Uncertainty Evaluation of Preparation of Organophosphorus Pesticide Mixed Standard Solution

The uncertainty of standard solution plays an important role in detection of pesticide residues. It may affect the accuracy of detection results. In this study, the 14 organophosphorus pesticides mixed standard solution was used as the material to analyze all the influencing factors for the preparation of mixed standard solution with uncertainty as the only judging index. The preparation uncertainty of mixed standard solution was calculated with the top-down calculation method. In the end, the expanded uncertainty was presented. The results showed that the preparation of mixed standard solution from stock solution with precise pipettes had a relatively low uncertainty.

Separation and Precise Measurement of Lithium Isotopes in Three Reference Materials Using Multi Collector-Inductively Coupled Plasma Mass Spectrometry

Lithium separation technique for three reference materials has been established together with precise determination of lithium isotope using a Neptune multi collector-inductively coupled plasma mass spectrometry （MC-ICP-MS）. The solutions of lithium element standard reference materials, potassium, calcium, sodium, magnesium and iron single element, were used to evaluate analytical methods applied. Three separate stages of ion-exchange chromatography were carried out using organic cation-exchange resin （AG 50W-X8）. Lithium was enriched for the three stages using different eluants, which are 2.8 M HCl, 0.15 M HCl and 0.5 M HCl in 30% ethanol, respectively. The columns for the first and second stages are made of polypropylene, and those for the third stage are made of quartz. Total reagent volume for the entire chemical process was 35 mL for three reference materials. The recovery yielded for the three stages is 98.9-101.2% with an average of 100.0%, 97.6-101.9% with an average of 99.9%, and 99.8-103.3% with an average of 100.6%, respectively. The precision of this technique is conservatively estimated to be ±0.72-1.04‰ （2σ population）, which is similar to the precision obtained by different authors in different laboratories with MC-ICP-MS. The δ7 Li values （ 7 Li/ 6 Li relative to the IRMM-016 standard） determined for andesite （AGV-2） and basalt （BHVO-2） are 5.68‰ （n=18）, 4.33‰ （n=18）, respectively. The δ7 Li value （ 7Li/6Li relative to the L-SVEC standard） determined for IRMM-016 is -0.01‰ （n=15）. All these analytical results are in good agreement with those previously reported. In addition, the results for the same kinds of samples analyzed at the MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, are consistent with those obtained at the Plasma Laboratory, University of Maryland, within analytical uncertainty. According to these experiment results, it is concluded that this proposed procedure is a suitable method for determining the lithium isotopic composition of natural samples.

EXPLICIT CONSTRUCTION FOR HARMONIC SURFACES IN U(N) VIA ADDING UNITONS

The authors give an algebraic method to add uniton numbers for harmonic maps from a simply connected domain ? ? R2∪{∞} into the unitary group U(N) with ?nite uniton number. So, it is proved that any n-uniton can be obtained from a 0-uniton by purely algebraic operations and integral transforms to solve the ?ˉ-problem via two different ways.