Question

20-acre raisin vineyard has possibly been exposed to a pesticide used on a neighboring peach orchard (after the harvest of the peaches but prior to the harvest of the raisins). Your task is to determine the level of pesticide exposure for the entire field using HPLC. Devise a sampling methodology to ensure a representative sample and devise a preparation method that will yield several 10-microlitre solutions for injection into the HPLC.

Answer 1

(1) Sampling methodology to ensure a representative sample:

20 Acre is a very big area. 1 Acre is almost equal to 4047 square metre. To determine the level of pesticide exposure for the entire field we need to specify the sampling according to unit area.

First divide 20 Acre in smaller units of 1-1 Acre. Now you have 20 Sample modules.

Now from every module you need to mark 5 spots of 1 square metre area. This is your actual sample collection area. Collect samples from every spot of 1 sq meter area. At the time of calculation use them as sample replicates the approximate answer of pesticide used for 1 Acre (1 sample module) will be the mean value of these five areas multiplied by 4047.

Then the level of pesticide exposure for the entire field can be calculated

Average of 20 sample modules X 20

(2) Sample Preparation :

As the pesticide is exposed at superficial level but not inside the raisin plants. And the pesticide is also exposed to the soil. So soil sample and plant samples from every of 5 spotted 1 square meter area of sample modules need to be collected and to be washed with minimum quantity of appropriate reagent to solubilize and collect contents of pesticides. Then from this solution the concentrate will be prepared. Then this solution can be run in HPLC against the known pesticide standard.