Fumed silica for the direct determination of lead in urine by differential-pulse anodic stripping voltammetry

The use of fumed silica for the direct determination of lead in urine by differential-pulse anodic stripping voltammetry was investigated. Fumed silica, added to urine prior to the nitrogen purge step, completely removed sorption interferences by urinary organic constituents. Values for lead in urine from eight unexposed individuals were 3 ± 2 μg l^?1 or 3 ± 2 μg g^?1 creatinine. This method is a fast, simple and effective means for the accurate determination of lead in undiluted urine without pretreatment.     

An assessment of contemporary atomic spectroscopic techniques for the determination of lead in blood and urine matrices

The preparation and validation of a number of clinical reference materials for the determination of lead in blood and urine is described. Four candidate blood lead reference materials (Lots, 047–050), and four candidate urine lead reference materials (Lots, 034, 035, 037 and 038), containing physiologically-bound lead at clinically relevant concentrations, were circulated to up to 21 selected laboratories specializing in this analysis. Results from two interlaboratory studies were used to establish certified values and uncertainty estimates for these reference materials. These data also provided an assessment of current laboratory techniques for the measurement of lead in blood and urine. For the blood lead measurements, four laboratories used electrothermal atomization AAS, three used anodic stripping voltammetry and one used both ETAAS and ICP-MS. For the urine lead measurements, 11 laboratories used ETAAS (most with Zeeman background correction) and 10 used ICP-MS. Certified blood lead concentrations, ±S.D., ranged from 5.9±0.4 μg/dl (0.28±0.02 μmol/l) to 76.0±2.2 μg/dl (3.67±0.11 μmol/l) and urine lead concentrations ranged from 98±5 μg/l (0.47±0.02 μmol/l) to 641±36 μg/l (3.09±0.17 μmol/l). The highest concentration blood lead material was subjected to multiple analyses using ETAAS over an extended time period. The data indicate that more stringent internal quality control practices are necessary to improve long-term precision. While the certification of blood lead materials was accomplished in a manner consistent with established practices, the urine lead materials proved more troublesome, particularly at concentrations above 600 μg/l (2.90 μmol/l).     

Determination of lead in whole blood with a simple flow-injection system and computerized stripping potentiometry

An automated (24 samples/hour) procedure is described for the determination of lead (0–1000 μg l^?1) in human blood based on flow-injection stripping potentiometry. The samples are diluted 20-fold with 0.5 M hydrochloric acid containing 100 mg l^?1 mercury and 40 μg l^?1 cadmium (II), and a 1.1 ml aliquot is injected into the flow system. With a mercury-coated carbon fibre as working electrode, lead (II) is determined by using cadmium (II) as internal standard and a calibration graph prepared from bovine blood. Analyses of two human blood reference samples yielded results of 335±37 and 691±24 μg l^?1 lead, the certified values being 332 and 663 μg l^?1, respectively.     

Rhodium as permanent modifier for atomization of lead from biological fluids using tungsten filament electrothermal atomic absorption spectrometry

Rhodium (Rh) was investigated as a permanent modifier for the atomization of Pb from biological fluids in W-filament atomic absorption spectrometry (AAS). Heating the W-filament with a Rh solution provided a protective coating for subsequent determinations of Pb in blood and urine matrices. The W-filament AAS instrumentation used was based on a prototype design that utilized self-reversal background correction scheme and peak area measurements. We found that Rh not only stabilized Pb during the pyrolysis step, but also facilitated the removal of carbonaceous residues during the cleaning step, requiring much less power than with phosphate modifier. Thus, the filament lifetime was greatly extended to over 300 firings. Periodic reconditioning with Rh was necessary every 30 firings or so. Conditioning the filament with Rh also permitted direct calibration using simple aqueous Pb standards. The method detection limit for blood Pb was approximately 1.5 μg dl⁻¹, similar to that reported previously. Potential interferences from concomitants such as Na, K, Ca and Mg were evaluated. Accuracy was verified using lead reference materials from the National Institute of Standards and Technology and the New York State Department of Health. Blood lead results below 40 μg dl⁻¹ were within ±1 μg dl⁻¹ of certified values, and within ±10% above 40 μg dl⁻¹; within-run precision was ±10% or better. Additional validation was reported using proficiency test materials and human blood specimens. All blood lead results were within the acceptable limits established by regulatory authorities in the US. When measuring Pb in urine, sensitivity was reduced and matrix-matched calibration became necessary. The method of detection limit was 27 μg l⁻¹ for urine Pb. Urine lead results were also validated using an acceptable range comparable to that established for blood lead by US regulatory agencies.     

Electrothermal atomization atomic absorption spectrometry for the determination of lead in urine: results of an interlaboratory study

Results of an interlaboratory study are reported for the determination of lead in urine. Two levels of a lyophilized material containing biologically-bound lead were prepared using pooled urine obtained from lead-poisoned children undergoing the CaNa₂EDTA mobilization test. The materials were circulated to a group of reference laboratories that participate in the `New York State Proficiency Testing Program for Blood Lead'. Results of the initial round-robin gave all-method consensus target values of 145±22 μg/l (S.D.) for lot 17 and 449±43 μg/l (S.D.) for lot 20. The interlaboratory exercise was repeated some 5 years later and consensus target values were re-calculated using the grand mean (excluding outliers) of results reported by laboratories using electrothermal atomization atomic absorption spectrometry (ETAAS). The re-calculated target values were 139±10 μg/l (S.D.) and 433±12 μg/l (S.D.). The urine reference materials were also analyzed for lead by several laboratories using other instrumental techniques including isotope dilution (ID), inductively coupled plasma (ICP) mass spectrometry (MS), flame atomic absorption with extraction, ICP-atomic emission spectrometry, ID-gas chromatography MS and flow injection-hydride generation AAS, thus providing a rich source of analytical data with which to characterize them. The materials were also used in a long-term validation study of an ETAAS method developed originally for blood lead determinations that has since been used unmodified for the determination of lead in urine also. Recently, urine lead method performance has been tracked in a proficiency testing program specifically for this analysis. In addition, a number of commercial control materials have been analyzed and evaluated.     

Determination of Total Selenium in Human Urine and Serum by Graphite-Furnace Atomic-Absorption Spectrophotometry with Palladium-Nickel-Ammonium Nitrates as a Matrix Modifier

After human urine or serum was diluted (1 + 9) with HNO₃ (0.2%, v/v) and standard additions of Se solution (100 μ L^?1), the diluted sample (10 μL) was introduced into the graphite cuvette. The matrix modifier [10μL, containing Pd (0.6 μg) + Ni (25 μg) + NH₄NO₃ (80 μg) in HNO₃ (0.2%, v/v) for urine, or Pd (0.3 μg) + Ni (30 μg) + NH₄NO₃ (80 μg) + Triton X-100 (0.04%) in HNO₃ (0.2%, v/v) for serum, respectively] was added and the mixture was heated according to a temperature program. The matrix modifier containing NH₄NO₃ in a suitable amount and a small amount of Pd enhanced the sensitivity for Se. The method detection limits (3σ) after dilution were about 4.9 ± 0.8 and 2.36 ± 0.18 μg L^?1 for urine and serum, respectively. The accuracy of this method was tested with SRM #2670 human urine Se and Seronorm Trace Elements #116 human serum Se, respectively, and the results of 97.6 – 101% and 100 – 104% were obtained with precision ± 0.3% and ± 2%, respectively. This method can be applied easily and accurately to the determination of concentration of total Se in human urine and serum.     

Determination of urinary chromium levels for healthy men and diabetic patients by electrothermal atomic absorption spectrometry

Urinary chromium levels for healthy and diabetic men were determined by direct graphite-furnance atomic absorption spectrometry. The average values were 0.72 ± 0.31 ng ml^?1 for 23 healthy men aged 23 to 35, 0.39 ± 0.19 ng ml^?1 for 19 healthy men aged 47 to 69, and 1.0 ± 0.9 ng ml^?1 for 23 diabetic patients aged 13 to 79. Some urines of diabetic patients exhibit values > 1.3 ng ml^?1, which are never found in healthy men. The proposed method involves direct injection of 20 μl of urine inot a pyrolytically-coated graphite tube, and a standard addition calibration procedure involving a pooled urine sample. The results are compared with those obtained by a liquid-liquid extraction method.     

The determination of low lead levels in the bone of lead-depleted mice by graphite furnace atomic absorption spectrometry

Low lead levels in the femurs of mice fed with a lead-depleted diet have been determined by use of electrothermal atomic absorption spectrometry with Zeeman-effect background correction. The method is based on the use of Mg(NO₃)₂/Pd as matrix modifier which enables significant reduction of the spectral interferences prevalent if chemical modifiers based on NH₄H₂PO₄ with either Ca or Mg are used for samples rich in Ca₃(PO₄)₂ matrix. The method was developed and validated by use of the NIST standard reference material 1486 bone. Bones were decomposed in a pressurized microwave-heated system using 70% nitric acid. Forty-three mice femurs, with a mass of 74.62 ± 12.54 mg, were dissolved in concentrated nitric acid. The lead results found in SRM 1486 (1.25 ± 0.15 μg g^–1, n = 9) were in good agreement with the certificate (1.335 ± 0.014 μg g^–1). Recoveries of 200 ng lead added to the SRM before or after digestion were 99.0 ± 1.4% and 98.5 ± 1.6%, respectively. The lead detection limit in bone samples is 0.06 μg g^–1 dry mass. This method is, therefore, suitable for the determination of very low lead levels (0.06–0.20 μg Pb kg^–1 bone) in the femurs of mice fed a diet with lead level of < 20μg kg^–1.     

Determination of Cd and Pb in seawater by graphite furnace atomic absorption spectrometry with the use of hydrofluoric acid as a chemical modifier

High concentration of added hydrogen fluoride converted the seawater chloride to the corresponding fluoride matrix, and the liberated hydrochloric acid could be removed during the drying step. The atomization of cadmium and lead could be performed at a relatively low temperature (∼1300 °C) at which the vaporization of the fluoride matrix was relatively slow, and the corresponding weak background signals could be separated from the analytical signals in time. Experimental conditions for the determination of Cd and Pb in seawater in the presence of HF were optimized with the use of the a priori calculation of the limit of detection. The experimental limit of detection obtained for Cd and Pb were, respectively, 0.007 and 0.25 μg l⁻¹ for a 15-μl seawater sample (3σ, 20 replicates). The concentrations of Cd determined in a SLEW-1 estuarine water and a CASS-2 seawater were 0.020±0.002 and 0.016±0.002 μg l⁻¹ Cd, respectively, in good agreement with the 0.018±0.003 and 0.019±0.004 μg l⁻¹ Cd certified values (At the 95% confident level, 10 replicates).     

Simple determination of betaine,l‐carnitine and choline in human urine using self‐packed column and column‐switching ion chromatography with nonsuppressed conductivity detection

A sequential online extraction, clean‐up and separation system for the determination of betaine, l ‐carnitine and choline in human urine using column‐switching ion chromatography with nonsuppressed conductivity detection was developed in this work. A self‐packed pretreatment column (50 × 4.6 mm, i.d.) was used for the extraction and clean‐up of betaine, l ‐carnitine and choline. The separation was achieved using self‐packed cationic exchange column (150 × 4.6 mm, i.d.), followed by nonsuppressed conductivity detection. Under optimized experimental conditions, the developed method presented good analytical performance, with excellent linearity in the range of 0.60–100 μg mL⁻¹ for betaine, 0.75–100 μg mL⁻¹ for l ‐carnitine and 0.50–100 μg mL⁻¹ for choline, with all correlation coefficients (R²) >0.99 in urine. The limits of detection were 0.15 μg mL⁻¹ for betaine, 0.20 μg mL⁻¹ for l ‐carnitine and 0.09 μg mL⁻¹ for choline. The intra‐ and inter‐day accuracy and precision for all quality controls were within ±10.32 and ±9.05%, respectively. Satisfactory recovery was observed between 92.8 and 102.0%. The validated method was successfully applied to the detection of urinary samples from 10 healthy people. The values detected in human urine using the proposed method showed good agreement with the measurement reported previously.     

A physically-coated mercury film electrode for anodic stripping voltammetry

The physically-coated Ag/AgHg/Hg film electrode described is easy to prepare and durable, and has excellent stability even when rapid stirring is used. It gives high sensitivity and provides well-defined voltammograms for zinc (1.8 ± 0.06 μg l^-1), cadmium (8.8 ± 0.6 ng l^-1) and lead (0.2 ± 0.008 μg l^-1) in 6-ml samples of sea water after a deposition time of 3 min.     

Detection of catecholamine metabolites in urine based on ultra-high-performance liquid chromatography–tandem mass spectrometry

The excretion of neurotransmitter metabolites in normal individuals is of great significance for health monitoring. A rapid quantitative method was developed with ultra-performance liquid chromatography–tandem mass spectrometry. The method was further applied to determine catecholamine metabolites vanilymandelic acid (VMA), methoxy hydroxyphenyl glycol (MHPG), dihydroxy-phenyl acetic acid (DOPAC), and homovanillic acid (HVA) in the urine. The urine was collected from six healthy volunteers (20–22 years old) for 10 consecutive days. It was precolumn derivatized with dansyl chloride. Subsequently, the sample was analyzed using triple quadrupole mass spectrometry with an electrospray ion in positive and multireaction monitoring modes. The method was sensitive and repeatable with the recoveries 92.7–104.30%, limits of detection (LODs) 0.01–0.05 μg/mL, and coefficients no less than 0.9938. The excretion content of four target compounds in random urine samples was 0.20 ± 0.086 μg/mL (MHPG), 1.27 ± 1.24 μg/mL (VMA), 3.29 ± 1.36 μg/mL (HVA), and 1.13 ± 1.07 μg/mL (DOPAC). In the urine, the content of VMA, the metabolite of norepinephrine and adrenaline, was more than MHPG, and the content of HVA, the metabolite of dopamine, was more than DOPAC. This paper detected the levels of catecholamine metabolites and summarized the characteristics of excretion using random urine samples, which could provide valuable information for clinical practice.     

Measurement of the polarization of thermal muonium in vacuum

We report the first measurement of the polarization of thermal muonium in vacuum. A 20 MeV/c beam of μ⁺ was stopped in a layer of SiO₂ powder which emitted (17±1)% of the stopped μ⁺ into vacuum as thermal muonium. The muonium Larmor precession was observed in a transverse magnetic field of 1.4 G, and the measured amplitude of the precession signal indicates that the μ⁺ polarization in the muonium is (39±9)%.     

Determination of lead in gasoline by a flow-injection technique with atomic absorption spectrometric detection

The gasoline sample is treated with iodine and Aliquat-336 and diluted with 4-methylpentan-2-one; 100 μl is injected into a flowing acetone stream for aspiration into an atomic absorption spectrometer. Calibration is linear in the range 0/2-16 mg l^?1 lead. Results for commercial gasoline samples agree well with those obtained by published titrimetric and atomic absorption methods. The precision for samples containing 300/2-400 mg l^?1 lead is ±1%; with increased recorder amplification, the limit of detection is 0.1 mg l^?1 lead. The method is rapid and economic.     

Certification of total arsenic in blood and urine standard reference materials by radiochemical neutron activation analysis and inductively coupled plasma-mass spectrometry

Radiochemical neutron activation analysis (RNAA) was used to measure arsenic at four levels in standard reference material (SRM) 955c Toxic Elements in Caprine Blood and at two levels in SRM 2668 Toxic Elements in Frozen Human Urine for the purpose of providing mass concentration values for certification. Samples were freeze-dried prior to analysis followed by neutron irradiation for 3 h at a fluence rate of 1 × 10¹⁴ cm^?2 s^?1. After sample dissolution in perchloric and nitric acids, arsenic was separated from the matrix either by retention on hydrated manganese dioxide (urine) or by extraction into zinc diethyldithiocarbamate in chloroform (blood). ⁷⁶As was quantified by gamma-ray spectroscopy. Differences in chemical yield and counting geometry between samples and standards were monitored by measuring the count rate of a ⁷⁷As tracer added before sample dissolution. RNAA results were combined with inductively coupled plasma-mass spectrometry values from National Institute of Standards and Technology and collaborating laboratories to provide certified values of 10.81 ± 0.54 and 213.1 ± 0.73 μg/L for SRM 2668 Levels I and II, and certified values of 21.66 ± 0.73, 52.7 ± 1.1, and 78.8 ± 4.9 μg/L for SRM 955c Levels II–IV, respectively. Because of discrepancies between values obtained by different methods for SRM 955c Level I, an information value of <5 μg/L was assigned for this material.     

Heavy metal-free electrochemical detection of pyrophosphate ions by Nafion/carbon dots decorated screen printed carbon electrodes

We employ Nafion-mixed carbon dots (CDs) and low-cost screen-printed carbon electrodes (SPCEs) as foundation matrices for the fabrication of electrochemical biosensors. The  NH₂ and  COOH functional groups present on the SPCE surface after Nafion/CDs deposition allow for pyrophosphate ions (PPis) collection. Using Fe(CN)₆³⁻ as the electrochemical mediator, the SPCE-Nafion/CDs are applied to the detection of aqueous PPi by square wave voltammetry. Between 50 and 1 μM, a linear connection is established between the square wave voltammetry current and the PPi concentration. The limit of detection is determined to be 1.01 μM, and recoveries of 113% (±1.9%) and 108% (±3.9%) are achieved for human urine samples spiked with 6 and 3 μM of PPi, respectively. Furthermore, this PPi assay is suitable for the usage of complicated urine matrices without the inclusion of heavy metals. We anticipate that this unique approach will be beneficial for PPi level monitoring in urine during therapeutic treatments of illnesses and malignancies.     

Intake of different chemical species of dietary arsenic by the japanese,and their blood and urinary arsenic levels

We calculated the intake of each chemical species of dietary arsenic by typical Japanese, and determined urinary and blood levels of each chemical species of arsenic. The mean total arsenic intake by 35 volunteers was 195±235 (15.8-1039) μg As day^?1, composed of 76% trimethylated arsenic (TMA), 17.3% inorganic arsenic (As_i), 5.8% dimethylated arsenic (DMA), and 0.8% monomethylated arsenic (MA): the intake of TMA was the largest of all the measured species. Intake of As_i characteristically and invariably occurred in each meal. Of the intake of As_i, 45-75% was methylated in vivo to form MA and DMA, and excreted in these forms into urine. The mean measured urinary total arsenic level in 56 healthy volunteers was 129±92.0 μg As dm^?3, composed of 64.6% TMA, 26.7% DMA, 6.7% As_i and 2.2% MA. The mean blood total arsenic level in the 56 volunteers was 0.73±0.57 μg dl^?1, composed of 73% TMA, 14% DMA and 9.6% As_i. The urinary TMA levels proved to be significantly correlated with the whole-blood TMA levels (r = 0.376; P<0.01).     

Development of a Biomimetic Enzyme‐linked Immunosorbent Assay Method for the Determination of Methimazole in Urine Sample

A fast and direct competitive biomimetic enzyme‐linked immunosorbent assay (BELISA) method was developed for the determination of methimazole (MMZ) in urine sample based on a molecularly imprinted film as an artificial antibody. This is the first example to monitor methimazole with a direct competitive biomimetic enzyme‐linked immunosorbent assay (BELISA) method. The imprinted film was directly synthesized on the well surface of MaxiSorp polystyrene 96‐well plate and characterized. The results showed that it exhibited an antibody‐like binding ability, rapid adsorption speed, high stability, which was particularly advantageous and suitable for BELISA development. The BELISA method established in this paper had a higher selectivity for MMZ than for the structurally related compounds and the IC₅₀ (calculated as the concentration giving 50% inhibition of color development) and the detection limit values under optimized experimental conditions were 70 ± 4 μg L^‐1 and 0.9 ± 0.04 μg L^‐1, respectively. The method was applied to the determination of MMZ in spiked urine sample with excellent recoveries ranging from 90% to 95%, and the imprinted film was able to be reused for 20 times without loss of sensitivity. The results obtained by BELISA correlated well with that obtained by the high performance liquid chromatography (HPLC) method.     

Anodic Stripping Voltammetric Determination of Lead in Tap Water at an Ordered Mesoporous Carbon/Nafion Composite film Electrode

A sensitive mercury‐free lead (Pb²⁺) sensor has been proposed based on an ordered mesoporous carbon and Nafion composite film (OMC/Nafion) coated glassy carbon electrode. The analysis of Pb²⁺ using anodic stripping voltammetry (ASV) includes two steps. Pb²⁺ ions are firstly reduced and deposited on the electrode surface in a Pb²⁺ solution (10 mL) during a preconcentration step biased at ?1.0 V, followed by a measurement step by differential pulse voltammetry (DPV) within the potential range of ?0.8 to ?0.3 V (scan rate: 20 mV/s, frequency: 20 Hz, amplitude: 50 mV, pulse width: 50 ms). Linear calibration curve was found to be from 20 nM to 2 μM for Pb²⁺ with a sensitivity of 17.4±1.38 μA/μM after a 5‐min of preconcentration. The detection limit was estimated to be around 4.60±0.12 nM at the signal to noise ratio of 3. Reproducibility (RSD%) was found to be 3.0% for a single sensor with eight measurements and 4.3% for five sensors prepared with identical procedures. The practical application of the proposed lead sensor was verified by determination of trace level of Pb²⁺ in tap water sample.     

Determination of Cefpodoxime Levels and Cefpodoxime Stability In Human Urine By Direct Injection HPLC with Column-Switching

Abstract

A semi-automated method providing on-line sample extraction and quantitative analysis for cefpodoxime in human urine, injected directly into the HPLC, is reported.

Samples were filtered by the analyst, injected into the HPLC system with an autosampler and loaded onto a 3 cm RP-18 precolumn with a mobile phase consisting of 10% methanol in 0.2% phosphoric acid and then automatically eluted onto a RP-18 analytical column using a mobile phase containing 7% acetonitrile in pH 5.2 sodium acetate buffer. the mean between-day precision of the standards was ± 4.29%. Spiked urine control recovery averaged 96 ± 6% for controls ranging from 1.0 to 20.0 μg/mL. the limit of quantitation for the method was 0.11 μg/mL.