Determination of rhodium in water samples using cloud point extraction (CPE) coupled with flame atomic absorption spectrometry (FAAS)

Cloud point extraction was applied as a method for preconcentration of rhodium after formation of a complex with 2-propylpiperidine-1-carbodithioate (2-PPC), and later determined by flame atomic absorption spectrometry using TritonX-114 as surfactant. Rhodium was complexed with 2-PPC in an aqueous phase and kept for 15 min in a thermostatted bath at 40 °C. Separation of the two phases was accomplished by centrifugation for 15 min at 4000 rpm. The chemical variables affecting the cloud point extraction were optimized and successfully applied to rhodium determination in various water samples. Under optimized conditions, the preconcentration system (100 mL sample) permitted an enhancement factor of 50. The detection limits obtained under optimal conditions was 0.052 ng mL⁻¹. The extraction efficiency was investigated at different rhodium concentrations (7.0–42.0 μg mL⁻¹), and good recoveries (96.42–99.14%) were obtained using this method. It has been applied to the determination of rhodium in water and was compared with reported methods in terms of Student’s ‘t’-test and variance ratio ‘f’-test.     

Cysteine‐capped ZnSe quantum dots as affinity and accelerating probes for microwave enzymatic digestion of proteins via direct matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometric analysis

Fluorescent semiconductor quantum dots (QDs) exhibit great potential and capability for many biological and biochemical applications. We report a simple strategy for the synthesis of aqueous stable ZnSe QDs by using cysteine as the capping agent (ZnSe‐Cys QDs). The ZnSe QDs can act as affinity probes to enrich peptides and proteins via direct matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS) analysis. This nanoprobe could significantly enhance protein signals (insulin, ubiquitin, cytochrome c, myoglobin and lysozyme) in MALDI‐TOFMS by 2.5–12 times compared with the traditional method. Additionally, the ZnSe‐Cys QDs can be applied as heat absorbers (as accelerating probes) to speed up microwave‐assisted enzymatic digestion reactions and also as affinity probes to enrich lysozyme‐digested products in MALDI‐TOFMS. Furthermore, after the enrichment experiments, the solutions of ZnSe‐Cys QDs mixed with proteins can be directly deposited onto the MALDI plates for rapid analysis. This approach shows a simple, rapid, efficient and straightforward method for direct analysis of proteins or peptides by MALDI‐TOFMS without the requirement for further time‐consuming separation processes, tedious washing steps or laborious purification procedures. The present study has demonstrated that ZnSe‐Cys QDs are reliable and potential materials for rapid, selective separation and enrichment of proteins as well as accelerating probes for microwave‐digested reactions for proteins than the regular MALDI‐MS tools. Additionally, we also believe that this work may also inspire investigations for applications of QDs in the field of MALDI‐MS for proteomics. Copyright © 2009 John Wiley & Sons, Ltd.     

High resolution detection of high mass proteins up to 80,000 Da via multifunctional CdS quantum dots in laser desorption/ionization mass spectrometry

CdS quantum dots (∼5 nm) are used as multifunctional nanoprobes as an effective matrix for large proteins, peptides and as affinity probes for the enrichment of tryptic digest proteins (lysozyme, myoglobin and cytochrome c) in laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS). The use of CdS quantum dots (CdS QDs) as the matrix allows acquisition of high resolution LDI mass spectra for large proteins (5000-80,000 Da). The enhancement of mass resolution is especially notable for large proteins such as BSA, HSA and transferrin (34-49 times) when compared with those obtained by using SA as the matrix. This technique demonstrates the potentiality of LDI-TOF-MS as an appropriate analytical tool for the analysis of high-molecular-weight biomolecules with high mass resolution. In addition, CdS QDs are also used as matrices for background-free detection of small biomolecules (peptides) and as affinity probes for the enrichment of tryptic digest proteins in LDI-TOF-MS.     

Surface modified silver selinide nanoparticles as extracting probes to improve peptide/protein detection via nanoparticles-based liquid phase microextraction coupled with MALDI mass spectrometry

We report the first use of functionalized Ag₂Se nanoparticles (NPs) as effective extracting probes for NPs-based liquid-phase microextraction (NPs-LPME) to analyze hydrophobic peptides and proteins from biological samples (urine and plasma) and soybean in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Surface modified functional groups such as octadecanethiol (ODT) and 11-mercaptoundecanoic acid (MUA) on Ag₂Se NPs were found to play an important role for efficient extraction of peptides and proteins from test samples through hydrophobic interactions. The peptides can be efficiently extracted using functionalized Ag₂Se NPs as extracting probes in the presence of high concentration of matrix interferences such as 4 M urea, 0.5% Triton X-100 and 3% NaCl. Ag₂Se@ODT NPs have shown better extraction efficiency and detection sensitivity for peptides than Ag₂Se@MUA NPs, bare Ag₂Se NPs and conventional MALDI-MS. The LODs are 20-68 nM for valinomycin and 100-180 nM for gramicidin D using Ag₂Se@ODT NPs-LPME in the MALDI-MS. The current approach is highly sensitive and the target analytes can be effectively isolated without sample loss and efficiently analyzed in MALDI-MS.     

Multifunctional ZrO2 nanoparticles and ZrO2-SiO2 nanorods for improved MALDI-MS analysis of cyclodextrins, peptides, and phosphoproteins

Multifunctional ZrO₂ nanoparticles (NPs) and ZrO₂-SiO₂ nanorods (NRs) have been successfully applied as the matrices for cyclodextrins and as affinity probes for enrichment of peptides (leucine-enkephalin, methionine-enkephalin and thiopeptide), phosphopeptides (from tryptic digestion products of β-casein) and phosphoproteins from complex samples (urine and milk) in atmospheric pressure matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) and MALDI time-of-flight (TOF) MS. The results show that the ZrO₂ NPs and ZrO₂-SiO₂ NRs can interact with target molecules (cyclodextrins, peptides, and proteins), and the signal intensities of the analytes were significantly improved in MALDI-MS. The maximum signal intensities of the peptides were obtained at pH 4.5 using ZrO₂ NPs and ZrO₂-SiO₂ NRs as affinity probes. The limits of detection of the peptides were found to be 75-105 fmol for atmospheric pressure MALDI-MS and those of the cyclodextrins and β-casein were found to be 7.5-20 and 115-125 fmol, respectively, for MALDI-TOF-MS. In addition, these nanomaterials can be applied as the matrices for the analysis of cyclodextrins in urine samples by MALDI-TOF-MS. ZrO₂ NPs and ZrO₂-SiO₂ NRs efficiently served as electrostatic probes for peptide mixtures and milk proteins because 2–11 times signal enhancement can be achieved compared with use of conventional organic matrices. Moreover, we have successfully demonstrated that the ZrO₂ NPs can be effectively applied for enrichment of phosphopeptides from tryptic digestion of β-casein. Comparing ZrO₂ NPs with ZrO₂-SiO₂ NRs, we found that ZrO₂ NPs exhibited better affinity towards phosphopeptides than ZrO₂-SiO₂ NRs. Furthermore, the ZrO₂ and ZrO₂-SiO₂ nanomaterials could be used to concentrate trace amounts of peptides/proteins from aqueous solutions without tedious washing procedures. This approach is a simple, straightforward, separation-and washing-free approach for MALDI-MS analysis of cyclodextrins, peptides, proteins, and tryptic digestion products of phosphoproteins.      

Visual detection of arginine,histidine and lysine using quercetin-functionalized gold nanoparticles

We report on the use of quercetin-functionalized gold nanoparticles (QC-AuNPs) as a colorimetric probe for the amino acids arginine (Arg), histidine (His) and lysine (Lys). The method is based on the aggregation of the QC-AuNPs that is caused by these amino acids and leads to a visually detectable color change from red to blue. The absorption maxima shift from 525 nm to 702, 693, and 745 nm, respectively. Aggregations are confirmed by dynamic light scattering (DLS) and transmission electron microscopic techniques (TEM). The effects of the QC concentration, temperature and reaction time for the preparation of QC-Au NPs were tested. Other amino acids do not interfere. Under the optimal conditions, linear relationships exist between the absorption ratios at 702/525 nm (for Arg), 693/525 nm (for His), and 745/525 nm (for Lys) over the concentrations ranges from 2.5–1,250 μM (Arg) and 1–1,000 μM (His and Lys), respectively. The respective limits of detection are 0.04, 0.03, and 0.02 μM. The method provides a useful tool for the rapid visual and instrumental determination of the three amino acids.

We report the use of quercetin as novel reagent for preparation and functionalization of gold nanoparticles to colorimetric sensing of three aminoacids (arginine, histidine and lysine). This is based on the aggregation of QC-AuNPs induced by three aminoacids.

     

Single drop microextraction coupled with matrix-assisted laser desorption/ionization mass spectrometry for rapid and direct analysis of hydrophobic peptides from biological samples in high salt solution

Single drop microextraction (SDME) coupled with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been applied for direct analysis of hydrophobic peptides (valinomycin and gramicidin D) from biological samples (urine and plasma) in high salt solution. The optimal conditions such as selection of extraction solvent, stirring rate, extraction time, effect of salt concentration and matrix-to-analyte ratio were investigated. The limits of detection (LODs) were found to be 73 nM to 170 nM for valinomycin and 96 nM to 5.5 μM for gramicidin D in high salt solution (1.7 M of NaCl) in MALDI-MS. The current approach can enhance the LODs by 11-320-fold for gramicidin D analysis in water, urine and plasma in high salt solution. Furthermore, the current approach has been successfully demonstrated for real-world sample analysis (β-carotene from carrots) by MALDI-MS. The current approach is a rapid, simple and efficient clean-up platform for direct analysis of hydrophobic molecules in biological samples from high salt solution.     

Evaluation of the odd-even effect in limits of detection for electron microprobe analysis of natural minerals

Limit of detection (LOD), being a fundamental quality parameter for analytical techniques, has been recently investigated and a systematic behavior has been observed for most odd-even element pairs for many techniques. However, to the best of our knowledge very few LOD data are available in published literature for electron microprobe analysis; these consist of three papers, two being on rare-earth elements and the third covering a large number of elements of atomic number between 21 and 92. These data confirm the systematic behavior of LODs for many odd-even pairs. To initiate to full this gap, we determined LODs for several major rock-forming chemical elements from Na to Fe with atomic numbers between 11 and 26, during the microprobe analysis of common minerals (olivine, plagioclase, pyroxene, amphibole, quartz, and opaques) in volcanic rocks. The odd-even effect of nuclear stability seems to be present in LOD data for most odd-even pairs investigated. Nevertheless, the experimental strategy concerning the reference materials, calibration procedure, and blank measurements, should be substantially modified to better evaluate the systematic behavior of LOD values in microprobe analysis.     

Rapid enrichment of phosphopeptides by BaTiO3 nanoparticles after microwave-assisted tryptic digest of phosphoproteins, and their identification by MALDI-MS

We show that BaTiO₃ nanoparticles (NPs) can be used as a novel substrate for the rapid enrichment of phosphopeptides from microwave tryptic digests of α-casein and non-fat milk prior to their identification by MALDI-MS. Protein digestion is achieved by microwave tryptic digest for 50?s, and the resulting phosphopeptides can be effectively adsorbed on the surfaces of the NPs. The phosphopeptides were selectively detected via MALDI-MS. Digestion, enrichment and detection are accomplished within ～60?min. The method was applied to the indentification of 24 phosphopeptides from α-casein and of 21 phosphopeptides (of the α-casein type) from nonfat milk.

Rapid separation of acetophenone and its monohydroxy isomers by capillary electrophoresis

This work describes the development of a capillary electrophoresis(CE)method for the simultaneous separation of acetophenone(AP),2-hydroxyacetophenone(2-HAP),3-hydroxyacetophenone(3-HAP)and 4-hydroxyacetophenone(4-HAP)in synthetic mixtures using 10 mmol/L of sodium tetraborate buffer(pH 9.5).The aim of this work is to demonstrate the effectiveness of CE to separate AP and its monohydroxy isomers and to defne how the separations are affected by buffers,buffer pH,sample matrices and separation voltage.This method was successfully used for the trace level separation and determination of 2-HAP,3-HAP and 4-HAP in synthetic mixture and 4-HAP in spiked plasma samples.