|1- Dadashi, M., Abdollahi, H., Tauler, R., "Error propagation along the different regions of multivariate curve resolution feasible solutions", Chemometrics and Intelligent Laboratory Systems, 162, 203-213, (2017).|
Evaluation of uncertainties due to rotational ambiguities and noise propagation is essential to ascertain the reliability of Multivariate Curve Resolution estimations. When ambiguity is present, every resolved profile can be represented by a band of feasible solutions instead of by a unique profile. In the presence of experimental noise the estimation of this band of feasible solutions is more difficult and uncertain. The aim of this work is to show how experimental noise and profiles overlapping affect the reliability of feasible solutions. For this purpose, feasible solutions of several two and three components data systems with different profiles overlapping and noise levels have been systematically investigated. Results obtained using simulated and experimental data showed that increasing noise levels and profiles overlapping in one mode (e.g. concentration profiles) make more uncertain the estimation of feasible solutions in the other mode (e.g. spectral profiles), and this uncertainty is propagated in a non-uniform and complex way.
|2- Akbari Lakeh, M., Rajkó, R., Abdollahi, H., "Local Rank Deficiency Caused Problems in Analyzing Chemical Data", Anal. Chem., 89: (4), 2259-2266, (2017).|
Multivariate curve resolution (MCR) is a powerful methodology for analyzing chemical data in different application fields such as pharmaceutical analysis, agriculture, food chemistry, environment, and industrial and clinical chemistry. However, MCR results are often complicated by rotational ambiguity, meaning that there is a range of feasible solutions that fulfill the constraints and explain equally well the observed experimental data. Constraints determine the properties of resolved profiles in MCR methods by enforcing different assumptions on data. The applied constraints on chemical data sets should be derived from the physical nature and prior knowledge of the system under study. Therefore, the reliability of the constraints in order to get accurate results is a critical aspect that should be considered by analytical chemists who use MCR methods. Local rank information plays a key role in the curve resolution of multicomponent chemical systems. Applying the local rank constraint can reduce the extent of rotational ambiguity considerably, and in some cases, unique solutions can be achieved. Local rank exploratory methods like Evolving Factor Analysis (EFA) method provide local rank maps in order to obtain the presence pattern of components on the main assumption that the number of components in each window is equal to its rank. It is shown in this work that the local rank is a mathematical concept that may not be in concordance with chemical information. Thus, applying the local rank constraint for restricting the rotational ambiguity in MCR methods can lead to incorrect solutions! This problem is due to “local rank deficiency”, which is introduced in this contribution.
|3- Omidikia, N., Abdollahi, H., Kompany-Zareh, M., Rajkó, R., "Analytical solution and meaning of feasible regions in two-component three-way arrays", Analytica Chimica Acta, 939: (5), 42-53, (2016).|
Although many efforts have been directed to the development of approximation methods for determining the extent of feasible regions in two- and three-way data sets; analytical determination (i.e. using only finite-step direct calculation(s) instead of the less exact numerical ones) of feasible regions in three-way arrays has remained unexplored. In this contribution, an analytical solution of trilinear decomposition is introduced which can be considered as a new direct method for the resolution of three-way two-component systems. The proposed analytical calculation method is applied to the full rank three-way data array and arrays with rank overlap (a type of rank deficiency) loadings in a mode. Close inspections of the analytically calculated feasible regions of rank deficient cases help us to make clearer the information gathered from multi-way problems frequently emerged in physics, chemistry, biology, agricultural, environmental and clinical sciences, etc. These examinations can also help to answer, e.g., the following practical question: “Is two-component three-way data with proportional loading in a mode actually a three-way data array?” By the aid of the additional information resulted from the investigated feasible regions of two-component three-way data arrays with proportional profile in a mode, reasons for the inadequacy of the seemingly trilinear data treatment methods published in the literature (e.g., U-PLS/RBL-LD that was used for extraction of quantitative and qualitative information reported by Olivieri et al. (Anal. Chem. 82 (2010) 4510–4519)) could be completely understood.
|4- Barati, A., Shamsipour, M., Abdollahi, H., "Carbon dots with strong excitation-dependent fluorescence changes towards pH. Application as nanosensors for a broad range of pH", Analytica Chimica Acta, 931, 25-33, (2016).|
In this study, preparation of novel pH-sensitive N-doped carbon dots (NCDs) using glucose and urea is reported. The prepared NCDs present strong excitation-dependent fluorescence changes towards the pH that is a new behavior from these nanomaterials. By taking advantage of this unique behavior, two separated ratiometric pH sensors using emission spectra of the NCDs for both acidic (pH 2.0 to 8.0) and basic (pH 7.0 to 14.0) ranges of pH are constructed. Additionally, by considering the entire Excitation–Emission Matrix (EEM) of NCDs as analytical signal and using a suitable multivariate calibration method, a broad range of pH from 2.0 to 14.0 was well calibrated. The multivariate calibration method was independent from the concentration of NCDs and resulted in a very low average prediction error of 0.067 pH units. No changes in the predicted pH under UV irradiation (for 3 h) and at high ionic strength (up to 2 M NaCl) indicated the high stability of this pH nanosensor. The practicality of this pH nanosensor for pH determination in real water samples was validated with good accuracy and repeatability.
|5- Barati, A., Shamsipour, M., Abdollahi, H., "Metal-ion-mediated fluorescent carbon dots for indirect detection of sulfide ions", Sensors and Actuators B: Chemical, 230, 289-297, (2016).|
Because of the fact that carbon dots (CDs) generally do not show satisfied fluorescence activities, developing indirect approaches to use these nanomaterials as fluorescence probes is of increasing interest. In this study, two novel metal-ion-mediated fluorescent probes based on CDs for the indirect detection of sulfide ions are presented. The first probe was established using CDs in the presence of Hg2+ ions and utilized as a fluorescence-enhancement probe. In this case, Hg2+ efficiently quenched the fluorescence of the CDs and subsequent addition of sulfide ions removed them from the surface of CDs resulting in regenerating the fluorescence. This probe was used for detection of sulfide over a linear concentration range of 2–10 μM and a detection limit of 0.32 μM. In the second probe, CDs in the presence of Ag+ was utilized as a fluorescence-quenching probe. Here, the fluorescence of CD/Ag+ was significantly quenched by sulfide while, Ag+ itself cause only a slight change in the fluorescence intensity of CDs. The quenching process was found to be based on the inner filter effect (IFE) of the formed Ag2S particles which absorb both the excitation wavelength and emission spectrum of CDs. This probe allowed detection of sulfide over the range of 1–100 μM and a detection limit of 0.43 μM. We validated the practicality of this probe for determination of sulfide ion concentration in tap and mineral waters with good recoveries.
|1- Omidikia, N., Kompany-Zareh, M., Abdollahi, H., "On uniqueness and rotational ambiguity in three-way models", XIII Chemometrics in Analytical Chemistry, Hungary, Budapest, 1-1, (2012).|