A N A L Y T I C A L CHEMISTRY, VOL. 51, NO. 1. J A N U A R Y 1979
convenient t o prevent t h e record from going off scale. Advantages of interferometry in such applications include near-universal applicability and unambiguous end points. T h e end point is always indicated by a break in a line, but the sign a n d magnitude of the slopes of t h e two legs will depend upon t h e particular reaction occurring. In several applications, a n important advantage of interferometry is t h a t sensitivity is proportional t o p a t h length. With a laser light source, the beam diameter can be very small without adversely affecting t h e interference pattern. T h i s means that long cells with small volumes are practical; a 50-cm cell with a volume as small as 10 pL would not be unreasonable. One obvious application of t h e present apparatus, modified only t o accommodate flow cells of such length, is a monitor for liquid chromatography. Image displacement refractive index monitors are already being used, particularlq for high pressure liquid chromatography. Although some of these are quite sensitive, a n interferometer with long cells would be a t least a n order of magnitude more sensitive. Provided t h e turbidity of samples were not prohibitively high, long cells could also be used to increase sensitivity for monitoring molecular interactions. Direct titrations in long cells would be awkward because of the difficulty in obtaining uniform mixing, but external titrations could be done and the reaction mixture circulated through a flow cell. Interferometry would be particularly useful in detecting interactions that lead
* 165
t o conformational changes not accompanied hy changes in ahsorption spectra. Kinetics of slow reactions, even en7yme reactions, could be followed hy mixing t h e reagents and in jecting a single aliquot into a flow cell.
ACKNOWLEDGMENT We t h a n k L. E. Lach for his help in designing. t h e com. pensator and G. Berg for his excellent machining. We also appreciate contributions made by .1. Piowaty a n d A . F Rehof in t h e early stages of t h e development of t h e apparatus.
LITER ATITRE CITED (1)
(2) (3) (4)
(5) (6) (7)
(8)
H.D. Cook and L A Marzetta.
J . Rps Natl Bi/r Stand ( 0 S ) Qer! C , 6 5 . 129 (1961). D. A . Wilkinson and J. F. Nagle. Anal Biochem . 84. 26.1 ( 1 9 7 8 ) For example, see N Bauer, K . Fajans, and S. 2 . Lewin. Refractometrv in "Physical Methods of Organic Chemistr)i", Vol I. Part TI. A Weissberger. Ed., Interscience, New York. 1960. F. P. Kupper and W J Mastop. Rev Sci Instrum.. 4 4 . 954 (!973) A . F. Behof, R . A. Koza, L. E. Lach. and P N YI. Riophys , I , 2 2 , 37 (1978). V. Vajgand and T. Todorovski. Jena R e v . . 15 (1). 37 (1970) F. M. Arshid, C. H. Giles, E. C. McClure. and A . Ogilvie. J Chwn SOC, 67 (1955). M. A. Leonard in "Comprehensive An.slytical Chemistry". Vol VIII. G Svehla, Ed.. Elsevier. Amsterdam. 1977.
RECEIVED for review .July 5 . I978 Accepted October 34. la78 LVork supported in part hv Researrh rorpnration
Inorganic Ion Exchangers for the Removal of Scandium and Rare Earth Elements in Neutron Activation Analysis of Geological Samples K. Akilimali," B. Lumu, and W. Mwamba Service d ' Analyse par Activation, C.R.E.N.-K-B.P. 868, Kinshasa XI. Zaire
Semiconductor detectors, which allou a better spectral resolution, ha\ e reduced the need for deLeelopment of detailed radiochemical separation< steps in neutron activation analvsic 'CVith these detectors, it is sometimes possible t o determine u p to 20 elements in biological or geological samples. Howeier some elements u h i c h are actirated rapidIL i e g., AI. Mn. Sc. Na, P , . ) can limit t h e use of theqe detectors either h\ a n merlapping of other lou activities. or h\ increasing the counting dead-time and therehy changing t h e real coiinting time of these activities, or hy producing high Compton edges which Influence t h e cal ulation of photopeak areas Suctsituations require select ve radiochemical r e m m a l of those elements with high activities. erpeciallv if their long d e t a \ overlaps t h e IOW activitieq to be determined After a long irradiation of geological samples. rocks. sediments or soili. 24Naand %Sc are t h e most troiihlwome elements be( ause of their nuclear characteristic< Sodium-24 can be remoFer1. after a n acidic dis~olutlonof the sample, h\ retention on a chromatographic column of hvdrated antirnonL pentouide i l , 2). or after f ' (iirardi r%tHI. (5).the f'cillowing four ion exchangers have h w n srlectetf: w r i u n i oxalate (COX. Carlo Erha). tin diwidr i7'Dn. ( ' a r l o Erha). hvdrated manganese dioxide IHMD. Carlr Erha) and lrnd fliioridp (PhE',. E313H). T h e anionic-exchange recin IAEK. Carlo Erha) has heen s t u d i e d f u r COmparaTiVe purposes "Ia tracer met hod. we have followed the dependence nf ionic r ~ t e n t i o nvq. acidity to select the best ion exchangers in HF and "0,.the r n d i a usually used for the dissolution of pec)lngic.:il ~amples..Atrc.ru.ardz rre have tested these 50111~' irradiated zecilogica! .-arnples (G-2, BCK. (;eological ';iir.\.t!. a i i t i some ferrallitic soil samples). AI! o p r a t i o r i h have brrn r a r r i e d o u t o r 1 a chromatographic coliimn A S d rrhed h y (;irardi et al. (SI. I n general. w c e p t ir.ith PhF,. the ~ I ( J ?rate S [vas very good even with Hh'II3 which wa.~I pulver;ihIe, Ti1 FINO , medium. better icvhich rrpresents the REE) and Sc"' characteri5tic.Cfor hoth are Gem on PhFI and HhlU: on other mchangere. t.he retention is variahle. with a tencleric;: to decrease nith increasing acidity. In HF tnPdiiiiri LVP ha\.e quaiitilaijve reiention on !'OX and AER i d ( , t i TI10 PbF, ft:r Ce'+. XVith a matrix of iinirradiatecj g:'~o!ogicni-ample t o which hrrcl h t > i i addrtl T'hF?. and AF:H retninrd R~.i.:llisr* *>t t h t : !lad tl( e 0 1 PbF,. n.c: have continued cuperiment. w i r h (.'OS and AEII ( y. LVith the i r r a d i a t e d smiple. aftrr diszolntion in FIF) HNO 1. A H 2 exhibited various tf L i d t o tw abandond. >. a : ~ obtained the following +
166
A N A L Y T I C A L CHEMISTRY, VOL. 51, NO. 1, J A N U A R Y 1 9 7 9
Irradiated Sample ( 2 weeks decay) HFIHNO, 3:l Solution 1 1 H,BO, Solution 2
1 I
cox \
Eluant
_____.__
Column - - ...
Cr 54Mn 59Fe
"Rb 9'Nb
46sc I4"La
Ih9Yb
I3'Ba
I4'Ce
9rZr
6oCo
IWCs
"'Sm
lJiHf
51
b5
Zn
"* Ta
152-iwEu
i
7
7
r
n
~
~
233pa
Afterwards, a modification in the procedure was introduced. Instead of using H,BO:, only as eluant, we added saturated H3B03 to the dissolved sample before loading the sample onto the column. This step is useful in cases where there is a precipitate of some insoluble fluoride after dissolution of the sample in HF medium; by formation of fluoride complexes, saturated H3B03allows the dissolution of that precipitate. This procedure also allows the use of normal vessels instead of Teflon vessels during the elution. Very interesting results were seen: %c '*'Hf, 233Paand the REE are quantitatively retained whereas oiher elements pass. The retention of '"Pa on the column allows the resolution of the 51Cr and elspa interference near 311 keV. On the other hand, Sc and REE do not impede the gamma spectra of lslHf or 233Pa,these radioelements being sufficiently active and having some other interference-free photopeaks.
'@Tb Figure 1. Proposed separation scheme
46Sc,"Zr, I4'Ce, '"Eu, '"Hf, and ""I'a were retained completely; 6oCo, "Rb, 95"b, ""Cs, and Ih'Ta passed directly in the eluate; 51Cr and "Fe were partially adsorbed; '"'Mn, retained in the beginning of the elution, began to pass partially in the eluate. Photopeaks of ""Zn (611 key, 1115 key) invisible before the removal of rare earth elements hecame visible in the eluate. The fact that "'Cr and "9Fe are partially adsorbed prompted us to look for another medium capahle of eluting these two ions completely. JVe tried various concent,rations of HCI and H,,B0,3. With HC1, "'cs and ""Fe are totally eluted. However "Sc begins to partition and, with saturated H:IRO,I.we obtained satisfactory results.
ACKNOWLEDGMENT Manuscript composition has been greatly improved by discussion with Y. Kasongo and M. Tshiashala, C.R.E.N.-K.
LITERATURE CITED (1) F. Girardi and E. Sabbioni. J . Radioanal. Chem., 1, 169 (1968) ( 2 ) G. H. Morrison and R. A. Nadkarni, J . Radioanal. Chem., 18, 153 (1973) (3) . . M. P. Menon and R. E. Wainerdi. Proc. Moder Trends in Activation Analvsis. Texas, 1965, p 152 (4) M. D. Tshiashala and 0. De Micheli Forma. RadioanalLett, 27, 101 (1976) ( 5 ) F. Girardi, R . Pietra, and E. Sabbioni. Techn. Rep. Eur. 4287e (1969)
RECEIVED for review ,July 24, 1978. Accepted August 11, 1978.
Vacuum Nebulizing Interface for Direct Coupling of Micro-Liquid Chromatograph and Mass Spectrometer Shin Tsuge" Department of Synthetic Chemistry, Faculty of Engineering, Nagoya University, Nagoya 464, Japan
Yukio Hirata and Tsugio Takeuchi School of Materials Science, Toyohashi University of Technology, Toyohashi 440, Japan
There has been an increasing interest in the direct coupling of a liquid chromatograph (LC) with a mass spectrometer (MS) (I -8). Among recent deLelopments in this field, are (1) moving wire ( I ) a n d moving belt (2). ('3) silicone membrane separator ( 3 ) ,( 3 )atmospheric preswre ionization (4,(4) direct introduction of a portion of t h e column effluent into t h e CT chamber (0-7), and (5) use of a jet separator for GC-MS (8). T h e latter two methods are similar to each other since hoth utilize t h e solvent vapor as the reagent gas for CI. However. both still have some disadvantages; in method 4, only a few percent of t h e effluent from a n ordinarv separation column is introduced into the ion source. and an uniform evaporation of t h e effluent is not always attained. while in method 5, relatively involatile compounds are difficult t o vaporize effectively with a conventional jet separator for GC-MS. T o overcome these problems, a new vacuum nebulizing interface for LAC-MScoupling was developed. With this interface, a more general system for I X - M S direct coupling can be established, where t h e wide range of flow rate of t h e solvent can be stably interfaced without any conventional splitting and even fairly Involatile compounds can effectively be introduced into t h e ion source a t relatively lower temperatures t h a n those required for nonnebulizing direct introduction. Further, this device is also quite effective for sample introduction of polar and/or large molecules of which 0003-2700/79/0351-0166$01 O O / O
mass spectra are otherwise difficult t o take (9).
EXPERIMENTAL Nebulizing Interface. A schematic diagram of the newly designed vacuum nebulizing interface is shown in Figure 1. The total effluent from a micro LC ranging between 2 and 16 pL/min was introduced into the nebulizer through a coaxial stainless steel capillary tube A (o.d.of 0.35 mm X i.d. of 0.15 mm with core-wire of 0.13 mm). The coaxial capillary nozzle is located at the center of the nebulizing tip F (i.d. of 0.4 mm). The top of the nozzle, however, is set about 0.3 mm above the nebulizing tip. Through a needle R , nebulizing gas of about 50 mL/min (at atmospheric pressure) was supplied to the nebulizer to form a jet stream at the narrow gap between the nozzle and the tip. The column effluent led to the top of the nozzle is continuously nebulized by the jet stream of He. Depending on experimental conditions such as the volatility of the solutes and boiling point and flow rate of the solvents. the nebulizing tube E (Pyrex) was heated to any desired temperature up to 300 "C, mostly to make up for the latent heat of vaporization of the solvents during nebulization. The distance between the nebulizing tip and the counter orifice (i.d. of O , , j mm) was adjusted to attain an optimum vapor pressure (ca. 1 Torr) at the CI chamber during full evacuation through G by a rotary pump at a rate of 170 L/min. For example, the optimum distances were about 2.0 and 2.5 mm for 16 pL/min of methanol and water solvent. respectively. In the following, only 16 pL/min of the flow rate was used, but it is possible to use higher '? 1978 American Chemical Society
