[ 9 7]
J.G. Llaurado
Highlights: I De te rminatio n o f me tals in c igare tte smo ke II On-site me rc ury analyze r III Hazardo us gas mo nito ring Enviro nme ntal Manage me nt and He alth
9 / 3 [1 9 9 8 ] 9 6 –9 9
It h a s b een est a blish ed t h a t for d et er m in a t ion of m et a l in a ir sa m p les t h e u se of a q u eou s st a n d a r d s is sa t isfa ct or y. Det ect ion lim it s a ch ieved by u sin g I-GF a t om ic a b sor p t ion sp ect r om et r y a r e id en t ica l t o t h ose ob t a in ed w it h con ven t ion a l a t om ic a b sor p t ion sp ec-t r om eec-t r y. Afec-t er sec-t a n d a r d iza ec-t ion of ec-t h e sy st em , r esu lt s for a sa m p le of a ir ca n b e ob t a in ed in a b ou t 5 m in u t es, h en ce t h e d esign a t ion of q u a si r ea l-t im e for t h is p r oce-d u r e.
T h e elem en t s Cd , Cr, P b a n d Mn w er e d et er -m in ed si-m u lt a n eou sly in la b or a t or y a ir in t h r ee exp er im en t a l sit u a t ion s: p r ior t o sm ok -in g, d u r -in g sm ok -in g a n d 4 h ou r s t h er ea ft er. Ba ck gr ou n d va lu es for P b w er e fr om 8 t o 25n g/ m3a n d in cr ea sed t o 88n g/ m3d u r in g sm ok in g; Cd va lu es r a ised for 8 t o 128 m g/ m3. Fou r h ou r s a ft er sm ok in g, va lu es for Cr, P b a n d Mn h a d r et u r n ed t o b a ck gr ou n d levels, bu t Cd levels r em a in ed t w ice t h e b a ck gr ou n d level.
T h e a u t h or s (Sn ed d on et a l., 1997) con clu d e t h a t t h ese r esu lt s sh ow t h e p ot en t ia l of t h e IGF sy st em con n ect ed t o a n a t om ic a b sor p -t ion sp ec-t r om e-t er for d ir ec-t a n d q u a si r ea l-t im e d el-t er m in a l-t ion of low con cen l-t r a l-t ion s of m et a ls in a er osols a s in ciga r et t e sm ok e. It is h op ed t o ext en d t h is a p p lica t ion t o t h e d et er -m in a t ion of -m et a ls in bu r n in g oil, w h ich is en v ir on m en t a lly of gr ea t sign ifi ca n ce.
II On-site mercury analyzer
Wh en im p r op er ly r elea sed in t o t h e en v ir on -m en t , -m er cu r y is ca u se of ser iou s con cer n . Cu r r en t ly m ost m er cu r y sp ills occu r a lon g n a t u r a l ga s p ip elin es ow in g t o lea k s a n d va n d a lism on m a n om et er s op er a t in g w it h m er -cu r y. In a r ecen t a r t icle by Fou st a n d Gu i (1997) it is p oin t ed ou t t h a t “[c]ost con t a in -m en t d u r in g sit e ch a r a ct er iza t ion is cr it ica l for t h ese sit es b eca u se of t h e la r ge n u m b er of m et er in g sit es a n d t h eir r ela t ively sm a ll size”.
Alt h ou gh t h e sit es con t a in in g m er cu r y r e p r esen t 1-2m3of con t a m in a t ed soil, t h er e a r e t h ou sa n d s of m et er in g sit es; t h er efor e, r a p id fi eld a n a ly sis is con sid er ed a t ech n ica l n ecessit y for t h ese loca t ion s. F u r t h er m or e, t h er e is a la r ge fi n a n cia l im p a ct a ssocia t ed w it h con t a m in a t ed sit es. Sign ifi ca n t ly, a gr ea t p or t ion of t h e cost is r ela t ed t o sit e a ssess-m en t . It sh ou ld b e n ot ed t h a t ext en d ed “d elay s b et w een sa m p le a cq u isit ion a n d a n a ly sis lea d t o lon g, id le p er iod s for p er son -n el a -n d eq u ip m e-n t ”. F ield a -n a ly sis h a s b ee-n d evelop ed a s a p r oced u r e for cost con t a in -m en t .
Alt h ou gh t h er e a r e sever a l t ech n iq u es for in -fi eld d et er m in a t ion of m er cu r y in
en v ir on m en t a l sa m p les, su ch a s X-r ay, fl u o-r escen ce, im m u n oa ssay oo-r va p oo-r a n a ly sis, t h er e exist ser iou s d r aw b a ck s, n a m ely “a la ck of sen sit iv it y, m a t r ix in t er fer en ces, lim it ed r a n ge, lim it a t ion s d u e t o t h e for m s of m er -cu r y, a n d / or t h e u se of h a za r d ou s r ea gen t s”. T h e a u t h or s r e p or t t h a t in t h eir la b or a t or y a t Gen er a l E lect r ic Co., Sch en ect a dy, N ew Yor k t h ey h ave d evelop ed a m et h od b a sed on t h e q u ick select ive ext r a ct ion of m er cu r y fr om a solid sa m p le, solu b iliza t ion a n d d et er m in a -t ion by elec-t r och em ica l m ea n s. T h e m e-t h od h a s b een sh ow n t o h ave ver y good cor r ela t ion w it h t h e “st a n d a r d la b or a t or y m et h od of sa m p le lea ch in g w it h st r on g, h ot a cid fol-low ed by a t om ic a b sor p t ion a n a ly sis of t h e lea ch a n t ”.
T h e m od u s op era n d iin volves a d d in g t o 1g of soil sa m p le in a p r essu r e t u b e 10m l of a n ext r a ct in g solu t ion m a d e of 1M KI a n d 0.5M I2. T h e t u b e is p la ced in a w a t er b oilin g b a t h for 30 m in . It sh ou ld b e em p h a sized t h a t t h e a q u eou s solu t ion of p ot a ssiu m iod id e (solu b i-lizin g a gen t ) a n d iod in e (oxid a n t ) ser ves a s ext r a ct in g m ed iu m . T h e u se of a h igh t em p er -a t u r e -a n d h igh er con cen t r -a t ion of oxid -a n t a llow s for t h e com p let e m er cu r y r em ova l in a m in im u m t im e fr om sa m p les in w h ich m er -cu r y exist s a s a n elem en t or com b in ed t o oxygen in su lfu r, t h u s:
H g + I2+ 2KI →K2H gI4
H gO + H2O + 4KI →K2H gI4+ 2KOH H gS + I2+ 2KI →K2H gI4+ S .
In fa ct , t h is ext r a ct ion m ixt u r e h a s b een u sed a s a d econ t a m in a n t for m er cu r y con t a in in g solid s. N ot e t h a t in a b ove ch em ica l r ea ct ion s n o a cid s or b a ses a r e n eed ed for t h e ext r a c-t ion of m er cu r y fr om c-t h e soil; c-t h u s “c-t h e ext r a ct ion p r ocess ca n b e con d u ct ed w it h ou t t h e u se of h a za r d ou s cor r osive a cid s”.
Aft er ext r a ct ion a n d coolin g, t h e fi lt r a t e is r ed issolved in a v ia l w it h a sp ecia l ca p con -t a in in g a Au d isk a s wor k in g elec-t r od e; a P -t w ir e a s a u xilia r y elect r od e; a n d a Ag/ AgI r efer en ce elect r od e. T h e elect r od es a r e con -n ect ed t o a com p u t er -co-n t r olled p ot e-n t iost a t for a n od ic st r ip p in g volt a m et r y (ASV). T h e r esu lt in g cu r r en t is t r a n sla t ed in t o m er cu r y con cen t r a t ion s by com p a r ison w it h st a n -d a r -d s. For r ea ssu r a n ce t h e r esi-d u a l p r o-d u ct s of t h e iod in e/ iod id e ext r a ct ion w er e r ea n a -ly zed by st a n d a r d t ech n iq u es w it h ver y good a gr eem en t .
[ 9 8]
J.G. Llaurado
Highlights: I De te rminatio n o f me tals in c igare tte smo ke II On-site me rc ury analyze r III Hazardo us gas mo nito ring Enviro nme ntal Manage me nt and He alth
9 / 3 [1 9 9 8 ] 9 6 –9 9
con t a m in a t ed soils r evea l v isible b ea d s of elem en t a l m er cu r y.
In t h e p a st , volt a m et r ic m et h od s h ave b een cr it icized b eca u se of a la ck of r e p r od u cib ilt y ow in g t o “fou lin g of t h e elect r od e su r fa ces”. H ow ever, in t h is ASV m et h od , a m on olayer of iod in e a t om s is a b sor b ed on t o t h e gold su r -fa ce a n d p r ot ect s t h is elect r od e fr om con t a m i-n a t ioi-n .
T h e ASV m et h od ca n n ot on ly b e u sed q u a n t it a t ively, bu t a lso a s scr een in g for m er -cu r y in soil.
Solu t ion s con t a in in g m er cu r y u sed d u r in g a n a ly ses ca n b e t r ea t ed w it h ir on fi lin gs t o r em ove h a za r d ou s con st it u en t s; m a n y com -p ou n d s in solu t ion s -p r eci-p it a t e a s elem en t a l m er cu r y a n d iod in e is r en d er ed t o h a r m less iod id e a ccor d in g t o t h e follow in g r ea ct ion s:
K2H gI4+ Fe →H g0+ 2KI + Fe 2 I2+ Fe →FeI2
T h e a u t h or s st a t e t h a t t h e ASV m et h od y ield s r esu lt s in t h e r a n ge of 1 t o 10,000p p m m er cu r y in soil sa m p les in less t h a n a n h ou r.
III Hazardous gas monitoring
T h e Am er ica n Con fer en ce of Gover n m en t a l In d u st r ia l H ygien ist s h a s id en t ifi ed sever a l ch em ica ls u sed in sem icon d u ct or fa b r ica t ion a s h ea lt h h a za r d s a n d est a blish ed a t h r esh old lim it va lu e (TLV) for ea ch su b st a n ce. T h e TLV is d efi n ed a s a n 8h t im e w eigh t ed aver -a ge -a ir b or n e con cen t r -a t ion of -a su b st -a n ce t o w h ich wor k er s m ay b e r e p ea t ed ly exp osed ever y wor k in g d ay w it h ou t a dver se effect s. Ch em ica ls w h ich a r e p ot en t ia lly fl a m m a ble a r e ca t e gor ized in t h e r a n ge of t h eir low er fl a m m a ble lim it (LF L); t h ose w h ich a r e p ot en -t ia lly exp losive a r e cla ssifi ed by -t h eir low er exp losive lim it (LE L). Accor d in g t o a n a r t icle by Scot t (1996) ch em ica ls ca n b e ca t e gor ized by t h eir TLV a n d LF L/ LE L levels in t h is w ay :
• TLVs a t p p b levels a r e for t oxic ga ses (m et a l h yd r id es);
• TLVs a t p p m levels a r e for a cid s, ga ses, solven t s a n d oxid izer s;
• LF L a n d LE L m ay r ea ch 100 p er cen t a t r oom t em p er a t u r es for t h ose ch em ica ls w h ich h ave a t en d en cy t o bu r n or exp lod e. For h ea lt h a n d sa fet y r ea son s t h r ee a n a ly t ica l t ech n iq u es a r e u sed in clea n r oom s t o m on it or ch em ica ls a ccor d in g t o t h e a b ove ca t e gor ies: 1 Fou r ier t r a n sfor m in fr a r ed sp ect r oscopy
for m on it or in g su b st a n ces in t h e p p m r a n ges;
2 m olecu la r em ission sp ect r oscopy for d et ect in g ga ses a t p p b ;
3 a cou st ic sen sin g t ech n iq u e for d et ect in g h yd r ogen ga s in t h e LE L r a n ge.
Fou r ier tra n sfor m in fra red sp ectr oscop y
(F TIR) is b a sed on t h e fa ct t h a t ea ch ch em ica l su b st a n ce a b sor b s r a d ia t ion in a ch a r a ct er is-t ic p a is-t is-t er n ; “a gr a p h of a b sor p is-t ion ver su s w avelen gt h (t h e sp ect r u m ) m ay b e u sed t o id en t ify com p on en t s in a ga s m ixt u r e by t h eir com p lex sp ect r a ”. Sin ce t h e q u a n t it y of ligh t a b sor b ed is p r op or t ion a l t o t h e con cen t r a t ion of ea ch com p on en t , t h e t ech n iq u e ca n a lso b e u sed for q u a n t it a t ive p u r p oses. Ap p lica t ion of t h e Fou r ier t r a n sfor m con fer s a dva n t a ges t o in fr a r ed m et h od s b eca u se “t h e sign a l-t o-n oise r a t ios a r e h igh er, t h e r esolu t ion is b et t er, t h e w avelen gt h a ccu r a cy is su p er ior, a n d d a t a a cq u isit ion t im es a r e sign ifi ca n t ly sh or t er ”.
Wit h F TIR low con cen t r a t ion s of va p or p h a se ch em ica ls, in clu d in g a ll or ga n ic com -p ou n d s, ca n b e d et ect ed . Com -p let e s-p ect r a ca n b e gen er a t ed t o fi n d su sp ect ed lea k s a n d / or u n k n ow n od or s em a n a t in g fr om loca -t ion s su ch a s exh a u s-t d u c-t s, ga s ca b in e-t s, p la n t em ission s, wor k er s’/ b r ea t h in g a r ea s, et c. An in t e gr a l p a r t of t h e op er a t ion con sist s of sh u t -off con t r ol a n d t h or ou gh com p ila t ion of in cid en t s a n d a la r m s. Ap p r op r ia t e soft w a r e a u t om a t ica lly t r a n sfor m s t h e in for m a -t ion in -t h e F TIR m a ch in e in -t o con cen -t r a -t ion s of ch em ica ls by em p loy in g r efer en ce sp ect r a .
T h e m on it or in g d ev ice m ay in clu d e 12 ga ses p er loca t ion a n d r eq u ir es on ly a b ou t 25s “for sa m p lin g, a n a ly sis, a n d d a t a p r esen t a -t ion ”. T h e F TIR -t ech n iq u e ca n d e-t ec-t a n y su b st a n ce a t low p p m in t h e va p or p h a se exce p t a t om ic a n d d ia t om ic ga ses (H e, H2, Cl2, O2). It is u sefu l for m on it or in g m ost com -p r essed ga ses, a cid s a n d solven t va -p or s in sem icon d u ct or fa cilit ies.
M olecu la r em ission sp ectr oscop y(ME S) m on it or s t oxic ga ses in t h e p p b r a n ge, i.e. a t con cen t r a t ion w ell b elow t h e est a blish ed TLV. T h is t ech n iq u e is fr ee fr om “cr oss-sen sit iv it y t o solven t s, a cid ga ses, a n d ot h er com m on ch em ica ls u sed in sem icon d u ct or fa b r ica t ion p r ocesses”.
For ME S a h yd r ogen fl a m e p h ot om et r ic d et ect or is em p loyed w h ich u n in t er r u p t ed ly h a n d les t oxic su b st a n ces, n a m ely m et a l h yd r id es. Wh en t h e t oxic ch em ica l in t h e sa m p le of a ir p en et r a t es t h e fl a m e cor on a , t h e ligh t em ission s p a ss t h r ou gh op t ica l fi lt er s a n d a r e con ver t ed t o elect r on ic sign a ls. An in d u st r ia l com p u t er w it h m u lt it a sk in g soft -w a r e is a t t a ch ed t o t h e ME S d et ect or, -w h ich a llow s for ch eck in g t h e p n eu m a t ic, elect r ica l a n d sa m p lin g com p on en t s; in a d d it ion , t h e com p u t er is con n ect ed t o a bu ild in g’s con -t r ols, gu a r d r oom s a n d em er gen cy s-t a -t ion s.
An ME S sy st em ca n seq u en t ia lly m on it or 20 loca t ion s a sp ir a t in g a ir sa m p les t h r ou gh t u b es.
[ 9 9]
J.G. Llaurado
Highlights: I De te rminatio n o f me tals in c igare tte smo ke II On-site me rc ury analyze r III Hazardo us gas mo nito ring Enviro nme ntal Manage me nt and He alth
9 / 3 [1 9 9 8 ] 9 6 –9 9
low a s 100p p m . Most in st r u m en t s h ave a t u b e w h ich sa m p les a ir con t in u ou sly fl ow in g a n d a n ot h er t u b e fi lled w it h a r efer en ce sa m p le a n d sea led . Sou n d is p r od u ced a n d t im ed by elect r on ic cou n t er s a s it t r avels t h r ou gh t h e a ir in ea ch t u b e. By exp r essin g r esu lt s a s r a t ios of clock cou n t s, sp u r iou s r esu lt s d u e t o d r ift a r e ca n celed .
An y level of h yd r ogen – even a low on e – in t h e sa m p led a ir m a r k ed ly ch a n ges t h e “t im e-of-fl igh t of a cou st ic w aves, m a k in g it ea sy t o d et ect h yd r ogen ”. H eliu m ca u ses a sim ila r bu t sm a ller ch a n ge t o t h e a cou st ic w aves. Ma n y t im es it is n ecessa r y t o d ist in gu ish b et w een h yd r ogen a n d h eliu m . T h is is a ch ieved by m ea n s of a p a lla d iu m ca t a ly st t h a t r ea d ily r em oves h yd r ogen , bu t n ot h eliu m a n d ot h er ga ses. H it h er t o, m on it or in g for h yd r ogen h a d b een ca r r ied ou t by ga s d et ect or s of t h e ca t a ly t ic or elect r och em ica l t y p e, bu t ga s d et ect or s h ave t o b e ch eck ed ou t a n d ca lib r a t ed p er iod ica lly w it h t h e con se-q u en t u se of m a n p ow er. T h ey a r e a lso p r on e t o gen er a t in g fa lse a la r m s a s t h ey ca n n ot d ist in gu ish a va r iet y of ch em ica ls fr om h yd r ogen . On t h e ot h er h a n d , a cou st ic sy s-t em s h ave a bu ils-t -in in s-t er n a l ch eck , n ever r eq u ir e ca lib r a t ion a n d a r e fr ee fr om in t er fer -en ces.
Comment
T h e F TIR m et h od ology id en t ifi es ga ses in a ir sa m p les by t h eir in fr a r ed a b sor p t ion sp ect r u m w h ich is lik e a fi n ger p r in ect id en ect ifi ca -t ion . Tech n iq u es u sin g ME S a n d a cou s-t ic d et ect ion h ave n ot t h e in t r in sic fi n ger -p r in t
id en t ifi ca t ion ; h ow ever, b ot h a p p r oa ch es p ossess a h igh d e gr ee of ch em ica l sp ecifi cit y. T h e ME S em p loy s t wo n a r r ow b a n d p a ss op t i-ca l fi lt er s, on e cen t er ed on t h e p ea k ligh t zon e of t oxic ga s em ission s a n d t h e ot h er on t h e p ea k ligh t zon e of in t er fer in g ch em ica ls. In t h is w ay ME S ca n com p en sa t e for in t er fer -en ces.
T h e a cou st ic d et ect or is “in h er en t ly sp e-cifi c t o ga ses h av in g ver y low m olecu la r w eigh t s, su ch a s h yd r ogen a n d h eliu m , b eca u se t h e t im e-of-fl igh t of t h e a cou st ic w ave b ecom es fa st er t h e m or e t h ese ga ses m ix w it h a ir ”. It is for t u n a t e t h a t fa st , sim p le, r elia ble a n d sen sit ive m et h od s of m on it or in g w it h in cr ea sed sp ecifi cit y for “a ir q u a lit y, t oxic ga ses, a n d exp losive ga ses, su ch a s h yd r ogen , [a r e] b ecom in g a r ea lit y … Cen t r a lized m on i-t or in g u i-t ilizin g p ow er fu l a n a ly i-t ica l
t ech n iq u es is u ser fr ien d ly a n d ca n b e op er -a t ed by n on -t ech n ic-a l p er son n el”.
References
Fou st , D.F. a n d Gu i, J .Y. (1997), “Ra p id m er cu r y a n a ly sis for t h e fi eld ”, A m er ica n E n v ir on m en -ta l L ab ora tor y, Vol. 9 N o. 4, Ap r il, p p. 17-18. Scot t , W.C. (1996), “T h r ee a n a ly t ica l t ech n iq u es
for a ir q u a lit y a n d h a za r d ou s ga s m on it or in g in clea n r oom s”, Clea n R oom s, Vol. 10 N o. 12, Decem b er, p p. 32-6.
