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Hafnium content and its change are of significance in geochemistry and cosmochemistry; however, the determination of hafnium has always been problematic in analytical chemistry. In this paper, a new idea is proposed for the determination of hafnium in geochemical samples, including rocks, soils, and stream sediments. Through the comparison of two conventional open-type acid digestion methods (HF-HNO3-HClO4 and HF-HNO3-H2SO4), it was found that although neither of these methods could fully digest the zirconium and hafnium in a sample, the zirconium and hafnium digestion behaviors in one sample were consistent in the 60 experimental geochemical reference materials with different properties, so the experimentally determined Zr/Hf ratio in solution could be used to calculate the hafnium content in a sample. In addition, possible mass spectral interferences during the determination of zirconium and hafnium by high resolution inductively coupled plasma mass spectrometry (HR-ICPMS) were studied, and it was found that the mass spectral interferences of the selected isotopes 90Zr and 178Hf could be neglected. The mass spectral behaviors of 90Zr and 178Hf were also very consistent during the determination by HR-ICPMS. Since the hafnium content was calculated using the ratio value, all of the errors (including the errors in weighing process, the accidental errors during operation and the instrument fluctuation in the determination) of the Zr/Hf ratio could be effectively reduced or even eliminated. The relative standard deviation of the actual samples was lower than 3.2%, and the detection limit of the method (considering the dilution effect and matrix effect during measurement of the Zr/Hf ratio and zirconium content) was 0.04 μg/g. The proposed method could satisfy the requirement for the determination of hafnium in geochemical samples. [ABSTRACT FROM AUTHOR]

Background: Preterm birth, the birth of an infant prior to 37 completed weeks of gestation, is the leading cause of perinatal morbidity and mortality. Preterm infants are at greater risk of respiratory, gastrointestinal and neurological diseases. Despite significant research in developed countries, little is known about the causes of preterm birth in many developing countries, especially China. This study investigates the association between sciodemographic data, obstetric risk factor, and preterm birth in five Maternal and Child Health hospitals in Beijing, China. Methods and Findings: A case-control study was conducted on 1391 women with preterm birth (case group) and 1391 women with term delivery (control group), who were interviewed within 48 hours of delivery. Sixteen potential factors were investigated and statistical analysis was performed by univariate analysis and logistic regression analysis. Univariate analysis showed that 14 of the 16 factors were associated with preterm birth. Inter-pregnancy interval and inherited diseases were not risk factors. Logistic regression analysis showed that obesity (odds ratio (OR) = 3.030, 95% confidence interval (CI) 1.166- 7.869), stressful life events (OR = 5.535, 95%CI 2.315-13.231), sexual activity (OR = 1.674, 95%CI 1.279-2.191), placenta previa (OR 13.577, 95%CI 2.563-71.912), gestational diabetes mellitus (OR = 3.441, 95%CI1.694-6.991), hypertensive disorder complicating pregnancy (OR = 6.034, 95%CI = 3.401-10.704), history of preterm birth (OR = 20.888, 95%CI 2.519-173.218) and reproductive abnormalities (OR = 3.049, 95%CI 1.010-9.206) were independent risk factors. Women who lived in towns and cities (OR = 0.603, 95%CI 0.430-0.846), had a balanced diet (OR = 0.533, 95%CI 0.421-0.675) and had a record of prenatal care (OR = 0.261, 95%CI 0.134-0.510) were less likely to have preterm birth. [ABSTRACT FROM AUTHOR]