Improving detection sensitivity of amino acids in thyroid tissues by using phthalic acid as a mobile phase additive in hydrophilic interaction chromatography-electrospray ionization-tandem mass spectrometry

In this work, 0.08 mmol L⁻¹ of phthalic acid was introduced as a mobile phase additive to quantify free amino acids (AAs) by hydrophilic interaction liquid chromatography (HILIC) coupled with electrospray ionization tandem mass spectrometry (ESI-MS/MS). The addition of phthalic acid significantly increased the signal intensity of protonated AA ions, resulting from the decrease of the relative abundance of AA sodium adducts. Meanwhile, the chromatographic peak shapes of AAs were optimized. As a consequence, there was a noticeable increase in the sensitivity of detection for AAs. The limits of detection (LOD) and quantification (LOQ) of the AAs ranged from 0.0500 to 20.0 ng mL⁻¹ and from 0.100 to 50.0 ng mL⁻¹, respectively, which were 4–50 times lower compared to the values measured without the addition of phthalic acid. The enhanced detection and separation of AAs were obtained by merely adding phthalic acid to the mobile phase without changing other conditions. Eventually, this simple method was validated and successfully applied to the analysis of twenty-four kinds of free AAs in human thyroid carcinoma and para-carcinoma tissues, demonstrating a significant increase of most AAs in thyroid carcinoma tissues (p < 0.05).     

Rapid Determination of Aristolochic Acids I and II in Some Medicinal Plants by High-Performance Liquid Chromatography

Aristolochic acids (AA) are toxic components of Aristolochia plants which result in diseases of the kidney such as urothelial cancer. It is, therefore, essential to monitor the amount of aristolochic acid in herbal medicines. In this study a reversed-phase high-performance liquid-chromatographic (HPLC) method has been developed for rapid determination of aristolochic acids I and II. Baseline separation was achieved within five minutes by use of an ODS C₁₈ column with methanol–water, 60:40, as mobile phase. Two kinds of aristolochic acid were successfully determined in 31 herbal samples of Aristolochia fangchi Wu and Caulis Aristolochiae Manshuriensis. The results indicated that in most samples the aristolochic acid I content is much higher than that of aristolochic acid II. The two kinds of aristolochic acid were not detected in Aristolochia fangchi from the Guangdong region, so Aristolochia fangchi from this region is recommended for use in herbal remedies.     

Determination of aristolochic acids in medicinal plant and herbal product by liquid chromatography-electrospray-ion trap mass spectrometry

This paper describes a liquid chromatography-electrospray-ion trap mass spectrometry (LC-ES-ITMS) method for the determination of aristolochic acid I and II (AA-I and AA-II) in medicinal plants and Chinese herbal remedies. A reversed phase C₁₈ column with gradient elution was utilized. The effects of mobile phase additives, acetic acid and ammonium acetate, on LC separation and ES ionization were investigated. For both AA-I and AA-II, the [M+NH₄]⁺ ion was found to be the precursor ion for target MS/MS analysis. The MS/MS product ion, [M+H−44]⁺, was used for the quantitative measurement of AA-I and AA-II. The linearity was good from 0.03 to 5 μg ml⁻¹ and good correlation (r²=0.999) over the range examined was determined for both AA. The detection limit based on a signal-to-noise ratio of three was 0.012 and 0.015 μg ml⁻¹ for AA-I and AA-II, respectively. Various Chinese herbal remedies obtained from renal failure patients and medicinal plants were examined by this newly developed method.     

Development of an immunoassay for rapid screening of vardenafil and its potential analogues in herbal products based on a group specific monoclonal antibody

Vardenafil is a phosphodiesterase-5 (PDE-5) inhibitor for the treatment of erectile dysfunction (ED). Undeclared vardenafil and related analogues adulterated in herbal products are a threat to public health. To screen vardenafil and its analogues in herbal matrix rapidly, an immunoassay based on a group specific monoclonal antibody (McAb) was developed.Glutaraldehyde was used to link vardenafil to immunogen and coating-antigen, respectively. Through the assessment of the structural specificity of eight anti-vardenafil McAbs, the McAb of 4B9 was characterized as being specific to the common structure of vardenafil and its analogues. An indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) was established based on this McAb, the limit of detection of vardenafil was 5.0 ng mL⁻¹, the calibration curve was linear from 5.0 to 40 ng mL⁻¹ (R² = 0.952) with an IC₅₀ value of 18.2 ng mL⁻¹. In the extracts of 20 Chinese traditional drugs, the detection capability (CCβ) of vardenafil was 0.08 mg g⁻¹, the recoveries were 76-116% and the coefficients of variation (CV%) were 9.7%-16.2%. The ic-ELISA was in good agreement with LC-UV when detected herbal products containing vardenafil and its analogue.The method is a suitable tool for screening vardenafil and its analogues as illegal additives in herbal products.     

Silica gel-polyethylene glycol as a new adsorbent for solid phase extraction of cobalt and nickel and determination by flame atomic absorption spectrometry

In this paper a novel solid phase extraction method to determine Co(II) and Ni(II) using silica gel-polyethylene glycol (Silica-PEG) as a new adsorbent is described. The method is based on the adsorption of cobalt and nickel ions in alkaline media on polyethylene glycol-silica gel in a mini-column, elution with nitric acid and determination by flame atomic absorption spectrometry. The adsorption conditions such as NaOH concentration, sample volume and amount of adsorbent were optimized in order to achieve highest sensitivity. The calibration graph was linear in the range of 0.5-200.0 ng mL⁻¹ for Co(II) and 2.0-100.0 ng mL⁻¹ for Ni(II) in the initial solution. The limit of detection based on 3S_b was 0.37 ng mL⁻¹ for Co(II) and 0.71 ng mL⁻¹ for Ni(II). The relative standard deviations (R.S.D.) for ten replicate measurements of 40 ng mL⁻¹ of Co(II), and Ni(II) were 3.24 and 3.13%, respectively. The method was applied to determine Co(II) and Ni(II) in black tea, rice flour, sesame seeds, tap water and river water samples.     

High-performance liquid chromatography with fluorescence detection and ultra-performance liquid chromatography with electrospray tandem mass spectrometry method for the determination of indoleamine neurotransmitters and their metabolites in sea lamprey plasma

We present a comparison of two sensitive methods, HPLC with fluorescence detector (HPLC/FLD) and UPLC with electrospray tandem mass spectrometry (UPLC/MS/MS), for the determination of indoleamine neurotransmitters (NTs) and their metabolites in sea lamprey plasma samples. Liquid–liquid extraction (LLE) and solid-phase extraction (SPE) were also tested for recovery and matrix effect. The recoveries of SPE determined by HPLC/FLD and UPLC/MS/MS ranged from 75 to 123% and 78 to 105%, respectively, while the recoveries of LLE ranged from 45 to 73% and 48 to 75%, respectively. SPE combined with HPLC/FLD and UPLC/MS/MS to determine the target analytes in plasma samples were validated of the sensitivity, reproducibility, accuracy and precision. Both methods exhibited excellent linearity in the range of 0.2–50 ng mL⁻¹ for all analytes. The limits of detection (LOD) varied from 0.04 ng mL⁻¹ to 0.13 ng mL⁻¹ for HPLC/FLD method and 0.003 ng mL⁻¹ to 0.02 ng mL⁻¹ for UPLC/MS/MS method. The inter-day accuracy ranged from 82.5 to 127.0% for HPLC/FLD and 93.0 to 113.0% for UPLC/MS/MS. The inter-day precision ranged from 9.9 to 32.3% for HPLC/FLD and 5.4 to 13.2% for UPLC/MS/MS. These results demonstrated that the values obtained by both methods were within the satisfactory range and the UPLC/MS/MS method provided more accurate and precise measurements than HPLC/FLD method. The comparison is of great importance to determine the available detectors, considering the complexity and expensiveness versus quality parameters. These two methods were applied to the analysis of four important indoleamine neurotransmitter analytes (5-hydroxytryptamine, 5-hydroxyindole-3-acetic acid, tryptamine and melatonin) in sea lamprey plasma samples.     

Evaluation of Chinese medicinal herbs fingerprinting by HPLC-DAD for the detection of toxic aristolochic acids

Aristolochic acids are known to contribute to various renal disorders; therefore, expanding the availability of analytical methodology to detect these compounds is important in order to assess the quality of Chinese herbal medicines in which they can be found. Twelve medicinal herbal samples were procured from various sources and extracted in duplicate prior to a "fingerprint" analysis using conventional HPLC-DAD. Multivariate analysis was performed on the entire chromatographed fingerprints. The resulting output was a partial least-square discriminant analysis model, which was able to evaluate the potential presence of aristolochic acids I and II as well as providing an individual herbal "fingerprint". The results of this study provide evidence that the presence of aristolochic acids contained within certain herbal extractions could be detected using a simple method, although some limitations apply to this method for quality control, since newly detected samples for aristolochic acid (positives) will need further confirmation with purity checks or MS hyphenation.     

Chromatographic analysis of serotonin, 5-hydroxyindolacetic acid and homovanillic acid in dried blood spots and platelet poor and rich plasma samples

An isocratic high-performance liquid chromatographic method has been developed for the measurement of serotonin, 5-hydroxyindolacetic and homovanillic acids in dried blood spots and in platelet poor and rich plasma samples. Analyses were carried out on a C18 reversed-phase column using a mobile phase composed of 13% methanol and 87% aqueous citrate buffer, containing octanesulfonic and ethylendiaminotetracetic acids. Coulometric detection was used, setting the guard cell at +0.100 V, the first analytical cell at −0.200 V and the second analytical cell at +0.400 V. For the pre-treatment of biological samples a novel solid-phase extraction procedure, based on mixed-mode reversed-phase – strong anion exchange Oasis cartridges, was implemented. Extraction yields of the analytes from all these matrices were satisfactory, being always higher than 89.0%. The calibration curve was linear over the on-column concentration range of 0.1–22.5 ng mL⁻¹ for serotonin and 5-hydroxyindolacetic acid and of 0.25–22.5 ng mL⁻¹ for homovanillic acid. The sensitivity was good with a limit of detection of 0.05 ng mL⁻¹ for serotonin and 5-hydroxyindolacetic acid and 0.12 ng mL⁻¹ for homovanillic acid. Results were also satisfactory in terms of precision, selectivity and accuracy. The analytical method was successfully applied to human platelet poor and rich plasma samples and to dried blood spots from volunteers and psychiatric patients.     

Direct hapten coated immunoassay format for the detection of atrazine and 2,4-dichlorophenoxyacetic acid herbicides

A novel immunoassay format employing direct coating of small molecular hapten on microtiter plates is reported for the detection of atrazine and 2,4-dichlorophenoxyacetic (2,4-D). In this assay, the polystyrene surface of microtiter plates was first treated with an acid to generate -NO₂ groups on the surface. Acid treated plates were further treated with 3-aminoprpyltriethoxysilane (APTES) to functionalize the plate surface with amino groups for covalent linkage to small molecular hapten with carboxyl groups. The modified plates showed significantly high antibody binding in comparison to plates coated with hapten-carrier protein conjugates and presented excellent stability as a function of the buffer pH and reaction time. The developed assay employing direct hapten coated plates and using affinity purified atrazine and 2,4-D antibodies demonstrated very high sensitivity, IC₅₀ values for atrazine and 2,4-D equal to 0.8 ng mL⁻¹ and 7 ng mL⁻¹, respectively. The assay could detect atrazine and 2,4-D levels in standard water samples even at a very low concentration upto 0.02 and 0.7 ng mL⁻¹ respectively in the optimum working range between 0.01 and 1000 ng mL⁻¹ with good signal reproducibility (p values: 0.091 and 0.224 for atrazine and 2,4-D, respectively). The developed immunoassay format could be used as convenient quantitative tool for the sensitive screening of pesticides in samples.     

Study on the resonance Rayleigh scattering spectra of the interactions of palladium (II)-cephalosporins chelates with 4,5-dibromofluorescein and their analytical applications

In pH 2.8-3.8 BR buffer medium, the third generation cephalosporin antibiotics (TGCs) such as ceftazidime (CZD), ceftriaxone (CTRX), cefoperazone (CPZ), and cefotaxime (CFTM) react with palladium(II) (Pd(II)) to form 1:2 yellowish-brown cationic chelates, which further react with 4, 5-dibromofluorescein (DBF) to form 1:3 brown ion-association complexes. As a result, not only the spectra of absorption and fluorescence are changed, but also the resonance Rayleigh scattering (RRS) is enhanced greatly and the new RRS spectra are observed. The four TGCs products have similar spectral characteristics and their maximum RRS wavelengths are all located at 291 nm. The quantitative determination ranges and the detection limits of the four TGCs are 0.0065-1.0 μg mL⁻¹ and 2.0 ng mL⁻¹ for CZD, 0.0070-1.1 μg mL⁻¹ and 2.2 ng mL⁻¹ for CTRX, 0.0090-1.6 μg mL⁻¹ and 2.7 ng mL⁻¹ for CPZ, and 0.014-2.2 μg mL⁻¹ and 4.2 ng mL⁻¹ for CFTM, respectively. The optimum conditions of the reactions and the effects of foreign substances are investigated, and the composition of ion-association complexes is discussed also. Based on the ion-association reaction, a highly sensitive, simple and rapid method has been proposed to the determination of TGCs.     

Quantitative determination of chlorogenic acid in Honeysuckle using microwave-assisted extraction followed by nano-LC-ESI mass spectrometry

The chlorogenic acid (CA) in Honeysuckle is determined and identified by nano-liquid chromatography-electrospray ionization mass spectrometry (nano-LC-ESI/MS) after extraction with microwave-assisted extraction (MAE). As a new sample preparation method for Honeysuckle, the MAE procedure is optimized, validated and compared with conventional methods including reflux extraction (RE) and ultrasonic extraction (USE). It is found that MAE gives the best result due to the highest extraction efficiency within shortest extraction time (only 4 min). Here, CA is determined by nano-LC-ESI/MS based on the calibration curve of its authentic standard. The method linearity, detection limit, precision and recovery are studied. The results show that the combined MAE and nano-LC-ESI/MS method has a linearity (R² 0.991, 0.8-20 ng mL⁻¹), a low limit of detection (0.5 ng mL⁻¹), good precision (R.S.D. = 2.54%) and a recovery (84.8%). The experiment has demonstrated that the nano-LC-ESI/MS following MAE is a fast and reliable method for quantitative analysis of CA in Honeysuckle.     

Enforcement of the ban on aristolochic acids in Chinese traditional herbal preparations on the Dutch market

In traditional chinese medicine several Aristolochia species are used. Aristolochia spp. contain a mixture of aristolochic acids (AAs), mainly AA I and AA II which are nephrotoxicants and carcinogens. After AA-related nephropathy (AAN) and urothelial cancer were described in female patients in Belgium following intake of AA-contaminated herbal preparations, herbs with AAs were prohibited worldwide. Confusing nomenclature can cause AA contamination of certain Chinese traditional herbal preparations (THPs). Here we report the results of investigations by the Dutch Food and Consumer Product Safety Authority (VWA) into the presence of AAs in THPs sampled on the Dutch market using a liquid-chromatography–-mass spectrometry method. Between 2002 and 2006 we sampled 190 Chinese THPs using recent information on Chinese THPs potentially containing AAs. AA I was found in 25 samples up to a concentration of 1,676 mg/kg. AA II was also found in 13 of these samples up to 444 mg/kg. All 25 positive samples including Mu Tong, Fang Ji, Tian Xian Teng and Xi Xin were part of a group of 68 THPs identified as possibly containing AAs. In a worst-case scenario, use of a sample of Mu Tong with the highest AA content over a 7-day period would result in the same intake levels of AAs which significantly raised the cancer risk in the Belgian AAN cases. Our results show that contaminated THPs still can be found on the market following worldwide publicity. Therefore, it can be concluded that testing of possibly AA-contaminated THPs is still essential. Figure Various Chinese Herbs     

A high-throughput method for determination of metabolites of organophosphate flame retardants in urine by ultra performance liquid chromatography–high resolution mass spectrometry

Organophosphate triesters are common flame retardants used in a wide variety of consumer products from which they can migrate and pollute the indoor environment. Humans may thus be continuously exposed to several organophosphate triesters which might be a risk for human health. An analytical method based on direct injection of 5 μL urine into an ultra performance liquid chromatography system coupled to a time-of-flight mass spectrometry has been developed and validated to monitor exposure to organophosphate triesters through their respective dialkyl and diaryl phosphate metabolites (DAPs). The targeted analytes were: di-n-butyl phosphate (DNBP), diphenyl phosphate (DPHP), bis(2-butoxyethyl) phosphate (BBOEP), bis(2-chloroethyl) phosphate (BCEP), bis(1-chloro-2-propyl) phosphate (BCPP) and bis(1,3-dichloro-2-propyl) phosphate (BDCIPP). Separation was achieved in less than 3 min on a short column with narrow diameter and small particle size (50 mm × 2.1 mm × 1.7 μm). Different mobile phases were explored to obtain optimal sensitivity. Acetonitrile/water buffered with 5 mM of ammonium hydroxide/ammonium formate (pH 9.2) was the preferred mobile phase. Quantification of DAPs was performed using deuterated analogues as internal standards in synthetic urine (averaged DAP accuracy was 101%; RSD 3%). Low method limits of quantification (MLQ) were obtained for DNBP (0.40 ng mL⁻¹), DPHP (0.10 ng mL⁻¹), BDCIPP (0.40 ng mL⁻¹) and BBOEP (0.60 ng mL⁻¹), but not for the most polar DAPs, BCEP (∼12 ng mL⁻¹) and BCPP (∼25 ng mL⁻¹). The feasibility of the method was tested on 84 morning urine samples from 42 mother and child pairs. Only DPHP was found above the MLQ in the urine samples with geometric mean (GM) concentrations of 1.1 ng mL⁻¹ and 0.57 ng mL⁻¹ for mothers and children respectively. BDCIPP was however, detected above the method limit of detection (MLD) with GM of 0.13 ng mL⁻¹ and 0.20 ng mL⁻¹. While occasionally detected, the GM of DNBP and BBOEP were below MLD in both groups.     

Rapid confirmatory analysis of non-steroidal anti-inflammatory drugs in bovine milk by rapid resolution liquid chromatography tandem mass spectrometry

A rapid method has been developed to analyse carprofen (CPF), diclofenac (DCF), mefenamic acid (MFN), niflumic acid (NIFLU), naproxen (NAP), oxyphenylbutazone (OXYPHEN), phenylbutazone (PBZ) and suxibuzone (SUXI) residues in bovine milk. Milk samples are extracted with acetonitrile and sample extracts were purified on Evolute™ ABN solid phase extraction cartridges. Aliquots were analysed by rapid resolution liquid chromatography tandem mass spectrometry (RRLC-MS/MS) with a runtime of 6.5 min. The method was validated in bovine milk, according to the criteria defined in Commission Decision 2002/657/EC. CCα values of 0.46, 1.08, 0.92, 1.26, 1.29, 2.12, 0.55 and 2.86 ng mL⁻¹ were determined for CPF, DCF, MFN, NIFLU, NAP, OXYPHEN, PBZ and SUXI, respectively. CCβ values of 0.79, 1.85, 1.56, 2.15, 2.19, 3.62, 0.94 and 4.87 ng mL⁻¹ were determined for CPF, DCF, MFN, NIFLU, NAP, OXYPHEN, PBZ and SUXI, respectively. The measurement uncertainty of the method was estimated at 9, 28, 28, 45, 46, 45, 10 and 39% for CPF, DCF, MFN, NIFLU, NAP, OXYPHEN, PBZ and SUXI. Fortifying bovine milk samples (n = 18) in three separate assays, show the accuracy of the method to be between 82 and 108%. The precision of the method, expressed as RSD values for the within-lab reproducibility at the three levels of fortification (5, 7.5 and 10 ng mL⁻¹) was less than 16%, respectively. The advantage of the method is that low ng mL⁻¹ levels can be detected and quantitatively confirmed rapidly in milk and that 3 batches of samples can be analysed within a single day using RRLC-MS/MS with a runtime of 6.5 min.     

Preparation and evaluation of an immunoaffinity sorbent with Fab′ antibody fragments for the analysis of opioid peptides by on-line immunoaffinity solid-phase extraction capillary electrophoresis–mass spectrometry

An immunoaffinity (IA) sorbent with antibody fragments was prepared for the analysis of opioid peptides by on-line immunoaffinity solid-phase extraction capillary electrophoresis–mass spectrometry (IA-SPE-CE–MS). The antibody fragmentation was evaluated by MALDI-TOF-MS. Fab′ fragments obtained from a polyclonal IgG antibody against Endomorphins 1 and 2 (End1 and End2) were covalently attached to succinimidyl silica particles to prepare the IA sorbent. An IA-SPE-CE–MS methodology was established analyzing standard solutions of End1 and End2 and acceptable repeatability, linearity ranges and LODs (0.5 and 5 ng mL⁻¹, respectively) were obtained. The LOD of End1 was slightly better than that previously obtained using an IA sorbent with intact antibodies (1 ng mL⁻¹). In human plasma samples, End1 and End2 could be detected at 1 and 50 ng mL⁻¹, respectively, which meant an improvement of 100 and 2-fold with regard to the LODs using an IA sorbent with intact antibodies (100 ng mL⁻¹).     

Flow-injection catalytic spectrophotometic determination of molybdenum(VI) in plants using bromate oxidative coupling of p-hydrazinobensenesulfonic acid with N-(1-naphthyl)ethylenediamine

A novel flow-injection spectrophotometry has been developed for the determination of molybdenum(VI) at nanograms per milliliter levels. The method is based on the catalytic effect of molybdenum(VI) on the bromate oxidative coupling of p-hydrazinobenzenesulfonic acid with N-(1-naphthyl)ethylenediamine to form an azo dye (λ_max = 530 nm). Chromotropic acid (4,5-dihydroxy-2,7-naphthalenedisulfonic acid) acted as an effective activator for the molybdenum(VI)-catalyzed reaction and increased the sensitivity of the method. The reaction was monitored by measuring the change in absorbance of the dye produced. The proposed method allowed the determination of molybdenum(VI) in the range 1.0-20 ng mL⁻¹ with sample throughput of 15 h⁻¹. The limit of detection was 0.5 ng mL⁻¹ and a relative standard deviation for 10 ng mL⁻¹ molybdenum(VI) (n = 10) was 2.5%. The interfering ions were eliminated by using the combination of a masking agent and on-line minicolumn packed with cation exchanger. The present method was successfully applied to the determination of molybdenum(VI) in plant foodstuffs.     

Flow injection chemiluminescence determination of the total phenolics levels in plant-derived beverages using soluble manganese(IV)

This study established a flow injection (FI) methodology for the determination of the total phenolic content in plant-derived beverages based on soluble manganese(IV) chemiluminescence (CL) detection. It was found that mixing polyphenols with acidic soluble manganese(IV) in the presence of formaldehyde evoked chemiluminescence. Based on this finding, a new FI-CL method was developed for the estimation of the total content of phenolic compounds (expressed as milligrams of gallic acid equivalent per litre of drink) in a variety of wine, tea and fruit juice samples. The proposed method is sensitive with a detection limit of 0.02 ng mL⁻¹ (gallic acid), offers a wide linear dynamic range (0.5-400 ng mL⁻¹) and high sample throughput (247 samples h⁻¹). The relative standard deviation for 15 measurements was 3.8% for 2 ng mL⁻¹ and 0.45% for 10 ng mL⁻¹ of gallic acid. Analysis of 36 different samples showed that the results obtained by the proposed FI-CL method correlate highly with those obtained by spectrophotometric methods commonly used for the evaluation of the total phenolic/antioxidant level. However, the FI-CL method was found to be far simpler, more rapid and selective, with almost no interference from non-phenolic components of the samples examined.     

Speciation of arsenic using capillary gas chromatography with atomic emission detection

A gas chromatography method with atomic emission detection (GC-AED) for the determination of dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and inorganic arsenic was optimized. The analytes were derivatized in the sample solutions with methyl thioglycolate (TGM) and the products were extracted into cyclohexane before an aliquot of this organic phase was directly injected into the chromatograph. The procedure was applied to the analysis of seawaters, wines, beers and infant foods, the last requiring an additional enzymatic reaction prior to analyte derivatization. Detection limits in seawaters and beverages were 0.05, 0.15 and 0.8 ng mL⁻¹ for DMA, MMA and inorganic arsenic, respectively. In infant foods the detection limits were 1, 10 and 25 ng g⁻¹ for DMA, MMA and inorganic arsenic, respectively. Inorganic arsenic was detected in some of the seawater samples and three of the wines analyzed at concentration levels in the range 1-40 ng mL⁻¹, and DMA in several of the infant foods in the range 20-80 ng g⁻¹. The method was validated by analyzing a certified reference material and by recovery studies. All the samples were also analyzed by hydride generation and atomic fluorescence spectrometry (HG-AFS), which provided data for the total arsenic content.     

Determination of naphthalene-derived compounds in apples by ultra-high performance liquid chromatography-tandem mass spectrometry

Naphthylacetic acid, naphthyloxy acetic acid and naphthylacetamide belong to a group of synthetic substances known as “auxin-like” compounds which are used as growth regulators in vegetables and fruits due to their structure similarities with the indoleacetic acid, the most important plant auxin. This paper reports a selective, sensitive and fast ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC–MS/MS) method for the determination of naphthylacetamide (NAD) and the isomers (α and β) of naphthylacetic acid (NAA) and naphthyloxy acetic (NOA) acid in apple samples. A baseline separation between the respective isomers was achieved using an RP-Amide column with gradient elution. The UHPLC-MS/MS method developed, using electrospray and selected reaction monitoring (SRM) acquisition mode led to a reliable determination of these family of compounds in apple samples at low quantitation levels, down to 1.0 μg kg⁻¹ and 0.25 μg kg⁻¹ respectively. For confirmation of NAA accurate mass measurement is proposed giving at these conditions quantitation limits of 10 μg kg⁻¹ for this compound. The UHPLC-MS/MS method developed was used for the analysis of apple samples harvested in three different apple fields from Lleida (Spain) during the blooming period. NAD and NAA were found in samples collected during 4–5 weeks after application at concentrations between the quantification limits and 43 μg kg⁻¹ and 24 μg kg⁻¹, respectively.     

Simultaneous detection of four biomarkers with one sensing surface based on redox probe tagging strategy

In this paper, a simple and sensitive amperometric immunosensor for simultaneous detection of four biomarkers by using distinguishable redox-probes as signal tags was proposed for the first time. In sandwich immunoassay format, four kinds of capture antibodies (C-Ab) were immobilized by gold nanoparticles (AuNPs) electro-deposited on the surface of glass carbon electrode (GCE); four kinds of detection antibodies (D-Ab) labeled with different redox probes (including anthraquinone 2-carboxylic acid (Aq), thionine (Thi), ferrocenecarboxylic acid (Fc) and tris(2,2’-bipyridine-4,4’-dicarboxylic acid) cobalt(III) (Co(bpy)₃³⁺)), were combined with 3,4,9,10-perylenetetracarboxylic acid (PTCA), poly(diallyldimethylammonium chloride) (PDDA) and AuNPs functionalized carbon nanotubes, and served as signal tracer. When four target antigens were present, differential pulse voltammetry (DPV) scan exhibited four well-resolved peaks, each peak indicated one antigen, and its intensity was quantitative correlational to the concentration of corresponding analyte. To verify the strategy, four biomarkers for diagnosis of colorectal carcinoma, including carcinoembryonic antigen (CEA), carbohydrate antigen (CA) 19-9 CA125, and CA242, were used as model analytes, the immunosensor exhibited high selectivity and sensitivity, and peak current displayed good linear relationship to logarithm concentration in the ranges from 0.016 to 15 ng mL⁻¹ for CEA; 0.008 to 10 ng mL⁻¹ for CA19-9; 0.012 to 12 ng mL⁻¹ for CA125; 0.010 to 10 ng mL⁻¹ for CA242, and low detection limits of 4.2, 2.8, 3.3 and 3.8 pg mL⁻¹, respectively.