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PubMed1998

Capillary electrophoresis of peptides and proteins in fused-silica capillaries coated with derivatized polystyrene nanoparticles.

High-resolution capillary electrophoretic separation of proteins and peptides was achieved by coating the inner wall of 75 microm ID fused-silica capillaries with 40-140 nm polystyrene particles which have been derivatized with alpha-omega-diamines such as ethylenediamine or 1,10-diaminodecane. A stable and irreversibly adsorbed coating was obtained upon deprotonation of the capillary surface with aqueous sodium hydroxide and subsequent flushing with a suspension of the positively charged particles. At pH 3.1, the detrimental adsorption of proteins to the capillary inner wall was suppressed efficiently because of electrostatic repulsion of the positively charged proteins from the positively charged coating which enabled protein separations with maximum efficiencies of 400000 plates per meter. A substantial improvement of separation efficiency in particle-coated capillaries was observed after in-column derivatization of amino functionalities with 2,3-epoxy-l-propanol, resulting in a more hydrophilic coating. Five basic and four acidic proteins could be separated in less than 7 min with efficiencies up to 1900000 theoretical plates per meter. Finally, coated capillaries were applied to the high-resolution analysis of protein glycoforms and bioactive peptides.

Animals↗
PubMed2004

Analytical potential of enzyme-coated capillary reactors in capillary zone electrophoresis.

Enzymes immobilized on the inner surface of an electrophoretic capillary were used to increase sensitivity and resolution in capillary zone electrophoresis (CZE). Sensitivity is enhanced by inserting a piece of capillary containing the immobilized enzyme into the main capillary, located before the detector, in order to transform the analyte into a product with a higher absorptivity. This approach was used to determine ethanol. In order to improve resolution, capillary pieces containing immobilized enzymes were inserted at various strategic positions along the electrophoretic capillary. On reaching the enzyme, the analyte was converted into a product with a high electrophoretic mobility, the migration time for which was a function of the position of the enzyme reactor. This approach was applied to the separation and determination of acetaldehyde and pyruvate. Finally, the proposed method was validated with the determination of ethanol, acetaldehyde, and pyruvate in beer and wine samples.

Alcohol Dehydrogenase↗
PubMed2004

Efficient and reproducible analysis of peptides by capillary electrophoresis using noncovalently bilayer-coated capillaries.

The usefulness of a noncovalent capillary coating consisting of two layers of oppositely charged polymers for the separation of peptides with capillary electrophoresis (CE) was studied. Capillaries were coated simply by subsequently flushing with solutions of 1% m/v Polybrene and 1% v/v poly(vinylsulfonate) (PVS) forming a bilayer, which showed to produce a strong and highly reproducible electroosmotic flow (EOF) at low pH. Using this coating in combination with a background electrolyte (BGE) containing sodium phosphate (pH 2.5) and 0.01% v/v PVS, initially broadened and overlapping peaks were obtained for some test peptides. By omitting the PVS from the BGE, the peak width and shape of the peptides improved resulting in baseline separation. A systematic study of the influence of the BGE composition showed that considerable further enhancement of the separation efficiency was achieved by increasing the ionic strength of the BGE. Using a BGE of 200 mM tris(hydroxymethyl)aminomethane (Tris)-phosphate (pH 2.5) plate numbers for the peptides were in the 300 000-600 000 range and the relative standard deviation of the peptide migration times was less then 0.3% (n = 5). The use of Tris-phosphate instead of sodium phosphate allowed the current to stay within acceptable limits when 30 kV was used as separation voltage. Overall, the bilayer coating showed a remarkable EOF repeatability, as well as long-term stability. Compared to bare fused-silica capillaries the intraday and interday repeatability of migration times was very favorable and coated capillaries could be used for over a month performing analyses with low and high ionic strength BGEs without any performance deterioration. The usefulness of the bilayer-coated capillaries for the analysis of positively charged peptides was demonstrated by the fast and efficient separation of various closely related enkephalins and the baseline separation of an isomeric peptide/peptoid couple exhibiting efficiencies of over 550 000 plates.

Electrolytes↗
PubMed2006

Array based capillary IEF with a whole column image of laser-induced fluorescence in coupling to capillary RPLC as a comprehensive 2-D separation system for proteome analysis.

Based on array CIEF (ACIEF) and a novel whole column imaging detection (WCID), a comprehensive 2-D system with laser-induced fluorescence was developed for protein mapping. By coupling capillary RPLC (CRPLC) as the first dimension and ACIEF as the second dimension, a high-throughput and high-resolution proteomic expression profiling was obtained. An array of up to 60 capillaries was assembled, with electrical connections made through filling small breaks, created on each capillary at positions of buffer reservoirs, with a porous polymer. A whole column image system with laser-induced fluorescence (LIF) was devised. Spot excitation was performed with a laser converted to produce linear light, and a CCD camera was employed to take images of the protein fluorescence during line laser scanning of the capillary array. Quantitative detection of thousands of focusing protein bands in the capillary array was achieved. Details on the capillary array fabrication and scanning LIF detection system devices are discussed. The efficiency of this CRPLC-ACIEF-LIF-WCID system was further demonstrated using samples of soluble proteins extracted from liver cancer tissue. The overall peak capacity was estimated to be around 18 000 in an analysis time of less than 3 h. The reproducibility of consecutive runs and different columns were assessed as having an RSD of 1.5% and 2.2% in focusing positions, respectively.

Animals↗
PubMed1986

Remodelling of the retinal pigment epithelium in response to intraepithelial capillaries: evidence that capillaries influence the polarity of epithelium.

Light- and urethane-induced retinopathies in rats are characterized by loss of photoreceptors. Retinal capillaries subsequently become incorporated into the normally avascular retinal pigment epithelium. These models provided an opportunity to study the response of epithelial cells to closely apposed capillaries, in order to determine if capillaries contribute to the polar organization of epithelial cells. Pigment epithelial cells reorganized their lateral plasma membrane where the latter faced intraepithelial capillaries. This normally flat, undifferentiated membrane developed attachment sites, folds and intracytoplasmic tubules, and exhibited endocytosis and putative basal lamina secretion. These structural and functional specializations are normally restricted to the basal plasma membrane - the normal vascular front of the cell facing the dense meshwork of capillaries constituting the choriocapillaris. We conclude that RPE cells, and perhaps epithelia in general, polarize in response to an adjacent capillary bed.

Animals↗
PubMed1995

Analysis of metallothionein isoforms by capillary electrophoresis: optimisation of protein separation conditions using micellar electrokinetic capillary chromatography.

Capillary electrophoresis (CE) techniques have been successfully applied to the separation of metallothionein (MT) isoforms and have proved to be rapid, practical and economical. Study of a variety of different electrolytes and capillaries has shown that electrolyte buffer composition and capillary wall surface modifications can have considerable influence on isoform separation and resolution. Ionic surfactants such as sodium dodecyl sulphate (SDS) form micelles at elevated concentrations and the partitioning of molecules between the hydrophobic micelle phase and the aqueous phase and their resulting migration in an electric field is the basis of the technique known as micellar electrokinetic capillary chromatography (MECC). In the present work, we have used sheep and rabbit MT to optimise MECC conditions for analysis of MT isoforms. Capillaries of 57 cm gave much better separations than shorter columns although analysis times were increased to about 12 min. Changing the buffer and SDS concentration or the pH affected the selectivity of isoform separation and up to 5 isoforms in sheep MT and 6 in rabbit MT were completely or partially resolved. Comparing different diameter capillaries we conclude that 25 microns I.D. columns give better separations than 50 or 75 microns I.D. columns although sensitivity is reduced by a factor of about 3 and 5, respectively. Using our MECC conditions, columns coated with C1 or C18 hydrophobic material were not found to be useful in improving MT separation or resolution although further evaluation of these columns is in progress.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Optimization of the separation of beta-agonists by capillary electrophoresis on untreated and C18 bonded silica capillaries.

The conditions of the separation of ten beta-agonists by capillary zone electrophoresis were studied. Several buffers were tested at different ionic strengths and different pH values. The experiments were carried out on two different supports, i.e. an untreated fused-silica capillary and a C18 covalently bonded silica capillary. The results showed that the optimum pH value was the same for the two capillaries. Separation efficiencies were slightly better for the fused-silica capillary whereas better selectivity and repeatability were obtained with the C18 bonded capillary, under optimal conditions.

Adrenergic beta-Agonists↗
PubMed1995

Calculation of oxygen pressures in tissue with anisotropic capillary orientation. I. Two-dimensional analytical solution for arbitrary capillary characteristics.

In tissue with a distinct orientation of the oxygen supplying structures, the capillaries, a mathematical description of oxygen transport is feasible in terms of two-dimensional diffusion in a plane perpendicular to the capillaries. Muscle tissue is an example of a highly anisotropic tissue. With some additional simplifying assumptions, a solution can be constructed in terms of capillary sources for arbitrary capillary characteristics, in particular, capillary locations. The solution includes facilitated diffusion by myoglobin in the tissue. For homogeneous tissue, the solution becomes explicit allowing direct calculation of tissue oxygen pressure at any location in a field of simple geometry (circular, rectangular). Also, the size of the area into which each capillary distributes its oxygen, the oxygen supply area, is readily calculated.

Animals↗
PubMed2004

Use of coupled open-tubular capillaries for in-line ion-exchange preconcentration of anions by capillary electrochromatography with elution by a transient isotachophoretic gradient.

Open-tubular capillaries have been joined together for use in on-column ion-exchange preconcentration of anions by capillary electrochromatography (CEC) with elution by a transient isotachophoretic gradient. This involved the coupling of a preconcentration capillary and a separation capillary using a PTFE sleeve. Such coupling allowed precise lengths of differently coated capillaries to be joined in-line to form a single multi-mode column. The different segments could be tailored to optimize a separation by either altering the length of each segment to precisely manipulate the amount of stationary phase present or by changing the internal diameter of each segment to alter the phase ratio in the chromatographic column without affecting the path length for UV detection. In this work, a segmented in-line capillary was used in conjunction with a fluoride-octanesulfonate discontinuous electrolyte system to increase the number of anions that could be preconcentrated and separated. Quaternary ammonium functionalised latex particles were used for creating the preconcentration segment and the separation segment was coated with poly(diallyldimethylammonium chloride). This allowed the detection of trace anions in drinking water and in situ sampling of river water for the analysis of trace inorganic anions. The repeatability of producing the quaternary ammonium functionalized latex-coated segments was assessed and the effect of segmentation on peak efficiency was investigated.

Anions↗
PubMed2004

Development of reactive thiol-modified monolithic capillaries and in-column surface functionalization by radical addition of a chromatographic ligand for capillary electrochromatography.

Reactive thiol-modified capillary columns for capillary electrochromatography (CEC) were developed by transforming the pendent 2,3-epoxypropyl groups of poly(glycidyl methacrylate-co-ethylene dimethacrylate) (poly(GMA-co-EDMA)) monoliths into 3-mercapto-2-hydroxy-propyl residues by a nucleophilic substitution reaction, employing sodium-hydrogen sulfide as nucleophilic reagent. Conditions for this modification reaction were systematically optimized with respect to different parameters, such as reaction temperature, pH-value, reaction time, type and concentration of organic modifier, and concentration of the sodium-hydrogen sulfide solution. The amount of thiol groups that was generated on the monolith surface was determined directly in the capillaries by a disulfide-exchange reaction employing 2,2'-dipyridyl disulfide (DPDS). This reaction in the capillary liberates pyridine-2-thione in equimolar amount to the surface sulfhydryls, which was collected into a vial and determined photometrically at 343 nm by RP-HPLC. About 17% of the total lateral epoxide moieties of the monolithic substrate could be transformed to reactive sulfhydryl groups, which corresponds to about 0.7 mmol g(-1) monolithic polymer, with a column-to-column repeatability of 3.2% R.S.D. The reactive thiol groups can be utilized to attach any chromatographic ligand with appropriate anchor in a second step, e.g. by radical addition, graft polymerization, nucleophilic substitution, disulfide formation or Michael addition reaction. To demonstrate the feasibility of the concept, we chose an anion exchange type chromatographic ligand based on a quinine derivative, O-9-tert-butylcarbamoylquinine (t-BuCQN) which was attached to the monolith in a radical addition reaction, for a further in-column surface functionalisation. About 78% of the sulfhydryl groups were derivatized with t-BuCQN as determined from differential DPDS assays before and after the selector immobilization reaction. The applicability of these surface-functionalised monolithic capillary columns could be shown by an electrochromatographic separation of the enantiomers of N-3,5-dinitrobenzoyl-leucine, which performed fairly well compared to an analogous capillary that was fabricated by an in situ copolymerization approach.

Chromatography, High Pressure Liquid↗
PubMed2005

Noncovalently bilayer-coated capillaries for efficient and reproducible analysis of proteins by capillary electrophoresis.

The suitability of noncovalently bilayer-coated capillaries for the analysis of proteins by capillary electrophoresis (CE) at medium pH was investigated. Fused-silica capillaries were coated simply by successively flushing with a polybrene (PB) and a poly(vinyl sulfonate) (PVS) solution. A protein test mixture was used to evaluate the performance of the coated capillaries. Comparisons with bare fused-silica capillaries were made. Several background electrolytes (BGEs) were tested in combination with the PB-PVS coating, showing that optimum performance was obtained for the proteins using high BGE concentrations. With a 300 mM Tris phosphate buffer (pH 7.0), good plate numbers (150,000-300,000), symmetrical peaks, and favorable migration-time repeatabilities (RSDs below 0.8%) were obtained for the proteins. Using bare fused-silica capillaries, the protein peaks were significantly broadened and the migration-time RSDs often exceeded 5%. It is concluded that the PB-PVS coating effectively minimizes adverse protein adsorption and provides a very stable electroosmotic flow (EOF). We also investigated the potential of a commercially available bilayer coating (CEofix) for protein analysis. It is demonstrated that with this coating, good plate numbers and peak symmetries for proteins can be achieved when the CEofix BGE ("accelerator") is replaced by a common BGE such as sodium or Tris phosphate. Apparently, the negatively charged polymer present in the "accelerator" interacts with the proteins causing band broadening. The utility of the bilayer coatings is further illustrated by the separation of proteins such as interferon-alpha 2b, myoglobin and carbonic anhydrase, by the analysis of a degraded insulin sample in time, and by the profiling of the glycoprotein ovalbumin. In addition, it is demonstrated that even in the presence of concentrations of human serum albumin in the sample of up to 60 mg/mL, the PB-PVS coating still provides reproducible protein separations of good performance.

Coated Materials, Biocompatible↗
PubMed2006

Monolithic silica-based capillary column with strong chiral cation-exchange type surface modification for enantioselective non-aqueous capillary electrochromatography.

A silica-based monolithic stationary phase prepared by the sol-gel process in a 100 microm I.D. fused-silica (FS) capillary has been modified chemically with 3-mercaptopropyl trimethoxysilane followed by immobilization of a strong cation-exchange (SCX) type chiral selector, (S)-N-(4-allyloxy-3,5-dichlorobenzoyl)-2-amino-3,3-dimethylbutane phosphonic acid, by radical addition reaction onto the reactive sulfhydryl surface. After a fine-tuning of the mobile phase composition, the enantioselective capillary column was evaluated for the separation of various chiral basic drugs by enantioselective non-aqueous capillary electrochromatography (CEC), in comparison to capillary column analogs packed with 3.5 microm silica particles having attached the same selector. The performance of the monolithic silica column was further compared to corresponding polymethacrylate-based organic polymer monoliths. The study indicated that strong counter-ions such as 2-aminobutanol or N,N,N',N'-tetramethylethylenediamine are needed, although they reduce the electroosmotic flow velocity and separation factors in comparison to less efficient counter-ions, in order to allow the elution of the oppositely charged solutes in the ion-exchange retention mode within reasonable run time and as sharp zones. In contrast, weak counter-ions such as N,N-diisopropylethylamine (Huenig base) provided stronger electroosmotic flow and much better separation factors, but relatively poor peak efficiencies. Overall, with the chemically functionalized monolithic silica column the high quality separations of packed column analogs could be approximated, with regards to both separation factors and peak performances. On the other hand, the monolithic capillary column certainly outperformed the packed column in terms of system robustness under capillary electrochromatography conditions and showed excellent column longevity. The enantioselective strong cation-exchange-type monolithic silica column performed also well in comparison to the organic polymer monolith.

Cation Exchange Resins↗
PubMed2006

Determination of purity degree and counter-ion content in lecirelin by capillary zone electrophoresis and capillary isotachophoresis.

Capillary zone electrophoresis (CZE) and capillary isotachophoresis (CITP) were applied for the determination of peptide purity degree and counter-ion content in lecirelin, the synthetic analogue of luteinizing hormone-releasing hormone (LHRH). CZE analyses were carried out in acidic background electrolyte (100 mM H3PO4, 50 mM Tris, pH 2.25) in bare fused silica capillary using UV-absorption detection at 206 nm. CITP analyses were performed in the electrophoretic analyzer with column coupling, equipped with contactless conductivity detectors both in preseparation capillary and in analytical capillary, and with UV-absorption detector (220 and 254 nm) in analytical capillary. Determinations of peptide purity were carried out in cationic mode with leading electrolyte (LE), 10 mM KOH/AcOH, pH 4.5, and terminating electrolyte (TE), 10 mM beta-alanine (BALA)/AcOH, pH 4.4. Degree of peptide purity determined by both CZE and CITP was in the range 60.1-80.9% for crude preparations of lecirelin and in the range 96.4-99.9% for HPLC purified batches. Concentrations of contaminating counter-ions, the anions of trifluoromethanesulfonic acid (TFMSA), trifluoroacetic acid (TFA) and acetic acid (AcOH), were determined by CITP analyses in anionic mode with LE 10 mM HCl/His, pH 6.0, and TE 10 mM 2-(N-morpholino)-ethanesulfonic acid (MES), pH 4.0, by the calibration curve method. Mass percentages of the counterion contents in the analyzed lecirelin batches varied from zero to ca. 9% (TFMSA), 3% (TFA) and 11% (AcOH), respectively.

Anions↗
PubMed2002

Neutrophil transit times through pulmonary capillaries: the effects of capillary geometry and fMLP-stimulation.

The deformations of neutrophils as they pass through the pulmonary microcirculation affect their transit time, their tendency to contact and interact with the endothelial surface, and potentially their degree of activation. Here we model the cell as a viscoelastic Maxwell material bounded by constant surface tension and simulate indentation experiments to quantify the effects of (N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)-stimulation on its mechanical properties (elastic shear modulus and viscosity). We then simulate neutrophil transit through individual pulmonary capillary segments to determine the relative effects of capillary geometry and fMLP-stimulation on transit time. Indentation results indicate that neutrophil viscosity and shear modulus increase by factors of 3.4, for 10(-9) M fMLP, and 7.3, for 10(-6) M fMLP, over nonstimulated cell values, determined to be 30.8 Pa.s and 185 Pa, respectively. Capillary flow results indicate that capillary entrance radius of curvature has a significant effect on cell transit time, in addition to minimum capillary radius and neutrophil stimulation level. The relative effects of capillary geometry and fMLP on neutrophil transit time are presented as a simple dimensionless expression and their physiological significance is discussed.

Biological Transport↗
PubMed2000

Analysis of codeine, dihydrocodeine and their glucuronides in human urine by electrokinetic capillary immunoassays and capillary electrophoresis-ion trap mass spectrometry.

Screening for and confirmation of illicit, abused and banned drugs in human urine is a timely topic in which capillary separation techniques play a key role. Capillary electrophoresis (CE) represents the newest technology employed in this field of analysis. Two rapid competitive binding, electrokinetic capillary-based immunoassays are shown to be capable of recognizing the presence, but not the identity, of urinary opioids, namely codeine (COD), codeine-6-glucuronide, dihydrocodeine (DHC), dihydrocodeine-6-glucuronide, morphine (MOR), morphine-3-glucuronide and ethylmorphine (EMOR). In these approaches, aliquots of urine and immunoreagents of a commercial, broadly cross-reacting fluorescence polarization immunoassay for opiates were combined and analyzed by capillary zone electrophoresis or micellar electrokinetic capillary chromatography with laser induced fluorescence detection. With the fluorescent tracer solution employed, the former method is shown to provide simple electropherograms which are characterized by an opioid concentration dependent magnitude of the free tracer peak. In presence of dodecyl sulfate micelles, however, two tracer peaks with equal opioid concentration sensitivity are monitored. These data suggest the presence of two fluorescent tracers which react competitively with the urinary opioids for the binding sites of the antibody. Assay sensitivities for COD and MOR are comparable (10 ng/ml), whereas those for DHC and EMOR are about four-fold lower. Furthermore, glucuronides are shown to react like the corresponding free opioids. Analysis of urines that were collected after administration of 7 mg COD and 25 mg DHC tested positively in both assay formats. The presence of the free and conjugated codeinoids in these urines and their identification was accomplished by capillary electrophoresis-ion trap mass spectrometry (CE-MS). This confirmatory assay is based upon solid-phase extraction using a mixed-mode polymer cartridge followed by CE hyphenated to the LCQ mass spectrometer with electrospray ionization in the positive ion mode. With this technology, MS2 is employed for proper identification of COD (m/z 300.4) and DHC (m/z 302.4) whereas MS3 provides unambiguous identification of the glucuronides of COD (m/z 476.5) and DHC (m/z 478.5) via their fragmentation to COD and DHC, respectively. MSn (n > or = 2) is shown to be capable of properly identifying the urinary codeinoids on the 100-200 ng/ml concentration level.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2001

Strategies for in-capillary derivatization of amino acids in capillary electrophoresis using 1,2-naphthoquinone-4-sulfonate as a labeling reagent.

This paper examines the potentiality of in-capillary derivatization for improving the sensitivity of the spectrophotometric detection of amino acids in capillary zone electrophoresis. 1,2-Naphthoquinone-4-sulfonate was selected as the labeling agent of amino acids. The underivatized sample and the reagent solution segments are injected by pressure into the capillary prior to applying the running voltage. The corresponding derivatization reaction occurs inside the capillary once the potential is applied, as it induces mixing of the sample with the reagent. Several introduction modes consisting of tandem or sandwich configuration have been evaluated. These techniques result in a straightforward and automated way of carrying out a derivatization. Furthermore, in-capillary procedures may become much more attractive than conventional pre-capillary derivatization in terms of sensitivity and reproducibility. The optimum operation mode found consists of a sandwich system where the sample is injected in between two reagent segments. The method was applied to the determination of amino acids in feed samples. Results show a good concordance with those given by a standard amino acid analyzer.

Amino Acids↗
PubMed2002

Capillary zone electrophoresis in laboratory-made fluorinated ethylene propylene capillaries.

Capillaries made of fluorinated ethylene propylene (FEP) with an inner diameter of 50 microm have been employed in capillary zone electrophoresis with UV-Vis absorbance detection. The capillaries were made in the laboratory with a recently developed technique using fluoropolymer heat shrink/melt tubing and a tungsten wire as a template for the channel. An electroosmotic flow was obtained in the channels and it is shown that an FEP capillary is more effective for a cationic test solute than a fused-silica capillary. The compatibility of FEP capillaries with optical detection is evaluated briefly.

Alkenes↗
PubMed2003

Speciation of chromium by in-capillary reaction and capillary electrophoresis with chemiluminescence detection.

A sensitive method for the simultaneous determination of chromium(III) (Cr3+) and chromium(VI) (CrO4(2-)) using in-capillary reaction, capillary electrophoresis (CE) separation and chemiluminescence (CL) detection was developed. The chemiluminescence reaction was based on luminol oxidation by hydrogen peroxide in basic aqueous solution catalyzed by Cr3+ ion followed by capillary electrophoresis separation. Based on in-capillary reduction, chromium(VI) can be reduced by acidic sodium hydrogensulfite to form chromium(III) while the sample is running through the capillary. Before the electrophoresis procedure, the sample (Cr3+ and CrO4(2-)), buffer and acidic sodium hydrogensulfite solution segments were injected in that order into the capillary, followed by application of an appropriate running voltage between both ends. As both chromium species have opposite charges, Cr3+ ions migrate to the cathode, while CrO4(2-) ions, moving in the opposite direction toward the anode, react with acidic sodium hydrogensulfite which results in the formation of Cr3+ ions. Because of the migration time difference of both Cr3+ ions, Cr(III) and Cr(VI) could be separated. The running buffer was composed of 0.02 mol l(-1) acetate buffer (pH 4.7) with 1 x 10(-3) mol l(-1) EDTA. Parameters affecting CE-CL separation and detection, such as reductant (sodium hydrogensulfite) concentration, mixing mode of the analytes with CL reagent, CL reaction reagent pH and concentration, were optimized. The limits of detection (LODs) of Cr(III) and Cr(VI) were 6 x 10(-13) and 8 x 10(-12) mol l(-1) (S/N=3), respectively. The mass LODs for Cr(III) and Cr(VI) were 1.2 x 10(-20) mol (12 zmol) and 3.8 x 10(-19) mol (380 zmol), respectively.

Buffers↗