Manganese

11

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Manganese T h e origin of manganese i n various petroleum matrices is not well understood. Traces of it i n crude o i l may arise as oil-soluble compo nents native to the oil reservoir, as entrained brine, or as corrosion products from equipment used i n production. The fate of this manganese i n the refinery is likewise unclear. Although it may be concentrated i n distilla tion processes, it has also been deposited on spent cracking catalysts. In addition to "native" forms, part-per-million levels of manganese may be introduced into petroleum matrices as an additive to improve fuel o i l combustion or as an antiknock additive to gasoline.

Available A n a l y t i c a l Methods Generally, the manganese reported in petroleum has been measured as part of trace-element survey analyses by neutron activation (1, 2, 3) or by emission spectroscopy ( 4 ) . Prior to the work of the Trace Metals Project no procedure was available specifically for the determination of traces of manganese i n petroleum. Manganese levels above 1 μg/ml have been determined colorimetrically after oxidation to permanganate with periodate (5). Concentrations as low as 0.001 μ g / m l have been measured by the catalytic effect of manganese on the oxidation of diethylamine by periodate (6). In both methods, however, chromium must be eliminated before measurement. After removal of nickel and iron, manganese has been measured polarographically down to 0.2 μ g / m l (7). Pulse polarography has extended the detection limit to ≥0.03 μg Mn/ml ( 8 ) . Flame atomic absorption has a sensitivity of 0.024 μ g / m l when applied directly to aqueous media ( 9 ) . This sensitivity has been extended to less than 0.01 μ g / m l by solvent extraction with cupferron and M I B K (10). Heated vaporization atomic absorption (HVAA) has been used at the μ g / m l level in aqueous media (11, 12, 13, 14). In addition, H V A A has been used directly to determine manganese i n petroleum matrices at the part-permillion level (15). The Trace Metals Project has extended the use of direct H V A A to allow the determination of manganese down to 10 n g / g in a variety of petroleum matrices. The work has been described i n detail; i n general, it involves the use of standard additions to a solution of the sample i n tetrahydrofuran (16). 125 In Analysis of Petroleum for Trace Metals; Hofstader, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.

126

ANALYSIS

Role of Neutron

OF P E T R O L E U M FOR TRACE

METALS

Activation

Manganese can be readily determined i n petroleum matrices INAA.

T h e p r i n c i p a l r a d i a t i o n at 847 k e V [ (

5 5

M n (ny)

5 6

by

M n ) ] can be

u s e d to detect less t h a n 10 n g / g after 1-hr i r r a d i a t i o n at a n e u t r o n flux of 10

1 2

c m " sec" . 2

1

C o u n t i n g times are o n l y 1 0 - 3 0 m i n . T h e presence

l a r g e amounts of i r o n m a y cause i n t e r f e r e n c e f r o m the daughter produced

fission

neutrons i n the reactor.


interference, the i n t e n s i t y r a t i o of the 1099 K e V

5 9

5 5

F e (n,p)

5 6

T o correct f o r this Fe/847 Kev

5 6

M n is

d e t e r m i n e d b y s i m u l t a n e o u s i r r a d i a t i o n of a p u r e i r o n s o l u t i o n . m a g n i t u d e of t h e interference is c a l c u l a t e d f r o m the 1099 K e V i n t e n s i t y i n the s a m p l e .

of Mn

The

F e peak

5 9

T h i s t e c h n i q u e w a s a p p l i e d i n the P r o j e c t to

v a l i d a t e the H V A A p r o c e d u r e w h i c h w a s d e v e l o p e d . Special Analytical

Considerations

I n the d e v e l o p m e n t o p e r a t i n g parameters investigated

(of

The

(16).

" s h e a t h i n g " gas affected

of the p r o c e d u r e , the effect of several

HVAA

a V a r i a n Techtron C R A - 6 3 atomizer) ashing temperature

and composition

were of

the

the a t o m i z a t i o n p e a k h e i g h t at h i g h a s h i n g

t e m p e r a t u r e s , c a u s i n g some losses of manganese.

T h i s is consistent w i t h

r e p o r t e d losses of manganese w h e n d r y a s h i n g is c a r r i e d out a b o v e 700° C (17).

T h e i n t r o d u c t i o n of h y d r o g e n i n t o the s h e a t h i n g gas reduces

the

a t o m i z a t i o n p e a k h e i g h t e v e n w h e n the ' n o r m a l " a s h i n g t e m p e r a t u r e w a s u s e d . T h e m e c h a n i s m that reduces the s i g n a l is u n c l e a r . Once atomization conditions h a d been optimized, "native" manganese c o u l d b e successfully a n a l y z e d d i r e c t l y i n p e t r o l e u m samples b y

HVAA.

S i n c e a fixed a m o u n t of m a n g a n e s e as the sulfonate ( C o n o s t a n )

or the

cyclohexanebutyrate

( N B S ) gave i d e n t i c a l p e a k heights, the m a n g a n e s e

s i g n a l appears to b e i n d e p e n d e n t of its c o m p o u n d f o r m . T o demonstrate q u a n t i t a t i v e r e t e n t i o n , the d i r e c t t e c h n i q u e w a s a p p l i e d to several m a t rices, a n d the results w e r e c o m p a r e d w i t h those o b t a i n e d b y alternate techniques.

S o m e representative d a t a f o r m a n g a n e s e are g i v e n i n T a b l e

11.1, w h e r e the d i r e c t H V A A results are c o m p a r e d w i t h those o b t a i n e d Table 11.1.

Comparison of Direct H V A A Procedure with Results Obtained after Ashing Manganese

Sample N o . 6 fuel o i l Crude oil Ε Heating oil Crude oil F

Direct HVAA 306 104 32.5 42.4

Concentration AshAqueous HVAA 283 112 39.0 38.0

(ng/g) AshFlame 300

In Analysis of Petroleum for Trace Metals; Hofstader, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.

11.

HOFSTADER E T A L .

127

Manganese

b y H V A A a n d flame A A after a s h i n g . I n t h e l a t t e r cases the s a m p l e w a s c h a r r e d w i t h s u l f u r i c a c i d , i g n i t e d at 450° C for 2 h r , a n d the r e s i d u e t a k e n u p i n aqueous acid. T h e agreement between the two methods indicates t h a t " n a t i v e " m a n g a n e s e w a s n o t lost p r i o r to the a t o m i z a t i o n i n t h e direct procedure. W h e n e v e r the d i r e c t t e c h n i q u e is a p p l i e d to k n o w n c o m p o u n d s , t h e v a l i d i t y m u s t b e e s t a b l i s h e d . F o r e x a m p l e , the a d d i t i v e m e t h y l c y c l o p e n t a -


d i e n y l manganese t r i c a r b o n y l m a y b e too stable t o b e a n a l y z e d b y d i r e c t H V A A w i t h o u t p r e - a t o m i z a t i o n losses.

S o m e w o r k has suggested

that

losses of this c o m p o u n d o c c u r e v e n i n a c i d d i g e s t i o n p r o c e d u r e s

(4).

N o studies w e r e m a d e o n this c o m p o u n d as p a r t of t h e Project. Sample

Preparation

I n t h e d i r e c t H V A A p r o c e d u r e a 2.5-g s a m p l e is d i l u t e d to 5 m l w i t h tetrahydrofuran.

F u r t h e r d i l u t i o n s are m a d e i n t h e same solvent w h e n

t h e i n i t i a l s o l u t i o n c o n c e n t r a t i o n is too h i g h . Measurement T h e a t o m i z a t i o n c o n d i t i o n s f o r the C R A - 6 3 w e r e o p t i m i z e d e m p i r i c a l l y to g i v e a r a n g e of 0 - 5 0 pg/ml w i t h 1-/J injections of d i l u t e standards (16).

U n d e r these c o n d i t i o n s the l i n e a r i t y c o v e r e d 0 - 4 0 0 n g / m l , a n d t h e

c a l c u l a t e d d e t e c t i o n l i m i t ( S / N = 2 ) w a s 0.5 p g . B a c k g r o u n d corrections, w h e r e necessary, w e r e m a d e u s i n g the 2 8 0 . 2 - n m l e a d l i n e .

A

HGA-70

a t o m i z e r w a s u s e d i n one of the c o o p e r a t i n g laboratories after a s i m i l a r empirical optimization. W h e n the absorbances for a d d i t i o n of a k n o w n q u a n t i t y of a m a n g a nese s t a n d a r d to s e v e r a l m a t r i c e s w e r e c o m p a r e d , s u b s t a n t i a l differences were

observed

(Table

11.11).

I f the d i r e c t H V A A

technnique

were

i n d e p e n d e n t of m a t r i x effects, a l l the n u m b e r s w o u l d b e i d e n t i c a l to the 1.80 v a l u e i n T H F alone. H o w e v e r , the m a t r i x effects e q u i l i b r a t e d after a s i n g l e i n j e c t i o n , a n d t h e y w e r e r e t a i n e d after t h e s a m p l e h a d b e e n analyzed.

T h i s "matrix m e m o r y " was eliminated b y m u l t i p l e atomiza-

tions at m a x i m u m p o w e r b e t w e e n samples. s i m i l a r to that for C r or V (see

A l t h o u g h t h i s b e h a v i o r is

C h a p t e r s 8 a n d 1 4 ) , n o r e l a t i o n s h i p has

b e e n e s t a b l i s h e d b e t w e e n t h e M n response a n d the levels of F e , N i , o r V i n these m a t r i c e s ( 1 6 ) .

C o n s e q u e n t l y , t h e m e t h o d of s t a n d a r d a d d i t i o n s

is r e c o m m e n d e d to c o m p e n s a t e for these effects. Recommended

Method

I n the p r o c e d u r e , a 2.5-g s a m p l e is d i l u t e d w i t h t e t r a h y d r o f u r a n , i n j e c t e d i n t o t h e H V A A a t o m i z a t i o n t u b e , a n d the h e a t i n g p r o g r a m is


128

ANALYSIS O F P E T R O L E U M

Table 11.11.

METALS

Effect of M a t r i x on the Determination of Manganese by Direct H V A A Procedure

Sample


FOR TRACE

THF Crude Crude Crude Crude Crude

Change in (X 1000)/ppb

Absorbance

Mn Added

1.80 1.82 0.88 1.93 1.75 1.23

A Β C D Ε

started. T h e s a m p l e c o n c e n t r a t i o n is d e t e r m i n e d f r o m the b a c k g r o u n d corrected sample signal b y standard additions using a computation w h i c h has b e e n d e s c r i b e d (16). T h e d a t a i n T a b l e 11.1 d e m o n s t r a t e t h a t the c o m b i n a t i o n o f s t a n d a r d a d d i t i o n s a n d b a c k g r o u n d c o r r e c t i o n successfully o v e r c o m e s m a t r i x effects to g i v e a c c u r a t e results. S i m i l a r excellent agreement has b e e n o b t a i n e d b e t w e e n H V A A a n d n e u t r o n a c t i v a t i o n d a t a , as d i s c u s s e d b e l o w . T h e precision of t h e procedure

was established at t h e initiating

laboratory i n a variety o f matrices. Some representative data, presented in

F i g u r e 11.1, i n d i c a t e a 1 7 % r e l a t i v e s t a n d a r d d e v i a t i o n f o r t h e

procedure. S i x samples w e r e p r e p a r e d f o r a cross-check p r o g r a m .

T h e resuts

o b t a i n e d at f o u r p a r t i c i p a t i n g laboratories are s h o w n i n F i g u r e 11.2. F o r c o m p a r i s o n t h e v a l u e s o b t a i n e d b y n e u t r o n a c t i v a t i o n are i n d i c a t e d b y

DIESEL OIL

Η

19% (2)

Η

RESIDUUM A

10% (2)

*6 FUEL OIL Β

CRUDE Η

8% (4)

Η 24%

(5)

I

CRUDE Κ CRUDE L

Η

[-·—I

·

1

19% (7)

1 150

1 200

1 250

6% (2)

I 50

1 100

1 300

ngMn/g •

Average value;|

Figure 11.1.

JData Spread, % is RSD, ( ) degrees of freedom

Intralaboratory data for of manganese

determination


11.

HOFSTADER E T A L .

129

Manganese

t h e triangles. T h e r e l a t i v e s t a n d a r d d e v i a t i o n at a n y one site w a s a p p r o x i m a t e l y 1 0 % o n the N o . 2 h e a t i n g o i l a n d t h e E l l e n b e r g e r c r u d e a n d 3 0 % on the L i g h t A r a b i a n crude.

T h i s includes one laboratory where t h e

d a t a w e r e o b t a i n e d w i t h a P e r k i n - E l m e r H G A - 7 0 after t h e o p e r a t i n g p a r a m e t e r s w e r e a d a p t e d . W h e n the p r e c i s i o n b e t w e e n laboratories w a s c a l c u l a t e d , w i t h s t a t i s t i c a l e l i m i n a t i o n o f some d a t a , t h e r e l a t i v e s t a n d a r d deviations were 2 0 %

f o r the N o . 2 h e a t i n g o i l a n d E l l e n b e r g e r c r u d e


a n d 2 6 % f o r the L i g h t A r a b i a n c r u d e .

a

#2 HEATING OIL - Unspiked - Spiked

fe]

NAA Values

20% (11)

ELLENBERGER CRUDE - Unspiked - Spiked

|^-|

19% (11)

LIGHT ARABIAN - Unspiked - Spiked

1 26%

I — — -· 40

_L

80

120

(11)

119%

1

_L

160

200

240

(8) 280

ng Mn/g ·,

Average Value,|

Figure 11.2.

Detailed

|data spread, % - is RSD,

( ) degrees of freedom

Interhboratory data for determination of manganese

Procedure

Scope. T h e m e t h o d is d e s i g n e d t o d e t e r m i n e m a n g a n e s e

concentra

tions d o w n t o the 10 n g / g l e v e l i n p e t r o l e u m a n d p e t r o l e u m p r o d u c t s . A f t e r setup, e a c h s a m p l e r e q u i r e s a b o u t 3 0 m i n u t e s f o r analysis. H o w e v e r , sample preparation a n d apparatus setup limit output generally to 12 samples i n o n e d a y . S u m m a r y o f M e t h o d . T h e s a m p l e is d i l u t e d w i t h t e t r a h y d r o f u r a n , a n d the m e t a l i n the s o l u t i o n i s m e a s u r e d w i t h a n a t o m i c

absorption

spectrophotometer e q u i p p e d w i t h a c a r b o n r o d a t o m i z e r ( C R A - 6 3 ) . T h e c o n c e n t r a t i o n o f m e t a l is c a l c u l a t e d o n t h e basis o f changes i n the a b s o r p t i o n r e s u l t i n g f r o m s t a n d a r d a d d i t i o n s to the s a m p l e s o l u t i o n . Apparatus ( 1 ) Carbon

rod atomizer,

V a r i a n T e c h t r o n m o d e l 63 o r e q u i v a l e n t .

( a ) 9 - m m P y r o l y t i c a l l y c o a t e d a t o m i z a t i o n furnaces ( V a r i a n - T e c h t r o n ). ( b ) F X - 9 I s u p p o r t electrodes ( P o c o G r a p h i t e ) .


tubes

130

ANALYSIS OF P E T R O L E U M

FOR TRACE

METALS

( 2 ) Atomic absorption spectrophotometer (AAS), J a r r e l l - A s h 82-532 or equivalent. ( a ) S t r i p c h a r t r e c o r d e r , 0 - 1 0 m v w i t h 0.5-sec response t i m e ( L e e d s & N o r t h r u p Speedomax W or equivalent). ( b ) M a n g a n e s e h o l l o w c a t h o d e l a m p ( J a r r e l l A s h or e q u i v a l e n t ) .


(c)

L e a d hollow cathode lamp (Jarrell A s h or equivalent).

( 3 ) Syringe, w i t h T e f l o n t i p or T e f l o n n e e d l e , c a p a b l e of d e l i v e r i n g l - / d samples r e p r o d u c i b l y . ( 4 ) Micropipettes, 5-, 10-, a n d 50-μ\ ( c a p i l l a r i e s , s y r i n g e , or E p p e n dorf pipettor). Reagents ( 1 ) Tetrahydrofuran ( T H F ) A C S reagent grade. (2)

Standards ( a ) C o n o s t a n , M n s t a n d a r d , 5000 p p m ( w / w ) m a n g a n e s e i n oil (Continental O i l Co.). ( b ) S t o c k l O O O - ^ g / m l standards. W e i g h 2 g C o n o s t a n 5 0 0 0 - p p m ( w / w ) s t a n d a r d i n t o a 1 0 - m l v o l u m e t r i c flask a n d d i l u t e to v o l u m e with T H F . ( c ) C a l i b r a t i o n s t a n d a r d ( 5 / x g / m l ) . D i l u t e 50 μΐ of 1 0 0 - j u g / m l stock s t a n d a r d to 10 m l w i t h T H F . Procedure. I n i t i a l l y a l l glassware m u s t b e c l e a n e d w i t h ( 1 : 1 ) n i t r i c a c i d p r i o r to use. T h e e q u i p m e n t is t h e n rinsed s e v e r a l times w i t h T H F . ( 1 ) W e i g h 2.5 g o i l s a m p l e i n t o a 5 - m l v o l u m e t r i c flask a n d d i l u t e to v o l u m e w i t h the solvent. ( 2 ) O p t i m i z e the H V A A f o r manganese w i t h the t u b e f u r n a c e i n the optics u s i n g the f o l l o w i n g settings as a g u i d e . Wavelength (nm) I n e r t gas- ( 1 / m i n ) / p s i Furnace A l i q u o t used C R A - 6 3 program dry ash atomize

279.4 N 4/10 9-mm tube 1μ\ (V/sec) 2/20 6.5/30 8/3 2

W h e n the o p e r a t i n g parameters are o p t i m i z e d , scale e x p a n s i o n s h o u l d b e u s e d so t h a t e a c h 25 n g M n i n 5 m l s o l v e n t gives b e t w e e n 10 a n d 20 scale units. I f samples c o n t a i n > 5 X d e t e c t i o n l i m i t levels of M n , a f u r t h e r d i l u t i o n of the s a m p l e s h o u l d b e m a d e b e f o r e s t a n d a r d a d d i t i o n s . T h i s d i l u t i o n t e c h n i q u e is r e c o m m e n d e d r a t h e r t h a n c h a n g i n g o p e r a t i n g p a r a m e t e r s . T h e r e s i d u a l h e a t i n the a t o m i z a t i o n t u b e c o n t r i b u t e s to the r e p e a t a b i l i t y of s a m p l e signals. T h i s effect m a y b e m i n i m i z e d b y i n j e c t i n g samples o n a fixed schedule. F o r the m e t h o d d e s c r i b e d here, injections m a d e at 90-sec i n t e r v a l s g i v e g o o d r e p e a t a b i l i t y . ( 3 ) A l i q u o t 1 μ\ of the s a m p l e s o l u t i o n i n t o the s y r i n g e , i n i t i a t e the C R A - 6 3 p r o g r a m , a n d inject the s a m p l e a l i q u o t i m m e d i a t e l y . (4) R e c o r d the peak height caused b y absorbance observed d u r i n g t h e a t o m i z a t i o n step of the p r o g r a m .


11.

HOFSTADER E T A L .

131

Manganese

( 5 ) R e p e a t Steps 3 a n d 4 t w o m o r e t i m e s ; c a l c u l a t e t h e average. I f t h e three signals are w i t h i n ± 10% of t h e average, u s e this v a l u e i n t h e final c a l c u l a t i o n ; i f not, repeat t h e sequence Steps 3 a n d 4 t w o m o r e times a n d use t h e average of t h e five r e a d i n g s . ( 6 ) R e c o r d t h e average r e a d i n g of t h e s a m p l e s o l u t i o n as A . 0


( 7 ) A d d 5 μ\ of t h e c a l i b r a t i o n s t a n d a r d ( e q u i v a l e n t t o 2 5 n g ) t o t h e same s o l u t i o n , m i x w e l l a n d c a r r y o u t Steps 3 - 5 . R e c o r d t h e average p e a k h e i g h t as Αχ. ( 8 ) A d d a s e c o n d 5 / J o f t h e c a l i b r a t i o n s t a n d a r d ( 2 5 n g , a t o t a l of 50 n g ) to t h e s a m p l e s o l u t i o n a n d a g a i n c a r r y o u t Steps 3 - 5 . R e c o r d t h e average p e a k h e i g h t as A . 2

( 9 ) A d d a t h i r d 5 / J of the calibration standard (25 n g , a total of 75 n g ) to t h e s a m p l e s o l u t i o n a n d a g a i n c a r r y o u t Steps 3 - 5 . R e c o r d t h e a v e r a g e p e a k h e i g h t as A . 3

( 1 0 ) Reset w a v e l e n g t h t o 280.2 n m a n d i n j e c t t h e s a m p l e s o l u t i o n ( Step 9 ) t o m e a s u r e b a c k g r o u n d . R e c o r d t h e r e a d i n g as b. Calculation ( 1 ) C a l c u l a t e the concentration of manganese i n the sample from the first a d d i t i o n ( S t e p 7 ) as:

( 2 ) Repeat the calculation for the second a d d i t i o n :

&

/

&

A— 2

A

^

0

2.5 g

( 3 ) Repeat the calculation for the third addition: n g M n / g = ^ ^ X A 0

/ N

^ 2.5 g

( 4 ) A v e r a g e t h e three v a l u e s (Steps 1 - 3 ) a n d r e p o r t t h a t n u m b e r as n g M n / g i n the sample.

Literature Cited 1. Shah, K. R., Filby, R. H., Hullar, W. Α., J. Radioanal. Chem. (1970) 6, 185. 2. Hitchon, B., Filby, P. H., Shah, K. R., Am. Chem. Soc., Div. Pet. Chem., Preprints (1973) 18 (4), 623. 3. Agrawal, Β. B., Gulati, I. B., Pet Hydrocarbons ( 1972) 6, 193. 4. Milner, Ο. I., "Analysis of Petroleum for Trace Elements," Pergamon, New York, 1963. 5. Sandell, Ε. B., "Colorimetric Determination of Traces of Metals," 3rd ed., pp. 608-611, Interscience, New York, 1959. 6. Kundig, S., Kuhn, G., Automat, Chem. Technicon Symp. 3rd, 1967 (1968) 2, 361.



132 ANALYSIS OF PETROLEUM FOR TRACE METALS

7. Pinta, M., "Detection and Determination of Trace Elements," Engl, edit., pp. 429-430, Ann Arbor Science, Ann Arbor, 1971. 8. Lagron, Α., Verbeck, F., J. Electroanal. Chem. Interfacial Electrochem. (1973) 19, 413. 9. "Analytical Methods for Flame Spectroscopy," Sec. 54.94, Varian-Techtron, Palo Alto, Calif., 1972. 10. Van Ormer, D. G., Purdy, W. C., Anal. Chim. Acta (1973) 96, 93. 11. Welz, B., Wiedeking, E., Fresenius Z. Anal. Chem. (1970) 252, 111. 12. Segar, D. Α., Anal. Chim. Acta (1972) 58. 13. Ebdon, L., Kirkbright, G. F., West. T. S., Anal. Chim. Acta (1972) 58, 39. 14. Welz, B., Wiedeking, Fresenius Z. Anal. Chem. (1973) 264, 110. 15. Everett, G. L., West, T. S., Williams, R. W., Anal. Chim. Acta (1974) 70, 204. 16. Robbins, W. K., Anal. Chem. (1974) 46, 2177. 17. Gorsuch, T. T., "The Destruction of Organic Matter," International Series of Monographs in Analytical Chemistry, Vol. 39, p. 116, Pergamon, New York, 1970.


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