Inter-laboratory comparison of SiO₂ analysis for geothermal water chemistry

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• 作者：Mahendra P. Verma ; Georgina Izquierdo ; Guima A. Urbino ; Sophie Gangloff ; Roberto Garc¨ªa ; Alfredo Aparicio ; Thibauld Conte ; Ma. Aurora Armienta ; Mayela S¨¢nchez ; June Rizza P. Gabriel ; Irene D. Fajanela ; Roberto Renderos ; Cherry Bernadette A. Acha ; Rasi Prasetio ; Irma Cruz Grajales ; Lisette Reyes Delgado ; Kizito Opondo ; Regina Zendejas Esparza ; Luz Ang¨¦lica Panama ; Ruth Tapia Salazar ; et al.
• 关键词：Geothermal water ; Silica ; Inter-laboratory comparison ; Atomic absorption spectrometry (AAS) ; Colorimetry ; Inductively coupled plasma (ICP)
• 刊名：Geothermics
• 出版年：2012
• 出版时间：October, 2012
• 年：2012
• 卷：44
• 期：Complete
• 页码：33-42
• 全文大小：1084 K

文摘

The results of an inter-laboratory comparison of silica analysis of seven water samples (coded as IIE19-IIE25) are presented. The first six samples (IIE19-IIE24) were prepared by diluting a certain amount of silicon (Si) standard 1000 ¡À 0.1 %  ppm, HYCEL, Mexico, in distilled water, while the seventh sample IIE25 is natural geothermal water. The conventional true values for the silica (SiO₂) concentration of IIE19-IIE24 are 61.1, 213.9, 366.7, 520, 825, and 978 ppm, respectively.

The present analysis database consists of 27 datasets, analyzed by colorimetry (13 sets), atomic absorption spectrometry (7 sets) and inductively coupled plasma (7 sets) techniques. The analyses were performed with two procedures: (i) individual laboratory procedure (or conventional procedure) and (ii) dilution of samples in the range 50-200 ppm SiO₂. The mean () and standard deviation (s) calculation after eliminating extreme values (outliers) with method was used for the statistical data treatment. Presently, the overall error in the analysis is at least ¡À10 % . A comparison of analytical error and uncertainty for individual analytical technique suggests that the inductively coupled plasma (ICP) and colorimetry are relatively better techniques for the analysis of SiO₂ in geothermal waters; however, there are some statistical artifacts on the colorimetric results because their number of measurements was double that of atomic absorption spectrometry (AAS) and ICP. The analysis quality (i.e., precision and accuracy) may be improved by using the data control procedure with some high quality standard (e.g., NIST standards). One of the factors of systematic error is associated with the preparation of laboratory standards.