Lurr Connrc tor
w
w
guide plate prevents rotation of the Kel-F rod once it is adjusted (Figure 1). The 0.030-inch holes on the Kel-F rod are made with a No. 68 drill bit introduced through the male luer connector and a ?/*-inchpiece of 17-gauge tubing used as a guide. First, with the solenoid deenergized, a hole on the top and another on the right connector are drilled until they meet at the axis of the Kel-F rod. Then the solenoid is energized and the operation repeated drilling on the top,and the left connector, Finally, the Teflon septums and luer connectors are set tight and the plunger moved manually several times so the septum surface seals perfectly against the Kel-F rod. Then the connectors are loosened until the plunger can be moved freely by the return spring.
\
RESULTS AND DISCUSSION
Figure 3. Detail of the male h e r connector alignment with the holes on valve plunger Note that a hole is either aligned with septum hole or blocked by the speetum surfac
under the top connector is centered when the solenoid is deenergized and moves to 0.010 inch from the edge when energized (Figure 3). A sector cut at the end of the rod and a
The valves described have been in operation for almost two years with only occasional tightening of the Teflon septums. They are used with 5N solutions of perchloric acid or potassium hydroxide without problems. The liquid flows are between 0.5 and 2.5 ml per minute with a pressure drop of less than a psi. The seals have been checked up to 100 psig without leaks. If Viton septums are used insted of Teflon, the valve will hold 200 psig pressures without leaks. The three-way valve adapts itself to any automatic reagent dispenser o r reagent pump and can be easily connected for automatic refill from a reagent reservoir. This valve can also be made as a two- o r four-way valve by drilling the '/,,-inch holes distributed symmetrically around the Kel-F plunger. Several on-off or two-way valves are now being used in automated Karl Fischer water titrators to control the addition of water standard in methanol and Karl Fischer reagents. RECEIVED for review April 5 , 1971. Accepted June 29, 1971.
Direct Sample Injection into a Helium Ionization Gas Chromatograph Hugh C. Dodd Department of Environmental Medicine, The Medical College of Wisconsin, Allen-Bradley Medical Science Laboratory, 8700 West Wisconsin Aoenue, Milwaukee, Wis., 53226
OUR LABORATORY purchased a Helium Ionization Gas Chromatograph (Varian Aerograph-Helium Detector Instrument-Mode1 No. 1532) normally equipped with a sample loop injector because this instrument possesses parts per billion sensitivity to all gases and vapors-specifically, COS, CO, 02,CHa, N2, and H2 ( I ) . Only ultrapure helium carrier gas meets the requirements of the instrument. Our applications require that we be able to take air samples from any source (room air, saran bag, blood reaction vial, etc.) and immediately inject them via syringe through a septum into the gas chromatograph. In addition, to calibrate several
types of analytical instruments simultaneously, we must prepare our calibration air mixtures ( 2 ) in a saran bag. To give the analyst direct access to the sample loop system without exchanging atmospheric gases through the septum, we have designed and constructed a helium purge chamber (Figure 1 shows the chamber added to the standard instrument) consisting of two aligned septa, 1 and 2 , close enough together for a long syringe needle, 3, to inject the sample into the pre-sample loop chamber, 4. A tee, 5 , diverts part of the helium flow to purge the interseptal purge chamber, 6, constantly and then to vent to the atmosphere through tubing,
( I ) C. H. Hartmann, and K. P. Dirnick, J . Gas Chromatogr.,4,163 ( 1966).
(2) R. D . Stewart, and H. C. Dodd, Amer. Ind. Hyg. Ass. J . , 25,439
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ANALYTICAL CHEMISTRY, VOL. 43, NO. 12, OCTOBER 1971
IONIZATION INSTRUMENT
Figure 1. Helium purge chamber 1. 2. 3. 4. 5.
Outer septum Inner septum Syringe needle Pre-sample loop chamber Tee
Table I.
Sample 1
2 3 4
Carbon monoxide added, ppm 2.5 5
6. 7. 8. 9. 10.
Interseptal purge chamber Vent tubing (to atmosphere) Polyethylene tubing Stainless steel tubing Tubing connector or fitting
Artificial Breath Samples
Number of injections
Helium ionization found, mean
Standard deviation
14 11
2.8 4.8 59.1 127.5
zt0.4 +0.6 f4.0 18.4
60
11
125
11
7. A helium flow rate (controlled by a coarse flow control type Hoke Valve placed before the polyethylene tubing, 8) of about 5 ml/minute is adequate. To estimate the flow rate, a drop of leak testing solution is applied to the end of the vent tubing, 7, and the bubble growth rate is observed. The inner septum, 2, can leak only helium ineither direction. Our helium detector instrument has a fine metering valve (not shown) downstream from the sample loop, and by placing an on-off Hoke Valve just prior to the pre-sample loop chamber, 4, we are able to create a ciosed system in the sample loop. An air sample (it is imperative that all sample and calibration mixture volumes and procedures be duplicated) is injected through the two septa with the system closed, ten seconds are counted off to permit thorough mixing, and then the sample loop valve is returned to the sampling position, and the two valves are re-opened. Helium purges the sample loop until the valves are closed for the next injection. Two helium cylinders must be used; the first is for ultrapure quality carrier gas and the second to charge the sample loop and to purge the interseptal purge chamber, 6. Unlike
Relative standard deviation, f14.3 112.5 f6.8 1k6.6
Range 2.3-3.55 4.15-5.6 53.9-67.8 114-138
the carrier gas required, the sample loop gas need not be ultrapure. Advantages are ease of sampling with a syringe, ability to calibrate the instrument efficiently and often without using the exponential dilution flask ( I ) , and ability to readily change sample sizes by altering syringe volumes. In considering an addition to the closed system portion of the sample loop, the volume should be kept minimal and the construction material should be stainless steel tubing, 9 (all of the tubing on our instrument chamber is l/s-inch o.d.), and fittings which adsorb the atmospheric gases less readily than copper, brass, etc. Table I shows the results of repetitive sampling o n artificially prepared breath samples made up by injecting pure carbon monoxide into human breath (endogenous CO predetermined) collected in 15-liter saran bags. The sample concentrations were confirmed o n a Beckman IR-10 Infrared Spectrophotometer, equipped with a scale expander and a 10-meter gas cell. RECEIVED for review May 11,1971. Accepted June 28,1971
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