Anal. Chem. 1981, 53, 1133-1134
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Flgwe 1. Electronic control module and modification of gel-permeatlon
chromatograph. (c) 4-A, 12-V dc power supply (Straco, Inc., Dayton, OH), Model PS-4 or equivalent, $19.05; (d) 12-V relay, toggle switches, power cords. Construction. A moclifcation of the conventional GPC system used in our laboratory ia shown in Figure 1. The basic system consists of a metering pump (Milton Roy), a six-position sample injector fitted with 5O-lriL sample loop (Cheminert), a 900 X 25 mm gel column (Ace Gk),and a W detector (254 mm) (Varian). To automate the sample injection, we inserted two three-way solenoids in the sample ltmp (Figure 1). The sample is still loaded into the loop through the six-position injection valve; however, with the injector in the “hject” pasition, flow through the sample loop occurs only when the inject solenoids are activated. At a constant solvent flow rate, controlling the time the solenoids are activated precisely controls the volume of injection. Automation of the fraction collection is accomplished by adding a three-way solenoid to ithe effluent line from the column. The normally open side of the solenoid is connected to the waste solvent receiver and the normally closed side to the sample receiver. The electronic control module is constructed without soldering by connecting the three variable-time-delay relays in series as shown in Figure 1. The terminals (Figure 1)correspond to the
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terminals on the mounting bracket of the timer. Functionally, the timers are connected as a momentary-start interval timer and two on-delay timers in series. The momentary-start timer activates the injector solenoids when the “inject start” switch is depressed. The solenoids remain activated for the duration of the timing cycle, after which power is applied to the next timer through terminal 1. The second timer is connected as an on-delay timer which activates the sample-collection solenoid at the end of the timing cycle. Thus,the adjustment of this timer controls the time between sample injection and sample collection during which the lipids elute from the column and into the waste receiver. At the end of the timing cycle the collect solenoid is activated, and power is applied to the third timer. This timer is a reset delay which allows collection of the sample until the end of the timing cycle when it activates the 12-V relay and sends a reset pulse to the first timer. When the first timer is reset, the others return to the initial conditions, and the next aliquot of the sample is injected into the column. This process cycles until the power is turned off. Procedure. The tissue extract is concentrated to less than 50 mL in methylene chloride and centrifuged to remove particulates. After the GPC system has been flushed thoroughly and a flow rate of approximately 3.5 mL/min is attained, the injector block is moved to the load position and the 50-mL sample is drawn into the sample loop. The injector block is moved to the “inject” position, which transfers control to the inject solenoids. Initially the three timers may be set at 1.2 min, 36 min, and 30 min, respectively,which corresponds to a 1.2-min injection (4.2 mL), a 36-min waste cycle (126 mL), and a 30-min collection cycle (105 mL). After the first injection, the waste timer is adjusted so that sample collection coincides with the end of the elution of the lipids. RESULTS AND CONCLUSIONS The cleanup of large tissue samples for GC/MS analyses frequently requires approximately 1 week of technician time/sample when manual GPC systems are used. Automating this procedure allows each sample to be cleaned up unattended within 24 h. Moreover, if the GPC columns are adequately matched with respect to performance, a single control model will control several GPC systems simultaneously. We have used this system for the past 2 years without a single failure because of the solenoids or timing network. LITERATURE CITED (1) Tlndle, R. C.; Stalling, D. L. Anal. Chem. 1972, 44, 1768-1773. (2) Kuehl, D. W.; Leonard, E. N. Anal. Chem. 1978, 50, 182-185.
RECEIVED for review July 18,1980. Resubmitted January 22, 1981. Accepted January 22,1981.
Qualitative Determlnatlon of Volatfie Compounds In Solids by Vaporizatlon/Mass Spectrometry Alan J. Power Materials Research Labonntorles, Defence Science and Technology Organlsation, Melbourne, 3032, Australia
In many branches of materials science it is sometimes necessary to identify gases and low molecular weight organic compounds in solids. Sophisticated equipment for quantitative thermal volatilization analysis of solids has long been available, and interfacing such instrumentation to a mass spectrometer for identification of volatiles is quite common. At these laboratories there is a need for rapid, qualitative analysis of low molecular weight compounds in solids, particularly polymers, and a simple, low cost device to be used in conjunction with a gas chromatograph/mass spectrometer (GC/MS) system has been developed to meet this requirement. 0003-2700/81/0353-1133$01.25/0
The device (Figure 1) comprises a brass container fitted with a removable stainless steel lid and is connected by stainless steel tubing to the injection port and molecular separator inlet inside the GC oven, thereby replacing the GC column. Substitution of a “dead volume” device in place of the GC column has been described previously (1, 2). A wire gauze filter (Figure 1,item A) covers the outlet tubing to prevent entry of any fine solid material into the molecular separator. A custom-built, stainless steel holder (Figure 1,item D)is used for loading powders and other particulate solids. The tolerance between the holder disks and the container walls is minimized to ensure that most of the helium carrier gas flows through 0 1981 American Chemical Society
Anal. Chern. 1981. 53. 1134-1136
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conditions can 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).
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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. I t 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
