312
ANALYTICAL EDITION
a high pH in most cases, while the reverse would be true for acid sewages and wastes. That these procedures are not sufficiently regulated so that an accurate measurement of free ammonia nitrogen is possible will be shown later. The work of Phelps in 1904 (2), upon which the caution in Standard Methods relative to the hydrolyzing action of sodium carbonate was based, has shown that distillations carried out with the addition of sodium carbonate (concentration not stated) give a part of the nitrogen from certain nitrogenous compounds. Urea gave 2.0 per cent of the total nitrogen present, gelatin 1.4 per cent, casein 0.68 per cent, egg albumen 3.2 per cent, and peptone 1.4 per cent. Phelps also showed that sodium carbonate was active in the breaking down of some of the insoluble compounds. Samples of sewage effluents which had first been filtered through paper to remove the insoluble portion gave 7.0 per cent less free ammonia upon distillation with sodium carbonate than those which had not been filtered. Recognizing the wide divergence in the pH values of liquids from which free ammonia nitrogen is recovered, it was decided to determine the effect of various alkaline intensities of the solution on the recovery of this fraction and evaluate the errors if such exist. The first point of attack was to determine the lowest possible pH a t which free ammonia nitrogen in the form of chloride and sulfate could be quantitatively recovered, and the second to determine what amounts of organic nitrogen would be liberated at this pH and a t higher pH values. I n other words, would it be practical to adjust the distillation mixture with a buffer and recover quantitatively only the free ammonia nitrogen?
VOl. 3, No. 3
Only when the solution was adjusted with the buffer to the pH value of 7.4 did quantitative recovery exist. It seems safe to predict that any free ammonia distillation conducted below approximately this value will be in error proportional to the pH depression, initial and final. Effect of Kind and Quantity of Adjusting Solution
After the minimum pH value for the complete recovery of free ammonia nitrogen was determined, it was then possible to measure what effect the kind and concentration of the adjusting solution had on the recovery from solutions of these ammonium salts. I n these experiments a constant amount of ammonium salts was used and the quantities of the phosphate buffer pH 7.4 and the 5 per cent sodium carbonate solution were varied. The results are given in Table 11. Table 11-Comparative Effect of Phosphate Buffer a n d S o d i u m Carbonate Adjusting Solution
I
0.5 M PHOSPHATE BURRER pH = 7.4 VOl. Initial Final Nitrogen Rebuffer pH pH found covery ~
Mg.
CC.
I
SODIUM
5% Vol. soh.
-~
%
CARBONATE SOLUTION,
Initial Final Nitrogen ReDH PH found covery
-
Cc.
%
Mg.
AMMONIUM SULFATE PRESENT EQUIVALENT TO 20 MG. NITROGEN
0 1 2 5 10 20 30 40 50
7.0 7.2 7.4 7.4 7.4 7.4 7.4 7.4 7.4
4.9 3.8 4.7 6.4 6.8 7.2 7.2 7.3 7.3
1.4 5.9 12.0 19.35 19.6 19.8 19.8 19.8 19.8
7.0 29.5 60.0 96.8 98.0 99.0 99.0 99.0 99.0
0 0.5. 1.0 1.25 1.5 1.75 2.0
ILO.0
7.0 8.6 8.9 9.0 9.1 9.2 9.4 9.Sa
4.9 5.2 6.0 6.2 9.8 9.8" 9.8"
1.4 8.2 14.3 17.5 19.6 19.7 19.8 9.8a 19.8
7.0 41.0 71.5 87.5 98.0 98.5 99.0 99.0
AMMONIUM CHLORIDE PRESENT EQUIVALENT TO 20 MG. NITROGEN
Adjusting Solutions Sodium carbonate, 5 per cent solution. Phthalate buffer 0.5 M. 500 cc. 1 M potassium acid phthalate X cc. 1 M sodium hydroxide. Diluted to 1000 cc. Phosphate buffer 0 5 M. 500 cc. 1 M potassium acid phosX cc. 1 M sodium hydroxide. Diluted to 1000 cc. phate
+
+
Recovery of Free Ammonia Nitrogen from Ammonium Sulfate
I n order to determine the percentage of recovery of free ammonia nitrogen at stated constant pH values, the distillation of aqueous solutions of known quantities of ammonium sulfate was conducted. Adjustment was made by using a n appropriate buffer of phthalate or phosphate depending upon the pH value desired. To the flask were added the solution of the ammonium salt, 50 cc. of 0.5 M buffer solution, and enough ammonia-free water to make the total volume amount to 250 cc. An initial colorimetric pH reading was made before distillation was begun and a final pH reading recorded on the residual liquid in the flask after distillation was completed, A 180-cc. portion of the distillate was collected under 25 cc. of N/14 acid and the excess acid titrated with N/14 sodium hydroxide using methyl red as an indicator. The results are given in Table I. Table I-Effect
of pH on Recovery of Free Ammonia Nitrogen f r o m A m m o n i u m Sulfate
NITROGEN INITIAL IN
SAMPLE
PH'
FINAL PH
*ITRoGEN
FOUND ME.
a
RECOVERY
%
All samples buffered with 50 cc. of appropriate buffer to initial pH.
It will be seen that a t an initial pH of 4.9 only 11 per cent of the nitrogen was recovered, with increasing quantities as the pH value of the distillation mixture was made higher.
0 1 2 5 10 20 30 40 50 4
6.8 7.2 7.4 7.4 7.4 7.4 7.4 7.4 7.4 pH greater than this point but not determined.
From these results it is seen that, using either the phosphate buffer or the sodium carbonate solution, the concentration of the adjusting solution must be great enough to maintain the pH of the solution at approximately 7.4 or above to obtain quantitative recovery of the ammonia. While a, small amount of sodium carbonate is capable of raising the initial pH to the quantitative point, the final pH drops through a wide range owing to the slight buffering action of this salt. With only 1 cc. of a 5 per cent solution of sodium carbonate, the initial pH is 8.9, somewhat above the quantitative point of 7.4, with the phosphate buffer, but the final pH is seen to drop to 6.0 with only 71.5 per cent recovery. It is evident that it is necessary to raise the initial pH to above 9.0 with sodium carbonate in order to have the final pH above the quantitative point and the recovery satisfactory. With the use of the phosphate buffer, a concentration above the necessary amount shows no effect on the initial or final pH with the recovery satisfactory. It is also evident that if an excess of sodium carbonate is used, the recovery is satisfactory but the initial and final pH values are very high. Recovery of Free Ammonia Nitrogen from Organic Nitrogenous Compounds
In order to determine what amounts of organic nitrogea would appear as free ammonia, several organic nitrogen compounds were subjected to distillation after preliminary adjustment to a pH of 7.4 and higher pH values with phosphate buffer and sodium carbonate solution. Aqueous solutions of a number of such substances of a high degree of purity were tested. The results appear in Table 111.
July 15, 1931
INDUSTRIAL AND ENGINEERING CHEMISTRY Notes on Method
PREPARATION OF SAMPLES-If convenient, it is suggested that a roller mill be used in place of a glass muller for the dispersion of the carbon black in the varnish medium. The authors have adopted the procedure of subjecting the paste (carbon black 1, varnish 10) obtained from a preliminary mixing to three runs of 3 minutes' duration on the roller mill. The sample thus prepared was used for the test. CALIBRATION OF PImTs-It is very necessary, when more than one pipet is employed for this test, that every precaution be taken to assure unifowity in the magnitude of the drops delivered by them. The volume of ten drops from each pipet used should be carefully determined, and any necessary adjustment be made in the bore of the tip so as to assure the same volume being delivered from each. TEMPERATURE OF TEsri-our findings indicate that the higher the temperature a t which the test is conducted the greater will be the differentiation between the flow characteristics of different inks (Figure 2). The curves A', A2, and Aa represent the flow in millimeters obtained on a longflow carbon black at go", 45", and 30" C., respectively, while B1,B2,and BS show the results obtained a t the same temperatures for a short-flow carbon black, from which it will be noted that the greatest difference was obtained at
31 1
60" C. A temperature of 45" C. was selected as one well served by the limitations of the size of the glass plate, and at the same time offering a range of flow between the carbon blacks likely to be examined, sufficient to allow proper classification. I n addition, the seasonal changes in atmospheric temperature are less likely to effect the accuracy of the test if carried out throughout the year at a temperature slightly exceeding that experienced in the hot summer. TIMEOF TEST-The flow time adopted for the test was selected on the basis of that point in the time-flow curves (see Figure 2) at which the effect of time on the amount of flow was uniform and at the same time gave the widest possible range of difference between samples. Seven minutes best satisfied these requirements. EVALUATION IN POISES-It may be desirable to have flow information in terms of poises. A translation of results can be easily accomplished by determining this value on a standard sample with a Stormer viscometer, and running this standard with the unknown by the method suggested in this paper. By comparison of the flow values in millimeters, the equivalent in poises for the unknown may be calculated. If necessary, the graduation of the glass plate may be made in terms of poises by the same method.
Distillation of Free Ammonia Nitrogen from Buffered Solutions' M. Starr Nichols and Marian E. Foote WISCONSIN STATELABORATORY OB HYGIENE, UNIVERSITY OB WISCONSIN, MADISON, WIS.
A constant pH of 7.4 or above is necessary for the quantitative recovery of free ammonia nitrogen from aqueous solutions of ammonium chloride and ammonium sulfate. When a sodium carbonate solution is used to adjust the pH, it is not possible to determine the minimum quantity necessary to maintain a pH at or just above 7.4. In fact, if such an adjustment is attempted, either the final pH will fall below the quantitative point of 7.4 and recovery be incomplete or an excessive alkaline intensity will be produced and an appreciable quantity of organic nitrogen will be included in the free ammonia nitrogen result. A phosphate buffer of pH 7.4 has been shown to permit
I
F THE free ammonia and organic nitrogen values of
sewage and industrial wastes are to have real significance, it is imperative that a quantitative separation of these constituents be effected. For the evaluation of free ammonia, the usual procedures are either direct nesslerization or distillation. Direct nesslerization offers distinct advantages in some cases bht it is not applicable to all wastes. When free ammonia nitrogen is to be determined by distillation, a standardized procedure should be followed which can be applied to various wastes to separate this form of nitrogen completely with the release of little or no organic nitrogen. The Standard Methods of Water Analysis of the American Public Health Association (1) recommend the addition of 0.5 gram of sodium carbonate to waters which are acid to methyl orange in the determination of free ammonia nitrogen. Received April 8, 1931. Presented before the Division of Water, Sewage, and Sanitation Chemistry at the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 to April 3, 1931.
quantitative recovery of the free ammonia nitrogen from ammonium sulfate and chloride and yet not yield any appreciable hydrolytic property toward pure nitrogenous compounds. In most of the wastes studied it was found that 01 greater recovery of free ammonia nitrogen was obtained when a phosphate buffer of pH 7.4 was used than when there was no adjustment of the pH. While it is not possible to state that a phosphate buffer of pH 7.4 does not act slightly on the organic compounds of nitrogen in wastes, its action is materially less than that of sodium carbonate.
The range of methyl orange extends from a p H of 3.1 to 4.4. A water having a pH of from 4.4 to 6.8 would be sufficiently alkaline to comply with the procedure given in Standard Methods. Furthermore, if a water were acid to methyl orange and 0.5 gram of sodium carbonate were added, this quantity would produce a pH of varying alkalinity, depending upon the water, up to the intensity of 0.02 N sodium carbonate a t the beginning of the distillation and of about 0.1 N a t the end. The pH of 0.1 N solution of sodium carbonate is 11.6, Again we find in Standard Methods (page 70) the caution that sodium carbonate added to sewage and effluents may give high ammonia nitrogen through hydrolysis of the nitrogenous matter; under section 4,Procedure (page 71), it is stated that if acid to methyl orange, neutralize with sodium carbonate solution. This is done, presumably, with the thought that only enough sodium carbonate solution should be added to produce ap alkalinity measured in terms of p H of about 4.4. The procedure given for water would produce
ANALYTICAL EDITION
314
Vol. 3, No. 3
Copper Determinatron in Organic Matter‘ Stefan Ansbacher, Roe E. Remington, and F. Bartow Culp SOUTH CAROLINA FOOD R E S E A R C H COMMISSION AND
DEPARTMENT OF NUTRITION OF THE M E D I C A L CHARLESTON, S. C.
COLLEGE OP
THE STATE OF SOUTH CAROLINA,
A critical study has been made of methods for the the xanthate or the Biazzo S I N C E copper is found micro-estimation of copper in biological materials. method difficulties and errors to play a physiological Organic matter can be destroyed without loss of are encountered. role, chemists have been copper in small samples by wet combustion, using The xanthate method as o b l i g e d t o find ways and sulfuric acid, perchloric acid, and fuming nitric acid. developed by S u p p l e e and means of estimating, not only Larger samples can be burned in silica dishes at a Bellis is intended to-be ap.approximately but quantitatemperature not above 400’ C., followed by treatment plied to the determination of tively, the small amounts of with fuming nitric acid. copper in milk only. Asam$copper normally present in The use of ammonia to remove iron and other metals ple of 15 grams of a drum ’organic matter. leads to results which are too high. Precipitation of process dried milk was anaThe electrolytic determicopper by hydrogen sulfide is quantitative if acid conlyzed following exactly the nation of copper g e n e r a l l y centration is properly controlled, some sulfur is pred i r e c t i o n s of Supplee and u s e d i n c h e m i s t r y is uncipitated with the copper and suitable precautions are Bellis. The value obtained doubtedly the most accurate taken in the filtration, washing, and re-solution of the was 4.0 y copper per gram method which could be emprecipitate. (ly = 0 001 mg.) for the comp l o y e d , b u t it can be apOn the solutions so prepared, the xanthate reagent bined filtrates from the amplied to biological m a t e r i a l tends to give high results, the error being least if from m o n i a precipitations. The only when a huge amount 100 to 200 y of copper are present in the solution. s e c o n d a m m o n i a precipi‘ofsample is taken. That is The carbamate reagent is applicable to solutions contate, after t h o r o u g h washin some cases (e. g., a spleen taining about 50 y of copper, giving results agreeing ing, was dissolved, treated of a new-born rat) imposvery closely with those obtained by the chromotropic with hydrogen sulfide, sible, and in other cases it reagent, which can be used to estimate quantities as and 0.2 y per gram of copis impracticable, as a great small as 2 to 3 y with an accuracy of 0.5 7. per recovered by the chromoamount of organic m a t t e r The Biazzo reagent is most reliable for 50 to 150 y of tropic m e t h o d . The total must first be destroyed. copper, but tends to give results which are slightly low. a m o u n t of c o p p e r f o u n d The credit for having deThe method of preparing and using the chromotropic was, t h e r e f o r e , 4.2 y per seloDed a method ten veare reagent is described in full. gram, but when the entire ago,hhich is still used, goes to a n a l y s i s was made by the Bupplee and Bellis @a),who applied to milk Scott and Derby’s (19) method for detecting, chromotropic method, only 1.5 y per gram were recovered. with potassium ethyl xanthate, traces of copper in salts That this latter value is correct is shown by the recovery of CrystalliEed in copper containers. This method, usually known amounts of copper added before destruction of the called the LLxanthate method,” was found not to be sufficiently organic matter. Precipitation with ammonia is proposed by accurate for the estimation of copper in all kinds of biological Supplee and Bellis to separate from iron without resorting to material by Elvehjem and Lindow (8). These investigators hydrogen sulfide, thinking that it is not possible to precipitate developed, a t about the same time as Schonheimer and completely small amounts of copper from an acid solution with Oshima (18),a method by use of the Spacu ($1) reaction (for- hydrogen sulfide. The results obtained by this method as mation of a copper-rhodanine-pyridine complex). Usually this modified by Drabkin and Waggoner are much lower, the method is called the “Biazeo (2) method.” A few months most important reason being that by adding pyrophosphate later, Callan and Henderson (a) suggested substituting sodium the removal of iron by ammonia is made more quantitative. diethyldithiocarbamate for potassium ethyl xanthate in the Iron interferes so markedly that about the same color was xanthate method. This method is called the “carbamate obtained with the xanthate from 50 y of iron alone as from method.” The next year, 1930, Kleinmann and Klinke (IS) 12.3 y of copper alone. Actually, hydrogen sulfide is conpublished another modification of the Biazzo method, and sidered in analytical chemistry to be the best means of separatCherbuliez and Ansbacher (6) proposed a titrimetric method ing metals of the second from those of the third group. I n by the use of nitrosochromotropic acid, called in this paper working with very small amounts of copper, the acid concen“chromotropic method.” tration must be more carefully controlled, and sulfur should During the last year some very promising reagents for the be precipitated to adsorb and carry down the cupric sulfide. detection of copper have been suggested by Feigl and Kapu- A few drops of nitric acid will produce sufficient sulfur to prelitzas (9, IO), Kolthoff (IC), and Sisley and David (20). vent a colloidal solution. That the copper sulfide precipitaWhereas Kolthoff states that by the use of p-dimethylamino- tion is quantitative is also shown by Gebhardt and Sommer, beneyridenerhodanine the amount of copper can be approxi- who apparently even succeed in collecting it quantitatively by mated, it is found that the color change is not sufficiently chloroform. sensitive for quantitative work. Sisley and David’s direct The reasons that the copper sulfide precipitation may somegreen B is very sensitive for the detection of copper, but the times not be quantitative are: (1) that the acid concentration technic is not suitable for quantitative determinations, is too high; (2) that the amount of sulfur precipitated is not More recently, new modifications of the xanthate and sufficient to adsorb copper sulfide; (3) that the time allowed Biazzo methods have been proposed-i. e., those by Drabkin for settling is not sufficient; (4)that the use of paper filters and Waggoner (7) and Gebhardt and Sommer (11). When is accompanied by losses; and ( 5 ) that the wash water used is one tries to recover known amounts of copper by either not acid enough. That the precipitat,ion of copper with hydrogen sulfide can 1 Received April 18, 1931. I
~
