Gas-liquid chromatography of polychlorinated biphenyl congeners

Walter L. Zielinski, Jr.,*1 Michele M. Miller,2·3 George Ulma,1 and Stanley P. Wasik2. Gas and Particulate Science Division, Center for Analytical Ch...
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Anal. Chem. 1986, 58, 2692-2696

Gas-Liquid Chromatography of Polychlorinated Biphenyl Congeners between a Nematic Liquid Crystal Phase and a Nonpolar Phase Walter L. Zielinski, Jr.,*’ Michele M. Miller,2JGeorge Ulma,’ and Stanley P. WasikZ Gas and Particulate Science Division, Center for Analytical Chemistry, National Bureau of Standards, Gaithersburg, Maryland 20899, and Chemical Thermodynamics Division, Center for Chemical Physics, National Bureau of Standards, Gaithersburg, Maryland 20899

transition temperature liquid cryst& appropriate to GLC oven The gas-tlqukl chromatographic retention behavkr of 54 potemperatures typically required for conventional separations lychlorhated Mphenyl (PCB) congeners contakrlng one to ten were developed and evaluated in these studies. One of these, chiorlne atoms was evaluated on a nematic llquld crystal (BMBT), (N,N’-Ms[p- m u t h O x y b e n z y ~ ~ ~ ~ , ~ ~ ’BMBT). - b l - ~ - t ~N,”-bis[p-methoxybenzylidene]-a,a‘-bi-p-toluidine , was selected for the present study on PCB’s, based on its To a first approxlmatlon, as antklpated, retention on the Ilqukl solid-nematic transition temperature (181 “C) (3) and its crystal appeared to be emhmced wtlh an increahg molecular ability to retain ita nematic order in a supercooled state for length-to-breadth ratlo for congeners containlng the same a prolonged period of time at GLC column temperatures as number ofchlorlne atoms. The retention behavior of 38 ofthe low as 120 “C (7). In addition of PAH isomer separations, PCB’s abo was examlned on a nonselectlve, nonpolar stathis liquid crystal also has been used for improved GLC tionary phase (Apolane-87) In whlch retention Is controlled separations of methyl naphthalenes (7), underivatized steroid more by solute vapor pressure differences than by soluteexperimental pharmaceuticals (9), azaheterocyclic epimers (8), statkonary phase free energy effects. The difference in the compounds (IO),and a restricted number of PCB isomers (11). free energy of mixing of PCB sdute pals between the two During the past several decades, the physical and chemical phases was found to be predominantly greater In the llquld attributes of PCB’s have satisfied numerous industrial uses; crystal phase, demonstrating an enhanced aelectMty for PCB these same properties, typical of chlorinated aromatic hyisomer separatlons over nonpolar phases. The retentton data drocarbons, render the PCB’s stable to many degradation suggest that the separation of many of the congeners mlght pathways (12). The ability to understand and awess the levels be Improved by uslng a liquid crystal stationary phase. and movement of PCB’s throughout the environment will remain speculative and semiquantitatable until sampling and analytical difficulties are resolved (13). The most common approach to quantifying PCB concentrations has been to Difficult definitive separation problems often arise in compare GLC retention data of a sample with those of gas-liquid chromatography (GLC) in the case of highly comstandards. However, difficulties and uncertainties have been plex mixtures. Such problems can be formidable when such encountered when attempting to identify isomers in a given mixtures are comprised of solutes that have very similar PCB mixture (13),considering that there are 209 possible PCB structural functionalities or that contain isomers having similar congeners containing from one to ten chlorine atoms in their vapor pressures, as exemplified by polycyclic aromatic hymolecular structures (Figure 1). Some, but not all, of these drocarbons (PAH’s) and polychlorinated biphenyls (PCB’s). difficulties (e.g., incomplete resolution of PCB congeners) have The earlier pioneering work of Kelker ( I ) and Dewar (2) been reduced in recent studies using fused silica capillary revealed substantial improvements in the GLC separations columns (14-16), including the use of Apolane-87 (17). of disubstituted benzene isomers, compounds having identical In addition to the complexity of PCB mixtures, many of functional structures and similar vapor pressures, using a the PCB congeners are difficult to separate on conventional moderately low temperature transition liquid crystal stationary GLC stationary phases. Packed GLC columns containing phase at a column temperature within its ordered mesophase SE-30, QF-1, or Apiezon L yield chromatograms containing range; to a first approximation, the isomers eluted in order numerous unresolved peaks (18). Albro and co-workers (19) of their increasing molecular length-to-breadth ratio. Hence, suggested the use of paired packed GLC columns (OV-3 and GLC liquid crystal stationary phases offer a third dimension Poly-MPE or OV-25 and Poly-MPE) or the use of a triplet for achieving successful separations (i.e., in addition to sepof columns (OV-lOl,OV-25,and Poly-MPE or OV-3, AN-600, arations based on solute vapor pressure differences or based and Poly-MPE) for improving the separation of some of the on polar solutestationary phase interactions), viz., differences PCB congeners. Support-coated open-tubular columns conin solute molecular shape. The use of this added dimension taining Apiezon L (20) or SE-30 (21) also resulted in incomfor separations has been shown to be especially potent for the plete separation of many of the PCB congeners. Temperaresolution of structurally rigid isomers (e.g., PAH’s, PCB’s, ture-programmed GLC analysis of PCB Aroclor mixtures on steroid epimers). a glass capillary column coated with Apolane-87 only partly The application of high transition temperature nematic resolved this problem (22). Using carefully prepared capillary liquid crystals for the GLC resolution of three to seven ring columns coated with various stationary phases in a GLC-MS PAH isomers was initially demonstrated (3)and subsequently study of PCB analysis, Peliazzari and co-workers (23) found elaborated (4-6) by Janini and co-workers. A variety of high Apiezon L, a nonpolar, nonselective phase, to give the best separations. Mullin and associates (14) reported retention data on a 50-m SE-54 fused capillary column for all 206 PCB Gas and Particulate Science Division. Chemical Thermodynamics Division. congeners, with only 11pairs of congeners having similar or Present address: Organic Analytical Research Division, Center identical relative retention times. Alford-Stevens et al. (15) for Analytical Chemistry, National Bureau of Standards, Gaithersdescribed an interlaboratory study for the determination of burg, MD 20899. This article not subject to U.S. Copyright. Published 1986 by the American Chemical Society

ANALYTICAL CHEMISTRY, VOL. 58, NO. 13, NOVEMBER 1986

Cln

Table I. Retention of Selected PCB Congeners on BMBT Liquid Crystal 150 ‘C

congener 5’

6’

6

Figure 1. Potential congeners of polychlorinated biphenyls. CI, and CI,‘ represent the number of chlorine atoms attached to each ring, where n and n’ range from 0 to 5.

EXPERIMENTAL SECTION Reagents. The PCB congeners were obtained as single com-

pounds from standard commercial sources at their highest stated purity. Solutions of the PCB’s for GLC analysis were prepared in pure n-pentane. The liquid crystal (BMBT, N,N’-bis[pmethoxybenzylidene]-a,a’-bi-p-toluidine) and Apolane-87 stationary phases were obtained from commercial sources. GLC analysis using BMBT revealed a single peak for each of the 54 congeners studied. Instrumentation. GLC analyses were performed using conventional gas chromatographs equipped with flame-ionization detection and one of the following columns: (a) a 6 f t X 2 mm i.d. glass column containing 1.5% BMBT on 100-120 mesh HP Chromosorb W, and (b) columns of 1.5- to 4-ft lengths containing 3 % Apolane-87 on 100-120 mesh HP Chromosorb W. All columns were operated at 150 “C using a He carrier flow rate of 30 mL/min. RESULTS A N D DISCUSSION

Initial retention studies of the PCB’s on BMBT at 190 “C (Le., above its solid-nematic transition of 181 “C) revealed that the congeners eluted too rapidly, with the perchlorinated decachloro congener eluting in less than 11 min (Table I). Since it has been established that this liquid crystal can retain its nematic configuration for at least 8 h in a supercooled state below its solid-nematic transition at temperatures as low as 120 OC (7), lower column temperatures were explored. A column temperature of 150 “C was subsequently selected as a useful temperature for the purposes of this study. To attain the supercooled state, the column was taken to 190 “C, held for 1h, and then cooled to 150 OC. A comparison of retention data for ten of the congeners on BMBT at 150 “C and a t 190 “C is shown in Table I, illustrating the utility of this choice. Retention times and relative retentions (to the 2-chlorobiphenyl congener) on BMBT a t 150 “C are summarized in Table 11. An examination of these data confirmed the expected behavior of increased retention on a nematic liquid crystal stationary phase for congeners having a relatively greater molecular length-to-breadth ratio (e.g., retention of 4C1> 3-C1> 2-C1; retention of 4,4’-diCl> 3,3’-diCl> 2,2’-diC1; retention of 2,4’,5-triC1 > 2,3’,5-triC1 > 2,2’,5-triCl). This behavior on a nematic liquid crystal phase can be explained

t,’

a

3.06 3.13 4.33 4.98 8.68 9.82 27.77 29.27 44.43 63.42

2,4‘,5 2‘,3,4 2,2’,4,4’,6 2,2’,4,4’ 2,3‘,4,4‘,6 4,4‘ 3,3‘,4,4’ 2,2’,3,3’,4,4’,6 2,2’,3,3’,4,4’

5

PCB’s in contaminated sediments using GC-MS with SE-54 or DB-5 fused silica capillary columns, reporting a relative standard deviation of 38%. Cooper and co-workers (16) evaluated the use of relative response factors, electron-capture detection, a 60-m DB-5 fused silica capillary column, and surrogate PCB congener mixtures since they contained a more manageable number of congeners for calibration rather than Aroclor mixtures. Bush et al. (17)using a 60-m Apolane-87 soda glass capillary column demonstrated an improvement in PCB peak structure assignments over similar Apiezon L columns. The present study evaluated the retention behavior of 54 PCB congeners containing one to ten chlorine atoms on BMBT and contrasted this to the retention behavior of 38 of the congeners on a nonpolar, nonselective phase, Apolane-87. The differences in the degree of separation of pairs of PCB congeners between the two phases were examined on the basis of the differential free energy of mixing of a congener pair between the two phases.

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DECA

190 o c ab

1.00 1.02 1.42 1.63 2.84 3.21 9.08 9.56 14.52 20.73

t,’

ab

0.95 0.98 1.21 1.42 2.26 2.64 6.72 6.16 9.50 10.76

1.00 1.03 1.27 1.49 2.38 2.78 7.07 6.48 10.00 11.32

t,’ = corrected retention time (min) = t,(congener) - t,(metha = relative retention = t,’(congener)/t,’(2,4’,5).

ane).

Table 11. Retention of PCB Congeners on BMBT Liquid Crystal at 150 ‘C

congener biphenyl 2 2,2’ 2,6 3 2,s 2,2’,5 2,4,6 2,4 293 3,5 2,2’,6,6’ 2,4’ 4 2,2’,5,6’ 2,2’,4,6 2,3‘,5 3,3‘ 2,2’,4,6,6’ 2,2‘,4,4‘,5,5‘ 2,2’,5,5’ 2,3,5 2,3‘,4,6 2,2’,4,5,6 2,2‘,3‘,5 2,4’,5 394 2’,3,4

t,’

an

congener

t,‘

CY

0.41 0.50 0.64 0.65 0.88 0.97 1.15 1.36 1.41 1.43 1.49 1.50 1.66 1.69 1.76 1.82 1.91 2.06 2.13 2.15 2.30 2.32 2.88 2.90 2.98 3.06 3.10 3.13

0.82 1.00 1.28 1.30 1.76 1.94 2.30 2.72 2.82 2.86 2.98 3.00 3.32 3.38 3.52 3.64 3.82 4.12 4.26 4.30 4.60 4.64 5.76 5.80 5.96 6.12 6.20 6.26

2,2‘,3,5 2,3’,5,5’ 2,3,5,6 2,2’,4,4‘,6,6’ 2,2’,3,5,6 2,3’,4,5’,6 2,3,4 2,2’,4,4’,6 2,2’,3,4,6 2,2‘,3,3‘ 2,2’,4,5,5’ 2,2’,4,4’ 2,4,4’,6 2,3,3’,4,4’,5 2,3’,4‘,5 2,3,4,5 2,2’,3,4,5 2,3’,4,4’,6 4,4’ 2,3,4,5,6 2,3,4,4‘,6 2,2‘,3,4,4‘,5‘,6 2,3,3’,5,6 3,3‘,4,4’ 2,2’,3,3’,4,4’,6 2,2’,3,3’,4,4’

3.22 3.50 3.56 3.56 4.08 4.08 4.18 4.33 4.40 4.62 4.81 4.98 5.23 5.26 6.17 6.33 6.58 8.68 9.82 10.04 15.27 15.76 21.84 27.77 29.27 44.43 63.42

6.44 6.60 7.12 7.12 8.16 8.16 8.36 8.66 8.80 9.24 9.62 9.96 10.46 10.52 12.34 12.66 13.16 17.36 19.64 20.08 30.54 31.52 43.68 55.54 58.54 88.86 126.84

DECA

a = t,’(congener)/t,’(2-chlorobiphenyl); t,/ in

minutes.

as follows: molecules of a more “rodlike” isomer, due to their more favored geometry, can more closely approach the ordered “rodlike” liquid crystal phase molecules, resulting in a more ordered solution and stronger solute-solvent enthalpic interactions. The data in Table I1 also show PCB congeners of higher chlorine content eluting, in some cases, prior to PCB congeners of lower chlorine content. This is attributed to the coupling of solute vapor pressure differences with differences in the degree of ethalpic interactions resulting from entropic-related molecular shape differences of the PCB solutes. Despite this complexity, several rules can be derived from examination of the data in Table 11: (a) a chlorine atom located in the 4 or 4‘ position has the most pronounced effect on increased PCB retention; (b) the order of chlorine positional attachment decreases PCB congener retention from 4 to 3 (or 5) to 2 (or 6); (c) the attachment of chlorine atoms on only one of the two rings can produce a greater retention than that obtained if the same number of chlorine atoms are distributed on both rings (consistent with the greater rodlike character

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ANALYTICAL CHEMISTRY, VOL. 58, NO. 13, NOVEMBER 1986

Table 111. Retention of Selected PCB Congeners on BMBT Liquid Crystal at 150 OC t,’

biphenyl

O1Q

0.41

mono 2 3 4

0.50 0.88 1.69

1.00 1.76 3.38

2,2‘ 2,6 2,5 2,4 2,3 3,3’ 4,4‘

0.64 0.65 0.97 1.41 1.43 2.06 9.82

1.00 1.02 1.52 2.20 2.23 3.22 15.34

2,2‘,5 2,3’,5 2,3,5 2,4’,5 2‘,3,4 2,3,4

1.15 1.91 2.32 3.06 3.13 4.18

1.00 1.66 2.02 2.66 2.72 3.63

2,2’,6,6’ 2,2’,5,5‘ 2,2‘,3,3‘ 2,2’,4,4’ 3,3‘,4,4‘ penta 2,2’,3,5,6 2,2’,3,4,6 2,2’,3,4,5

1.50 2.30 4.62 4.98 27.77

1.00 1.53 3.08 3.32 18.51

4.08 4.40 16.05

1.00 1.08 3.93

2.15 3.56 44.43

1.00 1.66 20.67

15.76 29.27

1.00 1.86

di

tri

Table IV. Relative Retention of PCB Congeners at 150 OC on BMBT Liquid Crystal and on Apolane-87 ((387) congener

C87

BMBT

biphenyl

0.62 1.00 1.56 1.71 2.51 2.84 3.05 3.06 3.89 3.92 4.20 4.43 4.72 5.24 5.28 6.16 6.28 6.49 7.40 7.57

0.82 1.00 1.28 1.30 1.94 2.86 3.32 2.82 2.30 2.72 2.98 3.00 4.12 19.64 6.20 3.52 3.64 3.82 6.12 6.26

2 2,2’ 2,6 2,5 23 2,4’ 2,4 2,2‘,5 2,4,6 395 2,2‘,6,6’ 3,3‘ 4,4‘ 394 2,2’,5,6’ 2,2’,4,6 2,3’,5 2,4’,5 2’,3,4

congener 234 2,2’,5,5’ 2,3*,4,6 2,2’,3’,5 2,3,5,6 2,2’,3,5 2,2’,4,4’ 2,4,4’,6 2,2‘,3,3‘ 2,3’,5,5’ 2,3,4,5 2,3’,4’,5 2,2’,4,5,5’ 2,3,4,5,6 2,2‘,3,3‘,4,4‘,6 3,3’,4,4’ 2,2’,3,3’,4,4’ 2,2’,4,4’,6,6’

DECA

C87

BMBT

7.62 9.32 9.93 10.18 10.21 10.93 11.22 11.39 11.70 15.49 17.84 19.38 25.01 27.90 28.72 37.82 86.71 222.89 449.08

8.36 4.60 5.76 5.96 7.12 6.44 9.96 10.46 9.24 6.60 12.66 12.34 9.62 20.08 31.52 55.54 88.86 7.12 126.84

tetra

2,2‘,4,4‘,5,5’ 2,2‘,4,4‘,6,6‘ 2,2‘,3,3‘,4,4’

hepta 2,2’,3,4,4’,5’,6 2,2’,3,3’,4,4’,6

= t,’(congener)/t,’(first eluting congener in class); t,’ in min-

utes. ~

Case I: Heptadecane (Column 2) vs. 1-Heptadecene (Column 1) (45 0C)a

hexa

‘01

Table V. Two-Column Regression Analysis: log 01 (Column 2) vs. log 01 (Column 1)

~~

solute class

no. of solutes

slope

Rb

n-alkanes branched alkanes n-alkenes trans-n-alkenes n-chloroalkanes

3 13 3 5 3

1.0004 1.0090 1.0152 1.0062 1.0032

0.9999 0.9999 1.0000 0.9999 0.9999

Case 11: C87 (Column 2) vs. BMBT (Column 1) (150 “C)‘ PCB class 0-10

c1

mono-C1 of the former case); and (d) the PCB molecular length-tobreadth ratio (Le., “rodlike” character) varies with the addition of chlorine atoms. Consistency of these rules with the observed retention data on BMBT can be seen more clearly by grouping the data according to classes containing the same number of chlorine atoms (Table 111). I n accordance with rule (a), and as illustrated earlier, increased retention is obtained with increased PCB “rodlike” character for PCB congeners containing one to three chlorine atoms. This correlation also is observed for PCB’s containing four to six chlorine atoms: viz., 2,2’,4,4’ > 2,2’,3,3‘ > 2,2’,5,5‘ > 2,2’,6,6‘, with 3,3’,4,4’ being the most “rodlike” and the most retained; 2,2’,3,4,6 > 2,2‘,3,5,6 and 2,2’,3,4,5 >> 2,2’,3,4,6; and 2,2’,3,3’,4,4’ >> 2,2‘,4,4‘,6,6‘ > 2,2’,4,4’,5,5’. In order to assess the relative magnitude of the interaction

of the PCB congeners with an ordered liquid crystal stationary phase, comparative retention data were developed on a nonpolar stationary phase (Apolane-87) using the same column temperature and carrier flow rate. On this nonpolar phase, solute retention predominantly is controlled by solute vapor pressure differences and weak solute-solvent interactions. Numerous cases of retention reversals were observed (Table IV) between BMBT and Apolane-87, most of which can be attributed to strong PCB congener-BMBT interactions which override vapor pressure effects. The most dramatic reversals were observed for PCB congeners having high molecular length-to-breadth ratios (e.g., 4,4’-dichlorobiphenyl, 2,2‘,4,4‘,6,6‘-hexachlorobiphenyl).

di-C1

tri-C1 tetra-C1 penta-C1 hexa-C1

no. of solutes

slope

Rb

39 6 10 6 15 2 2

0.7319 1.3571 1.5667 1.4759 1.2886 6.7307 -2.6736

0.8622 0.9412 0.8543 0.9351 0.9332

“Data from ref 26. bCorrelation coefficient. EThiswork. Typically, if solute retention on two different stationary phases is only governed by solute vapor pressure effects and nonselective solute-stationary phase interactions (i.e., using two nonselective stationary phases), a linear regression analysis of the logarithm of the relative retentions of solutes in a given solute class on one column against the relative retentions of the same solutes on the second column will provide a linear slope close to unity with a high correlation coefficient. This is exemplified in the top portion of Table V for various alkane and alkene classes on n-heptadecane vs. 1-heptadecene. This approach was used as a test of the difference in retention control afforded between BMBT and Apolane-87 (bottom portion of Table V). This test afforded regression slopes that were widely scattered from unity having low correlation coefficients for the various PCB isomer classes, confirming the inherent selectivity of BMBT for separations of PCB congeners. Apolane-87 has previously been shown to separate solutes on the basis of vapor pressure differences and nonselective (“conventional”) solute-stationary phase interactions (24, 25). The underlying thermodynamics controlling GLC retention were examined in an attempt to quantify the stationary phase

ANALYTICAL CHEMISTRY, VOL. 58, NO. 13, NOVEMBER 1986

Table VI. Ge Differences” of PCB Congener Pairs between BMBT and Apolane-87 (C87)

PCB congener pair

2,4/2,3 2,2‘,4,4’/2,3,4,5 2,4‘/2,4

3,3’/2,2’ 2,4,5/2,3’,5

(AGcs7 AGBMBT), CY**

cal/mol

0.959 0.795 1.14 1.16

1.20 1.34

34/24

4,4‘/3,4 4,4’/3,3’ 2,2‘,3,3’,4,4‘/2,2’,4,4‘

-35.5 -193 109 123 150 244

3.14

964

4.22

1212

32.08

2920

a @ is the difference in the partial molar excess free energy of mixing of two solutes at infinite dilution in the same stationary phase. ba* = (BMBT)/(C87).

selectivity differences observed qualitatively between BMBT and Apolane-87. Thermodynamic Basis of Selectivity between B M B T and Apolane-87. Solute retention (expressed as the specific retention volume, Vgo) on a given stationary phase (having a molecular weight, ML)at a given column temperature may be expressed as

Vgo = 273R/poyML where R is the gas constant (62 361 cm3 mm/(deg mol)), p” is the vapor pressure (mm) of the pure solute at the column temperature, and y is Henry’s law activity coefficient of the solute. Then the relative retention ( a )of two solutes, 1 and 2, on the GLC column at the same temperature, defined as the ratio of the retention values of the two solutes, may be written as

When the retention data for the same two solutes are determined on two different stationary phases, A and B, a new quantity (a*) may be defined as the ratio of the relative retention of the two solutes on phase A to that on phase B. Using eq 2, a* may be written as

a* =

~ ~ 1 ° ~ 1 / ~ 2 0 ~ 2 ~ A ~ ~ 2 0= ~ [Y1/Y2IA[YP/YlIB 2 / ~ l o ~ l ~ B

(3) Since the solute partial molar excess free energy of mixing (G-e) a t infinite dilution in a given stationary phase is given by RT In y, and the difference in the partial molar excess free energies of mixing between the two solutes in the given stationary phases (A@) is given by RT In [-y2/y1],a relationship may be developed from eq 3 as In a* = AGge/RT - AGAe/RT

(4)

which may be expressed as

R T In a* = (AGge - AGAe)

(5)

From eq 5 and the retention data developed for the PCB congeners on BMBT and Apolane-87 a t 150 “C, values may be calculated for CY* and ( AGApolane.87- AGBMBT)for selected pairs of the PCB congeners, with the latter values representing the magnitude of the differences in the free energies of mixing of two solutes between the two stationary phases (i.e., the magnitude of the difference in selectivity afforded by the BMBT liquid crystal phase over a nonselective phase (Apolane-87) for separating two PCB congeners). Such values are depicted in Table VI for nine selected pain of PCB congeners, ranging from -193 to 2920 cal/mol. Negative cal/mol values indicate that the separation of the congener pair is controlled

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more by vapor pressure differences of the two solutes, while positive cal/mol values indicate the magnitude of selectivity of BMBT over Apolane-87 for separating the PCB congener pairs. Clearly, this exercise could be carried out for a number of PCB congener pairs to assess thermodynamically based improvements in GLC separations of such pairs on a nematic liquid crystal in its ordered mesophase state. Despite the marked improvement in separations obtained for a number of the PCB congeners on BMBT over the nonselective Apolane-87 phase, it is obvious even the use of a very selective phase cannot resolve all of the members of the PCB class, due to its high complexity. However, by combining the retention data obtained from both phases, many of the PCB congeners can be resolved due to the selectivity differences attainable on two such phases. Hence, the coupling of retention data obtained on a liquid crystal column with retention data obtained on a high-efficiency capillary column (e.g., ref 17) should further enhance the confirmation and measurement of PCB congeners in complex PCB mixtures. Registry No. BMBT, 55290-05-6; 2-C1, 2051-60-7; 3-C1, 2051-61-8; 441, 2051-62-9; 2,2’-diCl, 13029-08-8; 2,6-diC1, 33146-45-1; 2,5-diCl, 34883-39-1;2,3-diCl, 16605-91-7;2,4’-diC1, 34883-43-7;2,4-diC1, 33284-50-3;3,5-diCl, 34883-41-5; 3,3’-diC1, 2050-67-1; 4,4‘-diC1, 2050-68-2;3,4-diCl, 2974-92-7;2,2’,5-triCl, 37680-65-2; 2,4,6-triCl, 35693-92-6; 2,3’,5-triCl, 38444-81-4; 2,4’,5-triCl, 16606-02-3; 2’,3,4-triC1, 38444-86-9; 2,3,4-triCl, 55702-46-0; 2,3,5-triC1,55720-44-0; 2,2’,5,6’-tetraCl,41464-41-9; 2,2‘,4,6-tetraCl,62796-65-0; 2,2’,5,5’-tetraCl, 35693-99-3; 2,3‘,4,6tetraC1, 60233-24-1; 2,2’,3’,5-tetraCl,41464-39-5;2,3,5,6-tetraCl, 33284-54-7;2,2‘,3,5-tetraCl, 70362-46-8;2,2’,4,4’-tetraCl, 2437-79-8; 2,4,4’,6-tetraCl, 32598-12-2; 2,2’,3,3’-tetraCl, 38444-93-8; 2,3’,5,5’-tetraCl,41464-42-0; 2,3,4,5-tetraCl,33284-53-6; 2,3’,4’,5tetraC1,32598-11-1;3,3’,4,4’-tetraCl,32598-13-3;2,2’,6,6’-tetraCl, 15968-05-5; 2,2’,4,5,5’-pentaCl, 37680-73-2; 2,3,4,5,6-pentaCl, 18259-05-7; 2,2’,4,6,6’-pentaCl, 56558-16-8; 2,2’,4,5,6-pentaCl, 55215-17-3; 2,2’,3,5,6-pentaCl, 73575-56-1; 2,3’,4,5’,6-pentaCl, 56558-18-0; 2,2‘,4,4’,6-pentaCl, 39485-83-1; 2,2’,3,4,6-pentaCl, 55215-17-3; 2,2’,3,4,5-pentaCl, 55312-69-1; 2,3’,4,4’,6-pentaCl, 56558-17-9; 2,3,4,4’,6-pentaCl, 74472-38-1; 2,3,3’,5,6-pentaCl, 74472-36-9;2,2’,3,3’,4,4’-hexaCl,38380-07-3; 2,2’,4,4’,6,6’-hexaCl, 33979-03-2; 2,2’,4,4’,5,5’-hexaCl,35065-27-1; 2,3,3’,4,4’,5-hexaCl, 52663-71-5; 2,2’,3,4,4’,5’,638380-08-4; 2,2’,3,3’,4,4’,6-heptaCl, heptacl, 52663-69-1; Apolane-87, 75536-64-0;biphenyl, 92-52-4. LITERATURE C I T E D Kelker, H. 2.Anal. Chem. 1963, 8 6 , 254. Dewar, M. J. S.; Schroeder, J. P. J . A m . Chem. SOC. 1984, 86. 5235. Janini, G. M.; Johnston, K., Zielinski, W. L., Jr. Anal. Chem. 1975, 47, 670. Janini, G.M.; Muschik, G. M.; Zielinski, W. L., Jr. Anal. Chem. 1976, 4 8 , 809. Janini, G. M.; Muschik, G. M.; Schroer, J. A.; Zielinski, W. L., Jr. Anal. Chem. 1978, 4 8 , 1879. Zielinski, W. L., Jr.; Janini, G. M. J . Chromatogr. 1979, 186, 237. Wasik, S . ; Chesler, S. J . Chromatogr. 1978, 722, 451. Zielinski, W. L., Jr.; Johnston, K.; Muschik, G. M. Anal. Chem. 1976, 4 8 , 907. Hall, M.; Mallen, D. N. B. J. Chromatogr. 1976, 118, 268. Paiter, M.; Hlozek, V. J . Chromatogr. 1976, 728, 163. Analabs Tech. Note 1977, September. Woodburn, K. B. Masters Thesis, University of Wisconsin-Madison 1982. Polychlorinated Biphenyls; National Research Council, National Academy of Sciences: Washington, DC, 1979; p 12. Mullin, M. D.; Pochini, C. M.; McCrindle, S.; Romkes, M.; Safe, S. H.; Safe, L. M. Environ. Sci. Technol. 1984, 18, 468. Alford-Stevens, A. L.; Budde, W. L.; Bellar, T. A. Anal. Chem. 1985, 57,2452. Cooper, S. D.; Moseley, M. A.; Pellizzari. E. D. Anal. Chem. 1985, 57, 2469. Bush, B.; Murphy, M. J.; Conner, S.; Snow, J.; Barnard. E. J . Chromatogr. Sci. 1985. 2 3 , 509. Albro, P. W.; Fishbein, L. J. Chromatogr. 1972, 6 9 , 273. Albro, P. W.; Haseman, J. K.; Ciemmer, T. A.; Corbett, B. J. J. Chromatogr. 1977, 136, 147. Sissons, D.; Welti, D. J . Chromatogr. 1971, 6 0 , 15. Stalling, D. L.; Huckins, J. N. JAOAC 1971, 54, 801. Mullin, M. D.; Filkins, J. C. I n Advances in the Identification and AnalYSlS Of Organic Pollutants in Water; Keith, L. H.. Ed.; Ann Arbor Sci-

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Anal. Chem. 1986, 58, 2696-2699

ence Publishers: Ann Arbor, MI, 1981, Vol. 1, p 167. (23) Pellizzari, E. D.; Tomer, K. B.; Moseley, M. A. In Advances in the Identification and Analyss of Organlc Polluants in Water; Keith, L. H., Ed.; Ann Arbor Science Publlshers: Ann Arbor, MI, 1981; p 197. (24) Riedo, F.; Fritz, D.; Targan. G.; Kovats, E. sz. J . Chromtogr. 1976, 126, 63. (25) Haken. J. K.; Ho, D.K. M. J . Chromatogr. 1977, 142, 203.

(26) Zielinski, W. L., Jr. Ph.D. Thesis, Georgetown University, Washington, DC, 1972.

RECEIVEDfor review January 15, 1986. Resubmitted June 9, 1986. Accepted June 9, 1986.

Identification of Polycyclic Aromatic Hydrocarbons in Extracts of Diesel Particulate Matter by Supercritical Fluid Chromatography Coupled with an Ultraviolet Multichannel Detector Kiyokatsu Jinno*

School of Materials Science, Toyohashi University of Technology, Toyohashi 440, Japan Tadao Hoshino

School of Medicine, Keio University, Tokyo 160, Japan Toshinobu Hondo, Muneo Saito, and Masaaki Senda

JASCO Japan Spectroscopic, Co., Ltd., Hachioji 192, Japan

The identnlcatkn d POrycycUc aromatic hydrocarbons (PAHs) present in the fraction of an extract from diesel particulate matter has been performed in order to demonstrate the performance of supercritkai fluid chromatography with carbon dioxide as the mobile phase coupled with an ultraviolet multichannel detection system. As a result, 11 of 16 EPA priority pollutants, PAHs and benzo[elpyrene, were identitied by performing two actual analyses assisted by a microcomputerized retention predictlon system without any triai-anderror experhrents. Thls work clearly strows that the approach discussed herein has a high potential for analysis of various klnds of complex mixtures of poiyaromatlcs.

The resolution and identification of the components in complex mixtures continue to represent difficult analytical tasks in spite of improvements in instrumentation and methodology. It appears that the increasing complexity of analytical problems will exceed the current state-of-the-art in separation and analysis. Since chromatograms of complex samples are always very complicated, the problem of overlapping peaks becomes a nearly universal concern in the practice of analytical separations. T o improve this situation, it is valuable to recognize that the use of multichannel detectors in chromatography can significantly increase the number of independent informational degrees of freedom in the measurements (1-6). In order to expand the possibility of ultraviolet (UV) multichannel detectors, a coupling with supercritical fluid chromatography (SFC) (7) is a promising direction in practical analysis, since SFC has several advantages compared to gas chromatography (GC) and liquid chromatography (LC). As is well-known, the properties of a supercritical fluid are intermediate between gases and liquids. Solute diffusivities are about 100 times higher than those in the liquid phase and

viscosities are similar to those in the gas phase. Furthermore, the greater density of supercritical fluids compared with gases imbues the mobile phase with solvating powers, which can readily be controlled by application of pressure and temperature. In addition, common supercritical fluids such as carbon dioxide have high transparency in UV wavenumber regions. As a result, these properties should enable greatly enhanced chromatographic efficiency compared to LC, shorter analysis time than in LC, and the possibility of separating high-molecular-weight and thermally labile compounds that cannot be separated by GC. In order to demonstrate the capability of SFC coupled with UV multichannel detector, identification of priority pollutants polycyclic aromatic hydrocarbons (PAHs) in extracts of diesel engine particulate matter has been described in this communication. The supercritical fluid chromatography-ultraviolet (SFC-UV) multichannel detector system was assessed for approximate identification of PAHs contained in a sample extract by the microcomputer-assisted retention prediction system developed in our previous study (8).

EXPERIMENTAL SECTION The SFC system used here was a JASCO (Tokyo, Japan) Model Super-100 directly coupled SFE/SFC system (supercritical fluid extraction/supercritical fluid chromatography). The system consists of a microscale extraction apparatus and supercritical fluid chromatograph, that allows direct introduction of the SFE extract of a sample into the SFC section of the system. The detection was performed by JASCO MULTI-320 UV photodiode array detector, which is controlled by an if-800 microcomputer (Oki Electrie, Tokyo, Japan). Data processing was performed by using an if-800 and NEC PC-9801 VM2 (16 bits, Nippon Electric, Tokyo, Japan). The column was stainless steel packed with Develosil ODS-5(Nomura Chemicals, Seto, Japan, 4.6 mm i.d. x 15 cm long). The mobile phase was carbon dioxide, pressurized between 100 and 250 kg/cm2, and the temperature was controlled at 40 "C. Standard UV spectra of 16 EPA priority pollutants PAHs were previously stored on a floppy disk by the system

0003-2700/86/0358-2696$0 1.50/0 0 1986 American Chemical Society