AOAC Final Action Methods in 2019

( )

A

− b

Unk

A

=

IS

Unk

m

concn

where A Unk = integrated peak area of the unknown, A IS = integrated peak area of postcolumn injection peak (IS), m  = slope of the calibration curve of the nearest eluting arsenic species, and b = y -intercept of the calibration curve of the nearest eluting arsenic species. ( a )  Calibration and analytical solution concentrations .—Use a weighted calibration curve (1/ x 2 ) to calculate the concentrations of individual arsenic species from the integrated peak areas in the analytical solutions. Do not choose an algorithm type where the y -intercept must pass through zero (use the “Ignore” option for “Intercept”). ( b )  Sample concentrations .— Calculate the concentration of the individual arsenic species in the samples as follows: where [C spl ] = concentration of As(III), As(V), DMA, or MMA in the sample (micrograms per kilogram), [C soln ] = concentration of As(III), As(V), DMA, or MMA in the analytical solution (nanograms per gram). ( ) ( ) = + Dilution factor RTD M M M RTD DIW RTD where M RTD = mass of 2 g aliquot of RTD equivalent (either RTD juice or the diluted concentrate; grams) and M DIW = mass of 4 g of the portion of DIW (grams). ( ) ( ) ( ) = + × + Dilution factor concn M M M M M M concn DIW concn RTD DIW2 RTD where M concn = mass of the 1 g aliquot of the juice concentrate (grams), M DIW =mass of the DIWused to dilute the juice concentrate Table 2016.04E. Recommended Data Analysis Method a settings for m/z 75 Data point sampling: 1 Start threshold: 0.3 Baseline reset (No. of points): >10 If leading or trailing edge: <50 Baseline preference: Drop else tangent skim b Peak area, counts: >2000 All other parameters should be left  at default values a  Integration parameter values are specific to the MassHunter Data Analysis software. b  Specific terminology used by MassHunter Data Analysis software for dropping a baseline from the start to the stop of the peak rather than a tangent line. Smoothing: enabled Stop threshold: 0.5 Peak location: Top Detection filtering: 5 point = × × µ × 1 g 10 ng 3 ( ) µ ( ) C C Dilution factor 10 g 1 kg spl g kg soln ng g 3

( 5 )  Unknown peaks .—( a ) If unknown peaks are detected with a S/N > 3:1, they should be added to the analyte list (in the Data Analysis Method Editor) and named “Unk X” (where “X” is the approximate RT). Unknown peaks are defined as peaks that do not match the expected RTs (as described previously) of As(III), As(V), DMA, or MMA. ( b ) These peaks can be integrated using the above parameters, but care should be taken to ensure that unknown peaks are not integrated as known peaks and vice-versa. ( c ) Once integrated, use the unknown’s peak area to estimate the approximate concentration of the unknown in the sample (based on elemental arsenic concentration). See H . J. Calculations When using the postcolumn injection IS, MassHunter, when configured properly, will automatically perform IS correction calculations. To calculate the concentration of a given unknown peak with MassHunter, add the unknown peak to the “Data Analysis” method, then under the “FullQuant” task, go to the “Basic Calibration Parameters” table and check the “CIC” box which then adds a “Substitute” column to the analyte table. From the drop-down menu, choose the nearest eluting arsenic standard and process the data as “normal.” Alternatively, the calculation of the concentration of an unknown peak can be manually calculated using the following equation: Figure 2016.04B. Example HPLC–ICP–MS chromatograms. (A) Resolution check solution [5 ng/g AsB and As(III)]. (B) Multianalyte standard [5 ng/g each of As(III), DMA, MMA, and As(V)]. (C) Apple juice. IS = Internal standard peak.

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