ISSN 10619348, Journal of Analytical Chemistry, 2015, Vol. 70, No. 8, pp. 956–961. © Pleiades Publishing, Ltd., 2015. Original Russian Text © V.G. Amelin, T.A. Krasnova, 2015, published in Zhurnal Analiticheskoi Khimii, 2015, Vol. 70, No. 8, pp. 835–840.
ARTICLES
Identification and Determination of Polysulfonic and Polycarboxylic Acid Oligomers in Construction Materials Using MatrixAssisted Laser Desorption/Ionization Mass Spectrometry V. G. Amelina, b and T. A. Krasnovab, c a
Federal Center for Animal Health, Yur’evets, Vladimir, 600901 Russia bVladimir State University, ul. Gor’kogo 87, Vladimir, 600000 Russia c Superplast Trading House, Promyshlennyi proezd 5, Vladimir, 600000 Russia email:
[email protected] Received: March 6, 2014; in final form, June 26, 2014
Abstract—Methods for the identification of polymethylene naphtalene sulfonates (PMNS) and polycarbox ylate ethers and the determination of PMNS in finished construction materials based on Portland cement using matrixassisted laser desorption/ionization mass spectrometry (MALDI MS) are proposed. Modifiers were extracted from construction materials using a mixture of water with acetonitrile. The analytical range for PMNS was 0.3–0.9% of dry substance in relation to the cement weight. The relative standard deviation of the results of PMNS determination in concrete did not exceed 10%. The time of analysis was 40–50 min. Keywords: MALDI MS, polymethylene naphthalene sulfonates, polycarboxylate ethers, construction mate rials, modifiers DOI: 10.1134/S1061934815060039
INTRODUCTION Plasticizer C3 is one of the most commonly used modifiers of construction materials based on Portland cement; it represents a mixture of oligomers of polym ethylene naphthalene sulfonic acids with the number of units in the molecule from 2 to 25. It is used in world practice for more than 50 years. Plasticizer C3 is the first specialpurposed synthetic modifier of construc tion materials used in the relatively low amounts. Additives based on polycarboxylate ethers also occupy a special place. In Russia they are used for not more than 10 years. At present, the effect of these substances on concrete is insufficiently studied; however, these modifiers are used in smaller amounts than PMNS; therefore, it is more difficult to detect them in con struction materials [1–3]. Disputable situations concerning construction chemistry can be associated with the falsification of products and the replacement of one type of plasti cizer with another, which affects the quality of the concrete. Occasionally overdoses of modifiers take place, which are caused by the malperformance of feeders at plants. All this can result in the formation of defects often noticeable only in the finished products. The detection and determination of modifiers in the finished construction materials is one of urgent prob lems in the determination of causes of defects in con struction materials. At present, methods for the iden
tification of organic modifier in construction materials based on Portland cement are not known. The aim of this work was the development of meth ods for the identification and determination of modi fiers based on polymethylene naphthalene sulfonic acids and polycarboxylate ethers in construction materials. EXPERIMENTAL An Autoflex III Smartbeam MALDI mass spec trometer with a timeof flight mass analyzer (Bruker Daltonik, Germany) was used. Positive and negative ions in the mass range of 200–7000 Da were measured in the refractron mode (PepMix standard mode). The main parameters of analysis were as follows: ultraviolet nitrogen laser with the wavelength 337 nm, pulse dura tion 3 ns, and power density of laser radiation 106– 107 W/cm2. An automatic suppression of signals with masses below 400 Da was used. Mass spectra were recorded using a FlexControl ver. 3.3 software. The spectra were analyzed using a FlexAnalysis 3.3 soft ware (Bruker Daltonik, Germany). A standard steel target plate (MTP 384 groundsteel TF plate) was used in the work with the mass spectrometer. In the process of sample preparation, a Minispin plus F451211 laboratory centrifuge (Eppendorf, Germany), a PSB133505 ultrasound bath (PSB Gals, Russia), a Multi RS60 programmable rotator
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(Biosan, Latvia), and a Retsch RM 200 mechanical mortar (Retsch, Germany) were used. Samples of industrial PMNS produced by Kompo nent Ltd. (Vladimir, Russia, TU 5700197474489 2007) were used:
C H2
H
n
SO3H
SO3H
Commercial forms of modifiers based on polycar boxylic acid ethers produced by China (Lot no. PAF 130228), Russia (Patent RU2469975), and Korea (Batch no. SD512130915B) were used: CH3 CH2 C COOM
CH3 CH2 C COO(CH2CH2O)qR m
n
where R is an alkyl or an aryl radical. 4Hydroxy3,5dimethoxycynnamic (sinapinic) acid (Bruker Daltonik, Germany, lot no. 2010 201345001), αcyano4hydroxycinnamic acid (Bruker Daltonik, Germany, lot no. 10.255344.284001), and 2,5dihydroxybenzoic acid (Bruker Daltonik, Germany, lot no. 2010 201346001) were used as matrices. Sample preparation. A concrete sample was crushed in a mechanical mortar until a powder with particles not larger than 1.25 mm was obtained. A weighed portion (20 g) was placed in a 100mL plastic tube and 40 mL of a (1 : 1) mixture of water with ace tonitrile was added. The tube was placed in an ultra sonic bath and sonicated for 30 min. One milliliter of the extract obtained was taken into a 2mL tube, acid ified with 1 M H2SO4 to pH 3–3.5, and centrifuged for 5 min at 4500 rpm. The obtained liquid phase and matrix (αcyano4hydroxycinnamic acid) were mixed in the volume ratio 1 : 1, then 1 μL of the obtained mixture was placed on the target of a steel substrate. After the crystallization of the sample mass spectra were recorded. RESULTS AND DISCUSSION Identification and determination of PMNS. To assess the possibility of the identification and determi nation of modifiers based on PMNS by MALDI MS, we found the conditions of material sample prepara tion and massspectrometric study. The identification of a modifier based on PMNS was performed by the presence of peaks of oligomer ions [Mn – H]–. The modifier represents a mixture of oligomers with the number of units in the molecule JOURNAL OF ANALYTICAL CHEMISTRY
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from 2 to 25, which are adsorbed on the surface of cement grains on the addition of modifiers with mix ing water. Different fractions differently work with minerals of Portland cement when added to a con struction material at the stage of its solidification. Large molecules of heavy fractions are built into the structure of new mineral phases, whereas light and medium fractions can be desorbed from the finished material. Therefore, the use of precisely the C3 plas ticizer can be judged from the presence of peaks of ions of several oligomers with n = 2–6 in the mass spectra. Note that the presence of peaks of ions of one or two oligomers (most often dimer and trimer with molecu lar masses of ions 427 and 647 Da) cannot reliably confirm the presence of precisely the modifier based on PMNS, because, in the addition of this type of modifier, only dimers and trimers should be desorbed, but oligomers of light and medium fractions as well. Therefore, the presence of PMNS was found by the presence of peaks of ions of successive oligomers, dif fering by the mass of an elemental unit, 220 Da. The peaks of the major ions of PMNS macromolecules are presented by an isotope distribution rather than by one ion. The presence of isotopes is reflected in the mass spectrum as a sequence of decreasing peaks with a dif ference of 1 Da. For each compound, depending on its gross formula, one can calculate a distribution of such type, which is actually unique for different substances. The isotopic distribution for the PMNS oligomers was computed automatically using a FlexAnalysis soft ware. The presence and type of the isotopic distribu tion were used for the identification of a modifier in a construction material. Figure 1 presents mass spectra of extracts from heavyweight concrete BSG V25 P4 F150, manufac tured with the addition of a C3 plasticizer in amounts of 0.5 and 0.6% of the dry substance in relation to the concrete weight. The presence of peaks of oligomer ions with the number of units from 2 to 5 (6) is quite clearly seen in the spectra of extracts, and the intensi ties of the peaks are indicative of different numbers of oligomers in the body of the construction material. By the presence of peaks of oligomer ions with the differ ence 220 Da and by the shapes of their isotopic distri bution one can judge about the presence of the modi fier based on PMNS. The possibility of the determination of PMNS in construction materials was also evaluated. With this purpose, mass spectra of PMNS were studied using solutions with the concentrations 0.001, 0.005, 0.01, 0.05, 0.1, 0.3, 0.5, and 1 mg/mL. It was found that peaks of oligomer ions were observed only at the PMNS concentration 0.005 mg/mL and higher. To improve the repeatability of the results of analysis, an internal standard was used. With this purpose, sub stances with similar structures, molecular weights, and properties were tested. The possibility of using several types of peptides, oligosaccharides, and antibiotics macrolides was studied. It was found that avilamycin No. 8
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AMELIN, KRASNOVA
0 400
500
600
700
800
900
1000
2 1
1100
1200
0 400
600
800
1000
1308.117 [M6–H]–
3
1087.926 [M5–H]–
4
427.160 [M2–H]–
Intensity × 104, arb. units
5
867.725 [M4–H]–
0.25
1087.958 [M5–H]–
0.50
867.747 [M4–H]–
647.495 [M3–H]–
1.00 427.173 [M2–H]–
Intensity, × 105, arb. units
1.25
0.75
(b) 6
647.472 [M3–H]–
(а)
1.50
1200
1400 m/z
m/z
Fig. 1. Mass spectra of extracts from concrete BSG V25 P4 F50 in using αcyano4hydroxycinnamic acid, initial concentration of plasticizer C3 in concrete (a) 0.5% and (b) 0.6%, and the duration of sonication 30 min.
of molecular weight of 1404 Da was the optimum internal standard, because no competition in desorp tion/ionization of PMNS was observed in its applica tion. To build a calibration curve, the concentration of PMNS was plotted along the abscissa axis and the ratio of the sum of peak areas of oligomer ions (n = 2–7) with the masses 427, 647, 867, 1088, 1308, and 1528 Da found in the mass spectrum to the sum of peak areas of avilamycin with the masses 1420 and 1421 Da was plotted along the ordinate axis. A linear relationship was obtained for PMNS at its concentra
tions in solution 0.01–1 mg/mL; the correlation coef ficient was 0.994. To take into account the recoveries of PMNS from concrete, the calibration curve was built using extracts from concrete with additions of PMNS and avilamycin as an internal standard. A lin ear dependence was obtained in the range 0.3–0.9% the dry modifier in relation to the weight of concrete with the correlation coefficient 0.983 and relative standard deviation not worse than 10%. PMNS was determined in heavy concrete BSG V25 P5 W4 pro duced with the use of the CEM I 42.5 B cement man
Determination of plasticizer C3 in heavy concrete BSG V25 P5 W4 (n = 3, P = 0.95) Age of concrete in the determination of PMNS, days
Added PMNS, % of the cement weight (kg/m3)
Found PMNS, % of the cement weight (kg/m3)
RSD, %
30
0.50 (1.75)
0.47 ± 0.07 (1.7 ± 0.3)
6
7
0.60 (2.10)
0.6 ± 0.1 (2.1± 0.4)
8
7
0.60 (2.10)
0.6 ± 0.1 (2.0 ± 0.4)
10
7
0.60 (2.10)
0.55 ± 0.06 (1.9 ± 0.2)
6
28
0.50 (1.75)
0.52 ± 0.08 (1.8 ± 0.3)
7
28
0.50 (1.75)
0.50 ± 0.09 (1.8 ± 0.3)
8
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1004.059 960.018 1048.113 915.970 1092.157 871.921
1.5
827.875
995.896 951.861
40
1136.206
1180.254
1.0
783.827 1224.305 739.784 1268.355 656.361
0.5
863.773 1039.944
Intensity × 10, arb. units
Intensity × 104, arb. units
(а)
959
1313.395
695.729 1356.446
819.725 775.691
30
1083.985
1128.033 606.310 731.644
20
1172.072
687.629 1216.108 1260.152
10
1400.492 1444.536 1488.576
1348.210
0
0 700
900 800
1100 1300 1500 1000 1200 1400 1600 m/z
600
800 700
1000 900
1200 1100
1300 m/z
Fig. 2.Mass spectra of a solution of PCE manufactured in Russia: (a) 0.5 mg/mL and (b) extract from concrete with the indicated modifier; using αcyano4hydroxycinnamic acid, concentration of modifier based on PCE in concrete is 0.3%, and sonication for 30 min.
ufactured at the Mordovcement plant. The results of determination of the modifier are presented in the table. Identification of polycarboxylate ethers (PCE). For the study of modifiers based on PCE, αcyano4 hydroxycinnamic, 2,5dihydroxybenzoic, and sinap inic acids were used as the matrix. Acetonitrile and acetone with additions of small amounts of an aqueous solution of trifluoroacetic acid were used as solvents for matrices. When 2,5dihydroxybenzoic and sinap inic acids were used, peaks of PCE ions were not detected in the mass spectra. Mass spectra of various modifiers based on PCE we succeeded to obtain using αcyano4hydroxycinnamic acid. The mass spectra were recorded only in the positive ion mode. As is seen in Figs. 2–4, the mass spectra of modifi ers based on PCE are characterized by a set of well resolved peaks of ions of various oligomers in a rather narrow mass range compared to PMNS. The peaks of ions of particular oligomers are presented by an isoto pic distribution. Moreover, along with the main peaks of the [Mn + Н]+ ions, the [Mn + Н2О]+ ions were also observed in the mass spectra. PCE macromolecules can attach water molecules with the formation of glob ules; however, this phenomenon was usually observed at high pH values. It is likely that the presence of an organic solvent in the system, as well as mixing with an organic matrix, facilitates the attachment of water. It should be noted that, when the intensities and peak areas of the main ions and ions with attached water JOURNAL OF ANALYTICAL CHEMISTRY
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were compared, the latter represented not more than 7% of the total amount of ions. Taking into account that the structure of side chains, the presence of additional functional groups, etc. are unknown, it would be difficult to determine the structure of the elemental unit of PCE. However, a common feature of all compounds is that the differ ence in masses between two adjacent peaks in the spectrum is 44 Da. This mass corresponds to the ele mental unit (–СН2–СН2–О–, Fig. 5), characteristic for compounds of the polyether class. The obtained mass spectra of solutions of samples of different mod ifiers based on PCE and extracts from concretes of a standard composition including these modifiers in optimum amounts were used for the identification of modifiers in construction materials. The identification was performed by comparing mass spectra of extracts from concrete containing no modifier and concrete containing one or another modifier. Spectra of sam ples of modifiers and extracts from concretes are pre sented in Figs. 2–4. For the extraction of a modifier, a 1 : 1 (v/v) mix ture of acetonitrile with water was used. It was found that, in the extraction of modifiers with organic sol vents, the sonication of a construction material for 30 min was optimum. Mass spectra of extracts from concretes with the known modifiers were obtained. For this purpose, a finished construction material which attained not less than 50% of the specified strength was used. After 3 days of solidifying, the age of the concrete was not No. 8
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AMELIN, KRASNOVA (а)
(b)
1772.751
25
2096.916 1904.871
20
2037.997
20
15
2214.150
1552.539
2258.190
1508.503 1464.467
2346.270 2390.307 2434.358
12.88.288 1200.187 1068.059
2362.155
1832.659
1789.625 2450.246 1744.579
10
2302.233
1420.426 1376.367 1332.332
2317.903
15
2126.077
1640.627 1596.582
5
Intensity × 102, arb. units
Intensity × 102, arb. units
2082.031
10
2230.046
1920.737
1992.943 1684.663
1700.540
2494.034 2538.336
1656.469
2582.338 2626.156 2714.220
5
3063.783
2478.394 2522.415 2566.470 2654.540
0
0 1000
1400 1200
1800 1600
2200 2000
2600
1200
2400
1600 1400
m/z
2000 1800
2400
2800 2600
2200
3000 m/z
Fig. 3. Mass spectra of a solution of PCE manufactured in China: (a) 0.5 mg/mL and (b) extract from concrete with the indicated modifier using αcyano4hydroxycinnamic acid, concentration of modifier based on PCE in concrete 0.3%, and sonication for 30 min.
important in the extraction of modifiers of various nature. To the third day, the weakening of the bond between the modifier and cement grain occurred as a result of the formation of a dense crystalline structure
in the body of materials, as well as a decrease in the reactivity of the binder. Figure 5 presents mass spectra for the identification of four samples of heavy concrete. It was found that
(а) 1904.943
25
(b)
1993.023
2534.168 2126.152
20
1816.861 2446.070 2214.227
1728.773
2402.012
2258.276
15
1684.723 2302.319 2346.354
1640.679
15 10
1596.641 1552.601 2390.388
1508.556 1464.506 1420.462 1244.278
2434.440 2478.474 2522.500 2566.559 2610.597 2654.615 2698.695
5 0 1200
1600 1400
2000 1800
2400 2200
Intensity × 102, arb. units
20
Intensity ×
102,
arb. units
1772.812
2600 m/z
2622.232 2710.332
2313.923
2798.393 2224.847 2842.435 2886.450 2930.525
10 2137.748 2093.767
5
2005.817
3018.539 3432.815
0 1600 2000 2400 2800 3200 1800 2200 2600 3000 3400 m/z
Fig. 4. Mass spectra of a solution of PCE manufactured in Korea: (a) 0.5 mg/mL and (b) extract from concrete with the indicated modifier using αcyano4hydroxycinnamic acid, concentration of modifier based on PCE in concrete 0.3%, and sonication for 30 min. JOURNAL OF ANALYTICAL CHEMISTRY
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IDENTIFICATION AND DETERMINATION
961 (b)
(а) 25 Intensity × 102, arb. units
2534.168
20
0 400
600
2402.012 2666.290
2357.989
2710.332
15
SO3H
800
1000
1200
2224.847 2842.435 2181.818
10
1308.127 [M6–H]–
0.25
220 Da
1088.061 [M5–H]–
0.50
CH2
867.689 [M4–H]–
0.75
427.542 [M3–H]–
1.00 427.542 [M2–H]–
Intensity × 105, arb. units
1.25
2886.450 2930.525
2093.767
2974.532
2049.716
5
1960.608 3432.815
1000 1500 2000 2500 3000 3500
1400 m/z
m/z
(c)
(d) 995.896
951.861
44 Da
(–CH2–CH2–O–) 1128.033
606.310
20
731.644
1172.072
687.629 1216.108 1260.152
10
0.8 0.6 0.4 0.2
1348.210
0
0 400
600 700 800 900 1000 1100 1200 1300 m/z
968.691
1083.985
729.553
819.725 775.691
30
575.154
1.0
1039.944
559.163
863.773
Intensity × 105, arb. units
Intensity × 102, arb. units
40
600
800
1000
1200
1400 m/z
Fig. 5. Mass spectra of extracts from concrete: (a) no. 1, (b) no. 2, (c) no. 3, and (d) no. 4 using αcyano4hydroxycinnamic acid and sonication for 30 min.
sample of concrete no. 1 contained plasticizer C3. Peaks of oligomer ions with the number of units from 2 to 5 were observed in the mass spectra. Sample of concrete no. 2 contained modifier based on PCE manufactured in Korea, and sample of concrete no. 3 contained modifier based on PCE manufactured in Russia. Sample no. 4 was an extract from concrete containing no modifier (model composition). The identification of modifiers based on PCE was per formed by comparing the obtained spectra with the spectra of solutions of these modifiers and extracts from concretes containing modifiers in the optimum amounts (Fig. 2–4). JOURNAL OF ANALYTICAL CHEMISTRY
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REFERENCES 1. Batrakov, V.G., Modifitsirovannye betony. Teoriya i praktika (Modified Concretes: Theory and Practice), Moscow: Tekhnoproekt, 1998. 2. GOST (State Standard) 304592008: Admixtures for Concretes and Mortars: Determination and Estimation of the Efficiency, Moscow, 2010. 3. Krasnova, T.A. and Amelin, V.G., Zavod. Lab., Diagn. Mater., 2013, vol. 79, no. 8, p. 7. Translated by I. Duchovni No. 8
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