- Research article
- Open Access
Investigation of tin adsorption on silica nanoparticles by using flow field-flow fractionation with offline inductively coupled plasma mass spectrometry
© The Author(s). 2018
- Received: 8 July 2018
- Accepted: 7 September 2018
- Published: 18 September 2018
Flow field-flow fractionation (Fl-FFF) for silica nanoparticles with offline inductively coupled plasma mass spectrometry (ICP-MS) was applied to investigate the adsorption behavior of tin onto silica nanoparticles. Effect of carrier solutions and membranes was studied to achieve better separation for silica nanoparticles prior to tin detection using ICP-MS. Investigation was carried out by using 0.25 mM ammonium carbonate and 0.02% FL-70 with 0.02% NaN3 as carrier solutions with 1 kDa regenerated cellulose (RC), 10 kDa regenerated cellulose (RC), and 10 kDa polyethersulfone (PES) membranes. Ammonium carbonate carrier solution with suitable ionic strength provided good separation with minimization of particle-membrane interaction. Better retention was shown by employing 10 kDa RC membrane. Furthermore, Fl-FFF was employed for the separation of silica nanoparticles incubated with tin. Fractions eluted from Fl-FFF were collected and then introduced into ICP-MS. Tin was adsorbed onto silica nanoparticles with different adsorption capabilities depending on particle size. Adsorption of tin was greater on the smaller size of silica nanoparticles compared to the bigger size with the adsorption percentage of 98.5, 44.9, and 6.5 for 60 nm, 100 nm, and 200 nm, respectively. Size-dependent adsorption of tin was in good agreement with surface area per volume of silica nanoparticles.
- Flow field-flow fractionation
- Silica nanoparticles
- Adsorption behavior
- Inductively coupled plasma mass spectrometry
Synthetic nanosilica or silica nanoparticles have been used in diverse applications. They offer great stability with easy synthesis protocol (Rao et al. 2005). Synthetic silica nanoparticles are available in various forms such as powder, gel, precipitate, and colloid (Fruijtier-Polloth 2012). Addition of silica nanoparticles into dairy products provides the advantages of quality enhancement, such as to prevent caking and to act as thickening or emulsion stabilizer of some products such as coffee creamers, milk, soups, salts, sauces, and flours (Heroult et al. 2014). Silica nanoparticles with particle size of 30–200 nm were found in food products with concentration range of less than 0.1 to 6.9 mg g−1 (Dekkers et al. 2011). The use of silica nanoparticles in food has attracted huge attention from researchers regarding their safety. Several potential toxicity risk investigations have been reported (Dekkers et al. 2011; van Kesteren et al. 2014; Peters et al. 2012). The presence of silica nanoparticles additive in food products changes the cell cycle of fibroblast cell in human which can undergo expression of stress reaction as well as antioxidant enzyme secretion (Athinarayanan et al. 2014).
Nowadays, food products are easily found as canned food. Canning process provides food preservation to extend the shelf life. Thin layer of tin or known as tinplate is coated inside the can body to enhance the robustness of food packaging. Tinplate minimizes the use of preservative due to the nature of tin as fungicide and bactericide. However, the use of tinplate triggers the dissolution of tin into foodstuff and exposing potential toxicity to consumers (Blunden and Wallace 2003). Several investigations have noted that high level of inorganic tin contained in foods has possibility to trigger acute toxicity such as fever, headache, nausea, vomiting, diarrhea, bloating, and abdominal cramps. Concentration above 200 mg kg−1 is known to provoke short-term effect as mentioned above (Perring and Basic-Dzorvak 2002). Moreover, storage condition of canned food, particularly the temperature, is predicted to have a non-trivial effect to the dissolution rate of tin. Dissolved tin from cans is likely bound to solid particles of food, and attachment of tin is known to be difficult to break (Weber 1987). In the presence of silica nanoparticles as food additive in canned food, dissolved tin would also be possible to bind onto silica nanoparticles. Several researchers have investigated the adsorption behavior of metal onto silica nanoparticles (Karnib et al. 2014; Ragab et al. 2017), and their adsorption of metal immensely enhanced the toxicity (Ragab et al. 2017). However, the adsorption behavior of tin onto silica nanoparticles has never been reported.
Assessment of adsorbed metal onto nanoparticles includes two steps, i.e., the separation of nanoparticles and the detection of metal residual by element determination techniques such as flame atomic absorption spectrometry (FAAS) or electrothermal atomic absorption spectrometry (ETAAS) (Karnib et al. 2014; Ragab et al. 2017). Field-flow fractionation (FFF) is a separation technique which has great ability for separating particles, molecules, and colloids in the range of nanometers up to micrometers. With FFF, various types of external field can be used, resulting in various FFF sub-techniques. Since flow field-flow fractionation (Fl-FFF) is known to provide excellent separation for many types of nanoparticles, it is interesting to explore the capability of Fl-FFF for this purpose. It is supported by many works that have successfully demonstrated separation, quantification, and characterization of silica nanoparticles (Dekkers et al. 2011; Grombe et al. 2014; Barahona et al. 2015; Aureli et al. 2015). Nonetheless, particles interaction with carrier solutions and accumulation wall under separation circumstance of Fl-FFF could not be neglected. Carrier solutions and membranes have critical influences to determine the quality of separation (Bendixena et al. 2014; Jochem et al. 2017; Benincasa and Caldwell 2001; Moon et al. 1998). Hence, the effects of carrier solutions and membranes for silica nanoparticles separation need to be examined.
Considering high dilution occurred during Fl-FFF separation, high sensitivity spectrometry technique needs to be employed for tin detection. Based on previous works for tin determination, inductively coupled plasma mass spectrometry (ICP-MS) revealed the highest sensitivity among spectrometry techniques (Knápek et al. 2009; Yuan et al. 2005; Trandafir et al. 2012). Therefore, in this study, Fl-FFF for silica nanoparticles with offline ICP-MS was employed to investigate adsorption behavior of tin onto silica nanoparticles. Effect of carrier solutions and membranes on the separation behavior of silica nanoparticles was also examined to achieve better separation.
Non-functionalized sphere silica nanoparticles (10 mg mL−1) with the size of 60, 100, and 200 nm were purchased from Nanocomposix, Inc. (San Diego, CA, USA). FL-70 detergent (Fisher Chemical, Waltham, MA USA). Magnesium nitrate was bought from BDH VWR Analytical (Poole, England). Ammonium carbonate was purchased from Ajax Finechem (New South Wales, Australia). Tin dichloride was from Schalarau Chemie (Barcelona, Spain). Hydrochloric acid 37% was from ACI Labscan (Bangkok, Thailand). Sodium azide, sodium hydroxide, and palladium nitrate were bought from Merck (Darmstadt, Germany).
Fl-FFF operating conditions
FFF channel dimensions (cm)
28.7 cm long × 1.8 cm wide × 0.021 cm thick
Sample volume (μL)
Delay time (s)
Equilibrium time (min)
1 kDa RC, 10 kDa RC, 10 kDa PES
0.02% (v/v) FL-70 with 0.02% (w/v) NaN3, ammonium carbonate 0.25 mM
Channel flow rate (mL min−1)
Cross flow rate (mL min−1)
ICP-MS operating condition for tin-silica nanoparticles investigation
Agilent technologies 7900 ICP-MS
Quartz with id of 2.5 mm
Monitored isotopes (m/z)
Rf power (W)
Rf matching (V)
Nebulizer gas flow (L min−1)
Sample depth (mm)
Chamber temperature (°C)
Hydrodynamic diameter of silica nanoparticles in different carrier solutions was determined by Zetasizer Nano-SZ from Malvern Instruments Ltd. (Malvern, UK).
The examination of silica nanoparticles contained in void fractions was carried out using transmission electron microscopy (TEM, JEM-1400HC, JEOL, Tokyo, Japan).
Moreover, scanning electron microscopy (SEM) model SU810 from Hitachi (Tokyo, Japan) was also used to find out membranes morphology in both surface mode and cross-section mode.
Incubation of tin-silica nanoparticles
Interaction of tin-silica nanoparticles was investigated by incubation of silica nanoparticles in tin stock solutions, where 200 μL silica nanoparticles (10 mg mL−1) was added into 40 μL of tin dichloride solutions (100 mg L−1). Sonication was applied for 20 min, and the solution was left at room temperature for 24 h.
Offline Fl-FFF with ICP-MS for silica nanoparticles
Silica nanoparticles were firstly incubated as mentioned above before introducing into the Fl-FFF system. The incubated silica was injected into Fl-FFF system by using the selected carrier solutions and membranes. Fractions from the separation peak were collected and diluted into the detectable range of ICP-MS. The diluted fractions were then subjected to ICP-MS detection.
Retention time of silica nanoparticles in various carrier solutions and membranes
Particle size (nm)
Retention time (min)
RC 1 kDa
RC 10 kDa
PES 10 kDa
RC 1 kDa
RC 10 kDa
PES 10 kDa
Effect of membranes and carrier solutions on the separation behavior of silica nanoparticles
Effect of membranes
Increasing the MWCO led to decreasing the void peaks, suggesting that membrane with larger MWCO performed better matrix removal efficiency (Kavurt et al. 2015). The void peak observed when using 1 kDa RC with 0.02% FL-70 with 0.02% NaN3 carrier was very high as compared to the other two membranes. Void fractions of 100 nm and 200 nm silica nanoparticles were collected and introduced into TEM imaging for examination. We examined two zones in the TEM grid to get reliable results. Surprisingly, small number of silica nanoparticles was found in the collected fractions shown in Fig. 2. In void fraction of 100 nm, mean size of silica nanoparticles found was 86 nm and 92 nm for zone 1 and zone 2, respectively. For the void fraction of 200 nm, however, 178 nm was found in zone 1 and 83 nm found in zone 2. Regarding this finding, we speculate that in the presence of membrane fouling, the back pressure inside the channel was increased resulting in incomplete equilibrium occurred during relaxation step. Some of particles were deposited on the membrane causing membrane fouling, and some other particles nearer to injection port were not retained completely during the equilibrium time; therefore, some of particles were eluted as void fractions.
Effect of carrier solutions
Properties of carrier solutions
0.02% (v/v) FL-70 with 0.02% (w/v) NaN3
0.25 mM ammonium carbonate
Type of chemical
Surfactant with inorganic salt
Ionic strength (mM)
Relative fractionation recovery
Percentage of recovery decreased along with increasing the particle size in the case of 1 kDa RC, in the case10 kDa RC with ammonium carbonate carrier (Fig. 4b), and in the case of 1 kDa RC and 10 kDa PES with FL-70 with NaN3 carrier (Fig. 4a). Opposite trend was shown by 10 kDa RC with FL-70 with NaN3 carrier that the percentage of recovery increased with increasing particles size. For 10 kDa PES with ammonium carbonate carrier, the percentage of recovery was similar to all particle sizes studied herein. With the smallest MWCO of membrane, lower retention of silica nanoparticles (smaller separation peak height) in both of carrier solutions was observed. This effect will be worse for larger size of nanoparticles as they have lower self-diffusion, so they are prone to stay closer to the membrane, as the result poor recovery was shown for 200 nm. Both carriers provided desirable recoveries with negligible difference in case of 10 kDa membranes. Considering the excellent percentage of relative recovery obtained, 10 kDa RC was considered for further experiment.
Investigation of tin adsorption onto silica nanoparticles by Fl-FFF with offline ICP-MS
Fractions of silica nanoparticles were collected from the time when the peak started to show up until the peak reached the baseline. Collected fractions were then adjusted to the volume and introduced into ICP-MS system with operating conditions listed in Table 2. Tin standard solutions with the concentration ranging from 0.5–10.0 μg L−1 were introduced to construct calibration curve prior to fractions analysis. Calibration curve was constructed to perform the quantification of tin adsorbed onto silica nanoparticles. According to the work from Yu in 2010, 118Sn and 120Sn showed highest abundances and are less disturbed by oxides (Yu et al. 2010). Therefore, two tin isotopes were monitored in this work. 120Sn showed great linear relationship between intensity and tin concentration with the relation coefficient of 0.9984. Tin was found in the collected fractions suggesting that tin could be bound onto silica nanoparticles. Electrostatic interaction and strong coordinate bonds between adsorbed tin ions with weak acidity of hydroxyl from silanol groups on silica nanoparticles surface has known to be suitable adsorption mechanism (Ragab et al. 2017). Carrier solution flow did not ruin the interaction between tin with silica nanoparticles as we could see tin intensity in the collected fractions. It is interesting to note that the application of Fl-FFF with offline ICP-MS could be applied for investigation of adsorption behavior of tin onto silica nanoparticles.
Effect of silica nanoparticles size on tin adsorption
According to the results, tin intensity from fractions was influenced by size of silica nanoparticles. Decreasing tin intensity was observed along with increasing particle size. Tin adsorbed onto different-sized silica nanoparticles was further determined. It was known that amount of adsorbed tin increased with the decreasing size of silica nanoparticles. Percentage of tin adsorption onto silica nanoparticles was calculated using the equation:
Percentage of tin in different-sized silica nanoparticles
Fraction 60 nm
Fraction 100 nm
Fraction 200 nm
Adsorption behavior of tin onto nanoparticles was investigated by Fl-FFF with offline ICP-MS. Fl-FFF was employed for the separation of silica nanoparticles incubated with tin prior to the tin analysis by ICP-MS. Solid particles could be excluded from supernatant and accumulated as eluted fractions. Collected fractions were introduced into ICP-MS for tin detection. Effect of carrier solution and membranes was firstly investigated to obtain desired separation of silica nanoparticles. Ionic strength of carrier solution was considered. The nature of ammonium carbonate offers beneficial for both Fl-FFF and ICP-MS systems. Separation performance was also affected by MWCO and material of the membrane. Adsorption of tin onto silica nanoparticles depended on the size of silica nanoparticles. Tin adsorption was increased in the decreasing of particles size as their surface area per volume increased along with decreasing particles size. The order of tin adsorption capability of silica nanoparticles from the greatest to the least are 60 nm, 100 nm, and 200 nm, respectively. The size differentiation of silica nanoparticles was important. The advantages of using Fl-FFF in this work were emphasized by performing separation as well as giving size information of silica nanoparticles.
We sincerely acknowledge the research grant from Center for Innovation in Chemistry: Postgraduate Education and Research Program in Chemistry (PERCH-CIC) in collaboration with National Research Council of Thailand (NRCT) and International Foundation for Science (IFS). Thanks are also due to Thailand Research Fund (TRF) and Mahidol University for providing the research grant under the grant number BRG6180006. Funding from the Thailand Research Fund under the grant number IRN59W0007 is also acknowledged. We would like to thank Dr. Ronald G. Beckett for donating some parts of FlFFF system.
NLZ performed all the experimental works. AS coordinated and planned the work. All authors read and approved the final manuscript.
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