1Objectives: Measurement of mean population sodium and potassium intake typically 2 using laboratory-based assays which can add significant logistical burden and costs. A 3 valid field-based measurement method would be a significant advance. In this study, 4we used 166 24-hour urine collection samples to compare estimates of sodium, 5 potassium content and sodium/potassium ratio based upon assays done using the field-6 based Horiba twin meter versus a laboratory-based method. 7Design: Aliquots of urine were assayed for sodium and potassium using the ion-8 selective electrode method with the field-based Horiba twin meter and the laboratory-9 based method. The performance of the Horiba twin meter was determined by 10 comparing field-based estimates of mean sodium and potassium against those obtained 11 using the laboratory-based methods. 12Setting: 24-hour urine samples were collected as part of an ongoing study being done 13 in rural China. 14 Subjects: There were 166 subjects complete 24-hour urine samples available for 15 estimating 24-hour urinary sodium and potassium excretion. 16Results: Mean sodium and potassium excretion were estimated as 170.4 mmol/day and 17 37.4 mmol/day using the meter-based assays and 193.4 mmol/day and 43.8 mmol/day 18 using the laboratory-based assays. There was excellent relative reliability for both 19 sodium (ICC=0.986) and potassium (ICC=0.986). Bland-Altman plots showed 20 moderate-to-good agreement between two methods. 21Conclusions: Sodium and potassium intake estimation was moderately under-22 estimated using assays based upon the Horiba twin meter. Compared to standard lab-23 based methods, the portable device was more practical and convenient.

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Power generators that convert daily air temperature cycles to electricity should have both high power output and wide operating temperature range. Herein, a power generator combining a thermoelectric device and a mixture of various encapsulated alkanes that undergo continuous phase transitions induced by ambient temperature cycles is demonstrated. The operating temperature range of such a power generator can be extended by selecting appropriate alkane capsules to be incorporated into the device. A power generator with an operating temperature range of −0.2–37.2 °C is demonstrated; this operating temperature range is obtained when the temperature difference between the highest and lowest temperatures of the ambient temperature cycle is 14.2 °C, which is the equivalent environment in a Stevenson screen outdoors. The wide operating temperature range would permit power generation from daily temperature variations in many temperate and subtropical countries. The electric powers obtained by this power generator when placed in an indoor room and an outdoor Stevenson screen are 180 and 300 µW, respectively. Our temperature cycle‐based power generators pave the way for power sources that can generate electricity semi‐permanently in a broad range of environment.

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