Investigation of Synthetic PolymerInvestigation of Synthetic Polymer Characterization by means of...

MALDI/TOFMS method for general purposes because

high performance systems having high mass resolu-

tion are required for analyzing complex and detailed

mass spectra.

Although few reports exist on the SEC/ESIMS

method utilizing quadrupole mass spectrometers (q-

MS) having low mass resolution 7), important informa-

tion such as molecular weight and constitutional

repeating units, which are required for structural analy-

ses of synthetic polymers, should be obtained if limit-

ing the analysis targets to components having relative-

ly low molecular weights (up to around 10,000). In this

paper, we will explain what level of analysis can be

achieved using a q-MS by introducing spectrum analy-

sis methods and measurement procedures.

Furthermore, this paper consists of revised versions

of the reports released at the 54th Annual Conference

on Mass Spectrometry Osaka Japan 2006 and at a

workshop for mass spectrometry entitled “Recent

development of synthetic polymer analysis” 8) and the

9th and 11th National Symposium on Polymer Analysis

and Characterization 9), 10). The progress of systems

and methods in the field of synthetic polymer mass

spectrometry is extremely rapid. Please refer to the lat-

est data and documents for the current situation.

Information on SEC/ESIMS

SEC (size exclusion chromatography) is a liquid

chromatography technique which separates sample

substances according to their molecular sizes. It elutes

Introduction

For mass spectrometry of synthetic polymers,

MALDI/TOFMS1) is commonly used for general pur-

poses due to its simplicity. Although a matrix is used as

an ionization aid in the MALDI method, some trial and

error is necessary to apply the method to the analysis

of synthetic polymers and synthetic polymer com-

pounds having unknown structures, as an appropriate

matrix suitable for the target chemical substance(s)

must be carefully selected. Furthermore, samples hav-

ing large molecular weight distributions (Mw/Mn) are

not readily ionized, and such samples require pretreat-

ment refining. Therefore, in the MALDI method, it is

necessary as a principle to combine with a separate

fractionation system because online combination with

chromatography is difficult.2)

On the other hand, the ESI method 3), 4) is an effec-

tive ionization method for chemical substances having

high ionicity or polarity. Through this method,

hydrophobic synthetic polymers can also be ionized by

using an alkali metal salt or other similar substances as

a cationization agent, thus enabling a mass spectrum to

be obtained.5) Moreover, online combination with chro-

matography can be readily conducted in this method

because ionization is performed by spraying a sample

solution. This ionization method is most commonly

used in the LC/MS method. Therefore, some structur-

al analyses using SEC/ESIMS were reported in the

early 1990s.6) However, at the present time, the

SEC/ESIMS method is not as commonly used as the

1SUMITOMO KAGAKU 2008-II

Investigation of Synthetic PolymerCharacterization by means ofSEC/ESIMS

Sumitomo Chemical Co., Ltd.

IT-Related Chemicals Research Laboratory

Yoshinobu TSUCHIDA

Keiko YAMAMOTO

Hiromi YAMADA

It is difficult to analyze synthetic polymers using mass spectrometry, because they have a very wide moleculardistribution (Mw/Mn). But if we select a relatively low molecular species, we can obtain information on polymerstructure by means of MS. In this paper we describe an analysis method for synthetic polymers by means ofSEC/ESIMS (using q-MS), some analysis cases, and the problems of this method.

This paper is translated from R&D Report, “SUMITOMO KAGAKU”, vol. 2008-II.

substances having larger molecular sizes faster than

those with smaller sizes. It is more commonly referred

to as GPC (gel permeation chromatography). However,

in this paper, we will refer to this method as SEC

because this expresses its separation principle.

In the SEC/ESIMS method, SEC and ESIMS are

combined online 6), 7). Fig. 1 shows a block diagram of

the system used for the investigation that we conduct-

ed in this case. For the cationization agent, the post col-

umn addition method --in which the agent is added

after the column is eluted-- was used.

Evaluating Cationization Agents

In the SEC analysis of hydrophobic synthetic poly-

mers, THF (tetrahydrofuran) and chloroform are com-

monly used for the mobile phase. For the cationization

agent, NaI and KI are commonly used due to their solu-

bility in the mobile phase.5) In order to obtain a cation-

ization agent that can also substantially ionize macro-

molecular components, we compared KCl, NaI and KI.

The cationization agent was a 1:1 mixed solvent of

water and acetonitrile at a concentration of 1mM. The

mixed solvent was then added at a rate of 0.05mL/min

using the post column addition method. The samples

used for the evaluation were mixtures of different mol-

ecular weights of PMAA (poly-methylmethacrylate,

Fig. 2) from Polymer Laboratories, Inc., which was

commercially available as a molecular weight calibra-

tion reference standard,The molecular weights (MW)

used for mixing were 3100, 6540, 9400, 12700 and

29300. The concentration was 1mg/mL and the injec-

tion rate was 25µL.

Fig. 3 shows the chromatogram and Fig. 4 shows

the mass spectrum in the area A (with no background

processing).


Investigation of Synthetic Polymer Characterization by means of SEC/ESIMS

Fig. 1 Schematic Diagram of SEC/ESIMS Sys-tem

SEC System(Agilent 1100 LC)Agilent 1100 LC/MDS

0.25mL/min THF

50µL/min

LC Pump for addition

Fig. 2 PMMA (Poly-methylmethacrylate)

C5H8O2••

Exact Mass : 100.05243Mol. Wt. : 100.11582

C10H18O4••

Exact Mass : 202.12051Mol. Wt. : 202.24752O

OO

OO

O

n

Fig. 3 Size-exclusion Chromatograms of PMMA mixture

a)

b)

c)

d)

a) 220nm. b) TIC, +NaI. c) TIC, +KI. d) TIC, +KClA ; averaging area of spectrums in Fig. 4Column ; Tsk-gel Super HZ(4000*3+3000+2500*2)

A

mAU

02468

10

010000002000000300000040000005000000

0100000020000003000000400000050000006000000

100000020000003000000400000050000006000000

min45 50 55 60 65 70

min45 50 55 60 65 70

min45 50 55 60 65 70

min45 50 55 60 65 70

Fig. 4 SEC/ESIMS Spectrum at A

020406080

100

020406080

100

m/z500 1000 1500 2000 2500

m/z500 1000 1500 2000 2500

m/z500 1000 1500 2000 2500

020406080

100 a)

b)

c)

a) +NaI. b) +KI. c) +KCl

�

�

�

��

� ��

�

��

�

�

�

� � �

�

� ��

�

472.

7

622.

6

334.

9

922.

3

772.

4

1072

.2

413.

3

1222

.1

1971

.6

1521

.9

1372

.0

1671

.8

545.

3

1821

.7

301.

1

2342

.3

934.

4

2068

.8

830.

4

2225

.4

634.

7

2509

.5

2721

.226

29.2

2906

.228

16.2

408.

3

726.

6

Max : 2538

536.

6

370.

7

702.

4

1034

.2

2041

.6

2141

.8

1941

.5

564.

6

1791

.4

429.

2

704.

4

2242

.2

2342

.4

1531

.7

1200

.0

1365

.9

315.

1

868.

3

2442

.4

1704

.0

2575

.9

1062

.2

2862

.7

2052

.321

40.3

2722

.1

566.

6

1890

.0

459.

2

2982

.4

732.

7

1799

.7

2141

.7

2041

.7

1941

.5

2342

.0

2242

.3

2113

.3

2442

.0

1841

.5

2013

.1

2213

.8

2313

.5

336.

7

2542

.3

1006

.1

2642

.0

1741

.5

2104

.3

1912

.7

2413

.6

710.

3

2742

.6

429.

2

560.

5

2194

.0

2304

.2

2003

.0

2862

.3

313.

1

1641

.0

1229

.9

858.

2

2982

.6

1531

.6

1381

.6

1128

.2

980.

2

2572

.7

1810

.2

Max : 1986

Max : 2940

As a result, although there was no large difference

observed in TIC (total ion chromatogram), substantial

differences were observed in the mass spectra. For

NaI, a group of cluster peaks (�) caused by NaI and

with intervals of 150Da was detected more strongly

than the PMMA peak(indicated with a solid red line),

which was considered to be the background spectrum.

For KI, a group of cluster peaks (�) caused by KI and

with intervals of 166Da was detected more strongly

than the PMMA peak.

Conversely, for KCl, the background peaks were

weak (��) and the PMMA spectrum was detected as

the primary peak group. It was clear that the anionic

part of the cationization agent greatly affected the back-

ground spectrum, thus influencing the ionization of the

analysis target.

On the metal surface of the ESI probe tip, to which a

high voltage was applied, it can be assumed that the

following reaction with anions occurs: since Cl2 has

higher volatility than I2, it can be more readily dis-

charged outside the system (outside the mobile

phase), thus producing only a minimal amount of clus-

ter ions. Therefore, it is assumed that the sample itself

can be more readily ionized.

2Cl– – 2e– ➝ Cl2 2I– – 2e– ➝ I2

As a result of our investigation --we will not describe

the details here--, it has been clarified that both KCl

and KOH show the highest sensitivity to high-molecu-

lar-weight components and produce simpler spectra.

SEC/ESIMS Spectra of Synthetic Polymers

In general, when measuring high-molecular-weight

components using the ESI/MS method, an MS spec-

trum with multiply-charged ions can be obtained.11) In

the SEC/ESIMS spectra of hydrophobic synthetic poly-

mers when using a cationization agent, multiply-

charged ions to which several cationization agents are

added can be detected. In order to estimate the molec-

ular weight of the target substance based on the

SEC/ESIMS spectra, it is necessary to analyze the

peaks of these multiply-charged ions.

When considering the PMMA molecule as M, and

measuring it in a positive ion mode using KCl as the

cationization agent, the PMMA becomes ionized in the

form [M+zK]z+. z indicates the charge number. In this

case, it is equivalent to the number of K+ ions added

when the molecular weight is rather small, z=1. Howev-

er, when the molecular weight is large, it is detected as

multiply-charged ions in which z ≥ 2.

The threshold at which multiply-charged ions appear

differs depending on the type of chemical and cation-

ization agent. In the case of PMMA, divalent ions begin

to appear once n=20 and the molecular weight is

approximately 2000 (Fig. 2). As the molecular weight

increases, the number of charge numbers detected

increases to trivalent and further to tetravalent. In addi-

tion, these can be detected in the form of a sequence

of peaks, such as divalent, trivalent and tetravalent.

Figs. 5 and 6 show the actual measurement results.

As shown in Fig. 6, an ESIMS spectrum that does

not use SEC appears to be a single sheet diagram in

which all the spectra shown in the graphs B1–B4 are

overlaid. For this reason, it is generally considered that

multiply-charged ion spectra are complex and hard to

analyze.

However, when using SEC, the samples are mea-

sured in order of their molecular weights, thus enabling

the overlaid multiply-charged ions to become separated

from each other. As a result, the spectrum becomes

simpler, thus leading to easier analysis. However, as

shown in B1, it is still difficult to conduct SEC analysis

of high molecular weight areas having low separation

capability. On the other hand, this can also be evidence

that PMMA is ionized. Therefore, it can be considered

that once the separation capability of SEC is improved,

molecular weight estimation of high-molecular-weight

components will be possible.

The x-axis of a mass spectrum is m/z (mass-to-

charge ratio). m indicates the molecular weight of the

detected ion, and z indicates the charge number



Fig. 5 Size-exclusion Chromatograms of PMMA mixture

a) 220nm b) TIC, 1mM KCl +0.05mL/min B1~B4 ; averaging area of each mass spectrum in Fig.6B1 ; 49.0 – 49.2min B2 ; 51.5–52.0min B3 ; 57.0 –58.0min B4 ; 61.0 –62.0Column ; Tsk-gel Super HZ(4000*3+3000+2500*2)

a)

b) B1B2

B3

B4

mAU

05

1015

100000020000003000000400000050000006000000

min40 45 50 55 60 65 70 75

min40 45 50 55 60 65 70 75

(=charge state) as described previously.

In Fig. 6, we examined a PMMA molecule with n=55

(molecular weight 5708.6). The molecular weights of

the K+-added divalent and trivalent ions are shown

below. The molecular weight was used for the calcula-

tion, not the precise mass:

5708.6 + 2 × 39.1 = 5786.8 ------ [M+2K]+

5708.6 + 3 × 39.1 = 5825.9 ------ [M+3K]+

However, as the mass spectrum is detected using

the mass-to-charge ratio (m/z), peaks are detected at

the positions of 2893.4 [M+2K]+ and 1942.0 [M+3K]+.

The measured values shown in Fig. 6 are quite consis-

tent with the values obtained by the calculation.

Thus, in order to estimate the molecular weight from

the multiply-charged ion spectra (peaks), the charge

number must be determined. However, when measur-

ing macromolecules having completely unknown struc-

tures, the charge number must be determined from the

spectrum only.

Determining Charge Number Using Isotope

Peaks

Generally, charge numbers are determined by the

peak intervals between isotopes. Fig. 7 shows enlarged

[M+K]+ and [M+2K]2+ peaks of PMMA (n=27). The

mass spectrum peaks indicate the distribution of stable

isotopes corresponding to the numbers and types of

elements contained in the detected chemical com-

pound. As shown in a) of Fig. 7, several peaks appear,

showing a pattern which reflects the isotope distribu-

tion (abundance ratio). When measuring a 1+ charged

ion (i.e., z=1), the interval of these peaks (m/z interval)

is inversely proportional to the atomic mass unit (1Da).

Therefore, for a 2+ charged ion (z=2), the atomic mass

unit is 0.5Da; for a 3+ charged ion, the unit is

1/3Da=0.333…; and for a tetravalent ion 4+ charged

ion, the unit is 0.25Da. However, as shown in b) of Fig.

7, because a spectrum measured using a q-MS having

low mass resolution does not possess adequate mass

resolution capability, even the 2+ charged ions cannot



Fig. 6 SEC/ESIMS (+KCl) Spectrums at B1 to B4

1000 1250 1500 1750 2000 2250 2500 2750 3000 m/z

1000 1250 1500 1750 2000 2250 2500 2750 3000 m/z

1000 1250 1500 1750 2000 2250 2500 2750 3000 m/z

1000 1250 1500 1750 2000 2250 2500 2750 3000 m/z

n=24n=25

n=26

n=27*

n=23

n=22

n=21

n=26

n=27*

n=28

n=25

n=24n=23

n=22

n=21

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

1808

.4

1708

.1

1875

.0

1641

.5

2492

.925

42.5

2442

.5

2593

.0

2392

.5

1941

.8

2643

.0

2342

.4

2693

.127

42.9

1574

.7

2792

.7

2292

.4

2008

.5

2842

.9

2242

.4

2893

.1

1391

.3

2543

.4

2643

.4

1341

.3

1441

.4

2743

.5

2443

.3

1291

.3

2843

.6

1491

.4

1241

.2

2343

.3

2943

.6

1541

.4

1191

.2

B1

B2

B3

B4

n=55n=42

n=55

n=44

[M+K]+

[M+2K]2+

[M+2K]2+[M+3K]3+



cannot be determined. Since the resolution of a stan-

dard q-TOF mass spectrometer is approximately 10,000

(FWHM) even with precise adjustment, when using

isotope peak intervals, the charge numbers can be

determined only up to 4 at m/z=2,000, and up to 2 at

m/z=4,000. Thus, it is necessary to use FT-MS with

higher resolution or find other methods.

Estimating Charge Number Using Molecular

Weights of Constitutional Repeating Units

Fig. 9 shows an enlarged view of spectrum B2 (Fig.

6). In spectrum B2, the peaks are aligned from the low

m/z side (the left side) in the order of the higher

charge number 5,4,3 and 2. At this stage, because the

charge numbers of each peak is still unknown, they are

represented as +(z+1)K, +zK, +(z-1)K. a) and b) show

enlarged spectra of the parts indicated by the dotted

lines. Because there is not adequate mass resolution,

the isotopic peak intervals cannot be read. The figures

indicate the intervals between the peaks x1 to x8 and

those between the peaks y1 to y6. These intervals are

derived from the constitutional repeating unit (CRU) of

PMMA. Therefore, they match the molecular weight in

the CRU, and when measuring a 1+ charged ion, the

value is 100Da. However, as multiply charged ions are

being measured in the diagram, the values are smaller

than 100Da. In the previous section, it was explained

that the detected m/z value decreases as the charge

number increases, but in the same way, smaller molec-

ular weights are also detected in the CRU -- such as

be determined. In b) of Fig. 7, the resolution is approxi-

mately 2,000 (FWHM). Therefore, in order to measure

the molecular weight of synthetic polymers using the

SEC/ESIMS method, it is necessary to use a high reso-

lution mass spectrometer, such as TOFMS or TF-

MS.12)

Fig. 8 shows the mass spectra of the same sample

containing the same components, but measured using

a quadrupole time-of –flight (q-TOF) mass spectrome-

ter (q-tof Ultima of Micromass Ltd.). Although the

details of the measurement conditions are omitted

here, the mass resolution is approximately 6,000

(FWHM) for actual measurements. As the diagram

clearly shows, it is easy to determine 2+ charged ions.

However, even at a resolution of 6,000, 3+ charged ions

Fig. 9 Expanded Spectrum A2 14.3 × 7 = 100.1 16.7 × 6 = 100.2 z = 7

m/z1000 1250 1500 1750 2000 2250 2500 2750 30000

20406080

100B2

2041

.7

2055

.9

2084

.5

2099

.0

2027

.6

2113

.1

2127

.4

2070

.4

14.1 14.2 14.5 14.1 14.5 14.1 14.3

+zK +(z-1)K

+(z+1)K +(z-2)K

x1

2442

.2

2425

.4

2459

.0

2475

.3

2492

.2

2509

.1

16.8 16.8 16.3 16.9 16.9

x2 x3x4

x5 x6 x7 x8

y1 y2 y3y4 y5 y6

a)

b)

Fig. 7 Profile Spectrum of n=27 peek (see Fig.6)

m/z2930 2935 2940 2945 2950

m/z1480 1485 1490 1495 1500

δ δ δ

δδ

δ = 1Da

0

10

2030

40

50

0

20

40

60

80

100

2943

.6

2944

.6

2945

.6

2942

.6

2946

.6

1491

.4

a) n=27,[M+K]+

b) n=27,[M+2K]2+

Fig. 8 High resolution SEC/ESIMS Spectrumresolution = 6000(FWHM)

δ1

δ2

δ1

δ1

δ1

a) n=27,[M+K]+

b) n=27,[M+2K]2+

c) n=55,[M+3K]3+

m/z

100

%

2943.6

2942.6

2944.6

2945.6

m/z

0

100

%

0

100

%

0

1491.3

1490.8

1491.8

1492.3

1492.8

m/z1928 1930 1935 1940 1945 1950 1953

1478 1480 1485 1490 1495 1500 1503

2930 2935 2940 2945 2950 2955

1941.8

δ1 = 1Da

δ2 = 0.5Da



1/2, 1/3 and so on -- as the detected charge number

increases. The reason why the intervals on the high

molecular weight side shown in a) are greater than

those on the low molecular weight side shown in b) is

because each peak on the high molecular weight side

in b) is one charge number smaller than that on the

low molecular weight side in a). The average of the

+zK peak intervals is 14.3 and that of the +(z-1)K peak

intervals is 16.7. As charge numbers of these peaks are

equivalent to z and z-1, the following equation can be

established:

z × 14.3 ≈ (z -1) × 16.7

As this contains inaccuracies, it cannot be strictly

“=.” However, if making z=7, the following equations

can be obtained:

7 × 14.3 = 100.1 6 × 16.7 = 100.2

Therefore, the charge number and molecular weight

in the CRU can be estimated. In this case, the molecu-

lar weight in the CRU can be estimated as 100, and this

is certainly consistent with PMMA.

Naturally, because this method can be applied only

to cases in which the selected peaks are those of the

same kind of synthetic polymer, it is necessary to take

extra caution when applying the method to mixed poly-

mers. From our experience however, it can be said that

this molecular weight estimation method is highly

effective in many situations.

Mass Spectra and Molecular Weights of Com-

ponents Having High Molecular Weights

Once the charge number has been determined, the

molecular weight can be readily estimated. However,

when comparing with theoretical values, mass spectra

of components with high molecular weights have fur-

ther problems.

Fig. 10 shows the simulation results of M+ mass

spectra of 10-mer a) and 100-mer b) of PMMA. The

mass resolution is 10,000 (FWHM). However, it should

be noted that it is not strictly M+, as electron mass is

not taken into account. (10-mer and 100-mer refer to

the value “n” described in Fig. 2.)

As previously mentioned, the mass spectrum reflects

the abundance ratios of stable isotopes. Because the

molecular weight of the 10-mer is approximately 1,000

and the mass resolution is 10,000, the half-value width

of the isotopic peak is around 0.1Da. Therefore, ade-

quate separation and extremely sharp peaks can be

achieved. However, peaks on the low molecular weight

side are produced by molecules composed of a single

isotope, and are called a mono-isotopic peaks. The

value of such peaks is equivalent to the exact mass, and

is used when conducting accurate mass measure-

ments. Roughly speaking, this exact mass can be used

for estimating low molecular weight components with

molecular weights of up to approximately 2,000.

However, as the molecular weight approaches 10,000

in the 100-mer, the appearance of the spectrum sud-

denly changes. Even though the mass resolution is

10,000, the molecular weight is also 10,000. Therefore,

the half-value width of each isotopic peak becomes

1Da, thus allowing the peak width to expand to 10

times wider than that of the 10-mer. Also, because the

number of atoms constituting the molecule is large,

there are more varieties of isotope combinations, thus

increasing the number of peaks. For this reason, as

shown in b) of Fig. 10, each isotopic peak can be barely

separated, thus shaping the peak like a broad moun-

tain. In addition, as the mono-isotopic peak appears at

the foot of this broad peak, its peak cannot be identi-

fied. In other words, unless precise observation is con-

ducted to define which area of the peak is considered

as the molecular weight of the 100-mer, the molecular

weights obtained from the experiment cannot be accu-

rately compared. Although it is reasonable to regard

10213.3828 at the peak top as the molecular weight

measured using MS, because this value differs from

Fig. 10 Simulated PMMA oligomer Peak(M+) resolution = 10000(FWHM)

a) 10-mer b) 100-mer

C60H98O24

Exact Mass : 1202.6448Mol. Wt. : 1203.4057

C510H818O204

Exact Mass : 10207.3635Mol. Wt. : 10213.8295

Mono isotopic peak10207.3635

mass1194 1196 1198 1200 1202 1204 1206 1208 1210 1212 1214 1216

mass10230102251022010215102101020510200

Mono isotopic peak

a)

b)

0

100

%

0

100

%

1202.6448

1203.6448

1204.6526

10213.3828

OO

OO

OO

10

OO

OO

OO

100

Synthetic Polymer Mixtures

Figs. 11–13 show the measurement results of a

PPG/PMMA mixture. Needless to say, these two com-

ponents cannot be distinguished using a UV chro-

matogram or TIC, neither can the presence of the two

components be presumed. Although precisely analyz-

ing each peak using the spectra shown in Fig. 12 may

indicate that it is a PPG/PMMA mixture, it requires

time, effort and creativity. When only using an MS

spectrum for analysis, as soon as samples become mix-

tures, analysis becomes extremely difficult.

Therefore, we attempted the analysis via a two-

dimension plot (Fig. 13). In the diagram, the data

obtained from the SEC/ESIMS measurement are

the molecular weight (MW), when measuring and eval-

uating the molecular weight of a component having

high molecular weight using a mass spectrometer, it is

necessary to confirm the detected molecular weight

through the spectrum simulation method introduced

here. In this paper, the value at the peak top of the sim-

ulation spectrum was used as the theoretical molecular

weight and then compared to the actual measured

value using MS.

Accuracy of Molecular Weight Estimation

Using Multiply-charged Ion Peaks

Table 1 shows the results of estimates of the molec-

ular weights of the x5 and y5 components shown in

Fig. 9. In the calculated values, MW represents molec-

ular weights, which are shown for reference purposes.

Using a q-MS, components having molecular weights

of 14,000 or more were estimated from +6K and +7K

ions. As a result, it has been confirmed that the error is

within ±1Da. Therefore, the error is within 100ppm,

meaning an accuracy of ±0.1 in the m/z=1,000 conver-

sion. This is extremely good consistency, and we there-

fore believe that this method can be used for structural

analysis of actual synthetic polymers. According to our

investigation, molecular weights of up to approximately

18,000 can be accurately estimated with +8K ions when

using PMMA.

For reference purposes, the m/z detection accuracy

using a q-MS is usually ±0.1Da. For example, if the

detection accuracy for 6+ charged ions is ±0.1Da, the

error in the molecular weight obtained from the calcu-

lation becomes ±0.6Da. Therefore, theoretically, the

accuracy of molecular weight estimation from multiply

charged ions using a q-MS is acceptable. If the m/z

detection accuracy is improved by one order of magni-

tude, to approximately ±0.01Da, we believe that the

accuracy of molecular weight determination for syn-

thetic polymers will greatly improve, thus enabling

more detailed structural analysis by using a combina-

tion of a q-MS and SEC/ESIMS.



Table 1 PMMA MW from SEC/ESIMS Spectrum

2084.52492.2

Peak(m/z)

M+7KM+6K

ion type

14718.614317.8

ExperimentalMW

14718.714318.4

Peak topCalculated

14719.014318.6

MW

Fig. 11 Size-exclusion Chromatograms of PMMA+PPG

a) UV=220nm b) TIC(+KCl)C1~C3 ; averaging area of the mass spectrum in Fig.12Column ; Tsk-gel Super HZ (2500+2000*2+1000)

a)

b)C1

min27.5 30 32.5 35 37.5 40 42.5

mAU

1234567

min27.5 30 32.5 35 37.5 40 42.50

200000400000600000800000

1000000120000014000001600000

C2 C3

Fig. 12 SEC/ESIMS(+KCl) Spectrum at C1~C3

Sample ; PMMA+PPG

C1

C2

C3

m/z500 750 1000 1250 1500 1750 2000 22500

20

40

60

80

100

m/z500 750 1000 1250 1500 1750 2000 22500

20

40

60

80

100

m/z750 1000 1250 1500 1750 2000 22500

20

40

60

80

100

expressed as follows: the vertical axis represents m/z ;

the horizontal axis represents dissolution time (min-

utes); and the intensity gradation represents the

strength of each ion peak. The presence of the two

components can be presumed at a glance. Analyzing

the mass spectrum based on this information, it is clear

which peak groups correspond to PPG, and which to

PMMA, from among the components. In addition, with

respect to charge state, even the charge state of high

molecular weight components having complex mass

spectra (and therefore being difficult to have their

charge state determined) can be estimated from the

elution behavior of each component. From Fig. 13, it

can be observed that the separation of high molecular

weight components is not adequate when using SEC.

Furthermore, it can be readily understood that in order

to analyze high molecular weight components more

precisely, improving the separation capability can be

effective by increasing the number of columns, and by

other methods.

Thus, it is obvious that 2-D plots are extremely effec-

tive in order to analyze synthetic polymers having com-

plex compositions, as well as mixtures.

GB/MA Copolymer

Figs. 14–16 show the measurement results of a

GB/MA copolymer, which is a more practical sample.



Fig. 15 GB/MA copolymer SEC/ESIMS Spectrums at D

COC

R2

O O

R1

O

O

O

G M

149

GB MA

–149*3

1256.5(4, 2)

876.3792.2 960.3

b) Fr=400V –149*2

a) Fr=200V–149*4

(3, 3)1320.7

1384.7 1618.9

1683.8

(2, 4) (2, 5)

(1, 6)

020406080

100

m/z0 250 500 750 1000 1250 1500 1750

m/z0 250 500 750 1000 1250 1500 1750

020406080

100

a) Fragment Voltage=200V b) Fragment Voltage=400V

Fig. 13 2-D Plots of SEC/ESIMS of PMMA+PPG

Column ; Tsk-gel Super HZ (2500+2000*2+1000)

28 30 32 34 36 38 40 42 44

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800 m/zm/z

minmin

PMMA+PMMA+PPGPPG

PMMAPMMA

PPGPPG

+K+K+2K+2K

+3K+3K

+4K+4K

+6K+6K

+7K+7K

+K+K+2K+2K+3K+3K

Fig. 14 SEC of GB/MA copolymer

mAU

–500

50

min20 25 30 35 40 450

200000

400000

600000

a) 210nm

b) TIC

D

a) 210nm b) TIC of SEC/ESIMSD ; averaging area of mass spectrums in Fig.15Column ; Tsk-gel Super HZ (2500+2000*2+1000)



This sample was synthesized by radical polymerization.

The weight-average molecular weight (Mw) is ≈ 10,000

and the distribution (Mw/Mn) is ≈ 1.9 (indicated as

polystyrene). Although the Mw is rather small, the

sample has a wide Mw/Mn and a random sequence,

thus making its composition extremely complex. For

this reason, with ESIMS measurement using the flow

injection method that does not utilize SEC, it was diffi-

cult to determine whether or not the sample had been

ionized because the spectrum was extremely compli-

cated.

With the SEC/ESIMS (+KCl) method, the mass

spectrum that reflects the copolymer composition was

detected as a [M+K]+, thus making it easy to estimate

the molecular weight for low molecular weight compo-

nents (up to approximately MW=2,500). As a result,

the composition of each peak could be identified (Fig.

15, a)). It was also understood that more precise infor-

mation can be obtained through the capillary skimmer

CID method (Fig. 15, b)).

In addition, it was understood that information

regarding dissolution behavior and charge state, which

is useful for analyzing mass spectra, can be obtained

from 2-D plots (Fig. 16). In the 2-D plot, it was also

clearly confirmed that a 2+ charged ion that could not

have been identified in a regular mass spectrum was

also detected. However, because the spectrum of this

2+ charged ion was extremely complex, it was difficult

to specify the components and estimate the molecular

weight.

Fig. 17 shows the complexity of the mass spectrum

of a copolymer. We believe that from this model spec-

trum, it can be observed that although it is a mere A/B

copolymer, its mass spectrum can become unimagin-

ably complex. In order to analyze a complex copolymer

which has several (>3) kinds of constitutional repeating

unit, it is essential to use chromatography which has

high separation capability.

Fig. 16 GB/MA copolymer 2–D plot by SEC/ESIMS (1,6) means G=1, M=6

35 40 45 50 55 60 65

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

m/zm/z

minmin

(1, 6)

(3, 4)

(1, 5)(2, 4)

(1, 4)

+K+K+2K+2K

COC

R2

O OR1

O

O

OG M

(2, 3)

Fig. 17 Complexity of copolymer mass spectrum

α=2

α=3

α=4α=5

α

α β

(A)

(0,2)

(2,0)

(1,1)

(0,5)

(5,0) (2,3)

(A) (B)

a)

b)

m/z

m/z

a) homo-polymer model b) co-polymer model α, β=1,2,3 · · ·, (2,3) means α=2, β=3



Conclusion

From the results described above, the following fact

has been confirmed: although hydrophobic synthetic

polymers can be ionized up to molecular weights of

tens of thousands by the SEC/ESIMS method using a

cationization agent, if the composition of the polymer is

complex, it is hard to estimate its molecular weight.

Therefore, it can be concluded that in order to conduct

structural analysis of a synthetic polymer, it is more

important to use chromatography which has high sepa-

ration capability, rather than a high performance mass

spectrometer.

Furthermore, using the PMMA in Fig. 2 as an exam-

ple, when analyzing the molecular weight of the CRU,

if only n=100 compounds are extracted, refined and

measured, only the molecular weight of the n=100 com-

pounds can be clarified, not that of the CRU. In order

to obtain the molecular weight of the CRU, a group

having consecutive numbers such as n = -- - - 98, 99,

100 --- must be analyzed. Such groups cannot be ana-

lyzed using UV or TIC, but the 2-D plots shown in Figs.

13 and 15 are effective. We believe that if there is a

function which can plot only the trivalent ion spectrum

directly from a 2-D plot, and which can conduct back-

ground processing, mass spectra which are easier to

analyze can be achieved, resulting in more efficient and

precise analysis.

In recent years, there have been some reports on

new software for copolymer composition analysis.13) Its

development is expected to continue in the future.

Acknowledgements

Lastly, we would like to express our deep apprecia-

tion to Professor Ryuichi Arakawa, Faculty of Chem-

istry, Materials and Bioengineering, Kansai University,

for showing his interest in this research and providing

us with valuable advice and encouragement.

References

1) S. Asano, K. Yamamoto, O, Hiroaki, M, Kato, SUM-

ITOMO KAGAKU, 1998-!, 68 (1998).

2) X. Michael Liu, E. Peter Maziarz, David J. Heiler

and George L. Grobe, J.Am.Soc.Mass Spectrom., 14,

195 (2003).

3) T. Kashiwagi, O. Hiroaki, M. Kato, H. Takigawa,

SUMITOMO KAGAKU, 1993-!!, 71 (1993).

4) John B. Fenn, Matthias Mann, Chin Kai Meng,

Shek Fu Wong and Craige M. Whitehouse, Mass

Spec. Revi., 9, 37 (1990).

5) Ryuichi Arakawa, Syouji Okuno, Bunseki, 2002, 9,

502 (2002).

6) Laszlo Prokai and William J. Simonsick, Jr., Rapid

Commun. Mass Spectrom., 7, 853 (1993).

7) Michel W. F. Nielen, Rapid Commun. Mass Spec-

trom., 10, 1652 (1996).

8) Y. Tsuchida, K. Yamamoto, H. Yamada, S. Morimo-

to, K. Yamamoto, 54th Annual conference on Mass

Spectrometry Osaka Japan, 42 (2006).

9) Y. Tsuchida, K. Yamamoto, 9th National Symposium

on Polymer Analysis and Characterization, 147

(2006).

10) Y. Tsuchida, K. Yamamoto, H. Yamada, S. Morimo-

to, K. Yamamoto, 11th National Symposium on Poly-

mer Analysis and Characterization, 71 (2006).

11) Y. Yokoyama, J.Am.Soc.Mass Spectrom., 18, 1914

(2007).

12) David J. Aaserud, Laszlo Prokai and William J.

Simonsick, Jr., Anal.Chem., 71, 4793 (1999).

13) Steffen M. Weidner, Jana Falkenhagen, Sergey

Maltsev, Volker Sauerland and Marian Rinken,

Rapid Commun. Mass Spectrom., 21, 2750 (2007).



P R O F I L E

Yoshinobu TSUCHIDA

Sumitomo Chemical Co., Ltd.IT-Related Chemicals Research LaboratorySenior Research Associate

Hiromi YAMADA

Sumitomo Chemical Co., Ltd.IT-Related Chemicals Research LaboratoryResearcher

Keiko YAMAMOTO

Sumitomo Chemical Co., Ltd.IT-Related Chemicals Research LaboratoryResearch Associate

Investigation of Synthetic PolymerInvestigation of Synthetic Polymer Characterization by means of...

Documents

Transcript of Investigation of Synthetic PolymerInvestigation of Synthetic Polymer Characterization by means of...