2.5. Parameters of performance

A method for determining the concentrations of heavy metals in water by ICP‐MS was developed and validated. The performance parameters were within specifications of SR EN ISO 17294‐2: water quality—application of inductively coupled plasma mass spectrometry (ICP‐ MS). Limit of detection recorded by the validated method for the elements under study provides the minimum limit of quantification required for quantitative determinations of the concentrations of these elements in the investigated waters, very good linearity (with correlation factors R > 0.999) for most elements.

The minimum detection limit is the lowest concentration or quantity of analyte which can be measured with reasonable statistical certainty. To determine the limit of detection 3SD, a method developed by PerkinElmer (Estimating Instrument Detection Limits, Elan version 3.4., and Software Guide) was used. Ultrapure water of 18.2 MΩ cm−<sup>1</sup> was aspired, and signal intensities for blank were recorded. The limit of detection was calculated by Eq. (1) where SDblank is the standard deviation for the signal recorded on the blank for the element studied, conc.sample is the concentration (μg L−<sup>1</sup> ) of the analyte in the sample, and Isample and Iblank are the signal intensities recorded for the sample and blank, respectively:

$$\text{LOD} = \text{3} \cdot \text{SD}\_{\text{blank}} \cdot \text{conc}\_{\text{sample}} / (\text{I}\_{\text{sample}} - \text{I}\_{\text{blank}}) . \tag{1}$$

The limit of quantitation (LOQ) is the lowest concentration that can be quantitatively determined with an acceptable level of repeatability and accuracy. It is generally considered to be approximately ten times the minimum detection limit (LOD). The analytical quality control included daily analysis of standards and triplicate analysis of samples and blanks. The accuracy and precision of the analytical technique were evaluated by analyzing a certified standard reference material. Precision of the instrument was determined by introducing the same quantity of one sample ten times, and then, the relative standard deviation (RSD) was calculated. RSD values ranged from 0.4 to 6.4% confirming the high precision of the method. Accuracy expresses the correlation between the arithmetic mean of the measured values and


the accepted reference value. RE ranged from −0.3 to 13% confirming the accuracy of the implemented method (Table 1).

1 R—correlation coefficient; <sup>2</sup> SD—standard deviation; <sup>3</sup> RSD—relative standard deviation, RSD (%) = SD/[metal] mean × 100; <sup>4</sup> RE—relative error, RE (%) = ([metal] found − [metal] added/[metal] added) × 100.

Table 1. Performance parameters obtained for heavy metals studied.
