A sample whose analyte concentration has already been determined by a given analysis method is sometimes spiked with a solution of known concentration of the same analyte. (Analyte refers to the compound or element being analyzed.) The analyte concentration of the resulting solution is then determined and from this a spike recovery calculation is done. The better the recovery of the spike the better the accuracy of the method. Spiking is also done to see if the sample matrix has an effect on the effectiveness of the analysis method. (matrix refers to the solution the analyte is in.) The picture here is for illustration purposes only, the final solution should be homogeneous.

Here is an example. A surface water sample is analyzed for chlorides by the Mercuric Nitrate titration method. The data and calculated values are given below. On the first row of data, we calculated for the volume of spike needed to add a chlorides quantity that is 50% of the chlorides weight in the sample solution. The final solution volume and chlorides concentration are also calculated. The final volume is the total of the sample volume and spike volume. Here we also included the chlorides concentration in the final solution contributed by the sample and spike. This is done so you see the chlorides distribution. The total final chlorides concentration that is calculated here is the theoretical value or the value you would get if you have 100% spike recovery. Use the actual total final chlorides concentration that is determined by the analysis method to calculate the percent spike recovery in a separate calculator in this set called the Analytical Spike Recovery Calculator. We see that the spike volume needed is 0.9397 ml and we very much want to round this off to 1 ml because that is easier to measure. This is what we did in the second row of data where we input the volume of spike and we are now calculating instead for the spike chlorides quantity (as percent of sample chlorides weight) and also all the data for the final chlorides solution. This is a useful way of fine tuning our calculations.

Here are the equations used in the calculations.