Online solid‐phase extraction with high‐performance liquid chromatography and mass spectrometry for the determination of five tannins in traditional Chinese medicine injections

A rapid analytical method based on online solid‐phase extraction with high‐performance liquid chromatography and mass spectrometry has been established and applied to the determination of tannin compounds that may cause adverse effects in traditional Chinese medicine injections. Different solid‐phase extraction sorbents have been compared and the elution buffer was optimized. The performance of the method was verified by evaluation of recovery (≥40%), repeatability (RSD ≤ 6%), linearity (r² ≥ 0.993), and limit of quantification (≤0.35 μg/mL). Five tannin compounds, gallic acid, cianidanol, gallocatechin gallate, ellagic acid, and penta‐O‐galloylglucose, were identified with concentrations ranging from 3.1–37.4 μg/mL in the analyzed traditional Chinese medicine injections.     

Capillary electrophoretic assay of human acetyl‐coenzyme A carboxylase 2

Human acetyl‐coenzyme A carboxylase 2 catalyzes the carboxylation of acetyl coenzyme A to form malonyl coenzyme A, along with the conversion of magnesium‐adenosine triphosphate complex to magnesium‐adenosine diphosphate complex. A simple off‐column capillary electrophoresis assay for human acetyl‐coenzyme A carboxylase 2 was developed based on the separation of magnesium‐adenosine triphosphate complex, magnesium‐adenosine diphosphate complex, acetyl coenzyme A and malonyl coenzyme A with detection by ultraviolet absorption at 256 nm. When Mg²⁺ was absent from the separation buffer, the zones due to magnesium‐adenosine triphosphate complex and magnesium‐adenosine diphosphate complex both split and migrated as two separate peaks. With Mg²⁺ added to the separation buffer, magnesium‐adenosine triphosphate complex and magnesium‐adenosine diphosphate complex produced single peaks, and the reproducibility of peak shape and area improved for human acetyl‐coenzyme A carboxylase 2 assay components. The final separation buffer used was 30.0 mM HEPES, 3.0 mM MgCl₂, 2.5 mM KHCO₃, and 2.5 mM potassium citrate at pH 7.50. The same buffer was used for the enzyme‐catalyzed reaction (off‐column). Inhibition of human acetyl‐coenzyme A carboxylase 2 by CP‐640186, a known inhibitor, was detected using the capillary electrophoresis assay.     

Preparative isolation of flavonoid glycosides from Sphaerophysa salsula using hydrophilic interaction solid‐phase extraction coupled with two‐dimensional preparative liquid chromatography

An offline preparative two‐dimensional reversed‐phase liquid chromatography/hydrophilic interaction liquid chromatography coupled with hydrophilic interaction solid‐phase extraction method was developed for the preparative isolation of flavonoid glycosides from a crude sample of Sphaerophysa salsula . First, the non‐flavonoids were removed using an XAmide solid‐phase extraction cartridge. Based on the separation results of three different chromatographic stationary phases, the first‐dimensional preparation was performed on an XAqua C18 prep column, and 15 fractions were obtained from the 5.2 g target sample. Then, three representative fractions were selected for additional purification on an XAmide preparative column to further isolate the flavonoid glycosides. In all, eight flavonoid glycosides were isolated in purities over 97%. The results demonstrated that the two‐dimensional liquid chromatography method used in this study was effective for the preparative separation of flavonoid glycosides from Sphaerophysa salsula . Additionally, this method showed great potential for the separation of flavonoid glycosides from other plant materials.     

Investigation of free and conjugated seleno‐amino acids in wheat bran by hydrophilic interaction liquid chromatography with tandem mass spectrometry

An analytical method for determining seleno‐methionine, methyl‐seleno‐cysteine, and seleno‐cystine in wheat bran was developed and validated. Four different extraction procedures were evaluated to simultaneously extract endogenous free and conjugated seleno‐amino acids in wheat bran in order to select the best extraction protocol in terms of seleno amino acid quantitation. The extracted samples were subjected to a clean‐up by a reversed phase/strong cation exchange solid‐phase extraction and analyzed by chiral hydrophilic interaction liquid chromatography‐tandem mass spectrometry. The optimized extraction protocol was employed to validate the methodology. Process efficiency ranged from 58 to 112% and trueness from 73 to 98%. Limit of detection and limit of quantification were lower than 1 ng/g. Four wheat bran samples were analyzed for both total Se and single seleno‐amino acids determination. The results showed that Se‐ seleno‐methyl‐l selenocysteine was the major seleno‐amino acid in wheat bran while seleno‐methionine and seleno‐cysteine were both minor species.     

Analysis of microcystins using high‐performance liquid chromatography and magnetic solid‐phase extraction with silica‐coated magnetite with cetylpyridinium chloride

Microcystins (MCs), produced by freshwater cyanobacteria, can be serious water pollutants, so it is important to monitor their concentration in drinking water. We have developed a method for rapid and accurate determination of microcystin levels in environmental water, using magnetic solid‐phase extraction and high‐performance liquid chromatography with UV detection. The magnetic composite material, which was combined with cetylpyridinium chloride, was prepared by hydrothermal synthesis. The optimal extraction of microcystins in water sample was achieved by optimizing the amount of adsorbent, time of adsorption, ratio of eluting solvent, and volume of eluent. Under the optimal conditions, the limit of detection of MC‐LR was 0.001 μg/L, and the limit of quantification was 0.0028 μg/L. The limit of detection of MC‐RR was 0.001 μg/L, and the limit of quantification was 0.003 μg/L. These values are far lower than those established by the International Health Organization for the maximum concentration of microcystins in drinking water. The magnetic solid‐phase extraction adsorbent used in this method has the advantages of simple preparation, low price, and easy solid–liquid separation, and it can be used for the rapid and sensitive monitoring of trace microcystins in environmental water samples.     

Preparation of five high‐purity iridoid glycosides from Gardenia jasminoides Eills by molecularly imprinted solid‐phase extraction integrated with preparative liquid chromatography

Five iridoid glycosides were prepared using molecularly imprinted solid‐phase extraction combined with preparative high‐performance liquid chromatography. Hydrophilic molecularly imprinted polymers were synthesized using α‐1‐allyl‐2‐N‐acetyl glucosamine, which introduced an abundance of hydrophilic groups into the polymers. Using molecularly imprinted solid‐phase extraction as the sample pretreatment procedure, five iridoid glycosides, gardenoside, geniposide, shanzhiside, geniposidic acid, and genipin‐1‐O‐gentiobioside, were selectively enriched from Gardenia fructus extracts. Preparative high‐performance liquid chromatography then provided iridoid glycosides with a purity >98%. The structures were elucidated by using nuclear magnetic resonance spectroscopy, optical rotation and melting point measurements, and mass spectrometry. The results demonstrate that molecularly imprinted solid‐phase extraction combined with preparative high‐performance liquid chromatography was an efficient, rapid, and economical method for the preparation of bioactive compounds from natural products.     

Combination of a sub‐3 μm superficially porous particle packed column with charged aerosol detection for the simple and sensitive measurement of nine macrolides in human urine

Due to the lack of chromophores in many macrolides, analytical methods based on mass spectrometry and electrochemical detection coupled to liquid chromatography have been suggested to be suitable for the quantification of macrolides in complex matrices. In this study, a simple and sensitive analytical method was established for the simultaneous measurement of nine macrolides in human urine by combining a sub‐3 μm superficially porous particle packed column with charged aerosol detection. After thorough investigation of various sample preparation methods, including two liquid–liquid extraction methods and four solid‐phase extraction methods, HLB solid‐phase extraction was selected and further optimized. Absolute recovery of the optimized sample preparation method ranged from 99.5–110.2%, indicating its very high extraction/clean‐up efficiency. For chromatography, parameters influencing macrolide separation were systematically optimized, and the resulting conditions allowed baseline separation of nine macrolides within 24 min using a very simple mobile phase. The established method was validated for linearity, limit of detection, limit of quantification, absolute recovery, and precision. Based on its limit of detection (0.025–0.100 μg/mL), the method had similar or greater sensitivity than most methods based on electrochemical detection. It was found that the current method was appropriate for application to real human urine samples after drug administration.     

Ionic liquid vortex‐simplified matrix solid‐phase dispersion for the simultaneous determination of terpenoids,crocins, quinic acid derivatives and flavonoids in Gardeniae fructus by UHPLC

A novel ionic‐liquid‐based vortex‐simplified matrix solid‐phase dispersion method using 2,6‐dimethyl‐β‐cyclodextrin was established by ultra high performance liquid chromatography coupled with a photodiode array detector. 2,6‐Dimethyl‐β‐cyclodextrin was first used as a promising adsorbent in this proposed method for simultaneous determination of eight compounds in Gardeniae fructus. These compounds are terpenoids (geniposidic acid, genipin‐1‐β‐D‐gentiobioside, geniposide, 8‐o‐acetyl shanzhiside methyl ester), crocins (crocin‐I, crocin‐II), quinic acid derivatives (chlorogenic acid), and flavonoids (isoquercitrin), respectively. Several parameters were investigated in the adsorption and desorption processes to obtain the optimal conditions, including 2,6‐dimethyl‐β‐cyclodextrin as sorbent, 0.5 mL 100 mM 1‐dodecyl‐3‐methylimidazolium hydrogen sulfate as the extraction solvent, 2:1 of sample/sorbent ratio, grinding for 2 min and vortexing for 60 s. The recoveries of the eight compounds ranged from 96.6 to 100% (<3.50%). The limits of detection and quantification were in the range of 0.02–0.30 and 0.06–1.25  μg/mL, respectively. Meanwhile, a good linearity was attained with r values (>0.9997). The established method showed higher extraction efficiency and less reagent consumption than traditional matrix solid phase dispersion and ultrasonic‐assisted extraction. Hence, it could be applied for sample preparation and analysis of natural products.     

Trace determination of five triazole fungicide residues in traditional Chinese medicine samples by dispersive solid‐phase extraction combined with ultrasound‐assisted dispersive liquid–liquid microextraction and UHPLC–MS/MS

A novel and reliable method for determination of five triazole fungicide residues (triadimenol, tebuconazole, diniconazole, flutriafol, and hexaconazol) in traditional Chinese medicine samples was developed using dispersive solid‐phase extraction combined with ultrasound‐assisted dispersive liquid–liquid microextraction before ultra‐high performance liquid chromatography with tandem mass spectrometry. The clean up of the extract was conducted using dispersive solid‐phase extraction by directly adding sorbents into the extraction solution, followed by shaking and centrifugation. After that, a mixture of 400 μL trichloromethane (extraction solvent) and 0.5 mL of the above supernatant was injected rapidly into water for the dispersive liquid–liquid microextraction procedure. The factors affecting the extraction efficiency were optimized. Under the optimum conditions, the calibration curves showed good linearity in the range of 2.0–400 (tebuconazole, diniconazole, and hexaconazole) and 4.0–800 ng/g (triadimenol and flutriafol) with the regression coefficients higher than 0.9958. The limit of detection and limit of quantification for the present method were 0.5–1.1 and 1.8–4.0 ng/g, respectively. The recoveries of the target analytes ranged from 80.2 to 103.2%. The proposed method has been successfully applied to the analysis of five triazole fungicides in traditional Chinese medicine samples, and satisfactory results were obtained.     

Two‐dimensional solid‐phase extraction strategy for the selective enrichment of aminoglycosides in milk

An orthogonal two‐dimensional solid‐phase extraction strategy was established for the selective enrichment of three aminoglycosides including spectinomycin, streptomycin, and dihydrostreptomycin in milk. A reversed‐phase liquid chromatography material (C₁₈) and a weak cation‐exchange material (TGA) were integrated in a single solid‐phase extraction cartridge. The feasibility of two‐dimensional clean‐up procedure that experienced two‐step adsorption, two‐step rinsing, and two‐step elution was systematically investigated. Based on the orthogonality of reversed‐phase and weak cation‐exchange procedures, the two‐dimensional solid‐phase extraction strategy could minimize the interference from the hydrophobic matrix existing in traditional reversed‐phase solid‐phase extraction. In addition, high ionic strength in the extracts could be effectively removed before the second dimension of weak cation‐exchange solid‐phase extraction. Combined with liquid chromatography and tandem mass spectrometry, the optimized procedure was validated according to the European Union Commission directive 2002/657/EC. A good performance was achieved in terms of linearity, recovery, precision, decision limit, and detection capability in milk. Finally, the optimized two‐dimensional clean‐up procedure incorporated with liquid chromatography and tandem mass spectrometry was successfully applied to the rapid monitoring of aminoglycoside residues in milk.     

Extraction of ochratoxin A in red wine with dopamine‐coated magnetic multi‐walled carbon nanotubes

A new, rapid, green, and cost‐effective magnetic solid‐phase extraction of ochratoxin A from red wine samples was developed using polydopamine‐coated magnetic multi‐walled carbon nanotubes as the absorbent. The polydopamine‐coated magnetic multi‐walled carbon nanotubes were fabricated with magnetic multi‐walled carbon nanotubes and dopamine by an in situ oxidative self‐polymerization approach. Transmission electron microscopy, dynamic light scattering, X‐ray photoelectron spectroscopy and vibrating sample magnetometry were used to characterize the absorbents. Ochratoxin A was quantified with high‐performance liquid chromatography coupled with fluorescence detection, with excitation and emission wavelengths of 338 and 455 nm, respectively. The conditions affecting the magnetic solid‐phase extraction procedure, such as pH, extraction solution, extraction time, absorbent amount, desorption solution and desorption time were investigated to obtain the optimal extraction conditions. Under the optimized conditions, the extraction recovery was 91.8–104.5% for ochratoxin A. A linear calibration curve was obtained in the range of 0.1–2.0 ng/mL. The limit of detection was 0.07 ng/mL, and the limit of quantitation was 0.21 ng/mL. The recoveries of ochratoxin A for spiked red wine sample ranged from 95.65 to 100.65% with relative standard deviation less than 8%. The polydopamine‐coated magnetic multi‐walled carbon nanotubes showed a high affinity toward ochratoxin A, allowing selective extraction and quantification of ochratoxin A from complex sample matrixes.     

Dispersive solid‐phase extraction adsorbent of methamphetamine using in‐situ synthesized carbon‐based conductive polypyrrole nanocomposite: focus on clinical applications in human urine

Determination of methamphetamine is of great importance in clinical and forensic laboratories because there are low dosages of drugs in the biological media and social problems created due to the methamphetamine consumption. Polymeric carbon based‐nano composites are reasonable candidates for dispersive solid phase extraction method due to facial and affordable synthesis process and high selectivity and sensitivity. Nano graphene oxide polypyrolle composite was synthesized and employed as dispersive solid‐phase extraction adsorbent for methamphetamine extraction from complex urine matrix. Full characterization of the prepared nano graphene oxide polypyrolle composite was completed and the influential extraction parameters were investigated through one‐parameter‐at‐a‐time method. High‐performance liquid chromatography detectors were applied as detection and quantification instrument. The optimized extraction parameters included 300 µL of methanol, 10 min of extraction and desorption time, 6000 stirring rate, urine pH value of 10, 60 mg of adsorbent, and 6 mL of urine volume. After outlining the calibration curve, the linear range of the method was considered as 30–800 ng/mL. The detection limit for the suggested method was 9 ng/mL. The analysis of addicted subjects with the proposed method confirmed the utility of the method in different analytical and clinical laboratories.     

Quantitative analysis of N‐acylphosphatidylethanolamine molecular species in rat brain using solid‐phase extraction combined with reversed‐phase chromatography and tandem mass spectrometry

A novel method for the sensitive and selective identification and quantification of N‐acylphosphatidylethanolamine molecular species was developed. Samples were prepared using a combination of liquid–liquid and solid‐phase extraction, and intact N‐acylphosphatidylethanolamine species were determined by reversed‐phase high‐performance liquid chromatography coupled to positive electrospray tandem mass spectrometry. As a result of their biological functions as precursors for N‐acylethanolamines and as signaling molecules, tissue concentrations of N‐acylphosphatidylethanolamines are very low, and their analysis is additionally hindered by the vast excess of other sample components. Our sample preparation methods are able to selectively separate the analytes of interest from any expected biological interferences. Finally, the highest selectivity is achieved by coupling chromatographic separation and two N‐acyl chain specific selected reaction monitoring scans per analyte, enabling identification of both the N‐acyl chain and the phosphatidylethanolamine moiety. The validated method is suitable for the reliable quantification of N‐acylphosphatidylethanolamine species from rat brain with a lower limit of quantification of 10 pmol/g and a linear range up to 2300 pmol/g. In total, 41 N‐acylphosphatidylethanolamine molecular species with six different N‐acyl chains, amounting to a total concentration of 3 nmol/g, were quantified.     

Ultra‐trace level determination of diquat and paraquat residues in surface and drinking water using ion‐pair liquid chromatography with tandem mass spectrometry: A comparison of direct injection and solid‐phase extraction methods

Direct injection and solid‐phase extraction methods for the determination of diquat and paraquat in surface and drinking water were developed using liquid chromatography with tandem mass spectrometry. The signal intensities of analytes based on six ion‐pairing reagents were compared with each other, and 12.5 mM nonafluoropentanoic acid was selected as the best suited amongst them. A clean‐up method was developed using Oasis hydrophilic–lipophilic balance; this was compared to the direct injection method, with respect to limits of detection, interference, precision, and accuracy. Limits of quantification of diquat and paraquat were 0.03 and 0.01 μg/L using the direct injection method, and 0.002 and 0.001 μg/L using the hydrophilic–lipophilic balance method. When the hydrophilic–lipophilic balance method was used to analyze target compounds in 114 surface water and 30 drinking water samples, paraquat and diquat were detected within a concentration range of 0.001–0.12 and 0.002–0.038 μg/L in surface water, respectively. When the direct injection method was used to analyze target compounds in the same samples, the detected concentrations of paraquat and diquat were within 25% in samples being >0.015 μg/L using the hydrophilic–lipophilic balance method. The liquid chromatography with tandem mass spectrometry method using direct injection can thus be used for routine monitoring of paraquat and diquat in surface and drinking water.     

Anti‐inflammatory bioactive equivalence of combinatorial components β‐carboline alkaloids identified in Arenaria kansuensis by two‐dimensional chromatography and solid‐phase extraction coupled with liquid–liquid extraction enrichment technology

Bioactive equivalent combinatorial components play a critical role in herbal medicines. However, how to discover and enrich them efficiently is a question for herbal pharmaceuticals researchers. In our work, a novel two‐dimensional reversed‐phase/hydrophilic interaction high‐performance liquid chromatography method was established to perform real‐time components trapping and combining for preparation and isolation of coeluting components. Arenaria kansuensis was taken as an example, and solid‐phase extraction coupled with liquid–liquid extraction as a simple and efficient method for enriching trace components, reversed phase column coupled with hydrophilic interaction liquid chromatography XAmide column as two‐dimensional chromatography technology for isolation and preparation of coeluting constituents, enzyme‐linked immune‐sorbent assay as bio‐guided assay, and anti‐inflammatory bioactivity evaluation for bioactive constituents. A combination of 12 β‐carboline alkaloids was identified as anti‐inflammatory bioactive equivalent combinatorial components from A. kansuensis , which accounts for 1.9% w/w of original A. kansuensis . This work answers the key question of which are real anti‐inflammatory components from A. kansuensis and provides a fast and efficient approach for discovering and enriching trace β‐carboline alkaloids from herbal medicines for the first time. More importantly, the discovery of bioactive equivalent combinatorial components could improve the quality control of herbal products and inspire a herbal medicine based on combinatorial therapeutics.     

Boronate affinity monolithic column incorporated with graphene oxide for the in‐tube solid‐phase microextraction of glycoproteins

A poly(vinylphenylboronic acid–ethylene glycol dimethacrylate) monolithic material incorporated with graphene oxide was synthesized inside a poly(ether ether ketone) tube. This tube with boronate affinity monolith was coupled with a high‐performance liquid chromatography system through a six‐port valve to construct an online solid‐phase microextraction with high‐performance liquid chromatography system. The performance of this solid‐phase microextraction with high‐performance liquid chromatography system was demonstrated by standard glycoprotein in aqueous samples, namely, horseradish peroxidase. Some parameters that affect the extraction performance were investigated, including sampling rate, pH of sample solution, and sampling volume. Under the optimized conditions, the developed method showed high extraction efficiency toward horseradish peroxidase. The addition of graphene oxide greatly increased the extraction efficiency of boronate affinity monolith for horseradish peroxidase. The limit of detection of the proposed method was as low as 0.01 μg/mL by using ultraviolet detection. The recognition specificity was also evaluated by analyzing the mixture of bovine serum albumin (nonglycoprotein) and horseradish peroxidase. The results showed that this material could selectively extract horseradish peroxidase from the mixture, indicating its good specificity toward glycoproteins. The proposed method was further applied for analyzing rat plasma samples spiked with horseradish peroxidase. Good recovery and repeatability were obtained.     

Determination of Sudan dyes in chili pepper powder by online solid‐phase extraction with a butyl methacrylate monolithic column coupled to liquid chromatography with tandem mass spectrometry

A poly(butyl methacrylate‐co‐ethylene dimethacrylate) monolithic column was fabricated and used as a novel sorbent for online solid‐phase extraction coupled to liquid chromatography with tandem mass spectrometry for the simultaneous determination of Sudan I–IV in chili pepper powder. The prepared columns were characterized by scanning electron microscopy, nitrogen adsorption‐desorption, and pressure drop measurements. Online solid‐phase extraction was performed on the synthesized monolithic column using 10 mM ammonium acetate solution as the loading solution with the aid of an online cleanup chromatography system. The desorption of Sudan I–IV was achieved with acetonitrile as the eluting solution at the flow rate of 0.5 mL/min. The extracted analytes were subsequently eluted into a C₁₈ analytical column for chromatographic separation using a mixture of 10% acetonitrile/90% formic acid (0.5%) solution as the mobile phase. Under the optimized conditions, the developed method had linear range of 1.0–50 μg/kg, a detection limit of 0.3 μg/kg, and a quantification limit of 1.0 μg/kg for each analyte. The intraday and interday recoveries of Sudan I–IV in chili pepper powder samples ranged from 94.8 to 100.9% and 94.9 to 99.4%, respectively. The intraday and interday precision were between 3.37–7.01% and 5.01–7.68%, respectively.     

Dispersive solid‐phase extraction combined with dispersive liquid‐liquid microextraction for simultaneous determination of seven succinate dehydrogenase inhibitor fungicides in watermelon by ultra high performance liquid chromatography with tandem mass spectrometry

In this study, a simple and accurate sample preparation method based on dispersive solid‐phase extraction and dispersive liquid‐liquid microextraction has been developed for the determination of seven novel succinate dehydrogenase inhibitor fungicides (isopyrazam, fluopyram, pydiflumetofen, boscalid, penthiopyrad, fluxapyroxad, and thifluzamide) in watermelon. The watermelon samples were extracted with acetonitrile, cleaned up by dispersive solid‐phase extraction procedure using primary secondary amine, extracted and concentrated by the dispersive liquid‐liquid microextraction procedure with 1,1,2,2‐tetrachloroethane, and then analyzed by ultra high performance liquid chromatography with tandem mass spectrometry. The main experimental factors affecting the performance of dispersive solid‐phase extraction and dispersive liquid‐liquid microextraction procedure on extraction efficiency were investigated. The proposed method had a good linearity in the range of 0.1–100 µg/kg with correlation coefficients (r) of 0.9979–0.9999. The limit of quantification of seven fungicides was 0.1 µg/kg in the method. The fortified recoveries of seven succinate dehydrogenase inhibitor fungicides at three levels ranged from 72.0 to 111.6% with relative standard deviations of 3.4–14.1% (n = 5). The proposed method was successfully used for the rapid determination of seven succinate dehydrogenase inhibitor fungicides in watermelon.     

Covalently bonded aptamer‐functionalised magnetic mesoporous carbon for high‐efficiency chloramphenicol detection

A novel aptamer‐modified magnetic mesoporous carbon was prepared to develop a specific and sensitive magnetic solid‐phase extraction method through combination with ultra‐high performance liquid chromatography‐tandem mass spectrometry for the analysis chloramphenicol in complex samples. More specifically, the chloramphenicol aptamer‐modified Mg/Al layered double hydroxide magnetic mesoporous carbon was employed as a novel magnetic solid‐phase extraction sorbent for analyte enrichment and sample clean‐up. The extraction solvent, extraction time, desorption solvent, and desorption time were investigated. It was found that the mesoporous structure and aptamer‐based affinity interactions resulted in acceptable selective recognition and a good chemical stability toward trace amounts of chloramphenicol. Upon combination with the ultra‐high performance liquid chromatography‐tandem mass spectrometry technique, a specific and sensitive recognition method was developed with a low limit of detection (0.94 pmol/L, S/N = 3) for chloramphenicol analysis. The developed method was successfully employed for the determination of chloramphenicol in complex serum, milk powders, fish and chicken samples, giving recoveries of 87.0‐107% with relative standard deviations of 3.1‐9.7%.