chemical ionization mass spectrometry

JOURNALOI ANALYTICALand APPLIED PYROLYSIS

Journal of Analytical and Applied Pyrolysis 33 (1995) 111-119

ELSEVIER

Direct and rapid characterization of para-formaldehydes by pyrolysis-gas chromatography/chemical ionization mass spectrometry Yoshiaki

Matsushima

‘,*, Hiroyuki

QTougosei Co. Lid., I Funumi-cho, h Department

of Applied Chemistry,

Nagoshi

Minute-ku.

School of Engineering. 464-01. Japun

‘, Hajime

Ohtani ’

Nugo.vu. 455. Japan Nugow

Uniuersiry,

Nugc~yu.

Received 16 July 1994: accepted 31 August IV94

Abstract The distribution of formaldehyde oligomers in para-formaldehydes was directly determined by pyrolysis and/or vaporizing gas chromatography after converting para-formaldehydes into their trimethylsilyl derivatives. Most of the characteristic peaks in the gas chromatogram were identified by chemical ionization mass spectrometry using ammonia as reagent gas. The main derivatives proved to be a series of silylated polyoxymethylene glycols (TMSO-(CH,O),-TMS, 4 < n < 16) along with small amounts of silylated hemiacetals (TMS-0-(CH,O),&H,, 5
Trimethylsilyl

para-Formaldehyde; derivative

Gas

chromatography;

Mass

spectrometry;

Pyrolysis;

1. Introduction

para-Formaldehydes have been widely used as raw materials for plastics, antiseptics, medicine, adhesives, etc. A rapid bonding cyanoacrylate adhesive named Krazy Glue (Aron Alpha) has been also produced from para-formaldehyde and cyanoac* Corresponding

author.

0165-2370/95/$09.50 0 SSDI

1995 - Elsevier

0165-2370(94)00859-O

Science B.V. All rights reserved

112

Y. Marsushima et al. 1 J. Anal. Appl. Pyrolysis 33 (I 995) I 11~ 119

etate as shown in Fig. 1 [ 11. In the condensation step of this adhesive in ester solution, the average molecular weight (MW) of the condensed polymer frequently fluctuates depending on the para-formaldehydes used. When the MW of the condensed polymer becomes too high, abnormal phenomena such as bumping are often found to occur in the depolymerization step. The solubility of para-formaldehydes in esters in the first reaction stage may affect the reactivity for condensation to yield the condensed polymer. The solubility of para-formaldehydes is expected to change, depending mainly on their chemical composition. The concentration of formaldehyde and the contents of free acids, ash, heavy metals, chloride ions and iron in para-formaldehydes can be determined by various

F”

nCH2

+

n HCHO

A OOR

Condensation

n CH2=

LOOR

Fig. I. Scheme

of the synthesis

of cyanoacrylate

adhesive.

Y. Matsushima et al. / J. Anal. Appl. P~wl_vsis 33 (1995) 1 I I I 19

113

analytical methods [2]. The gas chromatography (GC) of formalin has been applied to separate formaldehyde from water and methanol [3-51. The amount of linear formaldehyde oligomers in formalin has been determined by GC and nuclear magnetic resonance [6]. However, the distribution of formaldehyde oligomers in para-formaldehydes has not been studied in detail. In this work, pyrolysis-(vaporizing) gas chromatography/chemical ionization mass spectrometry (Py-GC/CIMS) was applied to the direct and rapid characteri-

(A)

E

F

G

D I

,

J

e

;

‘:

:.

(min.)

I.r K

hl

1

;,

,

&

I

r ,

,

L

i

M

I

z

”

(min.) Fig. 2. Gas chromatograms of TMS derivatives of (A) paw-formaldehyde, sample Y. A-M and a-j correspond to Table I.

(B) sample

X, and

(C)

114

Y. Matsushima et al. / J. Anal. Appl. Pyrolysis 33 (1995) I1 I I19

(A) : lEEKI_

TMSO

(CH,O)

TMSO

(CH,O)

,TMS

,TMS

1000

(W E a

108

58

330

(M+13)

158

z Zil.ilB

1

NH,+

1

NH,+

2flel 2”

2

M/E

38.88

250

Fig. 3(A,B).

zation of para-formaldehydes. Trimethylsilyl derivatives of para-formaldehydes were investigated in terms of the distribution of formaldehyde oligomers. In this case, Py-GC is superior to normal GC because the concentrated TMS derivatives

Y. Mutsushima el al, 1 J. Anal. A@. P.vroiy.ds 33 (1995) 111 I I9

1aee I

(CHzO)

CH,O

,TMS

115

;r

1

NH,+

15.80

z lCl08,

272

15.00

(M+l3)

1 ;tl

I

8 1eee _

CH,O

55

302

(CH,O)

18%

,TMS

NH,+

150

zae

(M+18)

M/E

=a 2

JS.Bfl

Fig.

shown

3. Cl mass spectra of TMS derivatives of para-formaldehyde in Fig. 1: (A) peak A; (B) peak B; (a) peak a; (b) peak b.

observed

in the chromatograms

of para-formaldehydes can be subjected to GC separation after evaporation of the pyridine solvent. The observed results were correlated to the solubiiity of the para-formaldehydes in ester solution.

Y. Matsushima

et al.

/ J. And. Appl. Pyroiy.vis 33 (199.5) 1 I I I1 9

117

2. Experimental 2.1. Sample Two kinds of para-formaldehydes (92% formaldehyde) supplied by different companies, samples X and Y, were investigated. N,O-Bis( trimethylsilyl) trifluoroacetoamide (BSTFA) supplied by the GL Science Co. Ltd. was used for the silylation reaction of the para-formaldehydes. para-Formaldehyde samples were ground into powder by an agate mortar with a pestle. About 40 mg of the powder sample was dissolved in 10 ml of pyridine. 60 ~1 of the pyridine solution was mixed with 150 1.11BSTFA and held for 90 min at lOO‘C, to convert para-formaldehyde oligomers into the trimethylsilyl derivatives as follows: HO_(CH,O)

_H n

CF3C[Osi(CH3),1=Nsi(CH3>3 (CH,),SiO-( _ .__,

CH?O),,-Si(

CH,),

Pyridine 2.2. Pyrolysis -gas

chromatography

A vertical microfurnace-type pyrolyzer (GP- 1028; Y anaco) was directly attached to a gas chromatograph (G-5000; Hitachi) with a flame ionization detector and a fused-silica capillary column (DB-5, 30 m x 0.32 mm i.d., df = 0.25 pm; J & W). 10 ,~l of the pyridine solution of silylated para-formaldehyde was drawn into a platinum sample cup, which was heated on a hot plate to about 80°C in order to concentrate the TMS derivatives by evaporation of pyridine. The cup attached to the top of the pyrolyzer was dropped into the center of the furnace, where the TMS derivatives were pyrolyzed (vaporized) at 450°C under a flow of helium carrier gas. The 45 ml/min carrier gas flow-rate at the pyrolyzer was reduced to 1.7 ml/min at the capillary column by a splitter. The column temperature was programmed from 100 to 300°C at a rate of lO”C/min. Py-GC/CIMS measurements were carried out

Table 2 Comparison

of the solubility

Solvent

of para-formaldehyde Dissolved Sample

Esters Chlorinated organic solvent

amount X

49.4 (0.99’>0) Trace

in two different

organic

solvents

Sample

Y

’ (mg)

12.7 (0.26%) Trace

’ Completely ground paw-formaldehyde (5 g) was dissolved in solvent ( 50 g) by stirring vigorously for 1.5 h at room temperature. The solution was then filtered, and condensed in a water bath through solvent evaporation. Finally, the residue was dried under vacuum and vveighted.

118

Y. Malsushima et al. / J. Anal. Appl. Pyrolysis 33 (1995) I I1

119

(min.) Fig. 4. SEC curves of the condensed

polymers:

(A) produced

from sample X; (B) produced

from sample Y.

using a GC/MS system (JMX-DX 300 (JOEL)) to which the same pyrolyzer was also directly attached. Most of the characteristic peaks on the gas chromatogram were identified by chemical ionization mass spectrometry using ammonia as reagent gas, and the mass scan range was 30-600 u. 2.3. Size exclusion

chromatography

(SEC)

SEC measurements were carried out with a high-performance liquid chromatograph (HLC-8020, TOSOH Co., Ltd.) which was operated with TSK-gel G2500NXL-G2500HXL columns in series at 38°C on THF. The molecular weight distributions (MWDs) of the condensed polymers were calculated from a polystyrene standard calibration curve.

3. Result and discussion Fig. 2 shows the gas chromatograms of the TMS derivatives of para-formaldehydes for samples X and Y. A series of main peaks (A-H) is observed, along with another series of minor ones (a-j) in both chromatograms. Most of the characteristic peaks were identified by CIMS. Fig. 3 shows the mass spectra of peaks A, B,

a and b together with their identified structures. In the case of Peak A, the base signal at m/z 300 corresponds to a quasi-molecular ion of the TMS derivative of tetraoxymethylene glycol added to an ammonium ion, [TMas shown Fig. 3(A). Peak B was identified as that of SO(CH,O),TMS]NH,+, pentaoxymethylene glycol, [TMSO(CH,O),TMS]NH,+, as shown Fig. 3(B). Similarly, peaks C-M were assigned to those of hexaoxymethylene glycol and hexadecaoxymethylene glycol, respectively. However. for peak a, the base signal at m/z = 272 corresponds to a quasi-molecular ion of the TMS derivative of pentaoxymethyleneglycol mono methyl ether (hemiacetal) added to an ammonium. as shown Fig. 3(a). Similarly, peaks b-j were iden[CH,O(CH,O),TMS]NH,+, tified as those of hexaoxymethylene glycol mono methyl ether and tetradecaoxymethylene glycol mono methyl ether, respectively. Thus it was shown that the main products consisted of a series of silylated polyoxymethylene glycols A-M along with small amounts of silylated hemiacetals a-j. Table 1 summarizes the relative peak intensities of formaldehyde oligomers in samples X and Y, respectively. The total amount of hemiacetals in sample X is about twice as much as that in sample Y. Table 2 shows the solubility of the pura-formaldehyde samples in some organic solvents used in the production of adhesives. Although both the samples hardly dissolved in chlorinated organic solvents such as chloroform, it was found that the solubility of puvrr-formaldehyde in ordinary esters increased with the total amount of hemiacetals by comparison of two kinds of investigated PUrLI-formaldehydes. Fig. 4 shows SEC curves of the condensed polymers in ester solution, produced from samples X and Y, along with the estimated number average molecular weight (M,). It was found that M, of the condensed compound produced from sample X was higher than that from sample Y. Therefore it was concluded that the higher the content of hemiacetals in parer-formaldehydes, the higher the M,, of the condensed polymer.

References [I] [2] [3] [4] [5] [6]

D.L. Kotzev and V.S. Kabaivanov. Adhesion. 12 (1988) X2. JIS K9065. 1961. H.L. Gruber and H. Plainer, Chromatographia, 3 (1970) 490. K.J. Bombaugh and W.C. Bull, Anal. Chem., 34 (1962) 1237. F. Onuska. J. Janak. S. Duras and M. Kremarova. J. Chromatogr., 40 (1969) 209. W. Dankelman and Jacq. M.H. Daemen. Anal. Chem.. 48 (1978) 401.