MEASUREMENT OF TOTAL NICKEL IN BODY

Pure & Appl. Chem., Vol. 66, No. 2, pp. 357-372, 1994. Printed in Great Britain. @ 1994 IUPAC

INTERNATIONAL UNION OF PURE AND APPLIED CHEMISTRY

CLINICAL CHEMISTRY DIVISION COMMISSION ON TOXICOLOGY *

Working Party on Nickel Reference Levels?

MEASUREMENT OF TOTAL NICKEL IN BODY FLUIDS

ELECTROTHERMAL ATOMIC ABSORPTION METHODS AND SOURCES OF PREANALYTICAL VARIATION

(Technical Report)

Prepared for publication by DOUGLAS M. TEMPLETON

Department of Clinical Biochemistry, University of Toronto, 100 College St., Toronto, Canada M5G 1L5

*Membership of the Commission during the period (1989-93) when this report was prepared was as follows: Chairman: 1989-91 P. Grandjean (Denmark); 1991-93 Rita Cornelis (Belgium); Secretary: 1989-91 R. Cornelis (Belgium); 1991-93 B. Henizow (Germany); Titular Members: S . S . Brown (1989-91; UK); J. H. Duffus (1991-93; UK); R. F. M. Herber (1989-93; Netherlands); M. Jakubowski (1989-93; Poland); Jytte Molin Christensen (1991-93; Denmark); E. Nieboer (1989-91; Canada); D. M. Templeton (1991-93; Canada); C. Veillon (1989-91; USA); Associate Members: A. Cavalleri (1989-93; Italy); Sheila Dawling (1991-93; UK); AndrCe Lamberty (1989-93; Belgium); S. RendiC (1989-91; Yugoslavia); D. Rutherford (1991-93; Australia); Y. Thomassen (1991-93; Norway); Marie Vahter (1991-93; Sweden); C. Veillon (1991-93; USA); National Representatives: 0. August0 (1991-93; Brazil); I. DCsi (1989-93; Hungary); P. K. Ray (1989-93; India); W. King (1991-93; Ireland); W. A. Temple (1989-93; New Zealand); M. Repetto Jimenez (1989-93; Spain); Zeliha Imre (1989-93; Turkey); Repre- sentative of IUPHAR Section on Toxicology: J. G. Salway (1989-91; USA); Representative of ZUTOX P. Grandjean (1989-93; Denmark).

?Membership of the Working Party: Chairman: E. Nieboer (Canada); Members: R. Cornelis (Belgium); D. Dewally (France); F. W. Sunderman, Jr. (USA); D. M. Templeton (Canada); 0. Vesterberg (Sweden).

Republication of this report is permitted without the need for formal IUPAC permission on condition that an acknowledgement, with full reference together with IUPAC copyright symbol (0 1994 IUPAC), is printed. Publication of a translation into another language is subject to the additional condition of prior approval from the relevant IUPAC National Adhering Organization.

Measurement of total nickel in body fluids: Electrothermal atomic absorption methods and sources of preanalytic variation (Technical Report)

Synopsis

Before attempting to establish reference concentrations of Ni in blood serum or plasma, a laboratory must be working comfortably at the 2 nmol/L level. To achieve this, scrupulous acid-leaching of all materials that come into contact with the sample is essential, and blood collection with non-metalic systems i s advisable. A particle-free environment (clean-air laboratory) seems necessary. Values of Ni in serum above 1.7 to 5.1 nmol/L are suspect; values in the urine of people without occupational or other unusual environmental exposures are an order of magnitude higher. For reported concentrations to be meaningful, the reference population must be thoroughly described in terms of age, sex, place of residence, occupation, diet, alcohol and tobacco use, medications and medical history, as all such factors may influence the actual concentrations of Ni. Sampling procedures must be standardized (for instance for time of day, season, posture of the person, etc.) and reported. Storage, if necessary, should minimize opportunities for sample adulteration, and these must be evaluated empirically. Preparation of samples should also minimize processing; acidification or protein precipitation with ultrapure nitric acid are adequate for clear body fluids. Analysis by ET-AAS with Zeeman correction is the most useful approach currently available.

1. INTRODUCTION

Exposure to Ni is of occupational significance worldwide, occurring not only in those involved in Ni mining, smelting and refining, but also in such diverse settings as the petroleum and electronics industries. Nickel is ubiquitous in our environment; indeed, exposure of the general population through jewelry, coinage and dental alloys is well documented as a frequent cause of contact dermatitis [I, 21, and oral exposure can be greatly increased by leaching of Ni from plumbing fixtures and kitchen utensils. The International Agency for Research on Cancer (IARC) has recently concluded that “There is sufficient evidence in humans for the carcinogenicity of nickel sulfate. ... Nickel compounds are carcinogenic to humans (Group 1) [whereas] Metallic nickel is possibly carcinogenic to humans (Group 2B)” [ 3 1 . Nevertheless, exposure from natural sources is unavoidable.

There is also some evidence that Ni may be essential for human beings, as it is for numerous species of plants and lower animals t 4 1 . Therefore it is of the utmost importance to measure concentrations of Ni in human body fluids, both in order to understand the natural biology of this element and as a reference point for monitoring undue exposures. It is a goal of the IUPAC Commission on Toxicology to recommend reference substance concentrations for Ni in human blood serum or plasma, whole blood, and urine. At present, the accuracy of all published values remains in some doubt, and all but a few must clearly be rejected. The aims

358

Measurement of total nickel in body fluids 359

of t h i s report a r e :

i) t o review t h e recent l i t e r a t u r e i n order t o determine whether an approximate range of N i concent ra t ions i n body f l u i d s can be recommended a t t h i s time;

ii) t o suggest a l e v e l of accuracy t h a t any laboratory must achieve before it can se r ious ly con t r ibu te t o t h e e f f o r t of e s t a b l i s h i n g reference ranges f o r N i i n serum o r plasma;

iii) t o recommend condi t ions of sampling and s to rage t h a t a r e necessary before any ana ly t i ca l method with adequate s e n s i t i v i t y can be used t o e s t a b l i s h meaningful values i n a s p e c i f i e d re ference population; and

iv ) t o descr ibe current methods of measuring concentrations of N i b y e lectrothermal atomic absorption spectrometry (ET-AAS) . A companion document from t h i s Commission w i l l consider sampling c r i t e r i a f o r t r a c e elements i n general . T h i s repor t w i l l dea l with sampling c o n d i t i o n s s p e c i f i c f o r N i . Because s t a t i s t i c a l cons idera t ions f o r sampling a r e not s p e c i f i c f o r N i they a r e not d i scussed h e r e . Some gene ra l a s p e c t s of sample s t o r a g e a r e discussed, again with reference t o N i . Concluding t h a t ET-AAS i s the bes t candidate reference method f o r N i t w e a l s o review c u r r e n t methods of sample preparat ion f o r ana lys i s of b io log ica l f l u i d s f o r N i by t h i s technique.

Use of substance concent ra t ions f o r r epor t ing N i should be encouraged. Nevertheless, w i t h r a r e exceptions, ana lys t s continue t o report mass concentrations of N i i n body f l u i d s i n pg/L. Here we w i l l r e t a i n t h i s l e s s preferable uni t when quoting au thors ' o r i g i n a l data, and include t h e conversion t o molar u n i t s i n parentheses based on an atomic mass of N i of 58.69. A s o l u t i o n w i t h a mass concentrat ion of N i of 1 . 0 pg/L has a substance concentrat ion of 1 7 . 0 nmol/L.

2.

Over t h e pas t decade, i n common w i t h a number of o the r t r a c e elements, t h e t r e n d has been a progress ive lowering of repor ted concentrations of N i . T h u s , the chronology revea ls new record lows f o r t h e serum/plasma value i n pg/L (nmol/L) being set a s follows (mean f s . d . [year] - see Table 1) : 1 .3 f 0.37 ( 2 2 f 6) [1983], 0 . 4 6 f 0 . 2 6 (7 .8 f 4 . 4 ) [1984], 0 . 1 4 f 0 . 0 9 ( 2 . 4 f 1.5) [1989]. W e can conclude a t t h e ou t se t t h a t t he usual range of N i concentrat ion i n serum i s l e s s than 2 0 nmol/L i n heal thy people with no h i s t o r y of excess ive exposure, and t h a t e a r l i e r h i g h e r va lues were a consequence of sample contaminat ion , i nadequa te a n a l y t i c a l s e n s i t i v i t y , o r both. So, only the l i terature from 1983 onward need be ser ious ly considered. We cannot now s t a t e a value of N i i n body f l u i d s with much c e r t a i n t y . Examination of Table 1 suggests t h a t t h e l e v e l of s e r u m N i i s i n t h e range of 1 . 7 t o 3 .4 nmol/L. Concentrations of N i i n u r ine have been measured c o n s i s t e n t l y a t more than 17 nmol/L and therefore a r e probably an order of magnitude higher than i n serum. Intermediate values can be expected i n blood. Before a l a b o r a t o r y can c o n t r i b u t e t o t h e goa l of measuring concen t r a t ions of N i i n blood serum c o l l e c t e d from a chosen re ference populat ion, i t mus t work a t t h e u l t r a t r a c e l e v e l of 2 nmol/L and below. The accurate measurement of N i i n blood and ur ine should present less d i f f i c u l t y f o r ana lys t s who s u c c e s s f u l l y meet t he challenge of serum ana lys i s . T h i s repor t considers approaches t o sample handling t h a t w i l l help reduce the measured concentration i n a zero reference (method blank) f o r N i t o one where i t s accurate measurement i n serum i s f eas ib l e . I t a l so reviews f ac to r s t h a t m u s t be taken i n t o considerat ion when a reference population i s chosen fo r determining a reference value fo r N i .

Ni CONCENTRATIONS IN BODY FLUIDS

Tabl

e 1.

S

elec

ted

stud

ies

of n

icke

l con

cent

ratio

ns in

bod

y flu

ids

w

Q)

0

NS

+ +

+

+ (ne

edle

NS) NS

NS

Examined m

ater

ials

& so

luti

m

forc

onta

min

atio

n

Ni-DMG extraction in

MB

K

r51

(S)

95 f

20

10

(P) 2

2 f

6.3

(B) 4

1 f

8.5

20 (H

x, a

lcoh

ol,

Tob..

Rx.

161

19.4

f 5.4

O

ccup

.)

NS

+ +

- (3

A

mm

onia

buffi

x, D

MG

(B

) 24.0

f 6

.3 9

0 39

.1 f9

.9

9 (S

aliv

a) 42

.7 f

19.0

5

m

39 (S).

30 (B

) W. To

b., O

ccup

.) (S) 7

.8 f

4.4

(B)

21.4

f 5.

6 t81

+

+ +

- (?I

Dep

rot&

ized

sam

ples

Th

orou

gh do

cum

enta

tion o

f ap

para

tus &

solutions

Assessed c

onfo

undi

ng fa

ctor

s - ti

me o

f ser

um se

para

tiop.

sex. ex

erci

se, p

ost-p

rand

~al

& d

id

fluct

uatio

n

undi

gest

edse

nrm

mix

edw

ith

coat

amin

atio

n in

sam

plin

g devices.

fito

n X

-100

, AS

S~

SS

C~

cont

aine

rs. SS n

eedl

es

+ + PI

(S) 4

.8 f

4.1

(B)

5.8 f

4.8

t N

S +

(S) (

med

ian 1

7)

(40

- 51)

+(

SSne

edle

) +

+ +

0

z d x 0 E 0 <

18

10

10

6 30 (f

astin

g)

20

NS

NS

+ +

+ +

-@ro

nase

) -

+ +

+ -(s

onica

tion)

-

NS

+ +

+ +

NS

NS

NS

+(SS

need

le

+ +

+ vs

. teflon

cann

ula)

+ + (

by re

f.)

+ (by

ref.)

+

(by

ref.)

- c

?)

(S) 1

28 f

53

(S) 4

.25

f 1.7

0 14

f 8.5

Serum

dilu

ted with H

N03

/Tri

ton

X-1

00 fo

r dire

ct an

alys

is

(S) 1

1 f 6.

0

(S) 9

5 f

14

(S) 7

(3 - 9

) D

epro

tein

ized

senu

n; c

ompa

red

nd

e vs

cann

ulae

, ope

n vs

. clo

sed

COUe

ctioa

Deproturuzcdsenun

..

43 (Hospital

wo*

m)

(S)3

f3

(v) 2

5 f

25 m

ol

(S) 2

.4 f

1.5

(mea

n f 2

s.d)

lg -

Cle

an m

om. S

aum

:HN

03/T

riton

Mat

aiab

cm

taxk

g sa

mpl

e acid

le

ache

d, N

eedl

e blo

od ri

nsed

contamination c

ontro

l discussed

X-1

00 3:

1; m

ultip

le in

jcctim

38

(Phy

sica

l &lab

work;

fasti

ng)

+(SS

necd

le)

+ +

+ +

Tabl

e 7

(co

ntd

.)

+ i

+ (S) 2

0 f

1.3

385(

Dem

ogra

phie

i

Mdt

iele

mm

stud

s sp

ecifi

cs

(B) 3

9 f

2.7

36

excl

usio

n fo

r illn

ess.

for N

i not

giv

en.

(v)

15 f 1

.9 87

8 Rx. T

ob..

phys

iol.

stre

ss)

[ml

(S) 6

32 f 1

39

20

NS

+ i

Prea

ncen

mtio

n by

che

latio

n

Not

es to

Tab

le 1

ques

tionn

aire

; r1

91

01

Met

hods

N

otes

RC

fCXXN

X Q

uality

R

efer

ence

m

ater

ials

Ran

Pe

151

GF-AAS

Stan

dard

addi

tions

161

GF-

AA

S he

cisi

on &

reco

very

repo

rted

DP-

volta

mm

. R

eage

nt b

lank

s rep

olte

d St

anda

rd ad

ditio

ns.

+ + + + i

i

- (Liv

er)

+ + - (3

ZGF-

AA

S

Z-G

F-A

AS

GF-

AA

S

GF-AAS

Z-GF-AAS

Z-GF-AAS

Flam

e AAS

GF-AAS

ZGF-

AAS

ZGF-

AA

S

Z-G

F-AA

S

(NS)

NAA

Rep

eata

bilit

y & m

er

y repo

rted;

Interference by o

ther

met

als assessed

Rep

eata

bilit

y&rc

cova

yrep

ortc

d

Stan

dard

additions; m

atrix

mat

chin

g unsuccessful. used s

erum

-bas

ed st

anda

rds.

Prec

ision

. recovery &

long

term

repeatability reported.

Sero

nom

, Lan

onor

m - i

n ag

reem

ent; Seronorm ur

ine -

low

Sero

norm

- in

agre

emen

t; NEl

S bo

vine

seru

m - d

eter

min

ario

n too

low

Com

paris

on w

ith W

AC

refe

renc

e method with

AD

PC ex

tract

ion.

Sero

nonn

- in

agre

emen

t

Doc

umen

t full m

etho

ds de

velo

pmen

t.

Mdt

iele

men

t ana

lyse

s from 3

labs u

sing

Fla

me-

, GF-

. and

Z-GF-AAS.

IB-A

ES and

NA

A.

Whi

ch m

etho

ds us

ed fo

r Ni are n

ot discussed.

I+

0

P

*Val

ues an

my

re

pone

d by

auth

ors i

n m

ass c

on

me

on

. T

best

hav

e been c

onve

ned to

subs

tanc

e cm

cuud

on based

on an

atom

ic m

ass o

f Ni

of 5

8.69

. t S - b

lood

seru

m. P - b

lood

pla

sma,

B - w

hole

blo

od. U - u

rine

* Hx - m

edica

l history. Rx -

med

icat

ions

. Tob

. - tob

acco

use, O

ccup

. - oc

cupa

tion

1 (+) a

pare

ntly

adeq

uate

, (-)

poss

ibly

inad

equa

te. N

S - n

ot sp

ecifi

ed. SS

- stai

nles

s ste

el

W 9

362 COMMISSION ON TOXICOLOGY

3. PREANALYTIC SOURCES OF VARIATION

I t i s not y e t known whether N i i s e s s e n t i a l f o r human h e a l t h , o r t h e l i m i t s w i th in which i t s concen t r a t ion i n blood plasma may be r e g u l a t e d i n c h r o n i c exposure. Th i s l e a v e s open t h e q u e s t i o n of whether there i s an expected c o n c e n t r a t i o n t h a t i s h o m e o s t a t i c a l l y r egu la t ed , and t h e e x t e n t t o which concen t r a t ion of N i i s determined by i n d i v i d u a l c i r cums tances . However, ample evidence i s p r e s e n t e d below t o demonstrate t h a t i nc reased N i i n t a k e occur s f o r a v a r i e t y of r easons , and can i n c r e a s e c o n c e n t r a t i o n s i n b lood and u r i n e . Thus a l l f a c t o r s p o t e n t i a l l y a f f e c t i n g N i e x p o s u r e s h o u l d i n p r i n c i p l e be documented f o r t h e r e f e r e n c e popu la t ion . Furthermore, f a c t o r s such as age , s e x and g e n e r a l h e a l t h may have p o o r l y unde r s tood e f f e c t s on N i c o n c e n t r a t i o n s , and m u s t be c a r e f u l l y r epor t ed .

Age and sex A p a r t f rom p o s s i b l e d i f f e r e n c e s due t o p r e g n a n c y and

p a r t u r i t i o n (see below) , sex d i f f e r e n c e s i n serum N i c o n c e n t r a t i o n have no t been demonstrated. Hohnadel e t a l . [211 r e p o r t e d h i g h e r c o n c e n t r a t i o n s of N i i n sweat from females [131 f 65 pg/L (2.23 f 1.11 pmol/L); n=15] than from males [52 f 36 ( 0 . 8 9 f 0 . 6 1 ) ; n=331 as measured by flame atomic a b s o r p t i o n spec t romet ry . However, t h e s e va lues are c l ea r ly t o o high, and were compromised by t h e t echn iques a v a i l a b l e a t t h e t i m e ; N i c o n c e n t r a t i o n s i n sweat o f 1 0 h e a l t h y people ( sex not s p e c i f i e d ) has subsequent ly been r e p o r t e d t o be 4 . 4 f 2.5 pg/L (75 f 37 nmol/L) [ 1 2 ] . Furthermore, t h e r e i s no r e l i ab le in fo rma t ion on age e f f e c t s , p a r t i c u l a r l y i n t h e extreme p a e d i a t r i c and g e r i a t r i c p o p u l a t i o n s . No s i g n i f i c a n t d i f f e r e n c e s i n N i i n serum o r blood of h e a l t h y a d u l t s were found between groups over and under 40 y e a r s of age [ 9 1 . U n t i l t h e s e f a c t o r s are i n v e s t i g a t e d , r e f e r e n c e p o p u l a t i o n s should be well c h a r a c t e r i z e d wi th r e s p e c t t o t h e i r age and sex d i s t r i b u t i o n .

Geographic location A number of f a c t o r s i n the human environment determine exposure

t o N i , and t h e s e must be r e p o r t e d i n any pu rpor t ed r e f e r e n c e s t u d y . N i i n s o i l v a r i e s between about 0 . 0 9 and 9 pmol/g depending on g e o l o g i c a l f a c t o r s , w h i l e v a r i o u s u n p o l l u t e d water s u p p l i e s g e n e r a l l y have N i c o n c e n t r a t i o n s i n t h e range 0.02 t o 0 .85 pmol/L [ 2 2 ] . Water s u p p l i e s i n i n d u s t r i a l l y p o l l u t e d areas can have more t h a n 20 pmol/L. The l a t t e r can i n c r e a s e t o t h e mg/L r ange i n waters. I n t h e U.S.A., r u r a l a i r t y p i c a l l y c o n t a i n s N i a t a c o n c e n t r a t i o n of 0 . 1 0 nmol/m3, wh i l e i n urban a i r t h e c o n c e n t r a t i o n i s about 0 .43 nmol/m3 [23 , 2 4 1 . V a l u e s u p t o 2 . 9 nmol/m3 occur i n some i n d u s t r i a l c e n t e r s [ 2 4 ] . Hopfer e t a l . [17] have compared serum N i c o n c e n t r a t i o n s i n h e a l t h y h o s p i t a l workers i n H a r t f o r d , CT, U.S.A. (n=43) and Sudbury, Ont. , Canada (n=22) . T h e Sudbury cohort l i v e s i n a community of n i c k e l m i n e s and smelters, and i s exposed t o h ighe r concen t r a t ions of N i i n t a p water and s o i l . These people had h ighe r c o n c e n t r a t i o n s of N i i n t h e i r se rum [ 0 . 6 f 0.3 pg/L ( 1 0 f 5 nmol/L) i n Sudbury versus 0 . 2 f 0 . 2 pg/L ( 3 . 4 f 3.4 nmol/L) i n Hartford, p C 0.051.

Occupation Because of t h e h i g h worldwide p r o d u c t i o n and u s e of N i

compounds, occupa t iona l exposure i s widespread. Highest exposures occur i n N i r e f i n i n g and e l e c t r o p l a t i n g , arc welding and Ni-Cd s t o r a g e b a t t e r y p roduc t ion . I n d u s t r i a l exposure a l s o o c c u r s from t h e product ion of N i a l l o y s , i t s use as a c a t a l y s t f o r hydrogenation of o rgan ic compounds, as a f l u i d c a t a l y s t i n t h e petroleum i n d u s t r y , as a pigment f o r ceramics and g l a s s e s , as a mordant f o r dyeing c l o t h , and i n e l e c t r o n i c components and magnetic t a p e s [23, 2 4 1 . A s tudy of 8 workers exposed t o N i compounds i n t h e workplace r evea led a N i c o n c e n t r a t i o n o f 1 1 . 5 pmol/m3 i n a i r , whereas 103 we lde r s b r e a t h e d a i r wi th a mean N i con ten t of 1 . 6 pmol/m3 [ 2 5 1 . I n t h e


f i rs t group, high concen t r a t ions of N i i n u r i n e c o r r e l a t e d w i t h high c o n c e n t r a t i o n s i n blood; no such c o r r e l a t i o n was found i n t h e w e l d e r s . Occupa t iona l exposure can t h e r e f o r e have s i g n i f i c a n t though u n p r e d i c t a b l e e f fec ts on N i c o n c e n t r a t i o n s i n b i o l o g i c a l f l u i d s , and must be w e l l documented.

Diet A major source of N i exposure i s d i e t a r y , account ing t y p i c a l l y

f o r a t least 1.7 p o l / d a y of i nges t ed N i [ 2 ] . However, c e r t a i n d i e t s can r e s u l t i n c o n s i d e r a b l y h i g h e r i n t a k e s . While meats have N i con ten t s i n t h e range 1 . 0 t o 7.2 nmol/g, t h e corresponding range i n f r u i t s and v e g e t a b l e s i s 0 . 9 t o 150 nmol/g [ 2 2 1 . T h e r e f o r e , v e g e t a r i a n diets w i l l lead t o h ighe r N i i n t a k e . Nuts ( e . g . cashews 85 nmol/g), sp inach (150 nmol/g d ry we igh t ) , t ea l e a v e s (77 nmol/g f r e s h weight) [ 2 2 ] , cocoa (167 nmol/g) , soy p roduc t s and oatmeal [261 a r e e s p e c i a l l y high i n N i . Diets r i ch i n these foods can cause high r a t e s of u r i n a r y e x c r e t i o n [261 .

Tobacco and alcohol C i g a r e t t e s each con ta in 34 t o 105 nmol of N i l and 10 t o 20 % i s

r e l e a s e d i n i n h a l e d smoke [ 2 3 ] . The d a i l y i n h a l e d dose of N i has been e s t i m a t e d t o be 68 nmol f o r a smoker of 20 c i g a r e t t e s p e r day [ 2 ] . T h i s i s probably i n s i g n i f i c a n t i n r e l a t i o n t o i n t a k e from food, d r i n k i n g water and o t h e r s o u r c e s . However, smoking may a l s o i n c r e a s e t h e uptake of N i and C r from o t h e r s o u r c e s i n exposed workers, g i v i n g r i se t o e l e v a t e d u r i n a r y l e v e l s f a r i n e x c e s s of t h o s e a c c o u n t a b l e f o r by metals i n h a l e d from t h e c i g a r e t t e s themselves [ 2 7 1 .

Because of t h e f e w r e l i a b l e measurements of c o n c e n t r a t i o n i n serum t o d a t e , there i s i n s u f f i c i e n t information t o a l low comment on t h e e f f e c t s of a l c o h o l consumption on N i s t a t u s . The numerous e f f e c t s of c h r o n i c a l c o h o l consumption on g e n e r a l p h y s i o l o g y , h e a l t h , n u t r i t i o n and body composition d i c t a t e c a r e f u l documentation of p a t t e r n s of a l c o h o l u se of any r e f e r e n c e p o p u l a t i o n . The N i c o n t e n t of b e e r and wine i s g e n e r a l l y i n t h e range 0.17 t o 3.4 pmol/L [ 2 2 ] , a l though t h e d i u r e t i c e f fec t of i n t a k e of l a r g e volumes of these beverages on N i e x c r e t i o n i s not known, and t he i r impact on N i concen t r a t ions i s t h e r e f o r e hard t o p r e d i c t . Health status

A number of sys t emic d i s e a s e s may a l t e r N i c o n c e n t r a t i o n s i n body f l u i d s . P a t i e n t s i n r e n a l f a i l u r e have impaired e x c r e t i o n of N i . C h r o n i c h a e m o d i a l y s i s compounds t h e p r o b l e m , a n d hypernickelaemia i n s u c h p a t i e n t s i s w e l l documented. S e v e r a l of t h e more r e l i ab le r e p o r t s of N i c o n c e n t r a t i o n s i n serum of h e a l t h y a d u l t s have included comparative d a t a on haemodialysis p a t i e n t s [11, 1 7 , 1 8 , 2 8 1 . V a l u e s i n t h e r e n a l p a t i e n t s were 3.71 f 1.54 (63.2 f 26.2) versus 0.44 f 0.18 (7.5 f 3.1) pg/L (nmol/L) [ill, 5.4 f 2.1 (92 f 36) versus 0.3 f 0.2 (5.1 f 3.4) pg/L (nmol/L) [281 , 7.2 f 2.2 (123 f 37) versus 0.2 It 0.2 (3.4 f 3.4) pg/L (nmol/L) [171 , and 6.38

& 3.36 (108 f 57.1) versus 0.14 f 0.09 (2.38 f 1.53) pg/L (nmol/L) [ 1 8 ] . Thus i n c r e a s e s of n e a r l y 50-fold may occur i n a p o p u l a t i o n undergoing d i a l y s i s . A c u t e myocardial i n f a r c t i o n i s a s s o c i a t e d w i t h an i n c r e a s e i n serum N i i n t h e fol lowing 72 h [peak, 3.0 f 3.4 (51 f 58) pg/L (nmol/L) versus 0.28 f 0.24 (4.76 f 4.08) pg/L (nmol/L) i n h e a l t h y a d u l t s ] [ 9 ] . The same s t u d y a l s o no ted h i g h e r v a l u e s i n u n s t a b l e angina p e c t o r i s [peak concen t r a t ion 1.4 f 0 . 9 pg/L (24 f 15 nmol/L) J , Ch r i s t ensen & Pedersen [ 1 2 ] found h i g h e r v a l u e s i n serum N i i n 10 rheumatoid a r t h r i t i s p a t i e n t s [0.64 f 0.3 pg/L (11 f 5.1 nmol/L)] compared t o 10 h e a l t h y c o n t r o l s [0.25 f 0.1 pg/L (4.25 f 1.70 nmol /L) ;p< 0.0251. The same s tudy a l s o r epor t ed inc reased N i i n u r i n e [2.26 f 1.8 pg/L (38.4 f 30.6 nmol/L) versus 0.82 f 0.5 pg/L (13.9 f 8.5 nmol/L)] and sweat [10.6 f 6.7 pg/L (181 f 114 nmol/L) versus 4.4 f 2.5 pg/L (75 f 43 nmol/L)] , b o t h s i g n i f i c a n t a t t h e l e v e l of p < 0.025.


Other p u t a t i v e medical causes of hypernickelemia a r e poorly documented and a r e found i n publ ica t ions repor t ing highly suspect 'normal' values; f o r a c r i t i c a l discussion see Versieck & Cornel is [ 2 9 ] . P a r t u r i t i o n may lead t o modest increases i n N i i n maternal serum, perhaps due t o r e l ease of N i from t h e p l acen ta . E a r l i e r su rp r i s ing r epor t s of dramatic increases [ 3 0 ] , however, have been re fu ted by the more r e l i a b l e data of Nomoto e t a l . [311 , who report concentrations of 2 . 1 f 0 . 9 0 pg/L (36 f 15 nmol/L) i n heal thy adul t women versus 2.85 f 0 . 6 7 pg/L ( 4 9 f 11 nmol/L) 60 min post partum. There i s l i t t l e r e l i a b l e da ta t o support proposed changes i n N i s t a t u s i n d i abe te s , hepa tob i l i a ry d i sease , cancer o r i n f e c t i o u s processes . Urinary t r a c t i n f e c t i o n s , o f t en overlooked, should always be diagnosed a t t h e time of co l l ec t ion and, i f present t he sample should be discarded.

Medication and iatrogenic exposure Cer ta in medicat ions can a f f e c t N i concen t r a t ions i n body

f l u i d s . Disulfiram increases N i uptake by che la t ing it i n t he gut [ 2 4 ] . Oral cont racept ives were considered a p o t e n t i a l source of d i f fe rences i n serum N i concentrat ions among women [ 2 1 1 . Although the s tudy repor ted no s i g n i f i c a n t d i f f e rences , it was conducted without t he benef i t of present technology, and concentrat ions above 35 nmol/L were found i n both groups. Contamination of intravenous f l u i d s p re sen t s a r i s k of t r i g g e r i n g a l l e r g i c r e a c t i o n s t o N i ; concentrat ions of up t o 1 . 7 pmol/L N i have been found i n var ious l o t s of commercial human serum albumin [ 3 2 ] . Such i a t r o g e n i c exposure might account f o r t he high concentrat ions i n hosp i t a l i zed p a t i e n t s undergoing invasive t reatment , f o r example t h e increases t h a t were noted i n c a r d i a c p a t i e n t s . Leaching of N i from orthopaedic prostheses i s a po ten t i a l ly ins id ious route of exposure [l, 33, 3 4 1 . Dental prostheses m u s t a l s o be considered. A 30-fold r i s e i n concentration of N i i n s a l iva , a t t r i b u t a b l e t o leaching from denta l pos ts of white gold, was found i n a p a t i e n t with extensive o ra l surgery [351. Corrosion of pacemaker wires i s another po ten t i a l source of N i [ 2 4 1 .

Seasonal and diurnal variation Variat ion i n exposure may be seasonal . In one repor t , t he N i

content of urban a i r rose from 0 . 2 9 nmol/m3 i n summer t o 0.43 nmol/m3 i n $ t he winter [ 2 4 1 , probably through an inc rease i n t h e burning of f o s s i l fue l s i n t he winter months. Leach e t a l . [ 9 1 found no d iu rna l v a r i a t i o n i n serum N i i n two vo lun tee r s . Although concentrat ions i n u r ine f luc tua ted , they d id not appear t o do s o s y s t e m a t i c a l l y . I n t h e absence of f u r t h e r d a t a on c i r c a d i a n v a r i a t i o n , s tandard ized time of c o l l e c t i o n ( e . g . e a r l y morning, f a s t ing ) i s recommended.

4. SAMPLE COLLECTION FOR Ni MEASUREMENT

Preparation of skin Carefu l washing of t h e sk in t o remove a i r -borne dus t i s

mandatory, i n o rder t o avoid contamination. A f i n a l wash with e thanol and drying by evaporation has been recommended [ E l . The washing procedure a l s o serves t o remove sweat from t h e sk in . The N i concentration i n sweat i s about 5 times [ I21 o r even 1 0 t o 20 times t h a t of ur ine [ 2 4 ] . Contaminant N i , and a l s o Cu, Zn and Pb, were found i n sweat co l lec ted i n a sauna [ 2 1 ] . Evaporation increases the concentration of N i on the skin surface [361. Similar ly , t he person taking t h e sample should wear p l a s t i c gloves t o avoid contamination from sweat on the hands, and the gloves should not be of t he t a l c - powdered va r i e ty .


Selection of needle Recognizing t h e po ten t i a l f o r leaching N i from s t a i n l e s s s t e e l ,

t he IUPAC reference method f o r N i i n serum recommends t h e use of Teflon o r polyethylene cannulae f o r blood c o l l e c t i o n 1 3 7 1 . This p rac t i ce seems w e l l founded, and most s tud ie s i n recent years have adopted t h i s prac t ice (see Table 1 ) . Versieck e t a l . 1381 drew 20 mL por t ions of blood a t 37 O C through a steel needle (19G-11/2) a f t e r i r r a d i a t i o n . Neutron a c t i v a t i o n a n a l y s i s revea led s u b s t a n t i a l leaching of N i i n t o the sample. An addi t ion of 1.28 p o l / L t o the f i r s t por t ion decreased i n subsequent port ions, but was s t i l l 0 . 2 2 p o l / L by t h e fou r th . Clear ly these values suggest t h e need f o r extreme caution, although leaching f a c i l i t a t e d by i r r a d i a t i o n damage t o the needle cannot be ruled out i n t h i s s t u d y . Sunderman J r . e t a l . [El col lec ted blood from one arm of 2 1 people through a s t a i n l e s s s t e e l needle (Monoject; mass f r a c t i o n of N i 0 .091) and through an intravenous polyethylene cannula i n t he con t r a l a t e ra l arm. The mean N i concentration i n serum from the s t a i n l e s s s t e e l needle was 0 . 7 4 k 0.25 pg/L ( 1 2 . 6 f 4.3 nmol/L), versus 0.37 f 0.18 pg/L (6.3 f 3 .1 nmol/L) with t h e cannula. The mean pa i red d i f f e rence was 0.38 k 0.23 pg/L ( 6 . 5 f 3.9 nmol/L). Blood from the cannula was co l lec ted i n t o ac id washed p l a s t i c syringes, whereas blood from t h e needle was co l lec ted i n t o blue-stoppered "metal-free" Vacutainer tubes (Becton- Dickinson), s o it was r e a l l y the e n t i r e co l l ec t ion system t h a t was being compared and d i f f e rence cannot be a t t r i b u t e d t o t h e needle a lone . Col lec t ion of cerebrospina l f l u i d with s t a i n l e s s s t e e l needles was shown t o r e s u l t i n excessive contamination precluding ana lys i s f o r N i [391. Platinum needles with gold-plated Luer hubs have been f ab r i ca t ed f o r N i measurement i n serum samples [ 4 0 1 , but a r e q u i t e expensive and not gene ra l ly a v a i l a b l e . S i l i c o n i z e d needles may i n some cases be s u f f i c i e n t l y hydrophobic t o prevent leaching of N i i n t o blood [29]. However, extreme caut ion m u s t be exe rc i sed i n r e l y i n g on s i l i c o n i z a t i o n . For example, Becton- Dickinson s ingle-use hypodermic needles ( e . g . No. 51751, o f t e n descr ibed by ana lys t s a s s i l i con ized , a r e a c t u a l l y s i l i con-coa ted only on the outs ide, f o r lubr ica t ion and comfort of the p a t i e n t .

Important exceptions t o the prudent u s e of p l a s t i c cannulae a re t o be found. Bro e t a l . [161 compared concentrations of N i i n blood s e r u m of 2 0 hea l thy a d u l t s a f t e r c o l l e c t i o n i n t o acid-washed polye thylene sy r inges through e i t h e r s t a i n l e s s s t e e l sy r inges (Terumo; 18 G , s i l i con ized ) or 1 7 G o r 18 G t e f l o n cannulae. The f i r s t 5 mL of blood was discarded. Confidence i n t e r v a l s of 95 % f o r d i f f e rences between t h e samples from the needle and e i t h e r cannula were ca lcu la ted , and no s ign i f i can t d i f fe rences were found. A mean N i concentration of 0 . 4 pg/L (6 .8 nmol/L) was reported [range 0 . 2 t o 0 .5 pg/L (3.4 t o 8 .5 nmol/L) 1 ; a s imi l a r value was found with an open c o l l e c t i o n system ( t e f l o n cannula t acid-washed polyethylene t u b e ) . Nixon e t a l . [ 1 8 ] employed a c l a s s 100 clean l a b and leached a l l p l a s t i c labware with n i t r i c ac id . Blood was drawn through a s t a i n l e s s s t e e l needle (Becton-Dickinson No. 5175) a f t e r discarding the f i r s t 3 mL. The N i concentrat ion i n serum obtained by these authors , 0 . 1 4 f 0 . 0 9 pg/L ( 2 . 4 f 1 . 5 nmol/L), i s among t h e lowest values ye t reported. The use of a f lushed s t a i n l e s s s t e e l needle remains t o be re-evaluated under t h e otherwise r igorous condi t ions employed by t h i s group.

Blood collection General awareness of vascular physiology i s needed t o c o l l e c t

r e l i a b l e samples. Changes i n pos ture may a f f e c t i n t r a v a s c u l a r volume. Pooling of blood i n the lower ex t remi t ies on s tanding can cause a 1 0 % inc rease i n non-d i f fus ib le components i n t h e upper ex t r emi t i e s [361, a s well a s an increase i n apparent haematocri t . Because a major f r a c t i o n of N i i s bound t o t h e macroglobulin nickeloplasmin, a s w e l l a s t o albumin and o ther p ro te ins [ 2 4 1 , an


increase i n these non-diffusible components r e s u l t s i n an apparent i n c r e a s e i n concen t r a t ion of N i . Furthermore, because t h e concentrat ion of N i i n whole blood i s severa l t i m e s t h a t i n serum [a], i n c r e a s e s i n haematoc r i t w i l l b e r e f l e c t e d i n h igh concent ra t ions i n blood. Application of a tourn ique t can force water from t h e vascular space, f u r t h e r i nc reas ing t h e apparent concentrat ion of non-diffusible components [ 3 6 1 . Blood should be co l lec ted w i t h t he donor rec l in ing and use of a tourniquet should be avoided. Use of a l a rge r gauge needle o r cannula (preferab ly 1 9 gauge o r l a rge r ) w i l l reduce the volume of the sample contact ing the surface, and w i l l minimize haemolysis from turbulent flow when blood components ( e .g . serum, red c e l l s ) a r e t o be separated. Tourniquets and rap id withdrawal of blood a l s o cont r ibu te t o haemolysis. The IUPAC Reference Method [ 3 7 ] c a l l s f o r co l l ec t ion v i a polyethylene cannula (d iscard ing a t l e a s t t h e f i r s t 2 mL) i n t o a polypropylene sy r inge and t r a n s f e r t o a po lye thylene t u b e . An appea l ing a l t e r n a t i v e , dropwise c o l l e c t i o n d i r e c t l y i n t o t h e tube under pa r t i c l e - f r ee a i r flow, may not be p r a c t i c a l w i t h any but t he most dedicated volunteers .

Blood should be allowed t o c l o t under s tandardized condi t ions ( e . g . 45 min a t 2 0 "C) and serum separated a t 900 x g f o r 15 m i n . Prolonged c l o t t i n g time, excessive cen t r i fuga l forces and delays i n s epa ra t ing serum from t h e c e l l p e l l e t w i l l a l l c o n t r i b u t e t o haemolysis. The u s e of plasma a f f o r d s immediate and g e n t l e r separa t ion , but addi t ion of ant icoagulants t o t h e c o l l e c t i o n tube probably poses insurmountable d i f f i c u l t i e s f o r a n a l y s i s a t t h e u l t r a t r a c e l e v e l . Heparin i s a po lye lec t ro ly t e t h a t av id ly binds d iva len t ca t ions , including N i [41], and i s d i f f i c u l t t o pu r i fy . Other Ca2+ scavengers ( c i t r a t e , oxalate , EDTA, f l uo r ide ) pose a high r i s k of contamination [36].

Washing of labware A l l surfaces coming i n t o contact w i t h the sample f o r u l t r a t r a c e

ana lys i s m u s t be scrupulously cleaned. This i s of course t r u e when the ana ly t e i s N i i n body f l u i d s . A p r a c t i c a l i l l u s t r a t i o n of po ten t i a l p i t f a l l s i s given by Nixon e t a l . [ l a ] . Forty-seven serum samples were co l lec ted i n acid-washed Monovette syr inges and handled throughout f o r ana lys i s by ET-AAS i n a c lean room. However, they were e i t h e r t r a n s f e r r e d i n t o non-acid-leached Sa r s t ed t tubes , o r a l iquoted w i t h non-acid-leached p i p e t t e t i p s . Against a reference concentration of N i of 0 . 1 4 f 0 . 0 9 pg/L ( 2 . 4 f 1 .5 nmol/L) f o r t he lab, f a i l u r e t o leach the tubes produced a value of 0.93 f 0 . 6 4 pg/L ( 1 6 f 11 nmol/L) (n=22), whereas unwashed p i p e t t e t i p s gave a value of 3 .3 f 4 . 0 pg/L ( 5 6 f 68 nmol/L) (n=25). Moody and Lindstrom [42] have compared the amount of N i leached from several types of p l a s t i c and Teflon, by hydrochloric and n i t r i c ac ids (Table 2 ) . Although n i t r i c ac id always leached more N i l t he r e l a t i v e e f f i c i e n c i e s of the two ac ids d i f f e r e d w i t h t h e mater ia l , and t h e au thors recommend sequent ia l use of both ac ids . They have a l s o recommended t h a t f i n a l r i n s i n g and soaking should be w i t h t h e pu res t water a v a i l a b l e , although reagent-grade ac ids a r e adequate f o r t h e leaching s t e p s . They f u r t h e r recommend s torage of vesse ls f o r severa l weeks ( u n t i l u s e ) f i l l e d with u l t rapure water, t o allow t h e cleaning process t o continue ,

Guidelines f o r cleaning labware f o r t r a c e and u l t r a t r a c e metal ana lys i s can be found i n many excel lent sources. Some a r e compiled i n Table 3 . A f e w make spec i f i c comments about N i l b u t one i s bes t advised t o follow general p r inc ip les and e r r on the s ide of caut ion. Any of t hese precaut ions can be relaxed only when t h e impact of t h e i r omission on t h e a n a l y t i c a l r e s u l t has been thoroughly evaluated.

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ir


5.

When consider ing long-term s torage of a sample, t h e ana lys t must be aware of t h e r i s k of loss or add i t ion of t h e ana ly te by adsorpt ion t o , o r leaching from, the s torage container ; water l o s s from poorly sea led o r permeable containers ; and changes i n sample homogeneity, €or instance formation of a p r e c i p i t a t e i n s tored ur ine t h a t may adsorb N i . The chance of leaching imposes t h e same cons idera t ions a s i n sample co l l ec t ion , although c r i t e r i a may be even more s t r ingen t because of prolonged contact with t h e container . Adsorpt ive l o s s e s of N i t o most p l a s t i c s a r e probably not s i g n i f i c a n t . Stoeppler [221 found no adsorpt ion of r a d i o a c t i v i t y onto the walls of polyethylene b o t t l e s when 6 3 N i was added t o f resh ly voided u r ine . No adsorpt ive lo s ses were observed over 6 months. when ur ine was spiked with small amounts of N i and s to red a t 4 O C

(container not spec i f ied) [361 . The IUPAC reference method f o r N i i n u r i n e recommends s t o r a g e o f u r i n e a t -20 O C i n screw cap polypropylene tubes , a f t e r a c i d i f i c a t i o n with n i t r i c a c i d [ 3 7 1 . Stoeppler has a l s o reported adsorption of 6 3 N i t o t h e sediment t h a t forms when ur ine i s s tored . This occurred even when t h e sample was ac id i f i ed , accounting fo r about 6% of t he N i a t pH 6 and about 1% a t pH 1 [ 2 2 1 . Sunderman Jr . [451 recommends ac id i f i ca t ion by addi t ion of 1 0 mL H N 0 3 / L ur ine and s torage a t 4 O C f o r up t o a week ( -20 O C f o r longer s t o r a g e ) . Medium- t o long-term s torage of ur ine a t -20 O C

without ac id i f i ca t ion i s preferred by some authors [ 4 6 ] .

The r a t e of water l o s s from va r ious Teflon and p l a s t i c conta iners was inves t iga t ed by Moody and Lindstrom [ 4 2 1 . Annual l o s ses var ied from 0.03 t o 0 . 0 5 % from polypropylene and 0 . 0 5 % from Teflon FEP, t o 1 . 6 t o 2 . 0 % from polycarbonate . Losses from t r ansp i r a t ion versus around the closure were not d i s t inguished . I f long-term storage i s necessary, use of well-sealed polypropylene o r Teflon vesse l s should be considered, and surface a rea f o r leaching and adsorpt ion should be minimized by avoiding conta iners t h a t a r e la rger than necessary.

STORAGE OF SAMPLES FOR ANALYSIS

6. SAMPLE PREPARATION FOR ATOMIC ABSORPTION SPECTROMETRY FOR Ni IN SERUM AND URINE By f a r t h e most widespread method a v a i l a b l e t o many

i n v e s t i g a t o r s wanting t o measure N i i s e l e c t r o t h e r m a l atomic absorp t ion spectrometry (ET-AAS); c f . Table 1. Numerous o the r methods have been reviewed [ 2 2 , 4 7 , 4 8 1 . Though d e f i n i t i v e methods based on i so tope-d i lu t ion mass spectrometry w i l l undoubtedly be developed, suggested reference l eve l s w i l l continue t o be based on ET-AAS. The requirements f o r sample processing f o r t h i s technique i n some ways d i c t a t e short-term handling and pre-storage condi t ions. For example, i f u r ine i s t o be a c i d i f i e d f o r s to rage and l a t e r ana lys i s , an ac id compatible with the ana lys i s would be chosen. A s another example, i f serum i s t o be wet ashed f o r a n a l y s i s , g r a t u i t o u s t r a n s f e r t o an intermediate s torage conta iner may be undes i r ab le . Therefore , it i s appropr i a t e i n a d i scuss ion of sampling and s torage f o r N i measurement t o consider a l s o sample preparation f o r ET-AAS ,

The e a r l i e r IUPAC reference method f o r N i i n serum and ur ine [371 involved complexation of N i i n an a c i d d iges t with ammonium pyrrolidin-1-yldithioformate fol lowed by e x t r a c t i o n wi th 4 - methylpentan-2-one. Advances i n ET-AAS have rendered t h i s extensive manipulation unnecessary. Sunderman Jr . [451 has recommended protein p r e c i p i t a t i o n with n i t r i c a c i d and hea t f o r a n a l y s i s of blood, serum, cerebrospinal f l u i d and sa l iva , and a c i d i f i c a t i o n with d i l u t e n i t r i c ac id f o r ur ine . I n general , commercially ava i lab le u l t rapure n i t r i c ac id ( e . g . J . T . Baker, Merck "Suprapur") i s adequate without fu r the r pu r i f i ca t ion [ 3 7 ] , and i n general does not cont r ibu te t o the


blank i f used spa r ing ly [ 2 2 ] . A l i s t of e a r l i e r dry-ashing procedures , and of wet-ashing i n H N 0 3 - H C 1 0 4 mixtures has been compiled by Stoeppler [ 2 2 ] . The IUPAC re ference method f o r N i required complete d iges t ion of both serum and u r ine w i t h an equal volume of H N 0 3 : H C 1 0 4 : H 2 S 0 4 i n volume r a t i o s of 0 . 6 , 0 . 2 and 0.2, res- pec t ive ly . Decomposition i s accomplished i n open b o r o s i l i c a t e tubes with stepwise increases i n temperature over 4 . 5 h, f i n i sh ing a t 300 O C with evaporation of a l l b u t H2SO4. Andersen e t a l . 1131 d i l u t e d serum w i t h 10-3 mol/L HNO3 (volume r a t i o 0 . 5 ) i n Tri ton X-100 (volume f r a c t i o n 0 . 0 0 1 ) f o r d i r e c t ana lys i s ; Drazniowsky e t a l . 1101 simply used a d i lu t ion w i t h 20 mL/L Triton X-100 (volume r a t i o 0 . 5 ) . Urine was analyzed a f t e r d i lu t ion w i t h an equal volume of 3 mol/L HNO3 i n aqueous Tri ton X-100 (volume f rac t ion 0.005) [ 4 9 1 . Nixon e t a l . a l so used a d i luen t of mol/L H N 0 3 i n aqueous Tr i ton X-100 (volume f r a c t i o n 0.001), and found no increase i n blank values when t h r e e i n j e c t i o n s of 50 FL were made i n t o t h e furnace i n s t e a d of one. Detergent serves a s a wetting agent and reduces carbon build-up i n the furnace, and i n t hese s t u d i e s T r i ton X-100 appears free of s i g n i f i c a n t con tamina t ion . Neve r the l e s s , it mus t always be considered a s an addi t iona l source of po ten t i a l contamination. The recommendations of Sunderman Jr . [ 4 5 ] seem t h e s a f e s t , al though decreased recovery because of p rec ip i t a t ion of protein-bound N i mus t be addressed. T h i s appears t o be a t h e o r e t i c a l cons idera t ion ; a c i d i f i c a t i o n should be su f f i c i en t t o d isp lace N i from binding s i t e s on known p ro te ins . Concentrated n i t r i c ac id (50 pL) i s added w i t h vortexing t o 1 mL serum and the mixture i s heated t o 70 O C f o r 5 min i n a s toppered tube . The c l e a r superna tan t i s analysed a f t e r cen t r i fuging . Urine i s d i l u t e d w i t h two p a r t s of ca . 0 . 2 % (w/v) HNO3 and centr i fuged only i f t u rb id .

7.

T h i s d i scuss ion focuses on ET-AAS a s t h e most important and genera l ly ava i l ab le approach f o r measurement of N i i n body f l u i d s . The preceding sec t ions have dea l t w i t h pre-analyt ical considerat ions appl icable t o t h i s technique. Several t echnica l improvements i n the p a s t decade have lowered d e t e c t i o n l i m i t s below t h e presumed concentration of N i i n most or a l l body compartments. These include g r e a t e r ins t rument s e n s i t i v i t y , t h e implementation of Zeeman background cor rec t ion , and furnaces t h a t provide rap id temperature r i s e during atomization [8 , 4 7 1 .

Ni MEASUREMENT BY ATOMIC ABSORPTION SPECTROMETRY

Table 4 - Temperature programs f o r N i measurement b y Zeeman- corrected ET-AAS. Data i n columns (i) t o ( i v ) a r e from refs . [8, 13, 16, 1 8 1 , r espec t ive ly .

T ( "C) Ramp ( s ) Hold ( s ) Gas

(i) (ii) (iii) (iv) (i) (ii) (iii) (iv) (i) (ii) (iii) (iv)

loo, loo, loo, - 1, 40, 10, - 1, 20, 80, - on 140, - 140, 120 60, - 60, 1 10, - 10, 10 on 190, 206, 190, 160 30, Qo, 30, 70 5, io, 5, 5 on

Chadash -, 700 -. -, 30 -, -, -, 10 on 1200, 1250, 1100, 1500 80, 30, 80, 10 50, 20, 50, 25 on4

Dry*

Atomize 2600, - 2500, - 0, -, 0, - 5, - 5, - of& -, 27b0, 2700, 2750 -, 0, 1 ,O -, 8, 3, 5 Off

Clean 2700, 2800, -, 2800 1, 1, - 9 1 3, 2, - 9 2 on

*These steps are repeated with a second sample introduction in study (lv). *In study (i), the gas flow is not turned off but is reduced from 300 mWmin to 30 mL/min for the last 5 s at 1200 OC and for the atomization step.


Tabla 5 - Performance characteristics of several protocols for analysis for Ni in blood serum by Zeeman-corrected ET-AAS.

Ref. Serum:Diluent Sample vol. Detection Limit Within-run Long term (nmol/L) imprecision imprecision

(C.V.) (C.V.) W)

[ E l 1 :0.05 50 0.85* 3.4% at 6.8 mom 8.1% at 6.0 nmoVL

El31 1 : 1 50 1.534

[161 1 :0.05 60 8% at 12 nmol/L 11% at 12 nmol/L

[lE] 1 :0.33 2 x 5 0 1 .o$ 3.2%at17nm0VL -

*95% confidence level 43 stanclad deviations above the blank

Four studies 18, 13, 16, 181 were selected from Table 1 on the basis of i) the apparent ability of the authors to approach the putative target value, ii) the reporting of analytical performance and experimental detail, and iii) geographic diversity. These four studies from Europe [13, 161 and the U.S. [ 8 , 181 all used Zeeman- corrected ET-AAS and Perkin-Elmer instruments (either the PE 5000 or PE 3030). Similar temperature programmes were used (Table 4); there is no reason to suggest that the slight differences were of analytical significance.

The various methods of sample preparation result in different dilutions of serum, with a consequent need to introduce different volumes into the graphite furnace. Table 5 shows that when serum was deproteinized by the addition of small volumes of concentrated acid, analysis of 50 FL was feasible; with dilution, multiple injections may become necessary (cf. [18]) . Within-run and long-term imprecision with coefficient of variation in the range 5% and lo%, respectively, was generally attainable, with detection limits lower than 1.7 nmol/L.

8. REFERENCES

1. H. F. Hildebrand, C. Veron and P. Martin, Biomaterials i 19891 Ui 545.

2. P. Grandjean, G. D. Nielsen and 0. Andersen, in 'Nickel and the Skin: Immunology and Toxicology', (T. Mend and H. I. Maibach, ed.), CRC Press, Boca Raton, Florida, 1989.

3. IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, 'Nickel and nickel compounds in: IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Vol. 49 : Chromium, Nickel and Welding', IARC, Lyons, 1990.

4. C. T. Walsh and W. H. Orme-Johnson, Biochemistrv , 1987, 26, 4901.

5. U. Vollkopf, 2. Grobenski and B. Welz, m m i c SpectroscoDv,, 1981, 2, 68.

6. U. E. Pazzaglia, C. Minoia, L. Ceciliani and C. Riccardi, &Za W p . S U , 1983, 3, 574.

Measurement of total nickel in body fluids 37 1

7. P. Ostapczuk, P. Valenta, M. Stoeppler and H. W. Nurnberg, in 'Chemical Toxicology and Clinical Chemistry of Metals' , ( S . S. Brown and J. Savory, ed.) , Academic Press, London, 1983.

8. F. W. Sunderman Jr., M. C. Crisostomo, M. C. Reid, S. M. Hopfer and S. Nomoto, Annals. T a b . S Ci, 1984, JA, 232.

9. C. N. Leach Jr., J. V. Linden, S. M. Hopfer, M. C. Crisostomo and F. W. Sunderman Jr. , Clin.Chem. , 1985, 556.

10. M. Drazniowsky, I. S. Parkinson, M. K. Ward, S. M. Channon and D. N. S. Kerr, €lin. , 1985, MI 219.

11. M. R. Wills, C. S. Brown, R. F. Bertholf, R. Ross and J. Savory, Clin. Chim. Act& 1985, m, 193.

12. J. M. Christensen and L. M. Pedersen, BCta Phaxmacol. Toxicol., 1986, 52, 399.

13. J. R. Andersen, B. Gammelgaard and S. Reimert, Analvst, 1986, JJJ, 721.

14. S. Hosokawa, H. Nishitani, K. Umemura, T. Tomoyoshi and K. Sawanishi, JJeDhron, 1987, 45, 151.

15. M. Kiilunen, J. Jarvisalo, 0. Makitie and A. Aitio, ;Lnt. Arch. n. He-, 1987, 52, 43.

16. S. Bro, P. J. Jargensen, J. M. Christensen and M. Harrder, J- A, 1988, 2, 31.

17. S. M. Hopfer, W. P. Fay and F. W. Sunderman Jr., &.L, 1989, U, 161.

18. D. E. Nixon, T. P. Moyer, D. P. Squillace and J. T. McCarthy, 1989, ;L;L4, 1671.

19. C. Minoia, E. Sabbioni, P. Apostoli, R. Pietra, L. Pozzoli, M. Gallorini, G. Nicolaou, L. Alessio and E. Capodaglio, Sci. Tot, Egviron., 1990, 25, 89.

20. N. Lavi and 2 . B. Alfassi, m v s t , 1990, U, 817.

21. D. C. Hohnadel, F. W. Sunderman Jr., M. W. Nechay and M. D. McNeely, €Ih. Chem. , 1973, u, 1288.

22. M. Stoeppler, in 'Nickel in the Environment', (J. 0. Nriagu, ed.), John Wiley & Sons, New York, 1980.

23. D. L. Tsalev and 2 . K. Zaprianov, 'Atomic Absorption Spectrometry in Occupational and Environmental Health Practice, Vol. l', CRC Press, Boca Raton, Florida, 1984.

24. F. W. Sunderman Jr., in 'Handbook on Toxicity of Inorganic Compounds', (H. G. Seiler and H. Sigel, ed.), Marcel Dekker, New York, 1988.

25. J. Angerer, R. Heinrich-Ram and G. Lehnert, Bna;l. C h a , 1989, 25, 81.

26. G. D. Nielsen, L. V. Jepsen, P. J. Jargensen, P. Grandjean and F. Brandrup, -, 1990, U, 299.

27. P.-L. Kalliomaki, E. Rahkonen, V. Vaaranen, K. Kalliomaki and K. Aittoniemi, W. Arch. Occup. Rnviron. H e m , 1981, a, 67.


28. S. M . Hopfer, J. V . Linden, M . C . Crisostomo, F . A . Catalanat to ,

29 . J . V e r s i e c k a n d R . C o r n e l i s , 'Trace E l e m e n t s i n Human Plasma and

3 0 . G . Rubanyi , I . B i r t a l a n , A . G e r g e l y and A . G . B . Kovach, Am. J .

M . Galen a n d F . W . Sunderman Jr . , -, 1985, 2, 68.

Serum' , CRC P r e s s , Boca Raton, F l o r i d a , 1 9 8 9 .

Qbstet. Gynecol . , 1982, MI 1 6 7 .

3 1 . S. Nomoto, T . H i r a b a y a s h i and T . Fukuda, i n 'Chemica l T o x i c o l o g y a n d C l i n i c a l C h e m i s t r y of Metals', ( S . S. Brown a n d J . S a v o r y , ed . ) , Academic P r e s s , N e w York, 1983.

3 2 . C . N . Leach Jr. a n d F . W . Sunderman Jr, u e w F n g l . J . Me&, 1985, U, 1232.

3 3 . D. A . T i l s l e y a n d H . R o t s t e i n , Contact D e r m a t - , 1980, 6, 1 7 5 .

3 4 . F . W. Sunderman J r . , , 1989, 1312) , 205.

3 5 . M.-A. Vaughan, A . D . Ba ines and D . M . Templeton, U n . Chem,, 1991, x, 210.

36 . A . A i t i o a n d J . J a r v i s a l o , W p l . -, 1984, 5 6 1 4 ) , 549.

3 7 . S. S. B r o w n , S . N o m o t o , M . S t o e p p l e r a n d F . W . Sunderman J r . , U i n . Fiochem., 1981, 14, 295.

3 8 . J . V e r s i e c k , F . Barbier , R . C o r n e l i s a n d J . Hoste, 1982, 2, 973.

3 9 . E.-L. Lakoma, i n 'Trace Element A n a l y t i c a l C h e m i s t r y i n Medic ine a n d B i o l o g y ' , ed . ) , Walter de G r u y t e r , B e r l i n , 1980.

4 0 . E . C r o n i n , A . D . D i M i c h i e l a n d S . S . Brown, i n ' N i c k e l T o x i c o l o g y ' , ( S . S . Brown and F . W . Sunderman J r . , e d . ) , Academic Press, London, 1980.

4 1 . D. Templeton, BiQchim. BioDhvs. , 1987, p26, 94.

42 . J . R . Moody a n d R . M . Lindstrom, u. Chem., 1977, 4 9 ( 1 4 \ , 2264.

4 3 . E . Nieboer and A . A . J u s y s , i n 'Chemica l T o x i c o l o g y and C l i n i c a l C h e m i s t r y of Metals ' , ( S . S . Brown a n d J . Savory , e d . ) , Academic Press, London, 1 9 8 3 ,

4 4 . T . M. F l o r e n c e , Talanta, 1982, 29, 3 4 5 .

45. F . W. Sunderman J r . , S . M . Hopfer a n d M. C . Crisostomo, Methods -, 1988, m, 382.

4 6 . M . S t o e p p l e r , i n 'Chemica l T o x i c o l o g y and C l i n i c a l C h e m i s t r y of Metals ' , (S . S . Brown and J . S a v o r y , e d . ) , Academic P r e s s , N e w York, 1983.

4 7 . M . S t o e p p l e r , i n 'Trace E l e m e n t - A n a l y t i c a l C h e m i s t r y i n Medicine and B i o l o g y , V o l . 3 ' , ( P . Bra t te r and P . Schramel , e d . ) , Walter de G r u y t e r , B e r l i n , 1984.

48. F . W. Sunderman J r . , p u r e & ADD^. Chem,, 1980, 2, 527.

49. D . C . P a s c h a l a n d G . G . B a i l e y , S c i . T o t a l E n v i r o n , 1989, Be, 305.

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MEASUREMENT OF TOTAL NICKEL IN BODY