Table 1.
Compounds Tris-1-(2-methy1)aziridinyl-
phosphine oxide
Method Thiosulfate
Indicator Assay Average Std. dev. Potentiometric 96.79
r . .
I ris-1-( "-met,h?.l):tairidiri?1- T h i o q anate Hrnmothyniol hluc phosphinc cxide
Phenyl-bis-1-( 2-methyl)aziridinylphosphine oxide
'I'hioc.y:matc
Trimesnyl-I-( 2-ethyl)aziridine
Thiocyanate Phenol red
Tris(2-methy1)aziridinyltriazine
potassium thiocyanate; however, the salt does not interfere with the determination. The average value for the analysis of tris-l-(2-methyl)aziridinylphosphine oxide is higher when analyzed by the thiosulfate method than when analyzed by the thiocyanate method. An explanation for the difference is that thiosulfate is decomposed in acid solution with the loss of hydrogen ion, as a result of hydrogen sulfide evolution. With the loss of hydrogen ion, a higher assay is obtained . Table I shows the results of the determinations and expresses the precision as standard deviation.
Assay of Aziridinyl Compounds
RIixcd
Thiocyanate Bromuthymol blue
97.49 96.98 97.32 97.35 9G,20 96.17 96.18 96.15 96.09 91 .G8 91.82 91.35 91.62 91.53 84.72 85.05 84.94 85.23 85.30 87.72 87.77 87.55 87.81 87.71
97 ' l8
*' '290
96.35
f0.0.12
o1
10,175
85.04
i0.232
ACKNOWLEDGMENT
The author thanks the AerojetGeneral Corp. for permission to publish this work and to P. Stanley Gisler for his suggestions and assistance in the determinations.
*0.099
LITERATURE CITED
gives a pink color when added to the potassium thiocyanate solution. The color causes no difficulty in the determination and actually helps to anticipate the end point. When a pink color develops, the procedure is changed so that the mixture is titrated without the indicator until near the end point, where the pink color begins to fade. The
(1) Allen, E., Seaman, W., ANAL.CHEM. 27, 540 (1955). (2) Epstein, J., Rosenthal, R. W., Ess, R. J., Zbid., 27, 1435 (1955). (3) Meguerian, G., Clapp, L. B., J. Am. Chem. SOC.73, 2121 (1951). (4) Powers, D. H., Jr., Schatz, V. B., Clapp, L. B., Zbid., 78, 907 (1956). (5) Rosenblatt, D. H., Hlikka, P., Epstein, J., ANAL.CHEW.27, 1290 (1955).
indicator is then added and the titration continued. For the samples assayed, the only reaction time necessary before backtitrating with base is a short mixing period of approximately 20 seconds, Frequently a precipitate of potassium p-toluene sulfonate will form upon the addition of p-toluene sulfonic acid to
RECEIVEDfor review February 15, 1963. Accepted April 15, 1963.
Elimination of Chloride Interference in the Chemical Oxygen Demand Test RICHARD A. DOBBS and ROBERT T. WILLIAMS Robert A. Taff Sanitary Engineering Center, 4676 Columbia Parkway, Cincinnati 26, Ohio
b A method i s described for measuring the chemical oxygen demand (COD) of waste water that eliminates the necessity for a chloride correction. The method involves the addition of mercuric sulfate to the sample forming a soluble mercuric chloride complex that completely resists oxidation under the conditions of the C O D test. The mercuric sulfate modification of the C O D determination permits more rapid testing, is more accurate, and extends the usefulness of the test. Test results are reported on pure organic solutions and various sewage effluents containing known additions of chloride.
T
RECOMMENDED procedure ( I ) for determination of chemical oxygen demand has definite limitations. The values obtaincd reflect thc oxitla-
HE
1064
ANALYTICAL CHEMISTRY
tion of both organic and oxidizable inorganic materials contained in the sample. It is necessary to apply a theoretical correction for the presence of chlorides. Moore, Kroner, and Ruchhoft (4) have reported quantitative oxidation of chlorides over the range 250 to 20,000 mg. per liter when 50% by volume of sulfuric acid was used with 0.25N potassium dichromate. The authors have obtained identical results up to 4000 mg. per liter of chloride. It should be emphasized, however, that quantitative oxidation of chlorides in a pure system does not have as a corollary a quantitative effect in the presence of organic matter. This aspect will be discussed in more detail in a later section. Moore and Walker ( 6 ) latcr found that chloi idc oxidation varied from 02
to 1027, in synthetic samples containing 8 to 350 mg. per liter of chloride. I n the presence of silver sulfate, approximately 40 mg. per liter was oxidized at the same chloride levels. These results were obtained using 0.025N potassium dichromate. The extent to which chlorides are oxidized when 0.25N potassium dichromate is used and when silver sulfate is added immediately has been determined by the authors. The results are shown graphically in Figure 1. I n contrast to the limiting 40 mg. per liter oxidized with 0.025147 potassium dichromate reported by Moore (6), the amount of chloride oxidized increases continuously as the chloride concentration increases. Thus, the addition of silver sulfate, at the start of the digestion in the conventional procedure on samples containing morc than 100 rng. pcr litcr of chloride,
loo0
*
L 7 .-I I c1-
1000 m p / 1
-
x 4
300r
;7 5 0
-
-9,. I-
;7 500
.-
1
2z
:0 8:
//'
1' I
3,1-,
I
/'
A 1
i ;L'" ~
.L
_ _ ! L
+
0.226
'I'hcsc results indicate that significant errors can occur in the COD test when 100 mg. per liter or more of chlorides are present. Errors are particularly pronounced when high-chloride lowCOD samples are testcd and when highchloride high-COD samples are analyzed. l'he data shown in Ij'igure 2 were subjected to a statistical analysis. The best mathematical represcntation of the data is a straight line 1% hose equation, by the method of least sqiiaxes, is: 1~ = 13.0 0.0072; u = & 21 (1)
+
2
250
-
-100mpIl
- .
.-i..-1---i.-. 1~ -..I
will lead to error, since the amount of chloride oxidation is variable. In addition to the unknown degree of chloride oxidation when silver sulfate is addctl immediately, the following disadvantages are encountered: the loss of silver ion by precipitation results in less catalytic activity; and the resultant turbidity can cause some difficulty in determining the end point. To avoid these dificulties, the usual procedure has beel: to oxidize the chlorides by digesting the sample for 45 minutes without silver sulfate; then the catalyst is added and the required digestion period is completed. Under these condition3 a separate chloride analysis must be performed and a quantitative chloride correction applied. The current investigation resulted from data showing that a quantitative correction for chloride content has yielded negative COD values for some waste water samples. The effect of chlo-ide on the COD measurement was investigated. The COD values for a rumber of sewage effluents were measured. Chloride was added to increase the concentration by 100, 500, and 1000 ing. per liter and the COD was again measured. The results are shown graphically in Figure 2 , where the milligrams per liter of chloride oxidized was plotted against the original COD value of the effluents. The milligrams per liter of chloride oxidized \vas calculatPd as follows: COD original C1- - COD original
~--
-4-
s
1
nliere y
=
- -_I
0
!=
I25
-
GI-
375
500
COD measured, nig./litcr
5 = z1
+ 0 . 2 2 6 ~nig./liter ~
Table 1. Effect of Chloramine Cycle on Measurements of COD
x1 = COD original, mg.jlitcr x2 = C1- added, mg./lit'er
'I'he significant information gained from the statistical analysis is that the coefficient of z is less than one (0.907) and a positive bias is present (13.0). The statistical equation differs appreciably from the conventional equation y =
21
+ 0.22622
(2)
These differences reflect a n interaction between the organic matter and chloride content of the sample when oxidized in the standard procedure for COD determination. When a preliminary digestion to oxidize chlorides is used, another difficulty is encountered. I n the presence of chlorides and high concentration of ammonia, organic amine, or nitrogenous matter, a continuous reduction of dichromate occurs. The mechanism for this reduction is thought t o involve a series of cyclic changes from chlorine t o chloride through the formation of chloramines. The magnitude of this effect is illustrated in Table 1. using glycine and urea as a source of nitrogen. The increased consumption of dichromate can only be explained on the basis of the chloramine cycle. Another objection to a preliminary digestion for the oxidation of chlorides is the possibility that the gaseous chlorine may react with organic components in a waste water sample. -4s a result of this interaction the physical and chemical properties of the components are altered. The extent to which particular components are oxidized can be significantly affected. hioore, Ludzack, and Ruchhoft ( 5 ) have reported that benzene is 8% oxidized while chlorobenzene is over 40% oxidized. Hence, chlorine liberated from chlorides could conceivably chlorinate a benzene-containing sample t o chlorobenzene an(1 alter the W L , results. '1'0 overcollie the difficulties piwentecl by chlorides, it was theorized that a complexing technique viould eliniinato If chloride chloride from rcaction.
C01) nig./liter Theo1)cvi:treti- hIe:ts- tion,
____._-_
Sample
identity Glycine
tired
(tit1
+ +
Glycine 500 mg./literCIGlycine 1000 mg./literClGlycine + 2000 nig./literClCrea Urea 100 mg./!iterCP
+ Urea + 200 rng./literCl-"
300
2!)S
413
532
29
526
611
16
752 0
658
14
21.5
0.7
..
4 3 . 8 273
523
6 6 . 1 315
377
.
a Theoretical is t;tlien as rncssured blank of solution plus CUI) uf ohltrride.
reactions could be prevented. a simpler and more accurate assessment of organic COD would be possible. hiedalia (3) reported that the suppressing action of chloride in the ironperoxide procedure for trace amounts of organics in water could be prevented by adding mercuric nitrate. The chloride ion is tied up as a soluble mercuric chloride complex that eliminates it from further reactions. Gleu (2) has reported that chloride interference in the titration of Ce(IV) and As(II1) could be eliminated by complexation of the chloride with mcr curic perchlorate. EXPERIMENTAL
Apparatus and Procedure. T h e digestion apparatus consisted of a 300-ml., round-bottom flask with a ground-glass neck, 24/40, connected t o a Friedrichs reflux condenser. The standard procedure ( I ) was followed in all control determinations to compare the conventional technique with the suggested modification. 1-nless otherwise specified, ail data were obtained by using a 50% by volume sulfuric acid rcflux mixture a ~ i d0 . 2 5 ~ ) ~ VOL. 35, NO. 8, JULY 1963
1065
Table 11. Chemical Oxygen Demand of Organic Compounds Oxidation conditions-0.25.h' potassium dichromate and 50% sulfuric acid plus: 1000
Compound Acetic acid, 1.049 gram/liter yo Theoretical Acetone 0.792 gram/liter yoTheoretical ABS, (sodium salt) 1.000 gram/liter yo Theoretical Benzene, 0.879 gram/ liter (cooled) yo Theoretical Ethyl alcohol, 1 ml. 95y0/liter yo Theoretical D-Glucose, 1.0088 gram/liter yo Theoretical Glycine, 1.000 gram/liter Theoretical Pyridine, 0.982 gram/liter yo Theoretical
Table 111.
Hg804
i1gzS04 and HgSOd
152 13.6
1105 98.8
1114
1118
98.7
1102 63.1
1656 94.8
1173 67.1
1684 96.4
1695 97.0
1748
1849 78.8
2245
1930 82.3
2251 96 .O
2255 06.2
2345
1116
1165 43.2
2700
\I7ithou t catalyst
97 8.7
AgzS04 1104
95.7 1152 42.7
923
580
1530 97.5
739
1048
97.5
985 36.5
34.2
41.3
ical,
mg. /liter
99.7
1496
95.4
1498 95.6
156s
47.1
1020 94.9
1058 98.4
1037 96.4
1064 98.9
1075
632 98.7
635 99.2
637 99.6
636 99.4
643 100.5
640
16.1
25.0 1.1
34.8
25.9 1.2
43.7
2185
37.0
0.74
1.6
2.0
Application of Mercuric Sulfate Modification of Chemical Oxygen Demand to Waste Water Samples
Little Miami primary Loveland nrimary Eastern Abe.
224
Loveland" primary
112
"
raw sewage
86 106
500
1000
1600
2000
323 298
303 248
300 239
300 237
238
301
302 243
523 53.0
499 27.7
481 26.6
484
488 29.7
480 20.5
27.8
0.025N Potassium dichromate used.
potassium dichromate. All samples were run in triplicate with duplicate distilled water blanks. The new modification involves changing the standard procedure as follows. To a 50-ml. sample, or an aliquot diluted to 50 ml. with distilled water, add 1 gram of mercuric sulfate (A.R.). Add 5 ml. of concentrated sulfuric acid to dissolve the mercuric salt. Add 25.0 ml. of standard potassium dichromate followed by 70 ml. of concentrated sulfuric acid. Add 0.75 gram of silver sulfate and digest for 2 hours. Cool, transfer to a 500-ml. Erlenmeyer flask, and dilute to 300 ml. Titrate the excess potassium dichromate with ferrous ammonium sulfate using 1,lo-phenanthroline ferrous sulfate (ferroin) as internal indicator. To employ successfully the principle of complexing chlorides with a mercuric salt, several conditions had to be met. The complexing agent must not interfere with the basic COD procedure and must quantitatively inhibit chloride oxidation, while not adversely affecting 1066
ANALYTICAL CHEMISTRY
the extent to which organic compounds are oxidized. The principle must also be applicable t o a wide variety of waste water samples of complex composition. COD Procedure Interference. Mercuric nitrate was tried initially in accordance with Medalia's (3) work, but the dichromate titration end point was not definitive. The difficulty was attributed to the nitrate ion since an identical effect was observed when potassium nitrate was used to spike samples. The nitrate ion oxidized the reduced form of the indicator, thereby shifting the end point of the titration beyond the equivalence point. To overcome this effect, mercuric sulfate was substituted since large quantities of sulfate ion were already present in the digestion mixture. Fortunately, the choice was most satisfactory and no other interferences with the COD procedure were encountered. Inhibition of Chloride Oxidation. T o determine whether mercuric sulfate completely prevents chloride
oxidation, samples of distilled water containing 100 to 2000 mg. per liter of chloride, complexed with 1 gram of mercuric sulfate, were analyzed for COD. The maximum deviation in titration volumes between the blanks and chloride-complexed samples, in the range studied, was 0.05 ml. The results demonstrated complete inhibition of chloride oxidation. It was necessary to determine the experimental excess of mercuric ion required to prevent oxidation of chloride at any concentration. Samples containing 500 and 1000 mg. of chloride were complexed with varying amounts of mercuric sulfate. The ratios of mercuric to chloride ion used were 3 : 1, 4: 1, and 5 : 1. When analyzed for COD, the deviation in titration volumes between blanks and chloride-complexed samples were 1.33, 0.25, and 0.22 mi., respectively. The results indicate that a 4 : l ratio is sufficient to prevent chloride oxidation in a pure system. The 5 : 1 ratio is preferable since mercuric ion is known to form complexes with certain other anions found in waste waters. RESULTS
Oxidation of Organic Compounds. The results obtained with eight different organic compounds are shown in Table 11. The compounds selected represent different classes of organic substances t h a t may be found in waste water samples. No a t t e m p t was made to repurify these compounds. Approximately 1 gram of the organic compound to be tested was dissolved in distilled water and diluted to 1 liter. The sample size was based on the theoretical COD. The values for COD were measured under the oxidation It conditions shown ill Table 11. should be emphasized that, although mercuric sulfate had no adverse effect on the oxidation of the organic compounds tested, the use of silver sulfate remains essential for improved oxidation of certain organic compounds. Oxidation of t'he added chloride was prevent.ed in all the solutions tested. Application to Waste Water Samples. The most practical aspect' of t h e study was evaluation of the principle as applied to the analysis for COD of various waste waters. Results obtained with wast'e water samples from three different sewage treatment plants are shown in Table 111. Incrcments of chloride from 500 to 2000 mg. per liter were addrd to each of the effluents tested. The maximum variation in COD within a series containing mercuric sulfate and 0.252%' potassium dichromate mas only 1.7%. The per cent variation using 0.025,V ~iotassium dichroinate was somewhat greater, but was not considered significant at the low level of COD involved. CONCLUSIONS
\Yitli tlie motlific.;tt'iouthe test can be applied t o samples with high chloride concentrations that could not Le meah-
ured by the regular procedure. The use the chlorOf mercuric amine cycle and the preliminary digestion for chloride oxidation. Since chloride are a separate chloride analysis is not necessary. The quantitative inhi bition of chloride oxidation in all the systems considered has demonstrated the usefulness of the mercuric sulfate modification in obtainOf the ing a more organic content of was1,e water samples.
ACKNOWLEDGMENT
(2) Gleu, K., 2. Anal. Chem. 95, 305
The authors are indebted to K. A. Bus& and Gerald Stern for the statistical evaluation of the data in ~i~~~~ 1, and to B. A. McDonald for her assistance in the early stages of the investigation,
(3) Medalia, A. E., ANAL. CHm. 23,
LITERATURE CITED
(1) Am. Public Health ASSOC.,"Standard
Methods for the Examination of Water and Waste Water; 11th ed. p. 399, New York, 1960.
(1933).
1318-20 (1951). (4) Moore, W. A., Kroner, R. C., Ruchhoft, C. C., [bid., 21,953-7 (1949). (5) M ~ W.~ A., ~ ~ ~~ d, F.~ J.,~ Ruchhoft, C. C., Ibzd., 23,1297 (1951). (6) Moore, W. A., Walker, W. W., Ibad., 28,164-7 (1956). RECEIVEDfor review March 12, 1963. Accepted April 22, 1963. Division of Water and Waste Chemistry, 143rd Meeting, ACS, Cincinnati, Ohio, January 1963.
Determination of Surface Areas of Phosphates from Adsorptioin Measurements in Nonaqueous Media R. E. MESMER and R. R. IRAN1 Research Deparfment, Inorganic Chemicals Division, Monsanfo Chemical Co., St. Louis, M o .
b A method for the determination of surface areas of powders in acetic acid-toluene solutions has been developed and applied to various phosphates with surface areas between 1.3 and 71 sq. meters per gram. O n powders with surface areas below 8 sq. meters per gram, cluplicates agree within 0.2 sq. meter per gram and are in agreement with va8ues determined b y the conventional BET method. The method i s based on the Langmuir equation for adsorption and it utilizes only common laboratory reagents and equipment. It i s especially useful for measuring small surface areas, and for use with materials that are reactive in aqueous solutions.
T
measurement of surface areas has long been of concern in applications of powders where reactivity or absorptivity is imporLant. Numerous methods for acquiring these data have been reported in the literature. The most important and widely used is that of Brunauer, Emmett, and Teller (BET) ( 2 ) . I n the B E T metho'i, the amount of gas adsorbed as a function of gas pressure is measured in a ';acuum system, and the surface area is calculated according to the B E T eqL.ation. More recently, continuous gas flow methods have been uscmd by Innes ( 4 ) and n'elsen and Eggerken (8). Other :tppruaches have been described, such as gas permeability (9), microscopic examination, x-ray scattering, and others which are listed by Adamson ( 1 ) and the Kational B u r e w of Standards
(3, 9, 12) have been used most commonly, since these materials form monolayers on the adsorbent, and therefore, approach a saturation limit on the adsorbent. Acetic acid forms multilayers a t concentrations higher than 0.25M, and this fact has probably concealed its usefulness in determining surface areas. We have found t h a t the adsorption of acetic acid from toluene on inorganic phosphates obeys the Langmuir isotherm in dilute solutions. With careful performance of titrations, greater precision than that achieved by the conventional R E T method was obtained on surfaces that are affected by the sample preparation procedures required with the B E T method.
HE
(T). l'hc detci,itiiri:Ltioii ( J f surface areits by adsorption from solution has also been invcstigatcd. DJ-cs ( 5 ) and fatty acids
EXPERIMENTAL
Materials. T h e calcium phosphates were prepared by reaction of lime with phosphoric acid under various conditions ( I S ) . The sodium polyphosphate sample was a commercial grade material. The toluene and acetic acid were reagent grade quality. Procedure. Handle a n d transfer all solutions as described below. Keigh about 10 grams of t h e adsorbent for each of three 100-ml. glass-stoppered volumetric flasks. For surface areas below 5 sq. meters per gram, i t is advantageous to keep the solid-to-liquid ratio as large as possible vet permitting the re~novalof an aliquot after settling. Add by pipet 25 ml. of the toluene-. acetic acid solution. Three different concentrations in the range of 0.05iTf to 0 . 2 X should be used for precise work--Jf refers t o concentration in moles per kilogram of solution. Record the weights of these solutions to 0.5%.
Shake the flasks on a wrist-action Burrell shaker for 1 hour at room temperature. (Equilibrium is known to occur in this period, because there is no increase in the quantity of acetic acid adsorbed between 1 and 3 hours.) Allow 15 minutes for the solids to settle before withdrawing a 5-ml. aliquot. Add this aliquot to a 125-m1. Erlenmeyer flask containing 25 ml. of distilled water (COz-free) and 5 d r o p of phenophthalein solution. Record the weight of the aliquot and proceed with the titration, described later, using 30 t o 50 ml. of 0.01X to 0.02M standard base. Handling of Scluticns. Several precautions in t h e handling of these solutions are necessitated by their high volatility. Stock solutions must be transferred to t h e reaction flasks and from reaction flasks t o t h e titration vessel by pipets which are filled by t h e application of pressure instead of suction, as is the customary proccdure. This can be accomplished by using a wash-bottle-type apparatus with glass tubing and rubber stoppers or tubing for making the connections. Pipets are allowed to drain into a rcceiver in the usual manner without lobs due to volatility. Care must also be taken that the vessels are kept ne11 stoppered during the shaking and weighing steps. It is necessary t'o adjust the solid-toliquid ratio in the renction flask so that after settliiig there is srifficient clear supernatant solution for the withdrawal of an aliquot for analysis. A filter pipet (11) can be employed for this purpose, lmt thfJ ordinary pi1wt8 is i i w d l y :id(.q119te.
Titrations. l'he critical p r t of this nirtliotl is tlic c:iw and accuracy VOL. 35, NO. 8, JULY 1963
1067
~
k
,
