Document Detail


Spatial Emission Profiles for Flagging Matrix Interferences in Axial-Viewing Inductively Coupled Plasma-Atomic Emission Spectrometry: Part II - Statistical Protocol.
MedLine Citation:
PMID:  23198881     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
A statistical protocol was developed and verified for automated signaling of matrix interferences in inductively coupled plasma-atomic emission spectrometry (ICP-AES). Spatial emission profiles in ICP-AES are versatile indicators for flagging matrix interference. A family of calibration curves is first generated by measurements of standard solutions at different spatial locations in the plasma. The determined-concentration profile of the analyte along a spatial measurement axis of the plasma is then obtained by analyzing the sample at each spatial location by reference to the respective calibration curve. The absence or presence of a matrix interference is gauged from the shape of the determined-concentration profile of the analyte. A flat determined-concentration profile indicates absence of matrix interference whereas a dissimilar (i.e., curved) concentration profile offers a clear warning signal that the analytical results are compromised by interferences. The developed protocol automatically classifies a spatial profile as flat or curved; it involves the computation of three statistical parameters: relative range0.05-0.95, σsample and σsuccessive. The term relative range0.05 0.95 refers to the ratio of the range to the mean of the relative-intensity (or determined concentration) values between the 5th and 95th percentiles in a spatial profile, whereas σsample and σsuccessive refer to the sample standard deviation and the standard deviation of successive values, respectively, of all values in a spatial profile. It was found that whenever the relative range0.05-0.95 of a spatial profile is below 1.5%, the profile can be considered to be flat and no further statistical testing is needed. If relative range0.05 0.95 > 1.5%, the σsuccessive / σsample ratio provides useful information on the flatness of the profile. If the profile is flat, σsuccessive will be statistically equivalent to σsample (i.e., σsuccessive / σsample = 1). In contrast, if curvature is present in the profile, σsuccessive will be statistically smaller than σsample (i.e., σsuccessive / σsample < 1). A statistical test, based on the transformation of the experimental σsuccessive / σsample ratio to the z-value of a standard normal distribution, was used to judge if the difference between σsuccessive and σsample is statistically significant. This statistical protocol for characterization of flatness in a spatial profile was verified in experiments carried out under the influence of various matrix interferences and different plasma operating conditions.
Authors:
George C Chan; Gary Martin Hieftje
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-12-3
Journal Detail:
Title:  Analytical chemistry     Volume:  -     ISSN:  1520-6882     ISO Abbreviation:  Anal. Chem.     Publication Date:  2012 Dec 
Date Detail:
Created Date:  2012-12-3     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0370536     Medline TA:  Anal Chem     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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