Anal. Chern. 1981. 53. 1134-1136
1134
A
conditionscan vary from 0.1 to 1.5 h; the rate of volatilization or diffusion depends in part on whether the compound is adsorbed to the surface or interstices of the solid and, in the latter case, criteria such as component concentration and the density of the solid are significant. It is envisaged that this device should he useful for identification of volatile compounds present in many different types of solid materials. A t these laboratories its main application has been in assessing the compatibility of polymers with other materials in hermetically sealed environments, which is an important consideration for long-term storage of defence materiel. The device has also been used for baking out organic compounds from dried plant material, and in one case a compound with molecular weight as high as 314 was identified. In another investigation of forensic significance, trace amounts of residual kerosine were detected in carpet which had been damaged hy fire in the foyer of a public building (3).
A
Fyure 1. Device used: (A) wire gauze filter, (B) 2.54-mm SwaWk nut and ferrule, (C) parallel f!ats (lor tightening). (D) sample holder. the central holes. For larger samples or fibrous material it is not necessary to use the holder. Care should he taken, however, to ensure that the samples are loosely packed to avoid impeding the carrier gas flow. The loaded sample container is connected inside the GC oven and, after allowing ca. 5 min for the carrier gas to flush air out of the system, the molecular separator is adjusted to give an ionization chamber pressure similar to that used in GC/MS work (ca. 5 x lo4 Torr).Evolution of volatile compounds from the sample is continuously monitored by the mass spectrometer. As general procedure, the GC oven temperature is increased from 40 "C a t 2 'C/min to an upper temperature limit which is just below the temperature at which the particular solid undergoes thermal decomposition. This constraint applies mainly to organic materials. For samples such as metals or soils, the upper temperature limit is that recommended for the GC oven. The slow oven temperature programming rate minimizes the temperature differential between the sample container and the oven and also significantly reduces simultaneous evolution of cornpounds which have different volatilities. The evolution times of compounds released from solids under these
CONCLUSION For rapid, qualitative analysis of volatile substances in solids, the method presented in this paper offers the following advantages over other techniques: (1) The device can he constructed from cheap, readily available materials. (2) No modification to GC/MS instruments is necessary. (3) Large loadings of samples (10-20 g) can he used, thus facilitating detection of trace compounds. (4) Samples do not require preliminary preparation. (5)Analyses are usually completed in less than 2 h. Because of the proliferation of GC/MS instruments during the last decade, this simple device could he utilized to advantage in many investigations. It provides an inexpensive alternative to that of interfacing sophisticated thermal volatilization equipment to the mass spectrometer. LITERATURE CITED (1) P o w . A. J. "An Inlet System la VOlatM Llqulds fw a Gsa Chromatagaphylwa?, Spctromehy (GC/MS) System". Technical Note 381; Materials Resaarch Labaatorks. Department 01 DeIence: Melbourne, Australla. 1975. (2) Schiller, J. E.: Knudaon. C. L. Anal. Chem. 1978. 48. 453. (3) Keiso, A. G.: Power. A. J. "The Detectbn 01 Resldusl Kerwlne in Carpet Damaged by F W . Tedlnlcal Report OCD 7812; MBIBrlaB R b search Laboratwies. Department 01 Defence: Melbourne. Australla. 1978.
RECEIVED for review June 21,1979. Resubmitted March 6, 1981. Accepted March 6,1981.
Temperature Correction for the Specific Conductivity of Dilute Aqueous Ammonia Solutions Alfred Pebler Westlnglwuse Research 8 Dewbpnmnt Center, Pinsburgh, Pennsyivanla 15235
The specific conductivity II (0-l em-' or S cn-') of an ionic solution is a sensitive indicator for the concentration of dissolved ions. For this reason, flow-through type conductivity cells are extensively used to monitor changes in the ion concentration in feed streams relative to a predetermined value, range, or limit that is optimal for a specific ionic environment in question. Since the specific conductivity depends on the chemical identity and concentration of dissolved ions, as well as the temperature, numerical values measured in different 0003-270018110353-113801.25/0
environments cannot readily be compared without a detailed knowledge of the chemical makeup and temperature of respective sample streams. As part of an Electric Power Research Institute (EPRI) contract, we have collected, among other information, specific conductivity data on low-pressure (LP) turbine steam condensate in 16 power plants representing various steam supply and water treatment systems. The specific conductivity was measured with a Barnstead conductivity bridge (Model PM8 1981 Amerlcan Chsmlcal Soclshl
ANALYTICAL CHEMISTRY, VOL. 53, NO. 7, JUNE 1981
70CB) and a glass flow-through cell which was attached to the sample outlet. The water sample temperatures varied depending on local conditions. The major solute in the steam condensate was found to be ammonia. In order to correlate the specific conductivities with the analytical NH3 corncentrations,we temperature-corrected the measured data. A temperature correction for dilute ammonia solutions, typical for steam condensate, is derived in this paper from primary data and applied to the measured conductivity data. CALCULATION According to solution theory, the specific conductivity K is given by
1135
Table I. Equivalent Ion Conductivities of NH,+ and OHat Infinite Dilution and Ionization Equilibrium Constants Kb for Ammonia in Water hoNH +, s haOH-, s 105~,,, t, "C cmz/Gquiv cml/equiv mol/& 0
40.2 63.9 73.6
18 25
105
1.368
171 198
1.770
44 7
1.854 1.690 1.292
50
75 100
20.6
where zj = valency of ion j , cj = ion concentration (mol/cm3), F = Faraday constant = 96 487 (A s)/mol, and uj = ion mobility (cm2/(s V)). Ions have different mobilities depending on their size, charge, and degree of solvation. The temperature of the solution also ha.s a strong effect on the ion mobility. Moreover, toward higher concentrations, ions cannot be treated as independent charge carriers, but their mobility is altered by ion-ion interactions and uj becomes a function of Cck For a single z+z- valent electrolyte, eq 1 reduces to K
= ZpC(U+ + U-) = ZC(A+
+ A_)
(2) o
or
io
20
30
40
50
M)
70
m 90
io0
Temperature t P C
A=
ZC
= A+
+ X.
(3)
where h, X+, and A- are the equivalent conductivities of the electrolyte and the individual positive and negative ions, respectively. Values of X have been determined and are tabulated for solutions approaching infinite dilution, where the ion-ion interaction disappears. In a few cases, equivalent ion conductivities have been measured over a wide temperature range. If the compound is only partially dissociated, eq 2 is modified to K
:=
ZCoa(A+
+ h)
(4)
where CY denotes the degree of dissociation and co the total solute concentration in mol/cm3. Using the molality mo (moles of solute/kilograms of solvent) of the solution as a measure for its concentration, we write K
= 10." zmopa(h++ A_)
(5)
where p is the density of the solution, which for low concentrations approximates that of pure water. Ammonium hydroxide is a relatively weak base; its dissociation via NH,(aq)
+ HzO, = NH40H = NH4++ OH-
(6)
is governed by the base1 equilibrium constant Kb
[",+I
[OH-]
(7)
["daq
Noting that for a pure hlH3solution [NH4+]= [OH-] = amo, one derives the degree of dissociation to be a=
"[
2m0
(1 +
- 1]
Figure 1. The relative specific conductivity k,lk2,ec of aqueous NH, solutions at different NH3 concentrations in mg/kg as a function of temperature.
If we express the total dissolved NHS concentration in ppm (=mg/kg) and the specific conductivity in pS/cm, we get
The latest and most reliable numerical values for the equivalent ion conductivities for NH4+and OH- between 0 and 100 "C were taken from Quist and Marshall's (I) compilation, and those for the ionization equilibrium constant Kb for NH3(aq) from Hitch and Mesmer's (2) work. Both sets of data are compiled in Table I. Values at intermediate temperatures were derived by graphical interpolation. In the case of A'",+ and XOOH- this was aided by plotting the Walden product X O V H ~ (7~ = dynamic viscosity) against the temperature because the product is relatively independent of temperature compared to Xo. Values for the dynamic viscosity and density p of water at different temperatures were taken from D'Ans-Lax (3). RESULTS Specific conductivities of ammonia solutions were calculated between 0 and 100 O C in 10 O C intervals as well as at 26 OC (reference temperature) and for total NH3 concentrations of 0.01, 0.1, 1, and 10 mg/kg using a programmable calculator (TI 56). Relative specific conductivities K ~ / K were ~ ~ ~ derived c thereof and are plotted in Figure 1as a function of temperature. It is seen that the temperature correction is practically independent of the NH3 concentration between about 10 and 70 O C with a temperature coefficient of about O.O2/OC. The information was used to standardize specific conductivity measurements of LP turbine steam condensate that were
1136
Anal. Chem. 1981, 53, 113’6-1138
1
o Plant Data
0.01
0.1 1 Mi3 Concentrationlug kg-1
10
Figure 2. Specific conductivity of NH, solutions and LP turbine steam condensate samples at 25 O C .
conducted at a number of power plants along with chemical analyses. The major ionizable substance in LP steam was found, by ion chromatographic analysis, to be ammonia which is added to the feedwater for pH control. Thus, the specific conductivity of LP turbine steam condensate is expected to approximate those of NH3 solutions. A plot of the standardized (25 “C) specific conductivitiesof LP steam condensate as a function of the measured NH3 concentration in Figure
2 shows that the expected correlation is, by and large, supported by the experimental data. The extent and direction by which the experimental data deviate from the expected conductivity at a given NH3 concentration may be taken as an indication of the type and concentration of other minor impurities. For instance, anionic species such as bicarbonate, chloride, and organic acids will depress the specific conductivity (as long as their total equivalent concentration is less than that of ammonia), whereas cationic species such as alkali ions will tend to raise the specific conductivity. Thus, the simultaneous monitoring of the ammonia concentration by way of an ion-specific electrode and the specific conductivity of LP steam turbine condensate may be a sensitive diagnostic indicator for undesirable steam impurities. ACKNOWLEDGMENT The author is indebted to W. T. Lindsay, Jr., for advice and assistance. LITERATURE CITED (1) Quist, A. S.; Marshall, W. L. J. fhys. Chem. 1965, 69, 2984. (2) Hitch, B. F.; Mesmer, R. E. J. Solution Chem. 1976, 5, 667. (3) D’Ans-Lax “Taschenbuch for Chemlker and Physiker”, 3rd ed.; 1967; p 1-802 (density of H,O) and p 1-622 (dynamic viscosity of YO).
RECEIVED for review November 17,1980. Accepted February 27, 1981. This work was sponsored by the Electric Power Research Institute under Contract RP-912 to the Materials Evaluation & Application Department of the Westinghouse R&D Center.
Proposed Certlfled Reference Material for Pond Sediment Yasuo Iwata, Kazuko Matsumoto, Hiroki Haraguchl, and Keiichiro Fuwa‘ Department of Chemistry, Faculty of Science, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan
Kensaku Okamoto* National Instltute for Environmental Studies, P.0. Yatabe, Ibaraki 305, Japan
In recent years, the importance of certified reference materials (CRMs) for elemental analysis has been well recognized. The present authors, in a cooperative study with National Bureau of Standards (NBS) research groups, have provided some biological reference materials such as Japanese tea leaves (I) and “wet” shark meat (2). The National Institute for Environmental Studies (NIES) has recently initiated a CRM program. The objective of this program is the preparation and certification of environmental reference materials to serve the needs of environmental scientists and laboratories. The first CRM certified was a botanical sample, pepperbush, the preparation, analysis, and certification of which were described in the previous literatures (3,4). More recently, we have performed the preparation of a proposed environmental CRM, “pond sediment”, as the second CRM to be issued by NIES. The material was collected from the Sanshiro-ike pond at the University of Tokyo, which is centrally located in Tokyo, Japan. The material represents a stratum called Kanto loam, which probably consists of volcanic ash erupted a long time ago from Mt. Fuji and other volcanos. Therefore, this pond sediment is significantly different in ita composition from the river sediment Also affiliated with the National Institute for Environmental
Studies.
0003-2700/81/0353-1136$01.25/0
Table I. Homogeneity Test of Pond Sediment Samples’ cu Mn Pb co
X,b&g/g
721 220 0.75 1.3 2.3 1.7 OD/_‘ (%) 0.90 O E / X (%) ~ 2.1 Analytical data are expressed as the Samples were dried at 110 “C for 4 h in OA/~‘(%)
103 1.1 3.1 1.8
29.1 1.4 3.2 2.4
dry weight.
an oven. average concentration. ‘OA, homogeneity of samples. OD, error of digestion. e OE, error of measurement.
from NBS (5). Hence, we report the potential of the pond sediment powder as a new environmental CRM. EXPERIMENTAL SECTION Sampling and Pretreatment. In May 1977, the sediment was collected to a 1-m depth from the bottom surface at the center of the Sanshiro-ikepond. It was stored in polyethylene bags for about 1 year. Before preparing the CRM,a small quantity of distilled water was added initially to the sample and the sample was stirred well. The wet sample was sieved through a nylon sieve (2 mm) to remove gravel and leaves. Drying. The wet-sieved material was filtered by suction to remove interstitialwater, and it was air-dried on fdter paper (Toyo No. 2) at room temperature for 2-3 weeks. About 70 kg of dried pond sediment was obtained. 0 1981 American Chemical Society
