694 ANALYTTCAL CHEMISTRY, VOL. 50, NO. 6. MAY 1 9 7 8

+0.22i, correlates with the ninleciilar relaxation energies for the chlornrnethanes.

ACKNOWLEDGRIENT Helpful discussion with G. Theodorakopoulos and I. G.

Csizmadia of t h e LJniT-ersity of Toronto concerning the t,heoreticai aspectc: of AES is gratefu!ly acknnmledged.

LTTERATURE CITED (1) M, Thornpsor. P. A, Hewit! and D. S. Woollscicfl, Anal. Cnem., 48, 1336

(1976). (2) M Thompsori 7a12flta. 24, 399 (1977). (3) M T. Okland, K. Faeg:i. Jr., and R. Manne, Chem. Phys. /..sit., 40, 185

(1976). (4) R. H. A. Eade, M. A. Robb, I . G. Csizmadia, and G. Theodorakopoulos,

Chern. Phys. Lett., 52. 526 (1977) (5) A . Fahlrnan, K . Harnrin, ,I, Hedman, R. Norlhara, r: Nn-dlipg, ntid V,

Siegbahn, Plafure (landon), 210, 4 (1966). (6 ) G. W. Stupian, J. Appl. Phys.. 45, 5278 (1974). (7 ) F L! FzalCowski and G. A . Scmerjai. J. Chem ,rh)? . 61. 2064 (1974). (8) C. D Wagner, Anal. Chem , 44, 967 (1972). (9) C D Wagner, Anal. Chem , 41 , 1203 (1075).

(10) W. E. Moddernan Ph.E. Thesis. LJr>iversity of Tennessee. 1970. (1 1) R . Spohr, 1 . Bergmark, N. Maynussori, 1.. 0. Wetrne, C Noidliiig, end

K Siegbah:?, Phvs. So.,, 2. 31 (1970j.

(12) W. B Perry and W. L. Jolly, Chem. Fhys Lett., 23, 529 (1973). (13) W E. Moddeman, T. A. Carlson, M. 0 . Krause, €3. P. Pullen. W. E. Bull.

and G K Sweitzer, b/, Chem Phys , 55. 2317 (19711 (1-11 h! rhompsm. P A Hwi t t . and 0 S W3okcrof f . IJnplhlished work 115! rC, Slgbahn, f.. Nordlirg, G Johansscn. J Hedman, P. F . tied&?, K Hamrin.

U. Gelius, T. Bergmark, L . 0. Werme, P.. Manne, and Y . Baer, "ESCA Applied to Free Molecules", North-Holland, Amsterdam, 1969.

(161 D W. Turner, C. Baker, A R Baker. and C R, Brundle, "MOleCUlar Dhotoelectron Spectrcscowy". Wiley-Interscience, London. 1970

!17i A W. Fotts, H. J. Lernpke D. G Streets and W. C. Price, Phil. Trans. R . SOC. London, Ser . P , 268, 59 (1970).

(18) F Hcptgarten and P. Mame, J . Electron Spectrosc Pela:. Pbenom ,

(19) T. D. Thomas, J . Am. Chem. SOC., 92 , 4184 (1970). (20) W B Perry and W. L Jcily, Inorg. Cheni., 13, 1211 (1974) (21) I . B. Ortenburger and P. S, Bagus, Phys. Rev. A , 11. 1501 (1975). (22) U. Geiius, Phys. Scr., 9, 133 (1974). (23) D. A. Shirley, Cbem. Phys. Lett., 17, 312 (1974), (74; fi T Sat:derson, "Chenical Periodicity", Reinhold. Ne-# Y n 4 N.Y 1960.

2. 13 (1973).

Determination of Main Components and Impurities in Lithium-Boron Alloys

L. E. DeVries" and Elmer Gubner

Naval Surface LVeapons Cenfer, Electrechemistry B/anch, Marenals Dwis/e?. Wh'e Oak l&oratory S A er Sprmg, Llaijland c"09 10

A procedure has been developed for dissolving lithium-boron alloys and analyzing the solutions for the main components and major impurities. Water, a known amount of excess perchloric acid, and hydrogen peroxide were used to dissolve a sample. The amount of acid remaining after dissolution was determined by titration and used to calculate the amount of lithium in the sample. After adding D-mannitol, the boric acid formed from the boron in the alloy was determined by titration. The major impurities were chromium, iron, manganese, and nickel determined by atomic absorption spectrophotometry. When necessary, nitrogen was determined using an ammonia cornbination electrode and unoxidized boron by direct weighing

(11, a need de\elopetl for a g o d and icd procedure Lithiem. h(von, and major impurities neFdri1 tri he determined 111

iindischarged a l lqs 1,ithium serves rlc the N T I W element in the alloy, and lithium ions are formed during diicharge 7'0 calculate the amount of lithium lost t" parasitic processes, the amount of unoxid17ed lithium in the rle-trode at the end of discharge must he determined It is rompnied with the amount of lithium oxidiwd hy discharge and the amount initially present. For these reasons, there mas a need to determine the amount of unoxidized lithium rather than total lithium. We suspected that LizB remained after discharge in the alloy (1 ) . However, the composition might be Li9R4. For the lithium-aluminum system, I,igA14 has been reported (2). The diffprence hetween the two possible lithium boron ccimpounds I S less thnn 3 weight percent (a ' 0 1 . An aCcuratP procedure was needed for deteimining the composition of any cornpoiiwis formed in the alloys. The procedure developed

irivol;es dissolving the alloy and determining the lithium and tioron hy titration. 'l'he major impurities are nietalq deter- mined hy atomic abwrption spectroph"tc,inetr..

EXPERIMENTAL Ins t rumenta l Parameters . A Metrohni hlodel I? 336 1 ) ~ -

tentioyraph equipped with a Metrohm Model EA 34-10 buret (sv.pplied bs Brinkmann Instruments, Inc.. Cantiague Road, Westbury, N.Y. 11599) w a j used for all acid--base titrations. 'The electrode uscd was a hletrolim Model EA I20 pH combination glass electrode. Metal impurities and silicon were determined with a 'Techtron Atrimic Absorption Spectrophotonieter 'I'ype A.4-5 (L'arian Techtron, 611 Hanson Way, Palo Alto, Calif. 91303). A \ m~iltielement hollow cathode lamp (neon filler gas) was operated 31 a current nf 8.5 n i A for chromium. iron, mangaiiese, and nickel. "i slit width of .X pni !%as used with the 248.3 nni line for iron, nith the 279.5 nni line for marigan~se. with the 232.0 rim line for nickel. and with the 7.9 nm line Cor chromium. For silicon. a hnl l -xv cathide lamp (neon filler gas) &-as operated a t 15 RIA. A slit width of 30 p,m was u ~ e d with the 251.6 nm line for silicon. For siiic.c;n. tt rlitro~us oxide-acetylene flame was used with a T'echtrnn Tj-pe ARiO Iiurner. For t h e other elements. an air-- acetylene flame W R P used with a Techtron Type AB51 burner. Ammonia was demmined with an Orion Model 95-19-00 ammonia romhinatiw electrode used with an Orion Model 407A Cpecific inn meter ((:)ricin Research I:?( nrporated, 11 Hlackstone Streer, Cambridge, >lass. 021391.

Reagents and Standards. Reagent grade chemicals wpplied by Fisher (Fisher Scientific C'onipany, 71 1 F o r b e s Avenue, Pittsburgh. Pa. 15219) were used except where stated. Atomic absorption standards were prepared from 1000-ppm solutions supplied by F & .J Scientific (79 Far Horizon Dr., Monrne, Conn. 06268). Boron of 99.9% purity was supplied by Atomergic ('hemetals Corporatinn 1100 Fairchild Avenue. Plainview, N.C. 11803). Pot msium hydrogen 1.2-hen7,ene-dicailio~ylate (Fisher, Acidimetric Standard) was used after drying at 393 I i for 2 h. The P-amino-2-!h\drcisvmethvl~-l ,~-prnpane~inl i Aldrich. [:I-

This paper not subject to U S . Copyright. Published 1978 by the American Chemical Society

ANALYTICAL CHEMISTRY, VOL. 50, NO. 6, M A Y 1978 695

solution was cooled in an ice bath. The plain distillation column was rinsed, with the rinsings going into the flask. After rinsing, the plain distillation column was replaced with a West condenser. R i t h rapid stirring, about 35 g of standardized perchloric acid were added from a weight buret. The acid was added slowly to minimize foaming especially near the point where the lithium hydroxide already formed would be neutralized. Eleven milliliters of 30% hydrogen peroxide were added. The ice bath was removed, and the hot plate turned on. The solution was refluxed 70 min. After the heat was turned off, the solution was cooled in an ice bath. From this point on, all rinsings were done with carbon dioxide-free water. The condenser was rinsed and removed from the flask. The solution was transferred to a previously weighed bottle and weighed.

Titration. The procedure described is for mixtures of perchloric acid and boric acid. Using a weight buret, about 35 g of solution were delivered to a 150-mL graduated heaker. The sample was diluted to 100 mL with carbon dioxide-free water. With the potentiograph in the pH mode, standardized sodium hydroxide was delivered from a weight buret until the pH of the solution reached between 3.0 and 3.4. The potentiograph was put in the derivative mode. The titration through the end point was recorded using a 1/20 to 1/100 (weightjvolume) dilution of the standardized base in the automatic buret. Twenty grams of D-mannitOl were added to the solution. With the potentiograph in the pH mode, standardized sodium hydroxide was added from a weight buret until the pH reached 5.6 to 6.0. With the potentiograph in the derivative mode. the titration was finished with the automatic buret as mentioned above.

,Vitrogen Analysis. A 250-mL Erlenmeyer flask was mounted in an ice bath over a hot plate with a magnetic stirrer. One hundred milliliters of about 1.25 N perchloric acid were cooled in the flask. This amount of acid was sufficient to ensure that the solution was acid after the lithium had been dissolved from the alloy. About 1 g of alloy was placed in the flask. A gas scrubber (of the type described above) was placed on the flask and the stirrer turned on. After the foaming had stopped, the gas scrubber was rinsed, with the rinsings going into the flask. The ice bath was removed and the solution heated to boiling to ensure that all of the lithium had been dissolved from the alloy. The ammonia trapped in the acid was measured using the combination ammonia electrode by taking a direct reading with the specific ion meter.

RESULTS A N D D I S C U S S I O N Dissolution Procedures . The initial idea was to dissolve

the lithium in the alloy with water and filter the solution. The boron would be determined by weighing the remaining solid, and the lithium would be determined by titrating the filtrate with acid. It was found tha t the alloy had to be boiled in an acid solution to rapidly remove the lithium. For this reason, it was decided to use a known excess amount of standardized perchloric acid to dissolve the lithium in the alloy. The sample had to be boiled in water first t o oxidize as much lithium as possible. If a sample is added directly to the acid solution, the reaction is vigorous enough to cause some loss of solution. T h e hydrogen evolved from the water carried a fine mist of lithium hydroxide out of the plain distillation column. By using a gas scrubber and not starting stirring until after t he scrubber was in place! no solution was lost.

It was noted when trying to remove the lithium from t h e alloy with water t ha t part of the boron was dissolving.

2B + 2 0 H - f 2H,O - 2BO;- 3H, (1)

A portion of the boron was in colloidal form. Amorphous or colloidal boron reacts with many materials including water ( 4 ) and hydrogen peroxide ( 5 ) . It was decided to oxidize t,he boron completely with hydrogen peroxide.

2B + 3H202- 2H,BO, ( 2 )

Experiments indicated tha t it was best t o add the hydrogen peroxide to a solution containing the alloy after the perchloric acid had been added. For complete oxidation of t he boron,

1 5 MM G L A S S B E A D S

1

L - - i ” l

Figure 1. Details of apparatus used for dissolving alloy samples

trapure from Aldrich Chemical Company, Inc., 940 W. Saint Paul Avenue, Milwaukee, Wis. 53233) was recrystallized (3) . “Baker Analyzed“ boric acid was recrystallized while ULTREX boric acid was used as received (both from J. T. Baker Chemical Co., 222 Red School Lane, Philipsburg, N.J. 08865). “Matrix“ soluticns of lithium chloride were prepared from ultrapure grade lithium chloride supplied by Alpha Products (152 Andover Street, Danvers, Mass. 01923). Nessler’s Reagent Solution (Fisher, A.P.H.A.) was used for the qualitative tests for ammonia. The sodium hydroxide solution was prepared from a concentrated solution from which the solid sodium carbonate had been removed. Distilled water was used throughout the work. The perchloric acid, sodium hydroxide, and boric acid solutions were prepared with carbon dioxide-free water (boiled under partial vacuum 20 min.).

Apparatus. Part of the apparatus is shown in Figure 1. The dissolution of the lithium-boron alloys was carried out in a 250-mL Erlenmeyer flask. The flask was fitted with a plain distillation column. The plain distillation column was fitted with a gas scrubber consisting of a column with indentations to hold glass beads. The column was packed with glass beads (3-mm diameter) to a depth of 55 mm. For refluxing the solution, the columns were replaced with a West condenser (100-mm jacket). The column, gas scrubber, and condenser had drip tips, and all pieces had 24/40 standard taper joints. The flask with the columns was mounted on a hot plate with a magnetic stirrer.

Procedures . S a m p l e Manipulation. The samples were cut from ingots in a helium-filled glove box. The helium was con- tinuously circulated through purification trains to remove nitrogen, oxygen, water, and carbon dioxide. The ingots as received were dark on the sides and bottom with what appeared to be a thin layer from the Type 316 stainless steel crucible in which they were made. In addition, the top of the ingot had a layer of oxides and nitrides which may have come from impurities originally in the lithium and boron. As a result, the outer skin of the soft ingot was cut away with a knife and discarded before any analysis of the ingot composition was made.

Dissolution. Much of the apparatus discussed in the dissolution procedure is in Figure 1. Both empty and sample filled bottles were weighed filled with helium. Fifty milliliters of water were placed in the Erlenmeyer flask. A sample of about 1 g was added to the flask through the plain distillation column. The gas scrubber (wet with water) was immediately put in place, and the stirrer turned on. The solution was stirred until foaming nearly stopped. The gas scrubber was rinsed and removed. The solution was heated until it had boiled 10 min or until no ammonia was present in the vapor phase. The heating was stopped, and the

696 ANALYTICAL CHEMISTRY, VOL. 50, NO. 6, M A Y 1978

Table I. Determination of Boric Acid

Standardization of Solutions and

Re1 Std stand

Milliequivig dev dev No. of Solution b y titration x l o 4 x 10' samples

Potassium hydrogen 1,2-benzenedi~arboxylate~

NaOH-1 0.9890 3 3 6 NaOH-2 1.0072 1 1 6

2-Amino-2-( hydroxymethy1)-1,3-propanedioP

HC10,-2 4.4703 5 1 6 HC10,-1 4.5124 6 1 5

Sodium hydroxide-la

HC10,-1 4.5124 8 2 5

Sodium hydroxide-2a

HC10,-2 4.4703 4 1 6

Boric acid (0.7097 mequiv/g)b

%BO, 0.7099 2 3 6

Perchloric acid (0.5364 mequiv/ ) t boric acid (0.2464 mequivig) E

H3BO3 0.2463 1 4 5 I-IClO 0.5364 2 2 5

a The standard. Made u p to the concentration in- The solutions were 0.2 N with dicated in parentheses.

respect t o lithium chloride and were titrated with so- dium hydroxide, acid contained 20 g mannitol.

Each solution when titrated for boric

t he acid solution of peroxide must be boiled under refluxing conditions. If the solution is not refluxed. some boric acid will distill out of the solution (6). A relatively large excess of hydrogen peroxide is needed so that it will oxidize all of t he boron before it is decomposed in the acid solution ( 5 ) . Small particles speed up the decomposition of the hydrogen peroxide to oxygen and water (7, 8). The exceSs hydrogen peroxide was found to decompose after 55 min of refluxing. Seventy minutes of refluxing were done on the solutions. No tests for peroxide were then considered necessary.

We were concerned by the fact that we were using boro- silicate glass flasks for dissolving the alloy samples. We could obtain high results by introducing detectable amounts of boron into our system. We found that none of our glass containers which had been previously boiled several times with con- centrated sodium hydroxide and with lithium hydroxide gave detectable amounts of boron to either acidic or basic solutions boiled in them.

T i t r a t i o n . The weights of all materials were reduced to vacuo. Excellent results were obtained for the standardi- zations of the acids and bases, Table I. This is in part the result of titrating on a weight basis and of depending on the automatic buret to contribute only 1 7 ~ or less to the total weight of titrant. Boric acid is weak enough, pK = 9.234 (9), so tha t perchloric acid can be titrated in its presence. On addition of polyalcohols or sugars, the pK is decreased so that boric acid can easily be titrated with sodium hydroxide ( I O . 11). A recommended alcohol, D-mannitol, has been found to work best in nearly saturated solutions or where the ratio of moles of mannitol to moles of boric acid was a t or above 16/1 (12,13). Twenty grams of mannitol for each solution titrated maintained the above conditions over the entire range of alloy compositions studied. The pK is also lowered by high con- centrations of various ions including lithium (13, 14) . As a result, we t i trated boric acid solutions containing the max- imum amount of lithium (0.2 mequiv/g) expected in our

Table 11.

Ingot- Titrated Titrated Li from Metal Total Samplea Lib B" Li,SiO, impurit,iesC percentd

A-1 80.14 19.26 0.57 0.08 100.05 2 79.99 19.44 0.51 0.08 100.02 3 79.42 19.94 0.49 0.08 99.93 4 79.81 19.58 0.48 0.08 99.95

B-1 70.09 27.46 0.35 0.07 99.97 2 71.34 28.19 0.37 0.07 99.96 3 70.64 28.90 0.40 0.07 100.01 4 71.08 28.44 0.38 0.07 99.97

C-1 69.10 29.98 0.73 0.11 99.92 2 69.59 29.47 0.77 0.11 99.94 3 70.13 28.96 0.84 0.11 100.04 4 70.30 28.93 0.64 0.11 99.98

Weight Percent of Constituents in the Alloys

Average total percent is 99.98, and 0 is 0.04

Ingot- Titrated Titrated Weighed Metal Total Samplea Lib Bb B impuritiesC percentd

D-1 57.65 41.48 0.66 0.14 99.98 2 56.02 43.10 0.68 0.14 99.99 3 56.95 42.23 0.68 0.14 100.05 4 55.58 43.58 0.66 0.14 100.01 5 56.72 42.45 0.67 0.14 100.03

E-le 3.27 95.10 1 .43 0.18 99.98

a Ingots A , B, and E were dissolved in Pyrex glass flasks; ingot C was dissolved in an alkali resistant glass flask; ingot D was dissolved in a TeflQn flask. five titrations for each sample with a relative standard de- viation of (1-3) /10 000. Table I11 lists a value for each metal f o r each ingot. less than 0.01% nitrogen. Ingot D contained 0.05% ni- trogen which is included in the total percentage. E had the lithium extracted before the analysis given in the table.

Average total percent is 100.01, and a is 0 .03

There were four or

Ingots A, B, C, and E contained

'' Ingot

solutions. The results are given in Table I. There were no adverse effects from adding lithium ions to the perchloric acid-boric acid solution. Our main problem trying to use boric acid as a standard was weighing the crystals which are easily given a static charge. We noted no difference between the types of boric acid used.

I t might be assumed that reaction 1 would cause a problem in determining the amount of lithium in the alloy. The lithium is determined from the difference between the amount of perchloric acid added to aid in dissolving the lithium and the amount of perchloric acid left after the lithium is dissolved. However, the third reaction

( 3 )

shows that for the amount of hydroxide ions lost in reaction 1, an equal amount of hydrogen ions is lost. No errors are caused by reaction 1.

Many alloys are inhomogeneous. By comparing the results of analysis for the lithium in different samples of the same ingot, the da ta in Table I1 indicate that this is also true for the lithium--boron alloy. The largest variation in lithium (57.6,5--,55.58 \vi/()) was found in the ingot with the lowest lithium content.

Atomic Absorption, Impur i t ies . Table I1 indicates that there were a series of problems dealt with to obtain good results. Qualitative test,s revealed metallic impurities in the alloys for which the quantitative measurements are given in Table 11. The metals would be in the unoxidized state in the lithium alloy and would react with the perchloric acid. The value of the lithium found by titration takes this into account. A comparison was made using single element standards and multielement standards containing all four metals (chromium, iron, manganese, and nickel) with and without a lithium- chloride matrix. The multielement standards gave thp same

BO; + H' + H,O 4 H,BO,

ANALYTICAL CHEMISTRY, VOL. 50, NO. 6, MAY 1978 697

amount of hydrogen peroxide in the acid solution before boiling it did not help. T h e solutions were filtered and the undissolved boron was weighed. Under a microscope, the relatively large particles of boron looked like crystalline boron. Xormally the boron from ot,her ingots was amorphous. I t dissolved in acid solution when hydrogen peroxide was added, and the solution was heated to boiling. In ingot D, we suspect that the boron, which did not dissolve in the perchloric acid-hydrogen peroxide solution, had not formed an alloy.

Ni t rogen Analysis, The lithium-boron alloys react more rapidly with air than pure lithium does. We expected to have some lithium nitride formed when a sample was manipulated in air after weighing. .4mmonia is formed when lithium nitride reacts with water.

( 6 )

Our analysis, based on ammonia, indicated that less than 0.01 w/o nitrogen was in the samples. However, samples from one ingot had 10 times more nitrogen. The analysis for other components was not completed. A check was made, and we were told that the ingot had been made after the purification train for nitrogen removal had broken down. When it malfunctioned again, the amount of nitrogen picked up by the ingot was determined to be 0.05 wjo , Table 11. Different pieces of ingot were used for nitrogen analysis than were used for determining the other components. The samples for nitrogen analysis were dissolved in acid with the loss of about 0.5 volume percent (v/o) of the solution because of vigorous hydrogen evolution.

Boron R i c h Phase. One sample was supplied to us for analysis from which the hulk of the lithium had been extract,ed (with methanol). The results are included, Table 11, to show tha t a boron-rich sample can be analyzed even though the procedure was developed for lithium-rich samples. For this analysis, the perchloric acid solution was decreased to 20 g and the 30% hydrogen peroxide was increased to 15 mL. The sample was 0.7 g. The acid and sample were mixed in the flask with enough water to equal 125 mL total volume. There was no initial treatment of the sample by boiling in water. T h e solution was cooled in an ice bath before the hydrogen peroxide was added. Then it was refluxed 70 min. The rest of the procedure was identical to that used for the lithium-rich samples. A Pyrex glass flask was used since there was no chance for lithium hydroxide to attack the glass. Thirty grams of mannitol were used for each sample titrated.

Polyethylene bottles manufactured by Nalge Company (76 Panorama Creek Dr., Rochester, K.Y. 14602) were used for weighing alloy samples because of problems associated with the screw caps of many types of glass bottles ( 2 3 ) . These bottles were individually selected after their helium leakage rates were found to be a t or below 1 X lo4 cm3/s. Stored in a helium atmosphere, the bottles either gained or lost from tenths of a milligram to a few milligrams over a period of several hours. A large number of bottles would change weight nearly the same amount each day over a period of weeks. As a result. the average change in weight of a few empty bottles weighed a t the same time sample-filled bottles were weighed was used as a correction factor (24 ) .

C 0 NCLU S I 0.N S Excellent analytical results are ob1 ained for lithium-boron

alloys using either glass or Teflon containers. For glass, the average value of the original sample accounted for was 99.98% with a standard deviation of 0.04. For Teflon, the average value of the original sample accounted for was 100.01% with a standard deviation of 0.03. The estimated error is f0 .057~. T o obtain these results, a t least three things are necessary. Both a non-oxidizing atmosphere for manipulating the samples

Li,N t 3H,O - 3Li' A 30H- + NH,

Weigh ing in P l a s t i c Bot t les .

Table 111. Weight Percent Trace Metal Impurities

Ingot Chromium Iron Manganese Nickel

A 0.00 0.05 0.01 0.02 B 0.00 0.04 0.02 0.01 C 0.01 0.06 0.02 0.02 D 0.01 0.10 0.02 0.01 E 0.02 0.12 0.02 0.02

results as the single element standards. There was no effect caused by the lithium ion on the standards. The amount of each metal impurity in a sample was small and was rounded off to the nearest 0.01 9%. As a result the amount of each metal impurity was constant in all samples from the same ingot, Table 111.

Li th ium Metasil icate. Table I1 indicates that part of the lithiimi was in the form of lithium metasilicate for three ingots. Lye knew that silicon dioxide in glass would act like an acid and he dissolved by hydroxide ions (15) . The simplified reaction is given by 4.

SiO, + 2 0 H - + SiO;*- + H;O (4)

The form of the silicate ion probably is meta in basic solutions and ortho in acidic solutions (16. 17) as implied by reactions 4 and 5.

( 5 )

If sodium hydroxide were the source of hydroxide ions, re- action 4 would cause no problems in the titration of perchloric acid because of reaction 5 (18. 19). For every hydroxide ion lost to the formation of a silicate ion. a hydrogen ion is lost to the formation of a molecule of orthosilicic acid. Orthosilicic acid is too weak! pK about 10. (17. 20) . to interfere in the titration of perchloric acid. I t does not react with mannitol to form a stronger acid (21) . On the preliminary analyses, the results were low on the total percent of constituents. The acid solutions of the alloy were found to contain small white spheres containing lithium and silicate ions. A search of the literature revealed that when lithium and silicate ions in solution are heated to or above 353 K , lithium metasilicate precipitates as small white spheres (22. 23). Because the silicate ions are not available for reaction 5 . the larger amount of perchloric acid found hy titration causes the calculated lithium value to be low. T h e bulk of the particles of lithium metasilicate tended to remain suspended in the solution and passed through 0.2 pm pores. As a result, we used atomic absorption to determine the amount of silicate suspended in the solution. Standard solutions were made up with and without a matrix ot' lithium. chromium, iron, manganese, and nickel. The concentration of the transition metal ions in the alloy solutions being analyzed was low enough to cause no change in the absorption of silicon. There was some enhancement caused by the lithium ion.

!ye decided to try alkali resistant glass to remove the problem caused by lithium metasilicate formation. Flasks (from Corning Glass Works, Corning. N.Y. 14830) made of alkali resistant Corning No. 7280 glass were substituted for flasks made of Corning No. 7740 glass (Pyrex). The results were discouraging as indicated in Table 11. For ingot C (70 w , o lithium). more lithium metasilicale was formed ( 1 . 4 7 ~ of ' the total lithium) using the alkali resistant glass than for ingot A 180 w,io lithium) using Pyrex glass where 0.6% of the total lithium formed the metasilicate.

In another attempt to avoid dissolving glass. Teflon flasks supplied by Berghof America, Inc. (64550 Research Road. Bend. Ore. 97701) were substituted for glass flasks. The results are given in Table I1 for ingot D. Ingot D was the ingot with the highest amount of boron (13 wlo) . Table I1 indicates tha t 1.6% of the boron did not dissolve. Increasing the

+ 2 H + HZO - Si(OH),

698 ANALYTICAL CHEMISTRY, VOL. 50, NO. 6, M A Y 1978

and the use of blanks when weighing samples in plastic bottles are needed. Titrations must be made on a weight basis. If one is not overly concerned with the total amount of lithium in the alloy, Pyrex glass flasks can be used and the small loss of lithium (0.6%) ignored. For high lithium alloys and if one is especially interested in the total lithium content as well as dissolved boron (such as from lithium-boron compounds), Teflon flasks are suitable for dissolving the alloy.

ACKNOWLEDGMENT The authors thank Leonard A. Kowalchik for the ingots that

were analyzed and Raymond J. Zehnacker for making the helium leakage rate measurements. They thank Steven Dallek and Donald W. Erns t for the material from which the lith- ium-rich phase had been extracted.

LITERATURE CITED (1) S. D. James and L. E. DeVries, J . Nectrocbem. SOC.. 123, 322 (1976) (2) K. M. Myles. F. C. Mrazek. J. A. Smaga, and J. L. Settle. "Proceedings

of Symposium and Workshop on Advanced Battery Research and Design, March, 1976", U.S. ERDA Report No. ANL-76-8, p 8-50,

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RECEIVED for review November 18, 1977. Accepted January 19. 1978. This work was supported by the Independent Research Program, the Molten Salt Battery, and Lithium- Chlorine Battery Programs of the Naval Surface Weapons Center, White Oak, Md.

Problem of Artifacts in the Analysis of A/-Nitroso Compounds

I. S. Krull." T. Y. Fan, and D. H. Fine

Cancer Research Division, Thermo Electron Corporation, 45 First A venue, Walfham, Massachusetts 02 154

Methods are presented to ensure the accuracy and precision of analytical results obtained in the analysis for N-nitroso compounds. Such procedures are designed to prevent both positive and negative artifact formation during an analysis, and to improve the reliability of N-nitroso analyses as currently performed. Specific examples of the various types of causes for artifact formation are presented.

I t has become apparent in the recent years that N-nitroso compounds represent a potentially large source of exposure for man to chemical carcinogens ( I , 2). A partial listing of the different materials which have been found to contain varying levels of N-nitroso materials would include: air, water, soil, cheese, meats, fish, eggs, cutting fluids, cigarette smoke, pesticides, cosmetics, shampoos, and drugs. It may be ex- pected that additional routes for man's exposure to N-nitroso compounds will be found in the future.

Various advances in methods and instrumentation for the detection of both volatile and nonvolatile 1l'-nitroso com- pounds have led to the determination of new routes of sig- nificant exposure. As a result of the development of a thermal energy analyzer (TEA), it has been possible to rapidly analyze for most volatile and nonvolatile <V-nitroso derivatives in a wide diversity of samples (3-5). The N-NO bond is thermally ruptured in the TEA, releasing the nitrosyl radical, which then undergoes a luminescent reaction with ozone. The intensity of t he emission observed is proportional to the amount of N-nitroso compound originally present in the sample. Both gas chromatography (GC) (6) and high pressure liquid chromatography (HPLC) (7) have been applied in combination with the TEA, for the rapid analysis of N-nitroso contami-

nants. There has, however, been widespread concern about the possibility of both false positive and false negative findings a t the low parts per million (ppm) to parts per billion (ppb) concentration levels generally reported. Such artifacts could arise during sample preparation, extraction, and/or subse- quent chromatographic analysis. Because of the critical importance for correctly determining the presence or absence of potentially carcinogenic N-nitroso compounds in consumer products and the environment, a thorough discussion of this problem is appropriate.

Contamination Control in N-Nitroso Analysis. A specific detector, such as the TEA, enables the analyst concerned with trace amounts, to limit his concern to con- tamination by N-nitroso compounds and their precursors. This reduces the overall problem of contamination to more manageable levels. However, when performing routine analyses in the ppm-ppb range, the problem of contamination is still present. The problem can be reduced by destroying any X-nitroso compounds present in one of three ways. First, by washing all glassware in chromic acid, followed by repeated washings with distilled water, and then a series of organic solvents. Second, by treating all glassware with a freshly prepared solution of 5-10% HBr in glacial acetic acid a t 40 "C for a t least 1-2 h in the absence of even trace amounts of water or methanol (8). The glassware is then rinsed as above. Third, by the use of continuous, ultraviolet light exposure (germicidal lamps) overnight (9).

Demonstration of the efficacy of any method for the prevention of trace contamination depends on the performance of suitable negative blanks. When low levels of N-nitroso materials are being determined, such blank experiments should be carried out regularly and should include every step used in the analysis, including the use of the same batches

0003-2700/78/0350-0698$01 O O / O C 1978 American Chemical Society