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ANALYTICAL CHEMISTRY, VOL. 59, NO. 8, APRIL 15, 1987 Reagent Loop
Reagent Loop
LOAD
INJECT
Reagent
A
Sample
Reagent
Sample
Reagent
Figure 7. Double sample injection. Two plugs of the same sample
in LS1 and L,, are injected either (A) with different sample volumes or (B) with plugs separated by a reaction column.
,@, L
Salnple Reagent Loop
To Detector LOAD
Reagent
which may merge with reagent downstream, again allowing observation of response a t times corresponding to various concentration ratios (IO). Another configuration is shown in Figure 7 , which results in a double injection of sample separated by a plug of the reagent stream which can result in two separate peaks. By use of sample loops of different volumes, the dynamic range of the system can be increased by calibrating high concentrations from the smaller injection volume and low concentrations by the larger injection volume. A fiagram identical to that obtained with a split stream manifold (11) will be obtained, but since the present method does not rely on hydrodynamic balance of split streams, reproducible results over extended dynamic range and time periods will be observed. The reagent loop can also be replaced by a packed reactor. An example of the use of this configuration is the analysis of nitrate and nitrite. The reagent loop is replaced by a copper/cadmium reaction column as used by Anderson (12). Two loops are filled with the sample. When injected, the first sample passes directly to the reaction manifold where it is merged with reagent and nitrite is detected. The second, however, first passes through the copperized cadmium reduction column converting nitrate to nitrite, allowing measurement of total nitrate plus nitrite. Nitrate concentration can then be calculated by difference. Note that each peak position must be calibrated separately, since the second peak travels a greater distance causing additional dispersion. Figure 8 shows a similar arrangement which allows injection of two separate samples. It may also be used for injections similar to those shown in Figure 6 but where a small plug of the carrier is placed between the sample and reagent, standard, or interferent.
LITERATURE CITED
INJECT
1 Sample 1 I Reagent I Sample 2 I
(1) (2) (3) (4) (5)
Reagent
Figure 8. Double injection. Two separate loops LS1 and L,, are filled
with distinct samples (similar to Figure 7). Alternatively, sample in Ls2 may be injected with reagent, standard, or interferent (similar to Figure 6) in L,, separated by a small plug of the carrier. stream (and then merging with a reagent stream if necessary), response can be observed at times corresponding to various sample/standard concentration ratios. This valve configuration can also be used for interference studies where the sample plug is immediately followed by a plug of potential interferent. The interferent partially disperses into the sample plug while both mutually disperse into the carrier stream,
(6) (7)
(8) (9) (10) (11) (12)
Ruzicka, J.; Hansen. E. H. Anal. Chlm. Acfa 1975, 78, 145-157. Ruzicka, J.; Hansen, E. H. Anal. Chlm. Acta 1986, 779, 1-58. Ruzicka, J. Anal. Chem. 1983, 55, 1040A-1053A. Mindegaard, J.; Anal. Chim. Act8 1979, 104, 185-189. Bergamin F., H.: Zagatto. E. A. G.; Krug, F. J.; Reis, B. F Anal. Chim. Acta 1878, 101, 17-23. Toei, J.; Baba, N. Anal. Chem. 1986, 58, 2348-2350. Rios, A.; Luque de Castro, M D.; Valcarcel, M. Anal Chem 1986, 58,663-664. Betteridge, D ; Fields, B. Anal. Chem. 1978, 5 0 , 854-656. Zhaolun, F.: Harris, J. M.; Ruzicka, J.; Hansen, E. H. Anal. Chem. 1985, 57, 1457-1461. Hansen, E. H.; Ruzicka, J.; Krug, F. J.; Zagatto, E. A. G. Anal. Chim. Acta 1983, 148, 111-125. Ruzicka, J.; Stewart, J. W. B.:Zagatto, E A Anal. Chim. Acta 1976, 81, 387-396. Anderson, L. Anal. Chim. Acta 1979, 770, 123-128.
RECEIVED for review December 1, 1986. Accepted January 13, 1987. This research was supported in part by the Office of Naval Research.
CORRECTION Sampling and Excitation of Refractory Solids with a Theta Pinch Discharge Designed as aa Atomic Emission Source Jeffrey S. White and Alexander Scheeline (Anal. Chem. 1987,59, 305-309). On page 309, ref 2 should read as follows:
Carr, J. W.; Horlick, G. Spectrochim. Acta, Part B 1982, 37B(1), 1-15.
