1832
ANALYTICAL CHEMISTRY, VOL. 50, NO. 12, OCTOBER 1978
Polarographic Determination of Some Azomethine-Containing Pesticides Malcolm R. Smyth" and Janet G. Osteryoung Department of Microbiology, Colorado State University, Fort Collins, Colorado 80523
and vapor action (9). Methods of analysis for this compound are based either on the determination of its hydrolysis product, 4-chloro-o-toluidine, by colorimetry or gas chromatography ( I O ) , or determination of the intact compound by thin-layer and flame ionization gas chromatography (11). In both cases, separation of 4-chloro-o-toluidine-containing interferences is required prior to analysis. Drazoxolon (IV) is highly active as a foliage fungicide and is also effective against a number of seed and soil-borne diseases (12). It has been reported that, in aprotic solvents, this compound exists predominately as IVa [in which hydrogen bonding occurs between the carbonyl and -NH groups (13)] but that in aqueous sodium hydroxide solution it exhibits tautomerism to form IVb.
The polarographic behavior of the insecticides Cytrolane, Cyolane, and Chlordimeform and of the fungicide Drazoxolon has been investigated over the pH range 0-14. The best defined waves for the differential pulse polarographic determination of these compounds were obtained in BrittonRobinson buffers of pH 6, 6, 8, and 8 respectively. This technique has been applied to the determination of Draroxolon in a grain forrnulatlon.
Although polarographic methods of analysis have found widespread application for the determination of many drug substances containing the azomethine (>C=N-) group, e.g., 1,4-benzodiazepines ( I , 2 ) , antidiabetic compounds ( 3 ) ,and benzhydrylpiperazine derivatives ( 4 ) ,there are relatively few published methods for the determination of pesticides containing this moiety. This is surprising, considering the analytical usefulness of the waves obtained following reduction of this group at the dropping mercury electrode (DME). Those azomethine-containing pesticides which have been investigated using polarographic methods of analysis include the heterocyclic substances terbutryne, ametryne, and atrazine ( 5 ) . These compounds could be determined in pond and canal water down to 50 ng mL-' and the polarographic method was found to compare favorably with a gas chromatographic procedure usually employed for their determination. T h e compounds we have chosen t o study in this investigation all contain a n extranuclear azomethine group conjugated t o a heterocyclic ring system. The syst,emic insecticides Cyolane (I) and Cytrolane (11)
Cl
IVa
EXPERIMENTAL Apparatus. Polarographic curves were recorded using a PAR Model 174 polarographic analyzer in conjunction with a 3-electrode cell system having a saturated calomel (SCE) as the reference and platinum as the counter electrode. The polarograms were recorded on an Omnigraphic Model 2000 X-Y recorder. The dropping mercury electrode used had a flow rate of 0.81 mg s-' and a drop time of 7.95 s in 0.1 M KC1 and at a mercury head of 76 cm. For the cyclic voltammetric experiments, a PAR Model 9323 hanging mercury drop electrode was used in conjunction with the PAR Model 174. Drop times were controlled using a PAR 172 drop knocker. Controlled potential electrolysis experiments were conducted at a stirred mercury pool cathode. Reagents. Samples of Cyolane and Cytrolane were obtained from American Cyanamid Co., Princeton, N.J. A sample of Chlordimeform was obtained from the Quality Assurance Section, Environmental Toxicology Division of the Environmental Protection Agency. A sample of primary analytical standard of Drazoxolon and a sample of 60% w/w Drazoxolon in grain formulation was obtained from Imperial Chemical Industries, Plant Protection Division, Bracknell, England. Stock solutions of these compounds (1-5 X M) were prepared in AnalaR methanol and stored in the dark under refrigeration. A stock Britton-Robinson (BR) buffer solution, 0.04 M in each of glacial acetic acid, orthophosphoric acid, and boric acid, was prepared from analytical grade reagents; buffer solutions of varying pH (2-12) were prepared by the dropwise addition of 0.2 M sodium hydroxide and measurement of the pH using a glass electrode. Techniques. Polarographic investigations were carried out on solutions that had previously been deaerated with oxygen-free nitrogen for 10 min. Current-potential curves were recorded in
0
It
(C2H5O)z-P-N
'/ S ,
C'
"ti2
CHR
/
I,R=H 11, R = CH,
are effective against both sucking and chewing insects. Blinn and Boyd (6) developed a colorimetric method of analysis for these compounds based on the determination of thiocyanate liberated following a hydrolytic procedure. Gas chromatographic methods of analysis have been developed for these compounds based on selective phosphorus-sensitive detection (7). These compounds can also be determined by a bioassay procedure utilizing the larvae of Culiseta inornata (8). Chlordimeform (111) is a broad spectrum acaricide and insecticide.
I11
It is effective against mites resistant t o organophosphorus insecticides and kills eggs, larvae, and adults both by contact 0003-2700/78/0350-1632$01.00/0
IVb
Methods of analysis for this compound are based on colorimetric procedures utilizing its strong absorption characteristics at 400 nm (12). This paper is concerned with a fundamental study of the polarographic behavior of these compounds in aqueous solution and in optimizing conditions for their determination by differential pulse polarography.
C
1978 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 50, NO. 12, OCTOBER 1978 9 1633 18
7! 108 0 4
14
-E
v YS
0
--_0
. . A . . i -
2
4
6
8
A00 0 0 1 0 1 2 1 4
PH
(a,
Figure 1. Plots of E,,* (-) or E , )-( and iIi, -0-) or i (+, -0-) vs. pH for main waves exhibited by Cytrolane (5 X lo-' M) across the pH range 0-12. Conditions: v = 2 mV s-'; t = 1 s; A € = -100 mV
the direct current (dc) sampled dc, normal pulse (npp) and differential pulse (dpp) polarographic modes. Currents reported in the dpp mode are 0.1 X the PAR 174 output, i.e. they are "true" dpp currents. The solutions were blanketed by an atmosphere of nitrogen during analysis and each solution was scanned between -0.1 V and the potential of electrochemical reduction of the supporting electrolyte. A scan rate ( u ) of 2 mV s?, drop time ( t ) of 1 s (sampled dc, npp, and dpp), and a modulation amplitude ( a E )of 100 mV (dpp) were typically employed in most investigations. For each of the waves studied, investigations were carried out on the mercury head dependence ( h )of the limiting current (ilim);for diffusion-controlled processes il&~'". Values of n,a were then obtained from plots of Ede vs. log i/& - i and values of the diffusion coefficient (D)by assuming the value of n and substituting into the Ilkovic equation (14). Cyclic voltammetric (cv) experiments were carried out at a hanging mercury drop electrode (HMDE). Solutions were prepared for analysis as in the polarographic experiments. Cyclic voltammograms were then obtained using scan rates of 50-200 mV s?. Controlled potential electrolysis (cpe) experiments were carried out a t a stirred mercury pool electrode. The solutions to be analyzed were first deaerated with oxygen-free nitrogen for 10 min before applying the required potential across the cell. The solutions were then analyzed using dc polarography a t various time intervals following onset of electrolysis. For the determination of Drazoxolon in 60% w/w formulated grains, the following procedure should be carried out. Prepare a standard Drazoxolon solution containing 0.1 mg mL-' by dissolving 10 mg pure material in 100 mL AnalaR methanol. Transfer in turn 0.1, 0.2, 0.3, 0.4, and 0.5 mL of this solution to five 10-mL volumetric flasks. To each flask add 0.9, 0.8, 0.7, 0.6, and 0.5 mL AnalaR methanol and make up to the mark with BR buffer pH 8.0. To prepare the calibration graph, deaerate each solution for 10 min and scan between -0.4 to -0.8 V in the dpp drop time 1 s; modulation mode (conditions: scan rate 2 mV amplitude 100 mV; current range 10 PA). To determine the % Drazoxolon in the formulated grains, dissolve 10 mg of the product in 100 mL methanol. Take 0.5 mL of this solution and dilute to 10 mL with 0.5 mL AnalaR methanol and 9 mL BR buffer pH 8.0. Run the differential pulse polarogram as above and relate the peak height to the previously prepared calibration graph.
RESULTS AND DISCUSSION Polarography of Cytrolane and Cyolane. The effect of p H on the E l I 2 (or EP)and ili, (or i,) values of the main diffusion-controlled waves exhibited by Cytrolane in dc and differential pulse polarography is shown in Figure 1. In solutions of p H G2, Cytrolane is reduced in a single 4 e- wave. A post-adsorption wave was manifested at a slightly more negative potential to this wave indicating that product adsorption is also involved in the overall electrode process. A catalytic wave was also observed at a potential close t o that
Table I. Polarographic Characteristics of Azomethine-Containing Pesticides Cyo- Cytro- ChlordiDrazocompound lane lane meform xolon logarithmic analysis "a" .__ BR buffer pH 2.0 2.11 2.23 BR buffer pH 6.0 1.34 1.38 BR buffer pH 8.0 1.25 0.61; 0.99 0.01 N NaOH 1.17 1.09 diffusion coefficients D (cm2s - l x l o 6 ) BR buffer, pH 6.0 3.22 3.06 BR buffer, pH 8.0 1.24 4.59 of the reduction of the supporting electrolyte. This is likely to be due to the evolution of H2 released following reduction of the C=N-P moiety (see below). In the p H range 4 -6, the wave height (in both dc polarography and dpp) was found to be half the value in the p H range 0-2. From a consideration of the n,a values at p H 2 and 6 (Table I), it would appear that whereas the protonated form of Cytrolane (present in the bulk of solution) is reduced in a 4 e- process, the unprotonated form is reduced in only a 2 e- process. In the p H range 4-6, however, protonation of the azomethine group a t the electrode surface is also required in the overall electrode process, as evidenced by the p H dependence of the half-wave potential in this p H range. T h e break in the El,* vs. p H plot a t 4.6 represents the pK,' value corresponding to protonation of the azomethine group; similar values have been reported for protonation of the azomethine group in several 1,4-benzodiazepines (15) and benzhydrylpiperazine derivatives (16). T h e break in the E , vs. p H plot ( 3 . 7 ) occurs at a lower p H than in the E l l z vs. p H plot (4.6) since the potential in d p p is governed t o a large extent by the pulse amplitude (AE):
Therefore, for a cathodic-going pulse of 100 mV (for which AI3 is negative), the potential a t which the acid-base equilibrium occurs in d p p will be 50 mV more negative than in d c polarography. This accounts for the 0.9 unit difference in the pK,' values obtained using dc polarography and dpp. T h e following mechanism can therefore be postulated t o account for the behavior of Cytrolane in the p H range 0-8: 0 \ Ht ,C=N-P
!/OR
pK'=4.6
-H+
O 'R
*
\
' ,,C=N-P '3R
In solutions of p H > 8, the main wave is replaced by another wave a t a more negative potential. This wave was found to be independent of p H in the range 8-12. In order t o further investigate the reduction process giving rise to this wave, a 1X M solution of Cytrolane (in B R buffer p H 10) was electroreduced at a mercury pool electrode. The potential was set at -1.85 V vs. SCE and the electroreduced solution analyzed by dc polarography a t various time intervals following onset of electrolysis (Figure 2). lJsing this procedura, it was found that the product of electroreduction gave rise to an anodic wave in B R buffer p H 10 a t -0.34 V vs. SCE. This indicates, therefore, that the electroreduction process involves splitting of one of the C-S bonds in the heterocyclic ring
ANALYTICAL CHEMISTRY, VOL. 50, NO. 12, OCTOBER 1978
1634
I
izO
14t
I
Figure 2. Dc polarograms obtained at various time intervals following electroreduction of Cytrolane (5 X M) in BR buffer pH 10 at -1.85 V vs. SCE. (a) 0 min, (b) 5 min, (c) 10 min. Conditions: v = 2 mV s-': t = 1 s
"1 2
Figure 4. Plots of E, by Drazoxolon (5 X
v = 2 mV s-'; t = 1 s;
14
i
(-)
PH and i, ( - - - ) vs. pH for main waves exhibited M) across the pH range 5-14. Conditions: = -100 mV 4
78
05.A
6
8
PH
10
12
Flgure 3. Plots of E, (-0-0-)and i, (-A-A-)vs. pH for main wave M) across the pH range 4-12. exhibited by Chlordimeform (8.75 X Conditions: v = 2 mV s-'; t = 1 s; A € = -100 mV
JlPH Jl 2
system. This would result in the formation of a product containing a free -SH group which would then be capable of undergoing oxidation a t the DME. Since the electrode reaction does not involve the addition of protons (as evidenced by the pH independence of the wave) the following electrode mechanism can be postulated:
Figure 5. Effect of pH on dc wave shape of Drazoxolon (5 X M) in the pH range 8-12. Conditions: v = 2 mV s-': t = 1 s
I t is also interesting to note that the ratio of ilim:idpp for the second wave shows a disparity in that the dpp current is much lower than one would expect from theory (17). In acid solution, the ratio i d p p / i d c is equal to 3.25, whereas in alkaline solution the ratio falls to a value of 1.15 (Figure 1). This suppression of the dpp current is likely to be due to adsorption of the -SH-containing product a t the electrode surface. Adsorption has also been shown to have an effect on the magnitude of d p p currents in the case of some thioureacontaining pesticides (18). Cyolane gave rise to polarographic behavior similar to that of Cytrolane. The main differences in behavior between the two compounds lay in the fact that Cyolane was reduced a t a slightly more positive potential than Cytrolane and was less strongly adsorbed a t the DME. The small differences in potential (10-40 mV) could not be used, however, for the quantitative determination of one compound in the presence of the other. The differences in adsorption between the two compounds were reflected in their npp behavior; whereas Cytrolane exhibited a sharp maximum on its npp waves across the whole pH range, Cyolane exhibited a smaller maximum in solutions of pH 0-8 and showed no maximum on the pH-independent wave between pH 10-13. P o l a r o g r a p h y of Chlordimeform. The effect of pH on the E , and i, values of the single wave exhibited by Chlordimeform in dpp is shown in Figure 3. The wave was found
to be diffusion-controlled and corresponds to the 2 e- reduction of the azomethine group. The point of inflection on the E , vs. pH graph gave a pK, value for Chlordimeform of 7.8 (the pKb value is therefore equal to 6.2). This is in reasonable agreement with a previously published value of pKb = 7.2 for Chlordimeform (19) and corresponds to deprotonation of the adjacent tertiary amine moiety. Since the peak current falls off on passing through this pKb value, it appears that only the protonated form of Chlordimeform is reduced at the DME. In solutions of pH 1 1 2 the main wave is replaced by several new waves at -0.77, -1.01, and -1.38 V vs. SCE. These are likely to be due to products of the alkaline hydrolysis of Chlordimeform (19). P o l a r o g r a p h y of Drazoxolon. The effect of pH on the E, and i values of the main waves exhibited by Drazoxolon (5 X 10-!t M) in dpp is shown in Figure 4. The plot of i, VI. pH for the main wave shows a decrease in current between pH 9-5. This is due to the decreasing solubility of Drazoxolon at this concentration and in this pH range and appears to be related t o the break in the E, vs. pH plot at 8.2. This decrease in current was not observed a t the lo4 M level in solutions containing 30% v/v methanol. The effect of pH on the wave shape exhibited by Drazoxolon in dc polarography is shown in Figure 5. From this one can see that the shape of the main wave is well defined a t pH 8 but that the wave becomes distorted on increasing pH. Furthermore, a new wave is formed a t more negative potentials, the El,z of which was found to be virtually independent of pH. In an attempt to show whether this new wave was in fact due to a reduction
PH 8
-03V-03V
-03V
E
-
.
05v
c
ANALYTICAL CHEMISTRY, VOL. 50, NO. 12, OCTOBER 1978 L
n
A
1635 4
05-A
f
I \ X
I
-05V
-05V
-05V
-06V
-
-05V
E-
05v
-c
-0.1v
-0.lV
E ---~-
-0 1v
Figure 6. Effect of Triton X-100 concentration on dc wave exhibited M Drazoxolon, (b) by Drazoxolon in BR buffer pH 10; (a) = 5 X = (a) 0,001 % Triton X-100, (c) = (a) 0.003% Triton X-100, (d) = (a) -I-0.005% Triton X-100, ( e ) = (a) 0.008% Triton X-100. Conditions: v = 2 mV s-’: t = 1 s
+
+
+
process or was caused by a n artifact of adsorption, various concentrations of a neutral maximum suppressor, Triton X-100, were added to a 5 X M solution of Drazoxolon in BR buffer p H 10 (Figure 6). From this it can be seen that a small concentration of the maximum suppressor eliminated the maximum on the main wave. On increasing the concentration of Triton X-100, however, the main wave began to disappear whereas the second wave appeared to increase M in magnitude a t its expense. In the case of a 5 X solution of Drazoxolon in 1 M NaOH (a medium in which Drazoxolon did not exhibit the second wave), addition of Triton X-100 caused the main wave to disappear and be replaced by a second wave (at a potential near t h a t of the second wave observed previously). It would appear, therefore, t h a t the process giving rise to the second wave is not due to an artifact of adsorption but is caused by a separate reduction in the molecule. The disappearance of the first wave following addition of Triton X-100 can be attributed either to the dependence of this wave on the adsorption of the molecule a t the electrode surface prior to reduction or to a decrease in the rate of electron transfer caused by absorption of the Triton x-100. T h e relationship between these two waves was further investigated using cyclic voltammetry. The effect of scan rate on the cyclic voltammograms obtained for Drazoxolon in BR buffer pH 8 is shown in Figure 7a. From this it can be seen t h a t there are two main processes involved, a and b, which are likely to be associated with the two main waves obtained in the polarographic experiments. I t is worthy of note, however, t h a t although Drazoxolon exhibits a single wave in BR buffer pH 8 in dc polarography, analysis of the E d e vs. log i/id - i plot yielded two linear portions of slope -0.096 and -0.060 which gave rise to values of rz,a of 0.61 and 0.99, respectively (Table I). The existence of the prewave, indicates that reactant adsorption is involved in the overall electrode process. A small wave, d, was also manifested a t a more negative potential but this wave disappeared on increasing the pH. From Figure 7A it can be seen that wave a is predominant over wave b in BR buffer p H 8. On increasing the pH, however, wave b becomes predominant, as evidenced by the cv behavior of Drazoxolon in 0.1 M NaOH (Figure 7B). In 1 M NaOH, however, wave b decreases in height (cf. as in dc polarography where the second wave disappears altogether) a t the expense of wave a. The relationship between the two processes was further investigated using cpe, where the potential was set a t a n intermediate value between the two waves. When a solution M Drazoxolon in BR buffer pH 11 was subjected of 5 x
A
1OuA
B
+&JY (ai
-05V
rb)
-05V
fC)
-05V
E-
+
05v
*’
Figure 7. (A) Effect of scan rate on cyclic voltammograms obtained for Drazoxolon (2.5 X M) in BR buffer pH 8, (a) 50 mV s-’, (b) 100 mV s-’, (c) 200 mV s-’, (B) Effect of scan rate on cyclic voltM) in 0.1 M NaOH; ammograms obtained for Drazoxolon (2.5 X (a) 50 mV s-’, (b) 100 mV s-’, (c) 200 mV s-’
to cpe a t -1.0 V vs. SCE, the second wave was found to decrease in magnitude (with time) at a rate similar to that of the first wave. In addition, the maximum relating to the first wave disappeared on increasing electrolysis. This indicates that both waves involve processes occurring at the same electroactive center. It has been reported that Drazoxolon exists mainly as the hydrogen-bonded azomethine-containing species IVa in aprotic media and that it exists only as the azo-containing tautomer in aqueous sodium hydroxide solutions (12). Polarographic studies on the coupled products of 6-diketones (20) and 6-keto esters (21) with aryldiazonium chlorides have also suggested that these products exist predominately as their respective azomethine-containing species. The evidence obtained from this study suggests, however, that Drazoxolon exists predominately as the azo-containing tautomer in neutral to slightly alkaline media and that increasing the pH favors the formation of the azomethine-containing tautomer. Deprotonation of the -OH group around pH 11-12, however, again favors formation of the azo-containing tautomer, as evidenced by the decrease in the second wave on passing through the pK value relating to phenolic dissociation. In addition the fall off in i, on passing through this pK value (measured a t the lo4 M level in solutions containing 30% v/v methanol) indicates t h a t the neutral form of Drazoxolon is reduced in a 4 e- process corresponding to formation of the corresponding amino compounds and that the anion is reduced only in a 2eprocess to the hydrazo intermediate. The main evidence for suggesting this hypothesis comes from a comparison of the reduction potentials of similar compounds. The reduction potential of Drazoxolon in BR buffer pH 7 was found to be -0.57 V vs. sce; this can be in diazepam compared to the reduction of the X=N-group
1636
ANALYTICAL CHEMISTRY, VOL. 50, NO. 12, OCTOBER 1978 A
I,
-03v
A
-
-11v
-07v
E
11
--
Figure 8. Formation of Drazoxolon-Fe*+ complex in BR buffer pH 8; M Drazoxolon, (b) = (a) 3 X (a) = 5 X M Fe2+,(c) = (a) 7X M Fez+, (d) = (a) -k 1.1 X M Fez+, (e) = (a) -k 1.5 X M Fe2+. Conditions: v = 2 mV s-'; t = 1 s
+
+
a t -0.97 V ( I ) and that of the >C=N--N< group in an experimental benzhydrylpiperazine derivative at -0.83 V ( 4 ) in the same medium. The potential of reduction of Drazoxolon is therefore more in agreement with those of azo dyes which are reduced about 300-400 mV more positive than azomethine-containing species (22, 23). Further evidence for Drazoxolon existing predominately as the azo-containing species in neutral to slightly alkaline aqueous solution was obtained following a study of the complexation properties of Drazoxolon with various divalent metal ions. The effect of varying Fez+ ion concentration on the polarographic behavior of Drazoxolon in BR buffer pH 8 is shown in Figure 8. From this it can be seen that as the Fez+ ion concentration is increased, the wave height corresponding to uncomplexed Drazoxolon decreases and a new wave corresponding to the Drazoxolon -Fe2+ complex appears a t a more negative potential. A plot of wave height (due to unbound Drazoxolon) vs. the molar ratio ([Fez+]/[Drazoxolon]) gave a point of inflection corresponding to a 1:3 complex of Fez+ with Drazoxolon. Drazoxolon was also found to complex to Ni2+ions but the shift in potential was found to be only of the order of 120-130 mV (as compared to the shift of 350 mV with Fez+);similar behavior has been reported for the reduction of azo dye-metal complexes (20, 21). Choice of Waves for Analytical Purposes. The best defined waves for the determination of these pesticide compounds were chosen based on the following parameters (i) wave height, (ii) degree of separation from potential of reduction of the supporting electrolyte, (iii) half-peak width in dpp. In the case of Cyolane and Cytrolane, the best defined waves for analytical purposes were obtained in BR buffer pH 6.0 (Figure 9a). This choice was made because although the peak heights were much higher in acid solution (pH 0-2) due to the 4 e- reduction process, the waves were affected by adsorption and were closely followed by the reduction of the supporting electrolyte. In alkaline solution (pH >8),the waves were again affected by adsorption and the peak height of the second wave in dpp was lower than that of the first wave in BR buffer pH 6. In the case of Chlordimeform, the best defined wave for analytical purposes was obtained in BR buffer pH 8 (Figure 9b) where there was the greatest degree of separation between the potential of reduction of Chlordimeform and that of the supporting electrolyte. In addition, Chlordimeform was not adsorbed strongly in this medium, as evidenced by the shape of the npp wave which exhibited only a slight maximum on the plateau. In the case of Drazoxolon, the best defined wave for analytical purposes was obtained in BR buffer pH 8.0 (Figure 9c), a medium in which Drazoxolon was soluble at concentrations up to 1 X 10-j M. In addition the wave was well defined and showed none of the effects of adsorption exhibited a t higher pH values. It did, however, show a large degree of
npp (-.-), and dpp (---) curves for (a) 5 X low5 X M Chlordimeform in BR buffer pH 8.0;(c) 5 X M Drazoxolon in BR buffer pH 8.0. Conditions: v = 2 mV s-'; t = 1 s; A € = -100 mV
Flgure 9. DC (-),
M Cytrolane in BR buffer pH 6.0; (b) 8.75
reactant adsorption, as evidenced by the peak shape of the npp wave. In these respective media, calibration plots for Cyolane, Cytrolane, Chlordimeform, and Drazoxolon in the dpp mode proved linear in the range 1 X lo-' to 1 X M ( 5 x lo-' to 1 X lo-' M for Chlordimeform) with slopes of 0.038, 0.040, 0.039, and 0.080 nA ng-' mL with detection limits of 25, 25, 5 5 , and 10 ng mL-', respectively. These detection limits ( d l ) were calculated using the expression dl = 3 sb/m where s b = standard deviation of the background current and m = slope of the calibration curve. The reason for the high detection limit for Chlordimeform is due to the reduction of Chlordimeform being followed closely by the reduction of the supporting electrolyte (Figure 9b). Determination of Drazoxolon in Grain Formulation. As a method for formulation analysis, polarography offers the advantages of rapidity, sensitivity, convenience, and lack of interference from nonactive ingredients in the formulation. For this investigation, we were able to obtain only a sample of Drazoxolon as a formulation (60% w/w grains). Using the method outlined in the Experimental section, the polarographic method found the concentration of Drazoxolon in the formulated sample to be 60.2 0.4% (average of six runs). In addition, the polarographic method was found simpler to perform than the colorimetric method previously described for this compound (12) since it did not require the solvent extraction step prior t o analysis. I t is also foreseen that polarography could provide a convenient method for the determination of formulations containing the other azomethine-containing pesticides mentioned in this paper.
*
ACKNOWLEDGMENT The provision of samples from the previously mentioned sources is gratefully acknowledged. LITERATURE CITED (1) (2) (3) (4) '
(5)
J. M. Clifford and W. Franklin Smyth, Analyst(London), 99, 241 (1974). M. A . Brooks and J. A. F. de Silva, Taianta, 22, 849 (1975). W. U. Malik and R. N. Goyal, Talanta, 23, 705 (1976). M. R. Smvth. W. Franklin Smvth, and J. M. Clifford, AnalChim. Acta, 94, 119 (i977). C E. McKone, T H. Byast, and R. J. Hance, Ana/yst(London),97, 653 (1972) - -, R. C. Blinn and J. E. Boyd, J . Assoc. Off. A m i . Chem.,47, 1106 (1964). N. R. Pasareh and E. J. Orloski, Anal. Mthods Pestic. Pbnt CkoWth Requl., 7, 231 (1974). R. Kumar and C. C. Burkhardt, J . €con. Entomol.. 65, 1593 (1972). V. Dittrich. J . €con. Entorno/.. 59. 889 11966): 59. 893 11966). H Geissbuhler K Kossmann I Baunok, and V F Boyd J Aauc Food Chem , 19, 365 (1971) K. Kossmann, H Geissbuhler, and V F Boyd, J Agric food Chem , 19, 360 (1971) \
(6) 17)
(8) (9) (10) (1 1)
ANALYTICAL CHEMISTRY, VOL. 50, NO. 12, OCTOBER 1978 (12) S.H. Yuen, Anal. Methods Pestic. Plant Growth Regul., 7, 665 (1974). (13) L. A. Summers and D. J. Shields, Chem. Ind., 1964, 1264. (14) L. Meites, "Pobrographic Techniques", 2nd ed.,Interscience, New York, N.Y., 1965, p 203. (15) J. Barrett, W. F. Smyth, and I. E. Davidson, J . Pharm. Pharmacol., 25, 387 (1973). (16) M. R. Smyth, W. Franklin Smyth, R. F. Palmer, and J. M. Clifford, Anal. Chim. Acta., 86, 185 (1976). (17) J. G. Osteryoung and K. Hasebe, Rev. Polarog., 22, 1 (1976). (18) M. R . Smyth and J. G. Osteryoung, Anal. Chem., 49, 2310 (1977). (19) G. Voss, K. Kossmann. and H. Geissbuhler, Anal. Methods Pestic. Plant Growth Regul., 7, 21 1 (1974).
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(20) W. U. Malik, R. N. Goyal, V. K. Mahesh, and V . Verma, J . Electroanal. Chem., 62, 451 (1975). (21) W. U. Malik, R. N . Goyal, and R. Jain, Talanfa, 24, 586 (1977). (22) T. M. Florence, D. A. Johnson, and G. E. Batley, J . Electroanal. Chem., 50, 113 (1974). (23) T. M. Florence, J . Electroanal. Chem., 52, 115 (1974).
RECEIVED for review April 7, 1978. Accepted June 29, 1978. support for this work was provided through
NSF Grant Number CHE 75 00332.
Trace Determination of Tetrachloroethylene in Natural Waters by Direct Aqueous Injection High-pressure Liquid Chromatography Robert Kummert, Eva Molnar-Kubica, and Walter Giger * Swiss Federal Institute for Water Resources and Water Pollution Control (EA WAG), CH-8600 Dubendorf, Switzerland
A rapid method for quantitative routine determinations of traces of tetrachloroethylene In natural waters is described. Water samples of 10-mL volume are introduced directly into a reversed-phase high pressure liquid chromatography (HPLC) system (octadecylsillca, methanoVwater). Detection is performed by UV absorption at 208 nm. A precision of *2.5 % and a detection limit of 0.06 kmol of tetrachloroethylene per L of water were achieved. A wide concentration range (0.06-110 kmol L-') can be covered. The method was successfully applied in an actual water pollution case. Other possible applications of the same technique are discussed.
T h e investigation of the occurrence of organic compounds in water supplies is a current topic of environmental chemistry (1). Volatile halogenated hydrocarbons are among those components which are frequently encountered in raw and treated waters (2, 3). Some halogenated compounds are formed during water chlorination processes ( 4 , 5 ) ;others are produced industrially and reach natural waters via accidental or intentional release to the environment. Tetrachloroethylene often occurs as a major constituent of the volatile components in various waters (3,5 , 6). In one case ( 7 ) ,high levels of this organic solvent in a water supply (up t o 0.5 pmol L-l) could be traced t o a heavy contamination of a subsurface aquifer where concentrations u p to more than 600 pmol L-' were detected. T h e techniques for the determination of organic traces in waters usually include a preconcentration step (e.g., solvent extraction or gaseous stripping) and subsequent chromatographic analysis. These time-consuming methods are usually not very suitable for routine analyses. There is, however, an urgent need for rapid methods because in many cases large numbers of samples should be analyzed. In the course of our investigation of the acute contamination of a ground water by tetrachloroethylene ( 7 ) , we have developed several procedures for the determination of tetrachloroethylene in water samples. In this paper we report a rapid method based on direct injection of water samples into a high-pressure liquid chromatography system consisting of reversed-phase separation and ultraviolet absorption detection. 0003-2700/78/0350-1637$01 .OO/O
In this method, preconcentration, separation, and detection are performed in one single operation. Thus, a minimum of time is necessary and losses by preconcentration procedures are avoided.
EXPERIMENTAL Apparatus. The eluent for high-pressure liquid chromatography was delivered by a Model 6000 A pump (Waters Associates, Milford, Mass.). Samples were introduced through a Valco 7000 psig valve (Valco Instruments Co., Houston, Tex.), equipped with a 2-, 5 - , or 10-mL samples loop. A 50-mL syringe (Model 1050, Hamilton Co., Reno, Nev.) was connected to the inlet of a filtering device containing MF-Millipore filters (0.45 Fm). This filter is normally used for sample clarification (Waters Associates). The outlet end of the filter holder was mounted on the inlet port of the sampling valve. No significant losses through adsorption on the filters were observed. For analyses, 30 cm x 4 mm i.d. pBondapak CIScolumns (Waters Associates) were used, and effluents were monitored with a variable-wavelength detection system (Perkin-Elmer LC-55). Peak areas were determined with an electronic integrator (Minigrator, Spectra Physics, Santa Clara, Calif.). Solvents. Methanol (Spectra AR grade) was purchased for Mallinckrodt and used without further purification. Water which served as part of the HPLC eluent mixture was doubly distilled and stirred overnight to remove volatile contaminants. Standard Solutions. Special care was taken to prepare the spiked water samples. A 1-L volumetric flask with a magnetic stirrer was filled up to the ground glass joint with water. The volume of water above the 1-L mark had been measured in advance. Tetrachloroethylene was then added as a 4.8 mmol L-' solution in methanol by a microliter-syringe, immersing the needle as deeply as possible. Subsequently, the flask was closed with a glass stopper so that no air bubbles were left. This solution was then stirred for about 30 s. Samples. Water samples were collected in glass flasks which were closed with glass stoppers without leaving a head space volume. This was necessary to avoid evaporation losses. Procedure. The 50-mL syringe was filled with the water sample which then was delivered through the filter into the sample loop. A methanol/water mixture was pumped through the HPLC system. The sample was then applied to the column by switching the valve to the inject position. In this way, the sample plug was pushed through the column while any nonpolar solutes were retained by the nonpolar octadecyl-surface of the column material. The eluent mixture was chosen to achieve sufficient separation from more polar solutes also absorbing at the detection wavelength C 1978 American Chemical Society
