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The determination of traces of nickel by gas-liquid chromatography
THE DETERMINATION CHROMATOGRAPHY
OF
TRACES
OF
NICKEL
BY GAS-.LIQUID
The d~t~rI~lil~~~tio1~ of metals by the t~~lllli~~i~ of gas--liquid ~hr~~nl~ito~r~lpl~y was once considurecl ;t novelty. Howovcr. in thu past fen YCitrS, the gas chron~atography of metal complcxcs particularly with ligands ofjhc /&dikctonc type, has rcccivcd much and the early work on this topic has hecn comprchcnsivcly rcvicwcd’. attention. Although over thirty metals can now bc chromatographcd directly as /I-dikctonc compluxcs. analytical utility has been achicvcd only in a few casts. notably with beryllium and chromium{11 I) ; much of the recent work has been conccrncd with the d~t~rrnillati~~l~ of traces of thcsc metals in substunctzs as varied as human tissue and lunar material’ _ “, The application of gas chromatography in inorganic analysis has hccn limited by the problems involved in the quantitative conversion of metal ions in aqueous solution to it suitable metal chclatc which must possess adcquatc volatility and thermal stability for quantitative clution from a gas-chromatographic column. Earlier attempts to develop a suitable nickel chclutc based on a conventional /Idikctonc l&and have failed to provide thcsc roquisitcs for successful ~hrom~~to~raphy. Thus the nickel chelatc of h~pt~~fluorobutanoylpivalylm~th~~nc (or 1,1,1.2.2.3.3hcptafluoro-7.7-dimcthyl-4.6octancdione) has been found to exhibit unsatisfactory olution characteristics. and cannot be formed in quantitative yield 13. Nickel has been dctcrmincd by pyrolysis gas chromatography of the polychlorinatcd xanthatc’J. but it was not an actual nickel compound that was chromatographed and determined. The USCof monothio-/I-dikctones has increased in recent years owing to their ability to form stable monomeric chclatcs with many metals which form hydrated or polymeric chclatcs with the usual /I-dikctoncs. Thcsc chelates arc readily soluble in polar organic solvents. Studies. particularly of the nickel chelates of the monothio[&diketones. have shown them to possess several desirable analytical properties. Their cxcellcnt thermal stability and volatility have rcsultcd in favourablc gas-chromatographic bchaviour *s - Is. whilst thoir solvent extraction propcrtics have been exploited in a spectrophotometric dcterminat ion of nickel ’ ‘), The cxccllcnt solvent extraction propcrtics of these sulphur-containing ligands have been confirmed in a rcccnt report”‘. WC have examined the analytica utility of gas chromatography for the determination of nickcl(II) as the bis(monothiotrifiuoroacctylacctonato)nickcl(II) chclatc. which was selected in order to take advantage of the cxtrcme sensitivity of ____..I_ * Prcsonl address:
I)cp;lrtmcnt
of Chemistry.
University
of Massi~cht~sctts.
Amherst.
Mass.
01002,
U.S.A.
fltu~l. Chit% Acru. 59 (1972)
60
I<. s. llA.RRA*rT,
I<. I3ELCliEK.
w.
I. S7‘ES’ElEN.
I’. c.
UDliN
the clcctron capture detector to flL~~ri]l~ltc~ compounds. This particular chclatc has been found to bc cminentiy suitable for the spcctrophotomctric dctcrmination of nickel, which, togcthcr with the solvent extraction propcrtics of the chclatc. has ofthc dcvclopmcnt alrcady been rcportcd ’ “. The prcscnt paper includes ;t description of a gas chromatopraphic method for the dctcrmination of tracts of tlickcl. as WC!! as the results of some’ applications of the mcthoc! to II variety of spccimcns sclcctcd to dcmonstrutc the vorsatifity of the method.
Rcwgcwts
monothiotrifluoroucctylacctonc. was prcparcd as The cxtructing lipand, dcscri bed previously ‘(‘*IH* I” and was stored as the Icad chclatc. which was stublc for scvcrui months when kept in it rcfrigcrutor. Working strength solutions of the ligand wcrc prcparcd by passing hydrogen sulphicic (c)9.5”& B.O.C.) into a solution of the lead cllclatc (0.2 g) in dicthyf ether (20 ml). The solvent wits removed by simple distillation and the dark red ligund wils diluted to 50 ml with rt-hcxanc. This solution could bc stored in the rcfrigcrator for scvcrul weeks without advcrsc cffccts. Bis(monothiotrifluoroucctylacctonato)nickcl(! l),Ni(T-TFA),.wassynthcsizcd by shaking an aqueous solution of a nickc! salt with a solution of the ligand in ?Ihcxanc. The product was purified by vacuum sublimation“‘. Working strength solutions of Ni(T-TFA), wcrc prepared by ~lppropri~kt~ dilution of a stock so!utiotl containing IO0 p.p.m, Ni as the ohclate in zz-hcxane. An aqueous stock standard (I 000 i7.p.m.) was prcparcd from AnalaR nickc! nitrate hcxahydr:itc. ltnd other solutions wcrc obtained by appropriate dilution of this stock solution. Laboratory-grade solvents wcrc used throughout and wcrc found to bc pcrfcctly satisfactory. Ana!itR acids wcrc used for the mincra!isution of the specimens for analysis. Buffcr solutions wcrc prcparcd according to the formulac of Clark and Lubs’ ‘.
A Philips PV4QOO rcscarcll gas chrarnatograph furnished with a Pyc clcctron capture dctcctor containing a IO-tnCi O3Ni radioactive source wits used in a!! the work dcscribcd hcrc. The dctcctor was used in the pulsed mode with a pulse interval of 5 ~tscc for gcncral work. while an interval of 100 /fscc was used whore the maximum sensitivity was rcquircd. The pulse ~lrnplit~ldc wxs rn~lil~t~~incd at 45 V and the pulse width at 0.8 ccscc throughout. Analytical chromatography was cffcctcd on u 4-ft. tcflon column (3/!6-in. o.d.) B” (60-85 rncsh) support material coated with 5 ‘2, silicone packed with “Universal gum rubber (E350). Substrate materials wcrc obtained from Phase Separations B” being a piltcntcd. silaniscd support. A 6-ft. stainless stcc! column Ltd., “Univcrsa! (&-in_ o.d.) was also used with a packing of 2.5 ‘,!:;Apiczon L on “Universal B” (60-85 lrlcsh).
The carrier gas was oxygen-fret nitrogen (99.9 I?;. B.O.C.) which was passed through a molccuiar sicvc bcforc cntcring the chromatograph. The flow-rate was with a soap film flowmctcr. No scavcngcr flow was used. 90 ml min- ’ as mcasurcd For the analysis of aqueous solutions of nickel. the column tcmperaturc was
G.L.C.
I>E-l-ERMINATKW
OF
61
NfCKCL
maintained at 170”. while for the analysis of the tea and fat dipcsts, the column tcmpcraturc was proprammcd to give an initiuf isothermal period of 2 min at 140” followed by heating oVcr 1 min to 170”. which was maintained until the analysis was complctc. The injection port and dctcctor oven tcmpcraturus wcrc 170* itnd 200”. rcspcctivcfy. fnjcctions wurc made with a 10-/cl syringe (Scientific Glass 1Znginocring Pty. Ltd.) by a solvent flus11 tcchniquc in which rr-hcxanc was used to flush the solution . from t hc syringe. Thcrmuf itnalysis W;IS cnrricd out on II Pcrkin Eftncr TGS-I Thermobitfanco _-ml SitIllpfCS at a tumpcraturc sc;m rate of 20’.’ min ‘. Oxygen-froc nitroscn was with 3 passed through the apparatus at about 20 ml min ‘. spcctroUltraviolet spectra wcru muasurcd on a IJniciun SF’800 recording phatomctcr in sifica ccffs of 10 mm path length. Atomic absorption mcasurcments wcrc ohtaincci with ;I V:triarl ‘Tcchtron AA-5 atomic absorption spcctrophotomctcr fitted with a h-in. air, acetylene burner. A nickcf hollow-cathode fiimf> was used with ;I currsnt of X mA and thu mcasurcmcnts wcrc made at the most scnsitivc absorption fine (232.0 nm). The spectral slit width was SO pm.
of The following proccdtrrc was used for thu format ion and extmction Ni(T-TFA)? from the acfucous solutions of nickcf(ff). Adjust tflc sampfc. usuaffy cont:iining I 20 1l.g Ni in IO ml of aqueous solution. to pH 4.6 by iiddition of an ccfuaf vofumc of buffer t;olution folfowcd by the dropwisc addition of dilute aqueous ammonia solution (about 0.1 M). Shake the mixture for 5 min in a separating funnel with 1 ml of the solution of the chda!.ing agent. and, aftc: allowing the phuscs to scparntc. discard the lower aqueous phase. Curcfully dry the stem of the funnel with tt tissue and run the organic phase into a viul containing 3 .5 ml of 0.01 134sodium hydroxide solution. Shake the mixture for 30 SW to destroy rcsiduitl chelating agent. Anafysc the extract by injecting I 2 ~tf sampfcs into the chromatograph and comparing the peak arc;~s with those from aftornatc iii.icctions ofstandard Ni(T-TFA), solutions. it is not ncccssury to scparutc tflc extract from the sodium hydroxide solution as no loss of chcfatc occurs. Extraction volumes can bc m<;dificd according to the nickel solution bc-ing analyscd. and volume ratios varying from IO: f to 250: I wcrc used. It was nc’vc’r ncccssary to dilute the extract to a known \ofumc after equilibration. Stcwdard rrlloy. Dissofvc ;L samplrt of the alloy in 10 ml of (I + I) hydrochloric acid and add 2 ml ofconccntratcd nitric acid. Boil the mixture until no rcsiduc remains. :tnd dilute the solution to 250 ml. Dilute tt 2.5ml portion further to 250 ml to give the working solution. and extract %&ml afiquots of this with 5 ml of the solution of the chclatinp agent according to tho above procedure. Tea. The following wet and dry ashing procedures wcrc cvaluatcd in this study. Wet NSII.Accurately weigh the sampfc, containing lo-20 118 of nickcf. into a
At~cil,Cirinr.
Acrrr,
59 (1972f
I<. S.
62
I~ARRA-IT.
R.
I~ELCH~R.
W.
I. STEPHEN.
1’. C.
UDEN
100-ml Pyrex beaker, add IO ml of nitric acid and cover the vcsscl with a clock glass. Evaporate the solution on an elccttic hot-plate and bake the residue for a few minutes bcforc allowing it to cool. Repeat this procedure three more timcs. Dissolve the final rcsiduc in ;I few drops of nitric acid and dilute to 25 ml with distilled water. Treat it lo-ml portion of this solution at pt-I I ” 2 with hydrogen sulphidc for 21few minutes, and then cxlract as described previously. D-y rtsh. Weigh the sample into a porcelain crucible, and heat for 20 h at 540” in II muffle furnace Rcmovc the crucihlc from the furnucc and moisten the ash with dilute hydrochloric acid (3 M); cover the crucible with a watch glass, and cvaporutc to dryness on an clcctric hot-plate. After cooling, dissolve the rcsiduc in distilled water (adding ;L littlc hytlrocl~loric acid if ncccssary) and dilute to 25 ml. Treat portions of this solution in the same way as those obtained by the wet ashing proccdurc. Fws. Weigh a sample of the crude hydrogenated triglyccridc (containing up to IO cqg of nickel) into ;I porcciain crucible and heat on an clcctrio hot-plate for about 4 h to rcmovc the more volatile components of the fat. Trimstir the t;ruciblc containing the dark brown or black tarry rcsiduc to a muffle furnace and heat for 2-3 h at 540” until only a few carbon particles remain. Rcmovc the crucible from the furnace ;md moistcn the rcsiduc with a few drops of dilute hydrochloric acid (3 M). Warm the mixture on the hot-plate for a few minutes, dilute the contents of the crucible to 25 ml and extract portions of the solution as described previously. RESULTS
AND
lXSCUSSlON
Gus c~lt,‘o~,lcttcl~~l-ccplty t$tlrr
IliCkd
c~llcJlictc~
Thcrmogravimctric analysis of Ni(T-TFA)2 indicated that the chclatc is completely volutilc and shows no sign of decomposition. In Fig. 1. the nickel thcrmogram is compared with those for the trinuoroacctylacctonatcs of beryllium and
G.L.C.
IX~TFXMINATION
OF
63
NICKfX
f-?g. 2. A comparison of the rcsponscs of the flnmc ionisation and clcctron capture dctcctnrs: G-ft. stainless L on “Univcrd 13”. Column tcmpcruturc 170” : dctcctor tClllpWilslccl column pi~chccJ with 2.5”,, Apiczon flow rate 60 ml min ‘. Amplifier ;itlcnu;ition 5. 10z. turn 3,101 ; injection port tcmpcraturc 2101’. Nitropcn Sample for FfD. 2 11g: sample for ECD. 0.3 fry.
~hrorni~lrn(II~) which show cxccllcnt chromatographic clution characteristics. These two chelates wcrc prcparcd by standard methods”‘*‘“. It could thercforc bc predicted that Ni(T-TFA), would show good ehromatographic characteristics. and the lirst reports showed that this was indeed the case. However, this workib*iH was carried out with a flame ionisation dctcctor ancl a G-ft. stainless steel column (&-in. o.d.) packed with 2.5’2; Apiczon L on “Universal B”. When this work was rcpcatcd with the electron capture detector some decomposition was found; the decomposition products had been masked previously by the FID rcsponsc to the solvent (Fig. 2). it was thcrcforc necessary to establish the best ~hrornato~r~~pl~i~ conditions for the elution as well as the detector conditions for maxima1 sensitivity, The use of the silicone gum stationary phase in a 4-ft. tcflon column gave good chromatography under the conditions previously described, the optimal gas flow rate being 90 ml min - ’ (Fig. 3). The USC of a higher column tcmperaturc dccreascd the column efficiency. Attuf.
Cftittt.
,4cfcr, 59 (1972)
1. 0
/ /
/’ 30.
/
I x ,/
I,’ ,.
,/ / 20,
/” 0, /
~ x
NI~T-TFA)~
/’
,‘:
,, ,/’
;
/’
injcClccl iocJ)
Fig. 4. The vuriotion ol’tho dctcctor response to Ni(‘l’-‘TI:A)2. ]. 10”. (_____) I’cak hcipht : (- .... .) peak ;LIVU. .‘itliJl.
CiJiltJ. a’tTttJ,
59 (1972)
;
hlsc
period
100 pscc. Amplifier
attenuation
G.L.C.
DETflKMfNATION
OF NICKEL
65
The dctcctor operating conditions wcrc also systematically cxumincd : it was found that for gcncral USCa pulse period of 5 /tscc was prcfcrablc. as this gavcgood sharp peaks. Maximal sensitivity was uchicvcd with ;I pulse period of 100 jtscc but the concomitant pcuk broadening and increased response to chclatiny agent residues did not favour the gcncrai USC of this period. When th~s~~hrom~~to~raphi~~~iiditions wcrc used, thcvariation ofthcdctuctor response with sitmplc size was found to bc linear over short ranges ;ts shown in Fig. 4. The fact that the graph dots not pass through thc,oripin suggests some sumplc loss by column adsorption itnd this was manifest in the slight increase in detector rcsponsc over a period of use. This fact combined with day-to-day variations in the calibration graph made it prcferahlc to make quantitative mcasurcments by rcfcrencl: to alturnatc injections of standard solutions of Ni(T-TFA),. The limit of dctcution was found to bc 5. IO ” g of nickel. Mass spectral analysis of the clutcd material showed that the Ni(T-TFA)? was clutcd unchanged.
The smitll response factor of the clcctron capture dctcctor to hydrocarbons makes thcsc idcal solvents. bCcause thcrc is no intcrfcrcncc from solvent tailing as has usually been found with the fIamc ionisation detector in those studies. rt-I-lcxanc was the soivcnt of choice bccausc under the ~onditio~ts of maximal sensitivity electron capturing impurities wcrc‘ well rcsolvcd from the ohclatc peak. which was not the cast with bcnzcne and tolucnc. Furthcrmorc. ,I-hcxunc hiid no tcndcncy to form pilitsc , and cmuisions with the aqueous the ncgligiblc voiumc cbungc on partition cnablcd anaiyscs to bc made on the extracts without dilution. Howcvcr, while the clcctron capture dctcctor is inscnsitivc to hydrocarbons, the rcsponsc factor to haiogCn;ttUd compounds is very large with tits rcsuit that the dctcctor is cxtrcmciy sensitive to the chelating agent. This was rcmovcd by washing the extracts with ayt~cous sodium hydroxide solution (0.01 M) before the dctcrmination; the brcakdown products were ciutcd before tho chclatc and so did not intcrferc with its dctcrmination. No loss of Ni(T-TFA), was obscrvcd after this treatment, and standard solutions of the chclatc gave the same rcsponsc when chromatographcd directly and when prcparcd with ligand, which was rcmovcd as described above. The results of a systematic investigation of the factors affecting the formation and extraction of Ni(T-TFA),, which have been reported more fully clsowhcrc“). arc summariscd in Figs. 5 and 6. It can bc seen that at pH 4.5-5.0 the chelation and extraction arc essentially quantitative after a sin&c S-min extraction step. Although this corrcsponds only to about 95 ‘;c, conversion to the chciatc, ncvcrthciess this was perfectly acceptable for most purposes and further extractions did not improve the rccovcrics. Howcvcr, if rcquircd, a correction factor could be applied.
Aqueous standard solutions of nickel nitrate wcrc analyscd by the method; Table I shows some typical recoveries. The precision of the rcsuits was quite acccptablc as shown in Table II. When the gas chromatograph was operated at the maximal sensitivity, it was possible to determine nickel in solutions down to 0.01 and 0.001 ~(6 ml- I. the results obtained being 0.009 and 0.0009 ~_cgml- I, respectively.
R.
s.
IbV~RA’l-T.
It.
ISELCHER,
W.
1. STEPHEN.
P. C’. UIIIEN
o\
Scvcral ions WOW cxamincd for intcrfcrcncc in the dct~rmin~~tion of nickel. Thcsc ions wcrc added in 100-fold amounts to solutions of nickel (1.0 ,~g ml- ‘f. which was then determined by the usual procedure. The results were expressed in terms of rccovcry compared to control solutions which contained no divcrsc ions and which wcrc analyscd simultaneously. Table III includes some of the results. It At~rl.Chirtr.
Actcr. 59 (1972)
G.L.C.
IlETliKhIfNAl'ION OF
WC-KEL
s * 0.07 :t_0.014
t-t&z(r)
cd(II) Zn(II) Mn(Ii) &(I 1) Cn(1 I) Pl(ll) ,...
t 59 96 92
103 279 262 96
s, + 7.2”,, .f: 15.5 ‘I,,
No. 4?f tl~‘trls.
7 5
(‘r(lII) Af(ll1) Fc(Ifl) f-c(iii)scitr~ttc(1:5) Sn(IV) VW)
was also found that rn~~~n~siun~(II), ~~~l~iurn(~I~ and b~riurn(l~~ did not intcrfcrc’“. In the cwc of coppcr(II) ;\ very large peak. attributed to decomposition of a copper chclntc formed in the extract. was elutcd boforc the Ni(T-TFA)2 peak and made it impossible to dctcrminc the nickel. This intcrfcrcncc of coppcr(l1) was easily climinatcd by passing hydropcn sulphidc into the aqueous solution (pH l-2) bcforc extraction : this proccdurc W;IS subscqucntly used in the analysis of tea. Table III shows that significant interferences wcrc also obtained in the prcscncc of cobalt(I I) and mer~ury(i,II). Iron(IIr) did not intcrfcrc, although a broad peak was etutcd bcforc the Ni(T-TFA)I peak. Again this was attributed to the decomposition of a chclatc formed in the extraction. but, unlike the cusc with coppcr(lI), the elution was sufficiently rapid to allow resolution of the nick4 chclatc. The prcscncc of citrate masked the iron(III), and so allowed grcatcr resolution of the Ni(T-TFA)2. but this could also Ar~rrl.Chint.
Acta,
59 (1972)
SOMli
hl’l’l,lC’A’l’lONS
01:
‘I’llli
Ml~‘I’IIOI~
A sampfc ol’an alloy a)ntaining 2.W I’.;,Ni (Sampfc No. 22x. 13urcau ofAnafysed was anafyscd to show that I Iail. ~~~f~~f~sb~~~~~~f~. Tccssidc) Sarnpfos Ltd., Ncwham tflo mutflocf was :tppficahfu to purccntug.c fcvofs of’nickcf. although it was first ncccssary to cfifiitc lflc cfigcstcrf sample to a managcubfc concentration to avoid tfic CISC of IargC ~iinounts of ~fl~liltill~ agcllt. aticf to prcvcnt ovcrfoading the dctcctor. A vafuc of ol’thc alloy, the rclativc standard deviation 2.5x ‘I;, wits obtainccf for tile nickel content being :k IO,8 ‘I:,. f:xtensivc difutioil of tf~ srAutiot1 bcforc analysis is not ii rccommcndccf pntctiuc owing to tfic loss of accuracy. but it was not cnvisapctf that (IX method woufd fincf USC iit StICIl L’otiuuntr;itions, and tfiu following cxampfcs arc applications at tfio tract fcvcf.
A sampfc 0l’ tcL\ W;lS cnnsicfcrctf to bc a CIScfUl ilf3pfiGlliOll of tflC t?lctfiod nat uraf nickel contctlts in the manuf’acttrrccf Icuf arc oficn itb<>ilt 10 pg 6.. ‘. l‘hc spccimcn obtained was known to contain traces of nickcf. copper and iron with larger amounts of m:IflgitttYcsC (Table IV. footnote). It was cxpcct~‘d that after dcstructiotl of the organic matter, the only intcrfcrcncc would bc from coppcr. and tflis wits f’ountf to bc the CiISC. but it was casify cfiminatcd by treatment with flydropcn sufphicfc fxc~~usc
II~‘lV
tr.sir
I 3.0
_I: 1.4
SpCL.lrO~~IIl1tOrllClry
14.0
:!.-
11.7
-k 1.5
10 ‘I,) k I ‘I.7 I’,,
12.x
:t 2.0
+ lS.6”,,
12.6
-i_ I.6
+ 11.7 I’;,
A.:l.s. Oil ;1q. ph:1sc Dr‘V cr.sir G.l.c. Spfctrophotontctry ” 1 t~dcpctltlcnl IO 20 /I&! p
;brl:tlysis Of the
SiIlllplC
by
I .J
atomic
’ c:ich of C’LI. 1’~. Ni. and IO00 /(g g
+ 10.x “(, k
;thsorptiotl ’ oI’ MII.
spcctropl~otomctry
gave tlic following
results:
as dcscribcd above. The organic milttcr in tflc sample was dcstroycd by wet and dry asftitig methods, and anafyscs often sainpl~s it3 each cast g;tv~ the rcsufts stimmariscd in Tabfc IV. For comparison the rcsufts obtained by sp~~tropl~otoxnctri~ analysis of tile cxtritets’” itnd by atotnic absorption spoctrophotomctry of the aqueous phases arc also incfudcd. Dry ashing has often been rcportcd to wusc fosscs by volatilisation or adsorplion. whifo the advantages of wet ashinp arc oftcn lost by contamination from the
A,~ill.ClIi,,l. Arttr. 59
(I 972)
G.L.C.
DETERMINATION
OF NIC-KliL
69
reitgents. 13urkc ~111tiAlbright” found both methods to hc satisfactory. although they rccommcndcd wet ashing for instant teas. The ahovc results shctw overall zigrccmcnt. although ths dry ashing method dots stem COproct~c a wider variation in the results. Blank v;llucs showed thitt no ~~~~t~t~~~i~~i~ti~~~ was produced from the lTilg!L’f’ltS.
The results wcrc chcckcd by the USC of stitndilrd additions to the tea sample hcforc ashing. the resultant solutions being anuiyscd by chromatography of the extracts and by atomic absorption sp’cctrophotomctry of the aqueous phases. Thcsc rcsufts arc shown in Fig. 7. which proves the v~~luc for the nickel concentration to bc 14.0& 1.5 jrg g- ’ and 13.52 1.5 jcg g _ ’ for the two rcspcctivc tcchniyucs. Figure X (13) shows ;t typical ~l~r~tni~t~~r~~ln for the extract from ii sampfc of tea. This chromatogram was ohtaincd by the USC of ;I tcmpcraturc programmc. Figure 8 also shows chromatograms obtoincd under isothermal conditions; it is clear that tcmpcraturc programming improves the resolution of the Ni(T-TFA), peak. while rctaininp the optimal peak shape.
Samples of crude hycjr~~~n~!t~d triglyccridcs ~~nt~~initl~ tracts of nickel wcrc obtained for analysis. and thcsc wcrc mincrafiscd by the dry ashing proccdurc. It was found that combustion of the samples in the furnaoc caused scvcre losses, and so
Amd. Chim. Actu, 59 (1972)
1~. S. I3ARHA’I”I’.
I<. 13f:LCHER.
W.
I. STEPHEN.
.:
r. ;:
cliromalogram Ni(‘l’-TFA)I
of il fill extract. Aniplificr solutiott (5 p,p.m.).
;1ttcnu;ltion
20.
UIIEN
,-,
i ,I
t:ig. 9. GilS of staltd;\rd
I’. C.
:
IO’. (A) 15 111of fat extr:wt
; (13) I .7 pl
the more volatile components of the fkt wcrc rcmovcd by preliminary hatting on the hot-plate. Similarly it wits found that ashinp the sample to tho cxtcnt that all of the carbon was removed also resulted in scvcrc losses. and so the sample was removed from the furnace when a little cat-bon residue rcmaincd. Analysis by gas chromatography according to the usuai procedure gave the results shown in Table V. Once again. the tcmpcraturc programmc was used. Thcsc results again show rcasonablc agrccmcnt with the itldcpcndcnt analysts for the
G.L.C.
I>ETliKMINATION
71
OF NICKEL
samples. and Fig. 9 shows a typical chromatogram for an extract and for an authentic sample of Ni(T-TFA),. The uneven base-lint is simply a cons~‘qucncc of the tcrnpcraturc programmc.
The use of pas-.liyuid chromatogrtuphy offers a sensitive method for the scparntion :tnd dctcrminotion of traces of nickel in a variety of samples. of non-flame cells in atomic absorption A rcccnt rcvicw’” of the applicittions and atomic fluorcscencc spootroscopy lists the limits of dctcction for nickel by various modifications. The sensitivity of the prcscnt method appears to compare very favourably with these various moditicutions and in terms of practicality. the g!as chrotnutographio method is equally convcnicnt. It is hoped that this work contributes in some way to the ultirnatc goal of metal ;tnalysis by pas chromatogr:tphy. which must surely bc the simultaneous determination
of several
metals.
WC arc indcbtccl to Intcrnutional Nickel Ltd. for the provision of the sample of it Brookc Bond frcozc-dried vcndinp tea. to Van den Bcrgh and Jurgens Ltd. for providiIlpthcsamples ofcrudc hydroycnutod fttts.and to the University of 13irmingh~lil~ for the provision of ;S rcscarch grant to R.S.B. SUMMARY
A rapid and scnsitivc mcthorl for the dctcrminution of trncc amounts of nickel hns been developed, in which it volatile nickel chelatu is analyscd by gas--liquid chromatography. The method involves extraction of the itqucous solution of nickel at pf-1 4.5-.S.O with a solution of rnonothiotriflL)oro~l~~tyl~l~~tone in n-hcxanc. tkc USC of a single extract ion giving rccovcrios in cxcoss of 90‘2;,. The extract is washed with sodium hydroxide solution (0.01 M) to destroy residual chelating agent. and the bis(monothiotrifluoroacctylacctonato)nickcl(lI) is dctcrmincd by gas chromatography on a 4-ft. tcflon column packed with 5:‘& silicone gum rubber (E350) on “Universal B” support. The cxtrcmc sensitivity of the clcctron capture detector cnablcs 5. IO- ’ ’ g of niokcl to be dctcctcd. while nickel concentrations down to 0.1 itg ml- ’ have been dctcrmincd in routine analyses. The cffcct of diverse metal ions is examined: the most significant intcrferencc. resulting from the presence of coppcr(l1). iscasily climinatcd by preliminary trcatmcnt ofthcsolution with hydrogen sulphidc. The new method has been applied to the dctcrmination of nickel at the pcrccntagc lcvcl in an alloy, and at tract levels in tea and fat samples. The results show good agrccmcnt with indcpcndcnt analysts for the sumplcs.
Une methode rapide et sensible est propost2e pour ie dosage de traces de nickel ; elle consiste li analyser un chetate volatil dc nickel par chromatographie gaz-liquide. On procede h une extraction ri I’aide d’une solution de monothiofluoroacetylacetone dans len-hexane. ApH 4.5-5.0. On examine I’influcnce de divers rnetaux. L’interference du cuivre(Il)est la plus importante;on l’dlimine facilement par traitement preliminaire And.
C&m
Acta,
59 (1972)
72
R. S. BARRA’I?‘,
I<. IELCXER.
W. I. STliPHEN.
I’. C. UDEN
ii l’hydrogtinc sull’urf. Cettc nouvcllc mQtlradc a 136 appliytlde au dosage du nickel dans WI ttlliagc et au dosrrgc dc traces dc nickd duns dcs &Azantillons de thti et dc mutic”rcs grusscs. %USAMMliNI:ASSUNCi
Es wurdc tine schnelle und cmpfindlichc Mcthodc fiir die Bcstimmung von Spur~n~n~n~cn Nickel entwickclt, bci dcr ein fliichtigcr Nickelchelat durch GasFtiissi~-Cllrctmuto~r~~~h~c analysiert wird. Bci dcr Mcthodc wird Nickel aus w%sriger Lijsung bci plf 4.5-5.0 mit einer L&ung von Monotl~i~tri~uor~~~etyl~~~eton in trHexan cxtruhicrt. wobci mit einer cinziyen Extraktion mehr als 90’,!;, crfasst werden. Der Extrakt wird zur Beseitigung dcs vcrbliebcnen Chelutisicrungsmittcls mit 0.01 N Natronluugc gcwuschcn und das Bis(manothiotrifluoracctylacctonato)-nickcl( I I) durch Gas-Ctlr~mutographie an ciner 4 ft~-~c~l~~ns~ulc bcstimmt. die rnit 5 IsI, Siiicongurnmi (EXO) auf “Universal B”-Triiger gcfUt ist. Die cxtremc Empfindlichkcit dos Etcktroncncinfang-Dctcktors errn6glich) den Nachwcis von 5. IO-‘ ‘I g Nickel, wlihrcnd Nickelkonzcntrationcn bis zu 0.1 pg ml- ’ hcrab bci Routineanulyscn bestitnmt wurden. Dcr Einfuss vcrschicdcncr Mctallioncn wurde untcrsucht. Die grbsstc Stiirung wird durch die Gcgcnwart von Kupfer(iI) vcrursucht: sic kann Icicht durch v~r~~~r~c~~~ndc B~h~!ndl~ln~ der Liisung mit S~hwc~~~w~~sserstoff vcrmicden worden. Die ncuc Mcthrzde wurdc auf die Bestimmung von Niokcl im Prozcntbcrcich in ciner Legicrung und itn Spurcnbcreich in Tee- und Fettprobcn angcwondct. Die Ergebnissc stimmcn mit unabhiingigen Annlyscn der Prohen put iibercin. REFERI3NCES
G.L.C.
I3ETEKMfNATIQN
OF
NICKEL
73
21 p/f i~irlrtc~s trrul rlwir l~c~fc~r~~ritlrrrir~rl. B.D.H. Chemicals Ltd.. Poole. England. 1970. 22 W. c’. FI:RNIXIUS ANI) IS. I<. I3H’I’As’r. in T. MOIU.EK. Itror~gtrtlir~.~~~wr/wsc~.s.Vol. V. McGraw-Hill. York, lY57. p. 105.
Atrtrl.
c-hil?L
Al’lti.
SC)
New
(1977)
OF
TRACES
OF
NICKEL
BY GAS-.LIQUID
The d~t~rI~lil~~~tio1~ of metals by the t~~lllli~~i~ of gas--liquid ~hr~~nl~ito~r~lpl~y was once considurecl ;t novelty. Howovcr. in thu past fen YCitrS, the gas chron~atography of metal complcxcs particularly with ligands ofjhc /&dikctonc type, has rcccivcd much and the early work on this topic has hecn comprchcnsivcly rcvicwcd’. attention. Although over thirty metals can now bc chromatographcd directly as /I-dikctonc compluxcs. analytical utility has been achicvcd only in a few casts. notably with beryllium and chromium{11 I) ; much of the recent work has been conccrncd with the d~t~rrnillati~~l~ of traces of thcsc metals in substunctzs as varied as human tissue and lunar material’ _ “, The application of gas chromatography in inorganic analysis has hccn limited by the problems involved in the quantitative conversion of metal ions in aqueous solution to it suitable metal chclatc which must possess adcquatc volatility and thermal stability for quantitative clution from a gas-chromatographic column. Earlier attempts to develop a suitable nickel chclutc based on a conventional /Idikctonc l&and have failed to provide thcsc roquisitcs for successful ~hrom~~to~raphy. Thus the nickel chelatc of h~pt~~fluorobutanoylpivalylm~th~~nc (or 1,1,1.2.2.3.3hcptafluoro-7.7-dimcthyl-4.6octancdione) has been found to exhibit unsatisfactory olution characteristics. and cannot be formed in quantitative yield 13. Nickel has been dctcrmincd by pyrolysis gas chromatography of the polychlorinatcd xanthatc’J. but it was not an actual nickel compound that was chromatographed and determined. The USCof monothio-/I-dikctones has increased in recent years owing to their ability to form stable monomeric chclatcs with many metals which form hydrated or polymeric chclatcs with the usual /I-dikctoncs. Thcsc chelates arc readily soluble in polar organic solvents. Studies. particularly of the nickel chelates of the monothio[&diketones. have shown them to possess several desirable analytical properties. Their cxcellcnt thermal stability and volatility have rcsultcd in favourablc gas-chromatographic bchaviour *s - Is. whilst thoir solvent extraction propcrtics have been exploited in a spectrophotometric dcterminat ion of nickel ’ ‘), The cxccllcnt solvent extraction propcrtics of these sulphur-containing ligands have been confirmed in a rcccnt report”‘. WC have examined the analytica utility of gas chromatography for the determination of nickcl(II) as the bis(monothiotrifiuoroacctylacctonato)nickcl(II) chclatc. which was selected in order to take advantage of the cxtrcme sensitivity of ____..I_ * Prcsonl address:
I)cp;lrtmcnt
of Chemistry.
University
of Massi~cht~sctts.
Amherst.
Mass.
01002,
U.S.A.
fltu~l. Chit% Acru. 59 (1972)
60
I<. s. llA.RRA*rT,
I<. I3ELCliEK.
w.
I. S7‘ES’ElEN.
I’. c.
UDliN
the clcctron capture detector to flL~~ri]l~ltc~ compounds. This particular chclatc has been found to bc cminentiy suitable for the spcctrophotomctric dctcrmination of nickel, which, togcthcr with the solvent extraction propcrtics of the chclatc. has ofthc dcvclopmcnt alrcady been rcportcd ’ “. The prcscnt paper includes ;t description of a gas chromatopraphic method for the dctcrmination of tracts of tlickcl. as WC!! as the results of some’ applications of the mcthoc! to II variety of spccimcns sclcctcd to dcmonstrutc the vorsatifity of the method.
Rcwgcwts
monothiotrifluoroucctylacctonc. was prcparcd as The cxtructing lipand, dcscri bed previously ‘(‘*IH* I” and was stored as the Icad chclatc. which was stublc for scvcrui months when kept in it rcfrigcrutor. Working strength solutions of the ligand wcrc prcparcd by passing hydrogen sulphicic (c)9.5”& B.O.C.) into a solution of the lead cllclatc (0.2 g) in dicthyf ether (20 ml). The solvent wits removed by simple distillation and the dark red ligund wils diluted to 50 ml with rt-hcxanc. This solution could bc stored in the rcfrigcrator for scvcrul weeks without advcrsc cffccts. Bis(monothiotrifluoroucctylacctonato)nickcl(! l),Ni(T-TFA),.wassynthcsizcd by shaking an aqueous solution of a nickc! salt with a solution of the ligand in ?Ihcxanc. The product was purified by vacuum sublimation“‘. Working strength solutions of Ni(T-TFA), wcrc prepared by ~lppropri~kt~ dilution of a stock so!utiotl containing IO0 p.p.m, Ni as the ohclate in zz-hcxane. An aqueous stock standard (I 000 i7.p.m.) was prcparcd from AnalaR nickc! nitrate hcxahydr:itc. ltnd other solutions wcrc obtained by appropriate dilution of this stock solution. Laboratory-grade solvents wcrc used throughout and wcrc found to bc pcrfcctly satisfactory. Ana!itR acids wcrc used for the mincra!isution of the specimens for analysis. Buffcr solutions wcrc prcparcd according to the formulac of Clark and Lubs’ ‘.
A Philips PV4QOO rcscarcll gas chrarnatograph furnished with a Pyc clcctron capture dctcctor containing a IO-tnCi O3Ni radioactive source wits used in a!! the work dcscribcd hcrc. The dctcctor was used in the pulsed mode with a pulse interval of 5 ~tscc for gcncral work. while an interval of 100 /fscc was used whore the maximum sensitivity was rcquircd. The pulse ~lrnplit~ldc wxs rn~lil~t~~incd at 45 V and the pulse width at 0.8 ccscc throughout. Analytical chromatography was cffcctcd on u 4-ft. tcflon column (3/!6-in. o.d.) B” (60-85 rncsh) support material coated with 5 ‘2, silicone packed with “Universal gum rubber (E350). Substrate materials wcrc obtained from Phase Separations B” being a piltcntcd. silaniscd support. A 6-ft. stainless stcc! column Ltd., “Univcrsa! (&-in_ o.d.) was also used with a packing of 2.5 ‘,!:;Apiczon L on “Universal B” (60-85 lrlcsh).
The carrier gas was oxygen-fret nitrogen (99.9 I?;. B.O.C.) which was passed through a molccuiar sicvc bcforc cntcring the chromatograph. The flow-rate was with a soap film flowmctcr. No scavcngcr flow was used. 90 ml min- ’ as mcasurcd For the analysis of aqueous solutions of nickel. the column tcmperaturc was
G.L.C.
I>E-l-ERMINATKW
OF
61
NfCKCL
maintained at 170”. while for the analysis of the tea and fat dipcsts, the column tcmpcraturc was proprammcd to give an initiuf isothermal period of 2 min at 140” followed by heating oVcr 1 min to 170”. which was maintained until the analysis was complctc. The injection port and dctcctor oven tcmpcraturus wcrc 170* itnd 200”. rcspcctivcfy. fnjcctions wurc made with a 10-/cl syringe (Scientific Glass 1Znginocring Pty. Ltd.) by a solvent flus11 tcchniquc in which rr-hcxanc was used to flush the solution . from t hc syringe. Thcrmuf itnalysis W;IS cnrricd out on II Pcrkin Eftncr TGS-I Thermobitfanco _-ml SitIllpfCS at a tumpcraturc sc;m rate of 20’.’ min ‘. Oxygen-froc nitroscn was with 3 passed through the apparatus at about 20 ml min ‘. spcctroUltraviolet spectra wcru muasurcd on a IJniciun SF’800 recording phatomctcr in sifica ccffs of 10 mm path length. Atomic absorption mcasurcments wcrc ohtaincci with ;I V:triarl ‘Tcchtron AA-5 atomic absorption spcctrophotomctcr fitted with a h-in. air, acetylene burner. A nickcf hollow-cathode fiimf> was used with ;I currsnt of X mA and thu mcasurcmcnts wcrc made at the most scnsitivc absorption fine (232.0 nm). The spectral slit width was SO pm.
of The following proccdtrrc was used for thu format ion and extmction Ni(T-TFA)? from the acfucous solutions of nickcf(ff). Adjust tflc sampfc. usuaffy cont:iining I 20 1l.g Ni in IO ml of aqueous solution. to pH 4.6 by iiddition of an ccfuaf vofumc of buffer t;olution folfowcd by the dropwisc addition of dilute aqueous ammonia solution (about 0.1 M). Shake the mixture for 5 min in a separating funnel with 1 ml of the solution of the chda!.ing agent. and, aftc: allowing the phuscs to scparntc. discard the lower aqueous phase. Curcfully dry the stem of the funnel with tt tissue and run the organic phase into a viul containing 3 .5 ml of 0.01 134sodium hydroxide solution. Shake the mixture for 30 SW to destroy rcsiduitl chelating agent. Anafysc the extract by injecting I 2 ~tf sampfcs into the chromatograph and comparing the peak arc;~s with those from aftornatc iii.icctions ofstandard Ni(T-TFA), solutions. it is not ncccssury to scparutc tflc extract from the sodium hydroxide solution as no loss of chcfatc occurs. Extraction volumes can bc m<;dificd according to the nickel solution bc-ing analyscd. and volume ratios varying from IO: f to 250: I wcrc used. It was nc’vc’r ncccssary to dilute the extract to a known \ofumc after equilibration. Stcwdard rrlloy. Dissofvc ;L samplrt of the alloy in 10 ml of (I + I) hydrochloric acid and add 2 ml ofconccntratcd nitric acid. Boil the mixture until no rcsiduc remains. :tnd dilute the solution to 250 ml. Dilute tt 2.5ml portion further to 250 ml to give the working solution. and extract %&ml afiquots of this with 5 ml of the solution of the chclatinp agent according to tho above procedure. Tea. The following wet and dry ashing procedures wcrc cvaluatcd in this study. Wet NSII.Accurately weigh the sampfc, containing lo-20 118 of nickcf. into a
At~cil,Cirinr.
Acrrr,
59 (1972f
I<. S.
62
I~ARRA-IT.
R.
I~ELCH~R.
W.
I. STEPHEN.
1’. C.
UDEN
100-ml Pyrex beaker, add IO ml of nitric acid and cover the vcsscl with a clock glass. Evaporate the solution on an elccttic hot-plate and bake the residue for a few minutes bcforc allowing it to cool. Repeat this procedure three more timcs. Dissolve the final rcsiduc in ;I few drops of nitric acid and dilute to 25 ml with distilled water. Treat it lo-ml portion of this solution at pt-I I ” 2 with hydrogen sulphidc for 21few minutes, and then cxlract as described previously. D-y rtsh. Weigh the sample into a porcelain crucible, and heat for 20 h at 540” in II muffle furnace Rcmovc the crucihlc from the furnucc and moisten the ash with dilute hydrochloric acid (3 M); cover the crucible with a watch glass, and cvaporutc to dryness on an clcctric hot-plate. After cooling, dissolve the rcsiduc in distilled water (adding ;L littlc hytlrocl~loric acid if ncccssary) and dilute to 25 ml. Treat portions of this solution in the same way as those obtained by the wet ashing proccdurc. Fws. Weigh a sample of the crude hydrogenated triglyccridc (containing up to IO cqg of nickel) into ;I porcciain crucible and heat on an clcctrio hot-plate for about 4 h to rcmovc the more volatile components of the fat. Trimstir the t;ruciblc containing the dark brown or black tarry rcsiduc to a muffle furnace and heat for 2-3 h at 540” until only a few carbon particles remain. Rcmovc the crucible from the furnace ;md moistcn the rcsiduc with a few drops of dilute hydrochloric acid (3 M). Warm the mixture on the hot-plate for a few minutes, dilute the contents of the crucible to 25 ml and extract portions of the solution as described previously. RESULTS
AND
lXSCUSSlON
Gus c~lt,‘o~,lcttcl~~l-ccplty t$tlrr
IliCkd
c~llcJlictc~
Thcrmogravimctric analysis of Ni(T-TFA)2 indicated that the chclatc is completely volutilc and shows no sign of decomposition. In Fig. 1. the nickel thcrmogram is compared with those for the trinuoroacctylacctonatcs of beryllium and
G.L.C.
IX~TFXMINATION
OF
63
NICKfX
f-?g. 2. A comparison of the rcsponscs of the flnmc ionisation and clcctron capture dctcctnrs: G-ft. stainless L on “Univcrd 13”. Column tcmpcruturc 170” : dctcctor tClllpWilslccl column pi~chccJ with 2.5”,, Apiczon flow rate 60 ml min ‘. Amplifier ;itlcnu;ition 5. 10z. turn 3,101 ; injection port tcmpcraturc 2101’. Nitropcn Sample for FfD. 2 11g: sample for ECD. 0.3 fry.
~hrorni~lrn(II~) which show cxccllcnt chromatographic clution characteristics. These two chelates wcrc prcparcd by standard methods”‘*‘“. It could thercforc bc predicted that Ni(T-TFA), would show good ehromatographic characteristics. and the lirst reports showed that this was indeed the case. However, this workib*iH was carried out with a flame ionisation dctcctor ancl a G-ft. stainless steel column (&-in. o.d.) packed with 2.5’2; Apiczon L on “Universal B”. When this work was rcpcatcd with the electron capture detector some decomposition was found; the decomposition products had been masked previously by the FID rcsponsc to the solvent (Fig. 2). it was thcrcforc necessary to establish the best ~hrornato~r~~pl~i~ conditions for the elution as well as the detector conditions for maxima1 sensitivity, The use of the silicone gum stationary phase in a 4-ft. tcflon column gave good chromatography under the conditions previously described, the optimal gas flow rate being 90 ml min - ’ (Fig. 3). The USC of a higher column tcmperaturc dccreascd the column efficiency. Attuf.
Cftittt.
,4cfcr, 59 (1972)
1. 0
/ /
/’ 30.
/
I x ,/
I,’ ,.
,/ / 20,
/” 0, /
~ x
NI~T-TFA)~
/’
,‘:
,, ,/’
;
/’
injcClccl iocJ)
Fig. 4. The vuriotion ol’tho dctcctor response to Ni(‘l’-‘TI:A)2. ]. 10”. (_____) I’cak hcipht : (- .... .) peak ;LIVU. .‘itliJl.
CiJiltJ. a’tTttJ,
59 (1972)
;
hlsc
period
100 pscc. Amplifier
attenuation
G.L.C.
DETflKMfNATION
OF NICKEL
65
The dctcctor operating conditions wcrc also systematically cxumincd : it was found that for gcncral USCa pulse period of 5 /tscc was prcfcrablc. as this gavcgood sharp peaks. Maximal sensitivity was uchicvcd with ;I pulse period of 100 jtscc but the concomitant pcuk broadening and increased response to chclatiny agent residues did not favour the gcncrai USC of this period. When th~s~~hrom~~to~raphi~~~iiditions wcrc used, thcvariation ofthcdctuctor response with sitmplc size was found to bc linear over short ranges ;ts shown in Fig. 4. The fact that the graph dots not pass through thc,oripin suggests some sumplc loss by column adsorption itnd this was manifest in the slight increase in detector rcsponsc over a period of use. This fact combined with day-to-day variations in the calibration graph made it prcferahlc to make quantitative mcasurcments by rcfcrencl: to alturnatc injections of standard solutions of Ni(T-TFA),. The limit of dctcution was found to bc 5. IO ” g of nickel. Mass spectral analysis of the clutcd material showed that the Ni(T-TFA)? was clutcd unchanged.
The smitll response factor of the clcctron capture dctcctor to hydrocarbons makes thcsc idcal solvents. bCcause thcrc is no intcrfcrcncc from solvent tailing as has usually been found with the fIamc ionisation detector in those studies. rt-I-lcxanc was the soivcnt of choice bccausc under the ~onditio~ts of maximal sensitivity electron capturing impurities wcrc‘ well rcsolvcd from the ohclatc peak. which was not the cast with bcnzcne and tolucnc. Furthcrmorc. ,I-hcxunc hiid no tcndcncy to form pilitsc , and cmuisions with the aqueous the ncgligiblc voiumc cbungc on partition cnablcd anaiyscs to bc made on the extracts without dilution. Howcvcr, while the clcctron capture dctcctor is inscnsitivc to hydrocarbons, the rcsponsc factor to haiogCn;ttUd compounds is very large with tits rcsuit that the dctcctor is cxtrcmciy sensitive to the chelating agent. This was rcmovcd by washing the extracts with ayt~cous sodium hydroxide solution (0.01 M) before the dctcrmination; the brcakdown products were ciutcd before tho chclatc and so did not intcrferc with its dctcrmination. No loss of Ni(T-TFA), was obscrvcd after this treatment, and standard solutions of the chclatc gave the same rcsponsc when chromatographcd directly and when prcparcd with ligand, which was rcmovcd as described above. The results of a systematic investigation of the factors affecting the formation and extraction of Ni(T-TFA),, which have been reported more fully clsowhcrc“). arc summariscd in Figs. 5 and 6. It can bc seen that at pH 4.5-5.0 the chelation and extraction arc essentially quantitative after a sin&c S-min extraction step. Although this corrcsponds only to about 95 ‘;c, conversion to the chciatc, ncvcrthciess this was perfectly acceptable for most purposes and further extractions did not improve the rccovcrics. Howcvcr, if rcquircd, a correction factor could be applied.
Aqueous standard solutions of nickel nitrate wcrc analyscd by the method; Table I shows some typical recoveries. The precision of the rcsuits was quite acccptablc as shown in Table II. When the gas chromatograph was operated at the maximal sensitivity, it was possible to determine nickel in solutions down to 0.01 and 0.001 ~(6 ml- I. the results obtained being 0.009 and 0.0009 ~_cgml- I, respectively.
R.
s.
IbV~RA’l-T.
It.
ISELCHER,
W.
1. STEPHEN.
P. C’. UIIIEN
o\
Scvcral ions WOW cxamincd for intcrfcrcncc in the dct~rmin~~tion of nickel. Thcsc ions wcrc added in 100-fold amounts to solutions of nickel (1.0 ,~g ml- ‘f. which was then determined by the usual procedure. The results were expressed in terms of rccovcry compared to control solutions which contained no divcrsc ions and which wcrc analyscd simultaneously. Table III includes some of the results. It At~rl.Chirtr.
Actcr. 59 (1972)
G.L.C.
IlETliKhIfNAl'ION OF
WC-KEL
s * 0.07 :t_0.014
t-t&z(r)
cd(II) Zn(II) Mn(Ii) &(I 1) Cn(1 I) Pl(ll) ,...
t 59 96 92
103 279 262 96
s, + 7.2”,, .f: 15.5 ‘I,,
No. 4?f tl~‘trls.
7 5
(‘r(lII) Af(ll1) Fc(Ifl) f-c(iii)scitr~ttc(1:5) Sn(IV) VW)
was also found that rn~~~n~siun~(II), ~~~l~iurn(~I~ and b~riurn(l~~ did not intcrfcrc’“. In the cwc of coppcr(II) ;\ very large peak. attributed to decomposition of a copper chclntc formed in the extract. was elutcd boforc the Ni(T-TFA)2 peak and made it impossible to dctcrminc the nickel. This intcrfcrcncc of coppcr(l1) was easily climinatcd by passing hydropcn sulphidc into the aqueous solution (pH l-2) bcforc extraction : this proccdurc W;IS subscqucntly used in the analysis of tea. Table III shows that significant interferences wcrc also obtained in the prcscncc of cobalt(I I) and mer~ury(i,II). Iron(IIr) did not intcrfcrc, although a broad peak was etutcd bcforc the Ni(T-TFA)I peak. Again this was attributed to the decomposition of a chclatc formed in the extraction. but, unlike the cusc with coppcr(lI), the elution was sufficiently rapid to allow resolution of the nick4 chclatc. The prcscncc of citrate masked the iron(III), and so allowed grcatcr resolution of the Ni(T-TFA)2. but this could also Ar~rrl.Chint.
Acta,
59 (1972)
SOMli
hl’l’l,lC’A’l’lONS
01:
‘I’llli
Ml~‘I’IIOI~
A sampfc ol’an alloy a)ntaining 2.W I’.;,Ni (Sampfc No. 22x. 13urcau ofAnafysed was anafyscd to show that I Iail. ~~~f~~f~sb~~~~~~f~. Tccssidc) Sarnpfos Ltd., Ncwham tflo mutflocf was :tppficahfu to purccntug.c fcvofs of’nickcf. although it was first ncccssary to cfifiitc lflc cfigcstcrf sample to a managcubfc concentration to avoid tfic CISC of IargC ~iinounts of ~fl~liltill~ agcllt. aticf to prcvcnt ovcrfoading the dctcctor. A vafuc of ol’thc alloy, the rclativc standard deviation 2.5x ‘I;, wits obtainccf for tile nickel content being :k IO,8 ‘I:,. f:xtensivc difutioil of tf~ srAutiot1 bcforc analysis is not ii rccommcndccf pntctiuc owing to tfic loss of accuracy. but it was not cnvisapctf that (IX method woufd fincf USC iit StICIl L’otiuuntr;itions, and tfiu following cxampfcs arc applications at tfio tract fcvcf.
A sampfc 0l’ tcL\ W;lS cnnsicfcrctf to bc a CIScfUl ilf3pfiGlliOll of tflC t?lctfiod nat uraf nickel contctlts in the manuf’acttrrccf Icuf arc oficn itb<>ilt 10 pg 6.. ‘. l‘hc spccimcn obtained was known to contain traces of nickcf. copper and iron with larger amounts of m:IflgitttYcsC (Table IV. footnote). It was cxpcct~‘d that after dcstructiotl of the organic matter, the only intcrfcrcncc would bc from coppcr. and tflis wits f’ountf to bc the CiISC. but it was casify cfiminatcd by treatment with flydropcn sufphicfc fxc~~usc
II~‘lV
tr.sir
I 3.0
_I: 1.4
SpCL.lrO~~IIl1tOrllClry
14.0
:!.-
11.7
-k 1.5
10 ‘I,) k I ‘I.7 I’,,
12.x
:t 2.0
+ lS.6”,,
12.6
-i_ I.6
+ 11.7 I’;,
A.:l.s. Oil ;1q. ph:1sc Dr‘V cr.sir G.l.c. Spfctrophotontctry ” 1 t~dcpctltlcnl IO 20 /I&! p
;brl:tlysis Of the
SiIlllplC
by
I .J
atomic
’ c:ich of C’LI. 1’~. Ni. and IO00 /(g g
+ 10.x “(, k
;thsorptiotl ’ oI’ MII.
spcctropl~otomctry
gave tlic following
results:
as dcscribcd above. The organic milttcr in tflc sample was dcstroycd by wet and dry asftitig methods, and anafyscs often sainpl~s it3 each cast g;tv~ the rcsufts stimmariscd in Tabfc IV. For comparison the rcsufts obtained by sp~~tropl~otoxnctri~ analysis of tile cxtritets’” itnd by atotnic absorption spoctrophotomctry of the aqueous phases arc also incfudcd. Dry ashing has often been rcportcd to wusc fosscs by volatilisation or adsorplion. whifo the advantages of wet ashinp arc oftcn lost by contamination from the
A,~ill.ClIi,,l. Arttr. 59
(I 972)
G.L.C.
DETERMINATION
OF NIC-KliL
69
reitgents. 13urkc ~111tiAlbright” found both methods to hc satisfactory. although they rccommcndcd wet ashing for instant teas. The ahovc results shctw overall zigrccmcnt. although ths dry ashing method dots stem COproct~c a wider variation in the results. Blank v;llucs showed thitt no ~~~~t~t~~~i~~i~ti~~~ was produced from the lTilg!L’f’ltS.
The results wcrc chcckcd by the USC of stitndilrd additions to the tea sample hcforc ashing. the resultant solutions being anuiyscd by chromatography of the extracts and by atomic absorption sp’cctrophotomctry of the aqueous phases. Thcsc rcsufts arc shown in Fig. 7. which proves the v~~luc for the nickel concentration to bc 14.0& 1.5 jrg g- ’ and 13.52 1.5 jcg g _ ’ for the two rcspcctivc tcchniyucs. Figure X (13) shows ;t typical ~l~r~tni~t~~r~~ln for the extract from ii sampfc of tea. This chromatogram was ohtaincd by the USC of ;I tcmpcraturc programmc. Figure 8 also shows chromatograms obtoincd under isothermal conditions; it is clear that tcmpcraturc programming improves the resolution of the Ni(T-TFA), peak. while rctaininp the optimal peak shape.
Samples of crude hycjr~~~n~!t~d triglyccridcs ~~nt~~initl~ tracts of nickel wcrc obtained for analysis. and thcsc wcrc mincrafiscd by the dry ashing proccdurc. It was found that combustion of the samples in the furnaoc caused scvcre losses, and so
Amd. Chim. Actu, 59 (1972)
1~. S. I3ARHA’I”I’.
I<. 13f:LCHER.
W.
I. STEPHEN.
.:
r. ;:
cliromalogram Ni(‘l’-TFA)I
of il fill extract. Aniplificr solutiott (5 p,p.m.).
;1ttcnu;ltion
20.
UIIEN
,-,
i ,I
t:ig. 9. GilS of staltd;\rd
I’. C.
:
IO’. (A) 15 111of fat extr:wt
; (13) I .7 pl
the more volatile components of the fkt wcrc rcmovcd by preliminary hatting on the hot-plate. Similarly it wits found that ashinp the sample to tho cxtcnt that all of the carbon was removed also resulted in scvcrc losses. and so the sample was removed from the furnace when a little cat-bon residue rcmaincd. Analysis by gas chromatography according to the usuai procedure gave the results shown in Table V. Once again. the tcmpcraturc programmc was used. Thcsc results again show rcasonablc agrccmcnt with the itldcpcndcnt analysts for the
G.L.C.
I>ETliKMINATION
71
OF NICKEL
samples. and Fig. 9 shows a typical chromatogram for an extract and for an authentic sample of Ni(T-TFA),. The uneven base-lint is simply a cons~‘qucncc of the tcrnpcraturc programmc.
The use of pas-.liyuid chromatogrtuphy offers a sensitive method for the scparntion :tnd dctcrminotion of traces of nickel in a variety of samples. of non-flame cells in atomic absorption A rcccnt rcvicw’” of the applicittions and atomic fluorcscencc spootroscopy lists the limits of dctcction for nickel by various modifications. The sensitivity of the prcscnt method appears to compare very favourably with these various moditicutions and in terms of practicality. the g!as chrotnutographio method is equally convcnicnt. It is hoped that this work contributes in some way to the ultirnatc goal of metal ;tnalysis by pas chromatogr:tphy. which must surely bc the simultaneous determination
of several
metals.
WC arc indcbtccl to Intcrnutional Nickel Ltd. for the provision of the sample of it Brookc Bond frcozc-dried vcndinp tea. to Van den Bcrgh and Jurgens Ltd. for providiIlpthcsamples ofcrudc hydroycnutod fttts.and to the University of 13irmingh~lil~ for the provision of ;S rcscarch grant to R.S.B. SUMMARY
A rapid and scnsitivc mcthorl for the dctcrminution of trncc amounts of nickel hns been developed, in which it volatile nickel chelatu is analyscd by gas--liquid chromatography. The method involves extraction of the itqucous solution of nickel at pf-1 4.5-.S.O with a solution of rnonothiotriflL)oro~l~~tyl~l~~tone in n-hcxanc. tkc USC of a single extract ion giving rccovcrios in cxcoss of 90‘2;,. The extract is washed with sodium hydroxide solution (0.01 M) to destroy residual chelating agent. and the bis(monothiotrifluoroacctylacctonato)nickcl(lI) is dctcrmincd by gas chromatography on a 4-ft. tcflon column packed with 5:‘& silicone gum rubber (E350) on “Universal B” support. The cxtrcmc sensitivity of the clcctron capture detector cnablcs 5. IO- ’ ’ g of niokcl to be dctcctcd. while nickel concentrations down to 0.1 itg ml- ’ have been dctcrmincd in routine analyses. The cffcct of diverse metal ions is examined: the most significant intcrferencc. resulting from the presence of coppcr(l1). iscasily climinatcd by preliminary trcatmcnt ofthcsolution with hydrogen sulphidc. The new method has been applied to the dctcrmination of nickel at the pcrccntagc lcvcl in an alloy, and at tract levels in tea and fat samples. The results show good agrccmcnt with indcpcndcnt analysts for the sumplcs.
Une methode rapide et sensible est propost2e pour ie dosage de traces de nickel ; elle consiste li analyser un chetate volatil dc nickel par chromatographie gaz-liquide. On procede h une extraction ri I’aide d’une solution de monothiofluoroacetylacetone dans len-hexane. ApH 4.5-5.0. On examine I’influcnce de divers rnetaux. L’interference du cuivre(Il)est la plus importante;on l’dlimine facilement par traitement preliminaire And.
C&m
Acta,
59 (1972)
72
R. S. BARRA’I?‘,
I<. IELCXER.
W. I. STliPHEN.
I’. C. UDEN
ii l’hydrogtinc sull’urf. Cettc nouvcllc mQtlradc a 136 appliytlde au dosage du nickel dans WI ttlliagc et au dosrrgc dc traces dc nickd duns dcs &Azantillons de thti et dc mutic”rcs grusscs. %USAMMliNI:ASSUNCi
Es wurdc tine schnelle und cmpfindlichc Mcthodc fiir die Bcstimmung von Spur~n~n~n~cn Nickel entwickclt, bci dcr ein fliichtigcr Nickelchelat durch GasFtiissi~-Cllrctmuto~r~~~h~c analysiert wird. Bci dcr Mcthodc wird Nickel aus w%sriger Lijsung bci plf 4.5-5.0 mit einer L&ung von Monotl~i~tri~uor~~~etyl~~~eton in trHexan cxtruhicrt. wobci mit einer cinziyen Extraktion mehr als 90’,!;, crfasst werden. Der Extrakt wird zur Beseitigung dcs vcrbliebcnen Chelutisicrungsmittcls mit 0.01 N Natronluugc gcwuschcn und das Bis(manothiotrifluoracctylacctonato)-nickcl( I I) durch Gas-Ctlr~mutographie an ciner 4 ft~-~c~l~~ns~ulc bcstimmt. die rnit 5 IsI, Siiicongurnmi (EXO) auf “Universal B”-Triiger gcfUt ist. Die cxtremc Empfindlichkcit dos Etcktroncncinfang-Dctcktors errn6glich) den Nachwcis von 5. IO-‘ ‘I g Nickel, wlihrcnd Nickelkonzcntrationcn bis zu 0.1 pg ml- ’ hcrab bci Routineanulyscn bestitnmt wurden. Dcr Einfuss vcrschicdcncr Mctallioncn wurde untcrsucht. Die grbsstc Stiirung wird durch die Gcgcnwart von Kupfer(iI) vcrursucht: sic kann Icicht durch v~r~~~r~c~~~ndc B~h~!ndl~ln~ der Liisung mit S~hwc~~~w~~sserstoff vcrmicden worden. Die ncuc Mcthrzde wurdc auf die Bestimmung von Niokcl im Prozcntbcrcich in ciner Legicrung und itn Spurcnbcreich in Tee- und Fettprobcn angcwondct. Die Ergebnissc stimmcn mit unabhiingigen Annlyscn der Prohen put iibercin. REFERI3NCES
G.L.C.
I3ETEKMfNATIQN
OF
NICKEL
73
21 p/f i~irlrtc~s trrul rlwir l~c~fc~r~~ritlrrrir~rl. B.D.H. Chemicals Ltd.. Poole. England. 1970. 22 W. c’. FI:RNIXIUS ANI) IS. I<. I3H’I’As’r. in T. MOIU.EK. Itror~gtrtlir~.~~~wr/wsc~.s.Vol. V. McGraw-Hill. York, lY57. p. 105.
Atrtrl.
c-hil?L
Al’lti.
SC)
New
(1977)