with basicities of the amines which are obtained on hydrolysis. Ammonia is a t least 50,000 times more basic than aniline or the naphthylamines, b u t acetamide is only six times more basic than acetanilide or the N-acetyl naphthylamines. This may be due a t least in part to the lack of coplanarity between the ring system and the resonating amide plane.
LITERATURE CITED
(1) Connors, K. A., Higuchi, T., ANAL. CHEM.32. 93 (1960).
”,
1940. (4) Higuchi, T., Connors, K. A., J. Phys. Chem. 64, 179 (1960). ( 5 ) Higuchi, T., Feldman, J. A., Rehm, C. R., ANAL. CHEM.28, 1120 (1956).
( G ) Kolthoff, I. M., Bruckenstein, S. J. Am. Chem. SOC.78, 1 (1956). (7) . . Rehm, C., Bodin, J. I., Connors, K. A,, Hieuchi’. T.. ANAL. CHEM. 31. 483
(1g59). ’ ’ (8) Rehm, C. R., Higuchi, T., Zbid., 29, 367 (1967). RECEIVED for review September 5, 1961. Accepted December 18, 1961. Division of Analytical Chemistry, 139th Meeting, ACS, St. Louis, Mo., September 1961.
Microdetermination of Carbon and Hydrogen Using Nondispersive Infrared and Thermal Conductivity Analysis J. A. KUCK, J. W. BERRY, A. J. ANDREATCH, and P. A. LENTZ Microanalytical and Instrument Groups, American Cyanamid Co., Stamford, Conn.
b An instrumental method has been developed for the rapid determination of carbon and hydrogen in 2-mg. samples. The conventional combustion tube i s retained but instead of weighing the gaseous combustion products, the combustion gas mixture i s collected to a constant volume and adjusted to a standard reference pressure for analysis. Carbon i s determined as carbon dioxide with a nondispersive, infrared gas analyzer, and hydrogen i s determined as the gas with a thermistor-type thermal conductivity cell. The hydrogen which i s equivalent to the Chemically bound -H in the sample i s obtained b y passing the water vapor from the combustion over calcium hydride. This new C and H method i s applicable to sample weights in the range of 4.0 to 0.5 mg. and i s operable with as little as 200 pg. of material. Trace analysis for carbon and hydrogen i s also possible. Satisfactory analyses have been obtained with compounds containing hetero atoms like B, N, P, and S, as well as with samples containing only C, H, and 0. Preliminary experiments have shown that the method here reported i s as good os or better than the classical gravimetric method of Pregl. On the basis o f its scientific principles, it is a strong competitor with other methods for use in possible automation.
A
for micro amounts of COZ and H20 has long been needed t o improve the classical Pregl procedure. Recent thinking along this line has centered on gas chromatography because of its sensitivity and good resolution (2, 18, 20). Attempts to improve the micro carbonRAPID INSTRUXEKTAL METHOD
hydrogen determination by this technique have been inadequate for two reasons-gas chromatography does not currently have the accuracy or precision required; and the thermal conductivities of 02 and COX lie close together. The latter fact precludes the use of an 02 sweep in the combustion tube if thermal conductivity is to serve for the COz measurement. The alternative-ie., burning the sample in helium by oxidation with inorganic oxidants in order to measure COP in a more favorable carrier gas-is not attractive from a chemical point of view. Electroconductimetry is another new approach. Malissa (13) determined carbon and sulfur by measuring the change of conductivity produced by COz and SO2 in suitable absorbing solutions. Gel’man and coworkers a t the University of Moscow (4, 5 ) have likewise used electroconductimetry to determine COz and H20 in the micro C and H . In this technique, the HzO in the oxygen stream is separated from the CO2 by a dry ice-acetone trap before the latter is adsorbed for conductimetric measurement. The water is subsequently vaporized and converted to an equivalent amount of C 0 2 which is determined in the same manner. This conversion is accomplished b y the water gas reaction in which water is converted to CO by passage over carbon a t 1140’ C. The CO is then oxidized to COP with hot CuO. Haber and Gardiner ( 7 ) in their instrumental method employ an electrolytic determination of hydrogen as water. Carbon dioxide from combustion of the sample is chemically converted to water which is similarly electrolyzed, and calculation for carbon is based on the equivalent amount of hydrogen produced in the second electrolysis. Fur-
ther refinement of the method is still in progress in an effort to bring the precision of the carbon analysis within the required limits. This paper describes still another instrumental approach to the carbonhydrogen determination. A rapid micro method involving both infrared absorptiometry and thermal conductivity is utilized. The carrier gas mixture is collected to a constant volume and adjusted to a standard reference pressure for analysis. Instead of being collected in a cold trap, water is converted t o hydrogen by reaction with calcium hydride. The combustion gases are collected in three 100-ml. glass hypodermic syringes. Determination of C 0 2 is made with a nondispersive infrared gas analyzer (1,12, 16, 1 7 ) . This instrument responds only to CO2 molecules. I t is insensitive to NO1 and other combustion gases, which therefore cannot interfere with the carbon dioxide determination. Hydrogen, equivalent t o the water produced in the combustion, is determined by its unusual thermal conductivity. Since thermal conductivity is not a method that is specific for hydrogen, interfering gases such as SO8, SO2, or any of the halogens must be removed. This is accomplished by fixation upon hot silver gauze within the combustion tube. I n burning the sample, a rapid combustion technique (3, 16) is used which combines the “empty tube” arrangement of Korshun (8) or Kuck (10) with the mixed cobaltous-cobaltic oxide catalyst as reported by T‘eceFa (19). In the search for a reliable, rapid technique, examination of the combustion products with a CO nondispersive infrared analyzer indicated the presence of CO when either of the above methods was used separately, VOL. 34, NO. 3, M A R C H 1962
403
but the combination of both techniques reduced CO to a negligible concentration. APPARATUS
Combustion Train and Instrument Assembly. Figure 1 is a diagram of t h e combustion train a n d instrument assembly. First i n line after t h e conventional gas reducing value is a lorn pressure or "pan cake" regulator (regulator valve No. 70B, Matheson Co., E a s t Rutherford, ?;. J.). This regulator has a n adjustable range equivalent t o 0 to 50 cm. of water a n d is normally set t o control a t approximately 25 em. of water pressure. S e x t in the train is the CuO preheater. This furnace is used to oxidize any traces of hydrocarbon present in the oxygen supply. Following the preheater is a suck-back trap and mercury relief valve. Removal of combustion products formed in the preheater is accomplished by the gas purifying unit. This is followed by a flowmeter. Since the oxygen flow is controlled by the rate of withdrawal of the hypodermic syringe pistons, the prime usefulness of the flowmeter is to indicate leakage in the system when the pistons are stationary and the system is closed. Combustion Furnace. T h e cornbustion unit may be identified as a modified E. H. Sargent furnace of the "static directional program" type. Its modification and general mod? of operation have recently been described (11).
Combustion Tube a n d Filling. T h e transparent quartz combustion tube used is of t h e conventional type except for the addition of a S o . 16/15 standard taper, inner ground-joint at t h e mouth, a Xo. 12/1.5 spherical ball a t the exit tip, and a right-angled capillary side-arm attached about 12 (-111. back from t h e mouth. T h e layers of tube filling starting n i t h t h e exit end are the following: 7 5 mni. of Ag gauze, 120 mm. of mixed CuO and CoO-ConOs catalyst, and another 35 mm. of ilg. I n the 100-mm. unfilled space between the sample capsule and the silver gauze, the temperature is held a t 800" to 850" C. The silver gauze a t the exit end is allon-ed to extend beyond the furnace so that its temperature decreases to 300" to 400" C. Within this temperature range, the silver n-ill absorb halogms and sulfur.
I
CUO
t
sn-itches are so set that the total gas volume collected is 250 cc. The moving hypodermic plungers are lubricated n-ith MoSz. T o guard against possible gas leakage, the syringes are mounted vertically and are provided Ivith a mercury seal collar a t the top of each syringe barrel. Pressure Control. d two-liquid manometer (6) with a sensitivity of 1 0 . 2 5 mm. of Hg is used to establish a constant gas pressure within the sample cell of the infrared analyzer, since the response of the analyzer is proportional to the number of C 0 2molecules within the cell. Constancy of temperature, obtained by therniostating the analyzer, is likewise important in this regard. The manometer also serves as a leak detector for the ap-
a 'a A
I R SOURCES CHOPPER
n
MICROMETER
Gas Collecting System.
The conibustion products are collected in three 100-mi. glass hypodermic syringes whose plungers are operated by a mechanical drive. T h e gear box and 11-orm drive permit a choice of 1.5, 2.75, 4.25, 7.25, 12, 20, or 40 minutes as t h e filling time. Direction of movement for injection or n-ithdranal is controlled by a reversing switch on the motor. The for\T-ard and backward travel of the syringe pistons is accurately defined by two limit switches which automatically cut off the motor a t either end of the stroke. These
404
ANALYTICAL CHEMISTRY
~
d
oPncAL WEDGE
DETECTOR
1
n
I
I
SAMPLE CELL
w ;Go:! 1
I
CO2
AMpLJF/ER
l500uf
IO H V RECORDEr7
Figure 2. Carbon dioxide infrared g a s analyzer
paratus, 11-hen the system is ohserved under static conditions. Carbon Dioxide Infrared Gas Analyzer. For the carbon determination, a modified Liston Becker (Beckman) hlodel 15 nondispersive infrared gas analyzer is employed. The operating principle of this instrument has been explaiiiecl ( I 7 ) . Uriefly (Figure a), the instrument consists of two infrared sources which ~ ) n s sradiat'ion through separate samlile and reference cells to a pressure-scmitive detector filled with the gas to he detected. Radiation energy differences are convert,ed to an electrical signal by the microphone capacitance detector, electrically amplified, and are recordtd a s per cent COS. The device is both highly sensitive and selective to COS. To obtain high sensitivity over a wide range of CO, concentration, the instrument, was modified to operate by an optical null balance princ+e. =In optical wedge of 4.5 mni. diameter stainless steel is moved into the reference beam by a micrometer scren-. Use of the null balance principle largelj- eliniinates the effect of changes in amplifier gain as well as effects caused by vnriat'ion in source temperature. Full insertion of the rod across t'he 19-mm. diameter cell reduced the int'ensit'y of the reference beam by 38%. With a sample cell lengt'h of 19 mm , this 38% reduction of intensity is equivalent to approximately 3000 pg. of C (as COz). i1s a null point detector, the 100 microammeter on the analyzer amplifier may be used, or the null point may be observed on a 10-mv. recorder. I n this manner, the concentration of carbon can be determined a t a nominal value of 1000 pg. of C to an accuracy of 0.5 pg. of C. Hydrogen Analyzer. C'onccntra-
C02 CALIBRATION CURVE
METER
Figure 3.
PQ c
Thermal conductivity cell and circuit
tion of lij-drogen in the combustion gas is measured with a Veco thermal conductivity cell using 2000-011n1 thermistors. (Veco thermistor cell, Model 182, Victory Engineering Corp., Union, S . J.). The bridge circuit is shown in Figure 3 . Readings of Hz eoncentration are obtained by obserT-iag the bucking voltage required to null the bridge output. These readings are observed on a 1000-dix-ision Helipot precision potentiometer. The sensitivity is such t'liat each division is equivalent t,o 0.3 pg. of hydrogen. The null point of the bridge is observed on tlie same 1O-niv. recorder used for tlie C 0 2 mrasureinent . The thermal conductivity cell is not tlierniostated, but is held a t room tempcrature by immersion in a m t e r bath. The 200 niicroammetrr is used to check lmth the bridge and null current. Infrared Carbon Monoxide Analyzer. In addition t o the CO, a n d H2 analyzer., a n infrared CO analyzer i; used at times t o detect CO in t h e coiiihustion gases n-hich may have escaped conversion to C 0 2 . Such ap1ilication enables one t o compare the effects crf differtnt O2 flow rates a n d furnace beating rates. When used a t its highest gain and n.ith a sample cell lrngth of 32 mni., the instrument has a CO sensitivity equiT-alent to 1 pg. of carbon. PROCEDURE
Introducing the Sample. 2.5-nig. sample is neighed in a 60 X 6 nim. quartz capsule, aiid the c~apsule is transferrcd t o its place of ignition in t h e combustion tube by a n extension tube which is provided with a S o . 16 "diort length," inner member, standard t'aper joint t o fit t h e corresponding outer joint a t the mouth of the combustion tube. The capsule is pushed into the center of the first ignition furnace. During this insertion and adjustment', oxygen is let flow through the forward section of the combust'ion tube from the oxygen inlet side arm bo the mouth a t a rate of 100 cc. per minute. The conibust'ion tube is then closed with the ground glass stopper, and the rear section of tthe com-
Figure 4.
Calibration curve for the C 0 2 analyzer
buatioii tube from tlie oxygen inlet to the exit end is swept a t the same rate. After thus sweeping the combustion tube, a purging run of the whole system with oxygen is carried out including one operation of the syringes to ensure complete COz removal here also. The last step takes 31/2minutes. The Combustion. I n general, a 12minute combustion time provides a coni-enient interim for weighing t h e nest sample, although only 7 . 5 minutes are actually needed for t h e combustion. I n this short combustion period, the first 3 minutes are needed for ignition furnace KO.1 t o reach 850" C.; the second and third ignition furnaccs can be left on continuously. Even a shorter combustion time might be obtained b y keeping the first ignition furnace continuously hot and introducing the sample capsule b y electromagnetic manipulation. Unstable or volatile compounds may require a 21om-er combustion. This is obtained by reducing the heating rate of the ignition furnace and selecting the appropriate gear ratio in the syringe motor drive. Before starting the combustion, the combustion section of the system is checked for leaks. The T-stopcock a t the exit end of the combustion is turned to block off the analyzer system and connect the syringe reservoir. Gradual descent of the flonmeter ball to the bottom of the column TTill indicate a gas-tight system. It is now permissible to start the combustion b y turning on the electrical switches which control the furnace ignition units and the syringe motor drive. At the end of the combustion n h e n the syringes h a r e stopped, the oxygen flow through the combustion tube will slow down as the pressure in the system builds up to the level set b y the pressure control valve. When the flow has stopped, the T - stopcock is again turned-this time to permit a direct flow of oxygen through the combustion tube arid the analyzing system. Readings are now taken on the instruments as described below. A check on possible organic contamination in the oxygen supply is available at this point by comparing the C 0 2 background of the
-
oxygen stream passing through t'lie hot combustion tube ("hot blank") with that of the osygen drawn directly from the cylinder. As soon as the syringes have been cut off from the main line by the T-stopcock, air cooling of the combustion tube by an electric fan can be start'ed for t h e next combustion. T h e Carbon Determination. To obtain t h e final instrument reading, t h e analyzer system is closed off from t h e combustion tube, a n d about half t h e gas sample is expelled through t h e analyzers. T h e syringes are then stopped for a CO, measurement', a n d a n arbitrary reference pressure is established by means of the manometer and needle T-alve. The infrared analyzer is then balanced by adjustment of the micrometer screw controlling the wedge. The depth of penetration of the wedge-Le., the differcnce betn-een the initial or zero micronicter reading of the screw position and the final a measure of the carbon setting-is dioxide concentration in the aaniple cell. The number of micrograms of carbon (equivalent to the COS determined) which corresponds to the nuniber of turns of the micromet'er SCI'W is then read from a calibration curve. Calibration of the Infrared Carbon Dioxide G a s Analyzer. The calibration of t h e CO2 analyzer can be accomplished in two n-ays-by introducing known volumes of CO?into the gas collecting system, or by burning samples of known carbon content. I n t h e first met'hod, small gas volumes are introduced b y a therniostated micro gas buret or injected by a small hypodermic syringe int'o the oxygen stream ahead of the gas collecting syringes (2 mg. of C = 4.06 ml. CO, at STP). For routine analytical work, hon-ever, a n empirical calibration is more practical and more precise. In this case, the curve is established from instrument readings taken in the actual combustion of pure compounds. Figure 4 is a typical calibration tun-e. This curve represent's data obtained by both calibration procedures. Seiren of the points were obtained by absolute calibration (hypodermic injection) and VOL. 34 NO. 3, MARCH 1 9 6 2
405
eight from analyses of a standard test compound, 1,1,2,2-@traethylethanetetracarboxylate (ETC). Although the calibration is nonlinear in the lower region, it is linear for C values from 1000 to 2000 fig. The significance of the good agreement between the absolute and empirical calibration is examined later. From this curve, a n empirical calibration table for routine work is established in terms of micrograms of carbon corresponding to a specific number of divisions on the micrometer. For daily use, a table listing micrograms of C for every 25 divisions on the micrometer is convenient, and additional values between readings can be obtained by interpolation Hydrogen Determination. Hydrogen is determined in the gas stream with t h e conductivity cell as follows: T h e Helipot precision potentiometer dial is first set a t zero for the d r y oxygen stream, and t h e corresponding recorder reading is noted. After t h e syringes have been stopped in the course of the analysis and the thermal conductivity cell has been filled with a portion of their gas content, the Helipot potentiometer is adjusted to restore the recorder to its previous indication, and the new reading on the Helipot dial necessary for balance is noted. Sincc the thermal Conductivity cell has already been calibrated in terms of
Table I. Hydrogen Correction for Volume Shrinkage after CO:! Removal
Mg.
Sample C, % % H T o/o H F 4.423 53.00 6.88 7.01 3.555 52.66 6.94 7.04 3.261 52.59 6.85 6.95 3.097 52.79 7.07 7.16 3.080 52.60 6.94 7.03 2.593 52.a 7. 011 7. 1 7 1.891 53.09 7.09 7.15 1,522 52.83 7.10 7.15 1.731 52.87 6.94 6.98 0.742 53.10 6.93 6.95 0.698 53.87 6.98 7.00 Theory 52.83 6.97 % H F = H value as measured. % ' H r = H value after correction. Standard deviation for H = 0.086% H.
micrograms of H per scale unit on the Helipot dial, the number of scale units times the calibration factor gives the micrograms of H in the gas. Calibration of Thermal Conductivity Cell. Calibration of the hydrogen analyzer is established from readings obtained b y injecting known volumes of pure hydrogen into t h e gas receiving system or b y actually burning samples. T h e straight line Calibration obtained has a slope of 3.25 Helipot potentiometer divisions for 1 pg. of H. Full scale range is a function of the nulling current which is checked by varying the Helipot and observing the millivolt output on the recorder. For example, 200 divisions of the Helipot might give a response of 50 mv., or 150 divisions on the recorder chart paper. The potentiometer in the nulling circuit can be adjusted to obtain higher or lower sensitivities. Scrubbing out COz from the gas mixture before its arrival at the thermal conductivity cell requires a correction in the hydrogen calculation, For example, if a sample equivalent to 1000 pg. of C yields 2.03 ml. of C 0 2 upon combustion, removal of this COS from thc total volume of combustion gas collected will decrease the original volume from 2.50 to 248 ml. Such a decrease in volume corresponds to an increase in H2 concentration by 0.8%. Therefore, for every microgram of C removed as CO,, the actual H2 concentration must be reduced by a factor per microgram of C of 0.8 x to give the correct hydrogen concentration on the reduced volume basis. The number of micrograms needed here is calculated from the sample weight and the amount of C present, found by analysis. Calculation for the corrected % H thus becomes:
% H T = H ~ [ 1 . 0- (0.8 X lo-')] 'A H T = the true H value
n here
pg.
C
5~ HF = the measured H value pg.
C = pg. sample X % C
Table I shows typical H values before and after correction. DISCUSSION OF RESULTS
Table
II.
Analysis by Pyrolysis in the Quartz Capsule
Anisic Acid, yo C %" Mg. Sample 63.15 5.30 2.331 62.93 5.42 2.087 63.30 5.43 2.218 63.08 5.23 5.52 1 ,745 63.04 5.46 2.256 63.34 1.956 63.09 5.68 Mean 63.13 5.45 Relative accuracy for series C = 0.3 parts per 1000. H = 28 parts per 1000. Standard deviation: C = 0.158% C. H = 0.146% H.
406
ANALYTICAL CHEMISTRY
Reliability of Method. A substantial number of routine analyses have been carried out in this laboratory with the present method; results have been generally satisfactory. Typical data are shown in Table 11. These represent a few microanalyses of anisic acid. Combustion was made by pyrolysis in t h e quartz capsule. The rcliability of the method as reflected in the analyses of the particular test sample used is excellent. The relative accuracy of 0.3 part per 1000 for C, and 28 parts per 1000 for H, is well within the traditional limits of 5 parts per 1000 for C and 30 parts per 1000 for H.
Likewise, the good agreement shown in Figure 4 between the absolute calibration of the COz analyzer on the basis of injected gas volumes and the empirical calibration from actual analyses of the E T C sample is significant. This indicates that the use of calcium hydride as a reagent for water in the presence of COZ from the combustion is permissible. KO significant amount of C 0 2 is retained by the calcium hydride. This fact was confirmed by careful independent experiments which showed that a tube of fresh hydride does not retain any more C 0 2than t h a t equivalent to 0.25 fig. of C. Used hydride might have an uptake equivalent to 0.5 pg. of C. Even this is negligible. Consequently, the question of possible COZuptake by any calcium hydroxide in the hydride reagent is answered b y complete absence of defective C figures from this possible source of error. Absence of any C 0 2 uptake by trace calcium hydroxide must therefore be attributed to a combination of circumstances which might include the following : the relatively small amount of calcium hydroxide available for reaction; the fast rate of gas flow; and the estreme dryness of any gas in contact with the calcium hydride. I n connection with the first point, fresh calcium hydride is used daily so that only a minimum amount of calcium hydroxide can accumulate. Analysis of Compounds with Hetero Atoms. T h e present instrumental method readily lends itself to the analysis of organic compounds with a wide variety of chemical elements besides carbon, hydrogen and oxygen. Since the infrared analyzer used is specific for COz, it does not respond t o the oxides of other elements such as ?rT2O3, S O 2 , SO3, SOz, or halogen. These gases pass through the instrument without effect and thus do not interfere in the determination. Phosphorus, of course, is another matter, since nith many P-containing compounds, the Pz05 produced causes trouble \Tithin the combustion tube itself rather than in the C 0 2 analyzer. There it may form a thin film on the carbon residue from the sample and prevent the carbon from burning. I n the case of the H analyzer, the instrument is not specific for gaseous hydrogen. The thermal conductivity cell responds to other common gasesviz,, COz, KO2, or halogen. Consequently, the hydrogen determination depends upon complete removal of every interfering gas generated in the combustion. I n the present work, SOZ, SOs, and CI2 were removed by the hot silver in the combustion tube, and COZ was taken out by Ascarite after its passage through the CO, analyzer, leaving HPto be determined alone.
A careful study has not yet been completed with respect to the oxides of nitrogen. Presumably the acidic oxides will be retained by the Ascarite, whereas nitrous oxide, if formed, might pass through to the conductivity cell and interfere in the H determination. The presence of nitrous oxide is unlikely, however, since i t decomposes into its elements upon heating, and this should have occurred in the combustion tube. Of all the nitrogen oxides, nitrogen dioxide is most likely to interfere. Fortunately, this is generated in small amount when the ignition is done in the capsule; less than 0.5% of the nitrogen in the sample (9, 10) appears as nitrogen dioxide when N-compounds other than nitroso or nitro are thus ignited. For the latter two cases, a tube with some reducing agent such as pyrophoric copper (14) or zinc may be necessary in the line before the analyzer to reduce any NOz if present. Table I11 lists some analytical results for a few compounds with other elements besides C, H, and 0. For certain types of nitrogen linkage such as ethyl p-nitrocinnamate, 2-amino-45-bromopyridine, a-chloroacetamide, or thiocarbanilide, the appearance of theoretical H figures suggests t h a t NO2 formation is actually small as indicated above. Experience with Method. Experience with t h e infrared instrumental method for carbon has pointed out several significant sources of error in t h e Pregl carbon-hydrogen determination which have long been suspected by experienced workers in t h e field. Among such are: possible loss of carbon through incomplete conversion of CO t o COZ in t h e rapid combustion; t h e positive error from atmospheric COz when the combustion boat is inserted (3 to 11 pg, of C); and increasing organic content in the oxygen supply as the cylinder pressure drops (up to 36 pg. of CO, per 250 ml. of 0 2 ) . Errors of this sort can be easily investigated and traced out on the recorder \\hen the COz analyzer is used to monitor the combustion stream, CONCLUSION
The new instrumental method for carbon-hydrogen by infrared absorptiometry for COS and thermal conductivity for Hz compares favorably with the classical Pregl procedure, and results with it have been equally satisfactory. The work now reported presents several attractive research leads. For example, the principle of infrared absorptiometry can be extended to other microchemical procedures. Among these is the oxygen determination, which immediately suggests itself as the one most urgently needed. Application of
Table 111.
Analysis of Compounds with Hetero Atoms
Substance 2-Amino-4-methyl-5-bromopyridine
a-Chloroacetamide 2-Iodobenzoic acid 2-Chlorobenzoic acid p-Bromobiphenyl Ethyl p-nitrocinnamate Thiocarbanilide Cystine Anisic acid Anthracene
Per Cent C Theory Found 32.23 31.93 32.34 25.46 25.68 25.71 34.11 33.90 34.26 53. 73 53.68 62.25 61.82 60.10 59.72 68.32 68.40 30.10 29.99 30.01 63.19 63.15 63.07 94.04 94.34 94.17
either a CO or COz gas analyzer for this determination-i.e., the conventional Unterzaucher procedure-will strengthen the determination considerably b y eliminating the present problem of interference from by-product gases such as CSZ, (CN)z. PHI, or CCl,. Accurate CO measurement will also throw light on the controversial blank and its origin. Furthermore, trace oxygen, like trace carbon, can be accurately determined with the analyzer. Additional sensitivity for such work can be obtained b y lengthening the gas sample cell or increasing the pressure of the gas mixture under examination. A cell 340 mm. long, for example, Fill give a detectable limit of 0.02 pg. of
coz.
The carbon-hydrogen procedure also lends itself well to automation. For this type of operation, pyrolysis in the capsule is a better ignition technique than distillation from the boat. Present total analysis time is about 30 minutes with all operations being performed manually. It should be possible to reduce the time to 15 minutes b y making several steps automatic and decreasing the combustion time. The latter change probably offers the best possibility for any substantial saving in time, although some slight saving might accrue by introducing samples in quick succession mechanically. The most obvious way to reduce combustion time is to take smaller samples and burn them more quickly. This requires high temperature ignition furnaces which will heat and cool more rapidly than those now in use, or mechanical propulsion of the capsule into a furnace kept continuously hot. Since the sensitivity of the instrumental techniques is sufficient for the next lower order of magnitude-Le., for decimilligram samples instead of micro samples-the remaining problem is t h a t of weighing with the necessary accuracy. The recent appearance of two new ultramicro chemical balances, now commercially available is encouraging.
Per Cent H Theory Found 3.20 3.22 3.15 4.25 4.31 4.13 1.66 2.03 1.85 3.22 3.24 3.82 3.89 4.85 5.01 5.08 5.30 4.82 5.03 4.66 5.44 5.30 5.28 5.76 5.66 5.44
Consequently, a reliable decimilligram procedure for carbon-hydrogen is now possible. LITERATURE CITED
(1) Beckman Instruments Inc., Bulletin 1005, L/B Infrared Analyzer, Model 15A, Fullerton, Calif., May 1957. (2) Duswalt, A. A., Brandt, W.W.. ANAL. CHEY. - _.-32. 272 f 1960). (3) Egorova, N. ‘F., Zabrodina, A. S., Vestnik Moskov. Uniu. Ser. Mat., Mekh., Astron, Fzz., Khzm. 13, 235 (1958). (4) Gel’man, N. E., Korshun, M. O., Van, V.-v., Balashova, pu’. A,, Doklady Akad. A-auk S.S.S.R. 129, 1046 (1959). ( 5 ) Gl’mnn. - - - - - - - N. E.. Van. V.-Y.. Zhur. Anal. K h z k 1 5 , T h (1960). (6) Gilmont, Roger, I n d . Lab. 6 , 3 3 (1955). ( 7 ) Haber, H. S.,Gardiner, Nicrochem. J , in press. (8) Korshun, M. 0 , Gel’man, N., “Novye Metody Elementarnogo Mikroanaliza (New Methods of Elementary Microanalysis),” pp. 27-55, State Scientific Technical Publishers of Chemical Literature, Moscoil-Leningrad, 1949. f9) Korshun. M. 0.. IClimova. V. A. Zhur. Anui. Khim. 3, 176-80 (1948). (10) Kuck, J. A,, Altieri, P. L., Nikrochim. Acta ( K e n ) 1955, 1554. (11) Kuck, J. A., Berry, J. W7., Barnum, L. H., Microchem. J . 5, 193 (1961). (12) Liston, M., Andreatch, A. J., Beebe, C., I S A Journal4,118 (1957). (13) Malissa, H., “Proceedings of the International Symposium on Microchemistry, 1958,” pp. 97-104, Pergamon Press, London, 1960. (14) Meyer, F. R., Ronge, G., dngew. Chem. 5 2 , 637 (1939). (15) Pfund, A. H., Science 90,326 (1939). (16) Schoniger, W., “Proceedlngs of the International Symposium on Microchemistry, 1958,” pp. 82-92, Pergamon Press, London, 1960. (17) Siggia, Sidney, “Continuous Analysis of Chemical Process Systems,” pp. 76-110, Wiley, New York, 1959. (18) Sundberg, 0. E., Maresh, C., .4N.4L. CHEM.32, 274 (1960). (19) VeFefa, M., VojtBch, F., Synek, L., I
-
~
\ - I
\
-
I
Collection Czechosloz. Cheni. Coniwiuns.
25, 93 (1960). (20) Vogel, -4.&I., Qnattrone, J. J., Jr., ANAL.CHEM.32, 1754 (1960).
RECEIVEDfor review October 13, 1961. Accepted December 15, 1961. Pennsylvania State Symposium, August 1960. (International Conference on Microchemjcal Techniques, Pennsylvania State Cniversity, Cniversity Park, Pa.) VOL. 34, NO. 3, MARCH 1962
407
