A new method for the improvement of data production in phytochemical analysis.
BACKGROUND
The use of the average analytical signal for the construction of curves by the least squares method (LSM) over the standard addition method (SAM) is widespread. It would be advantageous, however, to find a way to avoid intermediary averages, which are known to be the cause of significant increases in standard deviations (SD).


OBJECTIVE
To develop a protocol that uses all gathered data to create curves by LSM over SAM. To use Excel for the estimation of y = mx + b and R(2) rather than using LSM equations for the SD of m, x and b.


METHODS
The level of lead (II) in the bark (cork) of Quercus suber Linnaeus was determined using differential pulse anodic stripping voltammetry (DPASV). Three current samples were taken for each of the four standard additions. These signals were combined for adjustment by LSM. The results were compared with those obtained after averaging the current for each addition, and the expression of uncertainty in the measurements determined.


RESULTS
The new method shows an expanded uncertainty of +/- 0.3321 microg/g (nearly 1.42%). The difference between the results obtained by the new and the old method is 0.01 microg/g (23.41 and 23.40 microg/g). The limit of detection changed approximately from 4.8 to 4 microg/g and the relative SD approximately from 9 to 6%.


CONCLUSIONS
The absence of intermediary averages in curves improved the determination of lead (II) in cork by DPASV. Estimation of SD only with LSM equations produced results that were significantly worse. The changes are large enough to transform an apparently internally non-validated procedure (repeatability for precision) into an internally validated procedure.
Ponte-e-Sousa
João
J
Department of Chemistry, University of Evora, Rua Romão Ramalho no. 59, 7000-671 Evora, Portugal. jcps@uevora.pt
Neto-Vaz
António
A
D000465:Algorithms; D055664:Electrochemical Techniques / Q000295:instrumentation / Q000379:methods; D007854:Lead / Q000032:analysis*; D016018:Least-Squares Analysis; D057230:Limit of Detection; D024301:Plant Bark / Q000737:chemistry*; D029963:Quercus / Q000737:chemistry*
D007854:Lead