Table II.
Effects of Phosphates
Sample Fluorine Solution Found, y 35.2 y F-/50 ml. 35.2 400 y P 0 4 35.0 800 y POr 39.0 2000 y PO1 Bleaching of complex
+ + +
Interference None About 10% Complete
RESULTS AND DISCUSSION
A number of fluorine-containing organic compounds, all of which had given satisfactory values for carbon, hydrogen, and nitrogen [Nos. 1 to 4 analyzed by Steyermark (10) and Nos. 5 t o 8 by Francis (S)], were subjected to fluorine determinations (Table I). The precision obtainable is evident from the standard deviation, s = 0.11, arrived a t from 11 determinations of compound 1, and s = 0.08 calculated from the results of 26 determinations of compound 2 . The estimated overall accuracy of the method is *2%. Compound 4 contained a -CF3 group. It had been feared that on combustion, CFs might be at least partially volatilized, with a concomitant
loss of fluorine. This is not the case, as fluorine was completely recovered. I n another experiment the effect of phosphates on the absorbance of the fluoride-zirconyl complex was studied. As can be seen from Table 11, 400 y of phosphate per 50 ml. of final solution appeared t o be without effect on the absorbance. However, when 800 y were added, a positive error of about 10% resulted; 2000 y completely interfered with the determination. If the combustion of an organic fluorine compound, having up to two phosphorus atoms or phosphate groups per fluorine atom, is followed by hlegregian’s (8)photometric method, no interference need be expected. The presence of larger quantities of phosphates, however, necessitates a Willard-Winter (11) distillation. The method is very rapid, requiring less than 1 hour per determination. ACKNOWLEDGMENT
The authors are indebted to F. P. Mahn for valuable assistance, to J. A. Napoli for helpful suggestions, to A1 Steyermark, Hoffman-La Roche Inc., for the carbon, hydrogen, and nitrogen determinations of compounds 1 to 4,
and to Howard Francis, Jr., Pennsalt Chemicals Corp., for furnishing compounds 5 to 8, together with carbon, hydrogen, and nitrogen values. LITERATURE CITED
(1) Bennett, C. E., Debbrecht, F. J., Division of Analytical Chemistry, 131st
Meeting, ACS, Miami, Fla., A ril 1957. (2) Eger, C., Yarden, A., ANAL. 28, 512 (1956). (3) Francis, H., Jr., Pennsalt Chemicals Corp., Philadelphia, Pa., private communication. (4) Ma, T. S., ANAL. CHEM.30, 1557 (1958). (5) Ma, T. S., Microchem. J. 2, 91 (1958). (6) Ma, T. S., Gwirtsman, J., ANAL. CHEM.29, 140 (1957). (7) Mavrodineau, R., Gwirtsman, J.,
S HEX.
Contribs. Boyce Thompson Inst.
18,
181
(1955). (8) Megregian, S., ASAL. CHEW 26, 1161 i1954). (9j Schoniger, W., Mikrochim. Acta 1955, 123; 1956, 869. (10) Steyermark, Al, Hoffmann-La Roche Inc., Nutley, N. J., private communication. (11) Willard, H. H., Winter, 0. B., IND. ESG. CHEW,ANAL.ED. 5 , 7 (1933). RECEIVED for review November 17, 1958. Accepted March 18, 1959. Meeting-inMiniature, North Jersey Section, ACS, January 26, 1959.
Trace Analysis for Total Nitrogen in Petroleum Fractions Adsorption-ter Meulen Method EUGENE C. SCHLUTER, Jr. Research Deportment, Union Oil Co. o f California, Brea, Calif.
b Trace amounts of organic nitrogen compounds in petroleum fractions poison conversion catalysts. The determination of total nitrogen in petroleum fractions a t very low concentrations presents a serious analytical problem. By the method presented here the nitrogen compounds are concentrated from a relatively large volume of hydrocarbon by adsorption on a silica gel column. This column is then placed in a ter Meulen apparatus where the nitrogen compounds and the hydrocarbons wetting the gel are desorbed b y hydrogen and heat. The vapors pass through the ter Meulen catalyst with very little pyrolysis of hydrocarbons. The nitrogen compounds are converted to ammonia, which is collected in an absorber and determined by standard methods. The procedure may b e used to determine as little as 0.1 p.p.m. of nitrogen.
1576
ANALYTICAL‘ CHEMISTRY
T
petroleum industry is becoming increasingly aware of the deleterious effects of organic nitrogen compounds in various phases of petroleum refining. Nitrogen compounds reduce stability of refined products by gum formation and impart undesirable odor and color (6, IS). They also adversely affect the activity of cracking and other type catalysts (3, 7, 9, 1.2, 14). Nitrogen is particularly deleterious to the activity of platinum-type catalysts used in present day reforming operations. The charge stocks to reformers using platinum-type catalysts usually contain less than 20 pap.m. of nitrogen, the determination of which creates an analytical problem. The conventional (Kjeldahl, Dumas, and ter Meulen) methods available for the determination of total nitrogen are intended for the determination of nitrogen a t levels above 100 p.p.m., HE
and they are not directly applicable for the determination of trace amounts. Except for the Dumas, these methods have been modified to allow the detection of as little as 1 p.p.m. of total nitrogen. Because the ultimate sensitivity of the conventional Kjeldahl method is limited by a relatively large and variable blank, efforts to increase sensitivity have been aimed a t minimizing the effect of the blank. One solution is to increase the sample size. Bond and Harriz (1) concentrate the organic nitrogen compounds from a large sample by adsorption on a small silica gel column, which is then broken up into sections and digested by the conventional Kjeldahl method. Results with an accuracy of i.5% at the 1- to 10p.p.m. level are claimed. Bumping of the Kjeldahl flask during the digestion
Figure 1. A. E. C.
D. E, F. G. H.
1.
Schematic diagram of ter Meulen apparatus
Hydrogen cylinder and pressure regulator Needle volve Concentrated sulfuric acid bubble counter and trap Drying tube to trap sulfuric acid spray ond moisture Rotameter Manometer Needle valve Needle valve Adsorption column
of the gel sometimes results in flask breakage. Wankat and Gatsis (16) catalytically hydrogenate up to 1 liter of sample a t high pressure and temperature and absorb the resulting ammonia on acidic alumina, which is part of the catalyst. The gbsorbed ammonia is then determined by a conventional Kjeldahl distillation of the catalyst mixture. The method is not suited to routine analysis because of the special apparatus and excessive time required for an analysis, but can be used to determine as little as 1 p.p.m. of nitrogen with a catalyst mixture blank of about 2 p.p.m. Noble (11) partially solves the problem of a large blank by using specially purified reagents and determines the ammonia colorimetrically under carefully controlled conditions. Even so, a reproducible 4p.p.m. reagent blank remains which may cause uncertainty in analyses a t or below 4 p.p.ni. of nitrogen. Another technique is to extract the nitrogen compounds from the petroleum sample with 92y0 sulfuric acid, digest the extract by the Kjeldahl method, and determine the ammonia colorimetrically (IO). Whatever the approach to- increase the sensitivity of the Kjeldahl method, the precision and accuracy are ultimately limited by the reagent blank. The ter Meulen method is inherently free from reagent blank. The catalyst suggested by ter Meulen (8) had a short life and was subject to easy poisoning by sulfur and halogens. Holowchak, Wear, and Baldeschwieler (4) developed a catalyst which was resistant to poisoning by sulfur and halogens and
J. K. 1.
M.
N. U.
P. Q.
had an excellent life. They were able to determine as little as 100 p.p.m. of nitrogen, using an acidimetric end point. They indicated that as little as 10 p.p.m. of nitrogen could be determined by spectrophotometric detection. Sample size is limited to about 200 mg. to prevent deactivation of the catalyst by carbon deposition. King and Faulconer (6) were able to introduce up to 3 grams of low-boiling sample without destroying the effectiveness of the catalyst. Using a ter Meulen apparatus with a vertical reaction tube having separate pyrolysis and catalyst zones and determining ammonia with Nessler's reagent, they were able to determine as little as 1 p.p.m. with an accuracy of 1 p.p.m. To extend the determination of total nitrogen below 1 p.p.m., the ter Meulcn method appeared the most promising because it is rapid and conwnient and has little or no blank. Instead of developing a more sensitive method for detecting ammonia or of charging larger samples directly to the ter Meulen apparatus, a method of concentrating the nitrogen compounds of adsorption was chosen. The combination of adsorption and ter Meulen methods was suggested by Bond and Harriz (1); however, they did not elaborate on a technique for accomplishing this. In the present method, the entire adsorption column containing both the adsorbed nitrogen compounds and 5 to 20 ml. of liquid hydrocarbons was placed in the ter Meulen apparatus to avoid transfer loss of any volatile nitrogen compound. The nitrogen compounds and the liquid hydrocarbons were then desorbed and forced into the
Transite shield Reaction tube Nickel-wire plug Catalyst furnace Nickel-magnesium catalyst Absorber Overflow trap Burners
catalyst zone by hydrogen pressure and heat. No attempt was made to pyrolyze the relatively large amount of sample, in contrast t o previous similar methods where total sample pyrolysis was tried (4, 6, 8 ) . For maximum sensitivity a colorimetric method was used for detecting the ammonia formpd from the nitrogen compounds. APPARATUS AND REAGENTS
The general arrangement of the ztpparatus is shown in Figure 1. Hydrogen is sipplied from a conventional pressure cylinder and reducing valve, A . The flow of hydrogen is controlled with needle valve B and the rotameter, E. The manometer, F , indicates backpressure in the system. The hydrogen stream divides aftpr passing through the rotameter. One stream flows into the reaction tube and sw-veepsthe vapors surrounding the adsorption column into the catalyst zone. The other stream forces the hydrocarbon sample out of the adsorption column and into the catalyst zone. The flow is controlled by needle valves G and 11. Depending on adsorption column size, from 5 to 20 ml. of hydrocarbon are swept through the catalyst zone which is maintained a t 360' C. by an electric furnace, M . The catalytic reaction products are swept through the absorber, 0, where ammonia is absorbed and liquid hydrocarbons are condensed. Adsorption Column. The adsorption columns tested are shown in drtail in Figure 2. The columns are made of Vycor high-silica glass so that intense heat can be applied without danger of softening or rupture. A reservoir of suitable capacity is made from a globe-shaped leveling bulb by fitting with a spherical joint at the t o p for connection to a pressure system. VOL. 31, NO. 9 , SEPTEMBER 1959
1577
The adsorption column is connected to the reservoir with a short piece of l/4inch inside diameter Tygon tubing. Reaction Tube. Construction details of the reaction tube are shown in Figure 2 ; all parts are made of Vycor high-silica glass. Catalyst Furnace. A furnace capable of maintaining a temperature of 350" to 360' C. is required for heating the catalyst zone. A Hevi-Duty furnace, Type 70 (Hevi-Duty Electric Co., Milwaukee, Wis.), was used. The temperature was measured and controlled with an iron-constantan thermocouple and a variable autotransformer. Absorber. Construction details are shown in Figure 1. The absorber is not subjected to high heat and therefore is constructed from borosilicate glass. It consists of three parts: a gas bubbler, a conventional 50-ml. graduated cylinder, and an overflow trap. The trap is used to catch the occasional overflow caused by the sudden excessive foaming which may take pbce when the initial hydrocarbon condensate flows through the filter stick. Reagents. All reagents conformed to specifications established by the American Chemical Society Committee on Analytical Reagents. Other than commonly used reagents, the following were needed : SILICAGEL, 100-200 mesh, available from Davison Chemical Corp., Baltimore 3, Md., Code 923. Heat a t 500" C. overnight and keep in a tightly stoppered container. DEIONIZEDWATER. Pass distilled water through a monobed ion exchange column. QUARTZWOOL. Heat a t 500" C. overnight and keep in a tightly stoppered container. PROCEDURE
Calibration Curve for Colorimetric Determinations. Prepare a calibration curve by the phenol-hypochlorite colorimetric method described by Noble (11). Catalyst Preparation. Prepare the nickel-magnesium catalyst as described by Holowchak, Wear, and Baldeschwieler (4) and King and Faulconer (6). The wet unreduced catalyst is washed until it is nitrate-free as determined by the so-called "brown-ring" test using ferrous sulfate and concentrated sulfuric acid. It is important to obtain a catalyst free of nitrate. Residual traces of nitrate are reduced slou+lyto ammonia in subsequent determinations giving high and variable blanks. It is more economical to remove traces of nitrate by washing than by subsequent conversion to ammonia during reduction of the catalyst. Catalyst Reduction. Wad up a length of B & S 30-gage pure nickel wire and place it in the reaction tube. Using a wooden dowel of very nearly the same diameter as that of the inside of the reaction tube, press the wad into the constricted end of the tube. A plug about 0.5 inch long should be formed. Leave this plug in place, and, by the
1578
ANALYTICAL CHEMISTRY
k ISO M M . ~
50 M U - / -
700 - MM 820 ~ -MM
R E A C T I O N TUBE
'
4 4 0 MM.
I
SMALL ADSORPTION COLUMN LIP TO HOLD
-4 4 0
-
MM.
L A R G E ADSORPTION COLUMN
Figure 2.
Diagram of adsorption columns and reaction tube
same method, form another plug about 1.5 inches long. Remove this latter plug because it will be used to cap the reduced catalyst in place. Fill the reaction tube with 4- to 8mesh size unreduced catalyst to about twice the length of reduced catalyst needed, and cap with the nickel-wire plug. Suspend the reaction tube in a horizontal position from each end by means of conventional clamps and sweep out the air with a stream of hydrogen flowing a t 300 ml. per minute. Reduce the catalyst by applying the full heat of a Fisher-type burner to the reaction tube, starting a t the upstream end and progressing downstream until the exit nickel-wire plug is reached and no further moisture is given off. Advance the burner the full length of the reaction tube once more, this time using a wire gauze over the reaction tube to increase the heat. The catalyst will now have shrunk a t least 50%. Let the catalyst cool, then hold the reaction tube in a vertical position and tap gently so that the reduced catalyst will pack by gravity into the catalyst zone. The catalyst zone thus produced should be a t least 32 cm. long; if not, unreduced catalyst must be added and fhe reduction step repeated. When the proper length is obtained, push the nickel-wire cap into place, taking care not to compact the reduced catalyst. Slip the l/c-inch Transite shields on the reaction tube, and set the tube in place in the electric furnace. X o less than 40 mm. of the catalyst zone should protrude from the furnace past the Transite shield. Suspend the reaction tube from one end by the electric furnace and from the other end by a conventional clamp. Raise the clamped adsorbent column end very slightly so that liquid hydrocarbons being forced out of the adsorbent will flow by gravity toward the catalyst zone. Run blank determinations until the
ammonia from residual nitrate cannot be detected by the colorimetric method. Usually two or three blank runs will reduce the blank below the colorimetric detection limit provided prior washing of the catalyst was adequate. In subsequent operation air must be excluded from the ter Rfeulen catalyst. Adsorption of Nitrogen Compounds. Push a small wad of quartz wool against the indentation in the adsorption column so that it forms a plug t o retain adsorbent. Clamp the column in a vertical position with the plugged end (ball-joint end) down and attach a small funnel to the upper end with a short length of Tygon tubing. Add enough silica gel while tapping the column t o fill the column to within 1 cm. from the top. Remove the filling funnel and cap the silica gel with a small plug of quartz rrool. Pack this plug in firmly and in such a manner that later, when the column is heated and hydrogen pressure is applied, the plug will wedge against the lip on the column and prevent silica gel from spilling out into the reaction tube. Connect the upper end of the column to the reservoir with a short length of Tygon tubing and fill the reservoir with the requisite amount of sample. The volume of sample should be such that the amount of nitrogen from the blank is a small fraction of that from the sample, and such that enough nitrogen is available for an accurate determination. Connect the reservoir to the pressure system by means of the spherical joint and clamp tightly. Adjust the air pressure so that the sample passes through the column a t a rate of 60 to 90 ml. per hour for the small column or up to twice this rate for the large column. Release the pressure just before the final few milliliters enter the column. Allow the final flow to take place by gravity and let the column drain; air will not enter the adsorbent
unless the columns are left standing for extended periods of time. Generally, the columns should not drain any longer than it takes to run a sample through the ter Meulen apparatus. Disconnect the adsorption column from the reservoir and wipe off the exterior of the column with Whatman S o . 1 filter paper moistened with deionized water. This is not necessary if the adsorption time is short, but extraneous ammonia compounds may deposit on the exterior surface of the column when large samples are passed through because of the length of time the columns are exposed. The adsorption column is now ready for insertion in the reaction tube. Operation of ter Meulen Apparatus. Fill the absorber with 20 ml. of either a 0.005N sulfuric acid solution for the colorimetric determination or a 2.5% aqueous boric acid solution for the volumetric determination. Clamp the absorber onto the reaction tube by means of the spherical joint. Assemble the apparatus (Figure, l), except for the insertion of the adsorption column. (When the adsorption column is not in place in the apparatus, it is replaced with a rubber stopper to prevent entry of air.) After the temperature of the catalyst zone has been adjusted to 360" C., close needle valves G and H , and open needle valve B. Adjust the hydrogen pressure to 160 mm. of mercury with the pressure reduction valve on the hydrogen cylinder and the manometer, F . Setting the pressure a t a small arbitrary value is a precautionary measure. In case of plugging of the catalyst zoneduring the desorption step, no dangerous rupture of the apparatus is likely to occur. Close needle valve B and open needle valve G, then cautiously open needle valve B to give a hydrogen flow of about 350 ml. per minute as shown by the rotameter, E. Remove the rubber stopper and insert the adsorption column into the apparatus and clamp the spherical joints together tightly. The upper end of the adsorption column containing the nitrogen compounds will now be nearest the catalyst zone, and the bottom of the column (ball-joint end) will protrude from the apparatus. Connect the bottom of the column to the hydrogen supply through needle valve H with a suitable length of Tygon tubing. Open needle valve H and close needle valve G, then immediately place a Fisher-tj-pe burner a t full heat just below the adsorbent zone of the adsorption column. As soon as possible, cautiously open needle valve G to give a hydrogen flow of about 200 nil. per minute, keeping hydrogen pressure 160 mm. above atmospheric. Liquid hydrocarbon will be seen coming out from the column and nil1 run into the catalyst zone where the lighter fractions will be vaporized and pass into the absorber. At this stage, hydrogen flow rates greater than 200 ml. per minute tend to cause overflow of the absorber solution because of a characteristic foaming propensity. Advance the burner only
when it is apparent that a liquid front in the adsorption column is being pushed ahead by the heat and hydrogen pressure. At least 1 inch should exist between the flame front and the liquid front. Place a second burner after the first burner when the first one has advanced enough for the second to fit between the first Transite shield and the first burner. This second burner is also a t full heat and is used to prevent vapors from backing up and condensing into the cool zone should the first flame be advanced too rapidly. Move the burners forward simultaneously. When the burners reach that part of the reaction tube where the tip of the adsorption column is located, advance the burners very cautiously. The lighter fractions of the adsorbed hydrocarbons have already passed through and only the heavy material remains in that section of the catalyst zone which protrudes from the electric furnace. If this section is approached too rapidly, sudden vaporization of the heavy hydrocarbons may cause them to pass too swiftly through the catalyst zone with the consequent danger of incomplete conversion of organic nitrogen into ammonia. In addition, any sudden vaporization may cause overflow of the absorber solution from the increased gas flow. Advance the burners until the protruding catalyst zone is reached and the lead burner touches the second Transite shield. Increase the hydrogen flow t o 300 ml. per minute, and make a second pass Kith the burners a t full heat, heating the same section of the reaction tube covered the first time. This time use a wire gauze over the reaction tube to increase the heat. When this area has been at the maximum heat of the burners for no less than 3 minutes, advance the burners about two thirds of the length of the heated area. Continue in this manner until the burners reach the protruding catalyst zone and the second Transite shield, and apply maximum heat to this area for a t least 5 minutes. Shut off the burners and nllow them to cool while purging the system for an additional 30 minutes with hydrogen. Adjust the flow of hydrogen t o 10 ml. per minute. Disconnect the absorber from the apparatus, being careful not to lose any sample which may he in the tube connecting the absorber t o the overflow trap. Disassemble the absorber by removing the 50-ml. cylinder while rinsing the filter stick and the tube leading to the overflow trap. Use rinse water sparingly for the colorimetric determinations. Add any overflow and rinses from the overflow trap to the 50ml. cylinder. Dilute to 40 ml. with deionized n ater, stopper the cylinder and let stand for about 15 minutes to allow the oil phase to separate completely. "sing a glass tube drawn to a fine tip, cautiously and completely remove the oil phase by suction, taking care to remove little or no aqueous phase. The oil phase is most efficiently removed by looking a t the interface against a bright background while holding the cylinder a t eye level. The amount of
aqueous phase removed by this technique is barely detectable. Make a blank determination by filling the appropriate adsorption column with silica gel and purging with hydrogen to displace air. Carry out the same procedure as for an actual sample. Check the activity of the catalyst not only when freshly reduced, but also a t regular intervals, using a synthetic blend of known nitrogen content. The recovery should be a t least 95QJ,. No safety hazard is involved in the operation of the apparatus if precautions are taken to exclude air TT hen inserting and removing adsorption columns. Entry of air is minimized by having the hydrogen flowing at 300 to 350 ml. per minute when changing columns. As a precautionary measure, a safety shield should be worn. When the apparatus is not in use, a 5 to 10 ml. per minute hydrogen flow is maintained to keep up catalyst activity. Determination of Nitrogen. If nitrogen is detected colorimetrically, develop the color. in the same manner as that for the calibration curve. Obtain the adsorbance of the solution and, by reference t o the calibration curve, find the milligrams of nitrogen present. If nitrogen is detected acidimetrically, quantitatively transfer the contents of the 50-ml. cylinder to a 250-ml. Erlenmeyer flask and dilute to 100 ml. Titrate with standard 0.01S hydrochloric acid to a methyl purple end point. RESULTS AND DISCUSSION
The length of the small adsorption column was selected to give a heightto-diameter ratio of 36, although higher ratios may be desirable ( I , 2). However, increasing the length of the column increases adsorption and desorption time and requires a longer ter Meulen reaction tube. The adequacy of the column was tested by analyzing synthetic samples, simulating some reformer charge stocks and containing a relatively high aromatic fraction. The nitrogen was contributed equally from pyridine and pyrrole. Appropriate aliquot portions were added to iso-octane to give approximately 100-p.p.m. solutions, which were then passed through the adsorption column for analysis. Testing was carried out on 40 to 100 mesh 13X Molecular Sieve, on 60 to 100 mesh Florid, and on 100 to 200 mesh silica gel. Average recoveries of 97, 98, and 9970, respectively, were obtained for these adsorbents. The choice of adsorbent was made on the basis of analytical convenience. Silica gel was chosen because of its faster percolation rate for a given mesh size, the ease of observing colored bands both during adsorption and during desorption in the ter Meulen apparatus, and the minimum amount of foaming in the absorber during the desorption step. I n addition, silica gel gave better recoveries on naphtha samples which VOL. 31,
NO. 9,
SEPTEMBER 1959
0
1579
Table
I.
Analysis
of Synthetic Samples
DetecNitrogen, Mg. Recovery, Column tion Added Found % Size Method Solvent 0.107 99 Small Color 0.108 Iso-octane 102 Small Color 0.108 0.110 100 Small Color 0.108 0.108 Pyridine pyrrole, 1:1 RCS-I-NF. 0.061 0.058 95 Small Color 0.129 0.117 91 Small Color 93 Small Titration 5.6 ... .. RCS2b 5.5 p.p.m. None 85 Small Titration nitrogen 5 1 ... .. 110 Small Titration (as pyridine) 6 8 ... .. 0 095 91 Small Color 0.104 Gas oilc RCS1-NF' 100 Large Titration 1.04 1.04 200 96 Large Color PC57-36d 0.113 0.109 RCS-1-NFQ 200 Color 0.122 108 Large 0.113 200 Color 0.113 100 Large 0.113 200 Color 0.117 103 Large 0.113 200 Color 0.111 98 Large 0.113 200 Consists of 13y0aromatics, 43% naphthenes, and 4470 paraffins. a Reformer charge stock free of nitrogen by passage through silica gel. Reformer charge stock contains 0.5 p,p.m. total nitrogen. Same hydrocarbon composition as RCS-1. Material had been stored for several months and formed gum. c API-COAR cooperative sample contains 0.342% total nitrogen. d Sample of nitrogen concentrate from Wilmington, Calif., crude supplied by Bureau of Mines at Laramie. Obtained by adsorption on Florisil and contains 0.88% nitrogen, 1.9% oxygen, and 0.83% sulfur. Source of Nitrogen Compounds Pyridine pyrrole, 1:1
+
+
+
had formed gums. The nitrogen blanks for silica gel and Florisil are very nearly equal and amount to 0.006 mg. of nitrogen per column charge (7 grams); the blank on 13X Molecular Sieve is five times greater. These are absolute amounts of nitrogen and do not represent the total blank for a determination. Except for the 13X Molecular Sieve, the amount of blank is not a basis for decision. The small adsorption column did not have the adsorptive capacity to retain all nitrogen from samples having large amounts of more polar compounds. The length of the column was not increased nor was the ter Meulen a p p a ratus rebuilt; instead, the diameter of the column was doubled, giving approximately four times the adsorptive capacity. Where only partial recoveries were obtained with the small column on the same size sample, nearly quantitative recoveries were obtained using the large column. The small column is generally adequate for the analysis of freshly processed naphthas containing oxygenated and sulfur compounds of the same order of magnitude as the nitrogen. 'However, where gum formation has taken place or large amounts of more polar compounds are present, the larger column should be used (Table I). In m y case, sample size should be limited to that which ill give between 0.05 and 1 mg. of nitrogen, so that excessively large samples will not elute some of the nitrogen compounds. Although large amounts of hydrocarbon passed through the ter Meulen apparatus, there was relatively little coke deposition even after 60 determinations, because only a small amount of pyrolysis took place. Possibly water which came from entrapped air, the sample, and the silica gel dehydration 1580
ANALYTICAL CHEMISTRY
Solvent Volume, MI. 50 100 200 200 200 200 200 200 200
Nitrogen Concn., P.P.M.
Table II. Colorimetric Determination of Nitrogen in Reformer Charge Stocks
Column Size Small 200 0.22 Small 500 0.29 Large 500 0.29 Large RCS-20 200 0.47 Small 200 0.45 Small 200 0.44 Small 200 0.51 Small 200 0.45 Small API-COAR cooperative sample. Independent analyses of 0.5 and 0.3 p.p.m. were obtained by two other petroleum companies for this sample. Sample RCS-1
Volume, M1. 200
Mg./Kg., P.P.M. 0.22
reacted with the coke to produce hydrogen and carbon monoxide by the water gas reaction to help reduce coke accumulation. The minor accumulation of coke does not affect the catalyst activity but does cause a n increase in the amount of the nitrogen blank by retaining ammonia from a prior analysis. The amount of carbon is small for it cannot be seen nor detected by any back-pressure increase. The increase in the blank is more noticeable with continual use of the large-column. Data for a catalyst on which 60 analyses were performed showed a n increase in the blank from 0.01 to 0.03 nig. of nitrogen for the small column and from 0.04 to 0.09 mg. for the Iarge column. This nitrogen blank represented ammonia coming from the silica gel and held up from prior samples. Periodic tests on the activity of the catalyst using high nitrogen concentrations were performed. The blank before and after the activity test did not vary by more than the average blank varia-
tion. The average blank for the small column was 0.014 mg. of nitrogen with a standard deviation of 0.007 mg.; on the large column, 0.048 mg. with a standard deviation of 0.025 mg. As deposited carbon is believed to cause retention of ammonia, sample types other than those tested may cause greater retention because of more carbon deposition. One method for stripping off the retained ammonia is to purge the system with hydrogen for more than 30 minutes. However, the time required to reduce the ammonia concentration below detectability is more than a day. A better method is to pass about 1 to 2 ml. of water through the ter Meulen apparatus in the same manner as a sample. This water can be introduced by adding it to the silica gel in the adsorption column. The blank is reduced by about half; repetitive water treatments are usually not required but may be used. The catalyst activity is not adversely affected by this treatment. The method has not been applied to naphthas having end points higher than 400' F., but should be applicable to such naphthas if the end point is well below the cataIyst temperature. The hydrocarbons which condense in the absorber must be removed within a short time if nitrogen is t o be determined colorimetrically. If the oil and water phases are allowed to stand overnight, a competing reaction inhibits the indophenol color formation. Sometimes the color will form slowly and finally develop fully, but in most cases an entirely different color results. A hydrocarbon trap between the absorber and the ter Meulen apparatus was tried with little success, possibly because of ammonia adsorption on the
glass tubing before reaching the absorber. A recent report (1) has shown that silica gel is effective in retaining a wide variety of nitrogen compounds. The ter Meulen method is capable of determining an equally wide variety of nitrogen types (4, 6). Rather than run experiments on a large number of nitrogen compounds to test the effectivmess of the adsorption-ter Meulen combination, the author evaluated the method with synthetic samples prepared from hydrocarbon solvents and pure nitrogen compounds, with a gas oil containing naturally occurring nitrogen compounds, and with a concentrate of naturally occurring nitrogen compounds obtained from crude oil (Table I). The values given in Table I1 were obtained on a reformer charge stock and show the precision which can be obtained a t this low nitrogen con-
centration. The absorbance of the blank was about one fifth of that corresponding to the nitrogen in these samples. ACKNOWLEDGMENT
The author wishes to thank J. S. Ball for supplying the nitrogen concentrate from Wilmington crude. LITERATURE CITED
(I) Bond, G. R., Jr., Harrie, C. G., ANAL. CHEM.29, 177 (1957). (2) Helm, R. V., Latham, D. R., Ferrin, C. R., Ball, J. S., Chem. & Eng. Data Ser. 2', N o . ' l 95 '(1957). (3) Hettinger, b. P., ,Jr.., Keith. D. C..
Gring, J. L., Teter, J. W., Znd. Eng: Chem. 47,719 (1955). (4) Holowchak, J., Wear, G. E. C., Baldeschwieler, E. L., ANAL. CHEM. 24, 1754 (1952). (5'1 Kine. R. W.. Faulconer. W. M. B.. ' Ibid.,-Z8, 255 (1956).
(6) Mapstone, G. E., Petrol. Refiner 28, No. 10, 111 (1949). (7) Maxted. E. B.. J. SOC. Chem. Znd. (London)'67, 93 (i948). (8) Meulen, H. ter, Rec. trav. chim.. 43, 1248 (1924). (9) Mills, G. A., Boedeker, E. R., Oblad, A. G.. J . A m . Chem. SOC.72. 1554 (1950): (10) Milner, 0. I., Zahner, R. J., Hepner, L. S., Cowell, W. H., ANAL.CHEM.30, 1528 (1958). (11) Noble, E. D., Zbid., 27, 1413 (1955). (12) Schall, J. W., Dart, J. C., Petrol. Refiner 31, N o . 3, 101 (1952). 3) Thompson, R. B., Chenicek, J. A., Druge, L. W., Syman, T., Znd. Eng. Chem. 43, 935 (1951). 4) Voge, H. H., Good, G. M., Greens-
.,
\ - - - - ,
felder, B. S., World Petrol. Congr., PTOC., Srd Congr., Hague 1951, Sect. IV, 131. 5) Wankat, c., batsis, J. G., ANAL. CHEW25, 1631 (1953).
RECEIVED for review January 27, 1958. Accepted May 8, 1959. Division of Petroleum Chemistry, 132nd Meeting, ACS, New York, N. Y., September 1957.
Identification and Differentiation of Sympathomimetic Amines L. G. CHATTEN and LEO LEVI Food and Drug laboratories, Department o f National Health and Welfare, Ottawa, Ontario, Canada
b The reactions of some sympathomimetic amines with benzoyl chloride, p-nitrobenzoyl chloride, benzenesulfonyl chloride, picric acid, and ammonium reineckate have been studied. By the use of color and microcrystal tests, and the formation of derivatives, it is possible to differentiate d-amphetamine, dl-amphetamine, methamphetamine, and ephedrine. Photomicrographs and infrared absorption spectra of the reaction products are presented and their value for characterizing these clinically important drugs is discussed.
M
techniques for the identification of sympathomimetic amines have appeared in the literature. They include color tests (3, 4, 15, 18, do, 26, 31, 31, 34, 35, 39, 40, 42-44, 46-48, 52, 54, 56, 69), precipitation tests by alkaloidal reagents (21)) crystallographic examination of suitable derivatives (1, 2, 7-9, 11, 12, 16, 19, 22, 27, 28, SO, 58,49, 51, 55), spectrophotometric analyses (10, 41), ion exchange (63), and chromatographic procedures (50, 67). Reviews on the chemistry, . identification, and determination of many sympathomimetic amines have also been published (17, 29). ANY
Although restricted by law to sale on prescription only, these drugs are often obtained illegally; hence reliable criteria for their identification and differentiation are of great importance to the forensic chemist and toxicologist. It is the purpose of this investigation to improve existing procedures and develop new tests for these clinically important products.
Picric acid solution, 1 to 2 grams of picric acid in 100 ml. of water. Platinum chloride solution, 1 gram of platinum chloride in 20 ml. of 1N hydrochloric acid. Gold chloride solution, 1 gram of gold chloride in 20 ml. of water. Ammonium reineckate solution, 1 gram of salt in 100 ml. of water. RESULTS
EXPERIMENTAL
Reagents. Ephedrine hydrochloride, British Pharmacopoeia. Amphetamine sulfate, U. S. Pharmacopeia. &Amphetamine sulfate, U. S. Pharmacopeia. Methamphetamine hydrochloride, U. S. Pharmacopeia. Aqueous 1 and 0.1% solutions of each of the above sympathomimetic amines. Marquis reagent, 2 drops of 40% formaldehyde in 3 ml. of concentrated sulfuric acid, prepared freshly. Frohde reagent, 5 mg. of sodium molybdate per ml. of concentrated sulfuric acid. Mandelin reagent, 1 gram of ammonium vanadate in 200 grams of concentrated sulfuric acid. Sanchez reagent, 0.1 gram of dimethylaminobenzaldehyde in 20 ml. of ethyl alcohol and 4 drops of sulfuric acid.
Color Tests. The color reactions were carried out on a spot plate using 1 and 0.1% aqueous solutions of the sympathomimetic amines. One drop of reagent was added to 2 drops of solution (approximately 1 and 0.1 mg. of drug, respectively) and the color formations were observed a t various time intervals. The experimental data are recorded in Table I. Microcrystal Tests. One drop of 1 or 0.1% solution of the salt of each sympathomimetic amine was placed on a microscope slide. One drop of reagent was added and the time of crystal formation noted. Photomicrographs were taken before the slide became dry. The results of the tests are listed in Table I1 and photomicrographs are shown in Figures 1 and 2. Formation of Derivatives. All compounds were prepared by standard procedures (Table 111). ~-XITROBENZOYL DERIVATIVES &-ere VOL. 3 1, NO. 9, SEPTEMBER 1959
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