and the ozone reaction chamber. At a temperature of -154 OC, the vapor pressure of the nitrosyl radical is greater than one atmosphere, whereas the vapor pressure of almost all organic compounds except for methane, ethane, acetylene, etc., is substantially less than one atmosphere. Thus, if a cold trap were used, the only possible source of interference would arise from compounds with labile nitrosyl groups. The fact that reasonable recoveries of N - nitrosamines a t the sub-100 pg/kg concentration level have been obtained from foodstuffs ( 1 0 ) gives further evidence for the apparent selectivity of the technique.
ACKNOWLEDGMENT We are indebted to F. Campagna of Thermo Electron Corporation for technical assistance. We thank E. K. Weisburger of the National Cancer Institute, Bethesda, MD, for the N-nitroso compounds used in this study.
LITERATURE CITED (1) P. Magee and J. Barnes, Adv. Cancer Res., 10, 164 (1967)
(2) H. Druckrey. R . Preussman, and S. Ivanokovic. Ann. N.Y. Acad. Sci., 163, 676 (1969). (3) W. Lijinsky and S.S.Epstein, Nature (London), 225, 21 (1970). (4) J. M. Essigmann and P. issenberg, J. Food Sci., 37, 684 (1972). (5) W. T. Iwaoka, M. S.Weisman. and S. R. Tannenbaum, Third Meeting on the Analysis and Formation of N-Nitroso Compounds, Lyon, France, Oct. 1973, to be published by IARC, Nov. 1974. (6) J. F. Palframan, J. McNab. and N. T. Crosby, J. Chromatogr., 76, 307 (1973). (7) G. M. Telling, T. A..Bryce, and J. Aithorpe, J. Agric. Food Chem., 19, 937 (1971). (6) T. A. Gough and K. S.Webb, J. Chromatogr., 79, 57 (1973). (9) D. H.Fine, F. Rufeh, and B. Gunther. Anal. Lett., 6, 731 (1973). (10) D. H. Fine, F. Rufeh, and D. Lieb, Nature (London), 247, 309 (1974). (1 1) D. H. Fine and D. P. Roubehler, J. Chromatogr., In press (1975). (12) D. H. Fine, D. Lieb, and F. Rufeh, J. Chromatogr., 107,35~~-fl9757.-~ (13) E. M. Burgess and J. M. Lavanish, Tetrahedron Lett., 20, 1221 (1964). (14) C. H. Bamford, J. Chem. Soc., 12 (1939), (15) E. H. White and R . J. Baumgarten, J. Org. Chem., 29, 2070 (1964); 20, 3636 (1964). (16) E. H. White and C. A. Aufdermarsh. J. Am. Chem. SOC., 83, 1174 (1961).
RECEIVEDfor review December 23, 1974. Accepted January 28, 1975. This work was performed pursuant to Contract NOlCP45623 with the National Cancer Institute, U S . Department of Health, Education, and Welfare.
Application of the Methylthymol Blue Sulfate Method to Water and Wastewater Analysis J. M. Adamski and S. P. Villard Ontario Ministry of the Environment, P.O. Box 213,Rexdale, Ontario, Canada
The metallochromic indicator Methylthymol Blue, as described by Korbl and Pribil (I, 2) received much attention when Lazrus, Hill, and Lodge ( 3 ) applied it to an automated spectrophotometric technique for the determination of sulfate ion in rainwater. The gravimetric method is presently the specified standard sulfate method for water and wastewater analysis ( 4 ) ; however, the tedious, time-consuming nature of this method presents a definite disadvantage to environmental laboratories which must handle a large number of samples. The faster Methylthymol Blue technique is more adaptable to routine laboratory procedures if it can be applied to these same types of samples. A comparative study was therefore conducted to determine which technique was analytically preferable when applied to a series of water and wastewater samples.
EXPERIMENTAL Apparatus. A modified version of the Methylthymol Blue technique as described by Lazrus et al. (3)was employed using a Technicon AutoAnalyzer I system with the appropriate accessories described in Figure l . The ion exchange column designated in this figure is constructed from a 23-cm glass tube with an internal diameter of 2 mm. I t was packed with Amberlite IR-120 cationic exchange resin and plugged on both ends with glass wool. The premixer units, also shown in Figure 1, were constructed from short lengths of Solvaflex tubing inserted into each other to form a chain. All the appropriate apparatus for performing a gravimetric analysis is discussed in “Standard Methods” ( 4 ) . Reagents. T h e Methylthymol Blue colorimetric reagent was prepared by dissolving 0.1182 g of Methylthymol Blue [(3,3’bis(N,N- di(carboxymethyl)aminomethyl)thymolsulfone)phthalein pentasodium salt](Eastman Catalog No. 8068), in approximately 100 ml of distilled water. This solution was then mixed with 25 ml of barium chloride stock solution, 4 ml of 1.ON hydrochloric acid,
and 400 ml of 95% ethanol and diluted to 1 1. with distilled water. The barium chloride stock solution was prepared by dissolving 1.526 g of barium chloride dihydrate in distilled water and diluting t o 1 1. The dilution water used in the analysis contained small amounts of sulfate and a detergent concentrate, BRIJ-35 (Technicon Chemical Formula No. AR 110-62), in various proportions depending on the range of analysis. The dilution water required for analysis in the 0-50 mg/l. range was prepared by mixing 3 ml of a 1000 mg/l. sulfate standard and 3 drops of Brij-35 with distilled water and diluting to 2 1. The dilution water required for analysis in the 0-200 mg/l. range was prepared by mixing 0.75 ml of a 1000 mg/l. sulfate standard and 3 drops of Brij-35 with distilled water and diluting to 2 1. All the appropriate reagents for performing a gravimetric analysis are described in “Standard Methods” ( 4 ) . Procedure. The color reagent used in the Methylthymol Blue technique contained equimolar quantities of Methylthymol Blue and barium ion in an aqueous-ethanol solution adjusted to a p H between 2.5 and 3.0 with 1.ON hydrochloric acid. When a water sample containing sulfate reacts with this reagent, barium sulfate is produced. After allowing sufficient time for the production of barium sulfate, the pH is re-adjusted between 12.3 to 13.0 with 0.18N sodium hydroxide. A t this high pH, any barium ions remaining in solution will complex with available Methylthymol Blue leaving an amount of uncomplexed Methylthymol Blue in solution which is equivalent to the quantity of sulfate removed as barium sulfate. The uncomplexed Methylthymol Blue is then determined colorimetrically. Figure 2 was derived to show the locations of maximum colorimetric sensitivity. These scans were performed on a Unicam 1800 double beam spectrophotometer using 1-cm cells and distilled water as a reference. A wavelength of 460 nm was chosen for all our experiments. Calibration of the AutoAnalyzer system was performed for three sulfate ranges: 0-15 mg/l. (no dilution), 0-50 mg/l. (3-fold dilution). and 0-200 mg/l. as sulfate (18-fold dilution) (See Figure I). Curvature in the calibration was corrected by the addition of sulfate t o the dilution water when operating in the 0-50 mgil. and the 0-200 mg/l. ranges. Curvature could not be corrected in the 0-15 ANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975
0
1191
r
PROPORTIONING PUMP
-
Ab
1L
-
on
c3
WASTE
1
.BO A I R
1
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w
A
ION
I
EXCHANGE COLUMN
. 6 0 SAMPLE
I
‘-1
I
I
L
L--
I
2 . 0 0 SAMPLE
1.20
12“
I.
D. 1/16’’
4
2.42
1
w
it
RECORDER
.60 .IBN. NaOH
a
Y
WASTE
SOLVAFLEX
0-15 m p / 4 RANGE
.32 A I R
A
LENGTH
WASTE
COLOR1 M E T E R
-
1 TUBING
0”E’
. I 6 SAMPLE
01
-
3??N
2.90 D I L U T I O N WATER
*
TUBING
S.M.C.
SHORT M I X I N G COIL
L.M.C.
LONG M I X I N G C O I L
(IX) PREMIXER
50 m m F L O W C E L L 460 m p F I L T E R
ONE
PREMIXER PREMIXER
LINK
A B
-
IO
50
LINKS LINKS
Figure 1. AutoAnalyzer I analysis scheme for the determination of sulfate using Methylthymol Blue
1,
4BSORB4NCE
RESULTS AND DISCUSSION
WIVELENGTH
VI
0 , 00
~
~
300
’
m
~
‘ 340
~ 360
‘
‘
380
~ 400
WAVELENGTU
‘ 120
‘ 440
‘
1 460
I’
+no
I
1’ ’ ’ I ~I $00 120
’ 5‘0
lnml
Flgure 2. Spectral scan for a 50 mg/l. sulfate standard and its reagent blank using Methylthymol Blue The solid line represents a reagent blank while the dashed line represents a 50 mg/l. sulfate standard
mg/l. range. It was, therefore, important to include a sufficient number of standards in this calibration range to properly characterize any curvature. Aqueous solutions of Methylthymol Blue were reportedly unstable ( 3 ) ,so fresh reagent was prepared daily. Variations in sensitivity were routinely monitored by control standards inserted a t 10-sample intervals. The calibration was adjusted accordingly whenever sensitivity changes were detected. All gravimetric analyses were performed as specified in “Standard Methods” ( 4 ) . 1192
ANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975
1
Most metallic cations which are common constituents of natural waters will interfere with the Methylthymol Blue method by complexing with the Methylthymol Blue dye in much the same way as does barium. Calcium and magnesium are the most frequently encountered interferences. The use of a cation exchange column incorporated into the automatic analysis sequence provides for the efficient removal of these and any other cationic interferences. As a result, only the interference effects of the anions were considered. Table I summarizes the results of this inteference study. Sulfide, sulfite, phosphate, and tannic acid are major interferences but are seldom found in the quantity necessary to produce a major interference effect. The biggest problem associated with the Methylthymol Blue technique involves the release of calcium from the ion exchange column whenever an acidic or highly ionic sample passes through the automatic system. For example, samples containing sodium in excess of 2000 mg/l. will scrub any accumulation of calcium from the ion exchange column. Once this calcium passes into the colorimetric sequence, it causes a large negative interference effect. Interference effects on the gravimetric technique are discussed in “Standard Methods” ( 4 ) . Comparison between the Methylthymol Blue and gravimetric methods show that both produce practically identical results on a wide variety of natural water and wastewater samples. T o facilitate evaluation, samples were classified into three general categories which were designated as “waters”, “rivers”, and sewages”. “Waters” refer to domestic water supplies, i.e., treated water from treatment plants,
Table I. Substances Screened as Possible Interferences When Using the Methylthymol Blue Method for the Determination of Sulfate Sulfate concentration, m g l l .
Substance
Fc1-
Br1-
NO,-a s N NO3- as N CN-
B033- as B Si03?-as SiO, s203’HCO3-
co,2cos*C,H,O; SSSSO3‘-
so3?Tannic acid Tannic acid Tannic acid Tannic acid Phenol pod3-as P pod3-a s P pod3-as P pod3-a s P pod3-as P
mgll.
2 500 20 40 4 48 10 10 10 10 400 50 400 200 1
5 100 2 .o 20 10 20 50 200 0.4 0.6 0.8 1.o 2 .o 10 .o
Known
30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30
Detected
30 30 30 31 30 30 30 30 30 30 30 30 31 30 30 32 52 32 51 30 31 33 56 30 30 31 32 33 33
grab samples from trunk water mains, tap water samples, reservoir samples, and samples from private or community wells. “Rivers” refer to natural surface waters obtained from rivers, streams, lakes, and ponds. Most of these “River” samples contained small amounts of suspended solids and were somewhat yellow in color. “Sewages” refer to raw sewage inputs to waste treatment plants, primary, secondary, and final effluents from waste treatment plants, digester supernatants, mixed liquors, and a variety of industrial effluents which include pulp and paper, food processing, and mining wastes. All analyses using the Methylthymol Blue technique were performed directly on the original sample. Removal of suspended substances was automatically accomplished when the sample was pumped through the ion exchange column of the AutoAnalyzer. All “Waters” were clear; therefore the gravimetric analysis was performed without prior filtration. All “Rivers” and “Sewages” contained some suspended substances and were therefore filtered prior to gravimetric analysis. Pretreatment by ion exchange was not used when employing the gravimetric method. A total of 130 samples was analyzed in duplicate by both techniques. The results for samples containing less than 190 mg/l. sulfate are shown in Figure 3. An evaluation of these data, using a technique described by Snedecor and Cochran (51, was performed to test the hypothesis that the data were statistically indistinguishable from a line of slope one. Results of this evaluation showed that the actual slope was very close to one, Le., 1.005, but statistically different from one. Certain types of samples stand out as special cases be-
o
10
20
30
40
50
70 no P O loo I I O G R A V I M E T R I C SULFATE
60
120
30
140
150
SO
170
80
,so
(mq/t.l
Figure 3. Comparative performance of the Methylthymol Blue and gravimetric methods when applied to water and wastewater analysis The solid line represents the result of a linear regression analysis while the dashed line represents an ideal one-to-one relationship between the two methods
Table 11. Comparative Standard Deviations between the Methylthymol Blue and Gravimetric Methods Methylthymol Range,
Blue,
Gravimetric,
Sample type
mgll.
mdl.
mgll.
Waters Rivers Sewages Waters Rivers Sewages
0-50 0-50 0-200 0-200 0-200
0-50
10.27 10.35 1 0 .29 * O .59 10.76 11.14
i0.60 11.57 11.55 *0.92 11.85 12.80
cause of the different results reported by the two methods. Pulp and paper wastes analyzed gravimetrically were 3040% higher than the corresponding Methylthymol Blue results. Digester supernatants and mixed liquors analyzed gravimetrically were 20-70% lower than the corresponding Methylthymol Blue results. Sulfate spikes were recoverable from these types of samples using the Methylthymol Blue method. A similar investigation was not conducted for the gravimetric method. The precision for the two methods was evaluated by finding the differences between the duplicate analyses on each sample and then determining the standard deviation of these differences. The application of this technique is described by Youden (6). Table I1 summarizes these data according to sample type and range of analysis. Comparison between the two methods in the 0-15 mg/l. range was not included because of the limited capabilities of the gravimetric method without preconcentrating the samples.
CONCLUSION Experimental evidence has demonstrated that the automated Methylthymol Blue method is a satisfactory routine technique for the analysis of sulfate in water and wastewater samples. With respect to precision, sensitivity, and the number of interferences, it was analytically superior to the gravimetric method. Its economic advantages include a ANALYTICAL CHEMISTRY, VOL. 47, NO. 7 , JUNE 1975
1193
lower cost per analysis, greater speed of analysis, and smaller bench space requirements for performing the analysis.
LITERATURE CITED (1) J. Korbland R. Pribil, Chem. lnd., London, 233 (1957). (2) J. Korbl and R. Pribil, Chem. Listy, 51 1061 (1957). (3) A. L. Lazrus, K. C. Hill and J. P. Lodge, Proceedings from the 1965 Technicon Symposium "Automation in Analytical Chemistry", Medicad Inc.. 1966, p 291.
(4) American Public Health Association, "Standard Methods for the Examination of Water and Wastewater", 13th ed., APHA. Washington, DC, 1971, p 330. (5) G. W. Snedecor and W. G. Cochran, "Statistical Methods", 6th ed., Iowa State University Press, 1967. p 139. (6) W. J. Youden, "Statistical Methods for Chemists", Chapman and Hall, London, 1951, p 16.
RECEIVEDfor review October 25, 1974. Accepted January 20, 1975.
Formation Constant and the Structure of a Bridged Adduct of Triethylenediamine and Bis(0,O'-diethyldithiophosphato)nickel(ll) Walter Rudzinski, Motoo Shiro, and Ouintus Fernando Department of Chemistry, University of Arizona, Tucson, AZ 8572 1
For a number of years, we have been concerned with the relationship between the structures of the adducts of extractable metal chelates and their thermodynamic properties (1-3). The planar metal chelates, bis(0,O'-diethyldithiophosphato)nickel(II), Ni[S2P(OC2H5)2]2, or bis(0,O'dimethyldithiophosphato)nickel(II), Ni[S2P(OCH3)2]2, served as model compounds in most of our studies because they formed adducts very readily with a wide variety of heterocyclic nitrogen bases. Recently, Diemert and Kuchen ( 4 ) reported that pyrazine and 4,4'-bipyridyl reacted with the planar chelate, bis( diethyldithiophosphinato)nickel(II), Ni[S2P(CzHj)z]2, and formed 1:l adducts which were regarded as coordination polymers in which the nickel ions were six-coordinate. With 1,4-diazabicyclo[2.2.2]octane, however, a 2:l adduct was formed and the electronic spectrum of the compound indicated that the nickel ions were most probably five-coordinate. This unexpected result prompted us to study the interaction of 1,4-diazabicyclo[2.2.2]octane, (Dabco) with the nickel chelate, Ni[SeP(OC2Hj)2]2,and to determine the structure of the adduct that was formed.
and a t 524 nm were obtained by recording the absorption spectra of eight different solutions containing Ni(dtp)2 and Dabco; the Ni(dtp)z concentration varied from 2.94 X 10-4M to 4.93 X 10-3M and the concentration of Dabco in each of these solutions was a t least 500 times the concentration of the Ni(dtp)2. was 950 and that of c~~~~ was 90. The average value of Determination of the Adduct Formation Constant. The reaction of the nickel(I1) chelate C, with the base, B, to form the adduct, A, is represented by:
2C
1194
ANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975
B S
A
and the formation constant, K , of the adduct is given by:
where the quantities in brackets represent equilibrium concentrations in mol/l. If the initial concentrations of the base, Dabco, and the nickel(I1) chelate, Ni(dtp12, are COB and C 0 c mol/l., respectively, c"B
=
LB1
CAI
(21
2[A]
(3 )
+
and
EXPERIMENTAL Synthesis and Purification of Compounds. The ammonium salt of diethyldithiophosphonic acid was synthesized from ethanol and phosphorus pentasulfide as described before (3). The nickel complex, bis(0,O'-diethyldithiophosphato)nickel(II), Ni(dtp)2, was precipitated by the addition of nickel sulfate to an aqueous solution of the ammonium salt and recrystallized from acetone. The molar absorptivity of the compound in ethanol at 524 nm was found t o be 90 and was employed as a criterion of purity. Triethylenediamine, or 1,4-diazabicyclo[2.2.2]octane, or Dabco, was obtained from Houdry Process and Chemical Co., Philadelphia, PA. The compound was purified by sublimation under vacuum. The solid adduct was prepared by adding an excess of Dabco dissolved in ethanol to an ethanol solution of Ni(dtp)2. Red crystals were formed when the solution was allowed to stand for 24 hours. Spectrophotometric Measurements. The spectra of about forty different solutions containing varying concentrations of Ni(dtp):! and Dabco were recorded with a Cary 14 spectrophotometer. An isosbestic point was found at 505 nm, and the location of the band maximum of the 2:l adduct of Ni(dtp), and Dabco was at 468 nm. The molar absorptivities of Ni(dtp)g in ethanol a t 468 nm, (cc4"), and a t 524 nm, were calculated by recording the spectra of nine solutions varying in concentration from 2.20 X 10-3M to 6.16 X 10-3M. The average value of cc468was 50 and of ec524was 90. The molar absorptivities of the adduct a t 468 nm,
+
CoC = [C]
+
At 468 nm and a t 524 nm, the only absorbing species are the adduct A, and the nickel chelate, C. The values of the absorbance of a solution in a 1.00-cm cell containing Ni(dtp)Z, Dabco, and the adduct, a t 468 nm and a t 524 nm are given by the following equations which contain the experimentally determined molar absorptivities.
+
[A]
