Ill
-j
mately 0.5 ml by mild heating. The quartz vessels (Varian Aerograph) intended for the ion chamber of the mass spectrometer were heated to redness to pyrolize any contaminants. Finely spun silver wool (for elementary analysis, Riedel-De Haen AG, Seelze-Hannover,BRD) which had been previously extracted with DMF/isopropanol was stuffed loosely into the vessels, without finger contact, to provide a surface for substance retention and to prevent sample loss by spattering. The stuffed vessels were then heated to 120-140 "C, held fairly constant by a massive brass block on a hot plate. The substance was then introduced into the quartz vessel by means of a needle value assembly (Figure 2) and the solvent evaporated to dryness under a stream of NP.The component then lay on the surface of the silver wool, and a mass spectrum was run as for any solid substance. It should be noted that all parts and vessels which come into contact with the sample were extracted in a suitable solvent. The needle value assembly is so constructed that all parts and seals are of stainless steel, Teflon, and glass. This permits extraction with solvent between analysis. Between components in a chromatogram, it need only be flushed with the appropriate solvent.
RESULTS
0 m/e=02 i
-1'11
(':21
332
Mass Spectra. As can be seen in spectrum 1 (Figure 3), peaks occur a t regular intervals of mle = 125, which corresponds exactly to the fragmentation of homopolymer in integral multiples of monomer NEMI. The peak groups differing from the succeeding peaks by mle = 43 can be attributed to a fragmentation of the monomer unit NEMI ( 4 , 5 ) .The mass spectrum of peak 2 is characterized by masses mle = (n.82 m.125), and is in good agreement with the spectrum of an almost alternating copolymer containing CH- and NEMI-units (3).
+
LITERATURE CITED
Figure 3. Mass spectra of the eluted peaks. Spectrum 1: homopolymer. Spectrum 2: copolymer
As the two components eluted, they were collected in small bottles along with the solvent, and then their volumes reduced to approxi-
P. Jones and S. Yang, Anal. Chem, 47,1000 (1975). R. E. Lovins and C. R. McKinney, Anal. Chem., 45, 1553 (1973). E. Wipfelder, Dissertation, TU Munchen, 1976. . , W. J. Feast, J. Put, and F. C. d e Schryver, "Organic Mass Spectrometry", Vol. 3,Heyden and Son Limited, 1970,pp 507-517. (5) H. Budzikievicz, C. Djerassi, and D. H. Williams, "Mass Spectrometry of Organic Compounds", Holden-Day, San Francisco, Calif., 1967,pp 362-363.
RECEIVEDfor review March 5 , 1976. Accepted March 25, 1976.
Improved Fabrication Technique for Alkali Flame Ionization Detector Salt Tips Bruce M. Johnson,* Bernard D. Kaiman, and Richard W. Lambrecht Depadment of Human Oncology, University of Wisconsin, Center for Health Sciences, 1300 University Avenue, Madison, Wis. 53706
Various innovations in the design of an alkali flame ionization detector have improved its stability and reproducibility since it was first described in 1964 (I). The use of a flame tip, fabricated from a pressed pellet of the desired alkali salt, was shown to give improved operating characteristics (2-4). Stewart (5) described a procedure for pressing the salt mixture into a metal ring and drilling the resulting pellet t o the required dimensions. This method was found to be better than any technique previously tried in our labokatory. However, the preparation procedure involved drilling two rather small holes in a brittle pellet of alkali salt. Several disadvantages were evident: a) shop time for drilling was expensive, b) several pellets were usually broken during the drilling process, c) contamination of the pellets was difficult t o control in the shop, and d) reproducible dimensions were somewhat difficult to obtain. A procedure is described below for using a specially machined plunger for pressing a pellet which has the desired final configuration. A KBr mini die (Beckman-RIIC, Science Es-
sentials Operations, Anaheim, Calif.) is modified according to Figure 1.The plunger is machined from stainless steel drill rod and then hardened. The small diameter pin (Y, 0.020 in.) is a piece of wire pressed into the end of the plunger. The diameters X and Y are determined b y the configuration of the detector. X is determined to match the detector flame tip (Figure 2) and serves to hold the pellet in place on the detector. In our laboratory, the bottom half of a Tracor stacked thermionic detector is used. The dimension X is shown to fit the outside diameter of the flame tip upon which the pellet rests. Polarizing voltage is applied to the flame igniter coil only. I t is important that the connection of the salt pellet to the flame tip be firm and gas tight. Y, the flame orifice di; ameter, may be varied to determine mode of element selectivity (5,6). In this application, a 0.020-in. bore is used for the nitrogen-specific mode as described by Stewart (5).A Yls-in. 0.d. (0.189 in.) stainless steel collar is used as a mold to hold the salt pellet. A plunger guide is placed below the salt collar to act as a guide to prevent the fine wire from being distorted during the pressing operation. ANALYTICAL CHEMISTRY, VOL. 48, NO. 8, JULY 1976
1271
0.3431 0.069: 0. I 6 7 i
I' 'd-
PLUNGER HNCH,
N
a
0.074 LX
H-0.020
1
[VI
0.1601
10
PELLET COLLAR
0.241r L
[H3
PLUNGER GUIDE
0.10 ng. REL. AREA = I
A Nd
REL. AREA = 3.4
\
R I I C MINI DIE e h P 1
0
INJ.
,
,
2
1
,
4
rnin.
~
,
6
,
,
8
Figure 3. Chromatogram of pentamethylmelamine and phenanthrene. Two ft X 2 mm glass column packed with 15% DEGS on 60/80Chromosorb W; NP, 120 ml/min; coi. T, 150 OC: inlet T, 235 OC:Det. r, 280 O C ; H2,28.9 ml/min; air, 280 ml/min: electrometer, 2 X IO-" AFS
Flgure 1. Pellet press modified for pressing salt pellets for alkali flame ionization detectors
FLAME IGNITER SALT PELLET FLAME TIP
It
[XI
Figure 2. Cross section of salt pellet mounted on flame tip
In use, the die is assembled by first inserting the plunger guide followed by the pellet collar. RbZS04 is dried over a flame, ground to a fine powder, and desiccated prior to use. About 100 mg of the alkali salt is added. The plunger is then inserted and the pellet is pressed using a pressure of 2 tons for 30 min. The die is released and the plunger removed with a gentle rotation. Excess salt is removed from the bottom of the pellet with No. 400 emery paper. All materials are stored in a desiccator when not in use.
1272
ANALYTICAL CHEMISTRY, VOL. 48, NO. 8, JULY 1976
Pellets produced in this manner have been found to give less pellet-to-pellet variation in sensitivity and selectivity than those made using a drilling technique. Figure 3 is a chromatogram of 0.10 ng of pentamethylmelamine (C8H&6), and 500 ng of phenanthrene (C14H10) injected on column. The peak for pentamethylmelamine demonstrates a detection limit of less than 100 pg of injected sample. The peaks for phenanthrene and pentamethylmelamine have an area ratio of 3.4 and demonstrate an N:C selectivity of 17 000 for this pair of compounds.
LITERATURE CITED (1)A. Karmen and L. Giuffrida, Nature, (London), 201, 1204 1964. (2) W. A. Aue, "Pesticides Identification at the Residue Level", Adv. Chem. Ser., 104,39-72 (1971). (3) V. V. Brazhnikov, M. V. Gur'ev, and K. i. Sakodynsky, Chromatogr.Rev., 12, l(1970). (4) M. KrejEi and M. Dressler, Chrornatogr. Rev.. 13, 1 (1970). (5)W. H. Stewart, Anal. Chem., 44, 1547 (1972). (6)K. 0.Gerhardt and W. A. Aue. J. Chromatogr., 52, 47 (1970).
RECEIVEDfor review November 17, 1975. Accepted March 25,1976. Supported in part by Grants CA 13290 and CA 14520 from the National Cancer Institute, USPHS.
