Ammonium chloride salting out extraction/cleanup for trace-level quantitative analysis in food and biological matrices by flow injection tandem mass spectrometry

A sample extraction and purification procedure that uses ammonium-salt-induced acetonitrile/water phase separation was developed and demonstrated to be compatible with the recently reported method for pesticide residue analysis based on fast extraction and dilution flow injection mass spectrometry (FED-FI-MS). The ammonium salts evaluated were chloride, acetate, formate, carbonate, and sulfate. A mixture of NaCl and MgSO₄, salts used in the well-known QuEChERS method, was also tested for comparison. With thermal decomposition/evaporation temperature of <350 °C, ammonium salts resulted in negligible ion source residual under typical electrospray conditions, leading to consistent method performance and less instrument cleaning. Although all ammonium salts tested induced acetonitrile/water phase separation, NH₄Cl yielded the best performance, thus it was the preferred salting out agent. The NH₄Cl salting out method was successfully coupled with FI/MS/MS and tested for fourteen pesticide active ingredients: chlorantraniliprole, cyantraniliprole, chlorimuron ethyl, oxamyl, methomyl, sulfometuron methyl, chlorsulfuron, triflusulfuron methyl, azimsulfuron, flupyrsulfuron methyl, aminocyclopyrachlor, aminocyclopyrachlor methyl, diuron and hexazinone. A validation study was conducted with nine complex matrices: sorghum, rice, grapefruit, canola, milk, eggs, beef, urine and blood plasma. The method is applicable to all analytes, except aminocyclopyrachlor. The method was deemed appropriate for quantitative analysis in 114 out of 126 analyte/matrix cases tested (applicability rate = 0.90). The NH₄Cl salting out extraction/cleanup allowed expansion of FI/MS/MS for analysis in food of plant and animal origin, and body fluids with increased ruggedness and sensitivity, while maintaining high-throughput (run time = 30 s/sample). Limits of quantitation (LOQs) of 0.01 mg kg⁻¹ (ppm), the ‘well-accepted standard’ in pesticide residue analysis, were achieved in >80% of cases tested; while limits of detection (LODs) were typically in the range of 0.001–0.01 mg kg⁻¹ (ppm). A comparison to a well-established HPLC/MS/MS method was also conducted, yielding comparable results, thus confirming the suitability of NH₄Cl salting out FI/MS/MS for pesticide residue analysis.     

Assay of Ivermectin Including Determination and Identification of Its Related Substances in Ivermectin Injectable Product by a Stability-Indicating RP-HPLC Method

Chromatographia - Ivermectin injectable product is widely used as a parasiticide for the treatment and control of internal and external parasites of cattle and swine. A reversed-phase high...     

Polyolefin soluble polyisobutylene oligomer‐bound metallophthalocyanine and azo dye additives

Metallophthalocyanines prepared with polyisobutyl (PIB) substituents have very high solubility in organic solvents including saturated hydrocarbons, toluene, and other low polarity organic solvents. In heptane, PIB‐bound metallophthalocyanines have solubility of about 0.1 g/mL at 25 °C, solubility values that are significantly higher than other substituted metallophthalocyanines. PIB terminally functionalized with metallophthalocyanines as well as PIB containing terminal azo dye groups also dissolve in molten hydrocarbon polymers like polyethylene or polypropylene. Thus, these highly chromogenic PIB‐bound dyes can be incorporated uniformly into the polyolefins to form colored polymer solids on cooling. Because only a low concentration of a highly hydrocarbon compatible dye is used, the crystallinity and thermal properties of the colored polyolefin products are not significantly affected. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 545–551     

Separation of nucleotides by hydrophilic interaction chromatography using the FRULIC-N column

A stationary phase composed of silica-bonded cyclofructan 6 (FRULIC-N) was evaluated for the separation of four cyclic nucleotides, six nucleoside monophosphates, four nucleoside diphosphates, and five nucleoside triphosphates via hydrophilic interaction chromatography (HILIC) in both isocratic and gradient conditions. The gradient conditions gave significantly better separations by narrowing peak widths. Sixteen out of nineteen nucleotides were baseline separated on the FRULIC-N column in one run. Unlike other known HILIC stationary phases, there can be dual-retention mechanisms unique to this media. Traditional hydrogen bonding/dipolar interactions can be supplemented by dynamic ion interaction effects for anionic analytes. This occurs because the FRULIC-N stationary phase is able to bind certain buffer cations. The extent of the ion interaction is tunable, in comparison to stationary phases with embedded charged groups, where the inherent ionic properties are fixed. The best mobile phase conditions were determined by varying the organic modifier (acetonitrile) content, as well as salt type/concentration and electrolyte pH. The thermodynamic characteristic of the FRULIC-N column was investigated by evaluating the column temperature effect on retention and utilizing van’t Hoff plots. This study shows that there is a greater entropic contribution for the retention of nucleotide di and triphosphates, whereas there is a greater enthalphic contribution for the cyclic nucleotides with the FRULIC-N column.     

Sulfonated cyclofructan 6 based stationary phase for hydrophilic interaction chromatography

A stationary phase composed of silica-bonded sulfonated cyclofructan 6 (SCF6) was synthesized and evaluated for hydrophilic interaction chromatography (HILIC). The separation of a large variety of polar compounds was evaluated on different versions of the stationary phase and compared with the same separations obtained with commercially available HILIC columns. The new columns successfully separate polar and hydrophilic compounds including β blockers, xanthines, salicylic acid related compounds, nucleic acid bases, nucleosides, maltooligosaccharides, water soluble vitamins and amino acids. The separation conditions were optimized by changing the composition and the pH of the mobile phase. The dependence of analyte retention on temperature was studied using van't Hoff plots. The newly synthesized stationary phase showed broad applicability for HILIC mode separations.     

Polyethylene as a nonvolatile solid cosolvent phase for catalyst separation and recovery

The studies described here show that a relatively low molecular weight, narrow polydispersity polyethylene (PE) wax (Polywax) can serve as a nontoxic and nonvolatile alternative to alkane solvents in monophasic catalytic organic reactions where catalysts and products are separated under biphasic conditions. In this application, a polymer that is a solid at room temperature substitutes for a conventional alkane solvent at ca. 80 °C. In addition to the advantages of being a nonvolatile, nontoxic, reusable solvent, this hydrocarbon polymer solvent, like heptane, can sequester nonpolar soluble polymer-bound catalysts after a reaction and separate them from products. The extent of this separation and its generality were studied using polyisobutylene (PIB)- and poly(4-dodecylstyrene)-bound dyes and PE-bound Pd allylic substitution catalysts, PIB-bound Pd cross-coupling catalysts, and PE- and PIB-bound metathesis catalysts. Catalytic reactions were effected using single-phase reaction mixtures containing Polywax with toluene, THF, or THF/DMF at ca. 80 °C. These solutions either separate into two liquid phases on addition of a perturbing agent or separate as a solid/liquid mixture on cooling. The hydrocarbon polymer-bound dyes or catalysts either separate into the hot liquid Polywax phase or coprecipitate with Polywax and are subsequently isolated as a nonvolatile Polywax solid phase that contains the dye or the recyclable catalyst.     

Syntheses of terminally functionalized polyisobutylene derivatives using diazonium salts

A new strategy for the synthesis of end‐functionalized polyisobutylene (PIB) oligomers is detailed. Commercially available vinyl‐terminated PIB oligomers were modified to form aniline‐terminated PIB via an aromatic electrophilic substitution reaction. The PIB‐bound aryl amines so formed were then converted into diazonium salts using isopentyl nitrite and an acid in methylene chloride. These salts served as versatile intermediates in synthetic reactions affording azo dye‐containing PIB derivatives and other terminally‐functionalized PIB derivatives not readily available by other reactions. The advantages and limitations of various name reactions including diazo couplings, Sandmeyer reactions, dediazoniations, and Heck reactions are discussed. The kinetics of polar substitution reactions at the termini of these nonpolar oligomers and the effects of solvent on these reactions were also examined. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Evaluation of aromatic-derivatized cyclofructans 6 and 7 as HPLC chiral selectors

The two best aromatic-functionalized cyclofructan chiral stationary phases, R-naphthylethyl-carbamate cyclofructan 6 (RN-CF6) and dimethylphenyl-carbamate cyclofructan 7 (DMP-CF7), were synthesized and evaluated by injecting various classes of chiral analytes. They provided enantioselectivity toward a broad range of compounds, including chiral acids, amines, metal complexes, and neutral compounds. It is interesting that they exhibited complementary selectivities and the combination of two columns provided enantiomeric separations for 43% of the test analytes. These extensive chromatographic results provided useful information about method development of specific analytes, and also gave some insight as to the enantioseparation mechanism.     

Quantitative analysis of polycyclic aromatic hydrocarbons using high-performance liquid chromatography-photodiode array-high-resolution mass spectrometric detection platform coupled to electrospray and atmospheric pressure photoionization sources

Polycyclic aromatic hydrocarbons (PAHs) are common pollutants present in atmospheric aerosols and other environmental mixtures. They are of particular air quality and human health concerns as many of them are carcinogenic toxins. They also affect absorption of solar radiation by aerosols, therefore contributing to the radiative forcing of climate. For environmental chemistry studies, it is advantageous to quantify PAH components using the same analytical technics that are commonly applied to characterize a broad range of polar analytes present in the same environmental mixtures. Liquid chromatography coupled with photodiode array and high-resolution mass spectrometric detection (LC-PDA-HRMS) is a method of choice for comprehensive characterization of chemical composition and quantification of light absorption properties of individual organic compounds present in the environmental samples. However, quantification of non-polar PAHs by this method is poorly established because of their imperfect ionization in electrospray ionization (ESI) technique. This tutorial article provides a comprehensive evaluation of the quantitative analysis of 16 priority pollutant PAHs in a standard reference material using the LC–MS platform coupled with the ESI source. Results are further corroborated by the quantitation experiments using an atmospheric pressure photoionization (APPI) method, which is more sensitive for the PAH detection. The basic concepts and step-by-step practical guidance for the PAHs quantitative characterization are offered based on the systematic experiments, which include (1) Evaluation effects of different acidification levels by formic acid on the (+)ESI-MS detection of PAHs. (2) Comparison of detection limits in ESI+ versus APPI+ experiments. (3) Investigation of the PAH fragmentation patterns in MS² experiments at different collision energies. (4) Calculation of wavelength dependent mass absorption coefficient (MAC_λ) of the standard mixture and its individual PAHs using LC-PDA data. (5) Assessment of the minimal injected mass required for accurate quantification of MAC_λ of the standard mixture and of a multi-component environmental sample.