Experiment in quantifying metabolites in urine

I want to get some feed back on an experiment I'm planning on doing, and if the logic is sound, I'd like to get people to participate.

Hypothesis: THC immunoassay test strips will determine if the concentration of THC metabolites are <= 50ng/mL (PASS), or > 50ng/mL, (FAIL) with some error based on testing conditions and manufacture of test strip. Therefore it should be possible with dilution of a sample to determine the concentration in a sample by repeated testing.

Materials: graduated cylinder 10 ml, THC immunoassay test strips, mixing container, deionized water, stirring rod.

Procedure: Procure a large dirty sample in the morning.
1. Measure out 5mL of sample, pour into container, test with strip, note result.
2. Measure out 5mL of sample, pour into container, measure out 5mL deionized water, pour into container, stir, test with strip, note result.
3. Repeat step 2, each time with an extra 5mL of deionized water.

In the end you should have a table like this
Data:
(Concentration = volume of sample / total volume of solution)
Concentration, Pass/Fail
5/5 = 100%,Fail
5/10 = 50%,Fail
5/15 = 33%,Fail
5/20 = 25%,Fail
5/25 = 20%,Fail
5/30 = 16%,Pass

Discussion:
So, if you can only pass if the concentration is < 50ng/mL, then that means that 16% of your undiluted concentration is < 50ng/mL, or more importantly that the full strength is <= 50ng/16% = 312ng and >= 50ng/20% = 250ng. With access to more test strips, repeated measurements could be taken to try to improve this measurement.

Once you have this number, you could repeat the experiment every week and see how much the THC has been metabolized over the week. After a few weeks, you should have enough data to figure out how long it takes to metabolize the drug for your body.

If enough people do this, and posts their results, making sure to include their height, age, weight, body fat %, activity level, and when they started abstaining, we can put an end to all the 'how long to get clean' questions.

Unless anyone sees fault with this experiment, the only detail left to figure out is where to buy the most reliable test strips in bulk.

The thing is, you dont have a baseline ng/ml figure to draw from before you even begin your first test. And youre not going to obtain this by using an assay strip because assays are a "go/no-go" endeavor and lack the ability to quantify. The only proven accurate way to obtain quantitative values is to run the sample thru a GC/MS.

I understand there is no baseline, but consider the example data I posted, at 20%, the sample failed, which means it was > 50ng, and at 16% it passed, meaning it was < 50ng. Therefore, the concentration in the original sample is between 50/20% and 50/16%, or >250ng and <312ng. If you then tested 19%, 18%, 17%, and found it failed on all of them for example, then you know the original sample is >50/17% = 294ng, So your new range would be 294 to 312. If you wish for a more accurate result, then repeat the experiment.

Everything has some error, the thing to figure out is how much. Say a test strip can measure 50ng +/- 10ng, then the calculations are still sound, but need to incorporate this error. This error can be determined by repeated testing of a known concentration, this would require a GC/MS. But for the person trying to figure out if they're at 1000 or 100, this is unnecessary.

The feds have already done this. They say we're all clean after a week.lol