Interpretation of Proton Magnetic Resonance Spectra by Computer Program: An Enhanced Elimination Algorithm
Sir: I read with considerable interest the article which Beech, Jones, and Miller ( I ) published in your journal recently. The algorithm suggested falls roughly into three phases: selection from the table of the macrofragments which are consistent with the spectrum provided; elimination of macrofragments which do not comply with the rules given below; and molecule “building” with the remaining macrofragments. This latter state is computationally most complex and so. it is important that the elimination procedure should be as efficient as possible. Below I suggest a number of ways in which the elimination procedure outlined in the paper ( I ) could be considerably enhanced. If a macrofragment [the nomenclature used here is that introduced in ( I ) ] contains s identical peripheral groups (e.g. CH2 with CH and CH as peripheral groups), then the elimination rules for the macrofragments must be extended such that: if the peripheral group is non-proton containing and is of valency n then the group must appear a t least s X ( n - 1)times among the peripherals of the macrofragments derived from other multiplets (the n - 1 rule of ( I ) ) ; if the peripheral group is proton-containing, then it should be present as the middle group in s of the macrofragments derived from other multiplets in which the current middle group is a peripheral group. (And, of course, for a macro-
fragment to be acceptable, all of the peripheral groups must satisfy one of the above conditions.) Given a list of macrofragments, L, the above elimination rules should be applied until no further members of the list are eliminated. The reason for this is that macrofragment A may be retained because macrofragment B and C satisfy its requirements for peripheral groups. However, if B is subsequently eliminated, then A must also be eliminated unless there is another macrofragment to satisfy A’s peripheral groups. The list of macrofragments, L, is rejected if all the macrofragments suggested to explain a particular multiplet are eliminated. This rule should be applied a t the beginning of each elimination cycle.
LITERATURE CITED (1)
G.Beech, R. 1.Jones, and K. Miller, Anal. Chem., 40, 714-718
(1974).
D. H. Sleeman Centre for Computer Studies The University of Leeds Leeds LS2 9JT, England
RECEIVEDfor review December 26, 1974. Accepted February 14,1975.
I AIDS FOR ANALYTICAL CHEMISTS Titanium Sublimation Pump Method for the Determination of Noble Gases in Gas Mixtures R. W. Baker, J. N. Black, E. D. Sengl, and H. A. Woltermann Monsanto Research Corporation, Mound Laboratory, Miamisburg, OH 45342
A titanium sublimation pump (TSP) method has been developed for the determination of noble gases in gas mixtures. Although helium has been utilized for most of this work, the method is equally applicable to other noble gas determinations. Previous work by Stump and Newton has demonstrated the feasibility of this approach ( I , 2 ) . The method evolved as a means for the accurate determination of the 3He decay product in mixtures containing T2 and HT. Development of the T S P method was necessary since mass spectrometry, the usual technique for analysis, is limited by the interference of the Tf ion with the 3He peak. (The mass difference between this pair is only 1 part in 100,000). Equipment and Description. This method utilizes the chemical “gettering” action of titanium to separate chemically active gases from inert gases. A simple PVT calculation is used to determine the mole percent of inert gas present in the mixture. A mass spectrometer is interfaced di-
rectly to this system and provides verification of the composition of the residual inert gas following each determination. The equipment fabricated to accomplish this analysis is shown schematically in Figure 1. This three-liter volume is constructed of 316 stainless steel whose thickness is approximately l/4 in. The interior of the volume is polished and plated with a layer of gold approximately 0.01-in. thick to minimize absorption, adsorption, and exchange effects. A water jacket surrounds the three-liter volume and maintains it to within f0.05 “C of a constant temperature by means of a Lauda TK-30DH constant-temperature circulator. Likewise, the MKS pressure head and the T S P body are thermostated to the same temperature by parallel outlets from this circulator. The titanium sublimation pump consists of a T S P filament cartridge (Varian Model 916-0017) powered by a controller (Varian Model 922-0032) ( 3 ) . Iondevices supplied ANALYTICALCHEMISTRY, VOL. 47,
NO. 8,
JULY 1975
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! Y’ V A L V E
-
1 7 1 -
BARATRON PRESSURE H E A D
I !
YALYE
1
2
TSP PUMP BODY 112” lene m d 1 % ” , d.1
MASS SPECTROSCOPI S U I P L I N G LINE
T O V I L V E i AND 2!-dPI MASS SPECTROMETER
E L E C T R l C b L CONNECTION TO T I P
U Figure 1. Titanium sublimation pump (TSP) system
Table I. Results of Analyses Obtained by TSP Method for Helium in Hydrogen Primary (Weighed) Standards for Matheson Helium fabrication value, %
Me? value for inert gases by TSP, %
Re1 rtd dev, 96
2.01 0.02 5.10 i 0.05 10.10 i 0.10 20.20 * 0.20
1.997 5.118 10.126 20.440
0.16 0.10 0.06 0.03
No. of determinations
8
a 9
a
the filaments which are of the braided titanium design, and Mound Laboratory fabricated the water-jacketed T S P casing from 5C-in. thick 316 stainless steel. Also, Thermionics supplied the valves which are pneumatically operated; and pressures are measured by an MKS Baratron 145-AHS-1 mm pressure head and read out on a 100A-XR Auto Digital Indicator. The samples to be analyzed are either drawn from various remote locations via a capillary inlet manifold system, or from a gas sample bulb via a sampling port. The sample enters the TSP analysis system through valve No. 1. The pressure rise is monitored by the MKS Baratron gauge. When the desired initial pressure is reached, valve No. 1 (the inlet valve) is closed. The initial pressures used routinely cover a range of 100 to 700 pm Hg. The normal operating procedure utilizes an initial pressure of approximately 500 pm Hg. This gas introduction system has been used for years a t Mound Laboratory on mass spectrometers. No fractionation of gases has ever been observed providing the pressure of gas to be sampled exceeds 400 mm of Hg pressure. After the sample has reached thermal equilibrium (ap-
proximately 5 minutes), the initial pressure measurement, P I , is recorded to the nearest 0.01 pm Hg. Valve No. 2 (the high-conductance valve) is then opened and the sample flows into the pump, where a fresh deposit of titanium already has been sublimed onto the walls. After approximately 30 seconds, greater than 95% of the active gases have been gettered. The T S P filament is again activated to 42 amperes for approximately 30 seconds to complete pumping of the active gases. The remaining gases are then allowed to reach thermal equilibrium (approximately 15 minutes) and the second pressure reading, P2, is recorded. Using the volume ratios of the system established by repeating this procedure with a pure noble gas, the mole percent of inert gas in the sample can be calculated according to the following equation:
’
Pz
=
Pl(nob1e gas calibration) x 100 P2(noble gas calibration)
(1)
The PJP2 calibration factor for the TSP system currently in use is 1.1272. Following the measurement of Pz, valves No. 3 and 5 are opened and the residual gas flows into the DuPont 21-491 mass spectrometer for analysis. Data. The initial checkout of the T S P system was performed using weighed primary standard mixtures of helium-4 in hydrogen obtained from the Matheson Company. These standards covered a concentration range of 2-20% helium in hydrogen and had a quoted fabrication uncertainty of f1% relative. Typical results of analyses performed on these standards using the TSP system are given in Table I. When pure hydrogen was analyzed, the second pressure reading, Pg, was 0.00 pm Hg, demonstrating complete pumping of the active gas. Likewise, samples comprised of 100% inert gases, such as helium and argon, showed no pressure change after activation of the titanium filaments, demonstrating that they are not pumped by the titanium. Furthermore, mass spectrometric analysis of the residual gases after pumping indicated that the active gases were completely removed. Using an accurate volume-pressure balance technique, several standard mixtures of 3He in tritium were prepared a t Mound Laboratory. The results of analyses performed on these mixtures using the TSP method are shown in Table 11; the precisions and accuracies obtained are comparable to those shown in Table I. T o demonstrate the versatility and applicability of the T S P method, a variety of binary active gas-inert gas mixtures were prepared a t Mound using a simple PVT technique. These mixtures were analyzed by the T S P method and yielded the results as shown in Table 111. DISCUSSION For over a year, the T S P method has been used routinely in the determination of 3He in tritium gases. The precision
Table 11. Results of Analyses Performed over a Five-Day Period by TSP Method for Helium-3 in Tritium Standards Prepared at Mound Laboratory Helium
Fabrication value
Mean value for
fabrication value, %a
percent inert gases, totalb
inert gases by TSV, %
2.277 * 0.004 4.1 50 rt 0.008 12.70 i 0.02 32.31 i 0.06
2.285 i 0.008 4.16 i 0.01 12.74 i 0.03 32.33 0.07
2.291 4.171 12.737 32.290
No. of deterRe1 std dev, ?4
minations
0.18 0.08 0.06 0.04
15 15 15 15
a Uncertainty estimated from component uncertainties in mixing system. Increase in uncertainty is due to estimated error in argon impurity analyses. All values corrected for ingrowth of helium-3 due to decay of tritium.
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ANALYTICAL CHEMISTRY, VOL. 47, NO. 8, JULY 1975
Table 111. Results of Analyses Obtained by TSP Method for Various Binary Gas Mixtures Prepared a t Mound Laboratory PVT
Mixture
H, in Ar
H, in Ar CO in Ar CO, i n N e
fabrication value for inert gas, %
95.1 53.7 97.3 97.2
i
0.5
* 1.0 0.5
* 0.5
Mean value for inert
GmgF,e?
Re1 std dev, %
No. of determinations
95.14 53.06 97.34 97.15
0.02 0.06 0.03 0.03
10 6 6 6
in these determinations has been approximately twenty times better than that obtained by mass spectrometry. Also, indications to date are that proof of the accuracy of the TSP method is limited only by the accuracy of the prepared standards. In conclusion, the TSP method has been
demonstrated to be an accurate, highly precise, and versatile one for the determination of noble gases in active gas mixtures. LITERATURE C I T E D E. G. Walter, "Analytical Chemistry Quarterly Report: January-March 1971", University of California, Lawrence Livermore Laboratory, Livermore, CA, UCID-15644-71-1, p 12. (2) J. C. Newton, F. 6. Stephens, and R. K. Stump, "Determination of Trace Noble Gases in Air and Natural Gas", Lawrence Livermore Laboratory, Livermore, CA, UCRL 74695, September 1973. (3) B. E. Kietzmann and D. D. Robertson, "General Characteristics of Titanlum Sublimation Pumps", 2nd ed., No. VAC 2224A, Varian Associates, Paio Alto, CA. (1) R. K. Stump and
RECEIVEDfor review December 11, 1974. Accepted February 7, 1975. Mound Laboratory is operated by Monsanto Research Corporation for the U S . Energy Research Development Administration under contract No. AT-33-1-GEN53.
Quantitative Determination of Tartrate and Formate in Plating Baths M. K. Carter and Madeline Moore Dohrmann Division, Envirotech Corporation, 3240 Scott Boulevard, Santa Clara. CA 95050
Industrial process and wastewater facilities monitor and control total organic carbon (TOC) stream content (1, 2 ) . Analytical determinations of virtually any specific carboncontaining compounds, including all those found in wastewater and chemical process streams, can also be conducted using TOC analyzers (3). In this aid, the authors demonstrate a specific application for determination of the tartrate and formate content of copper process plating baths. The Dohrmann Model DC-50 TOC Analyzer, which uses a reductive conversion of carbon to methane, is sufficiently sensitive (range of 1 to 2000 ppm carbon) and accurate (to f 2 % or 1 ppm carbon, whichever is greater) to yield quantitative determinations of specific chemical components in a mixture of organic compounds. The boat inlet system of this analyzer makes the separation of volatile components from the total sample possible. Plating baths containing copper(I1) salts, formaldehyde, methanol, sodium formate, and potassium sodium tartrate are a mixture of volatile and nonvolatile components. Tartrates are used as a complexing agent to solubilize copper in alkaline solutions. During the plating operation, when copper is removed from solution, some tartrate is lost through dragout or decomposition. Make-up solutions, containing a predetermined quantity of tartrate and copper plus other constituents, must be added to reestablish the original bath condition. A simulated bath was prepared containing 40.4 mg formaldehyde, 13.2 mg methanol, 75.4 mg KNa tartrate, 18.9 mg Na formate, and 2.86 g CuCl2-2HzO dissolved in 100 ml deionized water. All chemicals used were of known purity (Baker Analyzed Reagent). The weight ratios, carbon content, and thermal data of the pure components of the bath are presented in Table I. Quantitative separations were obtained in the DC-50 TOC Analyzer based on widely spaced boiling points and decomposition temperatures. One portion of the bath was analyzed as prepared while another portion was adjusted to a pH 2 by addition of a small quantity of concentrated hydrochloric acid. A 30-111 portion of non-acidified sample was
placed in the platinum boat and held in the 90 "C vaporization zone for three and one-half minutes. The volatile component contained 203 f 2 ppm carbon (C) corresponding to methanol and formaldehyde. The boat was advanced to the 850 OC pyrolysis zone for an additional four minutes. A total (volatile plus residual) carbon content of 371 f 3 ppm C was measured. Analysis of the acidified sample yielded 237 f 1 ppm C as volatiles corresponding to methanol, formaldehyde, and formate (as formic acid) and 366 f 3 ppm C as the total carbon content. The difference of 371 366 or 5 ppm in total carbon values, although within specified error limits of the analyzer, may be due to loss of impurity carbonate upon sample acidification. Total analysis time for one acidified and one non-acidified sample is 15 minutes or 7.5 minutes per sample. Each value reported is an average of ten determinations. A measure of precision is reported by the standard deviations as a fl sigma error. Tartrate concentration of the bath was determined by taking a difference of the total and volatile measurements of the acidified sample. A result of 129 ppm C compares favorably with the theoretical value of 128 ppm C. Similarly, subtraction of the volatile portion of the nonacidified from
Table I. Plating B a t h Composition \ \ e i g h t ratio
Component
Formaldehyde Methanol Formic acid D L - Tartaric acid N a formate NaK tartrate CUC1, 2H2O
of compo-
Carbon contribution
nents in bath
to bath,ppm C
0.54 0.18
... ...
0.25 1.00 37.9
162 49
...
...
33 128 5 (a blank)
Thermal data of pure components,'
c
bp = -21 bp = 68 bp = 100 mp = 209-211 dec. mp = 253 mp > 250
.. .
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