Alpha and gamma spectrometry for determination of natural and artificial radionuclides in tea, herbal tea and camomile marketed in Italy

Several kinds of tea, camomile and herbal tea were analysed to determine natural and artificial radioactivity. The radionuclides were determined by alpha (²¹⁰Po) and gamma (²²⁸Ac, ²¹⁴Pb, ²¹⁴Bi, ²¹⁰Pb, ⁴⁰K and ¹³⁷Cs) spectrometry. ²²⁸Ac ranged between 0.6 and 9.0 Bq kg⁻¹_dry; ²¹⁰Po between 1.90 and 36.1 Bq kg⁻¹_dry; ²¹⁴Pb and ²¹⁴Bi between 0.7 and 4.9 Bq kg⁻¹_dry; ²¹⁰Pb between < 10.0 and 58.9 Bq kg⁻¹_dry; ⁴⁰K between 463 and 936 Bq kg⁻¹_dry; ¹³⁷Cs between < 0.3 and 2.6 Bq kg⁻¹_dry. The percentage of ²¹⁰Po extraction in infusion was also determined; the arithmetical mean value of percentage of ²¹⁰Po extraction resulted 20.7 ± 7.50.     

Determination of total arsenic and arsenic (III) in phosphate fertilizers and phosphate rocks by HG-AAS after multivariate optimization based on Box-Behnken design

In the present paper, a procedure for the determination of total arsenic and arsenic (III) in phosphate fertilizers and phosphate rocks by slurry sampling (SS) with hydride generation atomic absorption spectrometry (HG-AAS) is proposed. Arsenic (III) is determinated directly and total arsenic is determinated after reduction reaction. The procedure was optimized for the flow rate of NaBH₄, NaBH₄ and hydrochloric acid concentrations using a full two-level factorial and also a Box-Behnken design. Slurry preparation with hydrochloric acid in an ultrasonic bath allowed the determination of arsenic (III) with limits of detection and quantification of 0.1 and 0.3 μg L⁻¹, respectively. The precision of results, expressed as relative standard deviation (RSD), was always lower than 3%. The accuracy of this method was confirmed by analysis of certified sediment reference materials, while the procedure also allows for calibration using aqueous external standards. This method (SS/HG-AAS) was used to determine total arsenic and arsenic (III) in two phosphate rock samples and two phosphate fertilizer samples. In these samples, total arsenic concentrations varied from 5.2 to 20.0 mg kg⁻¹, while As (III) concentrations varied from 2.1 to 5.5 mg kg⁻¹, in agreement with published values. All samples were also analyzed using acid digestion/HG-AAS. Both, a paired t-test and a linear regression model demonstrated no significant difference (95% CL) between the results obtained using these two sample preparation procedures.     

Sequential radioanalytical method for the determination of U and Th isotopes, <Superscript>226</Superscript>Ra and <Superscript>210</Superscript>Po using alpha spectrometry in samples of the Brazilian phosphate industry

The phosphate rocks used for the production of phosphate fertilizers present in their composition radionuclides of the U and Th series. During the chemical attack, the radionuclides are distributed to final products and phosphogypsum. A sequential radiochemical procedure was implemented to determine the content of radionuclides alpha emitters in samples of fertilizers and phosphogypsum produced in Brazil. The results obtained show that the levels of radioactivity present in the fertilizers are of the same order of magnitude on those found in the phosphogypsum, reaching values up to 1158 and 457 Bq kg⁻¹, for the U and Th series, respectively.     

Characterization of gamma irradiated carboxymethyl cellulose (CMC) films loaded with metal salts and fertilizers

Carboxymethyl cellulose (CMC) films loaded with different metal ions and fertilizers have been successfully prepared by the solution casting technique. The prepared films were subjected to different doses of gamma radiation at room temperature. The preparation conditions such as effect of type of metals, fertilizers and radiation dose on gel fraction (%) and swelling (%) were investigated. The maximum value of gel fraction was obtained at 10 kGy radiation dose. The formation of CMC/metal complexes was confirmed by X-ray diffraction (XRD), infrared spectroscopy and scanning electron microscope (SEM) which confirm the existence of possible interaction between CMC and metal ions. The loading of various metal ions to CMC films were found to enhance the mechanical properties of the prepared films. The results provided confirmation that metal coordination between the metal cation and the carboxylate group of CMC occurred.     

Isolation of Pu-isotopes from environmental samples using ion chromatography for accelerator mass spectrometry and alpha spectrometry

A radiochemical method for the isolation of plutonium-isotopes from environmental samples, based on the use of specific extraction chromatography resins for actinides (TEVA^®, Eichrom Industries, Inc.), has been set up in our laboratory and optimised for their posterior determination by alpha spectrometry (AS) or accelerator mass spectrometry (AMS). The proposed radiochemical method has replaced in our lab a well-established one based on the use of a relatively un-specific anion-exchange resin (AG^® 1X8, Bio-rad Laboratories, Inc.), because it is clearly less time consuming, reduces the amounts and molarities of acid wastes produced, and reproducibly gives high radiochemical yields.In order to check the reliability of the proposed radiochemical method for the determination of plutonium-isotopes in different environmental matrixes, twin aliquots of a set of samples were prepared with TEVA^® and with AG^® 1X8 resins and measured by AS. Some samples prepared with TEVA^® resins were measured as well by AMS. As it is shown in the text, there is a comfortable agreement between AS and AMS, which adequately validates the method.     

Rapid determination of actinides in urine by inductively coupled plasma mass spectrometry and alpha spectrometry: A hybrid approach

A new rapid separation method that allows separation and preconcentration of actinides in urine samples was developed for the measurement of longer lived actinides by inductively coupled plasma mass spectrometry (ICP-MS) and short-lived actinides by alpha spectrometry; a hybrid approach. This method uses stacked extraction chromatography cartridges and vacuum box technology to facilitate rapid separations. Preconcentration, if required, is performed using a streamlined calcium phosphate precipitation. Similar technology has been applied to separate actinides prior to measurement by alpha spectrometry, but this new method has been developed with elution reagents now compatible with ICP-MS as well. Purified solutions are split between ICP-MS and alpha spectrometry so that long- and short-lived actinide isotopes can be measured successfully. The method allows for simultaneous extraction of 24 samples (including QC samples) in less than 3 h. Simultaneous sample preparation can offer significant time savings over sequential sample preparation. For example, sequential sample preparation of 24 samples taking just 15 min each requires 6 h to complete. The simplicity and speed of this new method makes it attractive for radiological emergency response. If preconcentration is applied, the method is applicable to larger sample aliquots for occupational exposures as well. The chemical recoveries are typically greater than 90%, in contrast to other reported methods using flow injection separation techniques for urine samples where plutonium yields were 70-80%. This method allows measurement of both long-lived and short-lived actinide isotopes. ²³⁹Pu, ²⁴²Pu, ²³⁷Np, ²⁴³Am, ²³⁴U, ²³⁵U and ²³⁸U were measured by ICP-MS, while ²³⁶Pu, ²³⁸Pu, ²³⁹Pu, ²⁴¹Am, ²⁴³Am and ²⁴⁴Cm were measured by alpha spectrometry. The method can also be adapted so that the separation of uranium isotopes for assay is not required, if uranium assay by direct dilution of the urine sample is preferred instead. Multiple vacuum box locations may be set-up to supply several ICP-MS units with purified sample fractions such that a high sample throughput may be achieved, while still allowing for rapid measurement of short-lived actinides by alpha spectrometry.     

Determination of plutonium and americium in environmental samples by inductively coupled plasma sector field mass spectrometry and alpha spectrometry

Application of inductively coupled plasma sector field mass spectrometry (ICP-SFMS) for the determination of americium and plutonium in environmental samples is described in comparison with alpha spectrometry. A sequential sample preparation method was employed using a co-precipitation step for pre-concentration and a separation step applying extraction chromatographic resins. The average recovery of sample preparation calculated from the concentration of the tracer before and after sample treatment was better than 80%. The method development focused on the elimination of possible interferences in mass spectrometric analysis caused by molecular ions (e.g. ²⁰⁰Hg⁴⁰Ar⁺, ²⁰⁴Pb³⁶Ar⁺, ²⁰⁸Pb¹⁶O₂⁺or ²³⁸U¹H⁺) employing matrix separation and desolvation prior to ICP-SFMS analysis. The effect of N₂ gas on signal intensity and oxide ratio was investigated. A two-fold signal improvement was obtained by adding 5 ml min^− 1 N₂ to the sample gas after the desolvation system. For ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Pu and ²⁴¹Am limit of detection (LOD) of 15, 9.2, 14 and 104 fg g^− 1 was achieved, respectively. Calculation of LOD was based on three times standard deviation of the method blank solution. Absolute detection limit was calculated to be 10-25 fg. For all investigated actinides the precision of the analysis was in the range 0.8-3% relative standard deviation. Results from the analysis of certified reference materials (IAEA-384 and IAEA-385) showed good agreement with recommended values and data available in the literature. The method was applied for analysis of environmental samples originated from Chernobyl and from Mayak region. The possibility of the determination of the origin and date of pollution was demonstrated using isotopic data obtained by ICP-SFMS and alpha spectrometry.     

QuEChERS-高效液相色谱-串联质谱法同时测定有机肥料中10种氟喹诺酮类药物残留

分析检测有机肥料中的兽药残留对于评价土壤微生物群落和人类健康的潜在风险至关重要。该文建立了一种QuEChERS联用高效液相色谱-串联质谱（HPLC-MS/MS）同时检测有机肥料中10种氟喹诺酮类药物残留的分析方法。样品经乙二胺四乙酸二钠（Na₂EDTA）-Mcllvaine缓冲溶液（pH=4.0）和乙腈提取，采用Atlantis T3 C₁₈色谱柱（250 mm×4.6 mm，5 μm），以0.2%（体积分数）甲酸水溶液和乙腈为梯度洗脱的流动相，采用电喷雾离子（ESI）源，在多反应监测（MRM）扫描模式下进行检测。10种氟喹诺酮类药物用内标法定量。结果表明，10种氟喹诺酮类药物在10~500 μg/kg范围内线性关系良好，相关系数均大于0.9930。方法检出限为0.5~2.5 μg/kg，定量限为1.7~8.3 μg/kg。该分析方法成功应用于9个有机肥样品的兽药污染调查。结果显示，样品的平均加标回收率为82.5%~117.1%，相对标准偏差为3.4%~10.2%。该方法准确可靠、灵敏度高，能够满足多种兽药残留的同时检测，该方法有望为有机肥料兽药风险评估提供依据。     

Chemically selective polymer substrate based direct isotope dilution alpha spectrometry of Pu

Quantification of actinides in the complex environmental, biological, process and waste streams samples requires multiple steps like selective preconcentration and matrix elimination, solid source preparations generally by evaporation or electrodeposition, and finally alpha spectrometry. To minimize the sample manipulation steps, a membrane based isotope dilution alpha spectrometry method was developed for the determination of plutonium concentrations in the complex aqueous solutions. The advantages of this method are that it is Pu(IV) selective at 3 M HNO₃, high preconcentration factor can be achieved, and obviates the need of solid source preparation. For this, a thin phosphate-sulfate bifunctional polymer layer was anchored on the surface of microporous poly(ethersulfone) membrane by UV induced surface grafting. The thickness of the bifunctional layer on one surface of the poly(ethersulfone) membrane was optimized. The thickness, physical and chemical structures of the bifunctional layer were studied by secondary ionization mass spectrometry (SIMS), scanning electron microscopy (SEM) and SEM-EDS (energy-dispersive spectroscopy). The optimized membrane was used for preconcentration of Pu(IV) from aqueous solutions having 3-4 M HNO₃, followed by direct quantification of the preconcentrated Pu(IV) by isotope dilution alpha spectrometry using ²³⁸Pu spike. The chemical recovery efficiency of Pu(IV) was found to be 86 ± 3% below Pu(IV) loading capacity (1.08 μg in 2 × 1 cm²) of the membrane sample. The experiments with single representative actinides indicated that Am(III) did not sorb to significant extent (7%) but U(VI) sorbed with 78 ± 3% efficiency from the solutions having 3 M HNO₃ concentration. However, Pu(IV) chemical recovery in the membrane remained unaffected from the solution containing 1:1000 wt. proportion of Pu(IV) to U(VI). Pu concentrations in the (U, Pu)C samples and in the irradiated fuel dissolver solutions were determined. The results thus obtained were found to be in good agreement with those obtained by conventional alpha spectrometry, biamperometry and thermal ionization mass spectrometry.     

A rapid dissolution procedure to aid initial nuclear forensics investigations of chemically refractory compounds and particles prior to gamma spectrometry

A rapid and effective preparative procedure has been evaluated for the accurate determination of low-energy (40–200 keV) gamma-emitting radionuclides (²¹⁰Pb, ²³⁴Th, ²²⁶Ra, ²³⁵U) in uranium ores and uranium ore concentrates (UOCs) using high-resolution gamma ray spectrometry. The measurement of low-energy gamma photons is complicated in heterogeneous samples containing high-density mineral phases and in such situations activity concentrations will be underestimated. This is because attenuation corrections, calculated based on sample mean density, do not properly correct where dense grains are dispersed within a less dense matrix (analogous to a nugget effect). The current method overcomes these problems using a lithium tetraborate fusion that readily dissolves all components including high-density, self-attenuating minerals/compounds. This is the ideal method for dissolving complex, non-volatile components in soils, rocks, mineral concentrates, and other materials where density reduction is required. Lithium borate fusion avoids the need for theoretical efficiency corrections or measurement of matrix matched calibration standards. The resulting homogeneous quenched glass produced can be quickly dissolved in nitric acid producing low-density solutions that can be counted by gamma spectrometry. The effectiveness of the technique is demonstrated using uranium-bearing Certified Reference Materials and provides accurate activity concentration determinations compared to the underestimated activity concentrations derived from direct measurements of a bulk sample. The procedure offers an effective solution for initial nuclear forensic studies where complex refractory minerals or matrices exist. It is also significantly faster, safer and simpler than alternative approaches.     

Americium and plutonium separation by extraction chromatography for determination by accelerator mass spectrometry

A simple method was developed to separate Pu and Am using single column extraction chromatography employing N,N,N′,N′-tetra-n-octyldiglycolamide (DGA) resin. Isotope dilution measurements of Am and Pu were performed using accelerator mass spectrometry (AMS) and alpha spectrometry. For maximum adsorption Pu was stabilized in the tetra valent oxidation state in 8 M HNO₃ with 0.05 M NaNO₂ before loading the sample onto the resin. Am(III) was adsorbed also onto the resin from concentrated HNO₃, and desorbed with 0.1 M HCl while keeping the Pu adsorbed. The on-column reduction of Pu(IV) to Pu(III) with 0.02 M TiCl₃ facilitated the complete desorption of Pu. Interferences (e.g. Ca²⁺, Fe³⁺) were washed off from the resin bed with excess HNO₃. Using NdF_3, micro-precipitates of the separated isotopes were prepared for analysis by both AMS and alpha spectrometry. The recovery was 97.7 ± 5.3% and 95.5 ± 4.6% for ²⁴¹Am and ²⁴²Pu respectively in reagents without a matrix. The recoveries of the same isotopes were 99.1 ± 6.0 and 96.8 ± 5.3% respectively in garden soil. The robustness of the method was validated using certified reference materials (IAEA 384 and IAEA 385). The measurements agree with the certified values over a range of about 1–100 Bq kg⁻¹. The single column separation of Pu and Am saves reagents, separation time, and cost.     

Preparation of magnetic polymer material with phosphate group and its application to the enrichment of phosphopeptides

As one of the most important post-translational modifications (PTM), reversible phosphorylation of protein is involved in many cellular processes. Enrichment and separation of phosphopeptides have become essential for large-scale identification of protein phosphorylation by mass spectrometry. In this work, five magnetic polymer materials with different numbers of phosphate groups were fabricated using a simple polymeric method and their abilities to enrich phosphopeptides were investigated. Our results showed that the enrichment efficiency is closely related to the number of phosphate groups attached to magnetic polymer sorbent. Under optimized condition (3% trifluoroacetic acid and 80% acetonitrile), magnetic polymer-particles with appropriate proportion of phosphate groups (Fe(3)O(4)@p(VPA-EDMA-1)-Zr(4+)) showed high performance for extracting phosphopeptides from complex peptides mixture of standard protein digestion. In this regard, a total of 988 unique phosphopeptides were successfully identified from proteolytic digestion of HeLa cell extracts by employing magnetic polymer-particles combined with nano-RPLC-MS/MS analysis.     

Determination of glyphosate and phosphate in water by ion chromatography--inductively coupled plasma mass spectrometry detection

Quantitative determination of trace glyphosate and phosphate in waters was achieved by coupling ion chromatography (IC) separation with inductively coupled plasma mass spectrometry (ICP-MS) detection. The separation of glyphosate and phosphate on a polymer anion-exchange column (Dionex IonPac AS16, 4.0 mm x 250 mm) was obtained by eluting them with 20 mM citric acid at 0.50 mL min(-1), and the analytes were detected directly and selectively by ICP-MS at m/z = 31. Parameters affecting their chromatographic behaviors and ICP-MS characteristics were systematically examined. Based on a 500-microL sample injection volume, the detection limits were 0.7 microgL(-1) for both glyphosate and phosphate, and the calibrations were linear up to 400 microgL(-1). Polyphosphates, aminomethylphosphonic acid (the major metabolite of glyphosate), non-polar and other polar phosphorus-containing pesticides showed different chromatographic behaviors from the analytes of interest and therefore did not interference. The determination was also interference free from the matrix anions (nitrate, nitrite, sulphate, chloride, etc.) and metallic ions. The analysis of certified reference material, drinking water, reservoir water and Newater yielded satisfactory results with spiked recoveries of 97.1-107.0% and relative standard deviations of < or = 7.4% (n = 3). Compared to other reported methods for glyphosate and phosphate, the developed IC-ICP-MS method is sensitive and simple, and does not require any chemical derivatization, sample preconcentration and mobile phase conductivity suppression.     

Gas chromatography/mass spectrometry characterization of historical varnishes of ancient Italian lutes and violin

The organic constituents of historical vanishes from two ancient Italian lutes and a Stradivari violin, kept in the Musée de la musique in Paris, have been characterized using gas chromatography-mass spectrometry. Results have been compared with the chromatograms and mass spectra of recent as well as old naturally aged reference materials. The three historical varnishes analyzed have been shown to be oil varnishes, probably mixtures of linseed oil with resins. Identification of diterpenoids and triterpenoids compounds, and of the resins that may have been ingredients of the varnishes, are discussed in this paper.     

Comprehensive characterization of natural organic matter by MALDI- and ESI-Fourier transform ion cyclotron resonance mass spectrometry

Natural organic matter (NOM) is a complex and non-uniform mixture of organic compounds which plays an important role in environmental processes. Due to the complexity, it is challenging to obtain fully detailed structural information about NOM. Although Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) has been demonstrated to be a powerful tool for providing molecular information about NOM, multiple ionization methods are needed for comprehensive characterization of NOM at the molecular level considering the ionizing selectivity of different ionization methods. This paper reports the first use of matrix assisted laser desorption/ionization (MALDI) method coupled with FT-ICR-MS for molecular characterization of NOM within a mass range of 200–800 Da. The mass spectral data obtained by MALDI were systematically compared with data generated by electrospray ionization (ESI). It showed that complementary molecular information about NOM which could not be detected by ESI, were provided by MALDI. More unsaturated and aromatic constituents of NOM with lower O/C ratio (O/C ratio < 0.5) were preferentially ionized in MALDI negative mode, whereas more polar constituents of NOM with higher O/C ratio were preferentially ionized in ESI negative mode. Molecular anions of NOM appearing at even m/z in MALDI negative ion mode were detected. The results show that NOM molecules with aromatic structures, moderate O/C ratio (0.7 > O/C ratio > 0.25) and lower H/C ratio were liable to form molecular anions at even m/z, whereas those with higher H/C ratio are more likely to form deprotonated ions at odd m/z. It is speculated that almost half of the NOM molecules identified by MALDI may be aromatic or condensed aromatic compounds with special groups which are liable to absorb electron from other molecules to generate free radical anions during MALDI ionization.     

Use of isotope ratio mass spectrometry to differentiate between endogenous steroids and synthetic homologues in cattle: A review

Although substantial technical advances have been achieved during the past decades to extend and facilitate the analysis of growth promoters in cattle, the detection of abuse of synthetic analogs of naturally occurring hormones has remained a challenging issue. When it became clear that the exogenous origin of steroid hormones could be traced based on the ¹³C/¹²C isotope ratio of the substances, GC/C/IRMS has been successfully implemented to this aim since the end of the past century. However, due to the costly character of the instrumental setup, the susceptibility of the equipment to errors and the complex and time consuming sample preparation, this method is up until now only applied by a limited number of laboratories. In this review, the general principles as well as the practical application of GC/C/IRMS to differentiate between endogenous steroids and exogenously synthesized homologous compounds in cattle will be discussed in detail, and will be placed next to other existing and to be developed methods based on isotope ratio mass spectrometry. Finally, the link will be made with the field of sports doping, where GC/C/IRMS has been established within the World Anti-Doping Agency (WADA) approved methods as the official technique to differentiate between exogenous and endogenous steroids over the past few years.     

Analytical characterization of natural waxes employing pyrolysis–gas chromatography–mass spectrometry

Three natural waxes (bleached beeswax, lanolin, yellow carnauba wax) were investigated by means of pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS). Pyrograms were obtained showing very characteristic signal patterns. Mass spectrometric detection enabled the structural identification of the pyrolytically formed fragments. For a more detailed investigation of the thermal degradation behaviour of waxy materials, relevant model compounds were selected. Hexadecylpalmitate, cholesterylstearate, heptadecanoic acid and 1-hexacosanol were examined under identical Py–GC–MS conditions. From the resulting product distribution general statements were able to be derived according to the thermal degradation pathways of typical wax constituents. The findings obtained from the model compounds were then applied to the interpretation of the real wax pyrograms. As a result, conclusions according to their origin from corresponding wax constituents were drawn for the majority of pyrolysis products. Thus, the extended potential of the method for the compositional analysis of natural waxes is demonstrated.     

The Relationship between Pendant Phosphate Groups and Mechanical Properties of Polyisoprene Rubber

It is still a great challenge to mimic the structure and function of natural rubber by introducing polar components into synthetic polyisoprene. In order to explore the function of phosphate groups on the mechanical properties of polyisoprene rubber, a terminally functionalized compound(PIP-P) containing phosphate groups was synthesized and further vulcanized to prepare the model compound V-PIP-P.Through analyzing the test results, it was found that these phosphate groups formed polar aggregates in non-polar polyisoprene rubber matrix,serving as an additional dynamic cross-linking sites, which increases the cross-linking density and improves mechanical properties. The influence of the phosphate groups on the strain-induced crystallization(SIC) was further investigated via synchrotron wide-angle X-ray diffraction(WAXD)experiment. These phosphate group aggregates not only reduced the onset strain of SIC, but also slowed down the molecular chain mobility,which hinder the crystal lateral growth. The above results help us to gain a deeper understanding for the function of phosphate groups in the formation of "naturally occurring network" and guide the molecular design of next generation polyisoprene rubber.     

Calcium-induced aggregation of bovine caseins: effect of phosphate and citrate

The formation of colloidal particles by Ca²⁺ precipitation of whole caseinates in the presence of phosphate (Pi), citrate (Cit), or both of the anions in concentrations found to be effective in previous works was followed comparing the colloidal particle size and the ionic and proteic composition of the precipitates obtained. Ca²⁺ was incorporated to the precipitate and colloidal particles in a different way than Pi, differences which were related to the presence of Pi and/or Cit in the media. A sequential salting-out process due to progressive Ca²⁺ binding to at least two kinds of sites was observed. The precipitation curves were fitted, and the affinity constants and binding site numbers were calculated with a modification of the Farrell’s equation based on the concept of Wyman’s linked functions. Precipitates obtained at low total Ca²⁺ concentrations in different conditions varied their casein composition. Colloidal particles appeared at the beginning of the second salting-out step, in different amount, and in average size according to the presence or absence of Pi and/or Cit in the media. Consideration of these differences showed that Cit favored the formation of bigger colloidal particles, acting especially in the first steps of the casein aggregation and conditioning the mechanism of this process.     

Immunoaffinity chromatographic and immunoprecipitation methods combined with mass spectrometry for characterization of circulating transthyretin

Transthyretin (TTR) is a small serum protein that is involved in distinct phenotypes of amyloidosis with different tissue localization, age of onset, and rate of progression. Some types of TTR-amyloidosis (such as familial amyloid polyneuropathy) are associated with various amino acid point mutations, while cardiac amyloid myopathy may also be associated with precipitation of the wild-type molecules, e.g., in senile systemic amyloidosis. Because of the unsettled relationship between circulating and precipitated TTR we here explore on-line immunoaffinity (IA) chromatography-MS and immunoprecipitation (IP)-MS methods for characterizing the circulating TTR population in normal individuals and in patients with known TTR-amyloidosis. It was found necessary to reduce the samples, e.g., with DTT, prior to ESI-TOF-MS. This reversed oxidative modifications to sufficiently resolve the two mass peaks isolated from sera of heterozygous patients. A simple IP technique without the use of centrifugal filtration was found to be convenient for the assessment of the TTR population in serum as demonstrated for both normal and variant (the Met111Leu mutation) TTR. This approach also readily allowed the identification of oxidation, S-sulfation, and S-cysteinylation in unreduced samples, while these modifications were less well resolved in the on-line IA chromatography-MS approach.