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Supercritical Fluid Chromatography Instrumentation
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Thomas L. Chester, J. David Pinkston
In practice, the API techniques are quite different. In the APCI interface, a corona discharge is used to produce reagent ions, usually from water in the air or from a protic solvent that is part of the nebulized effluent. These “primary” reagent ions ionize the analytes in a gas-phase process. The spectra produced by APCI are usually simple, often consisting of the protonated molecule with little fragmentation. In most cases, detection limits are in the low-nanogram to picogram range. Analytes must possess sufficient volatility and thermal stability to be transferred to the ionization region, via a heated region where the solvent is volatilized, without thermal degradation. Also, ions are generally singly charged, so APCI is most commonly used for molecules with molecular mass below 1500 to 2000 Da.
Methods for the Determination of Endocrine Disrupters
Published in Jason W. Birkett, John N. Lester, Endocrine Disrupters in Wastewater and Sludge Treatment Processes, 2002
The use of mass spectrometers linked to LC systems for the quantification of alkylphenols has become the method of choice, because it provides improved sensitivity and selectivity at low concentrations in difficult matrices. Fluorescence detection is still used by some workers (Table 3.6), and UV detection has also been utilized at 275 nm102 and 277 nm.100 The use of both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) techniques for the determination of the alkylphenols has been discussed by Petrovic and Barcelo.98 With the use of the ESI interface and an aprotic solvent, the NPEOs and OPEOs demonstrate affinity for the Na+ ion, forming [M+Na]+ ions. The use of protic solvents generates a more extensive range of adducts, with H+, K+, NH4+ and H2O. With the APCI source, regardless of the solvent, a range of adduct ions are formed, with some variability in abundance. As a result of these differences, the ESI interface offers improved sensitivity for a wider range of NPEO oligomers than APCI.103 However, the strength of APCI is that the technique will ionize a wider range of compounds, which facilitates the development of multiresidue methods. It has been used to this effect in monitoring for other surfactants along with the APEOs,104 although the halogenated derivatives only ionized with ESI.105
Analysis of Pesticide Residues by Chromatographic Techniques Coupled with Mass Spectrometry
Published in José L. Tadeo, Analysis of Pesticides in Food and Environmental Samples, 2019
Wan Jing, Jin Maojun, Jae-Han Shim, A.M. Abd El-Aty
APCI is a type of soft ionization technology that produces quasi-molecular ions. APCI mainly produces single-charged ions, with few fragment ions, so the molecular weight of the analyte is generally less than 1000 Da. Compared to ESI, APCI is less affected by the matrix and is suitable for analysis of less polar compounds. Some analytes cannot generate enough strong ions in the ESI source due to their structure and polarity, so the APCI source can be used to increase the ion yield. It can be considered that the APCI source is a supplement of ESI and is also mainly used for liquid chromatography–mass spectrometry.
Risk assessment of endocrine disrupting phthalates and hormonal alterations in children and adolescents
Published in Journal of Toxicology and Environmental Health, Part A, 2018
Dong Hyun Kim, Seul Min Choi, Duck Soo Lim, Taehyun Roh, Seung Jun Kwack, Sungpil Yoon, Min Kook Kim, Kyung Sil Yoon, Hyung Sik Kim, Dong Wook Kim, Byung-Mu Lee
Phthalates were extracted from serum samples by solid phase extraction (SPE), as reported previously (Cobellis et al. 2003). Briefly, 200 μl serum, 200 μl 50% phosphoric acid, 100 μl internal standard, and 1500 μl methanol were mixed and vortexed. Samples were then centrifuged at 2500 g for 10 min, and supernatants were passed through Waters Oasis WAX cartridges. After washing cartridges with 2% formic acid, samples were extracted with 5% NH4OH and methanol. Extracts were then evaporated under N2, dissolved in acetonitrile, and filtered through 0.2 μm syringe filters. Urine samples were extracted using the same SPE method after incubation with β-glucuronidase to deconjugate glucuronic acid (Blount et al. 2000). Briefly, samples were incubated at 37ºC overnight for deconjugation, acidified to pH 2 with hydrochloric acid (37%), extracted with tert-butylmethylether, mixed and vortexed for 10 min, and supernatants were prepared after centrifugation at 2,200 g for 10 min. All samples were re-dissolved in 200 ml methanol for HPLC–MS/MS analysis Two phthalate esters (DEHP, DBP) and their metabolites (MEHP, MBP, PA) in collected samples were chromatographically resolved on an ACQUITY ultra performance liquid chromatograph (UPLC) (Waters Corp., Milford, MA) equipped with a Phenyl column (Betasil, 5μm, 50 mm, 3 mm) and quantified by mass spectrometry (MS)(Waters Quattro Premier TM XE tandem mass system). HPLC was performed using a linear gradient of 2–90 % acetonitrile in 6 mM aqueous ammonium acetate. The column temperature used was 25°C, the injection volume was 20 μl, and the flow rate was 0.4 ml/min. Mass spectrometry was performed in negative ion APCI (Atmospheric pressure chemical ionization) mode. Limits of detection (LOD) were 1.92, 0.05, 0.09, 0.11, and 0.66 ng/ml for PA, MBP, DBP, MEHP, and DEHP, respectively, and their limits of quantification (LOQ) were 5.76, 0.15, 0.27, 0.33, and 1.98 ng/ml, respectively (Tables 2 and 3). The correlation coefficients of calibration curves for all phthalate compounds were between 0.9908 and 0.9957. Serum lipids (HDL (high density lipoproteins), LDL (low density lipoproteins), TG (triglyceride)), serum creatinine, the 8 hormones (free T3 (triiodothyronine), free T4 (thyroxine), TSH (thyroid stimulating hormone), insulin, LH (luteinizing hormone), FSH (follicle stimulating hormone), E2 (estradiol), testosterone) measured by radioimmunoassay (RIA), and urinary creatinine were quantified at the Eone Clinical Laboratory (Seoul, South Korea) (Tables 4–6).