High Spin I , 353°K, sluggish High Spin +

18 kbar ~ Low Spin Ambient T and P

[ Low Spin I

FIG. 3. Pressure-temperature relationships of Fe(phen)2- (NCS) 2.

High Spin

Ambient T and P

\

FIG. 4. Pressure-temperature (NCSe)z.

1

( 353°K~ sluggish High Spinl + I

8-10 kbar ) Low Spin j

Low Spini~

relationships of Fe(phen)~,

High Spin I ( 353°K~ sluggish High.Spin

Ambient 15 kbar ) Low Spin T and P

Spin

FIG. 5. Pressure-temperature relationships of Fe(bipy)~- (NCS)~.

N3-, and NCO-) at high pressures. No anomalous magnetic behavior for these complexes is reported over the temperature range 77 to 440°K (at 1 arm pressure).l Our preliminary results on Fe(phen)2(NCS)2 and Fe(phen)2(NCSe)2 indicate tha t it may be possible to completely convert the above Fe(phen)2X2 series to the low spin state using a combination of pressure and temperature.

The results of the low temperature conversion to low spin for these compounds were explained in terms of strengthening of the Fe-N(phen or bipy) and FeN(NCS and NCSe) bonds due to the back-donation of the % electrons of the metal to the ~r* orbitals of the organic ligand and NCS or NCSe. s This mechanism may also be operative at the outset of pressure application, but with increasing pressure, the back-donation of the metal is reduced by the accessibility of ~- electrons from the ligand to the ligand 7r* orbitMs. 4

The experiments were conducted in a diamond-anvil

cell using a 6 × beam condenser and a Perkin-Elmer model 301 far infrared spectrophotometer. Details of the technique are described elsewhere? ° For the low temperature studies a special anvil cell containing an entry and exit port and a cooling element surrounding the diamonds was used. This allowed the entry of helium which was previously cooled in a liquid nitrogen trap. We estimate the variation in temperature to be ± 5 ° K at 100°K. For the heated experiments we used a cell which contained a heating element surrounding the diamonds. The higher temperatures were measured with a standard chromel-alumel thermocouple. We estimate tha t the variation at 353°K was ± I ° K .

1. E. K6nig, Coord. Chem. Rev. 3,471 (1968). 2. E. X6nig, K. Madeja, and K. J. Watson, J. Am. Chem. Soc.

90, 1146 (1968). 3. E. K6nig and K. Madeja, Inorg. Chem. 6, 48 (1967). 4. D. C. Fisher and H. G. Drickamer, J. Chem. Phys. 54,

4825 (1971). 5. P. B. Merrithew and P. G. Rasmussen, Inorg. Cheni. 11,

325 (1972). 6. A. H. EwMd, R. L. Martin, I. G. Ross, and A. H. White,

Proc. Roy. Soc. A 280,235 (1964). 7. A. H. EwMd, R. L. Martin, E. Sinn, and A. H. White, Inorg.

Chem. 8, 1837 (1969). 8. J. H. Takenioto and B. Hutchinson, Inorg. Nucl. Chem.

Letters 8,769 (1972). 9. J. H. Takemoto and B. Hutchinson, Inorg. Chem. 12,705

(1973). 10. J. R. Ferraro, S. S. Mitra, and C. Postmus, Inorg. Nucl.

Chem. Letters 2,269 (1966).

A p p l i c a t i o n o f C a r b o n R o d A t o m i z e r for t h e A n a l y s i s o f M e r c u r y i n Air

Duane Siemer, Jerome Leeh, and Ray Woodriff

Department of Chemistry, Montana State University, Bozeman, Montana 59715

(Received 20 June 1973; revision received 21 August 1973)

INDEX HEADINGS: Carbon rod atomizer; Airborne mercury analysis.

The analysis of air for traces of poisonous metals usu- ally involves passing large volumes of air through filters or absorbing solutions followed by extensive manipula- tion before actual analysis. In order to simplify these analyses, several workers have reported upon the meas- urement of airborne particulates filtered onto spectro- scopic electrodes. 1-4 Woodriff and Lech 3 draw air through porous graphite cups which then are inserted into a graphite furnace atomizer. Analysis of lead partic- ulates at levels present in the atmosphere can be ac- complished on only 50 cc of air. Amos and co-workers 4 have described application of the carbon rod atomizer to the analysis of lead in air. An essentially standard

68 Volume 28, Number l, 1974 APPLIED SPECTROSCOPY

cup is perforated through the bot tom with many small holes. A disc of Millipore filter media is placed into the cup (£ la Buchner funnel), and air is drawn through. The cup is then placed into the atomizer, the filter is ashed off, and the lead is atomized in normal fashion.

The most common methods of mercury aonalysis of air are based upon the absorption of the 2537 A line of a mercury lamp by mercury vapor. In general, most of these techniques suffer from two problems: first, only elemental mercury vapor, not mercury present as par- ticulates is measured; secondly, fogs, dusts, smoke, and a host of organic compounds as well as mercury vapor are detected. Specific systems for mercury have been reported by Hawkes and Williston 5 and also by James and Webb. 6 Their approaches are similar: the air stream is split into two portions and each stream is passed through identical absorption cells. A selective filter removes the mercury vapor from one stream, and the difference in absorption is a measure of the mercury vapor. Excellent reviews of these and other analytical approaches used are available. 7-9

In view of the ready availability and also the great sensitivity of the Varian Techtron type of carbon rod atomizer, we deemed it desirable to adapt this atomizer to the direct analysis of mercury in air. Air is drawn through the walls of a short, gold-plated, porous graph- ite tube. Elemental mercury is retained by amalgama- tion with the gold and particulate mercury trapped by the filtering action of porous graphite. The tube is placed into the carbon rod atomizer and the mercury is driven off directly into the light path of an atomic ab- sorption spectromoeter , which measures absorption of the mercury 2537 A line.

The carbon rod atomizer was constructed at this laboratory and is similar to the Varian model 63 except tha t it is scaled upwards in size to accommodate 6-mm diameter rods and atomizer tubes. I t is powered with a 5 KVA GE transformer (9T21B1037G2) controlled with a type 242, 4.2 KVA, Powerstat autotransformer. This power supply provides from 0 to 13 rms volts and can furnish in excess of 400 A. Nitrogen gas at a flow rate of 10 CFH is used to flush the carbon rod during atomization of samples. The temperature of the carbon rod atomizer tube was measured with a Pyro optical pyrometer. The atomic absorption spectrometer com- ponents are those described in the paper by Woodriff et a l J °

The tubes are made by drilling a 4.5-ram hole (No. 13 drill) in 15-mm lengths of 6-ram diameter National AGKSP spectroscopic graphite rods. Each tube is plated on the inside with about 1.5 mg of gold in the following manner: one end is sealed off with a pinched- off rubber sleeve; 0.3 ml of a gold solution is placed into the tube; a P t wire anode is inserted; the plating current is applied between the tube and the anode for 15 rain with a 12-V automobile ba t tery in series with a 740-9 resistor. The solution of gold contains 5 mg/ml in dilute aqua regia.

Fig. 1 depicts the adaptor used to allow filtration of air by the atomizer tubes. I t is essentially similar to the one described by Woodriff and Lech 3 except that rubber

• AIR I~LET

FIG. 1. Air filtration device: A, butyl rubber gaskets; B, gold- plated tube; C, 100-cc syringe; D, acrylic plastic. The base is screwed up into the holder, enclosing the tube before air is drawn through with the syringe.

TABLE I. Removal of mercury from saturated air at 24°C.

Tube No. Type of tube Fraction Hg collected

1 Unplated -- O, 032 2 Unplated --0.015 3 Unplated +0.025 4 Unplated -0.015 5 Unplated +0.038 6 Unplated - O, 033 7 Unplated --0.015 8 Unplated +0,050 1 Plated 0,972 2 Plated 0.980 3 Plated 0.986 4 Plated 0.986 5 Plated 0.994 6 Plated 0.986 7 Plated 0.986 8 Plated 0.986

gaskets seal both ends of the tube. Air is drawn by means of a gas-tight 100-cc syringe into the adaptor and through the walls of the atomizer tubes at a rate of about 8 ml/sec. Mercury is retained by the gold on the inside of the tube.

Efficiency of mercury collection by the atomizer tubes was measured by drawing l0 cc of air saturated with mercury vapor (at 24°C) through both plated and unplated tubes. The filtered air in the syringe is then expressed into a 35 mm long, quartz-windowed, cold vapor oatomic absorption tube. The absorption of the 2537 A mercury line by the filtered air is measured. Table I shows the results of this experiment performed with eight graphite tubes both before and after they were plated with gold. The value for "Fract ion Hg collected" in this table is defined as one minus the ratio of the atomic absorbance of the mercury vapor in the air passed through a tube to the atomic absorbance of the same amount of air drawn through the filtration device with no tube in place. Essentially all of the mer- cury is collected by the plated tubes. AGKSP graphite tubes not plated with gold proved to be ineffective for trapping mercury vapor. These tubes were then placed between the rods of the atomizer and freed of entrapped mercury by heating them to 850°C. A current of 70 A at 3 V is sufficient to achieve this temperature in about

APPLIED SPECTROSCOPY 69

TABLE II. Effect of repeated heating on a gold-plated tube ' s ability to collect mercury.

Test Fraction mercury collected

1 0.980 2 0. 983 3 0. 986 4 0. 994 5 0. 994 6 0. 986 7 0.994 8 0. 994 9 0. 994

10 0. 994

TABLE III . Mercury collection as a function of the amount of gold on tubes.

No. Gold on tube (g) Fraction Hg collected

1 2.5 X 10 -~ 0.561 2 2.5 X 10 -8 0.808 3 1 X 10 -5 0.901 4 5 X 10 - s 0.970 5 5 X 10 -4 0.987 6 1.5 X 10 -3 0.994

I.O

LLI 0 0.8 Z <~

o.6

o o.4

oO

0.2

0.0 0 t 2 5 4 5 6

,~. H,j x I0 S

Fla . 2. Analytical curves for the method: A, curve based on filtration of sa tura ted air; B, curve based on addit ion of liquid s tandards to tube.

5 sec. This power setting quickly drives off the mercury but is low enough to leave the gold plate unaffected.

Performing the Hg retention experiment 10 times on one tube (driving off the mercury each time) revealed no change in the mercury retention efficiency of the plated tubes due to repeated heating. Table I I gives the results of this experiment.

This test was repeated except that air saturated at 4 and 26°C was sampled. No change in the collection efficiency over a 7fold concentration range was ob- served.

A series of six tubes were plated with differing amounts of gold, and the percentage retention of mer- cury in 10 cc of saturated (24°C) air was measured. Table I I I gives the results.

Fig. 2 shows the results of experiments to determine an analytical curve for the method. Approximately 5 g of mercury were shaken up in a stoppered, 2-liter, Erlenmeyer flask. Then the flask was placed into an ice-water mixture at 0°C for several hours. Various vol-

umes of this air were drawn through a series of plated tubes, and the mercury was atomized at 850°C and measured by the atomic absorption spectrometer. This figure shows two analytical curves. The first is based upon the filtration of various volumes of the mercury- saturated air with subsequent atomization and analysis. The amount of mercury was calculated using the ideal gas law and l i terature" values for the vapor pressure of mercury. The other curve was established by first drying and then atomizing aliquots of standard mercury solu- tion placed in the tubes with an Eppendorf pipette.

In flameless atomic absorption, the sensitivity of the analysis is often dependent on the geometry of the sam- ple deposition on the graphite tube. 12 A uniform deposi- tion can be expected for the air samples, while a stand- ard introduced as a solution would be deposited as a spot on the side of the tube. For this reason, the means of standardization involving sampling of Hg-saturated air at a carefully controlled temperature is probably the most reliable for general application to air-sampling problems. The reproducibility of individual points on the analytical curve proved to be bet ter with this method.

The reproducibility of the analytical process was measured by sampling a constant volume (10 cc) of air saturated at 4°C through five different tubes with subse- quent atomization and atomic absorption analysis. An average absorbance of 0.385 with a relative standard deviation of 6 % were the results observed. A blank absorbance value was measured by going through all of the analysis steps except actually drawing air through the tubes. This absorbance blank was 0.009 with a standard deviation of 0.004.

This technique of measuring mercury in air is both simple and quick. The Varian model 63 atomizer can be easily adapted to this technique by making a filter adaptor and some plated tubes. (These tubes should be 5 mm in diameter, 9 mm long, and be drilled with a No. 27 drill). The sensitivity of the method of analysis is 3 X 10 -1° g (1% absorption). The detection limit in terms of the lowest concentration detectable in air depends upon the volume of air sampled. An air sample of 50 cc is more than sufficient to establish whether mercury is at dangerous levels or not. The atomizer tubes and sampling device are easily carried to any location where dangerous spills or other contamination may occur, and as many samples as desired are taken for immediate or later analysis. Mercury in particulate form present in the atmosphere will also be retained by the graphite filter tubes and subsequently analyzed. For low level mercury detection an air pump may be used to draw the air through the tubes.

ACKNOWLEDGMENT

This work was partially supported by National Sci- ence Foundation Grant GP-28055.

1. W. Fagan, unpublished data. 2. J. L. Seeley and R. K. Skogerboe, Graphite Cup, Volatile

Halide Spectrographic Aaalysis of Atmospheric Particulates, 11th National Meeting, Society of Applied Spectroscopy, paper 104, Dallas, Texas, 10-15 Sept. 1972.

70 Volume 28, Number 1, 1974

3. R. Woodriff and J. Lech, Anal. Chem. 4.4, 1323 (1972). 4. M. D. Auras, K. G. Brodie, and J. P. Matousek, Direct

Analysis of Particulate Lead in the Atmosphere by Atomic Absorption Using a Carbon Cup Atomizer, The Pittsburgh Conference on Analytical Chemistry and Applied Spec- troscopy, Inc., paper 204, Cleveland, Ohio, 5-9 March 1973.

5. H. E. Hawkes and S. H. Williston, Min. Congr. J. 48, 30 (1962).

6. C. H. James and J. S. Webb, Trans. Inst. Met. 73, 633 (1964).

7. F. M. D'Itr i , Environmental Mercury Problem (CRC Press, Cleveland, 1972), 1st ed., Chap. 4, p. 33.

8. H. R. Jones, Mercury Pollution Control, (Noyes Data Corp., Park Ridge, N. J., 1971), 1st ed., p. 131.

9: EnvironmentalMercury Contamination (Ann Arbor Science, Ann Arbor, 1972), p. 97, Part 2.

10. R. Woodriff, B. Culver, D. Shrader, and A. B. Super, Anal. Chem. 45, 230 (1973).

11. Handbook of Chemistry and Physics (CRC Press, Cleveland, 1961), 44th ed., p. 2426.

12. R. D. Beaty, personal communication.

A F u r t h e r S t u d y o f t h e E f f e c t o f p H o n t h e A t o m i c A b s o r p t i o n A n a l y s i s o f Z i n c

model 303-0103 automatic null recorder readout module, a P-E Zn hollow cathode lamp, and a Varian model 135-1 strip chart recorder made up the spectrometer system used in this study. Solution pH was measured with a Beckman Zeromatic pH meter.

All solutions were prepared from reagent grade chemi- cals using deionized distilled water.

A 1000 ppm Zn stock solution was prepared by dis- solving 1.245 g of zinc oxide in 5 ml of concentrated HC1 and diluting to 1 liter with water. A second 1000 ppm Zn stock solution was prepared by dissolving 2.19 g of ZnCl~ in water and diluting to 1 liter. A 1000 ppm Fe solution was prepared by dissolving 1.000 g of Fe wire in 50 ml of hot concentrated HC1 and diluting to 1 liter. Ten solutions varying in pH from approximately 1 to 10 were prepared, as was done by Dong, by adding 1 M NH3 to 1 M HC1. The 1000 ppm Zn stock solutions were diluted to 10 ppm with water and then diluted to 1 ppm with the solution of appropriate pH. A similar set of 10 solutions containing 1 ppm Fe and 1 ppm Zn (from the oxide) were also prepared.

The percentage absorption of all the 1 ppm Zn solu- tions prepared from ZnO were measured using the instrumental parameters shown in Table I. The results (Fig. la) show no dependence, within experimental error, of Zn absorption on the pH of the solution. The

G. E. Bentley and M. L. Parsons*

Department of Chemistry, Arizona State Uni- versity, Tempe, Arizona 85281

(Received 18 June 1973; Revision received 27 August 1973)

INDEX HEADINGS: Atomic absorption; Zinc analysis; pH effect.

Recently it was reported by Dong 1 that for the analy- sis of zinc by atomic absorption spectrometry (AAS), the percentage absorption of zinc in the flame is a function of the pH of the zinc-containing solution. An examination of the recent literature 2-1° concerning the atomic absorption analysis of Zn by AAS failed to dis- close other reports of pH affecting this determination. EzelF reported that for the determination of Zn in alumina, using a set of standards prepared by adding Zn to solutions of alumina in 2 % sodium hydroxide, "The same values [Zn content of alumina samples] have been obtained using either acid or alkaline stand- ards." Fishman 3 made no mention of a pH effect in the analysis of natural waters for Zn and compared his analysis of Zn by AAS to the accepted dithizone extrac- tion method, n obtaining comparable values by either method. ,~ !

As a result of these conflicting reports, an attempt to duplicate the results reported by Dong ~ was made in this laboratory. The effect of small amounts of iron on the AAS determination of zinc was also studied.

A Perkin-Elmer model 303 atomic absorption spec- trometer equipped with a 10-cm single slot burner, a

* To whom all correspondence should be addressed.

TABLE I. Instrumental parameters.

Wavelength Lamp current Slit setting Scale expansion Noise suppression Acetylene flow Acetylene pressure Air flow Air pressure Aspiration rate

2138 16 mA 4 (approx. 1 mm) 1 1 9 (plastic ball) 10 psig 10.5 30 psig Adjusted for maximum absorbance

42 Z

0 41

I - - ~4o o 39 m "<38 ° 37

X

X X X X A X A

2 ½ 4 5 & 7 8 9 II0 1'I pH

Z 4~

041 E ~4C x x

~3g x x x X

<38

~37

pH FIG. i. a (upper), percentage absorption of i ppm Zn as a func- tion of pit ; b (lower), percentage absorption of 1 ppm Zn + 1 ppm Fe as a function of pH.

Volume 28, Number~l, 1974 APPLIED S P E C T R O S C O P Y 71