E Q U I P M E N T

Apparatus Logs Low Chloride Concentration Null point potentiometry system measures dilute samples rapidly; accuracy approaches 0.1%

An instrument for fast, accurate meas­uring of low concentrations of chloride ion has been developed by Ε. Η. Sargent & Co. Consisting of control and delivery units, it uses the method worked out by Dr. H. V. Malmstadt of the University of Illinois. The instru­ment measures concentration of chlo­ride ions in an unknown solution by comparing it potentiometrically with a known solution, then diluting or con­centrating the unknown to equivalence with the known.

Chief advantage is that measure­ment can be made in one to three minutes with accuracy that approaches 0.1% and is virtually independent of concentration down to 1 p.p.m., ac­cording to Dr. Paul Sherrick, vice president of engineering and manu­facture at Sargent. Thus, he says, the instrument is particularly useful in microanalyses such as determining chloride in water and serum.

Analytical chemists generally meas­ure chloride content by a titration method and detect end points by vis­ual, potentiometric, amperometric, and other means. These methods give good accuracy except when the chlo­ride concentrations are very low. One approach for dilute solutions has been potential measurements in a concentra­tion cell containing two Ag-AgCl elec­trodes. Big drawback with this tech­nique, though, is the need for a tem­perature control system, according to Dr. Sherrick. Also, the analyst has to correct for chloride contributed by the Ag-AgCl electrode and for the chlo­ride content of any reagents he uses. Null point potentiometry, however, overcomes these difficulties, Dr. Sher­rick says. It determines chloride over wide concentrations without a tem­perature regulating system or calcula­tion corrections, he points out.

Potential Approach. Principle of the null point technique, Dr. Sherrick explains, is potentiometric comparison. Simply stated, it consists of changing the chloride concentration of the un­known solution until it equals the con­centration of a known reference solu­

tion, while keeping the ionic strength constant. This procedure requires a potentiometric device coupled with an automatic buret to add solutions quan­titatively. Sargent's apparatus to do the job:

• Concentration cell for comparing solutions.

• Two solenoid-controlled burets for either diluting or concentrating the unknown.

• Null detector. • Semiautomatic buret control sys­

tem to deliver reagent or diluent to the concentration cell.

The concentration cell, Dr. Sherrick says, consists of three basic elements: a 50 to 600 ml. beaker for the un­known, an isolation compartment with fiber liquid junction for standard known solution, and two Ag-AgCl electrodes. The cell and a stirring sys­tem are mounted on a movable plat­form in a supporting structure. The two burets—one for diluent and the other for reagent—and two solenoid valves are clamped on vertical rods above the structure.

The null detector is a high input impedance, d.c. chopper amplifier fitted with a zero-center meter sensi­tive to 20 microvolts (less than 0 .1% difference in concentration). The di­rection the meter needle deflects indi­cates concentration deviation, tells you whether to add diluent or to add re­agent, Dr. Sherrick explains. An as­sociated switch selects the proper buret; a lever switches control of re­agent to either manual or semiauto­matic. Semiautomatic operation adds reagent to a point close to equivalence. At this point, exact balance may be made by using the manual control lever and observing the meter, Dr. Sherrick says.

Microquantities. This method can be used to measure concentration of all materials for which stable electrode systems can be devised, Dr. Sherrick says. It works best, so far, on chloride determinations, he points out. For instance, the technique takes less than

a minute to measure chloride in diluted serum samples containing only 0.02 ml. blood serum. Relative error is less than 0.5 % and total time for all operations is from one to three minutes.

Ground and river water samples containing 0.03 mg. to 30 mg. per liter of chloride have also been analyzed this way. And the entire procedure, from preparing sample through meas­uring chloride and calculating the final results, takes only about one minute, according to Dr. Malmstadt.

BRIEFS

Temperature indicating label, V4 in. square, sticks on most surfaces, turns black at any desired temperature be­tween 100° and 500° F., says its maker, Pyrodyne, Inc., Los Angeles, Calif. Its accuracy is ± 1 % , adds the company. Suggested uses include monitoring temperatures of miniature components and inaccessible machin­ery, says Pyrodyne. Ε 1

Buechner funnel from American Agile Corp., Maple Heights, Ohio, comes in two sections, allows cleaning of the filter plate located in the top section. The funnel is made of high den­sity polyethylene. The filter plate is 1 in. thick, has holes Vi« i n · in diameter on ; {/s in. centers. When the funnel sections are assembled, the sealing connection is leakproof, will withstand a vacuum of 30 in. Hg, says the company. Ε 2

Getter-ion type vacuum pump for ultrahigh vacuum work is now avail­able from Consolidated Vacuum, Rochester, N.Y. The PDV-300 Drivac pump has a nominal pumping speed of 300 liters per sec. and an ultimate pressure of 2 X 10 lfli mm. Hg, the company claims. The stainless steel pump casing will withstand bakeout temperatures to 450° C , the company adds. Ε 3

High vacuum system designed for long term testing in the 10-8 mm. Hg range is a new product of General Vacuum, Medford, Mass. The system will reach below 1 Χ 10~8 mm. Hg without baking, the company says. The pumping system includes a 6 in. diffusion pump and a polished stain­less steel baffle designed for liquid nitrogen. Ε 4

52 C&EN JAN. 9, 1961

INSTRUMENTS . . .

Strip-chart recorder with five steps of automatic zero suppression is now available from Wheelco Industrial In­struments Division, Barber-Colman Co., Rockford, 111. Zero suppression does not affect span, says Wheelco. Span range is 2 to 250 mv., with a maximum total span of 500 mv., it adds. The recorder has two pens, one for recording and one for showing at which step of zero suppression the instrument is operating. Ε 5

Radiation monitor from Nuclear-Chi­cago, Des Plaines, 111., is a gun type survey meter which gives both dose rate and accumulated dose measure­ments. The instrument is designed for

monitoring beta, gamma, and x-rays of low and medium intensity. Ac­cording to the company, the meter will also measure alpha radiation as low as 4.5 m.e.v. Two interchange­able ion chambers provide the two methods of operation. The rate chamber gives three ranges: zero to 25, zero to 250, and zero to 2500 milliroentgens per hr. The integrating chamber has five ranges: zero to 0.25, zero to 2.5, zero to 25, zero to 250, and zero to 2500 milliroentgens. Ε 6

Further useful information on keyed Equipment items men­tioned is readily available . . .

Use handy coupon on page 54 ^

January 9, 1961

Readers' Information Service Use this handy self-mailer to obtain further information or literature. Simply mark the items desired, fill out the information requested, clip the coupon, fold, staple, and mail.

(Please fill out coupon completely.)

Name:

Company:

Street:

City Zone State

Your Title:

Your Function (Check One): 1 • Corporate Management 5 Π Process Research 2 Π Technical Management 6 Π Process Design & Development 3 Π Product Research 7 Π Production—Processing 4 Π Product Design & Development 8 Π Purchasing

Other (Specify) CLIP COUPON—Fold along this line—fasten (staple, tape, glue) MAIL

Your Industry:

1 π Construction 11 π Petroleum Réf., Asphalts, 2 π Food & Kindred Products Lubricants 3 π Textile Mill Products 12 π Rubber; Plastic Products 4 π Paper & Allied Products 13 π Leather & Leather Products 5 π Printing, Publishing, etc. 14 π Stone, Clay, & Glass Products 6 π Chemicals & Allied Products 15 π Primary Metal Industries 7 π Plastics; Synthetic Resins 16 π Fabricated Metal Products 8 π Drugs 17 π Machinery & Equipment 9 π Soap, Detergents, Cosmetics 18 π Transportation Equipment

10 π Paints, Varnishes, etc. 19 π Instruments 0 π Other (Specify)

simplify tubing connections with

Vari-Grip* Teflon Fittings

No need to labor over glass ball joints or other intricate fittings or connectors with the new Beckman Vari-Grip* Teflon Tube Fittings. Simply insert glass or metal tubing into fitting and tighten nut for a perfect compression seal. Fitting design permits considerable variation in tube size. Since Teflon is more inert than glass it is unaffected by most liquids and gases. S3 A complete listing of time-saving Beckman Vari-Grip Fittings by size, type, and price is available from authorized Beckman laboratory apparatus dealers. Or write for Data File 13-2-09.

B e c k m a n / Scientific and Process Instruments Division

I Bechnan Instrumenta, Inc. I 2500 Fullerton Road,

& / Fullerton, California ^TRADEMARK, BIJ /

J A N . 9, 1961 C & E N 53