Question

What is detectiom limit? Why do I need it and where do I use?

Answer 1

detection limit: is the lowest quantity or say concentration level of a substance that can be distinguished from a blank( 99% confidence) or confidence limit of 1%. this is typically determined in the region where signal to noise ratio is greater than 5. LOD is matrix method and analyte specific. The detection limit is estimated from the mean of the blank, the standard deviation of the blank and some confidence factor.

or say

The detection limit of an individual analytical procedure is the lowest amount of analyte in a sample which can be detected but not necessarily quantitated as an exact value. Several approaches for determining the detection limit are possible.

Based on visual evaluation: The detection limit is determined by the analysis of samples with known concentrations of analyte and by establishing the minimum level at which the analyte can be quantified with acceptable accuracy and precision.

need for it: in detection of several incidences or things like study of any diseases on people:

also Method detection limits are a relative measure of the performance of a particular lab, method or analyst. In many instances, the Department pools data from many sources prior to evaluating the data or making a compliance decision. Standardization in data reporting significantly enhances the ability of resource managers to interpret and review data because it is comparable. Reporting a method detection limit along with lowlevel data alerts data users of the known uncertainties and limitations associated with using the data. Data users in turn must understand these limitations in order to minimize the risk of making poor environmental decisions. Censoring data below unspecified or non-statistical reporting limits severely biases data sets and restricts its usefulness. This and can lead to erroneous decisions by data users when they calculate averages, mass balances or interpret statistics. A number reported as "<4" with no corresponding information is very difficult to interpret, and often must be discarded. Just like we were taught in grade school to turn in our homework because "zeros don't average", in analytical chemistry, "less-thans" don't average.

where to use it: in analytical chemistry. For example, it might be necessary to heat a sample that is to be analyzed for a particular metal with the addition of acid first (this is called digestion). The sample may also be diluted or concentrated prior to analysis on an instrument. Additional steps in an analysis add additional opportunities for error. Since detection limits are defined in terms of error, this will naturally increase the measured detection limit. This detection limit (with all steps of the analysis included) is called the MDL. The practical method for determining the MDL is to analyze 7 samples of concentration near the expected limit of detection. The standard deviation is then determined.