Ash in Organic Compounds Determination by Microtechnique with Automatic Combustion A . R. NORTON, G. I,. ROI ER.
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R. hOEGEL. The Calco Chemical Company, Iiicb., Hound Brook, K. J .
0
The tubes are moved by a bcien, h', uhich 1s located in the ceiiter between the two bars, D, on nliich the tubes are s u p ported (Figures 2 and 3). The bais may be connected to the screws by small engaging pins, E, located on the sides of the bars, M hich make It possible to move the quaitz tubes independently 01 simultaneously. F is turned by a standaid, 2-speed governor controlled phonograph motor which is located in the box beneath the furnace and geared so that the doliest speed is 2.5-cm. (1-inch) travel in 10 minutes. The 2-speed control, G , makes it possible to double this speed, and the gokernor control, H , makes slight variations from these rates possible. Special-sized platinum boatb and cylinders are used, so that the large-sized samples (about 150 mg. ab contiasted to the usual microsample of 3 to 10 mg.) can easi11 be plated in them. The boats are 5 X 5 X 12 mm , and the cylinders are 50 mm. long and 7 mm. in diameter.
KE of the determinations specified for the analysis of pure organic materials is the ash or nonvolat'ile residue.
Usually a low percentage of ash is present, the quantity depending upon the purity of the product. I n the usual procedures 1- to 2-gram and sometimes 5-gram samples must be taken for analysis. I n commercial manufacture, this largesized sample is readily obtainable; but the main objection to its use is the long combustion period, and, consequently, the long time required for the completion of the analysis. Microtechnique applied to this problem resulted in reducing the elapsed time of the analysis without sacrificing accuracy or precision; furthermore, in order to utilize the time of the analyst to better advantage, the automatic combustion apparatus has been developed.
AishMicrodetermination
Apparatus
In the deteimination, saiiiples oi 100 to 150 nig are Heighed in the platinum boat on a niicrobalance nith the cylinder also included in the neighing. The empt v R eight of the boat nith the cylinder must be taken as acculatelj as posaible, but a sample of this size need only be v,eighed to the nearest 0.1 mg. The boat is then inserted In the cjliiider and tlie qlinder placed In the end of the quartz tube n ith the tube extending out of the furnace. A turn of a knob engages the tube ('airier to the moving sciert and nil1 continue to pull the tube into the furnace until the end of the tube is completelj in the furnace. Then the engaging pin runs off the end of the scien anti the tube moves no farthei A t this point the combustion has requiied 20 minutes and is complete. The cylinder and boat are removed, cooled for 5 minutes. m d rn eighed as accurately as possible.
The automatic apparatus is an adaptation of the original Pregl method (4). Figure 1 shows the side vievi and Figure 2 shows the top view with one of the quartz tubes similar to 3 removed. This apparatus provides for two quartz tubes which are drawn through the furnace, B , at a uniform speed, either separately or simultaneously. The samples are placed in the end of the tubes in platinum boats inserted in the Coombs-.Mber (1, 2 ) platinum cylinders. Oxygen is passed through the quartz tubes to aid in the combustion. The electric furnace, B , is \Tound in a manner somewhat similar to that, described by Hallett (3), except that 266.7 cm. (105 inches) of No. 30 ( 0.025-cm., 0.01-inch) platinum resistance n-ire, 63.4 ohms, are used. The four 0.32-cm. (0.125-inch) "thermal alumina" cores (furnished by the Thermal Syndicate Limited, 12 East 46th St., New York, N. Y.), on which the platinum resistance wire is wound, are mounted within a 2.54-cm. (1-inch) square Alfrax (trade name of refractory manufactured by the Carborundum Company, Kiagara Falls, E.Y.) tubing by fastening to end plates, also made of Alfrax. This in turn is encased in a nickelplated brass housing made from standard 5.08-cm. (2-inch) square stock tubing. Two holes in each Alfrax end plate act as supports for the quartz tubes as they travel into the furnace. A Varitran, C , located in the box beneath the furnace, is used to control the voltage applied to the platinum heating coils, so that any specific furnace temperature can be obtained. In the apparatus as used about 80 volts give a temperature of about 800' C. in the quartz tubes when they are completely in the furnace.
Ish Alacrodetermination The iiiacioniethod of ashing Ly means of $3Bunsen burlier is only mentioned in passing because i t is obviously not so reproducible, and in some cases not so accurate, as the muffle furnace macromethod. Just one example is cited, t o indicate what variations may be encountered. One sample on six consecutive analyses showed a variation of from -0.04 to a maximum of $0.29 per cent ash, the average being 0.12 per cent. The muffle macroprocedure ubed for coiiiparisoii with the microprocedure consists of weighing the samples in porcelain crucibles, ashing in an electric muffle a t a temperature cif 550" tci 600' C. for a period knclun to be long enough for complete combustion, then cooling, and neighing the ash. Because of the large sample, there usually is a gieat difference in the nature and time oi ashing various substances; theiefoie, it is difficult to be specific in regard to the time and the combustion teinperature This has to be learned by experience. I n the automatic microprocedure, the time of ashing is uniform for all materials because of the small sample employed and the siibstitutiori of oxygen for air.
Experimental Results The results obtained by the microand macroprocedures outlined above are given in Tables I, 11, and 111.
FIGGRE1. SIDEVIEW OF APPARATCS 121
*
ISDUSTRIAL AXD ENGISEERISG CHEMISTRY
lf2
TABLE 111.
TABLE I. METHYLENE BLUE Weight of Sample
Weight of Ash
Ash
Gram
Gram
%
1.000 1.000 1.000 1.000 1,000 1,000
RIacroprocedure, AlufFle Furnace 0.0047 0.0043 0.0046 0.0043 0.0042 0.0042 Av. 0.0044 Average deviation d 0 2 % hIicroprocedure Mg. 0.545 0.694 0.600 0.503 0.538 0.505 0.547 0.540 0.557 0.530 0.565 0.602 0.493 0.562 0.644 0.607 0.558 Average deviation * 0 . 0 2 ~ o
Mg. 125.7 128.9 136.5 123.3 116.6 135.0 119.2 136.8 137.; 126. i 134.8 144.9 123.3 129.9 133.0 135.0 Av. 130
0.47 0.43 0.46 0.43 0.42 0.42 Av. 0 . 4 8
Grams 2,000 2,000 2,000 2.000 2.000 2.000
0.43 0.46 0.44 0.41 0.46 0.37 0.46 0.40 0.41 0.42 0.4% 0.4% 0.40 0.43 0.48 0.45 0.43
.4sh
Gram
72
Average deviation * O . O l ~ o
0.10 0.12 0.09 0.08 0.11 0.11 .4v. 0.10
.Mg. 0.227 0.172 0.175 0.150 0.235 0.249 0 201 Average deviation +0 Ol'?'c
Blank Determinations The average blank of the platinum boat and cylinder vithout sample was *0.010 mg. based upon tvelve consecutive n-eighings n i t h 20-minute heating periods in the furnace. The average blank of the porcelain crucibles without sample used in the macromethod was *0.0004 gram based upon the alternate heating of six Coors KO. 1 crucibles of 30-cc. capacity in a muffle for about 7 hours at 500" to 600" C., cooling, and weighing on four consecutive days. It is calculated from the above that, considering the size of samples taken, the reproducibility error of weighing of the tare, expressed in terms of per cent ash, varies from *0.006 to *0.008 per, cent in the microdetermination of the three FIGCRE2 . TOP V I E W O F APPARATUS
2,000 2.000 2.000 2.000 2 000 2,000
hverage deviation - O , O l ~ o
132.7 146.2 152. , 148.3 135 3 140.0 Av. 143
.4-h
70 0.0R
0.03 0 02 0.02 0.04 0.03 Av. 0 . 0 4
Ma. 0,046 0.048 0.030 0,03: 0.040 0.037 0.039 Average deviatlon *0.0047c
0.13 0.14 0.12 0.11 0.15 0.14 0.13
0.03: 0.033 0.020 0.024 0.030 0.027 0.028
materials used; whereas, in the case of the macromethod, the corresponding values vary from *0.02 to *0.04 per cent.
Speed of Analysis For the ashing of one sample, the actual working time of the micromethod has a slight but not marked advantage over the macromethod; however, when the total elapsed time is considered, the macromethod is aliout 14 times as long as the micromethod. For six samples, the actual working time for the automatic micromethod is still equal to that of the muffle furnace macro-
TABLE IV. COMPARISON OF TIMEREQUIRED .Ictual Working Time For One Sample Min. AIufFle macromethod Automatic micromethod
Microprocedure Mg. 177.6 122.5 149.6 140.4 156.6 171.9 Av. 153
Gram8
Microprocedure
Weight of Ash
RIacroprocedure, Muffle Furnace 0.0020 0.0024 0.0018 0.0016 0.0022 0.0023
SULFAXILAMIDE
Weight of Ash Gram Alacroproceduie, 3Iuffle Furnace 0.0012 0.0010 0.0004 0 0004 0.0008 0.0006
Weight of Sample
MQ.
TABLE 11. GLOBEPEARL STARCH Weight of Sample
YOL. 12. NO. 2
T o t a l Elapsed Time Iiours 7 0.5
15 10
Ratio
llacro Micro
~
=
E
1
For Six Samples
Hours Aluffle macromethod Automatic micromethod
1.5 1.: natio
8 1,: Macro - 2 llicro 1
ANALYTICAL EDITIOK
FEBRUARY 15, 1940
123
An automatic electric microfurnace is described in which two samples may be ashed in a stream of oxygen either simultaneously or individually. I n order that the weight of the ash may not be too small, the analytical samples employed are larger than those customarily used even in semimicroprocedure but much smaller than those used in the macroprocedure. The saving of time resulting from this automatic modified microprocedure is considerable when compared to that required by the macromethod, even using the muffle furnace which allows the ashing of many samples at one time.
-Acknowledgment
FIG~JR 3E
method: however. when the total elapsed time is considered the macromethod'is about five times as long as the micromethod. Table Iv shows the comparison of time necessary for analysis tiy the two methods.
Summary Data are presented to contrast the usual macroprocedure regard to precision and modified microscheme With speed.
The authors wish to acknowledge the assistance of TT, L. Hattcin in the design and construction of the automatic ashing furnace.
Literature Cited (1I ;ilher, H. K., .lfikrochemie, 18, 95 ( I 935). ( a ) Coombs, H,I , , Biochem, J , , 21, 404 ( 1 ~ 2 ~ ) . (31 Hallett, L. T.. ISD. ESG.CHEW,Anal. Ed., 10, 101-3 (1938). (1) Roth. H., "Quantitative Organic Analysis of Fritz Pregl", by E. B. Daw, p. 136, Philadelphia. P. Blakiston's Son & Co., 1937. PRESEYTED before t h e Division of lMicroohemistry a t the 98th Meeting of t h e American Chemical Society, Boston, hlais.
Modification of Rauscher's Method for Determining Mercury ANTHONY SHUKIS, JR., AND RALPH C. TALLMAN Schieffelin & Co., New York, N. Y.
R
AUSCHER'S method ( 1 ) for the determination of mercury by reduction of its compounds with mono- or diethanolamine is generally satisfactory. However, certain difficulties have been encountered in its application as originally described which may be obviated by the modifications outlined belon-. The changes do not apply to the gravimetric determination. The principal source of error in the original method seems to be that,, despite all precautions, tiny particles of mercury tend to remain on the surface of the amine after reduction, held there presumably by surface tension. They are drawn off during the siphoning process anti never become part of the main globule of mercury. The difficulty can be overcome in the folloning manner: The sampie is weighed directly into a tared centrifuge tube of 15-ml. capacity, and the digestion and ail subsequent manipulations are carried out therein instead of in a Pyrex test tube as provided for by Rauscher. At the end of the digestion period, the tube and its contents are centrifuged for 5 minutes at about 2800 r. p. m. In t h i s n-ay, all the floating particles become combined viith the main globule in the bottom of the tube. The supernatant liquid is then sucked off, water is added t o wash the globule of mercury, and the tube and contents are centrifuged again. The washing operation may be repeated as many times as desired. Solution of the mercury and its determination by titration are carried out in general as indicated in the original method. In
order to complete the reaction in the same centrifuge tube, hobever, 0.1 to 0.2 N thiocyanate solution is used to avoid the large volume necessitated by the -maker solutions uwd by Rauscher. Accuracy In titration is achieved by the use of a microburet graduated in 0.02 ml. Samples for analysis x-eighing 100 to 200 mg. Ti-ere found the most satisfactory, the exact amount taken depending on the quantity of mercury believed to be present. Immersion of the lower part of the tube in an oil bath heated to 170" to 180" C. during digestion was more satisfactory than direct heating with a burner, since bumping and spattering are avoided in this way. A 15-minute digestion period ensures more complete reduction of the mercury compound than the %minute period originally prescribed. With the modifications above described, the method has given results entirely comparable with those reported by Rauscher in his original paper, over a wide variety of compounds. It remains a simple, short, accurate, and reliable general method of determining mercury. At the same time, sources of error are minimized by ensuring complete recovery of all mercury through centrifuging, and b y avoiding any loss in transfer.
Literature Cited (1) Rauscher, ISD. E m . C H E x . , dnal. Ed.. 10, 331 (1938).
