1631
Anal. Chem. 1983, 55, 1631-1632
Table 11. Determination of Boron in Steel Sample Sample: JSS 159-3 (certified boron (content 0.0013%) sample solution boron content (g/100 mL)" (%I 0.5040 0.00111 0.010 12 0 0.5032 0.4980 0.01011 3 0.5007 O.ClOl28 0.5027 0.0 0 121 0.00117 0.4988 0.5023 0.00111 0.4990 0.00 12 5 av 0.00118 std dev 0.00006 To 1 0 mL of thew solutions, 1mL of 1M trisodium citrate was added and the solution was neutralized with sodium hydroxide to pH 4.8 and then diluted to 50 mL with deionized water, The solution neutralized and diluted accurately, 10 mL was used. a
Effect of Coexisting Ions. The effect of coexisting ions was examined by using the TSK column according to the recommended procedure. Large amounta of coexisting anions, especially monovalent anions, affect the retention time of the boron complex. The variation in the iretention time causes the variation of the peak height, though the area is scarcely varied. In this work, huge amounts of bromide ion as TBA-Br were added to the sample solution to diminish the effect of anions. The following ions affect the peak height with an error of less than f 2 % , in determining 5 X IO4 M of boron: Na+, K+, C1-, SO4%(0.5 M); NO, (0.2 M); Fe3+,HCO,, H2PO; M); Ca2+,Mg2+,Fez+,Co2+,Ni2+,Cu2+,Zn2+,Cd2+,SCNM); Sr2+,Ba2+,C P , Mn2+,Mo(VI), W(VI), Si032-(loF4M). Application to the Determination of Boron in Practical Samples. According to the recommended procedure,
boron existing as boric acid in hot spring water, tap water, and seawater was determined. The results obtained are shown in Table I. Seawater and some of hot spring waters were diluted with deionized water and analyzed. The results obtained by using peak height are in good agreement with ones obtained by using peak area, and the boron contents obtained in this work are in good agreement with the contents obtained by the solvent extraction-spectrophotometric method with 2,6-dihydroxybenzoic acid and Malachite Green (6). In determination of hot spring water (Tochinoki B), the coefficient of variance was examined. The sample, which contains 1.80 ppm of boron, was diluted 10-fold with deionized water. The mean values of peak height and peak area in seven experiments were (133 f 1) mm and (18.5 0.3) X lo4 arbitrary units, respectively (detector sensitivity: 0.16 AUFS), and the relative standard deviations of peak height and peak area were 0.5% and 1.7%, respectively. Boron in steel sample was also determined by using the steel sample solution. The results obtained are shown in Table 11. The boron content obtained is in good agreement with the certified value. The relative standard deviation was 5%. Registry No. TBA-Br, 1643-19-2;chromotropicacid, 148-25-4; boron, 7440-42-8;steel, 12597-69-2;water, 7732-18-5.
*
LITERATURE CITED Andress. K.; Topf, W. Z . Anorg. A/@. Chem. 1047, 254,52. Kuemmei, D. F.; Mellon, M. G. Anal. Chem. 1957, 29,378. Lapid, J,; Farhl, S.; Koresh, Y. Anal. Lett. 1076, 9 , 355. Korenaga, T.; Motomlzu, S.; T b i , K. Analyst (London) 1078, 703, 745. (5) Korenaga, T.; Motomlzu, S.; TBel, K. Anal. Chlm. Acta 1980, 720, 321. (6) Oshima, M.; Motomizu, S.; TBei, K. Bunseki Kagaku 1083, 32,268. (1) (2) (3) (4)
RECEIVED for review February 2, 1983. Accepted April 18, 1983.
Determination of Trace Methanol In Liquid Butane F. P. DI Sanzo" anjd J. L. Lane Analytical Section, Mob1 Research and Dewlopment Corporation, Paulsboro, New Jersey 08066
Methanol contamination in butane destined for isomerization/alkylation plants is a major concern because of its adverse effect on catalysts employed in such units. Contamination of butane withi methanol can occur in one of four main areas: (1)at the crude oil producing llocation to control the problem of free water in crudes, (2) at the LPG delivery location to prevent severe freezing problems, (3) on board LPG vessels where in the event of equipment failure methanol is injected to prevent freezing, and (4)contamination from tanks previously employed for other purposes. This paper describes a simple method for the monitoring of trace methanol in liquid butane which allows for sample collection at any location.
EXPERIMENTAL SECTION A sample of liquid butane (-500 g) is transferred into a tared 1-L Hoke vessel (Mathleson,East Rutherford, NJ) following the practice outlined in ASTM D1265 (I)and reweighed to the nearest gram. A 6 in. X 1/4 in. skinless steel cartridge packed with 100-200 mesh activated (170 "C for 4 h) silica gel grade 923 (Fischer Scientific, King of Prussia, PA) is attached to the Hoke vessel with appropriate metal fittings. The silica gel is held in place by gas chromatographic grade glass wool. The liquid butane is passed through the silica cartridge by inverting the Hoke vessel over the cartridge for approximately 20 min (- 100 g nC4) after which time the trap is removed and the Hoke vessel reweighed
Table I. Recovery of Trace Methanol Spiked into Liquid Butane "actual" value, ppm amt found, ppm 0.7 7 10 a
-
0.6 0.6" 6 10 9a
Replicates on same sample.
to obtain sample weight. The cartridge is backflushed to desorb the methanol with approximately 5 mL of distilled water employing either a fluid metering pump (FMI, Oyster Bay, NY) or a 5-mL syringe. One milliliter of an internal standard solution of 2000 ppm tert-t-amyl alcohol in water is added to the eluent. One microliter is injected (250 "C) into a gas chromatograph equipped with a flame ionization detector (200 "C). The column, in. Teflon packed with 5% Carbowax 20M on 40/60 6 ft X mesh Chromosorb T, is operated isothermally at 40 "C with a helium flow of 20 cm3/min. Response factors relative to tert-amyl alcohol are obtained from aqueous standards containing methanol in the range of 10-5000 ppm. RESULTS AND DISCUSSION A gas chromatogram of oxygenates isolated from liquid butane is given in Figure 1. Methanol in liquid butane can 0 1083 American Chemical Society
1632
Anal. Chem. 1963, 5 5 , 1632-1634
Butane7
Acetone
7
11 ,t-Amyl
Alcohol
-
-
2 3 4 5 6 7 8 910 fvlinuies
Figure 1. Gas chromatogram of methanol (0.5 ppm) and other oxygenates isolated from llquld butane.
be determined in the range 0.5-250 ppm. Lower concentrations may be determined by employing larger sample sizes. Recovery of trace methanol from synthetic liquid butane standards which were analyzed by the proposed method is given in Table I. The synthetic liquid butane standards were prepared by injecting a weighed amount of methanol into
unsealed Hoke vessels which contained a weighed amount of chilled liquid butane. The Hoke vessels were sealed and allowed to equilibrate at room temperature prior to sampling. The accuracy and precision obtained are well within those required for the above proposed application. Generally, greater than 98% of the methanol is desorbed from the silica gel cartridge by the aqueous eluent as verified by injecting a known amount of methanol into the cartridge. During sampling, no methanol breakthrough was observed by placing two cartridges in series and analyzing each cartridge separately. To ensure that the silica gel is of the proper activity and to verify that complete trapping of the methanol has occurred, it is recommended that a synthetic blend of methanol in liquid butane be analyzed by placing two silica gel cartridges in series and analyzing each separately as described above. 2-Propanol and butyl mercaptan, if present, will interfere with the methanol analysis but other GC columns may be substituted, e.g., 10 ft X 1/8 in. stainless steel 3% SP1500 on 8O/lZO Carbopack B (Supelco, Inc., Bellefonte, PA) programmed at 4 OC/min from 70 to 190 OC. Other water-soluble oxygenates present in the liquid butane, e.g., acetone and ethanol, may also be determined. Water-insoluble polar solutes in LPG's may also be sampled and quantitated by this technique by employing an appropriate organic solvent for desorption. After the sample is taken, the silica gel cartridges may be capped with Swagelok fittings and stored or shipped to any location for analysis. Registry No. Methanol, 67-56-1; butane, 106-97-8.
LITERATURE CITED (1) "Standard Method of Sampllng Llquified Petroleum (LP) Gases"; American Soclety for Testlng and Materials: Philadelphia, PA, 1978; Part 23, pp 641-644.
RECEIVED for review January 3,1983.
Accepted April 15,1983.
Enhanced Electrochemical Reversibility at Heat-Treated Glassy Carbon Electrodes Kenneth J. Stutts, Paul M. Kovach, Werner G. Kuhr, and R. Mark Wightmen" Department of Chemistry, Indiana Unlversity, Bloomlngton, Indiana 47405
Carbon electrodes are frequently used for voltammetry and amperometry. Although these electrodes are useful over a wide potential range, it is generally true that the apparent rates of electron transfer are slower at carbon electrodes than at metal electrodes. Recently it has been shown that the electrochemical rate can be increased for the oxidation of ascorbate a t carbon fiber or graphite-epoxy composite electrodes by pretreatment with high current density ( ~ A 2cm-*) (1,2). Polishing the surface of glassy carbon with a-alumina has also been shown to accelerate the oxidation of ascorbate (3). The rate of the reduction of ferricyanide at carbon can be increased by the judicious use of polishing procedures (4). During an investigation of surface-attached redox mediators for ascorbate oxidation (5),we have found that the conditions employed prior to surface attachment reactions render a surface that greatly accelerates the apparent electrolysis rate for ascorbate and a number of other compounds. Specifically, it will be shown that heating glassy carbon to 500 OC at reduced pressure provides a surface which has greatly improved electrochemical properties.
EXPERIMENTAL SECTION Reagents. K,Fe(CN),, Ru(",),cl,, 3,4-dihydroxybenzylamine hydrobromide (DHBA), 3,4-dihydroxyphenylaceticacid
(DOPAC),ascorbic acid (AA), and 4-methylcatechol(4-MeCat) were reagent grade and used as received. McIlvaine buffers (0.1 M in buffer capacity and adjusted to 1.0 M ionic strength with KCl) were used in the electrochemical studies of all compounds except ferricyanide, which was in 0.5 M K2S04adjusted to the proper pH with concentrated H2S04or NaOH. All solutions were prepared in water distilled from alkaline permanganate and purged with nitrogen prior to use. Apparatus. Cyclic voltammetry was performed at glassy carbon rectangles of two different grades (0.8 X 2.5 cm, Tokai GC-10 or Tokai GC-20), which had been hand polished to a mirror finish with 5.0,0.3, and 0.05 pm alumina (Beuhler, Lake Forest, IL) successively. Identical results were obtained at both grades of carbon. Before use, the glassy carbon was freshly polished with 0.05 pm alumina and Soxhlet extracted in toluene for approximately 4 h. The extracted carbon served as the control electrode. For the reduction of Fe(cN)63-,but not AA oxidation, an increase in reversibility was seen for the refluxed carbon relative to carbon that was freshly polished with 0.05 pm alumina. Some of the refluxed electrodes were transferred t o a Pyrex glass tube that was heated (520-540 "C) under reduced pressure (-1 torr) for 2-24 h. These electrodes were returned to atmospheric pressure, removed from heat, and allowed to cool at the end of the heating period. The glassy carbon formed the floor of a cell fabricated from Plexiglas and a polyethylene gasket defined the electrode area ( A = 0.061 cm2). The cell was designed to allow semiinfinite
0003-2700/83/0355-1632$01.50/00 1983 Amerlcan Chemical Society
