The determination of isotope ratios of lead finds many important applications in earth and planetary sciences. In this study, we report the first independent and fully calibrated absolute isotope ratio measurements of a common lead since the seminal work by the NIST in the 1960s, which has provided the widely used standards SRM 981 and SRM 982. This work employs MC-ICPMS for the absolute isotope ratio measurements, which were calibrated using two independent methods: the full gravimetric isotope mixture method based on the use of all four near-pure lead isotopes (the first application of this primary method to lead) and the regression method with NIST SRM 997 thallium isotopic standard as the primary calibrator. Both calibration methods provide results consistent to a few parts in 10 4 , which were used to characterize isotope ratios of lead in an NRC candidate reference material, high-purity common lead HIPB-1.
Particle size measurements of cellulose nanocrystals (CNCs) are challenging due to their broad size distribution, irregular shape and propensity to agglomerate. Particle size is one of the key parameters that must be measured for quality control purposes and to differentiate materials with different properties. We report the results of an interlaboratory comparison (ILC) which examined atomic force microscopy (AFM) data acquisition and data analysis protocols. Samples of CNCs deposited on poly-Llysine coated mica were prepared in the pilot laboratory and sent to 10 participating laboratories including academic, government and industrial organizations with varying levels of experience with imaging CNCs. The participant data sets indicated that the central
Particle
size is a key parameter that must be measured to ensure reproducible
production of cellulose nanocrystals (CNCs) and to achieve reliable
performance metrics for specific CNC applications. Nevertheless, size
measurements for CNCs are challenging due to their broad size distribution,
irregular rod-shaped particles, and propensity to aggregate and agglomerate.
We report an interlaboratory comparison (ILC) that tests transmission
electron microscopy (TEM) protocols for image acquisition and analysis.
Samples of CNCs were prepared on TEM grids in a single laboratory,
and detailed data acquisition and analysis protocols were provided
to participants. CNCs were imaged and the size of individual particles
was analyzed in 10 participating laboratories that represent a cross
section of academic, industrial, and government laboratories with
varying levels of experience with imaging CNCs. The data for each
laboratory were fit to a skew normal distribution that accommodates
the variability in central location and distribution width and asymmetries
for the various datasets. Consensus values were obtained by modeling
the variation between laboratories using a skew normal distribution.
This approach gave consensus distributions with values for mean, standard
deviation, and shape factor of 95.8, 38.2, and 6.3 nm for length and
7.7, 2.2, and 2.9 nm for width, respectively. Comparison of the degree
of overlap between distributions for individual laboratories indicates
that differences in imaging resolution contribute to the variation
in measured widths. We conclude that the selection of individual CNCs
for analysis and the variability in CNC agglomeration and staining
are the main factors that lead to variations in measured length and
width between laboratories.
Vanillin, one of the world’s most popular flavor used in food and pharmaceutical industries, is extracted from vanilla beans or obtained (bio)-synthetically. The price of natural vanillin is considerably higher than that of its synthetic alternative which leads increasingly to counterfeit vanillin. Here, we describe the workflow of combining carbon isotope ratio combustion mass spectrometry with quantitative carbon nuclear magnetic resonance spectrometry (13C-qNMR) to obtain carbon isotope measurements traceable to the Vienna Peedee Belemnite (VPDB) with 0.7‰ combined standard uncertainty (or expanded uncertainty of 1.4‰ at 95% confidence level). We perform these measurements on qualified Bruker 400 MHz instruments to certify site-specific carbon isotope delta values in two vanillin materials, VANA-1 and VANB-1, believed to be the first intramolecular isotopic certified reference material (CRMs).
Graphical abstract
Microcystins are cyclic heptapeptides from cyanobacteria that are potent inhibitors of protein phosphatases and are toxic to animals and humans. At present, more than 250 microcystin variants are known, with variants reported for all seven peptide moieties. While d-glutamic acid (d-Glu) is highly-conserved at position-6 of microcystins, there has been only one report of a cyanobacterium (Anabaena) producing microcystins containing l-Glu at the variable 2- and 4-positions. Liquid chromatography–mass spectrometry analyses of extracts from Planktothrix prolifica NIVA-CYA 544 led to the tentative identification of two new Glu-containing microcystins, [d-Asp3]MC-ER (12) and [d-Asp3]MC-EE (13). Structure determination was aided by thiol derivatization of the Mdha7-moiety and esterification of the carboxylic acid groups, while 15N-labeling of the culture and isotopic profile analysis assisted the determination of the number of nitrogen atoms present and the elemental composition of molecular and product-ions. The major microcystin analog in the extracts was [d-Asp3]MC-RR (1). A microcystin with an unprecedented high-molecular-mass (2116 Da) was also detected and tentatively identified as a sulfide-linked conjugate of [d-Asp3]MC-RR (15) by LC–HRMS/MS and sulfide oxidation, together with its sulfoxide (16) produced via autoxidation. Low levels of [d-Asp3]MC-RW (14), [d-Asp3]MC-LR (4), [d-Asp3,Mser7]MC-RR (11), [d-Asp3]MC-RY (17), [d-Asp3]MC-RF (18), [d-Asp3]MC-RR–glutathione conjugate (19), and [d-Asp3]MC-RCit (20), the first reported microcystin containing citrulline, were also identified in the extract, and an oxidized derivative of [d-Asp3]MC-RR and the cysteine conjugate of 1 were partially characterized.
Background: Among the regulated mycotoxins that contaminate global food supplies, ochratoxin A is particularly harmful as a nephrotoxin and suspected carcinogen. Objective: To support global measurement comparability, certified calibration solutions for ochratoxin A and
[13C6]-ochratoxin A (OTAN-1 and OTAL-1, respectively) as well as a mycotoxin-contaminated rye flour certified reference material (CRM) known as MYCO-1 were developed. Methods: Quantitative proton NMR was used along with maleic acid as an external standard traceable
to the Système international (SI) to measure the concentration of ochratoxin A and [13C6]-ochratoxin A for the calibration solutions. OTAN-1 and OTAL-1 were then used as a pair in double isotope dilution MS to certify the mass fraction of ochratoxin A in MYCO-1.
The natural ochratoxin A CRM served as the primary standard for traceable quantitation, while the synthetic [13C6]-ochratoxin A CRM served as the internal standard. Results: The certified mass fraction of ochratoxin A or [13C6]-ochratoxin
A in the two mycotoxin calibration solution standards was established to be 11.03 ± 0.32 µg/g (k = 2) for OTAN-1 and 4.89 ± 0.18 µg/g (k = 2) for OTAL-1. The mass fraction of ochratoxin A in the rye flour standard MYCO-1 was certified at 4.05 ±
0.88 µg/kg (k = 2). Conclusions: These CRMs will support regulatory testing as they can be used in the method development, validation, calibration, and QC analysis of ochratoxin A. Highlights: This report highlights the methods used to certify OTAN-1, OTAL-1, and
MYCO-1 as well as the challenges associated with producing such materials, which can be applied to a wide variety of other CRMs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.