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ulfur and its com poun ds are present in m ost

petroleum products and lubricants in vary-

ing con centr ation s. The origin of sulfur in

th ese products m ay be from n atural sources or the

s u lf u r co m p o u n d s m a y h a v e b e e n a d d e d d u r i n g

product processing as performance enhancers.

The determin ation of sulfur con ten t of crude oil isan int egral part o f th e so-called cru de assay of oil ,

since its concentration contributes to the complexity

of th e crude oil refin ing step. The presen ce of sulfur

com poun ds in p etroleum produ cts is n ot desirable

s in c e t h e y im p a r t o d o r a n d m a y r e a ct w i t h e n d -

produ ct contain er vessels. Som e sulfur com poun ds

m ay corrode various metallic parts of interna l com-

bustion e ngines. Effects vary according to th e chem i-

cal type of sulfur comp oun ds present. Sulfur oxides

form ed during gasoline combu stion can h inder the

perform ance of catalytic converters and can also be

converted to acids, which prom ote rusting and corro-

sion of engine parts and p iston rings and cause cylin -

der wall wear. In aviation gasoline, sulfur com poun dsh ave a deleterious effect on t he an tiknock efficiency

of th e alkyl lead com pou nd s. Sulfur in diesel fuels

causes wear due to th e corrosive nature of th e com-

bust ion produ cts and in creases the am oun t of de-

posit s in the combust ion cham ber and on p istons .

High boilin g range fractions an d residual fuels usually

contain higher am oun ts of sulfur, which creates cor-

rosion and p ollution problem s. The conversion of sul-

fur to SO3 during combustion and later reaction with

water will form sulfuric acid, corroding t he m etal sur-

faces of equipm ent. In m any petroleum refining proc-

esses, low levels of sulfur in feed st ocks ma y poison

expen sive catalysts.

H i s t o r i c a l l y, th e biggest en viron m ent al con cern

wi th th e presence of su l fur in pet ro leum products

w as t he em i ss ion o f su l fu r ox ides fo rm ed du r in g

com bustion of various fuel oils in large comm erci a l

or dom estic app lications. Consequen tly, indu strialsulfur emissions are strictly controlled by most state

and national government environmental pollut ion

control agencies. With the advent of the 1990 Clean

Air Act an d action s by ind ividua l states such as Cali-

16 NOVEMBER 2000

S

Determ ination of su lfur in p etroleum produc ts

and lubricants: A critical review of

test perform ance

R.A. Kishore Nadkarni

A s an outcom e of this Euro p e a n

ro u n d - robin study , it is pro p o s e d

that the Wick bold and EDXRF

m ethods be dropped from furt h e r

consideration for analyzing fuels at

the 30 -m g/ k g sulfur lev el for the

ye ar 200 5.

Table 1Analytical test methods used for the determination of sulfur in

petroleum products and lubricants*Analysis* * ASTM IP DIN AFNOR JIS ISO

General bomb method D129 61 51– 577 T60-109 — —

Lamp method D 1266 107 — M07-031 — —

High-temperature D 1552 — — M07-025 — —

methodWDXRF D 2622 — 51-400T6 — K2541 14596

Oxyhydrogen burner D 2784 — — — — —

or lamp

Oxidative micro- D 3120 — — — — 16591

coulometry

Oxidative micro- D 3246 373 — M07-052 — —

coulometry

Hydrogeneolysis and D 4045 — — — — —

rateometric colorimetr y

EDXRF D 4294 336 — M07-053 — 8754

Additives WDXRF D 4927 407 51-391T2 — — —

Additives ICP-AES D 4951 — — — — —

Additives ICP-AES D 5185 — — — — —

UV-fluorescence D 5453 — — M07-059 — —WDXRF D 6334 — — — — —

Oxidative combustion D 6428 — — — — —

and electron capture

detection

Additives WDXRF D 6443 — — — — —

EDXRF D 6445 — — — — —

**This table was excerpted from a larger com pilation of equ ivalent

test meth ods by Nadkarni.4

**IP = Instit ute o f Petroleum (U.K.), DIN = Deutsche In stitut e fur

Norm an g (German y), AFNOR = Association Francaise de Norm ali-

zation (France), JIS = Japan Indu strial Stan dards, and ISO = Inter-

national Organization for Standards (Geneva, Switzerland).



SULFUR DETERMINATIONcontinued

continued

Table 2Test methods for sulfur determination in petroleum products*

ASTM Method Technique Scope Limitation Repeatability Reproducibility Bias

D 129 Bomb combustion and Petroleum products, lube Not applicable to samples Dependent on Dependent on 0.05%high

BaSO4 precipitation oils, adpacks, greases; that give insoluble residues: Fe level level

>0.1% S Al, Ca, Si, Pb, silica, MoS2,

asbestos, mica, used oi ls

D 12 66 Lamp combust ion: 0.01 – 0.04% S i n gasol ine, Aci d or base f orming compounds 0.00 5 0.0 10 + ( 0.025X) Not k nown

BaSO4 precipi tat ion, or kerosene, naphtha in t it rat ion; labor intensive

NaOHtitration, or tur-

bidometry if < 0.01%

D 15 52 Hi gh-t emper at ur e Sampl es wi th boi li ng poi nt s I odat e:> 1% chl or ine and Dependent on Dependent on Not k nown

combust ion:i odate > 177 °C and > 0.06%S; > 0.1% nitrogen interf ere sulf ur level level

titration or IR detection petroleum cokes up to 8%S IR:none from N or S

D2622 WDXRF Diesel and jet fuels, kerosene, Volatile samples may not be See the test See the test ~3– 5%

distillate oils, naphtha, suitable; standard and sample method method relative bias

residual oils, lube base oil, matrix must be matched for

hydraulic oil, crude oil, un- C–H ratio; expensive

leaded gasoline, M-85 and instrument

M-100 fuels; range 3 mg/ kg

to 5.3%D 2784 Oxyhydrogen burner or For liquid petroleum gas >100 ppm halogens interfere NA** NA NA

lamp combust ion and only; >1 ppm S

BaClO4 titration or

turbidometry

D 3120 Oxidative pyrolysis 3– 100 ppm S in light liquid >10XCl, 1000XN, and 500 28% 38% NA

and microcoulometry hydrocarbons, boiling range ppm heavy metals interfere

26–274 °C

D 3246 Oxidative pyrolysis 1.5– 100 ppm S in petroleum >10XCl, >1% N, and 500 0.4 ppm 5 ppm NA

and microcoulometry gas ppm heavy metals interfere

D 4045 Hydrogenolysis and 0.02– 10 ppm S in liquids 0.16X 0.5 0.26X 0.5 NA

rateometric colorimetry with boiling points 30–371 °C,

e.g., naphthas, kerosene,

alcohol, steam condensate,

distillates, jet f uel, benzene,toluene

D 4294 EDXRF 150 ppm– 5% in hydrocarbons Spectral interference from 0.02894 0.1215 None

such as diesel, naphtha, >0.1X of water, lead alkyls, (X + 0.1691) (X + 0.0555)

kerosene, residuals, base Si, P, Ca, K, halides; matrix

oils, hydraulic oils, jet fuel, effects; oxygen interferes in

crude oils, unleaded gasoline, oxygenates

and M-85 and M-100 fuels

D 4927 WDXRF Additives, lube oils with Spectral and matrix inter- See the test See the test NA

0.01– 2.0% S ferences can be compensated method method

D 4951 ICP-AES Lube oils and additives Viscosity index improver gives 0.016 for oils; 0.061 for oils;

low bias but can be suppressed 0.14 for additives 0.372 for additives

D 5185 ICP-AES Used lube oils, base oils Same as D 4951; particulates 0.49X 0.81 1.2X 0.75 None

wi th 900–6000 ppm S wi ll give low resul ts

D 5453 High-temperatur e Liquid hydrocarbons boiling > 0.35% halogens interfere 0.1867X 0.63 0.2217X 0.92 Nonecombust ion–UV at 25–400 °Cand viscosi ties

fluorescence detection 0.2–10 cSt at room temp-

erature; naphtha, distillates,

motor f uels, oil s containing

1–8000 ppm S

D 6334 WDXRF 15– 940 ppm S in gasoline Standards need to be matrix 0.04 0.1182 None

and oxygenate blends matched, e.g., oxygenates, (X + 97.29) (X + 54.69)

gasohols

D 6428 Oxidative combustion– 0.05– 100 ppm S in liquid Moisture produced in combustion 0.06 @ 1 ppm S; NA NA

ECdetection aromatic hydrocarbons needs to be removed before 7.64 @ 80 ppm S

detection



f o rn i a , a n e m p h a s i s r eg a r d in g m o b i le p o l l u t i o n

sources (vehicles) has also evolved. The current h igh-

profile sulfur control issue is surely clean (low-sulfur)

m otor fuels, specifically gasoline an d diesel.

O n t h e o t h e r h a n d , se v er a l m e t a l su l fu r c o m -

poun ds are purposely added to lubricating oils and

addi t ives to en han ce thei r perform ance. These in-

c lude su l fon ates of barium , ca lcium, m agnesium,

M o S2 , etc. Further in formation on the p resence and

impo rtance of sulfur in petroleum prod ucts can be

foun d in Boldt an d Hall,1 Dyroff,2 and Nadkarni.3

Sulfur test metho ds

Given th e im portan ce of kno wing the accura te

concentration o f sulfur in m ost petroleum produ cts,

it is not surprising th at a variety of analytical tech -

niqu es h ave been em ployed for this task. Th e meth -

ods vary from classical techn iques such as sam ple

com bus t ion u s ing a lam p o r a bomb fo l low ed by

gravimetric or t i t rim etric determination to m odern

techn iques such as ultraviolet or X-ray fluorescence

and induct ively coupled p lasma–atomic em iss ion

spectrom etry (ICP-AES). The former methods are sel-

dom used in m odern laboratories because th ey are la-

bor inten sive, altho ugh th ey are often considered as

referee methods.

Table 1 lists the standard test methods published

by th e ASTM (Am erican Society for Testin g and Mate-

r ia ls) DO2 Comm it tee on Pet ro leum Products and

Lubrican ts . Where avai lab le, equivalent in t ern a-

tion al stan dard test m ethod s are also included. It is

n ot implied that th e ASTM m ethods and their inter-

national counterparts are exactly identical, only that

the p ertinen t m ethods are sim ilar and based on simi-

lar analytical meth odology.

Table 2 i s a com parat ive sum m ary of availab le

ASTM sulfur t est m eth ods with possible int erferences

in th e analysis and th eir test precision.

Given t h e plethora of test m ethods available forsu l fu r de t e rmina t ion i n pe t ro l eum p roduc t s , t he

choice for a particular analysis would depend on the

m atrix, sulfur concen tration , and desired precision of

an alysis. It is equa lly im portan t to kno w the preci-

sion capab ilities of the laborato ries regardless of th e

met hod precision stated in the ASTM books. Experi-

ence sho ws that a large nu m ber of laboratories are

n ot capable of obtainin g the expected precision of

the m ethod. There could be m ultiple reasons for th is,

including laboratories not following the test method

p r e c i s e l y, no t doin g frequent enou gh calibrat ion s,

no t correctin g for test meth od interferences, and/or

not having satisfactory quality control in the labora-

tory operation s. These are not m ere speculations, but

are based on ac tual labora tory experience . On the

oth er han d, it has been observed th at sets of labora-

tories that are well managed in terms of test meth od

adherence, appropriate calibration, and strict quality

control obtain precisions equal to if n ot better th an

the on es espoused in t he ASTM test m ethods.

It is illumin ating to look at the th ree major studies

don e to review th e analytical performan ce of som e

m ajor test meth ods used in th e laboratories test in g

petroleum products.

ASTM Research Report D.02 -1456

In a ve ry t h o rough re sea rch s tudy don e a t t he

Sout h west Research Inst i tut e (SWRI, San Ant on io,

TX), thr ee sulfur m eth ods were com pared for fitness

for use .5 The th ree m e thods s tud i ed w ere D 2622

wavelength -dispersive X-ray fluo rescen ce (WDXRF),

D 4294 ene rgy -d i spe rs ive X -ray f l uo rescence

(EDXRF), an d D 5453 UV- fluo rescen ce for t h e an aly-

sis of fuels at <500 m g/kg sulfur. All three were fou n d

to be equivalen t for measuremen ts in th e 150–500

m g / k g r an g e . D 5 4 5 3 a n d D 2 6 2 2 d e m o n s t r at e d

equivalent fitness for use down to 20 m g/kg. Stron g

evidence was foun d that t he D 5453 meth od can be

fit for use in m ultilaboratory situations down to th e

1-mg/ kg sulfur level. A sin gle isooctan e m atrix was

used to m inimize the well-known carbon to h ydro-

gen rat io in terference in th e XRF test m eth ods. All

th ree test m etho ds were then evaluated for any bias

with respect to 24 commonly occurring organosulfur

compou nd s. No bias was found an d th e accuracy was

within th e precision limits for each of the test m eth-

ods. Of th ese three test meth ods, the best low-level

precision and accuracy were found in m etho ds D

2622 and D 5453. Of th ese two, D 5453 was foun d to

generate better dat a in t h e low (<50 mg/kg) sulfur

regime. This work suggests th at th e D 5453 m eth od

can be routinely used for the determination of sulfur

in liquid h ydrocarbon s at levels below 1 mg/ kg.

European sulfur cross-check

In a very recent ly com pleted, very large roun d-

robin stud y in Europe, 69 laboratories from n ine coun -

tries participated in the determination of sulfur at lev-

els between 5.0 an d 500 mg/ kg in eight gasoline and

seven d iesel samp les.6 Five met ho ds were principally


D 6443 WDXRF Lube oils and additives Spectral interference from Mo and None

with 0.5– 1% S Pb; in other elements, interf erence

reduced by alpha corrections

D 6445 EDXRF Gasoline 48– 1000 ppm S See D 4294 12.3 (X + 10)0.1 36.26 (X + 10)0.1 NA

**X is the m ean o f all results.

**NA= not available.



tested: W DXRF (ISO14596 , i.e., ASTM D 2622 ), EDXRF

( I P P M CX/00, i.e., ASTM D 4294), UV- f l u o r e s c e n c e

(MO7-059, i.e., ASTM D 5453), microcoulom etry (ISO

CD 16591, i.e., ASTM D 3120), and Wickbold com bus-

tion (EN 24260 , i.e., D 1266).

At th ese levels, all five test m eth ods were foun d to

produce essentially equivalent results, but the preci-sion of different m eth ods varied considerably (Table

3). Th e best reprod ucibility was obtain ed for W DXRF

and UV-fluorescence methods. Table 4 compares the

reprodu cib i li ty obta in ed in th is cross-check wi th

th ose suggested in th eir equivalent ASTM m e t h o d s .

The best reproducibility appears to be those of the D

2622 and D 5453 test meth ods. As an outcom e of this

European roun d-robin study, it is proposed th at the

Wickbold and EDXRF methods be dropped from fur-

t h e r cons ide ra t i on fo r ana lyz ing fue l s a t t he 30 -

m g/kg sulfur level for the year 200 5. Only th e UV-

fluorescence m ethod was considered suitable for the

determin ation o f sulfur at less than 10 mg/kg con-

ten t required in future Europ ean fuels.

ASTM interlaboratory cross-check program s

For n early a decade, th e ASTM DO2 Pet ro leum

Products an d Lubricants Comm ittee through its Coor-

dinating Subcommittee 92 has instituted a voluntary

p ro f i c i ency t e s t i ng p rog ram.7 Th i s p r o g r a m h a s

proved h ighly successful in th e oil in dustry world-

wide. At present, 11 prod uct lines are analyzed am on g

a total of over 1400 laboratory un its, nearly 35% of

these being non-U.S. laboratories. Most products are

Table 3Precision obtained in the Center for European Normalization

round-robin studyMethod Repeatability Reproducibility

Gasoline WDXRF 0.048X+ 0.0002 0.147X + 0.0003

EDXRF NA 0.0838X + 0.002

UV-fl uorescence 0.0417X + 0.0001 0.1573X + 0.0002

Mi cr ocoul ometr y 0.043X + 0.000 3 0.16 79X+ 0.0008

Wickbold NA NA

Diesel WDXRF 0.0293X+ 0.0003 0.0725X+ 0.0005

EDXRF NA 0.0289X+ 0.0016

UV-fl uor escence 0 .02 85X + 0.000 2 0.108 8X+ 0 .0 002

Microcoulometry 0.043X + 0.0003 0.1679X+ 0.0008

Wickbold NA NA

Table 4Comparison of reproducibility obtained in the European cross-

check with ASTM test method reproducibility*European cross-check ASTM method

Method reproducibility reproducibility

WDXRF 10 12.8 ( D 2622)

EDXRF 37 74 (D 4294)UV-fluorescence 10 8.1 (D 5453)

Microcoulometry 16 19 (D 3120)

Wickbold 17 101 (D 1266)

*All precision estima tes are at 50 m g/kg sulfur in gasoline.



analyzed th ree times per year. Since on ly a single anal-

ysis using ASTM DO2 m eth ods is carried ou t, on ly an

estimate of reprodu cibility (which ASTM defines as

the agreemen t between tw o laboratories analyzing th e

same sample using the same test method) can be cal-

culated. As can be imagined, a vast database exists

thr ough t his program regarding th e reproducibility of

various test m ethods u sed for a m ultitude of analyses.

A survey amon g th e participating laboratories con-

duc t ed in Augus t 1999 found tha t t he m os t com-

m only used test m ethods for sulfur determination in

m otor gasoline, #2 diesel fuel, reform ulated gasolin e

(RFG), an d aviation tu rbin e fuel were D 2622 WDXRF,D 429 4 EDXRF, an d D 5453 UV-fluorescen ce. Oth er

test meth ods, D 1266 lamp, D 3120 m icrocoulom etry,

D 4045 h yd rogeneo lysi s ra t eomet ry, an d D 6344

WD X R F, w ere used to a m uch lesser exten t.8 Table 5

gives typical an alyses obtain ed in t he se cross-ch ecks

using alternative sulfur m ethod s in different mat rices.

There is a vast am oun t of data available, but on ly the

typical data from 1999 cross-ch ecks are included t o il-

lustrate the p oint. Overall, th ere appears to be good

agreemen t between the m ean results obtained by al-

ternative methods for a particular product. However,

som etimes th ere is con siderable difference between

th e precisions ob tained associated with th e individual

test m etho ds. Th is point is more vividly illustrated inth e box and wh isker graphs plotted for two produ cts,

m otor gasoline an d autom otive lubricant ad ditive, in

F igures 1 an d 2 respectively.

These graphs p rovide a cross-reference of tes t

data genera ted from di fferent m ethods th a t de ter-

m ine th e same param eter. Th e graph separates th e

data by stand ard with th e shaded box representing

the m idd le 50% o f t e st da t a cen t e red a round th e

m edian . The h orizon tal l ines within th e box repre-

sent t he m edian of the reported data . Data poin ts

above o r be low th e w h i ske r a re inc luded , un l e ss

SULFUR DETERMINATION continued

Figure 1 Box and whisker graph for methods used for sul - fur determination of motor gasoline sample 9908.

Figure 2 Box and whisker graph for methods used for sul - fur determination of automotive lubricant additive 9910.

Table 5Alternate methods precision for sulfur determination in

petroleum productsAnalysis method Robust mean ± robust SD (#va lid results)

Motor gasoline (MG9904) mg/ kg

D 1266 115 ± 38 (5)

D 2622 96 ± 8.7 (30)

D 3120 69 ± 36 (13)

D 4045 82.8 ± 8.7 (4)

D 4294 105 ± 34 (49)

D 5453 78.7 ± 14.2 (15)

Reformulated gasoline (RFG9906) mg/ kg

D 2622 16.7 ± 6.0 (66)

D 3120 14.3 ± 3.7 (5)

D 4045 13.6 ± 3.5 (5)

D 4294 29 ± 21 (31)

D 5453 13.9 ± 1.6 (22)

Diesel fuel (DL9902)mg/ kg

D 129 614 ± 222 (10)

D 1266 360 (1)

D 2622 466 ± 19 (64)D 4045 422 ± 152 (4)

D 4294 487 ± 27 (142)

D 5453 471 ± 55 (20)



the d ata are off the y-axis scale, in wh ich case the

data , which wou ld be off the graph , are indica ted

with an arrow. The y -axis scale represen ts th e abso-lute value and th e x-axis scale pro vides an ident ifi-

cat ion of the tes t method an d nu mber of report ing

data points.

The sulfur concentrat ions in these two products

d i ffer a lmost by a factor of 100 . Even th ough th e

m ean values of each product are reason ably c lose

am on g different test meth ods, the range of results

and th us th e reprod ucibil ity of the an alysis varies

widely from u n acceptable (e.g., D 4927A in Figure 2)

to very precise (e.g., D 1552 in Figure 2). Thus, great

care mu st be exercised in m aking decision s regarding

product qu ality am ong buyers and sellers and by th e

r e g u l at o ry agen cies. Th e pr ecision of th e an alysis is

p e r h a p s e ve n m o r e im p o r t a n t t h a n t h e a ve r ag evalue in cases of dispu te.

In spite of th e resoun ding success of the ASTM

DO2 Committee’s interlaboratory crosscheck pro-

gram (ILCP) project, the p recisions calculated from

these roun d-robin studies were generally found to be

inferior to th ose required in th e stan dard test m eth-

ods. This situation was som ewhat im proved after th e

extrem e outlier rejection routine was included in the

stat ist ical calculat ion s. However, th e roun d-robin

precision was st i ll foun d to be better th an t he o ne

given in th e stand ard test meth od on ly in a smal l

nu mer o f cases. Typical data on cross-check and test

method reproducibility are compared in Table 6 . As

n oted earlier in th is article, a lack of strict adh erence

to test metho d detai ls, inadequate calibrat ion, and

prob able lack of qu ality con trol in th e laborato ry are

th e suspected reasons for th is discrepancy. The or igi-

nal reproducibil ity value in the standard test m eth-

o d s r e s u l t e d f r o m w e l l -c o n t r o l le d c r o ss - ch e c ks

amon g a lim ited num ber of leading industry labora-

tories. Hence, i t would n ot be judicious to replace

the current reproducibility limits given in the stan-

d a r d t e s t m e t h o d s w it h t h o s e fr o m t h e s e c r o ss -

checks amon g laboratories that m ay or may n ot be

technically well controlled.

Table 6Comparison of reproducibility of cross-checks and test method

for sulfur determinationMethod Sample Robust mean Reproducibility

Cross-check Test method

D2622 RFG 9910 18.0 mg/ kg 16.3 8.4

D3120 RFG 9910 16.3 mg/ kg 7.0 6.2

D5453 RFG9910 16.8 mg/ kg 5.5 3.0D1266 MOGAS9912 0.0158 M% 0.0122 0.0104

D2622 MOGAS 9912 0.01741 M% 0.00396 0.00208

D3120 MOGAS 9912 0.01559 M% 0.00517 0.00593

D4294 MOGAS 9912 0.0166 M% 0.0114 0.0088

D5453 MOGAS 9912 0.01475 M% 0.0061 0.0022

D2622 DL 9910 69.1 mg/ kg 16.9 10.4

D5453 DL 9910 55.3 mg/ kg 47 8.9

continued



Regulatory aspects of sulfur in gasoline

Redu ction of sulfur levels in gasoline an d diesel

with a view toward significan tly reducing dam age to

vehicular pol lu t ion cont ro l devices is an on going

goal o f th e U.S. EPA. The U .S. EPA ta rgets gaso lin e to

have an average sulfur level reduced to 30 mg/kg by

th e year 2004 from th e current average of m ore than300 m g/kg. It also prop oses that sulfur levels in diesel

will be reduced by 97% to 15 m g/kg by the year 2006.

To t h is end, th e U.S. EPA recently p rom ulgated i ts

Tier 2 moto r vehicle em ission stan dards an d gasoline

sulfur control requiremen ts in th e Federal Register.9, 10

These n ew laws are significant in th at th ey for the

first time treat automobiles and their fuel as a single

system. Included in these current an d p roposed regu-

l a t ion s i s t he requ i remen t t h a t on ly a si ng l e t e s t

m ethod for the determination of low levels of sulfur

in gasolin e, RFG, an d diesel fuels be used.11

There i s l it t le d isagreem ent am ong aut om ot ive

m anufacturers and th e envi ronm enta l comm un i ty

with th e U.S. EPA’s overall goal of red ucin g sulfur t onear-zero levels in th e next d ecade. However, th e re-

finers an d im porters have engaged in serious debate

about levels of sulfur reduction an d t im ing. While

no t as h igh profi le , o th er d iscussion has revolved

around th e appropriate test m ethods for measuring

th ese low levels of sulfur fuels of the n ot-too-distan t

futu re. In its fin al Tier 2 gasoline ru lema king, th e U.S.

EPA ha s man dated th e use of D 2622 W DXRF as the

sole regulatory sulfur test method for this analysis.

However, it is questionable wheth er th is ind eed is the

best choice of test m eth ods. Based on its precision ,

the UV-fluorescence test meth od D 5453 would be a

better choice rath er than t h e D 2622 WDXRF m etho d

for the m easurem ent of low sulfur level fuels. Indeed,som e years back, th e Californ ia Air Resources Board

(CARB) man dated D 5453 as the sulfur test m etho d

for the an alysis of gasoline con tain ing <10 mg/kg. It

w a s d e si g n a t e d a s a n a l t e r n a t i ve t o t h e D 2 6 2 2

m eth od for sulfur levels of >10 m g/kg; for diesel fuels,

D 5453 was established as an equ ivalent test meth od

to the D 2622 test meth od.12

In its notice, the U.S. EPA also seems to recognize

th at in certain situations D 2622 h as limitations. As

an exam ple , in t he range requ i red fo r Ca l ifo rn i a

fuels, the U.S. EPA agreed to recogn ize th e test meth -

ods allowed b y th e California EPA.10

The ASTM CS 92 cro ss-checks clearly in dicate t h at

for gasoline types of sam ple below th e 10-mg/kg sul-fur level , D 2622 has extrem ely poor precision. At

aroun d 30 mg/kg, D 2622 has impro ved reproducibil-

i t y, bu t D 5453 still ha s superior reprod ucibility at

this level (see Table 7 for th is comp arison). At sulfur

levels over and a bove 50 m g/kg, however, bo th D

2622 an d D 5453 prod uce equivalent r esults in RFG,

motor gasoline, diesel, and jet fuels based on ASTM

cross-checks between Jun e 1996 and December 1998

(Figure 3).

Based on t h e precision o f analysis, D 5453 appears

to be m uch sup e r io r t o D 2622 a t l e ss t han a 50 -

m g/kg sulfur level an d equ ivalent at above th is level.

T h u s , t h e r e i s n o t e c h n i c a l r e a so n w h y D 5 4 5 3

should n ot be th e primary meth od of analysis for sul-

fur in gasoline-type products. The cost of in strum en -

tation and m aintenan ce of D 5453 equipm ent is also

about th ree t imes lower than t hat n eeded for the D

2622 m ethod.

Reliability o f EDXRF Test Meth od D 4294

Although per its scope this meth od is not m eant for

th e ana ly si s o f sam p les con t a in in g l es s t han 150

m g/kg sulfur, it appea rs to be widely used in th e oil in-

d u s t ry in spite of its p oor reprod ucibility, a s seen in

th e ASTM cross-ch ecks. The reason fo r its widespread

use is prob ably th e low cost of purch ase an d m ainte-


Figure 3 D 5453 vs D 2622.

Table 7Precision of test methods as related to sulfur

concentration levelsASTM D 5453 D 2622sample* Mean SD % RSD Mean SD % RSD

Below 10-mg/ kg level

RFG9810 2.5 1 40 6.5 5.5 85

RFG9907 2.2 0.9 40 6 5.7 95JF 9711 3.5 1.8 51 13.9 13.3 96

RFG9806 4.5 1.4 31 9 7.1 79

RFG 9706 5 1.5 30 7.4 5.2 70

RFG 9712 5 1 20 8.8 5.3 60

RFG9612 8.7 1.9 22 12.2 5.7 47

Between 10 and 30 mg/ kg level

MG 9612 10 2 20 14 10 71

RFG9807 11 2 18 13 6 46

RFG 9709 13 3 23 14 6 43

RFG 9910 17 2 12 18 6 33

RFG 9609 14 3 21 15 6 40

RFG 9906 14 2 14 17 6 35

RFG 9703 27 5 19 28 6 22

RFG 9901 29 2 7 30 7 23

RFG 9803 30 4 13 34 10 29

RFG 9904 23 2 9 24 8 33

*RFG = reform ulated gasoline; JF = jet fuel; MG = m otor gasoline.



n a n c e o f t h e i n s t r u m e n t a t i o n u s e d i n t h i s t e s t

method. Table 8 com pares th e results obtained on sev-eral typical samples of petroleum products an alyzed

by th ree m ajor meth ods used in t he oil ind ustry: D

2622 W DXRF, D 4294 EDXRF, an d D 5453 U V-flu ores-

cence. In spite of the large num ber of laboratories us-

ing the D 4294 m eth od, poor reprodu cibility, some-

times approaching 100% or m ore of the m ean value,

m akes th is an alysis of very little use, particularly in

settling prod uct qu ality disputes between buyer and

seller. Again, at b elow a 30-m g/kg sulfur level, D5453

h as the best precision am ong th e three test m ethods

com pared.

Concluding remarks

There are over a dozen test meth ods available for

th e determin ation of sulfur in petroleum products and

lubrican ts. Each m ethod has its advantages and draw-

backs. An intelligen t cho ice m ust be m ade based on

th e meth od’s accuracy and p recision b efore deciding

wh ich m ethod to use for a specific product. Since th e

m ethod precision is depend ent on the sulfur concen-

tration level, this is a critical decision. Arbitrarily using

a test meth od withou t takin g these considerations into

accoun t can on ly result in produ cing data th at are un-

reliable, which do es not h elp in settling disputes in

com m ercial tran saction s or in regulatory affairs.

References

1. Boldt K, Hall BR, eds. Significan ce of Tests for PetroleumProduct s. STP 7C. ASTM, Philadelph ia, PA, 1977.

2. Dyroff GV, ed. Man ual on Significance of Tests for Petro-leum Products. 5th ed. MNL 1. ASTM, Philadelphia, PA,1989.

3 . Nadkarn i RA. Modern Ins t rumen t a l Met hods o f El e-m ent al Analysis of Petroleum Products and Lubricants.STP 1109. ASTM, Philad elph ia, PA, 1991 .

4. Nadkarni RA. Guide for the Analysis of Petroleum Prod-ucts and Lubricant s. MNL 44. ASTM, West Consho ho c-ken , PA, 2000.

5. Kohl K. ASTM Rese arch Report DO2-145 6. ASTM, We stCon shoh ocken, PA, 1999.

6. Tittarelli P. Roun d Robin Exercise for Sulfur Test Meth-ods for EN 228 an d EN 590 Fuel Specification s. CEN/TC19/WG 27, Apr 2000.

7. Bover WJ. ASTM Stan dardization News 1994; June:56–63 .

8. Bradley D. (ASTM). Private comm un ication to EPA, Sep

20, 1999.9. U.S. EPA. Federal Register, 62(133), 40 CFR Part 80, Part

II, p. 37337 . Jul 11, 1997 .

10. U.S. EPA. Federal Regist er, 64(92), 40 CFR Parts 80, 85,and 86, p. 26055, May 13, 1999.

11. U.S. EPA. Federal Register, 65(28), pp. 67 52–74. Feb 10 ,2000.

12. Title 13, California Code o f Regulations. Sections 2281and 2282, Sep 1992.

Table 8Comparison of three major test methods used in oil industr y

for sulfur analysis; values expressed as mean± reproducibility (number of valid results)

D 2622 D 4294 D 5453ASTM sample* (WDXRF) (EDXRF) (UV-fluorescence)

JF9811 6.1 ± 15.8 (34) 34 ± 83 (81) 2.85 ± 1.8 (16)

MG9812 184 ± 39 (27) 195 ± 111 (52) 165 ± 68 (16)MG 9904 96 ± 24 (30) 105 ± 94 (49) 79 ± 39 (15)

RFG 9811 218 ± 39 (69) 235 ± 75 (42) 214 ± 68 (20)

RFG9902 67 ± 24 (73) 72 ± 66 (39) 65 ± 20 (25)

RFG 9904 30 ± 19 (71) 42 ± 69 (39) 29 ± 7 (24)

RFG 9905 99 ± 27 (74) 114 ± 100 (44) 89 ± 22 (25)

RFG 9906 17 ± 17 (66) 29 ± 58 (31) 14 ± 4 (22)

DL 9810 441 ± 52 (63) 456 ± 102 (143) 440 ± 91 (16)

DL 9902 466 ± 53 (64) 487 ± 75 (142) 471 ± 152 (20)

*DL = diesel fuel.

D r. N adkarni is President, Millennium Analytics, Inc., 4 7 Helena St., East Brunswick, NJ 08816, U.S.A.; tel.: 732-

613-8710; e-mail: [email protected]. Dr. Nadkarni is Chairman of the ISO/ TC 28 Committee on Petroleum Prod - ucts and Lubr icants, Chairman of the ASTM DO2 Sub- Committee 3 on Elemental Analysis, and Vice-Chairman of the ASTM DO2 Sub-Committee 92 on Inter- L a b o r a t o ry Cross-Check Programs.

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