Table I. Recovery of Methyl Alcohol Added to a Wine Sample
+
methanol, PPm
Wine Wine Wine Wine Wine Wine
+ 10 + 25
+ 50 + 75
+ 100
Methanol found, PPm
Recovery, /o
17.1
...
27.7 42.4 65.9 90.2 117.2
106.1 101.2 97.6 97.4 100.1
Av 100.4
0
2
4
6
8
RETENTION TIME (MlNJ
typical gas chromatogram of Concord wine on Porapak OS column using flame ionization detector (FID) Figure 1. A
I) water, 11) methanol, Ill) acetaldehyde,and IV) ethanol
and ethyl acetate which had retention times of 1.8, 2.8, 4.0, and 19.5 minutes, respectively. Figure 1 shows a typical chromatogram of a Concord wine. The calibration curve for methyl alcohol was linear over the range of 10 to 1000 ppm and good recovery was obtained when methyl alcohol was added to a wine sample, e.g., Table I. The average recovery on 20 runs during a 5-day period was 100.6% with a standard deviation of f4.4%. To prevent interference from the buildup of organic matter in the system, the column was heated overnight at 200 O C and the glass insert in the injector port was changed every 3 days. Using this method, the methyl alcohol contents of 20 commercial wines ranged from 50-325 ppm.
Unlike other chromatographic support and substrate systems, ethylvinylbenzene polymers (Porapak) are durable and require no special handling in their separation and use, and Porapak QS yields an excellent separation of the common constituents of alcoholic beverages. The gas chromatographic procedure presented here can be completed in as little as 7 minutes and is a simple and accurate method for the routine analysis of methyl alcohol in alcoholic beverages. LITERATURE CITED (1) "Official Method of Analysis," Association of Official Analytical Chemists, 1 I t h ed., 1970,p 153. (2) R. H. Dyer, J. Assoc. Offic. Anal. Chem., 54, 785 (1971). (3)R. L. Brunelle, J. Assoc. Off. Anal. Chem., 50, 321 (1967). (4)A. Di Corcia, A. Liberti, and R. Samperi, Anal. Chern., 45, 1228 (1973). (5) R. N. Baker, A. L. Alenty, and J. F. Zack. Jr., J. Chrornatogr. Sci., 7,312 ( 1969). (6)T. R. Mon. Res./Dev., 22 (12),14(1971).
RECEIVEDfor review September 20, 1974. Accepted December 18,1974.
Gas Chromatographic Determination of Carbon in Fertilizer Materials David Bennett Fisons Limited-Ferfilizer Division, Levington Research Station, Ips wich, Suffolk. UK
A fertilizer manufacturing process involving the ammoniation of phosphoric acid in molten ammonium nitrate requires careful monitoring of carbon in the range 0.01 to 0.05%. In the original method of determination, carbon was oxidized to carbon dioxide which was weighed a.fter absorption on soda asbestos. For accurate analysis, it was necessary to separate quantitatively about 3 ml of carbon dioxide from a mixture containing some 8 liters of water vapor and 4 liters of nitrogen and nitrogen oxides, and to absorb the carbon dioxide quantitatively and specifically before weighing. Because of the difficulties involved in performing this analysis satisfactorily, unacceptable delays of 2-3 hours occurred. Several commercial instruments are available for carbon analysis, designed mainly for use with organic materials having significant carbon contents. Normally, these analyzers employ microgram quantities which aid oxidation and result in small gas samples that can be analyzed directly by, for example, gas chromatography. Such small samples of fertilizer would not be representative, and the low car748
ANALYTICAL CHEMISTRY. VOL. 47,
NO. 4 , APRIL 1975
bon contents involved would require equipment of very high sensitivity. The use of gas chromatography for the determination of carbon in various materials has been previously reported. In general, the methods are rapid and the precision and accuracy are similar to classical methods. One difficulty in their use is the need to introduce plug samples of gas into the chromatograph. Previous methods for achieving this involved collecting the oxidation products in liquid nitrogen traps (1-3) or on solid absorbents (4-7), or the use of rapid oxidation methods, e.g., high frequency induction furnaces (8-1 1 ) or direct injection of liquid samples onto heated oxidants (12-15). These methods either add considerably to the analysis time, or to the cost of the equipment, or are unsuitable for fertilizer materials in which the carbonaceous matter can be largely water insoluble. To provide a rapid, accurate analysis the following method was developed, based on the oxidation of carbonaceous material to carbon dioxide, followed by chromatographic analysis of samples of the gas. Wet oxidation using the acid
C O N C E N 1R A T E D SULFURIC A C I D
TORION
VALVE
5
NEEDLE AIR FREE t FROM CARBON DIOXIDE
CHROMATOGRAPH
PUMP
(,a, 3
ANDIARE STOPCOCKS
__
J
W _ - S A M P C E
Figure 1. Schematic diagram of the oxidation apparatus
mixture of Van Slyke and Folch (16) was chosen since this provided rapid results for a very wide range of materials (17-20 ).
EXPERIMENTAL Reagents. T h e oxidizing acid is prepared by mixing 100 g chromium trioxide and 20 g potassium iodate with 600 ml phosphoric acid (sp gr 1.75) and 1334 ml sulfuric acid (sp gr 1.84).The mixture is maintained for 15 minutes a t 150 "C with occasional stirring to remove carbon dioxide and then stored in a glass stoppered bottle. All reagents are of laboratory grade purity. Apparatus. The gas chromatograph used in this work is a Gas Chromatography Limited S6 Research Chromatograph operating under the following conditions. Detector: Katharometer fitted with four Gow-Mac code WX filaments; detector temperature: 40 "C. column: 350 cm X 0.32-cm i.d. copper packed with 175-300 pm Phasepak Q (Phase Separations Limited); column temperature: 40 "C; carrier gas: Helium a t 50 ml/min. The apparatus used to conduct the oxidation is shown schematically in Figure 1. Procedure. The method involves boiling concentrated acids in a sealed, glass system in which the pressure has been reduced to accommodate the gases evolved. T o safeguard against the result of improper operation of the apparatus, it is essential that adequate face protection be used. A sample (2-3 g) of liquid or lightly ground solid is weighed into the test tube which is then connected to the apparatus using condensed phosphoric acid as a lubricant for the ground glass joint, and retained with springs. Other joints and taps, with the exception of the Torion valve which operates dry, are lubricated with silicone stopcock grease. With 1, 4 , and 5 closed, the 1 liter round bottomed flask used as a collecting vessel and the test tube are evacuated. T a p 2 is closed, and 10 ml of the oxidizing acid introduced to the test tube by operation of the Torion valve. T h e test tube is gently heated with a burner so that the contents boil within two minutes. Heating is continued for a further two minutes. T a p 4 is opened and air, free from carbon dioxide, is admitted through the needle valve to pressurize the system to 150 mm Hg above atmospheric pressure. This sweeps the oxidation products from the test tube into the collecting flask. This is mounted in an inverted position and contains 125 ml of concentrated sulfuric acid which absorbs both the water and the higher oxides of nitrogen liberated during the oxidation process. It also fills those parts of the collecting flask in which mixing of gases is hindered. T a p 3 is closed, and after allowing one minute to ensure complete mixing of the contents of the collecting vessel, T a p 1 is opened to allow the mixture through the sample valve of the gas chromatograph. Samples (2.5 ml) are introduced and the height of the carbon dioxide peak is measured. Blank determinations are carried out on the acid and the results corrected for this contribution.
Figure 2. Calibration using calcium carbonate-aluminium sulfate
mixtures 0 A = carbon in aluminum sulfate 0.052%
A calibration graph is constructed using samples of mixtures prepared by grinding together known weights of' dried analytical reagent grade aluminium sulfate and calcium carbonate. The response is linear for samples containing up to at least 1 2 mg carbon, and sample weights are adjusted when necessary so that the linear range is not exceeded.
RESULTS AND DISCUSSION A calibration graph obtained using six different mixtures of aluminium sulfate and calcium carbonate is shown in Figure 2. The results have been corrected for a blank equivalent to approximately 30 fig carbon and, from the intercept of the graph, it is possible to obtain the carbon content of the aluminium sulfate used to dilute the calcium carbonate, in this case 0.052%. In this manner, the total carbon content of the standard mixes can be calculated for calibration purposes. It was demonstrated, by a further analysis of the cooled residue from a determination, that oxidation was complete under the conditions employed, as no additional carbon dioxide was detected. Also it was not possible to detect carbon dioxide in the gas remaining in the test tube after pressurizing with air free from carbon dioxide, thus indicating A N A L Y T I C A L CHEMISTRY, V O L . 47. N O . 4 , APRIL 1975
749
Table I. Determination of Carbon in Phosphoric Acid-Alcohol Mixtures No. of determinations
Material
Phosphoric acid (AR) Phosphoric acid + 4.17% n -hexanol Phosphoric acid + 7.01% n -hexanol Phosphoric acid + 3.65% n - heptanol
Carbon content Determined
.. .
5 4 ppm 5 294 ppm,
293 ppm
C V = 0.8% 5 483 ppm, cv = 0.9% 5 273 ppm, c v = 1.0%
494 ppm 264 ppm
A comparison of results using the gas chromatographic and gravimetric techniques is shown in Table 11. There is no bias, and similar precisions are obtained from both methods. Although the method was developed principally for application to fertilizers and phosphoric acid, other materials have been examined. These include sulfur (70-850 pprn C), sulfuric acid (8500 ppm), phosphate rocks (300-5000 ppm), potassium chloride (1000 ppm), sand (200 ppm), kaolinite (3000 pprn), carboniferous limestone (11.8%), vehicle exhaust deposits (30.0%),and an oil (88.2%).
LITERATURE CITED Table 11. Determination of Carbon using Gas Chromatographic and Gravimetric Methods KO. of Material
determinations
Fertilizer 1
5
Fertilizer 2
5
Unfiltered Phosphoric Acid
5
Gas chrom. method
Gravimetric method
163 ppm, cv = 1.0% 131 ppm, CV = 5.8%
158 PPm, CV = 5.6% 143 PPm, CV = 5.8%
473 ppm, CV = 3.8%
447 PPm, CV = 4.1%
that the carbon dioxide was transferred quantitatively to the collecting flask. The accuracy of the method was assessed by analysis of pure phosphoric acid to which known amounts of n- hexano1 or n- heptanol had been added. The results, shown in Table I, are reproducible and in agreement with the theoretical values. The method described takes approximately 15 minutes per determination compared with two hours for the gravimetric method.
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20)
A. A. Duswalt and W. W. Brandt, Anal. Chem., 32, 272 (1960). 0. E. Sundberg and C. Maresh, Anal. Chem., 32, 274 (1960). D. R. Beuerman and C. E. Meloan, Anal. Chem., 34, 1671 (1962). You Sun Kim, Youn So0 Son, and Q. Won Choi, Korean J . Chem., 8, 188 (1964). 0. A. Sukhorukov and N. T. Ivanova, Zavod. Lab., 31, 1070 (1965). L. G. Berezkina. N. A. Elefterova and M. V. Lesnaya, Zavod. Lab., 35, 157 (1969). L. G. Berezkina and N. A . Elefterova, Zh. Anal. Khim., 24, 269 (1969). C. F. Nightingale and J. M. Walker, Anal. Chem., 34, 1435 (1962). M. L. Parsons, S. N. Pennington, and J. M. Walker, Anal. Chem., 35, 842 (1963). W. K. Stuckey and J. M. Walker, Anal. Chem., 35, 2015 (1963). J. M. Walker a n d C . W. Kuo. Anal. Chem., 35, 2017 (1963). D. L. West, Anal. Chem., 36, 2194 (1964). S. Pennington and C. E. Meloan. Anal. Chem., 39, 119 (1967). R. A. Dobbs, R. H. Wise, and R. B. Dean, Anal. Chem., 39, 1255 (1967). F. R. Cropper, D. M. Heinekey, and A. Westwell, Analyst (London), 92, 436 (1967). D. D. Van Slyke and J. Folch, J. Biol. Chem., 136, 509 (1940). R. M. McCready and W. 2. Hassid, hd. Eng. Chem., Anal. Ed., 14, 525 ( 1942). A. A. Houghton, Analyst (London),7 0 , 118 (1945). I. Dunstan and J. V. Griffiths, Anal. Chem., 33, 1598 (1961). I. Dunstan and J. V. Griffiths, Anal. Chem., 34, 1348 (1962).
RECEIVEDfor review June 3, 1974. Accepted November 12, 1974.
Gas-Liquid Chromatographic Electron Capture Determination of Some Monosubstituted Guanido-Containing Drugs Paul Erdtmansky and Thomas J. Goehl Sterling- Winthrop Research Institute, Rensselaer, NY 72 144
Until recently, no sensitive method for the determination of guanido-type antihypertensive agents existed ( 1 - 4 ) . With the publication of a GLC method utilizing an FID or MID detector ( 5 ) ,this need was partially fulfilled. Unfortunately, for the analysis of nanogram/milliliter samples, a GLC-MS unit is needed. Their method also requires much sample manipulation and considerable time. Another method involving a tedious fluorescent assay has been proposed, but complete details have not been published (6). In developing a method for the determination of the mono-substituted guanido metabolite, 3,4-dihydro-l-methyl-2(1H)-isoquinolinecarboxamidine(IV), of the potential antihypertensive agent, 3,4-dihydro-l-methyl-2(lH)-isoquinolinecarboxamidoxime (111) (7, 8 ) , a general method for the determination of other compounds' of this type evolved. In the present paper, this extremely simple meth750
ANALYTICAL CHEMISTRY, VOL. 47, NO. 4, APRIL 1975
od for the determination of monosubstituted guanido-containing drugs in biological fluids is described. This method combines the extraction and derivitization steps into a single procedure. The derivative is quantitated by electroncapture detection in the nanogram/milliliter range. EXPERIMENTAL Apparatus. A Hewlett-Packard Model 402 gas chromatograph equipped with a tritium electron-capture detector (200 mCi) was used. The instrument was fitted with a 1.8-m glass column (id. 2 mm) packed with 3% OV-17 on 100-120 mesh Gas Chrom Q (Applied Science Labs, State College, PA). The flow rate of carrier gas (7% methane in argon) was 75 mlimin. The temperatures of the injection port, column, and detector were 200, 160, and 200 "C, re-
spectively. The mass spectral characterization of the derivatives was made with a JEOL Model JMSOLSC mass spectrometer.
