Iterative step-growth synthesis and degradation of unimolecular polyviologens under mild conditions

An iterative step-growth addition method was used to expedite the gram-scale synthesis of main-chain polyviologens by several days, while also producing the longest main-chain polyviologen (i.e., 26 viologen subunits) reported...

The prospect of using Shewhart control charts in assessing the quality of ionometric measurements by the method of adding a sample to a standard

Modern methods of quantitative physical and chemical measurements should necessarily include procedures for quality control of research results. Recently, the procedure for quality control of measurements using control charts is gaining particular popularity in the practice of analytical measurements. To date, the methods of potentiometric studies operating in the territory of the Russian Federation, in most cases, do not include quality control using this control procedure. However, despite the complexity of the implementation and interpretation of its results, it is the use of control charts that allows you to control the quality of ionometric measurements. This is especially important for potentiometric determinations based on the addition method, since the instability of the slope of the electrode function and its deviation significantly contribute to the uncertainty of the measurement results. This article presents the main results of evaluating the use of the Shewhart control chart method for monitoring the repeatability and accuracy of measurement results. The measurement results have been obtained using an improved method of quantitative potentiometric determination of high concentrations (more than 1 gm/cdm) of ammonium ions by the method of adding a sample to the standard. In addition, an experimental substantiation of the fact that the value of the slope of the electrode function significantly affects the accuracy of measurements by the addition method has been presented. It has been revealed that when the angular coefficient of the electrode function is more than 62 mV/pNH4+ at (25±5)°C, deviations of the measurement results from the control standard by more than 50% are observed. It has been found that at (25±5)°С the most accurate results of quantitative determination are achieved when the angular coefficient of the electrode function is from 54 mV/pNH4+ to 62 mV/pNH4+ inclusive.

Pipette Tip Solid-Phase Extraction Combined with Fluorescence Spectroscopy for Determination of Selenium in Green Tea Samples

In this study, the custom-built pipette-tip solid phase extraction (PT-SPE), was used for pre-concentrating the selenium (Se) in green tea samples. The PT-SPE was prepared using a pipette tip and C18 as the adsorbent that was placed between glass wool. This method afforded several advantages in terms of efficiency of extraction time (8 min), sample (2 mL), and solvent (1 mL) volumes with less wastage of solvent. Under optimal conditions of extraction, this method yielded good linearity (r2=0.998) for the Se calibration curve and good limit of detection (0.2 μg/L) and quantification (0.6 μg/L). The standard addition method was used to remove the matrix effect. The recovery percentages of tea samples spiked with different Se concentrations ranged from 97.7 to 106.0%, indicating that the proposed method would be suitable for the determination of Se in green tea samples.

A standard addition method to quantify serum lithium by inductively coupled plasma mass spectrometry

Background Therapeutic monitoring of lithium (Li) is important because of its narrow therapeutic range and therapeutic index. Here, the authors present the evaluation of an accurate method for the determination of lithium in serum. Method Serum samples were diluted with 0.3% ultrapure nitric acid and were spiked with an internal standard germanium (Ge). The Li/Ge ratio was detected in He mode; we utilized standard addition method to quantify lithium in human serum. The new inductively coupled plasma mass spectrometry (ICP-MS) assay was characterized for linearity, specificity, imprecision, trueness, accuracy, and comparison. Results The correlation coefficients (r) of linearity were all > 0.9999. The specificity proved to be good. The total coefficients of variation (CV) were 1.11% and 0.49% for the two serum samples. The mean bias from target values of standard reference materials (SRM 956d) was −0.71% for Level I, −017% for Level II, and 2.20 for Level III. External Quality Assessment Scheme for Reference Laboratories in Laboratory Medicine (RELA) gave satisfied results for the new method. Comparison with the ion-selective electrode routine method got reasonable results. Conclusion This high accuracy method is an attractive alternative for lithium measurement and can be used as a candidate reference method to improve quality of serum lithium in China.

Enabling Conducting Polymer Applications: Methods for Achieving High Molecular Weight in Chemical Oxidative Polymerization in Alkyl- and Ether-Substituted Thiophenes

Polythiophenes (PTs) constitute a diverse array of promising materials for conducting polymer applications. However, many of the synthetic methods to produce PTs have been optimized only for the prototypical alkyl-substituted example poly(3-hexylthiophene) (P3HT). Improvement of these methods beyond P3HT is key to enabling the widespread application of PTs. In this work, P3HT and two ether-substituted PTs poly(2-dodecyl-2H,3H-thieno[3,4-b][1,4]dioxine) (PEDOT-C12) and poly(3,4-bis(hexyloxy)thiophene) (PBHOT) are synthesized by the FeCl3-initiated oxidative method under different conditions. Polymerization was carried out according to a common literature procedure (“reverse addition”) and a modified method (“standard addition”), which differ by the solvent system and the order of addition of reagents to the reaction mixture. Gel-permeation chromatography (GPC) was performed to determine the impact of the different methods on the molecular weights (Mw) and degree of polymerization (Xw) of the polymers relative to polystyrene standards. The standard addition method produced ether-substituted PTs with higher Mw and Xw than those produced using the reverse addition method for sterically unhindered monomers. For P3HT, the highest Mw and Xw were obtained using the reverse addition method. The results show the oxidation potential of the monomer and solution has the greatest impact on the yield and Xw obtained and should be carefully considered when optimizing the reaction conditions for different monomers.

Sistem Pendukung Keputusan Penerima Bantuan Covid-19 Kelurahan Bugel Kota Salatiga Menggunakan Simple Additive Wieghting (Saw)

The purpose of this study is to facilitate decision making in providing COVID-19 assistance to underprivileged communities in Bugel Village, Salatiga City. This study uses the Simple Additive Wieghting method or commonly referred to as the weighted addition method. This method performs a weighted summation of the performance ratings of each alternative on all attributes. The results of the study from 5 families showed who was the most eligible to receive the Covid-19 assistance in the Bugel Village, Salatiga City, namely Sardianto with a final normalization result of 0.785. It is hoped that this research can be used to make decisions quickly and objectively

Developing On-Site Trace Level Speciation of Lead, Cadmium and Zinc by Stripping Chronopotentiometry (SCP): Fast Screening and Quantification of Total Metal Concentrations

Electrochemical stripping techniques are interesting candidates for carrying out onsite speciation of environmentally relevant trace metals due to the existing low-cost portable instrumentation available and the low detection limits that can be achieved. In this work, we describe the initial analytical technique method development by quantifying the total metal concentrations using Stripping Chronopotentiometry (SCP). Carbon paste screen-printed electrodes were modified with thin films of mercury and used to quantify sub-nanomolar concentrations of lead and cadmium and sub-micromolar concentrations of zinc in river water. Low detection limits of 0.06 nM for Pb(II) and 0.04 nM for Cd(II) were obtained by the standard addition method using a SCP deposition time of 180 s. The SCP results obtained for Pb(II) and Cd(II) agreed with those of inductively coupled plasma mass spectrometry (ICP-MS). The coupling of SCP with screen-printed electrodes opens up excellent potential for the development of onsite speciation of trace metals. Due to the low analysis throughput obtained for the standard addition method, we also propose a new, more rapid screening Cd(II) internal standard methodology to significantly increase the number of samples that can be analyzed per day.

Assessing the risk of heavy metals contamination in milk from Pakistan

Milk is an essential component of human food, and natural source of many important elements. Besides essential elements it is also became a source of toxic metals due to heavy environmental pollution. In order to assess the essential metals (calcium) and toxic metals (cadmium and lead) in milk, sixty different fresh milk samples were analyzed by using atomic absorption spectroscopy (AAS). Accuracy and precession were checked by external standard addition method. Calcium was found in all samples with highest concentration (24µg/L) in camel milk. Lead was found in all milk samples with mean level 3.14µg/L and highest concentration found in packed milk sample 6.7µg/L. Cadmium was detected in 33% of total samples analyzed with range of (1.1-3.1µg/L). Results of this study will be helpful in setting the standards in one of the most consumed commodities in Pakistan.