Determination of Traces of Lead in Igneous Minerals A. D. MAYNES and W. A. E. McBRYDE Department of Chemistry, University of Toronto, Toronto
A method was sought which would isolate and determine traces of lead in minerals, as in determinations of age b y radioactive decay. A procedure for the quantitative extraction and determination of microgram amounts of lead with dithizone was developed. By extraction with chloroform solutions of diethylammonium diethyldithiocarbamate, lead in hydrochloric acid solutions was separated from a number of elements known to interfere in the dithizone procedure. By successive extractions with diethylammonium diethyldithiocarbamate and dithizone the concentration of lead in a variety of minerals was determined. Precision within 2 to 3% was obtained for 17 to 2400 p.p.m. of lead.
lead are commonly extracted and determined by solutions of dithizone in a w:iter-immiscible solvent. Factors relating to application of this reagent to the determination of lead have been summarized by Sandell ( 8 ) . The reversion technique described by Irving, Risdon, and Andrew ( 5 ) appears to be :I decided iiiiprovement over published procedures based on the use of dithizone. It eliminates difficulties arising froin variations of reagent conccntration in the organic phme due to its initability and solubility in alkaline .solutions, and provides for maximurn sensitivity. Separation of lead from elements interfering in the ditliizone procedure was required, to extend the determinat'ion to a wide variet'y of minerals. Interfering substances include hisniuth and th:dlium, which are extract'ed vit>li lead, titanium, and calcium or niagnesium phosphate, which prevent comp1et.e extraction of lead with ditiiizone. (Indium, in the amounts norinally present in minerals, is not extracted in t'he presence of tartrate or citrate.) In a number of procedures diethylammonium diethyldithiocarbama t e or sodium diethyldithiocarbamate has been used to separate lead prior to its deterrninat'ion with dithizone ( 3 , 4, 6, 10-16). In the analysis of organic materials, possible interference of many element$ commonly present in minerals was not considered. I n some cases the ICIZOGKhhI AMOUSTS Of
5, Ontario,
Canada
accuracy and precision reported n ere not satisfactory for this work. Strafford, Wyatt, and Kershaw (10, 1 1 ) reported a scheme for the determination of a number of elements in pharmaceuticals, in nhich bismuth and lead were separated by the extiaction of ~ diethylammonium diethylbisniuth ' i ith dithiocarbamate from solutions 3-V in sulfuric acid and a t least 2 N in hydrochloric acid. I n the absence of other acids, solutions 4iy to 6 N in hydrochloric acid nere required to prevent extraction of some lead TI ith bismuth. Suitable conditions were sought for the isolation and determination of lead in minerals by successive extraction n-ith chloroform solutions of diethylammonium diethyldithiocarbamate and dithizone. It was important to establish the distribution of many metallic elements during extraction n i t h the former reagent. REAGENTS AND APPARATUS
Laboratory-distilled water, ammonia solution, nitric acid, diethylamine, and carbon disulfide were distilled in borosilicate glass stills. C.P. sulfuric acid, perchloric acid, and sodium carbonate were used rvithout further purification. Hydrochloric Acid. Concentrated hydrochloric acid was diluted 1 t o 1 with water a n d distilled in a borosilicate glass still. T h e first 20y0 and t h e last 10% of t h e distillate were discarded. Chloroform \vas purified b y t h e procedure reported b y Biddle (1). Nitric Acid, 1 to 99. One volume of distilled nitric acid was diluted with 99 volumes of redistilled I-iater. A m m o n i a - C y a n i d e Solution. Twenty grams of purified potassium cyanide a n d 150 nil. of distilled ammonium hydroxide (specific gravity = 0.90) were diluted t o 1 liter with water, and stored in a polyethylene bottle. T h e cyanide was purified b y dissolving 20 grams in 40 ml. of water, filtering into a separatory funnel, and extracting m-ith small portions of dithizone solution until t w o extracts showed t h e pure green color of dithizone. Dithizone remaining in t h e aqueous phase was removed b y shaking with portions of chloroform. Dithizone. A concentrated chloroform solution of t h e commercial product v-as shaken n i t h portions of a dilute ammonia solution until most of the dithizone v a s dissolved in t h e
aqueous phase. The organic phase was discarded. The ammoniacal extracts were combined and made slightly acidic with hydrochloric acid, and the dithizone was extracted with small portions of chloroform. The chloroform extracts were set aside to evaporate to dryness a t room temperature. Dithizone Solutions. Approximately 5 mg. of ditliizone were dissolved in 1 liter of chloroform. With experience, solutions of a suitable concentration ryere prepared b y visually estimating t h e intensity of the color of t h e solution, immediately before use. Diethylammonium Diethyldithiocarbamate Solutions were prepared from distilled diethylamine, carbon disulfide, a n d chloroform according t o the procedure outlined by Strafford, Wyatt, and Kershaw (10). The solution of this diluted 1 to 19 with chloroform is referred to as "dithiocarbamate." Ammonium Tartrate Solution. An approximately saturated solution was made slightly alkaline with ammonia, filtered, and shaken with dithizone solution to remove metals forming dithizonates. Dithizone in the aqueous phase v a s removed by shaking with chloroform. The tartrate solution was stored in a polyethylene bottle. Hydrofluoric Acid was purified with strontium chloride according t o the procedure recommended b y Rosenqvist ( 7 ) . Cotton. T h e cotton was washed with dithizone solution and then with chloroform t o remove dithizone. It \\-as dried, LT-ashed n-ith 1 t o 99 nitric avid until no dithizonate-forming metal was detected in t h e wash solution, rinsed rrith water until free o f acid, and dried at 110' C. Purified cotton should not be touched with the fingers. Pledgets were inserted in t'he stems of the separatory funnels with tiveezers and a stirring rod. Standard Lead Solution. A stock solution, containing 0.973 mg. of lead as t h e nitrate per ml. of 1 t o 99 nitric acid, Ii-as prepared from Specpure lead. The standard lead solution, containing 9.70 y of lead per ml., was prepared b y diluting aliquots of the stock solution with 1 to 99 nitric acid. As a check on possible change of concentration of the stock solution with time, a t the conclusion of the work a second set of stock and standard lead solutions was prepared. The slopes of the working curves (reversion value plotted against micrograms of lead taken) obtained with the two lead solutions were identical. VOL. 29, NO. 9, SEPTEMBER 1957
0
1259
,
Solutions of Metals. Solutions containing 1 mg. (or more in certain cases) of t h e metal per ml. of solution m-ere prepared from reagent-grade chemicals. Glassware. Borosilicate glassn are was used throughout for handling solutions of the mineral samples. I t \vas cleaned after each use in hot nitric and sulfuric acids, rinsed n i t h t a p water, and thoroughly rinsed with doubly distilled n a t e r . Extractions n e r e cairied out in Squibb-type borosilicate glass sepaiatory funnels. Those used for dithizone extractions were cleaned by rinsing t n i c e a i t h doubly distilled nater. once with 1 t o 99 nitric acid, and t n ice again with redistilled u a t e r . They were then dried either in tlie air or a n oven, in order t o avoid contamination thiough drying with a piece of filtei paper. Colorimeter. A Luineti on Model 402-EF coloiimeter was used to measure tlie absorbances of t h e dithizone solutions. The coloiimeter cells (path length 1 em.) nere fitted with groundglass stoppers to minimize el aporation losses of chloroform. Xeasurements \\-ere made with a “monochromatic” filter having maximum transmittance a t 595 mp, near the absorption maximum of dithizone. EXPERIMENTAL
Extraction of lead from a n alkaline (pH 9.5) cyanide solution with a single portion of dithizone solution containing excess dithizone was incomplete. On the average, approximately 5% of the lead present was not extracted, and could not be extracted by repeated shaking 17-ith fresh portions of dithizone solution. K h e n the extraction was carried out according to the “mixed color” procedure outlined by Sandell (9), the average deviation of the reversion value was of the order of *?.5% R-hen the volume and p H of the lead solution were similar. Results n-ere erratic when the volume and p H of the aqueous phase varied, although the p H was within the range reported to permit complete extraction. The difficulty was traced to the rapid loss of lead to glassware from the alkaline solutions. No rigid time schedule was maintained in carrying out the extractions, although in no case would the alkaline solution have remained in contact with glass for more than a few minutes before extraction. T h e extent of the loss was proportional to the concentration of lead, as evidenced by the agreement with Beer’s lan over the concentration range 0 to 1 y of lead per nil. dithizone extract. Lead lost in this manner v a s readily detected following the extraction by emptying the funnel, adding 1 to 99 nitric acid to dissolve the lead. adding ammonia-cyanide solution to give a p H of 9.5, and extracting with a small portion of dithizone solution. Procedure for Quantitative Recovery of Lead. L4cotton pledget was 1260
ANALYTICAL CHEMISTRY
inserted in t h e stem of a clean, dry separatory funnel and T\ ashed with approximately 5 ml. of dithizone solution. T h e solution to be analyzed, containing up to 25 y of lead, was transferred to the funnel. Sufficient dithizone solution was added to extract all, or most, of the lead present. Ammonia-cyanide solution was added to give a p H of 9 to 10, and the funnel m-as shaken vigorously for 30 seconds. When the phases separated, the dithizone extract 11-as tranqferred to a 25ml. volumetric flask. The aqueous phase was extracted with approuimately 1-ml. portion. of dithizone solution until two extract5 shoned no signs of the lead dithizoiiate; these extracts were combined in the volumetric flask. The alkaline aqueou. phase n a s poured out the top of the separatory funnel. Fifteen milliliters of 1 to 99 nitric acid and several milliliters of dithizone solution TT ere transferred to the funnel, n hich n as then shaken for a few seconds to dissolve the lead lost to the n-alls. Three milliliters of ammonia-cyanide solution were added, and the funnel was shaken for 30 seconds. The chloroform solution \\as combined with the previous extracts. After a second extraction n ith 1 ml. of dithizone solution. the extract was added to the volumetric flask. Chloroform nay added to the separatory funnel and shaken for 30 seconds, and sufficient was run into the volumetric flask to make the 1.01ume up to 25 ml. A portion of the combined extracts was transferred to a colorimeter cell. A second portion was reverted with a n equal volume of 5-Y sulfuric acid, and the reversion value obtained directly by measuring the absorbance of the reverted solution relative to the dithizone-dithizonate solution. Beer’s law n a s obeyed for concentrations of lead up to a t least 1 y per ml. of dithizone extract. The average of eight reversion values obtained with 9.7 y of lead (0.388 y of lead per ml. of extract) \\-as 0.158 &0.001. The range of values 77as0.166 to0.162. E o loss of lead was detected when double extractions were carried out in this manner. There n a s a significant improvement in precision over determinations preceded by a single extraction. The results recorded above have been corrected for the blank, n hich amounted to a n absorbance of 0.012. Differences in the evaporation loss from the tivo colorimeter cells and the loss of chloroform to the 5 5 sulfuric acid used in the reversion procedures contributed a reading of 0.009 to the blank value. Hence the blank value due to contamination amounted to 0.012-0.009=0.003 unit, or 0.2 y of lead. This value was confirmed qualitatively by extracting a blank solution n i t h a small volume of dithizone solution. Test for Complete Extraction of Lead. T h e reversion technique measures t h e concentration of dithizonel
.
equivalent t o t h e concentration of lead dithizonate. Hence t h e extinction coefficient of dithizone can be calculated from t h e reversion value obtained for a kn0n.n amount of lead extracted by a known volume of clithizone. ;Issuming the molar ratio of lead to dithizone in lead dithizonate to be 1 to 2! the molar extinction coefficient of dithizone in chloroform is calculated to be 4.22 x lo4 liters per gram mole per cm. T h e extinetion coefficient obtained by measuring tlie alxorbance of a solution of dithizoiic of known concentration \vas 4.05 x 10‘ liters per gram mole per cin. Thii difference in t h e two valucs for the extinction coefficient is 4yc>and t h e sign indicates 104% recov T h e difference is attributed to t h e uncertainty of t h e extinction coefficient obtained by direct measurement. Cooper and Sulliran ( 2 ) obtained by direct measurement t,lie value 4.15 i 0.05 liters per gram mole per ccm. for the extinction coefficient in chloroform solution a t 605 mp, although thpy used a different instrument. EXTRACTION OF LEAD WITH DITHIOCARBAMATE
Preliminary qualitative experiments showed that bismuth, lead, and thallium in hydrochloric acid solution could be separabed by extractions with diethylammonium diethyldithiocarbamate. Lead n-as not extracted from solutions 5 3 to 6 S in hydrochloric acid, but 40 y of bismuth were completely extracted. In solutions 4 . 5 g or less in hydrochloric acid. some lead was ext,racted. the proportion increasing as the normality decreased. At a normality of 1.5 to 2.05. 10-7 aniount,s of lead were coinpletely extracted by dithiocarbamate. Under these conditions. as well as a t higher normalities of hydrochloric acid, thallium vias not extracted. On the basis of these results a procedure for the quantitative separation of bismuth, lead, and thallium was devised. The rlistribubion of a number of elements found to be present in the mineral samples investigated LYas also studied. Procedure for Separation of Bismuth, Lead, and Thallium. A measured volume of the standard lead solution was transferred t o a separatory funnel, and the volume made u p to 3 ml. with water. Seventeen milliliters of distilled hydrochloric acid and 5 ml, of dithiocarbamate solution were added, and the separatory funnel was shaken for 30 seconds. K h e n the phases separated, the dithiocarbamate was t,ransferred to a beaker, and the aqueous phase extracted twice again with 5-ml. portions of dithiocarbamate solution. The three portions of dithiocarbamate solution (extract i) were combined, eraporat,ed to dryness under a heat lamp, and reserved.
Fifty milliliters of water were added to the separatory funnel, and the solution (approximately 1.55 in hydrochloric acid) was exbracted in the same manner with three 5-ml. portions of dithiocarbamate. All lead should be found in these extracts. Tlie three portions of dithiocar1)amat'e (extract i~') were combined in a beaker and evaporated to dryness under a heat lamp. The aqueous phase \vas transferred to a beaker. evaporated to dryness, and reserved. The organic matter in extract ii n-as destroyed by fuming n-ith 0.5 ml. of sulfuric acid to w1iic.h 1.5 nil. of nitric acid were atlded dropwise. (In later work, organic matter was destroyed l ~ y Iieating tlie sample n-itli 0.4 nil. of perrhloric arid and 1 1111. of nitric acid.) The solution 15-as cooled, diluted \\-it11 a few niilliliters of water, and evaporated t o fumes of sulfuric acid t o remove oxides of nitrogen. The solution \\-as again cooletl, clilutetl \\-ith xwter, and filtered t,hrough glass wool tightly packed in the stem of a niicrofmniel into a wparatory funnel prepared for determination of leat! h>the dithizone procedure. The Iieker was rinsed several t,inies with water and once with approxirnatelj- 3 nil. of 1 to 99 nitric acid, and the rinse solutioiis were filtered into tlie >eparato The total volume of the fil rinsings was approximately 25 nil. Ammonia-cyanide solution na atlded to give a pH of 9 to 10, and lead det'ermined n-ith dithizone according to the procedure outlined above.
Table I. Recovery of Lead Following Extraction with Dithiocarbamate
Lead, y Taken Found
__
9 7
9.6
9.i
9.3
9 7 9 i 48 50
9.8 9.7 43.5
Error,
7;
-1 -4 +1 0
0
5 nil. of standard lead solution used, requiring 28.3 nil. of distilled hydrochloric acid to give proper acidit?- for first dithiocarbamate extraction, after u-hich 84 ml. of water w r e added, and lead extracted in a
Table 11.
Separation of Lead from Bismuth and Thallium
Foreign Element Added Bismuth
- Lead, Y
~rror,
Taken
Found
5
0 0 9 7
0 0 9 8 9 6 0 0 9 4 9 7
0 $1
Y 100
9 7
0 o 9 7
~i~aiiil1111200
9 i
-1
0 -3 C
mine lead. Because sinall amounts oi t1ithioc;irbaniate solution decomposed dithizone solution, separator\- funnels used for dithiocarbainate extractions were not used for dithizone extractions. :inti cliloroform reclaimed from dit'hioc:irbnm:ite solution? n-:is not used to prepare tlithizone solutions. Gl \\-;is used :is filtering riiedium to avoid cont:imin:ition observed with filter piper. Evnpmition of the extmcts under a hrnt lamp was preferred t o evaporation on a steam bath. becnuse it prevented creeping of the residue up the sides of the beaker, mininizing t'he possibility of loss of lewd and simplifying the subaequent destruction of orgmic matter. Distribution of Other Elements during Extraction with Dithiocarbamate. Various amounts of certain elements were treated for t h e separation of bismuth, lead, and thallium. 11-ith R fen- exceptions. these elements were those found by spectroscopic anal!-sis in the mineral samples analyzed for lead (see below). Tlie alkali metals \{?ere not, tested, as it was extremely doubtful that t,hey would be extracted. Calcium and magnesium ryere selected :is represent,ative of the Group 2A elements. and cerium as representative of t,he Group 3 d elements. Generally speaking, anions were not investigated. The following elements were not es-
tractetl by three 5-nil. portions of [tithiocarbamate froni 20 nil. of 5 . 3 S or 70 nil. of 1.5-1' hydrochloric acid solutions (amount of metal ion taken ;hewn in parentheses). Titanium (20 mg.) Iron( 11)
Cei~iiirn(II1 ( 3 mg.) 1-raniuni(1-I!
Thorium
Aluminiini i1 nix. ,
(200 ",)
(300 -,)
( 100
-1)
Calcium ( 2 nig.
100 -, )
Zirconium (3 nip
I
The tiiitribution of eleineiith i i i extr,:tct
i or ii is given in Table 111. I.:stini:rtes c~i'the :iinount are only xpproxim:itc. Rehtively fen- elements accmnpaiiy le:itl in the procedure outlined. A certain :imount of any zinc.. cadmium. tinIl-),platinum. anti indium i- estrLicSted. One-iiiilligram amounts of zinc. (.:idiiiium. and platinum n-ere not detected 12). tlitliizone under the coiiditiona used. -It lenst :I tenfold excess of indium, lxicetl on x 10-y suniple of lead can be tolerated in tlie determination of 1e:l.d. Such amounts 11-ould not be expected in the minerals analyzed ( 1 ) . Large :tinouiits of tin(1T') could prevent complete extraction of lead by tlithizone. Bismuth, copper, iron(III), cadmium ''trace), molybdenum, tungsten. gerinaiiium (part,),chromiuin(1T) (part), and platinnm (part) were found in extract i. Large aniount's of these met'als rvould be tedious t,o separat'e from lead h>-estraction with dithiocarbamate. DETERMINATION OF LEAD IN MINERALS BY EXTRACTION WITH DITHIOCARBAMATE AND DlTHlZONE
111the general scheme u q ~ dfor the tleterrnination of lead in minerals lead 11 CI: ultiniatelv obtained in a d n t i o n
usual manner. Lead \viis determined \yith one fifth of the sample.
Table Ill.
The results are summarized in Table I . Blank determinations n-ere equivd e n t to 2.1 y of lead. Qualitative tests m-ith dithizone on extract i and the aqueow phase after destruction of organic matter n.it1i hot nitric and sulfuric acids indicated that lead was not present in these phases. The results of experiments in which 9.7 y of lend with bismuth or t'hallium were treated by the procedure are recorded in Table 11. Discussion. Accuracy and pre(,ision appeared t o be generally satisfact,ory. Approximately 3.5 hours \\-ere required t o separate and deter-
Sample Taken
Distribution of Elements in Dithiocarbamate Extraction
Ca 17 S o t detected
2593 Ca 5 0 5 Detecteda S o t detected Piot detected
Aqueous Phase C'a 907? Ca 75% C'a 50% Detected S o t tested S o t detected
Pt 500 110 ( V I ) lmg
Ca 35cc Detected
Ca sot;
Ca 5%
W (VI) 100
Detected
Y
Zn 100 Cd 100 Sn (I\-) 100 In (111) 150 Cu (11) 100 Fe (111)200
100 Ge CI (VI) 1mg
Extract i Not detected X o t detected Detected Detwted
20 t o 30cc
Detcxtrd
Extract ii Ca 10VC
ca
Trace (ea 2;
1
Tot tfetectcd S o t detrctrd S o t dptectpd
S o t detected Tot
detected
70 to sot,
Drtwted
Color of Extract Colorlesq Colorless Tellon Giwn turning P,ile \ ellon
hi own
1iitcn.e
vellov
tinning red Colorless Colorle-s RlW
ld(11'ion a Indium tested hr extracting n ith dithizone from alLnline c> anide solution of 2 ml of qaturated ammonlum tartrate iolution conipletei\ discharged roloi of indium dithi7onatc
VOL. 2 9 , NO. 9, SEPTEMBER 1957
1261
approximately 5 . 3 s in hydrochloric acid and containing no other acids in appreciable amounts, extracted with dithiocarbamate and determined in extract ii with dithizone. Following a wet acid attacli of a mineral, the solution was evaporated to dryness. or near dryness, and the residue taken up in 5 . W hydrochloric acid. For the routine determination of lead in a given mineral, time might be savcd by not evaporating the solution to dryness, but rather adding sufficient hydrochloric acid and water to adjust the acidity to permit removal of bismuth (and certain other elements) with dithiocarbamate without extracting lead. Bcids other t h i n hydrochloric acid were removed by evaporation, in order to develop a procedure applicable to minerals requiring different methods of attack. It was not possible t o predict the volumes of dithiocarbamate solution required for extraction from 5.3N and 1.5N hydrochloric acid solutions. For each mineral, lead was roughly determined to establish the total volume required for each extraction. In practice, a t least three portions of dithiocarbamate solution were used for each extraction. Of the elements extracted by dithiocarbamate from 5.3N hydrochloric acid solutions, iron predominated in the minerals examined. When present in large amounts, prior reduction to iron(11) would reduce the volume of dithiocarbamate required to complete extraction. This was not necessary for the minerals analyzed. More concentrated solutions of dithiocarbsmate were used to advantage-for example. for sphenewhen relatively large amounts of elements removed in this extraction were present. Bt least 50 y of lead were extracted from the diluted acid solution with 15 ml. of dithiocarbamate. Larger volumes were used in practice because a certain amount of other elements mas extracted as well, and the possibility existed that these Ivould be preferentially extracted and cause loss of lead. Possible interference in the determination of lead was checked by varying the volumes of the dithiocarbamate extractions, adding “spikes” of lead, and spectrographically examining the dithizone extract for the presence of metals other than lead. No significant (nor systematic) loss of lead was detected, and no evidence of coextraction of elements with lead by dithizone was obtained.
Preparation of Mineral Solution. T h e finely ground sample mas dried a t 110’ C. for 1hour and cooled, and a portion was accurately weighed. T h e sample size recorded in Table I V was c.hosen t o provide approximately 10 y of lead. 1262
ANALYTICAL CHEMISTRY
Table IV.
Determination of Lead
Lead, y Vol. of Dithiocarbamate. M1. Corr. for blank Wt. of Sample, G. Extract i Extract’ii Found
Pb
in Mineral, P.P.M.
DETERMINATION I N LYNDOCHITE
...
9.3 9.4
18.9
0.00500 0.00500
20 20 25 25 30
0
40
0
0.00500 0.00500
20 20 25 25 30
...
12.7 12.3 13.3 13.1
DETERMINATIOS I N
n 201
.cn ~.
0.201 0.201 0.213 0.19’7 + 9 . 7 P b 0.169 9 . 7 y Pb
40 40
0
30
+
0.159 0.494 0.503 0.502 0.501
50
40 40
30
30
+ 9 7 Ph + 9 7 -, Pb -/
40
30 40
20
20 30 25 25
11.4 12.4 12.2
...
2360 2280 2480 2440
FELDSPAR
20 20 ~.
11 8
...
2370 2400 ...
2.0 13 0
~~
0,
12.4 13.5 19.,5 20.2
DETERMISATION IN APATITE 30 0.9(6) 30 3.7 30 9.1 40 0 2 30 18.0 40 19 0
...
... 11 .o 7.7 10.4 11.5 17.5 18.2
Rejected 51.7
2 7
.. 17 0
8 1
16 4
8 2
54.7 54 0
16 3
17 0
18.0
DETERJfIN.4TION IX S P H E S E
0
0.0649 0.0663 0.0659
+ 9.7 y Pb
20 20 25 25
15 15 20 20
1 9
12 3 12 9 22.6
a Samples weighing 0.0785 and 0.100 gram were brought into solution in final volume of 100-ml. and 5-ml aliquots taken for analysis.
LYKDOCHITE. The sample was heated with 1 ml. of concentrated sulfuric acid near the boiling point until no brown mineral remained. The sample was cooled and diluted with several milliliters of water. The mixture was digested four times with 10-ml. portions of distilled hydrochloric acid for 20 minutes on a steam bath. Each portion of hydrochloric acid was filtered through a medium-porosity sintered-glass filtering tube. These portions were combined in a 100-ml. volumetric flask, and the solution was made u p to volume with water. Analyses were carried out on measured volumes of the hydrochloric acid solution, to which 3 volumes of distilled hydrochloric acid were added to give the required concentration of acid. FELDSPAR. The sample was warmed with 0.5 ml. of perchloric acid and 2.8 ml. of hydrofluoric acid in a platinum crucible. When effervescence ceased, the sample was heated to fumes of perchloric acid. K h e n cool, 2.1 mi. of hydrofluoric acid were added and the sample was evaporated to dryness. The cover and sides of the crucible were rinsed down with water, 0.5 ml. of perchloric acid was added, and the sample mas again evaporated to dryness. The residue was dissolved by digesting with portions of warm hydrochloric acid, and the solution filtered through glass wool tightly packed in the stem of a microfunnel into a separatory funnel.
The volume of hydrochloric acid n a s made up to 34 ml., and 6 ml. of m t e r were added. APATITE. The sample was heated in a covered platinum crucible with 0.5 ml. of perchloric acid and 10 drops of nitric acid for 0.5 to 1 hour. The cover was then removed and the sample was heated to fumes of perchloric acid. Hydrofluoric acid was added to remove silica, and the solution was evaporated to dryness. The cover and sides of the crucible n-ere rinsed down with water, 0.5 ml. of perchloric acid was added, and the sample was again evaporated to dryness. The residue was dissolved in hydrochloric acid and filtered through glass wool into a separatory funnel. The volume of the acid solution was made u p to 27 ml. with hydrochloric acid, and 5 ml. of mater were added. SPHENE. The sample was mixed with 0.50 gram of sodium carbonate in a platinum crucible, covered, and heated gradually to the full heat of a Meker burner for 8 minutes. When cool, 10 ml. of a 1 to 19 sulfuric acid solution mere added and the crucible was quickly covered. When effervescence ceased, 1.4 ml. of hydrofluoric acid were added and the sample was evaporated to near dryness. The cover and sides of the crucible were rinsed down with water, and the sample was heated again to near dryness to expel hydrofluoric acid. The bulk of the sample was transferred
to a beaker with water, and a final rinse with hydrochloric acid completed the transfer. The sample was evaporated to remove water. The residue \\-as dissolved in hydrochloric acid and filtered through glass no01 into a separatory funnel. The volume of solution was made up to 27 ml. with hydrochloric acid, and 5 ml. of water were added. Dithiocarbamate Extraction. Extractions were carried out with at least three portions of dithiocarbamate solution, first from t h e approxiniately 3 . 3 5 hydrochloric acid solution of t h e mineral piepared as described above, and again after dilution n i t h 11-ater t o 1 . 5 s . I n the case of sphene, a 1 to 9 dithiocarbamate solution was used. The organic matter in extract ii was destroyed with hot nitric-perchloric acid; the acid solution was diluted with water and filtered into a separatory funnel as in the dithiocarbamate procedure. Dithizone Extraction. Lead in ex-
tract ii\f-as determined bythe dithizone procedure, except t h a t 2 ml. of a saturated solution of ammonium tartrate 51 ere added to keep in solution traces of salts sometimes carried over with the dithiocarbamate extract, and to prevent extraction of indium. The results are recorded in Table IV. ACKNOWLEDGMENT
This investigation was assisted by a grant from the university’s Advisory Committee on Scientific Research, for which grateful acknowledgment is made. One author (A. D. 11.) was holder in turn of fellon-ships given to the university by Canadian Industries. Ltd., and by Union Carbide Corp. of Canada, for n-hich thanks are here recorded. The authors are also grateful to J. T. Kilson (Geophysics) and his associates at the University of Toronto for friendly interest and helpful discussions relating to this ivork.
LITERATURE CITED
(1) Biddle, D. -A,, IND.ESG. CHEM.,
ANAL.ED.8, 99 (1936). ( 2 ) Cooper, S,S.,Sullivan, 11.L., .ASAL. CHEX. 23, 613 (1051) 1 3 ) Gane. J. C.. dnalvst 80. 789 11955). )(: 4 ) Hayt,’ Ha& H. I-.’, I-.,Ibid.; I b z d ; 76, 602 (1951). ’ ( 5a ) Irving, H., H , Risdon, E. J Andrea, C, S o c 1949,’537. 1940.’15.37. G.,. .TJ. Chmn Chem. SOC. ((6) 6 ) Lockwood, H. G., dna21yst 79, 143
(1954).
171 Rosenavist. I. T.. A m . J. Sci. 240,
356 11942).
(8) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 2nd ed., Interscience, Sew York,
1950. (9) Ibid., pp. 307-8. (10) Strafford, T.,T \ - \ : i t t , P. F., Kershan-. F. G.. zlrzniiist 70. 232 (1945). (11) I b i d . , 78,624 (1953). (12) Tomp-sett, S. I,., Ibid., 81, 330 (1936).
RECEIVEDfor review March 12, 1057. Arcepted June 3, l 9 5 i .
Thermal Conductivity Behavior Importance in Quantitative Gas Chromatography DOUGLAS
M. ROSE
and ROBERT L. GROB’
Products Research Division, Esso Research and Engineering Co., linden, N. J.
b The thermal conductivity behavior of a variety of hydrocarbons was investigated as a preliminary step toward better quantitative interpretation o f gas-liquid chromatographic data. Differences in response output of a thermal conductivity cell for sirnilar hydrocarbons may be significantly large. By making corrections for each compound, precise qucntitative results are obtained.
A
S U h l B E R of
papers dealing with gasliquid chromatography (1-4, 6) have directed attention to quantitative interpretation of the data available from chromatograms. The main effort had been concerned with the choice of substrates, apparatus, and, in general, operating conditions for the resolution of various systems. This paper deals with the quantitative aspect of the technique. T h e n a thermal conductivity cell is used as the detector, it is advantageous t o use a carrier gas t h a t has a thermal conductivity vastly different from any compounds to be determined. Because Present address, Department of Chemistrv, Wheeling College, IYheeling, IT-.Va.
thermal conductivity is inversely related to the square root of the molecular weight, the molecular n-eight of the carrier gas should be extremely small or extremely large, in order to obtain as large a response as possible from the detector. The fact that helium has a lorn- molecular weight and is safe to handle makes it a suitable choice. The chromatogram is usually a plot of the response-output of the thermal conductivity cell against time (or volume of carrier gas). The area under a peak due to a single component, divided b y the total area under all the peaks, is sometimes related directly to the mole or weight per cent of that compound. The area associated with any given conipound is referred to as per cent area. Hausdorf ( 6 ) states that when helium is used as the carrier gas, the difference in its thermal conductivity and t h a t of the compounds most frequently analyzed is large, and all molecules may be assumed to have the same thermal conductivity in the first approximation. If it is further assumed t h a t the response of the thermal conductivity cell varies linearly with the concentration, the peak areas would be expected to be a direct measure of molar concentration. This assumption sometimes leads to sizable errors.
Other authors (2-4) have stated that the areas more closely represent the n-eight concentration of a mixture. Clearly this relation could be further improved b y calibration ( 2 , page 296). This paper records a series of such calibration factors, not only for direct use b y other workers in the field, but also as a basis upon which a suitable theory niay be ultimately established. Inability to obtain satisfactory quantitative results b y relating per cent area to mole per cent or weight per cent prompted this investigation of the thermal conductivity behavior of a variety of hydrocarbons. APPARATUS A N D MATERIALS
The hydrocarbons studied were of the highest purity obtainable from the Kational Bureau of Standards, Washington, D. C., or the American Petroleum Institute, Carnegie Institute of Technology, Pittsburgh, Pa. The instrument mas a Model 154 vapor Fractometer manufactured by the Perkin-Elmer Corp., Norwalk, Conn. The recorder was a 10-mv. Leeds &Northrup Speedomax recording potentiometer which had a 2-second fullscale response time. The chart paper used was Leeds 8: Northrup, No. 742. The partition columns were A columns purchased from the PerkinVOL. 29, NO. 9, SEPTEMBER 1957
1263
