A Certified Urea Reference Material (NMIJ CRM 6006-a) as a Reliable Calibrant for the Elemental Analyses of Amino Acids and Food Samples

Abstract

We examined the reliability of a certified reference material (CRM) for urea (NMIJ CRM 6006-a) as a calibrant for N, C, and H in elemental analyzers. Only the N content for this CRM is provided as an indicative value. To estimate the C and H contents of the urea CRM, we took into account the purity of the urea and the presence of other identified impurities. When we examined the use of various masses of the calibrant (0.2 to 2 mg), we unexpectedly observed low signal intensities for small masses of H and N, but these plateaued at about 2 mg. We therefore analyzed four amino acid CRMs and four food CRMs on a 2-mg scale with the urea CRM as the calibrant. For the amino acid CRMs, the differences in the analytical and theoretical contents (≤0.0026 kg/kg) were acceptable with good repeatability (≤0.0013 kg/kg in standard deviation; n = 4). For food CRMs, comparable repeatabilities to those obtained with amino acid CRMs (≤0.0025 kg/kg in standard deviation; n = 4) were obtained. The urea CRM can therefore be used as a reliable calibrant for C, H, and N in an elemental analyzer.

Absolute Quantification of Pure Free Radical Reagents by Combination of the Effective Magnetic Moment Method and Quantitative Electron Paramagnetic Resonance Method

“…A 2400 Series II CHNS/O System elemental analyzer (PerkinElmer, Waltham, MA, USA) was used for carbon hydrogen nitrogen (CHN) analysis. The experimental procedures reported in the previous study were followed . An EPR spectrometer (Bruker, E500) was operated at the Q-band EPR to obtain EPR spectra with a higher resolution than those of the X-band.…”

“…The experimental procedures reported in the previous study were followed. 31 An EPR spectrometer (Bruker, E500) was operated at the Q-band EPR to obtain EPR spectra with a higher resolution than those of the X-band. The powder sample for the Q-band of less than 1 mg was sealed in an evacuated quartz tube (2 mm diameter, 100 mm length).…”

Measuring Number of Free Radicals and Evaluating the Purity of Di(phenyl)-(2,4,6-trinitrophenyl)iininoazaniuin [DPPH] Reagents by Effective Magnetic Moment Method

“…The experimental procedures reported by previous studies were followed. 44,45 To obtain EPR spectra with higher resolution than those observed at X-band, EPR spectrometers (Bruker, E500 and E680) were operated at Q-and W-bands EPR, respectively, to obtain considerably higher resolution EPR spectra than those of X-band. A powdered sample for the Q-band of less than 1 mg was sealed in an evacuated quartz tube (diameter 2 mm, length 100 mm).…”