2127
Anal. Chem. 1982, 54. 2127-2129
m '$00
2'20
4'00
6'08
8'02
lies
T'ME
Flgure 1. A 20-s portion of a chromatogram wtth a peak due to 100 pg of 2,440luenediamine. The current Is In pucoamperes and the time is in seconds.
- -? i 41
51 v
2g I/\
=+-
iiae
~ I a a
1 138s
1800
zeaa
Flgure 3. The same data as Figure 1, after smoothing using eq 1. The same scales as in Figure 1 apply.
f l = 0.18 €32. A filter may be built with a variable frequency cutoff simply by switching in various values of a set of resistors. The filter may be simply realized using the tables of Horowitz and Hill (11). It must be appreciated that the Butterworth filter design may not always be appropriate. This filter has a flat frequency response where the gain is near 1, and a sharp "knee" in the log gain vs. log frequency plot. It does, however, alter the phase relationship %ong the various frequency components of the signal even when the gain is near 1. This leads to a "ringing" output from a step input. One may anticipate that rapid changes in the detector output (filter input) will lead to a distorted filter output. The Bessel configuration may be used if this proves to be a problem, though we have never found it to be a problem with normal chromatographic peaks.
LITERATURE CITED '2aa
0 E 5
2'30
8'6
a';.@ 0'25 a132 FREGJEUCY dERTZ
Flgure 2. The Fourier transform of .Figure 1. The real and imaginary components are the oscillating traces, while the absolute value of the spectrum is the top CUWB whlch demonstrates three peaks, one at 0 Hz (the chromatographic peak), one at 0.18 Hz, and one at 0.36 Hz representing the pulse fluctuations.
Horlick and Hieftje have written an excellent chapter on correlation (8). (2) Buy or build a high order classical RC filter (9-11). The former is more expensive, but will be versatile. The latter will be inexpensive to build at the cost of versatility. The second option may be implemented with a Butterworth or Bessel Filer. Using an eight-pole Butterworth filter, one can achieve fo = 0.08 142,f, = 0.14, and f1 = 0.06 Hz. These conditions would be apipropriate for the conditions described. If one were working routinly at 3.00 mL/min using the same hardware, one would require fo = 0.24 Ilz, f, = 0.42 Hz, and
Nikeily, J. G.; Ventura, D. A. Anal. Chem. 1979, 57, 1585-1568. Smith, D. E. Anal. Chem. 1976, 4 8 , 517A-526A. Singleton, R. C. Coqmun. ACM 1967, IO, 647-654. Bracewell, R. N.; Roberts, J. A. Aust. J. fhys. 1954, 7 , 615-640. BrlQham, E. 0. "The Fast Fourier Transform": Prentlce Hall: Enqlewood Cllffs, NJ, 1974. Bloomfield, P. "Fourier Analysls of Time Series"; Wiley: New York, 1976. . .
Hayes, J. W.; Glover, D. E.; Smith, D. E.; Overton, M. W. Anal. Chem. 1973. 45. 2771284. Horllck, G.; Hieflje, G. M. In "Contemporary Toplcs in Analytical and Clinical Chemistry"; Hercules, D. M., Hiefljd, G. M., Snyder, L. R., Evenson, M. A., Eds.; Plenum: New York, 1978; Vol. 3, pp 153-216. Graeme, J. G.; Tobey, G. E.; Huelsman, It. D. "Operational Ampliflers, Deslgn and Applications"; McGraw-Hill: New York, 1971; Chapter 8. Johnson, D. E.; Hllburn, J. L. "Rapid Practical Designs of Actlve Fllters"; Wiley: New York, 1975. Horowltz, P.; hill, W. "The Art of Electronics"; Cambridge University Press: Cambridge, 1960; p 158.
RECEIVED for review April 30, 1982. Accepted July 2, 1982. It gives me great pleasure to acknowledge the support of Grant GM-28112 from the National Institute of General Medical Sciences.
Phase Separator for Flow Injection Analysis Koreharu Ogata, Klyomi Taguchi, and Toshio Imanari" Faculty of Pharmaceutical1 Sciences, Chiba lJniversity, Yayoi-cho 1-33, Chiba-shi, Chiba 260, Japan
Flow injection analysis (FIA), first developed by Ruzicka and co-workers ( I ) , is a versatile technique in the field of 0003-2700/82/0354-2127$01.25/0
analytical chemistry. Recently, the concept of solvent extraction was coupled with FIA ( 2 , 3 )to enhance its versatility. 0 1982 American Chemlcal Society
2128
ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 16 fii)
Ap
Ec
& D Waste
u w u
4
b '
Ps-A Figure 1. Construction of phase separators: Ps-A, a newly designed membrane phase separator, (1) membrane, (2) orifice, (3)CTFE plug, (4) PTFE rod with the top cut at 45' angle; Ps-B, a comparative membrane phase separator, sandwich type membrane phase separator, (i) inlet of organic and aqueous phase segments, (ii) outlet of organic phase, (iii) outlet of aqueous and excess organic phase; (a) flow route of two segnents, (b) flow route of organlc phase, (c) flow routes of aqueous phase and excess organic phase. Consequently, a phase separator to implement continuous solvent extraction in an FIA system has been an object of study for design and construction ( 4 , 5 ) . It has been shown that a simple, practical phase separator consists of a membrane phase separator with a poly(tetrafluoroethy1ene) (PTFE) membrane between two pieces of Perspex or P T F E with grooves (6). However, this separator causes excessive dispersion of the extracted sample zone. In this paper, a new phase separator with a polyethylenebacked porous PTFE membrane was manufactured and compared to the membrane phase separator mentioned above. This new phase separator was demonstrated to be superior to that of existing systems by comparing the dispersion of peaks obtained by bromocresol green and caffeine samples in the FIA using both models.
EXPERIMENTAL SECTION Instruments. The equipment comprises the following items: two reciprocating pumps (PSU-2.5 for aqueous phase, PSD-3.5 for organic phase, Seishin Pharmaceutical Co., Japan); a rotary valve (NHMS-250120, Seishin Pharmaceutical Co., Japan) with a bypass line; a conventional segmentor [45/45 W type segmentor] (5) and an extraction coil of PTFE; and a spectrophotometer (UVIDEC-lWII,Japan Spectroscopic,Japan) with an 8-pL flow cell. All other connection tubes and connectors were of PTFE. Reagents. AU chemicals and solvents were of analytical grade. The organic and aqueous phases for the determination of the bromocresol green (BCG) sample by FIA were 1-pentanol and 0.01 N "OB, respectively, while chloroform and distilled water were used for the caffeine sample. The organic solvents were shaken with the aqueous phase to establish solubility equilibria between the two phases before use. Construction of Phase Separator. Construction of the phase separator is illustrated in Figure 1. The body consists of an inlet [(i) bore 0.8 mm i.d.1, two outlets [(ii) bore 0.8 mm i.d.; (iii) bore 1.0 mm i.d.1, and a separating compartment, and all of these are of poly(monochlorotrifluoroethy1ene) (CTFE). A small piece of cylindrical PTFE rod with the top cut at a 45' angle (4) is fitted in the bottom of the separating compartment and a polyethylene backed porous PTFE membrane [(l) Millipore FALP, pore size 1.0 pm] is sandwiched between the CTFE plug (3) and orifice (2). The cut surface is adjusted to angle toward the inlet (i) allowing the organic phase to be directed to the membrane surface. The organic phase which sucks through the membrane (i) is led to the flow cell through the outlet (ii). The aqueous and excess organic phases are discarded to the outside through the outlet (iii) after taking a circuitous route around the PTFE rod (4).
Figure 2. Flow diagram used in the study of phase separators: (Ap) aqueous phase; (Op) organlc phase; (P) reciprocating pump; (Da) damper; (Rv) rotary valve; (Sg) 45/45 W type segmentor; (Ex) extraction coil (0.5 mm i.d. X 300 mm); (Ps) phase separator; (D) detector; (Fc) fraction volume controller. Sample BCG
Sarrple Caffeine
Ratio of separated organic phases to flow cell
Flgure 3. Comparison of phase separators: (0)present membrane phase separator (Ps-A); (0)comparative membrane phase separator (Ps-B). Peak heights (a-1 and b-1) and peak widths (a-2 and b-2) are plotted against the ratio of the organic phase passing through the flow ceil. Organic and aqueous phase flow rates are 1.0 mLlmin and 0.8 mL/min. The phase separator (Ps-B; groove dimensions: 35 mm length, 2.0 mm width, and 0.5 mm depth) devised by Nord et al. (6) was also constructed as shown in Figure 1. Test Procedure. The flow diagram of FIA used to study the performance of different membrane phase separators is illustrated in Figure 2. The fraction volume of the organic phase was controlled by the controller (Fc). The present phase separator (Ps-A in Figure 1)or a comparative one (Ps-B in Figure 1)was placed in the phase separation site (Ps) to compare the performance. The test was carried out according to the procedure by Nord et al. (6) as follows: Twenty microliters of a sample solution was injected via the rotary valve (Rv) into the aqueous stream. After phase separation, the absorbance of the organic phase was measured at 435 nm for the BCG and at 275 nm for the caffeine. The detected peak heights and peak widths (at 5% peak height) were plotted against the ratio of the organic phase passing through the flow cell (volume of organic phase which was separated/volume of total organic phase).
RESULTS AND DISCUSSION For comparison of the Ps-A with the Ps-B, the variation of the fraction volume of the organic phase sucked through the membrane was considered. Thus, in Figure 3, peak heights and widths are plotted against the ratio of fraction volume of the organic phase passing through the flow cell. Those results indicate that the Ps-A causes smaller dispersion than the Ps-B especially a t large fraction volumes. It should be emphasized that, in the Ps-A, a significant decrease in dispersion really occurs when the volume of the separated fraction was increased; typically this decrease was about 30% (peak width of BCG) or 40% (peak width of caffeine) when the organic phase fraction volume ratio changes from 0.25 to 0.65 or 0.35 to 1.0. By contrast, the decrease in dispersion by the Ps-B was only about 22% or 20% under the same conditions. Consequently, the Ps-B is inferior to Ps-A with respect to these characteristics of dispersion. This result can be explained by the larger surface area and longer surface of the Ps-B's membrane [surface area: Ps-A, 7 mm2; Ps-B, 70 mm2 (2 x 35 mm)]. In conclusion it has been demonstrated that the newly designed phase separator described here might be more useful
Anal. Chem. 1982, 5 4 , 2129-2130
than the other membrane phase separators in practical use of FIA applications.
LIT'ERATURECITED (1) Ruzicka, J.; Hansen, E. H. Anal. Chim. Acta 1975, 7 8 , 145-157. (2) Klinghoffen, 0.;Ruzicka, J.; Hansen, E. H. Talanta 1980, 2 7 , 169-175.
2129
(3) Karlberg, 8.;Thelander, S. Anal. Chim. Acta 1978, 9 8 , 1-7. (4) Kawase, J.; Nakae, A.; Yamanaka, M. Anal. Chem. 1979, 51, 1640-1 643. (5) Kawase, J. Anal. Chem. 1980, 5 2 , 2124-2127. (6) Nord, L.: Kerlberg, B. Anal. Chlm. Acta 1980, 118, 285-292.
RECEIVED for review March 10, 1982. Accepted July 1, 1982.
Microsample-Filtering Device for Liquid Chromatography or Flow Injection Analysis Wayne S. Gardner" and Henry A. Vanderploeg Great Lakes Envlronmental Research Laboratow, National Oceanic and Atmospheric Administration, 2300 Washtenaw Avenue, Ann Arbor, Michigan 48 104
Direct injection techniques, such as high-performance liquid chromatography (HE'LC) and flow-injection analysis, are useful tools to analyze small (
