High-Performance Concentration System for the Isolation of Organic

26 High-Performance Concentration System for the Isolation of Organic Residues from Water Supplies

Downloaded by FUDAN UNIV on January 24, 2017 | http://pubs.acs.org Publication Date: December 15, 1986 | doi: 10.1021/ba-1987-0214.ch026

R. B. Baird, C. A. Jacks, and L. B. Neisess County Sanitation Districts of Los Angeles County, San Jose Creek Water Quality Laboratory, Whittier, CA 90601 Recovery of nonpolar hydrophobic model compounds from a four-resin concentrator system was in the 70% range, whereas hydrophilic organic compounds were not recovered well. The concentrator system consisted of a series of 45-75-μm macro -reticular resin columns (MP-1 [anionic], MP-50 [cationic], XAD-2 [nonionic, nonpolar], and XAD-7 [nonionic, moderate polarity]) through which 500-L water samples were pumped with a high-pressure Teflon diaphragm pump. Columns were eluted with acetonitrile; ionic resin columns were also eluted with saturated NaCl, and the salt solutions were extracted with dichloromethane at neutral, acidic, and basic pH. Most model compounds were recovered from MP-1. The hydrophobic materials breaking through this column were usually found on MP-50 and XAD-2. The lower amounts of hydrophilic organics recovered were retained by XAD-2 and XAD-7. CfHEMICAL A N D BIOLOGICAL ANALYSES of trace organic mixtures in aqueous environmental samples typically require that some type of isolation-concentration method be used prior to testing these residues; the inclusion of bioassay in a testing scheme often dictates that large sample volumes (20-500 L) be processed. Discrete chemical analysis only requires demonstration that the isolation technique yields the desired compounds with known precision. However, chemical and/or toxicological characterization of the chemical continuum of molecular properties represented by the unknov/n mixtures of organics in environ mental samples adds an extra dimension of the ideal isolation technique: 0065-2393/87/0214/0557S06.00/0 © 1987 American Chemical Society

Suffet and Malaiyandi; Organic Pollutants in Water Advances in Chemistry; American Chemical Society: Washington, DC, 1986.


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O R G A N I C P O L L U T A N T S IN W A T E R

the residues yielded should be representative of the entire mixture of chemicals whose properties are to be tested. Isolation techniques used for concentrating unknown organic mixtures f r o m water samples i n clude solvent extraction (I, 2), low-temperature vacuum distillation (3), reverse osmosis (4-6), adsorption (7-1 J), and purge and trap (12). Efforts to concentrate sufficient amounts of organic residues for biological testing have usually relied on reverse osmosis (13, 14) or resin adsorption (15, 16) to process the large volumes of water needed. Each of these methods offers some advantages over other methods, yet both present some operational drawbacks i n that certain classes of organic compounds m a y be discriminated against. E f f i c i e n c y evaluations for concentration techniques have relied on either individual compound analysis b y gas chromatography-mass spectrometry ( G C - M S ) and highperformance liquid chromatography ( H P L C ) or grosser measurements such as dissolved organic carbon ( D O C ) and mutagenicity recovery. Most of the compounds identified b y chromatographic methods have been volatile lipophiles representing less than 20% of the D O C (17,18); few hydrophiles have been identified, usually amino acids and carbohydrates. T h e b u l k of the unidentified residue t y p i c a l l y gets categorized as humic, fulvic, or proteinaceous material. It is reasonable to assume that much of the D O C that has proven difficult to isolate and identify is polar or ionic at ambient p H , and the toxicological importance of a large portion of this unknown residue is arguable because of molecular size (19). This chapter presents the results of a study designed to evaluate the ability of a resin-based concentrator to recover a broad spectrum of model compounds specified b y the U . S . Environmental Protection Agency ( U S E P A ) (20) f r o m 500-L volumes of fortified distilled water. Such an evaluation may indicate the degree to which residues recovered f r o m real samples represent an unknown mixture of organics covering a w i d e range of properties. T h e development of the concentrator (21) was based on the chromatographic properties of microparticulate, macroporous, ion-exchange, and nonionic resins and their ability to act as efficient liquid chromatographic ( L C ) adsorbents (22-27). Operational parameters of the four resins (anionic M P - 1 , cationic M P - 5 0 , nonpolar X A D - 2 , and polar X A D - 7 ) i n practical application to reclaimed, surface, and ground waters (28) were within D O C capacities and optim u m ratios of sample volume to resin mass described for various resins (22-27, 29, 30); these and other pertinent references were previously reviewed (21). T h e results of the experiments reported herein w i l l be compareu with other measurements of isolation efficiency during system development and application (21, 28, 31).


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High-Performance Concentration System

559


Experimental Reagents. NaCl (Spectrum Chemical Co.) was fired 4 h at 550 °C in a muffle furnace to remove trace organic contaminants. Acetonitrile (HPLC grade; J. T. Baker), dichloromethane (Burdick and Jackson), 5-dimethylamino-lnaphthalenesulfonyl chloride (dansyl chloride; Aldrich), 0-p-nitrobenzyl-N,2V'diisopropylisourea (PNBDI; Regis), and Ν-succinimidy 1-p-nitropheny 1 acetate (SNPA; Regis) were used as purchased. Recovery experiments were conducted with the following standards, which were used as received without further purification: 5-chlorouracil (Calbiochem), furfural (Aldrich), crotonaldehyde (Aldrich), caffeine (Aldrich), isophorone (Aldrich), 2,4-dichlorophenol (Aldrich), anthraquinone (Aldrich), biphenyl (Ultra Scientific), 2,4'-dichlorobiphenyl (Ultra Scientific), 2,6-bis(l,ldimethylethyl)-4-methylphenol (Aldrich), 2,2',5,5'-tetrachlorobiphenyl (Ultra Scientific), benzo[e]pyrene (Aldrich), bis(2-ethylhexyl) phthalate (Scientific Polymer Products), 4-methyl-2-pentanone (Aldrich), quinoline (Kodak), 1-chloro dodecane (Eastman), stearic acid (Kodak), quinaldic acid (Aldrich), trimesic acid (Aldrich), glucose (Aldrich), glycine (Aldrich), and chloroform (Burdick and Jackson). Concentration System Materials. The concentration system consisted of a Milton-Roy model FR141-144 Teflon diaphragm pump and four 4.9- X 60-cm stainless steel columns connected in series with 3.2-mm stainless steel tubing (Figure 1). Each column was sealed with a 10-μπι stainless steel frit held in place by stainless steel washers and a screw-on cap at each end (Figure 2). The first and second columns contained, respectively, MP-1 anion-exchange and MP-50 cation-exchange resins (BioRad). The third and fourth columns con tained nonionic, nonpolar XAD-2 and nonionic, moderately polar XAD-7 resins, respectively (Rohm and Haas). The particle size range for all resins was 45-75 μπι. The ion-exchange resins (200-400 mesh as purchased) were washed on a 45-μηι screen with a stream of deionized water to remove particles less than 45 μιτι. One-kilogram batches of the XAD resin beads were ground as methanol slurries in a 5-L ball mill by using 4.5-5 kg of burundum cylinders; XAD-2 was ground for about 4 h, but 30 min was sufficient for XAD-7. XAD-2 was wet-sieved in methanol in a continuous flow system previously described (21). XAD-7 slurry was wet-sieved with tap water through a 75-μιη screen onto a 45-μηι screen. Each resin was slurry-packed into its respective column by using suction. After filling, water was pumped through each column, and then additional resin was added to top off the columns. Resin purification was done on-column while monitoring column effluent at 254 nm to ensure complete elution of contaminants. MP-1 was purified by pumping 1 Ν HCI, 1 Ν NaOH, and 1 Ν HCI followed by distilled water, methanol, acetonitrile, ethyl ether, and methanol. MP-50 was purified by pumping 1 Ν NaOH, 1 Ν HCI, and 1 Ν NaOH followed by water and organic solvents as for MP-1. XAD-2 was purified by pumping 1 Ν NaOH, 1 Ν HCI, distilled water, and organic solvents as for MP-1. XAD-7 was purified by pumping methanol, acetonitrile, and distilled water. After resin purification, column blanks were obtained by using the proper elution solvents. Purity criteria included constant chromatographic profiles using GC-flame ionization detection (GC-FID) and HPLC-UV and a negative response in the Ames test (21).


Suffet and Malaiyandi; Organic Pollutants in Water Advances in Chemistry; American Chemical Society: Washington, DC, 1986. 3JJM FILTER

PUMP

Figure 1. Schematic of resin concentrator.


26.

BAIRD ET AL.

PIPE THREAD WITH SEVERAL LAYERS OF TEFLON TAPE

561

High-?erf ormance Concentration System SPACERS TEFLON A SS

3/16* SS CAP MACHINED A THREADED 1/8" PIPE TO 1/8* SWAGE 1/2" χ 10um SS FRIT PRESS FITTED


/ NOMINAL 2" I.D. SCHEDULE SO TYPE S18 SS PIPE ASTM-A-312 WITH MACHMED ENDS

SS FRIT 2 χ 5-10jim POROSITY MACHINED 318 SS SPACER 2 3/18' χ 1/8" WITH 1/2" HOLE

Figure 2. Schematic of stainless steel columns and end fittings.

Sample Processing. Solutions of 70 mg/L of NaHC0 , 120 mg/L of CaSU4, and 47 mg/L of CaC^^F^O were prepared by mixing the reagent chemicals with distilled water in 200-L stainless steel drums. After each drum was filled, the organic standards were added with a 2.5-mL syringe while the sample was stirred. The organic stock solution concentrations were either 5 mg/mL, 0.5 mg/mL, or 50 Mg/mL (in acetonitrile, acetonitrile/water, or methanol), depending on the desired concentration in the sample. Concentration of 500-L samples was usually performed at a flow rate of 150 mL/min and 500 lb/in. . A piston-type pulse dampener (Hydrodyne) was used to minimize breakdown of resin particles. Flow rates did not exceed 250 mL/min (0.2-cm/s linear flow velocity). A final 4-L aliquot of concentrator effluent was collected and extracted sequentially with dichloromethane at neutral, acidic (pH 2), and alkaline (pH 11) pH by using two extractions at each pH. The dichloromethane extracts were pooled and further concentrated by using Kuderna-Danish evaporators. Analyti cal results from this residue were used in mass balance determinations under the conservative assumption that the concentrations of compounds present in the column effluent were relatively constant and that there was good partition ing of each into dichloromethane. Samples were eluted in the reverse direction by using the Milton-Roy pump with the pulse dampener removed. The eluant flow (50-75 mL/min at 200-300 lb/in. ) was monitored at 254 nm by using an Altex 153 detector with a biochemical flow cell. Elution with each solvent was continued until the detec tor response returned to base line. All columns were eluted with acetonitrile; this solvent was preceded by 4.5 M NaCl/0.04 M HCI and 0.04 M HCI elutions on the MP-1 column and by 4.5 M NaCl and distilled water elutions on the MP-50 column. The aqueous column effluents were adjusted to pH 2 (MP-1) or pH 11 (MP-50) and then extracted three times with dichloromethane. The acetonitrile column effluents were saturated with NaCl to separate the water, which was extracted twice more with acetonitrile. Fifty percent aliquots of the processed organic solvents from each respective column were concentrated in Kuderna-Danish evaporators to a final volume of about 10 mL (any remaining water was removed as the low-boiling azeotrope in the process) to give 25,000:1 3

2

2


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concentrates. The remaining unevaporated aliquots (500:1 concentrates) were saved for possible HPLC analysis. Column blanks were obtained between samples by repeating the elution with fresh solvent; blank concentrates were saved for chemical evaluation. Solvent concentrates from each column were analyzed to determine percent recoveries. The drums that contained the sample were rinsed with approximately 1000 mL of acetonitrile after the sample was concentrated. The acetonitrile was separated from excess water as just described and concentrated to a final volume of about 10 mL. Chemical Analysis. Analytical LC was performed on a Hewlett-Packard 1084B HPLC with a variable wavelength UV detector and a Shimadzu dual monochromator spectrofluorometer. Gradient elutions were performed by using water and acetonitrile as the solvents at a flow rate of 1.5 mL/min. The reverse-phase column for all analyses was a 4.6- X 25-mm Whatman PXS 10/25 ODS-2 used at a column oven temperature of 45 °C. Sample injections were made with a Hamilton gas-tight syringe into the 100-μί loop of a Rheodyne 7125 injector. The majority of standards were analyzed directly by HPLC-UV at 215 nm [crotonaldehyde, isophorone, 2,4-dichlorophenol, anthraquinone, biphenyl, 2,4'-dichlorobiphenyl, 2,6-bis(l,l-dimethylethyl)-4-methylphenol, 2,2',5,5'-tetrachlorobiphenyl, bis(2-ethylhexyl) phthalate, and quinoline] or 271 nm (furfural and caffeine). Five- or ten-microliter injections of the 25,000:1 concentrates were chromatographed by using a 19-min gradient, 8-95% acetonitrile, a 2-min initial hold time, and a 9-min final hold time. Standards with a poor UV chromophore (4-methyl-2-pentanone, 1chlorododecane, and stearic acid) were analyzed on a Perkin-Elmer 3920 gas chromatograph with a flame ionization detector and a 30-m SE-54 wall-coated open tubular (WCOT) fused-silica capillary column (J & W Scientific). The in jector temperature was 200 °C; the detector interface temperature was 280 °C. The carrier gas was He at 16.5 lb/in. , and the makeup gas was nitrogen at a flow of 40 cmVmin. Splitless l-μί injections of the 25,000:1 concentrates were made by starting with an oven temperature of 45 °C and the oven door open; after 2.75 min, the oven door was closed and the temperature was programmed at 4 °C/min to 280 °C, which was held for 8 min. The syringe was kept in the injection port for 15 s after injection. Chloroform was determined on the 500:1 concentrate by using a Tracor 550 gas chromatograph with a 310 Hall electroconductivity detector in the halogen mode, connected to a Tekmar LSC-2 purge and trap system. The column was an 8-ft 1% SP-1000 on 60-80-mesh Carbopack B. An oven tempera ture gradient of 80-220 °C at 8 °C/min after an initial hold of 2 min was used. Fifty microliters of the acetonitrile concentrate was diluted to 5 mL with organic-free water in the purging vessel for the analysis. Glucose was analyzed by using the Folin-Wu procedure (32) modified as follows: 25-mL glass-stoppered tubes were used, the final volume was 15 or 20 mL, and colorimetric analysis was performed at 650 nm. The aqueous and acetonitrile column effluents were analyzed prior to further concentration; 200-μί aliquots were used in the Folin-Wu test. Samples were prepared for Folin-Wu analysis by extracting them with dichloromethane to remove other species and evaporating the remaining aqueous phase to about 5 mL. Quinaldic, trimesic, and stearic acids were derivatized with PNBDI to facilitate their chromatographic separation and UV detection (33). The procedure was as follows: 125 μ]~, of PNBDI (2.6 mg) in dichloromethane was mixed with 200 μL of concentrated column effluent in a 5-mL Reactivial and 2


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563

diluted to 1 mL with acetonitrile; the vial was sealed and heated 2 h at 75 °C; the derivatized samples were analyzed by HPLC-UV at 254 nm by using a 10-min 20-95$ acetonitrile gradient with a 9-min final hold. Glycine was too polar to be resolved on the ODS-2 column and was also a very poor UV chromophore. Fluorescence derivatization using dansyl chloride (34) was employed. Derivatives were made by mixing 500 μ\^ of the unextracted MP-1 or MP-50 NaCl effluent with 1000 of acetonitrile, mixing for 15 s, and evaporating 200 μία of the organic phase to dryness in a 1-mL Reactivial. Next, 20 μία of pH 10.5 NaHC0 buffer (0.2 M) and 50 μΐ, of dansyl chloride solution (1.25 ^g/^L) were added. The vial was capped, agitated vigorously for 15 s, and heated at 100 °C for 2 min in a block heater. Ten microliters of the cooled contents was analyzed by using a 20-min gradient, 20-40$ mobile phase B, and a 5-min final hold. Mobile phase A was 10 mM sodium acetate to which 0.1-mL/L acetic acid was added; the pH was adjusted to 3.0 with phosphoric acid. Mobile phase Β was acetonitrile to which 0.1-mL/L acetic acid and 0.77-mL/L phosphoric acid were added. The fluorometer monochromators were set at 298 nm (excitation) and 545 nm (emission). Benzo[e]pyrene was analyzed by using HPLC with fluorescence detection; for the Shimadzu, the optimum wavelengths were 280 nm (excitation) and 394 nm (emission). A lead blank (500 L of distilled water containing 25 μg/L of Pb(N0 ) ) was pumped onto the ion-exchange columns only. The aqueous eluents were combined with the acetonitrile eluant for each column; NaCl was added to separate the aqueous and organic phases. After separation, the aqueous phase was extracted twice with acetonitrile. The extracts from each column were pooled and reduced in Kuderna-Danish evaporators to a final acetonitrile volume of 4-6 mL and then diluted to a known volume with distilled water for atomic absorption spectroscopic (AAS) determination of lead. AAS analysis was on an IL 951 with an air-acetylene flame; the 217.0-nm lead line was used. A 500-L solution containing 2 mg/L of free chlorine residual in distilled water was pumped onto the four-column system; the columns were eluted and the eluants were processed as described earlier. This chlorine blank and resin eluant blanks were analyzed by GC-MS by using a Finnigan 4023 with the INCOS data system and a 31,000-compound National Bureau of Standards library. Electron impact spectra were obtained by using an electron energy of 70 eV and a scan time of 1 s for the mass range 33-550 amu. A 30-m WCOT SE-54 fused-silica capillary column (J & W Scientific) was used for separations. Injections were made with the oven at 40 °C and the door open, the injector at 220 °C, and the interface at 270 °C. Two minutes after injection, the door was closed and the temperature was raised ballistically to 60 °C, ramped at 4 °C/min to 280 °C, and held there for 4 min. The split and septum purge valves were closed for injection and opened after 1 min.


3

3

2

Results ami Discussion Average recoveries for model compounds from five repetitive 500-L experiments are shown in Tables I and II. Table I lists data for the low-to-medium polarity organics (broadly classified by retention through more than half of the reverse-phase H P L C gradient) of low aqueous solubility, whereas Table II summarizes data for the organic acids and hydrophilic neutrals of higher polarity. Although these are not


564


Table I. Distribution of Resin Recoveries of Low-Polarity Model Compounds Average Recovery (%)

a

Compound (Concentration) Isophorone (50 Mg/L) Anthraquinone (50 Mg/L) Quinoline (50 Mg/L)


2,4-Dichlorophenol (50 Mg/L) 2,4'-Dichlorobiphenyl (50 Mg/L) 2,2' ,5,5' -Tetrachlorobiphenyl (5 Mg/L) l,l'-Biphenyl (50 g / L ) M

Benzo[e]pyrene (10 ng/L) Bis(2-ethylhexyl) phthalate (50 Mg/L) 1-Chlorododecane (50 Mg/L) 5-Chlorouracil (50 Mg/L) 2,6-Bis(l,l-dimethylethyl)4-methylphenol (50 μg/L) Chloroform (50 g/L) M

MP-1

1

o t a l

Average Recovery (%)

MP-50

XAD-2 74.1 (14.2) nd

77.0

29,4 (2.9) 5.3 (4.2) 1.7 (1.5)

79.9

73.2 (9.5) 64.2 (7.3)

3.7 (0.8) 10.8 (10.6) 68.1 (19.6) 4.6 (0.0) 9.9 (12.1)

58.2 (8.7) 67.0 (5.6) 53.3 (24.0)

7.7 (7.5) 14.0 (12.8) 3.0 (0.0)

10.8 (10.1) 1.6 (0.4) nd

75.1

62.5 (37.2) 60.2 (31.1) 77.5 (32.3)

2.7 (0.0) 14.6 (3.6) nd

6.4 (6.3) 12.6 (13.4) nd

65.7

nd 63.8 (20.1) nd

33.5

3.5 composite -

17.2

74.6

76.2 72.4

81.6 53.9

76.5 77.5 54.1 67.9 (22.8) b

N O T E : Classification as low polarity is based upon elution in the last half of the reverse-phase H P L C gradient described in the Experimental section. Ν = 5 for these results; standard deviations are given in parentheses; nd indicates not de tected. For XAD-7, none of the compounds were detected except for bis(2-ethylhexyl) phthal ate, which gave an average percent recovery of 1.0 ± 0.0. Standard used for spiking was found to be deteriorated after three experiments; Ν — 3 for this result.

a

rigorous distinctions, there is an obvious difference in the average recoveries of the two groups of compounds. Most of the compounds in Table I, which would be considered lipophilic, showed recoveries greater than 10%. The hydrophiles (Table II), all being water soluble in the grams-per-liter range, were less than 45%, and half were less than 1% recovery. Results of mass balance and recovery calculations for the com ponents of the experimental system (sample drum, resin columns, and column effluent) are shown in Table III. Resin breakthrough was detected (and at high levels) for only three compounds: furfural,


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Table II. Distribution of Resin Recoveries of Organic Acids, High-Polarity Compounds, and Hydrophilic Neutrals Average Recovery (%f Compound

0

Stearic acid Quinaldic acid


Trimesic acid Glycine Glucose Furfural

MP-1

MP-50

33.6 (16.7) 31.8 (9.0) nd 1.9 (2.3) nd nd

nd

Crotonaldehyde

nd

Caffeine

nd

4-Methyl-2-pentanone

nd

nd nd 1.7 (0.9) nd 0.5 (0.2) nd 1.5 (0.2) nd

XAD-2

XAD-7

Total (%)

10.5 (0.0) na

nd

36.3

na

31.8

na nd

na nd

nd 3.3

nd 4.9 (1.5) 1.0 (0.4) 34.3 (4.0) 26.8 (15.7)

nd 1.3 (0.4) 0.2 (0.0) 6.3 (1.9) nd

nd 6.6 0.8 41.8 26.8

e

N O T E : nd indicates not detected; na indicates not analyzed. " A l l concentrations were 50 Mg/L. Ν = 5 for these results; standard deviations are given in parentheses. Compound formed azeotrope with water, and variable losses occurred in solvent reduction. c

crotonaldehyde, and caffeine. Breakthrough may have also occurred for glucose, glycine, trimesic acid, and quinaldic acid, but it was not determined: glucose and glycine would not have partitioned into dichloromethane and could not be analyzed directly in the effluents, and analytical problems were encountered with trimesic and quinaldic acids. Sample drum residues of only five of the model compounds were detected sporadically and at low levels (

High-Performance Concentration System for the Isolation of Organic

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