Determination of Nonfiller Magnesium in Polyesters JOHN E. NEWELL Chemical Division, United States Rubber Co., Naugatuck, Conn.
b A method is described for determining nonfiller magnesium in the presence of the magnesium in mineral fillers when they are together in cured or uncured polyesters. Low temperature pyrolysis of the cured sample followed by leaching of the residue with a buffered solution separates the nonfiller magnesium from that in the filler. The nature of the filler dictates the pH of the leaching solution and a method for identifying the filler by infrared spectrometry is included. For uncured samples, the acetone sohbility of the organically-bound magnesium permits its separation from the filler. The magnesium is determined titrimetrically with EDTA.
C
of making polyester products containing glass fibers involve the mixing of polyester, styrene, filler, and catalyst with glass fibers. The lower the viscosity of the polyester resin mixture, the more easily it mixes with the glass fibers. However, when the impregnated fibers are molded, the higher the viscosity of the mixture, the better are the flow characteristics in the mold. A good compromise is difficult to make. When magnesium oxide is added to the polyester resin mixture, it remains fluid for a sufficient time to be easily incorporated into glass fibers. The magnesium oxide reacts and the mixture becomes much more viscous. The impregnated glass fibers acquire much improved handling, storage, and molding properties (2, 3, 9). The requirements of low viscosity for easy incorporation and the high viscosity for satisfactory molding have been achieved. The thickening that occurs is due t o reaction of the magnesium oxide with the polyester resin, which is unsaturated and carboxyl-terminated. The acid number of the resin is from 20 t o 50. The dispersion of the glass fiber, the characteristics of the surface, and the resistance to solvents of the cured polyester are affected by the magnesium oxide content. When the history of the sample is uncertain, the magnesium oxide content must be determined by chemical analysis. Published methods for magnesium are mainly for its determination in the presence of other elements. The method proposed in this paper discriminates between the magnesium reacted with the
The pH of choice depends upon the filler which is identified by infrared spectrophotometry. EXPERIMENTAL
ONVENTIONAL METHODS
Figure 1. Diagram of furnace modified for pyrolysis a.
b. c.
d. e.
f.
Hydrogen peroxide reservoir Capillary tube Baffle Turntable Thermocouple Asbestos gasket
resin from the magnesium present in common mineral fillers. When the polymer is not cured, the organically-bound magnesium is separable from the filler and any excess magnesium oxide by its solubility in acetone. However, when the polymer is cured, it is insoluble in neutral organic solvents even a t high temperatures where solution might be effected by a reaction such as ester interchange. Acid or alkaline solvents which attack the polymer also attack the fillers. Ashing the sample by conventional combustion methods leaves a dehydrated filler. Magnesium in some fillers is much more soluble in aqueous solutions after ashing. In the method described, the organic matter in the sample is released by a controlled pyrolysis. Under the conditions chosen, the dehydration of the filler is much reduced. The nonfiller magnesium in the residue is separated from the filler by leaching with buffered water. Contribution of magnesium t o the solution by the filler or adsorption of magnesium from the solution is minimized by the choice of p H of the leaching solution.
Apparatus. The pyrolyses were done in a modified Thermolyne Type 1300 muffle furnace (Figure 1). The thermocouple supplied with the furnace was removed and a small fan was installed with its shaft going through the thermocouple opening. The speed of the fan was controlled by an autotransformer. A baffle prevented any breeze from the fan disturbing the contents of the crucibles. ii slowly rotating turntable below the baffle held five crucibles. The door of the furnace was made more airtight with asbestos sheet. A thermocouple was inserted through a hole drilled in the door and a second hole permitted the introduction of hydrogen peroxide by means of 1/8-inch 0. d. stainless steel tubing. The rate of rise and ultimate temperature were controlled by an F and M Model 240 power-proportioning temperature programmer connected to the furnace. The infrared spectra were obtained with a Model 421 Perkin-Elmer spectrophotometer. Reagents. ACID WASHEDCELITE. Celite Filter Aid m s soaked overnight in 1: 1 hydrochloric acid, filtered, water-washed, and dried a t 110' C. A BUFFERED LEACHING SOLUTION, pH 9.5, was made containing 3.6 grams of boric acid, 1.7 grams of sodium hydroxide, 1.5 grams of sodium bicarbonate, 5.0 grams of sodium oxalate monohydrate, and 1.5 grams of sodium sulfide nonahydrate in 2 liters of water. The pH was adjusted to 9.5 += 0.1 by the dropwise addition of sodium hydroxide solution or hydrochloric acid. A BUFFERED LEACHINGSOLUTION, pH 8.2, was made containing 30 grams of ammonium acetate, 2.5 ml. of ammonium hydroxide (29% NH3), 2.5 grams of sodium oxalate monohydrate, and 1.0 gram of sodium sulfide nonahydrate in 2 liters of water. The pH was adjusted to 8.2 =t0.1 by the addition of drops of ammonium hydroxide or acetic acid. A BUFFEREDLEACHINGSOLUTION, pH 4.7, WBS made containing 4.0 grams of sodium hydroxide, 12 ml. of acetic acid, 2.5 grams of sodium oxalate monohydrate, and 1.0 gram of sodium sulfide nonahydrate in 2 liters of water. The pH was adjusted to 4.7 =t0.1 with sodium hydroxide solution or acetic acid. BROMINATED N I T R I C ID. h n excess of bromine was added to 70% nitric VOL. 38, NO. 9, AUGUST 1966
1205
acid. The stoppered bottle stood overnight to become saturated. AMMONIUM HYDROXIDE-CHLORIDE BUFFER was made by dissolving 110 grams of ammonium chloride and 450 ml. of ammonium hydroxide (29% NHa) in sufficient water to make 1 liter. EDTA TITRANT, 0.0500M, was made by dissolving 18.61 grams of disodium ethylene diamine-tetraacetate dihydrate in distilled water and diluting to 1 liter. It was stored in a plastic bottle, The titrant was standardized as follows: magnesium turnings were washed with benzene and dried. An accurately weighed sample of 0.010 t o 0.012 gram was dissolved in 50 ml. of water to which had been added about 4 drops of hydrochloric acid. The solution was taken to dryness on a steam bath. The walls of the beaker were washed down with about 50 ml. of water and 10 ml. of 10% sodium cyanide solution, and 10 ml. of ammonium hydroxide-ammonium chloride buffer were added. With a few drops of Eriochrome Black T solution as the indicator, the solution was titrated with the EDTA titrant. Molarity =
1000 (wt. of turnings) 24.32 (titer - blank)
(1)
ERIOCHROME BLACKT INDICATOR was made by dissolving 0.25 gram of Eriochrome Black T in 50 ml. of triethanolamine. The indicator solution was kept stoppered as much as possible. Procedure. ANALYSISOF CURED SAMPLES. The sample was broken into small chips and a 2- to 3-gram portion was weighed into a porcelain crucible. The sample was pyrolyzed in the furnace by raising the temperature a t 0.5' C. per minute from 110' C. to 340" C. and holding the temperature a t 340' C. During the heat treatment the gases in the furnace were being circulated with the fan, the turntable was rotating, and 30oJ, hydrogen peroxide was being introduced at approximately 5 ml. per hour. The total heat treatment was 16.5 f 0.5 hours. The crucible was cooled and reweighed. The contents of the crucible were transferred to a 250-ml. beaker. Using spatulas, the fragile residue was teased apart until the glass fiber was fluffy and the filler was a lump-free powder in the bottom of the beaker. The contents of the beaker were poured into a second 250-ml. beaker, with tapping. .4 trace of filler remained in the first beaker as dust on the glass, and this dust was used to identify the filler. A small amount of finely-ground potassium bromide was added to the beaker and swirled to remove the traces of filler from the walls. The potassium bromide was transferred to a mortar, ground, and from it an infrared pellet or disk was made. From the infrared spectrum, spectra of known fillers (Figure 2), and the data in Table I, identification of the filler was made. The glass fiber and powder in the second beaker were treated with 200 ml. of buffered leaching solution. For all fillers except alumina and clay the 1206
ANALYTICAL CHEMISTRY
WAVELENGTH 3
4
w
(MICRONS)
7
6
5
Clay
10
8
12
15
( A S P 600)
0
z a m
a 0
cn m
a
i
I
i
I
I
I
I
I
l
i I
l
i
I
I
I
I
I
I I
I
I I
I
I
-I
I
i
I
I
3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600
FREQUENCY Figure 2.
(CM-~)
infrared spectra of common fillers and additives
The spectra are displaced vertically. Minimum absorbances are approximately 0.03. Absorbances 1.O are indicated b y horizontal liner
buffer with a p H of 9.5 was used. For alumina filler, the leaching solution with a p H of 8.2 was used and for d a y it was p H 4.7. Mixed fillers were leached with the buffer of pH 9.5. After stirring for two hours, the mixture was vacuum-filtered through a thin bed of Celite on a fine-porosity glass
filter. The beaker and filter were rinsed with small volumes of buffered leaching solution. When desired, the glass fiber content was found by washing the contents of the filter funnel through a small 325-mesh sieve. The fiber was retained on the sieve and was dried and
weighed. The filler content was determined by difference. The filtrate was evaporated to dryness in a 250-ml. beaker. To the residue were added 25 ml. of brominated nitric acid, 1.5 ml. of 70% perchloric acid, and a few carborundum boiling chips. The beaker was rovered with a watch glass and boiled down t o fumes of perchloric acid. The beaker was cooled and rinsed down with 100 ml. of water. The contents were reduced to about 50 ml. by boiling and were allowed t o cool. Using a p H meter, the p H was brought t o 9.7 rt 0.3 by the dropwise addition of strong sodium hydroxide solution. Ten milliliters each of 10% sodium cyanide solution and ammonium hydroxide-chloride buffer solution were added. The mixture was warmed to about 40" C. and titrated t o a permanent blue end point with 0.0500M EDTA solution. Eriochrome Black T was the indicator. The leachable magnesium was calculated as the oxide and expressed as a per cent of the polymer (polyester resin plus styrene) in the sample by Equation 2. yo Nonfiller Magnesium Oxide = 4.032144 (titer - blank) Loss in wt. on pyrolysis (2) where Af is the molarity of the EDTA solution, titer and blank are in milliliters, and the loss in weight of the sample on pyrolysis is in grams. When alumina was the filler, the "Loss in weight on pyrolysis" was corrected for the loss in weight of the filler due to its dehydration. ANALYSISOF RAW SAMPLES. Approximately 20 grams of raw sample was dissolved in acetone. The filler was separated by filtration through a large paper Soxhlet extraction thimble fastened to the lip of a wide mouth Erlenmeyer flask. Residual turbidity in the filtrate was removed by filtration through a Celite bed on a porous glass filter. The solution was taken to dryness and vacuum dried a t 70" C. to remove any residual solvent and styrene. One gram of the residue, accurately weighed, was ashed at 600" C. The ash was dissolved in dilute acid, and then taken to dryness. The residue was analyzed for magnesium by the method for cured polymers beginning with the addition of 200 ml. of the buffered leaching solution with a p H of 8.2. The organically-bound magnesium was calculated from: yo Organically-Bound Magnesium = 4.032M (titer - blank) (3) sample wt. Equation 3 expresses the organicallybound magnesium as the oxide, and as parts per hundred parts of the polyester resin in the raw sample. RESULTS
Preparation of Known Samples. I n compounding known samples, the following were varied: the polyester, the filler, and the amount of mag-
nesium oxide. Two polyesters were used, one having an acid number of 20, the other an acid number of 42. The stocks containing the low acid number polyester had an excess of magnesium oxide, those with the high acid number had an excess of polyester. The fillers chosen were two talcs, two calcium carbonates, two clays, a mica, and a hydrated alumina. T o permit more accurate compounding, glass fiber was omitted from the known stocks. The blank stocks contained no added magnesium oxide. The raw samples were stored a t room temperature for a few days to allow those with magnesium oxide in them t o thicken. Cured samples were made from the raw samples by the addition of benzoyl peroxide catalyst and heating overnight at 70" C. For the results from Equation 2 t o be accurate, the loss in weight by pyrolysis must be a close approximation of the actual polymer content. The data in Table I1 show that the loss in weight on pyrolysis is an adequate measure of the polymer content. The results of analyses of cured samples are given in Table I11 and for raw samples in Table IV.
Table II.
Table 1. Characteristic Absorption Bands for Common Fillers and Additives
(in cm.-', and in decreasing order of band intensity) Calcium carbonate 1425, 875, 711, 1797 Pulverized silica 1082, 797, 780, 694 Barytes 1082, 1118, 1176, 610, Barium sulfate Clay Talc Mica Asbestos Antimony oxide Alumina Titanium dioxide
634,984 1081, 1119, 1196,. 610,. 638, 984 1032, 1009,912, 3691, 3617, 3651 . 1018. 669. 3674 1017; 929,' 3617, 748 952, 1018, 1078, 601, 3685, 3635 742 735, 1070, 1152, 3084, 3289 675
DISCUSSION OF METHOD
The introduction of hydrogen peroxide into the furnace during pyrolysis permits the destruction of the organic matter at a lower temperature than when air or water vapor is the atmosphere. The pyrolysis of a sample with no filler was 98.2% efficient when hydrogen peroxide was introduced as
Polymer Content of Cured Samples, by Pyrolysis yGLoss in wt. on pyrolysis 47.3a 47.7a 46, ga 49.7 49.5 49.9 49.3 49.5 49.4 49.1 49.0 49.2 65.3 65.6 65.6 65.5 65.8 65.8 49.3 49.2 49.6 65.4 65.3 65.0
Filler yo Polymer Alumina, C31 Hydrated 48.4 49.8 CaCOa, Atomite 49.8 CaC03, Snowflake 49.8 Clay, ASP 400 66.3 Clay, ASP 600 Mica, Micro 3000 66.3 Talc, 42R 49.8 66.3 Talc, 5490 a Corrected for 28% loss in weight of filler. Table 111.
Analytical Data for Cured Known Samples
Mi@, % Filler None Alumina C31 Hydrated Calcium carbonate Atomite Snowflake Clay ASP 400 ASP 600 Mica
Micro 3000
Talc
42R 5490
Actual
Found
0.85
0 . 8 4 , 0.86, 0 . 8 6
0.00 0.86
o.oo,o.oo, 0.00 0.75, 0.76, 0 . 7 9
0.00 0.85 0.00 0.85
0.85, 0.86, 0.88 0.00, 0.00, 0.02 0.86, 0.87, 0.89
0.00 0.85 0.00 0.85
0.00, 0.01, 0 . 0 3 0.82, 0.84, 0.86 0.00, 0.00, 0.00 0.80, 0.82, 0 . 8 4
0.00 0.85
o.oo,o.oo, 0.02
0.00 0.85 0.00 0.85
0.02, 0.04, 0 . 1 4 0.96, 1.09, 1 . 2 9 0.10, 0.16, 0 . 2 0 0.96, 1.02, 1.06
0.01,0.01,0.02
0.78, 0.80, 0 . 8 0
VOL. 36, NO. 9, AUGUST 1966
1207
Table IV.
Filler Alumina C31 Hydrated
Organically-Bound Magnesium in Raw Samples Per cent Mg, as oxide Polyester
acid number
Calculated
Found
23 23 42 20 42 42 20 42 42 20 42 42 20 42 42 20 42 42 20 42 42 20 42
0.00 0.81-1.61 0.00 0.69-1.38 1.15 0.00 0.69-1.38 1.15 0.00 0.69-1.38 1.15 0.00 0.69-1.38 1.15 0.00 0.69-1.38 1.15 0.00 0.69-1.38 1.15 0.00 0.69-1.38 1.15
0.04, 0.04 0.64, 0 . 6 3
CaCOa Atomite CaC08 Snowflake Clay ASP 400 Clay ASP 600 Mica Micro 3000 Talc 42R Talc 5490
described, 95.9?& efficient when water was introduced and 97.1% efficient when only air was present. A minimum temperature of pyrolysis is necessary, for, if the filler loses water, it may become more soluble in the leaching solution. The temperature prescribed, 340’ C., was the optimum temperature. The efficiency of pyrolysis a t 329’ C. under hydrogen peroxide vapors was only 90.2%. The turntable wm used to ensure uniform heat treatment. Without it the efficiency of the pyrolysis was dependent upon the position of the crucible in the furnace. Raising the temperature slowly to 340’ C. allowed the decomposition products from the plastic to evaporate as they formed and reduced the amount of char. The temperature programming rate of 0.5’ C. per minute was an arbitrary choice. The infrared spectra given in Figure 2 are typical. However, fillers of the same variety differ from each other depending on their source (4-7). The infrared spectrum of a particular filler also may be sensitive to the severity of the grinding with potassium bromide. The variations exhibited are usually in the width of absorption bands and the relative intensities of bands, rather than the wavelength of the absorption band. The pyrolysis treatment to 340’ C. had negligible effect on the absorption spectra except for alumina. The dehydration of hydrated alumina reduced its absorption in the region of 3400 cm.+ Except for the reduction of absorption bands due to moisture, no changes in the infrared spectra of fillers have been observed when the potassium 1208
ANALYTICAL CHEMISTRY
o.oo,o.oo
0.75, 0.77 1.14, 1.16
o.oo,o.oo
0.80, 0 . 7 8 1.14, 1.16
o.oo,o.oo
0.82, 0 . 8 0 1.04, 1 . 0 6 0.01,0.01 0.78, 0 . 7 8 1.09,1.12 0.00, 0.00 0.79, 0 . 7 9 1.17, 1.19
o.oo,o.oo 0.79, 0 . 8 0 1.18,1.19 0.00, 0.00 0.79, 0 . 7 4 1.15, 1.17
bromide pellets are dried by the method of Sadtler and Sadtler (8). When simple mixtures of fillers have been encountered in unknown samples, the major components of the mixtures have been identifiable. When calcium carbonate was one of the components, the identification of the others was simplified by removal of the calcium carbonate by solution in dilute acid. The leaching solutions are buffered reagents containing oxalate and sulfide ions adapted from the method of Betz and No11 ( I ) . The oxalate and sulfide eliminate interference by calcium and heavy metals which otherwise could be titrated with EDTA. The use of pH 8.2 buffer for alumina fillers gives better recovery of the magnesium and avoids difficulties in the titration due to blocking of the indicator by aluminum. The p H 4.7 buffer for clay reduces the adsorption of magnesium on the clay. The loss in weight of all the fillers tested, except alumina, upon being When pyrolyzed, was negligible. alumina was the filler in cured polyester, the polymer content found by pyrolysis was in error due to the dehydration of the alumina. The correction that was applied was based on a similar heat treatment of alumina filler alone. DISCUSSION OF THE RESULTS
The analytical results in Table I1 show that the pyrolysis of the samples had an average efficiency of 98.8%. The efficiency could be improved by employing more severe conditions of pyrolysis but with an increased risk of dehydrating fillers that have hydroxyl groups in their crystalline structure.
When the filler in a cured sample is calcium carbonate, clay, or mica, the data in Table I11 show that the method gives satisfactory analytical results. Hydrated alumina as the filler withholds a small portion of the magnesium. The source of this loss seems to be the adsorption of magnesium on the hydrated alumina during the leaching with buffer. However, reaction between magnesium oxide and hydrated alumina during pyrolysis has not been eliminated as a possible cause. Talc gives a small amount of magnesium to the leaching solution. The values in Table IV under the heading “Calculated” are based on the assumption that the reaction between the polyester and the magnesium oxide proceeded to the complete exhaustion of the minor component. For the stocks made from a polyester with an acid number of 20, and an excess of magnesium oxide, the organicallycombined magnesium oxide can be from 0.69% to 1.38%. When the magnesium oxide joins two carboxylterminated molecules, the organicallybound magnesium oxide is 0.69%. However, if a basic salt should be formed, R-COOMg(OH), the combined magnesium oxide would be 1.38%. The stocks containing the polyester with an acid number of 20 had approximately a 50% excess of magnesium oxide over the amount necessary t o form the basic salt. The analytical data for these samples indicate that the magnesium oxide reacts with the polyester mainly by bridging the molecules. They also demonstrate the precision of the method. The accuracy of the method and freedom from interference by fillers is shown by the data for samples made with an acid number of 42.
When hydrated alumina was the filler, the water of hydration apparently competed with the polyester for the magnesium oxide. Magnesium hydroxide is relatively inert to the polyester. The low recovery for raw samples containing hydrated alumina was not due to incomplete reaction since there was no difference in the organicallybound magnesium in samples that had thickened for three days or for nine days. For the samples made with the polyester having an acid number of 42, the organic acidity was in excess by 30%. There is no indication of the excess acidity having reacted with magnesium in the fillers. The method proposed in this paper requires about 40 hours. Most of this time is used for slow operations requiring no supervision, such as the pyrolysis, and evaporation of solutions to dryness. When several samples are being analyzed simultaneously, the labor per sample is about an hour and a half.
ACKNOWLEDGMENT
The author expresses his appreciation to Helen Andersen for expert assistance and to Alan Baumgartner, William Thomasino, and Charles Moruska for the preparation of samples. LITERATURE CITED
(1) Bete, J. D., Noll, C. A,, J. Am. W’atm Works ASSOC. 42, 49-56 (1950).
(2) Farbenfabriken Bayer, A.G., German Patent 1,131,881 (June 20, 1962), British Patent No. 949,869 (Feb. 19, 1964). (3) Fisk, Charles F., (to U. S. Rubber Co.) U. S. Patent No. 2.628.209 , . (Feb. . 10,1953). (4) Grim, R. E., [‘Clay Mineralogy,’’ pp. .. 305-10, McGraw-Hill, New York, 1953. (5) Hunt, J. M., Turner, D. S., ANAL. CHEM.25,1169 (1953). (6) Keller. W. D., Pickett. E. E., Am. J. hci. 248; 264-73 (1950). ’
(7) Keller, W. D., Pickett, E. E., Am. Maneralogist 34, 855-68 (1949). (8) Sadtler, T., Sadtler, . P., “Improved
KBr Techniques,’: Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, (1965). (9) Walton, .J. P., “Pre-Thickened Polyester ?sins in RFP Molding Compounds, SOC.Plas. Eng., Reg. Tech. Conf., Oct. 4-5, 1965.
RECEIVED for review March 17, 1966. Accepted May 23, 1966.
Fast and Sensitive Method for Determination of Nitrogen Selective Nitrogen Detector for Gas Chromatography RONALD L. MARTIN Research and Development Department, American Oil Co
b A
fast method for determining as little as gram of nitrogen is applicable to both total- nitrogen determinations and selective detection of nitrogen compounds with gas chromatography. Nitrogen compounds are converted quantitatively to ammonia in a stream of hydrogen over a nickel-onmagnesium oxide catalyst. The ammonia is titrated automatically, using a newly devised procedure, with coulometrically generated hydrogen ions. For petroleum samples, the method is quantitative and essentially free of interferences; gas oils containing as little as 0.2 p.p.m. of nitrogen can be analyzed in less than 10 minutes. The system, applied as a selective nitrogen detector with gas chromatography, has been used to determine nitrogen-compound distributions in complex petroleum materials.
A
for organic nitrogen, while needed in most research and process laboratories, are particularly important in the petroleum industry. Because of harmful effects of nitrogen compounds, total nitrogen must be determined reliably down t o about 1 p.p.m. in a variety of feeds and products. Characterization of petroleum nitrogen compounds by types and boiling point also is often desired. This paper describes a new approach to determining nitrogen. Nitrogen compounds are converted quantitatively to ammonia over a catalyst in a stream of hydrogen, and the ammonia is titrated coulometrically. The catalyst is nickel on magnesium oxide of the type described initially by ter Meulen (fl), improved by Holowchak, Wear, and Baldeschwieler (S), and applied by NALYSES
., Whiting, Ind.
others (4) 1.2). Whereas earlier work with this catalyst was limited to samples in the naphtha boiling range (up t o about 250’ C.), improvements in operating conditions now extend the applicable range through heavy gas oil (up to about 500” C.), The ammonia is swept with hydrogen from the catalyst into a specially devised titration cell, to titrate it automatically and continuously with coulometrically generated hydrogen ions. Liberti and Cartoni (5, 6), Coulson and Cavanagh (1, a), and others-e.g., (7, 9)-have used coulometry for continuous automatic titrations. Coulson and Cavanagh designed a particularly sensitive coulometer, employing both variable current and variable voltage, and were able to titrate as little as 0.1 fig. of halide (1) and sulfur dioxide ( 2 ) . None of the earlier titration systemsincluding the one employing hydroxyl generation or degeneration from peroxide (2, 6)-were adaptable, however, to the automatic titration of ammonia in a stream of hydrogen. The catalytic and titration reactions in the new method occur so rapidly that the equipment can serve as a selective nitrogen detector for gas chromatography as well as t o determine total nitrogen. The application to gas chromatography is proving very valuable in the study of the complex nitrogen distributions in petroleum. I n determining total nitrogen,the new method is two orders of magnitude more sensitive than Dumas or earlier ter Meulen methods and one order of magnitude more sensitive than Kjeldahl methods. It is a t least as fast as automatic Dumas methods and an order of magnitude faster than Kjeldahl or earlier ter Meulen methods.
DISCUSSION OF METHOD
A schematic diagram of the apparatus is shown in Figure 1. Hydrogen is used as eluting gas for gas chromatography and as sweep gas. Use of the sweep gas, which bypasses the column and is humidified by bubbling through water, ensures a high velocity through the catalyst and thus preserves the narrowness of peaks eluting from the gas chromatography column. Sample-introduction ports, with silicone rubber septums for syringe injection, are provided a t both ends of the column; injection a t the effluent end allows determination of total nitrogen. The catalyst tube contains a 3 X ‘14 inch bed of catalyst and is housed in an oven or furnace kept a t 440’ f 10’ C. The exit end of the catalyst tube is connected directly to the titration cell. The coulometer (Dohrmann Instruments Co. Model C-200) supplies and controls the current used in generation of titrant within the cell. This current is recorded against time to give ordinary differential peaks, whose areas are direct measures of the amounts of titrant generated, The exact manner of connecting the catalyst tube is diagrammed in Figure 2. For convenience in changing the catalyst, the tube is connected from the outside of the oven, using an adapter ball joint on the exit end of a permanently fixed open tube, inside which the catalyst tube fits. The sweep gas is fed through the permanent fixed tube so that the column effluent is forced directly through the catalyst tube. The entire assembly up to the adapter ball joint is kept inside the oven. The nitrogen-analyzer apparatus, including the titration cell and other necessary equipment, is available from Dohrmann Instruments Co., which has been licensed by Standard Oil Go. (Indiana) to produce it commercially. VOL. 38, NO. 9, AUGUST 1966
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