ground joints made of quartz, second inlet tube of Pyrex, connected with Tygon tubing. First volumetric flask polypropylene, second Pyrex. (L, M) Combustion-hydrogenation tube, compare Figure 1 , (V) Short lengths, 30 mm, of opaque quartz capillary sealed in place to avoid strong heat radiation inside clear quartz. The radiation would cause polymerization of silicone grease and untight joints. (X) Quartz capillary, inner diameter 1.5.outer 7 mm. All conical joints are 814 except for that on (22),which is B10,and all ball and socket joints are 12/2lubricated with silicone grease. Thick-walled quartz tubing is used throughout because of its much long& life-time
RESULTS The spectrophotometric calibration curve run with a Beckman DU spectrophotometer follows Beer's law u p to 17 pg of fluorine. Under the described conditions, 10 pg of fluorine give an absorbance of 0.657. Results obtained with different organic and inorganic compounds are reported in Table I and 11. I t is remarkable that even the NBS opal glass releases 95% of its fluoride content in contact with the acidic flux. A few results of simultaneous determinations of fluorine and sulfur are given in Table 111.
Content of fluorine Substance
p-Fluorobenzoic acid
35. 5 50.0 103.8 112.5 85.0 Trifluoroacetanilide 197. 3" 48.5 F 3793, (C6F6CH),138.3" mannitolb 41.0 F 3794, C19Hlo04Fj,h 63.5" 116.7" F 3772, CloH1004F4b 251.0a 121.0"
Calcd, %
Found, %
Dev, %
13.6
13.6 13. 5 13.6 13.5 13.5 29. 7 29.9 39.8 39.8 37.8 38.1 28.3 28.5
0.0 -0. 1 0.0 -0.1 -0.1 -0.4 -0.2 0.0
30. 1 39.8 38.6 28.1
0.0 -0.8 -0.5 +0.2 +0.4
Volume of absorption solution made up. to the mark and aliSubstances obtained by courtesy of R. Belcher and A . M. G. Macdonald, Birmingham. Substances reported refractory for CH-determination. a
quot analyzed.
Dev, %
45.2
44.9 -0.3 45.0 -0.2 45.0 -0.2 45.1 -0. 1 48.7 48.4 -0.3 48.7 0.0 21.7 2 1 . 1 -0.6 0.0 21.7 22.0 +0.3 21.6 -0. 1 47.5 47.5 0.0 46.9 -0.6 48.4 +0.9 47. 1 -0.4 60.6 60.6 0.0 60.9 +0.3 57.1 -3.5 60.2 -0.4 3.4 3.3 - 0 . 1 0.0 3.4 3 . 3 -0.1 3.4 0.0 5.7 5.1 -0.6 5 . 5 -0.2 5.4 -0.3 5.4 -0.3 up to the mark and ali-
Table 111. Simultaneous Determination of Fluorine and Sulfur Weight of samples, Fluorine, %
UgU
No.
PFB
BTC
Calcd
Found
Sulfur, "c Calcd
Dev
Found
Dev
l b 102.3
110.0 13.6 13.5 - 0 . 1 15.8 15.8 0.0 96.2 125.0 13.5 - 0 . 1 15.8 15.8 0.0 64.3 135.7 13.5 - 0 . 1 15.8 0.0 85.7 106.3 13.6 0.0 1 5 . 5 -0.3 15.6 -0.2 97.2 132.0 13. 5 - 0 . 1 a Samples: p-Fluorobenzoic acid = PFB, S-Benzylthiuronium chloride = BTC. In analysis No. 1, the first absorption flask was charged with water only, and the buffer was added afterwards as described in the method for fluorine alone. In analyses 4 and 5. the time allowed for combustion-hydrogenation and sweeping was 25 minutes. 2 3 4 5
Table I. Determination of Fluorine in Organic Compounds Wei ht of sampje, ug
24.7 30.0 32.0 25. 3 Calcium fluoride 143. 5" 71.5' Barium fluoride 128.0" 106.0" 50.3 47.6 Potassium hexaf luo r o 147. 5" titanate 122.0" 22.5 59. 4" Sodium silicofluoride 109. 0" 98.5" 122. 5" 60.8" Phosphate rock, NBS, 222.0 BS 56 B 263.2 160.5 148.7 Opal glass, NBS, BS 9 1 172. 7 220.0 250.0 180.6 aVolume of absorption solution made quot analyzed.
Found, %
INTERFERENCES Up to 3 pl of concentrated orthophosphoric acid can be added to each sample. When 4 pl or more is added, low results are obtained. Between 200 and 600 p g of the following substances were added to 50-pl samples of p - fluorobenzoic acid and to blanks: A1203, As203, BaS03, Bi(N03)3, Be (metal), BrC6H&OOH, CaC12, CdC12, C1C6H4COOH, Ga (metal), HsB03, HgC12, In (metal), IC6H4COOH, K2Cr207, KMn04, MgO, NaaMoO4, N2CgH10, Pb203, Sb203, SC14H10, Se (elementary), SnC12, TlC13, V205, WO3, Zn(NO&. None of them interfered, and, no other interference has been discovered.
A N A L Y T I C A L CHEMISTRY, VOL. 47,
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DISCUSSION The apparatus is similar to that described earlier for the determination of sulfur (3, 4 ) . Modifications can be seen in the figures. The system for the introduction of ultramicro samples was described by Walisch ( 6 ) . Larger samples are burned in the conventional manner with split type furance (N1) slowly moving along a motor-driven spindle over the sample, which is placed in front of furnace (N2). In the ultramicrodetermination of sulfur ( 4 ) , the combustion furnaces must be kept a t about 700 "C. Higher temperatures will cause small blanks. The hydrogenation furnace needs 1200 "C to give a quantitative hydrogenation of sulfur. In the determination of fluorine alone, good results were also obtained with the combustion furnaces a t 900 "C and the hydrogenation furnace a t temperatures down to 800 "C. Phosphoric acid ( 1 0 ) should be added to all samples in the ultramicro determination of halogen and sulfur by dry combustion. It decomposes inorganic compounds and expels sulfate and halide and desorbs them also from any alkaline spots which can occur in the tube as contamination of the quartz itself br from samples. Accurate ultramicroanalyses are still obtained when thousands of samples including sulfate and sulfite liquor from paper mills have been analyzed without cleaning of the tube or other precautions. Alkali fluorides were quantitatively decomposed by phosphoric acid, but low results were obtained with calcium and barium fluorides, probably because the phosphoric acid was volatilized already before the salts had been completely decomposed. The flux mixture was therefore introduced. The method for the simultaneous determination of fluorine and sulfur is based on the fact that hydrogen sulfide
passes right through a slightly acid water solution where fluoride is quantitatively absorbed. Tank hydrogen contains frequently small amounts of sulfur compounds. They are decomposed in furnace (N3) and the hydrogen sulfide formed is retained in the soda lime tube. When the apparatus is started, furnace (N3) is cold, and the sulfur compounds are not decomposed. They wouid be partially ad.sorbed on the soda lime and slowly desorbed in the course of the day and cause small, steadily decreasing sulfur blanks. Stopcock (D)was therefore introduced. I t is turned so that the hydrogen, which has passed through the cold furnace, passes out into free air, and first when the furnace is hot, and the sulfur compounds are decomposed, the hydrogen is allowed to pass through the soda lime tube.
LITERATURE CITED Ehrenberger and S. Gorbach, "Methoden der organiscnen Elementar und Spurenanalyse," Verlag Chemie, Weinheim, Western Germany,
(1) F.
1973, pp 319-57. (2) W. J. Kirsten, Mikrochemie, 35, 2 (1950). (3) W. J. Kirsten, Proc. lnt. Symp. Microchem., 7958, 132 (1959). (4) W. J. Kirsten, Proc. 7967-Symp. Microchem. Techno/., 479 (1962). (5) R. Belcher, "Submicro Methods of Organic Analysis." Elsevier, Amsterdam 1966, p 62. (6) W. Walisch, Chem. Ber., 94, 2314 (1961). (7) L. Gustafsson, Talanta, 4, 227 (1960). (8)W. J. Kirsten and V . J. Patel. Microchem.J.. 17. 277 11972). (9) T . D. Rees, A 8. Gyllenspetz, and A. C. Doche;ty, Analyst, (London1..96.201 119711 (10) W J Kbsten, B Danielsson, and E Ohren, Mcrochem J , 12, 177 ( 1967)
RECEIVED for review June 10, 1974. Accepted July 30, 1974. The work was made possible by grants from The International Seminar in Chemistry of the University of Uppsala and from the Swedish Medical and Natural Science Research Councils.
CORRESPONDENCE Flame Photometric Detector for Liquid Chromatography Sir: Recent advances in the chemistry of stationary phases for liquid chromatography have reduced drastically the time necessary for separations. In particular, the pellicular ion exchangers, which offer extremely good mass transfer and flow characteristics, can be used to great advantage for inorganic separations. The sample capacity of these materials is low, however, necessitating the use of highly sensitive detectors. Several detectors suitable for metallic ions have been described (1-3); none, however, are commercially available and no reports on the use of pellicular ion exchangers for metal ion separations have appeared to date. Flame emission spectrometry, with its inherently high sensitivity, appears to be an ideal choice for coupling to a chromatographic column but, although many workers have used a combination of ion exchange and flame spectrometry (4-6), no on-line system has been described. We have constructed an integral flame photometric-ion exchange system which enables high-speed separations to be performed with detection limits in the low parts-per-million range. Troublesome matrix effects are eliminated and quantitative accuracy is better than 2% in the 1-10 partsper-million range. The following report describes some characteristics of this system. 186
EXPERIMENTAL Chromatographic System. A Perkin-Elmer Model 1240 Liquid Chromatograph was used, except that the pump supplied was replaced with a Waters Associates Model 6000 Solvent Delivery System. All materials of construction were either Teflon or Type 316 stainless steel. Columns were 2.6-mm i.d. (6.25-mm 0.d.) by 50 cm in length. On-colunn injections were performed with a Hamilton H P 305 syringe. The column packing used was Zipax SCX (DuPont Instruments, Inc.) and columns were dry-packed by the method of Kirkland (7). All separations were performed a t 75 O C . Flame Photometer. A Beckman Total Consumption burner was used with hydrogen as fuel and air as oxidant. Air and hydrogen flow were regulated with Matheson Model 701 Rotameters after the primary reducing valves. The outlet of the column was connected directly to the aspirating capillary of the burner by means of a 1-meter length of capillary tubing and a Swagelok capillary union. The flame is viewed by a Schoeffel Quartz Prism Monochromator (Model GM 100) which, together with an RCA 1P21 photomultiplier tube and an American Instrument, Inc. BlankSubtract Photometer, forms the readout system. Chromatograms were recorded on a Hewlett-Packard Model 680 recorder. Reagents and Chemicals. All chemicals were ACS reagent grade with the exception of the nitric acid which was J. T . Baker electronic grade. Double distilled, deionized water was used throughout. Metal ion solutions were prepared by appropriate dilution from 1000-ppm standard solutions supplied by Aztec Instruments, Inc.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 1 , JANUARY 1975
