Journal of Analytical Chemistry最新文献

A series of silica-based sorbents with zwitterions in the functional layer attached via a spacer based on 1,4-butanediol diglycidyl ether is synthesized. The effect of structural fragments of the stationary phase on the chromatographic properties in the hydrophilic chromatography mode is studied, and multifunctional capabilities for separating neutral polar, hydrophobic, and negatively charged compounds are demonstrated. Based on the revealed regularities, a sorbent with high separation capacity for carboxylic acids is created, which allows the separation of 13 organic acids in 25 min with a resolution of at least 1.0.

The work reports the multielemental characterization of topsoil samples from the area of the spent 'French mines' situated at Mt. Medvednica, near Zagreb, Republic of Croatia. Determination of the selected analytes was carried out by means of inductively coupled plasma optical emission spectrometry in three series of extracts that were prepared with deionized water, Mehlich-3 solution, and aqua regia. Results show that, with careful work, about 20 various chemical elements can be quantified in soil extracts prepared with deionized water. Also, it is shown that Mehlich-3 solution can be applied for the determination of many trace elements and not only for a set of 10 nutrients that were originally intended. A comparison of the efficiencies of the extraction methods was done by calculation of the ratios of the mass fraction values obtained by the three extraction reagents. Since weaker reagents allow the extraction of portions of elements that are relatively weakly bound to soil particles, the comparison of the mass fraction ratio values allows an assessment of the mobility of a metal(loid). Topsoil in the area of the spent mine is overloaded with metal(loid)s, as follows (the highest measured mass fractions values extracted with deionized water/Mehlich-3/aqua regia are given in brackets): As (0.521/1.44/337), Cd (0.011/0.911/4.24), Co (0.476/6.45/133), Cu (1.691/78.2/1227), Ni (0.851/6.81/152), Pb (4.40/893/11540), and Zn (1.25/38.4/817 mg/kg).

A new analytical method is proposed for the de termination and reporting of ‘acid-reactive silica’ under a fixed set of conditions that can be validated by a single laboratory. Acid-reactive silica exists as fluorosilicic acid during phosphate extraction processes. It is formed when fluoride inherent in the source rock (e.g., fluorapatite, francolite, fluorite) is liberated and reacts with siliceous minerals. To prevent corrosion, contamination with glassware, and volatile analyte losses—which have historically been major obstacles—the method involves acid digestion of the sample in Teflon-sealed cartridges during a microwave heating process, followed by elemental silicon analysis by inductively coupled plasma-optical emission spectroscopy. This method is useful for those in the mineral processing industry, particularly in processing phosphate minerals, where mineral acid is used to extract phosphate and other elements from geological ores. Predictive forecasting and quality control are needed in these industrial processes to control and recover fluorine byproducts, which pose enormous health and environmental concerns. Fluorosilicic acid itself is highly corrosive, but it is precipitated out in subsequent evaporation stages of phosphate production as sodium or potassium salts, thereby effectively making it a corrosion absorber for the holistic process. Due to this unique property, acid-reactive silica represents an invaluable but historically unestablished material property that requires definition.

A rapid, sensitive, inexpensive, and reliable analytical approach, directly suspended droplet microextraction (DSDME), was developed for the determination of aroma components in orange juice, coupled with gas chromatography-mass spectrometry. Hexane was used as the extraction solvent and placed on the top of the aqueous sample; several factors influencing the extraction and collection efficiency were optimized. The approach was used to determine some important aromas in orange juice, yielding relative recoveries of 91.66 to 109.94%, relative standard deviations of 2.04–6.91% (n = 5), and limits of detection of 0.2–1.9 μg/L. Satisfactory recoveries were obtained for all spiked compounds. The DSDME method requires minimal solvent, achieving high sensitivity with low detection limits for aroma compounds. The coupled miniaturized method was applied to the sensitive determination of aroma components in orange juice.

The special features of gas chromatographic identification of low-boiling organic solvents based on their retention index values on standard nonpolar polydimethylsiloxane stationary phases was considered with the use of 80 most common organic solvents as an example. It was shown that one-dimensional analytical parameters, such as retention indices, cannot provide unambiguous identification of all compounds of this group because their informative value R(RI) in this group is only about 29, which is lower than the number of objects in the group. To solve the problem, it is necessary to supplement the chromatographic data with independent characteristics, and refractive indices ((n_{D}^{{20}})) can be recommended as these characteristics because their determination requires minimal time and sample quantities. Nevertheless, about 10% of the solvents under consideration cannot be distinguished even based on the combinations of RI + (n_{D}^{{20}}). For comparison, the capabilities of using the dynamic viscosity of liquids as an additional analytical parameter were considered. The given table of retention indices for the most common organic solvents is of independent value for analytical practice.

Miniaturized methods for the adsorption separation and preconcentration of organic compounds include micro-solid-phase extraction (μ-SPE) and solid-phase microextraction (SPME). These methods are characterized by the reduced amounts of sorbents, test samples, and organic solvents; high preconcentration factors; and a combination of preconcentration and sample injection in a single device. Since the advent of μ-SPE (1989) and SPME (1990), numerous versions of these methods have been developed, which differ in the method of sample preparation, nature of sorbents used, and combination with methods of the subsequent determination of the preconcentrated substances. The popularity of these methods is illustrated by the large number of reviews summarized in this publication.

Specific features of the chromatographic retention of alkali and alkaline-earth metal cations on poly(styrene–divinylbenzene) cation-exchangers functionalized with carboxyl groups are considered. It was found that the retention of metal cations of equal charges correlates directly with their polarizability. The effects of eluent type and concentration on the retention of metal and ammonium cations were studied and the contributions of secondary processes to the retention and peak shape were evaluated. An increase in the eluent concentration improved the symmetry of the chromatographic peaks. Van’t Hoff plots were constricted and adsorption enthalpies (ΔH°) were estimated. Column efficiency increased with temperature. A possibility of the simultaneous determination of alkali and alkaline-earth metal ions and ammonium cations on carboxylic cation-exchangers with either direct or suppressed conductometric detection was demonstrated. The applications of these adsorbents to water analysis are discussed.

A capillary electrophoresis technology for determining synthetic polyphosphates (SPs) in meat products (MPs) has been developed and implemented. The SP content was monitored in filtered MP extracts. Extraction and separation modes were developed, and the geometric parameters of the capillary and SP detection were selected. It is proven that the content of tri- and diphosphates of MPs decreases differently over time (the content of triphosphates decreases faster than that of diphosphates at the same temperature) and depends on both the MP storage temperature and the technological processes during MP production.

This review considers the outcomes of two decades of the development of the technique of extractive freezing-out. The method introduces a novel extraction principle based on the low-temperature separation of the target analytes through the redistribution of the solutes between the liquid phase of a pre-added, nonfreezing hydrophilic solvent and the solid phase of ice formed during the freezing process. A significant advancement of the method resulted from the implementation of extractive freezing-out under centrifugal force conditions (EFC). The introduction of EFC as a sample preparation step into numerous protocols for the determination of organic compounds has enabled the successful application of the method to chemical toxicological analysis, food quality control, environmental monitoring, and hydrochemical investigations. The technique demonstrates clear advantages over conventional liquid–liquid extraction, headspace analysis, and solid-phase extraction. The immediate prospects for the further development of the method are noted.

A method is proposed for reducing the limit of detection for p-aminobenzoic acid and some of its medicinal derivatives in condensation reactions with p-dimethylaminobenzaldehyde, based on a combination of catalysis by anionic (effect of “micellar catalysis”) and preconcentration by non-ionic surfactants (effect of “micellar microextraction”). The conditions for obtaining saturated micellar phases of Triton X-114 in the absence and in presence of sodium dodecyl sulfate (SDS) ions and micelles, reactants, and salting-out agents (NaCl, Na₂SO₄, Na₃C₆H₅O₇) are optimized. Micellar-saturated phases of Triton X-114 and SDS are proposed as test means, ensuring the effective preconcentration of the analytical forms of Schiff bases of the studied analytes and their determination at the nanogram level in aqueous media, blood plasma model, and dosage forms at concentrations of an order of n × 10^–8 M by colorimetric methods using digital technologies.