Design and Optimization of a Teflon Helix Continuous Liquid-Liquid Extraction Apparatus and Its Application for the Analysis of Organophosphate Pesticides in Water C. Wu‘ and 1. H. Suffet* Environmental Studies lnstitute, Department of Chemistry, Drexel University, Philadelphia, Pa. 19 104
A statistical optimization study leading to the final design and operational parameters for extraction of organophosphate pesticides is described with a new “Teflon Helix Contlnuous Liquid-Liquid Extractor”. A coil length of 32 feet, helix winding diameter of 1 inch, aqueous flow rate of 900 ml/h, water to solvent ratlo of 1O:l without premixing were the optimal design parameters. Recoveries of I.cg to gg/i. concentrations of organophosphate pestlcides from fortified river water, sea water, and secondary sewage effluent were completed. Greater than 80 YO efficiency relative to batch extraction is demonstrated with contlnuous liquid-liquid extractlon and continuous evaporative concentration.
The unit operation of liquid-liquid extraction (LLE) has been used by many analysts for the isolation and concentration of organic pesticides from water with good results (I). Continuous liquid-liquid extraction (CLLE) is usually preferred over batch operation because of inherent continuous performance, labor savings, consistent sample handling, and the capability of sampling large volumes. However, many design and operational problems associated with the available continuous liquid-liquid extractors have limited the usefulness of this unit operation ( I , 2). A search for improvement in the design and the operation of the available continuous liquid-liquid extractors led to the design and construction of a new “Teflon Helix Continuous Liquid-Liquid Extractor”. The description and operational ,Jrocedures of this apparatus were reported previously (2).The mixing and extraction mechanisms of this new design are described in this paper. A statistical study leading to the final design and operational parameters for the extraction of organophosphate pesticides is also described. The analysis of pg to VgA. concentrations of organophosphate pesticides from fortified natural waters is demonstrated. Benzene is the solvent utilized as it appears to be an excellent solvent for extraction of organophosphate pesticides from aqueous solutions
Figure 1. Photographic view of the Teflon and glass modular designed, Teflon Helix Continuous Liquid-Liquid Extractor, mounted on a mobile cart (1) Solvent reservoir, (2) Sample reservoir, (2’)Sample reservoir and pre-filter (optional), (3) Micropump (4) Tee joint, (5)Premixer (optional), (6) Teflon helix mixer (7)Phase-separator, (8)Solvent phase exit, (9) Water phase exit, (10) Macroreticular resin bed (optional), (11) Solvent drying column (behind evaporator concentrator), (12) Evaporator concentrator, (13) Solvent reservoir recycle (optional), (14) Electrical power for parts 3, 5,and 12
(3,4).
EXPERIMENTAL Apparatus and Procedure. A picture of the Teflon Helix Continuous Liquid-Liquid Extractor is shown in Figure 1. Its design is based upon a modular concept for greater analytical flexibility and is mounted on a 2 X 2.5 X 3 ft movable cart. Figures 2 to 4 show the major parts of the extractor. They are a Teflon coil mixer, a glass phase-separator, and a continuous evaporative concentrator, respectively. The design criteria as well as the operational procedures have previously been reported (2).Figure 5 shows a simplified schematic of the extractor. In short, the dual-channel micropump pumps the water and the solvent from the respective reservoirs to the Teflon helix mixer via a tee joint. The resulting water-solvent mixture from the Teflon coil enters the bottom of the phase-separator where the water and the solvent separate into two streams by gravity. The lighter solvent phase (benzene in this study) exits from the top of the sepal
Present address, Gilbert/Commonwealth, Jackson, Mich.
49201.
Figure 2. Photograph of Teflon helix mixer (32 ft., 0.125-inch 0.d.
0.063-inch i.d. coil on a 1-inch diameter metal pipe)
rator. The heavier water phase exits from the bottom of the separator. The solvent phase is passed through a Na2S04 drying column and then into the continuous evaporative concentrator. The apparatus has the capabilities of performing continuous liquid-liquid extraction, sample enrichment, and solvent recycling. ANALYTICAL CHEMISTRY, VOL. 49, NO. 2, FEBRUARY 1977
231
-I 1
VENTING VALVE
%%GROUND JOINT
RECOVERED SOLVENT
INTERFACE
1
EXTRACT iNLET
U
CONCENTRACTED SAMPLE OUTLET
RAFFINATE OUTLET
1
GLASS CONNECTOR
Figure 4. Schematic diagram of continuous evaporator concentrator
WATER~SOLVENT MiXTURE INLET Flgure 3. Schematic diagram of glass phase separator-solvent than water type
PHASE
SEPARATOR
lighter
H E L I X TEFLON M I X I N G
COIL SOLVENT
MICROPUMP
Although the design of the Teflon Helix Continuous Liquid-Liquid Extractor is simple, the mixing and separation mechanisms that cause the water and the solvent to intimately mix and enable efficient extraction are very complex. This is due to interactions in the fluid acting simultaneously, Figure 5. Some components of the physical interactions believed to be responsible include pressure, inertia, gravity, viscosity, and dispersion. A quantitative description of these interactions was studied by a statistical design using an analysis of variance (anova) to analyze the experimental results. Statistical Optimization of Design Parameters. After the Teflon Helix Continuous Liquid-Liquid Extractor was designed, a set of preliminary statistical factorial experiments was made to optimize the design and operating parameters of the apparatus. The design parameters studied in a 25 statistical factorial experiment were (a) helix winding diameter, (b) coil length, (c) flow rate, (d) water to solvent ratio, and (e) the need for premixing. Table I lists the factors and levels studied in this experiment. The thirty-two runs of this preliminary statistical factorial experiment were made following a random order (5, 6). Results were then used as the input data and analyzed by an IBM 370/168 Computer, using available APL statistical package ANOVA (7). Subsequently, a final statistical design (23) was completed in replicate to pinpoint relationships. Analytical. Table I1 shows the group of 5 organophosphate pesticides studied. The aqueous concentrations are shown for the study of: a) the optimization of the continuous liquid-liquid extractor design (using distilled water) and b) recovery studies of natural water under different operational conditions. The gas chromatographic conditions, 232
Flgure 5. Simplified schematic diagram of the Continuous Liquid-Liquid Extraction Apparatus
Possible mixing and separation mechanisms are (1) Pressure, (2) Dispersion, (3) Gravity, (4) Viscosity, (5)Phase separation
Table I. F a c t o r s and Levels Studied in the P r e l i m i n a r y Statistical Factorial Experiments ( F ) Levels Factors
A , Helix winding diameter B , Coil length C, Flow rate (water) D ,Watwsolvent ratio E , Mixer
Low level
High level
1inch 4 ft 600 ml/h 1D:l With
2 inches 16 ft 900 ml/h 20:l Without
operational procedures of the extractor, and the water and solvent parameters were previously reported ( 2 ) . Table I11 shows the water quality characteristics of the natural waters used during fortification experiments. The natural water samples after collection were immediately centrifuged with a Sharples
ANALYTICAL CHEMISTRY, VOL. 49, NO. 2, FEBRUARY 1977
Table 11. Experimental Conditions for Continuous Liquid-Liquid Extraction-The Recovery Studies of a Mixture of Organophosphate Pesticides ExDerimental concentration Quoted purity, Chemical name
%
0,O-diethyl-0-p-nitrophenyl ester of phosphorothioic acid S,S,S-tributylphosphorotrithioate Tetraethylmethylene bisphosphoradithioate S - ((p-chlorophenyl) thiomethyl) 0,O-diethyl ester of phosphorodithioic acid 0-Phenyl-0-ethyl-0-p-nitrophenyl ester of phosphonothioic acid
99.7 95.2
Compound . Parathion
DEF Ethion Trithion EPN
Distilled water,u d1.
Natural waters, d .
51.5 101.5 81.6 157.1 132.0
25.8 50.8 40.8 75.4 66.0
.... 95.0
....
No enrichment, direct GLC analysis, 1 1. of water extracted with 50 or 100 ml of benzene (20:l or 1 O : l water to solvent ratio, respectively). Enrichment, 5 1. of water extracted with 100 ml of benzene recycled 5 times (1O:l water to solvent ratio). An enrichment to 1 ml and a 5000:l concentration factor was developed.
Table 111. Water Quality Characteristics of Schuylkill River Water, Synthetic Sea Water, and the Outfall of a Secondary Sewage Treatment Plant Schuylkill River water
Secondary sewage effluent (organic water)
Synthetic sea water
I
I1
Alkalinity (mg/l. as CaC03) Hardness (mg/l. as CaC03)
75 165
78 169
Color (units) Specific conductance (wmho) C1- (mg/l.) COD (mg/l.) SO42- (mg/l.) PH Dissolved solids (mg/l.) Total solids (mg/l.)
20 437 30 17.2 100 7.9 306 324
60 424 31 8.8 92 8.8 326 336
Alkalinity (mg/l.) Hardness (mg/l. as CaC03) Na+(mg/l.) Ionic strength C1- (mg/l.) F- (mg/l.) S042- (mg/l.) pH
113 1,672
10,550 0.72 18,980 1.3 2,649 7.8
I
I1
pH Settleable solids (mg/l.)
7.5 0
6.8 0
Suspended solids (mg/l.) Volatile solids, % Total carbon (mg/l.) Inorganic carbon (mg/l.) Total organic carbon (mg/l.)
66 91 97 2 95
70 84 99 19 81
Table IV. Three-Dimensional Presentation of the Experimental Results of the Preliminary Factorial Optimization Study (Apparent E-Value)
I
With mixer ( E l ) Water:solvent 1 O : l (01) 600 ml/h flow (C,)
900 ml/h flow ( C , )
4 ft (B1) 0.723 0.798 16 ft (6'2) 0.716 0.840 4 f t (B1) 0.696 0.841 Diam 1 inch (Ai) 16 ft (B,) 0.742 0.719 * Recalculated on a 1 O : l water to solvent basis.
Diam 2 inches ('42)
Water:solvent" 20:l (D,)
Without mixer (E,) Water:solvent 1 O : l (0,)
Water:solvent' 20:l ( 0 2 )
600 ml/h flow (C,)
900 ml/h flow (C,)
600 ml/h flow (Cl)
900 ml/h flow (C,)
600 ml/h flow (C,)
900 ml/h flow ( C z )
0.767 0.739 0.671 0.781
0.664 0.819 0.729 0.797
0.661 0.729 0.670 0.702
0.668 0.794 0.664 0.785
0.698 0.835 0.690 0.793
0.756 0.875 0.831 0.895
Super Centrifuge to remove the suspended solids. The water was pumped into the centrifuge by a Manostat Peristaltic pump at a flow rate of 125 ml/min while the centrifuge was operated at 40,000 rpm. The pH and the ionic strength of all water samples were adjusted to pH 4.2 and ionic strength 0.2 by adding KHzP04 except for sea water where only the pH was adjusted by adding concentrated H3P04. These conditions have been found t o minimize the effect of natural water character on the LLE process and maintain organophosphate stability ( 3 ) .The water samples after centrifugation, pH and ionic strength adjustment were stored in the refrigerator at approximately 3 "C. After the optimum conditions of continuous liquid-liquid extractions were completed, water blanks, fortified distilled and natural waters were analyzed. Solvent recycling and extract enrichment were
included t o recover the pesticides. Final studies were completed on a total volume of 5 1. of water solution. A solvent extract of approximately 1 ml was obtained (concentration factor of 5000:l). The aqueous pesticide concentrations in this final study was from 25-66 vg/l., Table 11.
RESULTS AND DISCUSSION Initial Factorial Experiment. Table IV is a three-dimensional presentation of t h e results obtained from the 25 statistical factorial experiments. Parathion d a t a are shown as a n example. T h e results are reported in terms of "apparent E-value'' which is the fractional amount of a solute partitioned ANALYTICAL CHEMISTRY, VOL. 49, NO. 2, FEBRUARY 1977
233
~~~~
~~~~~~~~~~~~
Table V. Computer Results of the Analysis of Variance for the Preliminary Factorial Optimization Experimentn
ss
Source A B AB C AC BC ABC D AD BD ABD CD ACD BCD ABCD E AE BE ABE CE ACE BCE ABCE DE ADE BDE ABDE CDE ACDE BCDE ABCDE Error Total
MS
F calcd
Prob. of F
0.0001805 0.0334111
2.9835 552.2500
0.6605 0.9248
1 2
0.0011281 0.0232201 4.0009031 0.0003920 0.0058320
18.6467 383.8037 14.9277 6.4793 96.3967
0.8319 0.9207 0.8180 0.7499 0.8962
3 4 5 6 7
0.0109520 0.0006480 0.0055651 0.0004061 0.0001901 0.003081 1 0.0000980 0.0001125 0.0000005 0.0003380 0.0080011 0.0001531 0.0004351 0.0005281 0.0001445 0.0063845 0.0204020 0.0000020 0.0022781 0.0013781 0.0066701 0.0000361 0.0067280 0.0000605 0.0000605
181.0248 10.7107 91.9855 6.7128 3.1426 50.9277 1.6198 1.8595 0.0083 5.5868 132.2500 2.5310 7.1921 8.7293 2.3884 105.5289 337.2231 0.0331 37.6550 22.7789 110.2500 0.5971 111.2065 1.0000
0.9095 0.7941 0.8951 0.7533 0.6673 0.8776 0.5740 0.5945 0.0985 0.7348 0.9034 0.6384 0.7599 0.7774 0.6304 0.8984 0.9190 0.1430 0.8664 0.8430 4.8994 0.4210 0.8996 0.5000
8 9 10 11 12 13 14
DF
0.0001805 0.0334111
0.0011281 0.0232201 0.0009031 0.0003920 0.0058320
1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000
0.0109520 0.0006480 0.0055651 0.0004061 0.0001901 0.0030811 0.0000980 0.0001125 0.0000005 0.0003380 0.0080011 0.0001531 0.0004351 0.0005281 0.0001445 0.0063845 0.0204020 0.0000020 0.0022781 0.0013781 0.0066701 0.0000361 0.0067280 0.0000605 0.0000605 0.1396600
1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 31.0000000
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Source-Main effects and interactions. A , Helix winding diameter. B , Coil length. C , Flow rate. D , Water:solvent ratio. E , W/Wo premixing. SS, Sum of square. DF, Degree of freedom. MS, Mean square. F , calcd, F distribution. Prob. of F , Probability of F distribution. into the solvent from the aqueous phase under a specific water to solvent ratio and water quality condition. Data presented in this paper have been converted to the same basis by recalculating all E-values on a 10:1 water to solvent basis for comparison purposes ( 2 ) . Tables V and VI show the computer results of the analysis of variance and summarizes the main effects of the factors studied, respectively. Table VI1 shows the two-way interactions of significance for the experiment. The greater the apparent E-value indicates the larger the effect. The other compounds (DEF, ethion, trithion, and EPN) behave similarily ( 4 ) . The conclusions that may be drawn from these factorial experiments are only preliminary as a “screening” experiment without replication.
Table VI. Computer Results of the Main Effects of the Factors Studied in the Preliminary Factorial Optimization Study
v
Levels of each factor
Factors A , Helix winding diameter B , Coil length C , Flow rate (water) D , Water:solvent ratio E , W/Wo premixing
Mean E’
1. Low (1 in.) 2. High (2 in.) 1. Low (4 ft) 2. High (16 ft) 1. Low (600 ml/h) 2. High (900 ml/h) 1. Low (1O:l) 2. High (20:l) 1.With 2. Without
0.750 0.755 0.720 0.785 0.780 0.726 0.734 0.771 0.753 0.753
Table VII. Two-Factor Interactionsn of Significance for the Preliminary Factorial Experiment (Apparent E-Value) BD interaction
( B i )4 ft (B2) 16 f t
BE interaction
DE interaction
( D l )1 O : l
(D2)20:1
Mean
(El) W
( E z )Wo
Mean
0.715 0.753
0.725 0.816
0.720 0.785
0.736 0.769
0.704 0.801
0.720 0.785
( 0 1 ) 1O:l ( D 2 ) 20:l
Mean (I
234
0.734
0.770
0.752
0.752
B. Coil length. D. Water:solvent ratio. E, W/Wo premixing. ANALYTICAL CHEMISTRY, VOL. 49, NO. 2, FEBRUARY 1977
0.752
0.752
El) W
( E * )Wo
Mean
0.759 0.745 0.752
0.709 0.796 0.752
0.734 0.770 0.752
Table VIII. Factors and Levels Studied in the Final Statistical Factorial Experiments (z3) Levels Factors A , Coil length E , Flow rate (water) C. Water:soIvent ratio
Low level
High level
16 ft
32 f t 900 mllh 20:l
600 mllh 1O:l
(a) The “helix winding diameter” (helix tube diameter) did not show any apparent effect on the yield. (b) The “coil length” showed a significant effect on the yield. The longer coil of 16 feet was much more efficient. (c) The “flow rate” showed a significant effect on the yield. The lower aqueous rate of 600 ml/h seems to give better yield than the higher rate of 900 ml/h. (d) The “water to solvent ratio” showed an effect on the yield. A 20:l water to solvent ratio gave a higher yield than a 1O:l water to solvent ratio. (e) The use of a “premixer” under the experimental conditions did not show significant effect on the yield. However, the use of the premixer showed interaction with “coil length” (BE) and “water to solvent ratio” (DE). Using a premixer increases the yield when a 4-foot coil was used. However, when a 16-foot coil was used, no apparent differences in yield were noted whether with or without a premixer. The relationship between the premixer and “water to solvent ratio” was not conclusive. With a premixer, better yield was obtained at a 10:1 water to solvent ratio. However, no explanation can be given as to why, a t a 20:l water to solvent ratio, better yield was obtained without premixing. A final factorial experiment was run with replicates. The results of the final study are statistically representative. A preliminary extraction efficiency of the continuous liquidliquid extraction apparatus of 81%was obtained for parathion by averaging the apparent E-values obtained with a 16-foot mixing coil and then dividing by the theoretical equilibrium E-values obtained from a batch liquid-liquid extraction study (2).
Final Factorial Experiment. The second fectorial optimization experiment (23) with replicates was run to finalize the design and the operating parameters of the continuous liquid-liquid extraction apparatus. Table VI11 lists the factors and levels studied in the final factorial optimization experiment. The factors of “helix winding diameter” and the use of a “premixer” were omitted since they had shown no significant effects in the preliminary experiment. The other factors studied in the second experiment were the same as in the first experiment. The only change made was the coil length which was increased from 4 and 16 feet to 16 and 32 feet. This change
was made to see if a greater yield could be obtained. The levels for flow rate and water to solvent ratios were not changed because of physical limitations of the equipment and ease of operation. Two replicates were made according to random order and the apparent E-values on a 1 0 1 basis was reported as the yield. Table IX shows the three-dimensional presen‘ tation of the results obtained for parathion. Table X shows the computer results of the analysis of variance and summarizes the main effects of the factors studied. Table XI shows the two-way interaction of significance. The conclusions that can be drawn from this factorial experiment are: (a) The different lengths of the mixing coil did not show any apparent effect on the extraction efficiency. Apparently a 16-foot long mixing coil will provide sufficient mixing for extraction of organophosphate pesticides from water by benzene. However, it is advisable to use the ?&foot mixing coil for the final design to ensure that best efficiency will be obtained for the extraction of other solutes. (b) “Flow rate” showed a significant effect on the performance of the apparatus. A flow rate of 900 ml/h showed a better yield than 600 mllh. Therefore, future extraction operation will use a flow rate of 900 ml/h. (c) “Water to solvent ratio” also showed an effect on the extraction efficiency. A 1 0 1 water to solvent ratio gave better extraction than a 20:l ratio. Since all future works will include continuous solvent recycling, solvent consumption is not a concern and a 1 O : l water to solvent ratio will be used for all future operations. The last two results seem to be in contrast to the first experiment; however, since replicates were made in the second study, the results should be more reliable. The other pesticides studied behave similarily to parathion ( 4 ) .After the final statistical factorial experiment, the optimal design and operating parameters for the water-benzenepesticides system were selected. Table XI1 lists these parameters. The efficiency of the final design of the continuous liquid-liquid extractor was 86% for parathion by the procedure utilized for the preliminary statistical design. An overall extractor efficiency ranged from 85 to 93% for all five organophosphate pesticides in the vgll. concentration range (2). Mixing a n d Extraction Mechanism. Unlike batch liquid-liquid extraction operation which is controlled by the thermodynamic equilibrium, continuous liquid-liquid extraction is controlled by the mass transfer step (8, 9). Although a thorough mixing of the solvent and the solution to be extracted is desirable in the liquid-liquid extraction operation, too intimate a mixture should be avoided to prevent subsequent separation difficulties due to the formation of an emulsion. An adequate mixing control in the continuous liquid-liquid extraction operation is essential. Emulsions were not observed to occur in this study. A consistent pattern of sample and solvent mixing appears to be occurring. No foam
Table IX.Three-Dimensional Presentation of the Experimental Results of the Final Factorial Optimization Study (Apparent E-Value)
0.721 0.805 ANALYTICAL CHEMISTRY, VOL. 46, NO. 2, FEBRUARY 1977
235
Table X. Computer Results of the Analysis af Variance for the Final Factorial Optimization Experiments
9s
BOU€CX
A
BF
B
Q,QQ23281 Q,O488&6
AI4
0,OQ(90226
e
0,0706231
AC BC ABC Error Total
0.0010081 0.0112891 0.0023766 0.0322685 0.1688674
Group means Grand mean is Correction factor A1 2 B1 2
c1 2
MS
P Calcd
Prob, Of F
OJi772
Q.82B9
12,1481 0.0Qb6
0.8818 O.1OQO
1,QQQQQQQ6,0023281 €,(9€iQ06OO QLM89816 1,800O0O0 Q.0000226 1.0000000 1.0000000 1.0000000 1.0000000
17.5089 0.2499 2.7988 0.5892
0.9968 0.3660 0.8696 0.5302
0,0706231 0.0010081 0.0112891 0.0023766 0.0040336
8.0000000 15.0000000
0.73831 8.7217 0.75037 0.72625 0.683 0.79362 0.80475 0.67188
Source-Main effects and interactions. A , Helix winding diameter. B, Coil length. C , Flow rate. D, Watersolvent ratio. E , W/Wo premixing. SS, Sum of square. DF, Degree of freedom. M S , Mean square. F calcd, F distribution. Prob. of F , Probability of F distribution. (I
Table XI. Two-Factor Interactiona of Significance for the Final Factorial Optimization Experiment (Apparent E-Value) C1 (1O:l)
Mean
C2 (20:l)
0.590 B1600 ml/h 0.776 0.834 0.754 Bz 900 ml/h 0.672 0.805 Mean a B, Flow rate. C, Water:solvent ratio.
0.683 0.794 0.739
Table XII. Optimal Design Parameters for the Continuous Liquid-Liquid Extraction Apparatus Coil length Helix winding diameter Aqueous flow rate Water:solvent ratio No premixing
32 ft
1inch 900 ml/h
1O:l
was observed as no air was present within the mixing system. Figure 5 is a simplified schematic diagram of the Teflon Helix Continuous Liquid-Liquid Extractor indicating the possible sites for the mixing and separation mechanisms. The first mechanism, the pressure transient, is contributed by the alternate “pulse” action delivered by the micropump, This alternate pulse pumping action delivers the water and solvent into the system in small successive segments. Every pulse introduces some disturbance between the many water and solvent segments in the system, thus creating contact between the two fluids. The second mechanism contributed to the mixing and extraction process is the combination of the alternate pulse pumping action and the use of a “tee joint” which connects the pump and the Teflon helix mixer. The water inlet from the micropump to the tee joint is %6-inch inside diameter while the inlet for the solvent is Y&-inch inside diameter. Since the water and the solvent ratio is either 1 O : l or 20:1, when a segment of solvent is being pumped into the tee joint, it forms 236
small droplets and/or a “jet” disperses into the water segment already in the system. This creates contact between the water and solvent. The third mechanism contributing to the mixing and extraction is gravity. Gravity operates because the Teflon helix mixer is set parallel to the ground. When the segments of water and solvent travel inside the helix coil, mixing and extraction occurs because of the difference in densities of the two fluids. The lighter phase apparently moves vertically upward through the heavier phase as the mixture moves respectively up and down the coil. The fourth factor that contributes to the mixing and extraction mechanism is friction between the walls and the droplets which causes rotation and internal stirring of the solvent in the water. The use of Teflon should aid this process. Teflon tubing was chosen for the helix coil mixer because it is chemically inert, nonbreakable, easy to work with, and has a %on-stick” property (10). This %on-stick” property was first observed by Fox and Zisman (11)when they studied the wetting ability of the Teflon surface by different liquids. They found that the cosine of the contact angle increases linearly with decreasing surface tension of the liquid. Liquids wet Teflon surfaces only if their surface tension at 20 OC is less than 20 dyn/cm, which means that comparatively few liquids will spread completely on Teflon. Since water has a contact angle of 1 0 8 O and a surface tension of 72.8 dyn/cm, Teflon is not wetted by water (11).Benzene, the solvent used in the continuous liquid-liquid extractor, has a contact angle of 4 6 O and a surface tension of 28.9 dynhm, which are considerably less than water (11).Therefore, Teflon is partially wetted by benzene. Because of the difference in their wetting abilities to the inside surface of the Teflon tubing, a “shear” or “viscous” potential results as the liquid streams (water and benzene) enter the Teflon mixing coil. This “shear” or “viscous” potential increases the contact between the water and the solvent, thus contributing to the mixing and extraction operation of the apparatus. The last factor is the flow of the two phases during phase separation. Continuous Liquid-Liquid Extraction of Organophosphate Pesticides from Fortified Waters. A series of fortification studies were completed with the designed Teflon
ANALYTICAL CHEMISTRY, VOL. 49, NO. 2, FEBRUARY 1977
Table XIII. Continuous Liquid-Liquid Extraction of Organophosphate Pesticides from 5 Liters of Fartified Waters Using Continuous 8 d v e n t Resyoling and @ampleEnrichment Yield (E')a
___
I _ . -
Compound
Distilled water (2)b
Diitillecl water without resinc
Distilled water with resin0
Parathion DEF Ethion Trithion EPN
0.498 f 0.025 0.789 & 0.039 0.867 f 0.039 0.862 f 0.056 0.819 f 0.057
0.786 0.766 0.798 0.902 0.915
0.771
0.771 0.795 0.810 0.941
Sea water with resin'
River water without reiin'
0.873 0.856 0.890 0.834 1.019
0.858 0.810 0.800 0.795 0.989
Secondary effluent without resinL 0.563 0.674 0.912
1.019 1.251
Reference 2,515-1500 VgA. concentrations, 1liter of water, no solvent recycling. 0 All data corrected for their respective blanks. Table 11,25-75 qg/l. concentrations.
Helix Continuous Liquid-Liquid Extractor including continuous sample enrichment. The group of five organophosphate pesticides shown in Table I1 were studied. Table XI11 shows the percent recoveries obtained for 25-75 qg/l. of organophosphate pesticides from 5 1. of different kinds of water, Table 111. These data are compared to the recovery of 5001500 ag/l. of organophosphates recovered from 11. of p H 4.2, orthophosphate buffered distilled water as completed in a previous study ( 2 ) .In the previous study an average recovery of 80% was obtained for four of the pesticides, while only 50% recovery was obtained for parathion. Table XI11 shows an average recovery of 82.6% was obtained for the recovery of five pesticides from distilled water unaffected by the use of resin. An interesting phenomenon noted was that the thermal breakdown problems associated possibly with parathion (2) were not observed in this study. No apparent reason for this difference can be given since all operational conditions were maintained as previously reported. The only difference was that the aqueous concentration of the pesticides were one-fifth the value of that previously used. The usefulness of a macroreticular resin was explored in this study. Rohm & Haas XAD-2 macroreticular resin (10 cmS)was put into a %inch i.d. glass column and connected to the water outlet from the phase separator to adsorb the pesticides that were not extracted by the solvent (Figure 1). After the liquid-liquid extraction was completed, the XAD-2 resin column was eluted with 20 ml of benzene. The benzene eluate was collected and concentrated to 1 ml for gas-liquid chromatographic analysis. However, no significant improvement of yield was obtained with the addition of XAD-2 macroreticular resin (Table XIII). The highly specific and sensitive flame photometric detector (P-mode) was used for all analyses, yet peaks were noted for all sample blanks (2). The distilled water blank shows the least number of peaks while the organic water blank exhibits the most peaks. One major peak a t a retention time of 5 min appears in all natural waters. The peaks observed may be due to glassware contamination, impurities in the solvent, thermal breakdown of some compounds existing in the natural water, or phosphorus compounds present in the natural waters. The retention times of these peaks were noted. The difference of the amount obtained from the fortified and the blank samples is reported as the recovery. I t is noted that the yield obtained from sea and river waters was consistent with the yield from distilled water, which averaged about 80%. This indicates the importance of consistent water quality parameter adjustment. Secondary treatment effluent results are not
consistent. Clean-up may be needed to remove or minimize interference of other organic compounds present in secondary sewage effluents. The continuous liquid-liquid extraction apparatus designed and constructed through this study meets most of the criteria for a continuous apparatus that is economic to build, easy to operate, compact in size, and has great flexibility and high efficiency. However. the thermal breakdown problem should be tested and the operational capacity could be increased to improve its usefulness in the analysis of extremely low concentrations of organic compounds. The statistical factorial experiments have been proved to be very useful in the optimization of the many design and operating parameters of the continuous liquid-liquid extraction apparatus. Further work with this apparatus on other types of trace organic compounds of interest is under investigation. The use of heavier-than-water solvents with this apparatus is also being explored. The extractor is mounted on a cart for possible field or mobile laboratory operation. LITERATURE CITED (1) S. D. Faust and I. H. Suffet, "Analysis for Pesticides and Herblcldes In the Water Envlronment" in "Water and Water Pollution Handbook", L. L. Claccio, Ed., Marcel Dekker, New York, N.Y., 1972, Vol. 3, Chapter 23, p 1249. (2) C. Wu and 1, H. Suffet, "Continuous L!quid-Llquld Extractlon of Organic Pesticides from Aqueous Solutions", Water Pollution Assessment: Automatic Sampling and Measurement", American Society for Testlng and Materlals STP 582, 90 (1975). (3) 1, H. Suffet, C. Wu, and D. T. L. Wong, "Guidelines for Quantitatlve LiquidLiquid Extractlon of Organophosphate Pestlcldes from Water" in "Water Quality Parameters", American Society for Testlng and Materials, STP 573, 167 (1975). (4) C. Wu, Ph.D. Thesis, Drexel University, Philadelphia, Pa., 1975. (5) 0. L. Davles, "Design and Analysis of lndustrlal Experiments", 26 ed., Hafner Publishing Co., New York, N.Y., 1971. (6)A. E. Waugh, "Statistical Tables and Problems", 36 ed., McOraw Hill Co., New York, N.Y., 1952. (7) J. Prlns, "Statistical Program Package in APL", 5th ed., State University College of New York, New Paultz, N.Y., 1973. (8)J. H. Perry, "Chemical Engineer's Handbook", 3d ed., 1960, p 714; and 4th ed., McGraw-Hill, New York, N.Y., 1963, pp 14-40. (9) H. R. C. Pratt, "Countercurrent Separation Processes", Elsevier Publlshers, New York, N.Y., 1963. (IO) R. E. Kirk, and D.F. Othmer, "Encyclopedla of Chemical Technology", 2d ed., Interscience Publishers, New York, N.Y., 1971, p 829. (11) H. W. Foxand W. A. Zlsman, J. ColloidSci., 11, 514(1950).
RECEIVEDfor review June 7,1976. Accepted October 13,1976. Presented in part at the 171st National Meeting of the American Chemical Society, New York, N.Y., April 1976. Financial support was provided by the Office of Water Research, Environmental Protection Agency, Washington, D.C., Grant No. 801179.
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