A certified reference material (CRM) for the analysis of nutrient elements in an edible mushroom (Ganoderma lyceum) powder has been developed (KRISS CRM 108-10-011). The mass fractions of calcium (Ca), iron (Fe), and zinc (Zn) were measured by isotope dilution inductively coupled plasma mass spectrometry (ID ICP/MS). To dissolve the fungi cell wall of mushroom consisted of chitin fibers, sample preparation method by single reaction chamber type microwave-assisted acid digestion with acid mixtures was optimized. The mean measurement results obtained from 12 sample bottles were used to assign as the certified values for the CRM and the between-bottle homogeneities were evaluated from the relative standard deviations. The certified values were metrologically traceable to the definition of the kilogram in the International System of Units (SI). This CRM is expected to be used for validation of analytical methods or quality control of measurement results in analytical lab-oratories when they determine the mass fractions of elements in mushroom or other similar samples.
In clinical diagnosis, it’s well known that the abnormal level of uric acid (UA) in human body is implicated in diverse human diseases, for instance, chronic heart failure, gouty arthritis, diabetes, and so on. As a primary method, an isotope dilution mass spectrometry (IDMS) has been used to obtain the accurate quantity of UA in blood or serum and also develop the certifi-cated reference material (CRM) so as to provide a SI-traceability to clinical laboratories. Due to the low solubility of UA in water, an ammonium hydroxide (NH 4 OH) has been considered as a promising solvent to increase the solubility of UA that enables the preparation of both UA and its isotope standard solution for next IDMS-based absolute quantification. But, because of using this NH 4 OH solvent, it gives rise to the unwanted degradation of UA. In this study, we sought to optimize condition for the stability of UA in NH 4 OH solution by varying the mole ratios of UA to NH 4 OH, followed by ID-LC-MRM analysis. In addi-tion, we also inspected minutely the effect of the storage temperatures. Additionally, we also performed the quantitative analysis of UA in the KRISS serum certificated reference material (CRM, 111-01-02A) with diverse mixing ratios of UA to NH 4 OH and then compared those values to its certification value. Based on our experiments, adjusting the mole ratio of 1/2 (UA/NH 4 OH) with the storage temperature of -20 o C is an effective way to secure both the solubility and stability of UA in NH 4 OH solution for next IDMS-based quantification of UA in serum.
A certified reference material (CRM) for the analysis of inorganic nutrients in nutritional supplements has been developed. Accurate mass fractions of chromium (Cr), iron (Fe), copper (Cu), and zinc (Zn) were determined by isotope dilution inductively coupled plasma mass spectrometry (ID ICP/MS). The measurement results were used to assign certified values for the CRM, which were metrologically traceable to the definitions of the measurement units in the International System of Units (SI). Production of a candidate reference material (RM) and the certification processes are summarized. Each nutrient in the CRM showed good homogeneity, which was estimated using relative standard deviations of the measurement results of twelve bottles in a batch. This CRM is expected to be an important reference to improve reliability and comparability of nutrient analy- ses in nutritional supplements and related samples in analytical laboratories.
A method based on flow injection-isotope dilution-cold vapor-inductively coupled plasma mass spectrometry (FI-IDCV-ICP/MS) has been applied to determine trace level of mercury in fly ash. 200Hg isotopic spike was added to 0.25 g of BCR176Rfly ash and then decomposed by microwave digestion procedure with acid mixture A (8 mL HNO3 + 2 mLHCl + 2 mL HF) and acid mixture B (8 mL HNO3 + 2 mL HClO4 + 2 mL HF) for applying IDMS. Mercury cold vapor was generatedby using reductant solution of 0.2% (w/w) NaBH4 and 0.05% (w/w) NaOH. The measurements of n(200Hg)/n(202Hg) isotoperatio was made using a quadrupole ICP/MS system. The accuracy in this method was verified by the analysis of certified referencematerial (CRM) of fly ash (BCR 176R). The indicative value of Hg in BCR 176R fly ash was 1.60 ± 0.23 mg/kg (k = 2). The determinedvalues of Hg in BCR 176R fly ash by the method of FI-CV-ID-ICP/MS described in this paper were 1.60 ± 0.24 mg/kg(k = 3.18) and the analysis results were in well agreement with the indicative value within the range of uncertainty.
A gravimetric standard addition method combined with internal standard calibration has been successfully developed forthe accurate analysis of total arsenic in a laver candidate reference material. A model equation for the gravimetric standard additionapproach using an internal standard was derived to determine arsenic content in samples. Handlings of samples, As standard andinternal standard were carried out gravimetrically to avoid larger uncertainty and variability involved in the volumetric preparation. Germanium was selected as the internal standard because of its close mass to the arsenic to minimize mass-dependent bias in massspectrometer. The ion signal ratios of 75As+ to 72Ge+ (or 73Ge+) were measured in high resolution mode (R≥10,000) to separatepotential isobaric interferences by high resolution ICP/MS. For method validation, the developed method was applied to the analysisof arsenic content in the NMIJ 7402-a codfish certified reference material (CRM) and the result was 37.07 mg·kg-1 ± 0.45 mg·kg-1 which is in good agreement with the certified value, 36.7 mg·kg-1 ± 1.8 mg·kg-1. Finally, the certified value of thetotal arsenic in the candidate laver CRM was determined to be 47.15 mg·kg-1 ± 1.32 mg·kg-1 (k = 2.8 for 95% confidence level)which is an excellent result for arsenic measurement with only 2.8 % of relative expanded uncertainty.
Mass spectrometric analysis was carried out using multicollector inductively coupled plasma mass spectrometry(MC-ICP-MS) for the precise and accurate determination of the isotope ratios of ultratrace levels of uranium dissolved in 3%HNO3. We used the certified reference material (CRM) 112-A at a trace level of 100 pg/mL for the uranium isotopic measurement. Multiple collectors were utilized for the simultaneous measurement of uranium isotopes to reduce the signal uncertaintydue to variations in the ion beam intensity over time. Mass bias correction was applied to the measured U isotopes to improve theprecision and accuracy. Furthermore, elemental standard solution with certified values of platinum, iridium, gold, and thalliumdissolved in 3% HNO3 were analyzed to investigate the formation rates of the polyatomic ions of Ir40Ar+, Pt40Ar+, Tl40Ar+,Au40Ar+ for the concentration range of 50–400 pg/mL. Those polyatomic ions have mass-to-charge ratios in the 230–245 m/zregion that it would contribute to the increase of background intensity of uranium, thorium, plutonium, and americium isotopes. The effect of the polyatomic ion interference on uranium isotope measurement has been estimated.