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

956

IDENTIFICATION AND DETERMINATION

(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

Vol. 70

957

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

2015

958

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

JOURNAL OF ANALYTICAL CHEMISTRY

Vol. 70

No. 8

2015

IDENTIFICATION AND DETERMINATION (b)

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

Vol. 70

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

2015

960

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

Vol. 70

No. 8

2015

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

Vol. 70

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

2015