John L. Molloy

Development of saw palmetto (Serenoa repens) fruit and extract standard reference materials

As part of a collaboration with the National Institutes of Health’s Office of Dietary Supplements and the Food and Drug Administration’s Center for Drug Evaluation and Research, the National Institute of Standards and Technology has developed two standard reference materials (SRMs) representing different forms of saw palmetto (Serenoa repens), SRM 3250 Serenoa repens fruit and SRM 3251 Serenoa repens extract. Both of these SRMs have been characterized for their fatty acid and phytosterol content. The fatty acid concentration values are based on results from gas chromatography with flame ionization detection (GC-FID) and mass spectrometry (GC/MS) analysis while the sterol concentration values are based on results from GC-FID and liquid chromatography with mass spectrometry analysis. In addition, SRM 3250 has been characterized for lead content, and SRM 3251 has been characterized for the content of β-carotene and tocopherols. SRM 3250 (fruit) has certified concentration values for three phytosterols, 14 fatty acids as triglycerides, and lead along with reference concentration values for four fatty acids as triglycerides and 16 free fatty acids. SRM 3251 (extract) has certified concentration values for three phytosterols, 17 fatty acids as triglycerides, β-carotene, and γ-tocopherol along with reference concentration values for three fatty acids as triglycerides, 17 fatty acids as free fatty acids, β-carotene isomers, and δ-tocopherol and information values for two phytosterols. These SRMs will complement other reference materials currently available with concentrations for similar analytes and are part of a series of SRMs being developed for dietary supplements.

Development and certification of green tea-containing standard reference materials.

AbstractA suite of three green tea-containing Standard Reference Materials (SRMs) has been issued by the National Institute of Standards and Technology (NIST): SRM 3254 Camellia sinensis (Green Tea) Leaves, SRM 3255 Camellia sinensis (Green Tea) Extract, and SRM 3256 Green Tea-Containing Solid Oral Dosage Form. The materials are characterized for catechins, xanthine alkaloids, theanine, and toxic elements. As many as five methods were used in assigning certified and reference values to the constituents, with measurements carried out at NIST and at collaborating laboratories. The materials are intended for use in the development and validation of new analytical methods, and for use as control materials as a component in the support of claims of metrological traceability. FigureGreen Tea - Camellia sinensis

Elemental analyses of soil and sediment fused with lithium borate using isotope dilution laser ablation-inductively coupled plasma-mass spectrometry

Quantitative analysis using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) remains challenging primarily due to the lack of appropriate reference materials available for the wide variety of samples of interest and to elemental fractionation effects. Isotopic dilution mass spectrometry (IDMS) is becoming the methodology of choice to address these issues because the different isotopes of an element represent near-perfect internal standards. In this work, we investigated the lithium borate fusion of powdered solid samples, including soils, sediments, rock mine waste and a meteorite, as a strategy to homogenously distribute, i.e. equilibrate the elements and the added isotopically enriched standards. A comparison of this methodology using two pulsed laser ablation systems (ArF* excimer and Nd:YAG) with different wavelengths as well as two ICP-MS instruments (quadrupole and double-focusing sector field) was performed. Emphasis was put on using standard equipment to show the potential of the proposed strategy for its application in routine laboratories. Cr, Zn, Ba, Sr and Pb were successfully determined by LA-ICP-IDMS in six Standard Reference Materials (SRMs) representing different matrices of environmental interest. Experimental results showed the SRM fused glasses exhibited a low level of heterogeneity (intra- and inter-sample) for both natural abundance and isotopically enriched samples (RSD <3%, n=3, 1σ). A good agreement between experimental results and the certified values was also observed.

Isotope dilution mass spectrometry for quantitative elemental analysis of powdered samples by radiofrequency pulsed glow discharge time of flight mass spectrometry

In recent years particular effort is being devoted to the development of pulsed glow discharges (PGDs) for mass spectrometry because this powering operation mode could offer important ionization analytical advantages. However, the capabilities of radiofrequency (RF) PGD coupled to a time of flight mass spectrometry (ToFMS) for accurate isotope ratio measurements have not been demonstrated yet. This work is focused on investigating different time positions along the pulse profile for the accurate measurement of isotope ratios. As a result, a method has been developed for the direct and simultaneous multielement determination of trace elements in powdered geological samples by RF-PGD-ToFMS in combination with isotope dilution mass spectrometry (IDMS) as an absolute measurement method directly traceable to the International System of Units. Optimized operating conditions were 70 W of applied radiofrequency power, 250 Pa of pressure, 2 ms of pulse width and 4 ms of pulse period, being argon the plasma gas used. To homogeneously distribute the added isotopically-enriched standards, lithium borate fusion of powdered solid samples was used as sample preparation approach. In this way, Cu, Zn, Ba and Pb were successfully determined by RF-PGD-ToF(IDMS) in two NIST Standard Reference Materials (SRM 2586 and SRM 2780) representing two different matrices of geological interest (soil and rock samples). Cu, Zn, Ba and Pb concentrations determined by RF-PGD-ToF(IDMS) were well in agreement with the certified values at 95% confidence interval and precisions below 12% relative standard deviation were observed for three independent analyses. Elemental concentrations investigated were in the range of 81-5770 mg/kg, demonstrating the potential of RF-PGD-ToF(IDMS) for a sensitive, accurate and robust analysis of powdered samples.

Measurement and modeling of the ability of crack fillers to prevent chloride ingress into mortar

A common repair procedures applied to damaged concrete is to fill cracks with an organic polymer. This operation is performed to increase the service life of the concrete by removing a preferential pathway for the ingress of water, chlorides, and other deleterious species. To effectively fulfill its mission of preventing chloride ingress, the polymer must not only fully fill the macro-crack, but must also intrude the damage zone surrounding the crack perimeter. Here, the performance of two commonly employed crack fillers, one epoxy, and one methacrylate, are investigated using a combined experimental and computer modeling approach. Neutron tomography and microbeam X-ray fluorescence spectrometry (μXRF) measurements are employed on pre-cracked and chloride-exposed specimens to quantify the crack filling and chloride ingress limiting abilities, respectively, of the two polymers. A two-dimensional model of chloride transport is derived from a mass balance and solved by the finite element method. Crack images provided by μXRF are used to generate the input microstructure for the simulations. When chloride binding and a time-dependent mortar diffusivity are both included in the computer model, good agreement with the experimental results is obtained. Both crack fillers significantly reduce chloride ingress during the 21 d period of the present experiments; however, the epoxy itself contains approximately 4 % by mass chlorine. Leaching studies were performed assess the epoxy as a source of deleterious ions for initiating corrosion of the steel reinforcement in concrete structures.

Software Package to Facilitate the Preparation of Intermediate-Range Fossil Fuel Standards from Certified Reference Materials

A PC software package has been developed in Visual Basic for Applications to assist analysts in mixing fossil fuel reference materials to produce standards of intermediate concentrations. Mixing appropriate reference materials of similar matrices permits the analyst to produce needed standards over a continuous concentration range for analytes of interest. The program automates selection of optimum mixtures and calculates the concentrations and associated uncertainties of analytes in the blends. A graphical interface depicting all possible blends and an automated quality control test to monitor the process for potential problems are included.