b Figure 1. Flask for concentrating trace amounts of material for direct application to mass-spectrometricanalysis
mass spectrometer. Following evacuation, the sample is introduced into the source region where it is heated as necessary. It is believed that the device is new in that it allows the operations of concentration to dryness and application to the mass spectrometer to be performed in a single unit, thus elminating the danger of contamination or loss of the sample through transfer or during evacuation of the pre-chamber of the instrument. Moreover, solutions may be dried down in the tube alone, or with preconditioned adsorhents. The latter procedure can he particularly useful when dealing with solutes of low boiling point, or ones that tend to adhere to glass. In addition, if operations should be interrupted and immediate use of the sample prevented, it may he sealed off and held indefinitely, ready for use. The device has been used successfully to obtain spectra of trace amounts of components isolated from natural sources. RECEIVED for review October 14, 1970. Accepted January 7, 1971.
ne Part-per-Million Level
Naperville Technical Center, Standard Oil Company (Indiana), Naperoille, Ill. 60450
Tm APPARATUS AND PROCEDURE for determining organic nitrogen with a coulometric detector (1) have been modified to allow temperature-controlled vaporization of samples and to achieve greater precision at the 1-ppm level by using large samples. Most of the basic equipment and materials, such as the furnace, titration cell, coulometer, and catalysts, are the same. However, there are three principal modifications: The reaction tube is now in. rather than in. in 0.d.; the relative amounts of catalysts are 3 in. of rhodium, 1 in. of nickel chips, and 11/%in. of nickel-magnesia; the vaporization zone is wound with No. 26 chrome1 A resistance wire which is connected to a powerstat for temperature control and the windings are spaced 'I4 in. apart and no insulation is used so that the zone can be cooled rapidly after a determination. In addition to these modifications, the silicone rubber septum has been glued in the inlet so that samples can be introduced either in capsules or by syringe injection. Thus, the modified apparatus can be operated at a constant temperature or at series of temperatures up to about 600 OC. In addition, the increased capacity for hydrocracking protects (1) I. J. Oita, ANAL.CHEM.,410,1753 (1968). 624
ANALYTICAL CHEMISTRY, VOL. 43, NO. 4, APRIL
1971
the nickel-magnesia catalyst from excessive coking when high-boiling samples are analyzed, and direct injection eliminates the possible errors of a capsule blank with lownitrogen samples. PROCEDURE
For temperature-controlledvaporization, all determinations are started with the vaporization zone at ro6m temperature. Samples containing 10 ppm or less of nitrogen are injected-a total of about 100 rng for the 1-ppm level, lesser amounts for higher concentrations. Samples containing more than 10 ppm are encapsulated in the usual way (I). Heating rate is controlled to suit the type of sample. That is, heavy high-boiling samples are heated rapidly (about 100 "Cjmin) to 240 "C, and then more slowly (about 60 "Cj min) up to 550 "C; whereas low-boiling or waste-water samples are heated at about 60 T/mio to 240 "C, and then at about 100 T j m i n to 550 "C. The maximum temperature is held constant until the recorder trace returos.to the base line. Finally, the heater is turned off, and the outside of the vaporization zone is cooled rapidly to room temperature with an airjet. Each temperature-controlled determination takes about 30 minutes, as compared with 10-15 minutes for the originally described procedure (I).
r - - - -
f
I
fhad\
---
Table I. Nitrogen Determination at the Part-per-Million Level Max. Extracdeviation tion Kjelfrom Sample dah1 Coulometric Mean mean 1.6 0.2 1 . 6 1.5, 1.8, 1.5, 1 . 4 Naphtha A 1.5 0.1 1 . 2 1 . 6 , 1.4, 1 . 4 B
-1 I
I
I
1%"
4 I
.II
- - --
C D
I
Reformer feed Reformate Light gas oil A
I I
I
B C Heavy gas oil A Lube oil I5/8" HYDROGEN)[
0
D.
a
1.4 1.4 0.7 0.2 0.16"
1.6, 1.2, 1 . 5 1.2, 1 . 6 0.6,O. 8 0.4,0.5 0.23, 0.22,O. 34, 0.30,0.13,0.13 0.24" 0.39,0.24,0.25,0.31 5.2 5.0,5.3, 5.4 2 . 0 2.1, 1 . 9 , 2.0, 2.0 1.1 1 . 0 , 1 . 2
1.4 1.4 0.7 0.5 0.23
0.2 0.2 0.1 0.1 ,0.11
0.29 5.2 2.0 1.1
0.10 0.2 0.1 0.1
Average of 12 determinations
'OUARTZTUBE
I
Table I shows typical results obtained with various lownitrogen samples. In all cases, the maximum deviation from the mean is within 0.2 ppm, and the results compare favorably with those obtained by a Kjeldahl method using a modified sulfuric acid extraction (2).
The Kjeldahl values for light gas oil A and B are the average of 12 determinations. Generally, the accuracy of the extraction Kjeldahl method for a single run is about 1 ppm. However, if the sample contains large amounts of olefins and easily sulfonated aromatics, the digestion procedure can be extremely tedious and the accuracy can decrease to 4-5 ppm. The coulometric method is not affected by the degree of olefinicity. Since the new equipment can be operated either as a programmed or a constant temperature unit, it can be used for samples containing less than 1 ppm nitrogen or as much as 5 nitrogen.
(2) 0. I. Milner, R. J. Zahner, L. S. Hepner, and W. A. Cowell, ANAL.CHEM.,30,1528 (1958).
RECEIVED for review November 2, 1970. Accepted January 7, 1971.
Figure 1. Hydrocracking hydrogenation tube RESULTS
z
Syringe Procedure for Transfer of Nanogram Quantities of Mercury Vapor for Flameless Atomic Absorption Spectrophotometry Michael P. Stainton Fisheries Research Board of Canada, Freshwater Institute, 501 Unicersity Crescent, Winnipeg 19, Manitoba
DETERMINATION OF MERCURY by flameless atomic absorption spectrophotometry is well known (1-6). Mercury in solution is reduced to the metal, partitioned with air and transferred, in a n air stream, to a flow-through cuvette in the spectrophotometer. High sensitivity is possible [ E = 4.1 X lo6 (5)] but usually the equilibrated vapor i s diluted with carrier gas and sensitivity is lost. It has been shown (5) that with one dynamic system only 7 % of available mercury may be present in the cuvette at the time of measurement.
The method described allows transfer of mercury vapor, in equilibrium with reducing solution, to the cuvette. By using a small volume cuvette, a small sample can be used. Sensitivity is good a t 0.2 pg per liter of mercury in liquid solution. Precision is excellent with a relative standard deviation of 1 at the 20 pg per liter level. Instrument output is between 40 and 60 samples per hour with n o special apparatus requirements except an atomic absorption spectrophotometer. EXPERIMENTAL
(1) N. S. Poluektov, R. A. Vitkun, and Yu. V. Zelyukova, Z h . Anal. Khim.,19, 937 (1964). (2) M. S . Dill, Bull. Y-1572, Union Carbide Corporation-Nuclear Division Y-12 Plant, Oak Ridge, Tenn., 1967. (3) H. Brandenberger and H. Bader, At. Absorption Newslett., 6 (3), 101 (1967). (4) W. R. Hatch and W. L. Ott, ANAL.CHEM., 40,2085 (1968). ( 5 ) J. F. Uthe, F. A. J. Armstrong, and M. P. Stainton, J . Fish Res. Ed. Can., 27, 805 (1970). (6) G. Wobeser, N. 0. Nielson, R. H. Dunlop, and F. M. Atton, ibid., p 830.
Apparatus. ATOMICABSORPTION SPECTROPHOTOMETER. A Perkin-Elmer Model 403 was used for this work. Either automatic readout of absorbance o r chart readout is essential. Either a mercury hollow cathode lamp o r a mercury vapor lamp may be used. The latter requires its own power source but gives a better signal to noise ratio. CUVETTE. Borosilicate glass, 15 cm long 7 mm o.d., 5 m m i.d., with silica end windows 1 mm thickness attached with epoxy cement was used. Approximate volume was 3 cc (See Figure 1).
z
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