Reg. Hplc standard curve calculation.
Please tell me how to calculate limit of detection, limit of quantification and signal to noise ratio. Please also explain what is the relation of these parameters with each other. Usually in papers it is mentioned that LOD and LOQ were measured based on signal to noise ratio at about 3 and 10, respectively?
LOD (limit of detection)
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 reliably detected.
Based on Signal-to-Noise Approach: Determination of the signal-to-noise ratio is performed by comparing measured signals from samples with known low concentrations of analyte with those of blank samples and by establishing the minimum concentration at which the analyte can be reliably detected. A signal-to-noise ratio between 3 or 2:1 is generally considered acceptable for estimating the detection limit.
Based on the Standard Deviation of the Response and the Slope: The detection limit (DL) may be expressed as:=3X STANDRD DEVIATION OF LOW CONCEN/ SLOPE OF THE CALIBRATION LINE
LOQ (limit of quantification)
The quantification limit of an individual analytical procedure is the lowest amount of analyte in a sample which can be quantitatively determined with suitable precision and accuracy. The quantification limit is a parameter of quantitative assays for low levels of compounds in sample matrices, and is used particularly for the determination of impurities and/or degradation products.
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.
Based on Signal-to-Noise Approach: Determination of the signal-to-noise ratio is performed by comparing measured signals from samples with known low concentrations of analyte with those of blank samples and by establishing the minimum concentration at which the analyte can be reliably quantified. A typical signal-to-noise ratio is 10:1.
Based on the Standard Deviation of the Response and the Slope: The quantitation limit (QL) may be expressed as: 10XSTANDRD DEVIATION OF LOW CONCEN/ SLOPE OF THE CALIBRATION LINE
Dear Praveen LOD and LOQ are the smallest amount of the particular compound that can by detected and quantiified by using the developed HPLC method.
The signal to noise ratio is that minimum amount which when injected in HPLC it gives minimum detectable peak area.
The value of amount at this point is multiplied by 3 to get LOD
and by 10 to get LOQ value. In short LOD is the thrice value of minimum value and LOQ is ten times of minimum value that can be injected in HPLC.
LOD= mean blank value x 3 s
LOQ= LOD x 3 (or x5, x6 or x10, this is depend on you)
If you measure some signal it should have some natural variation. You could make a frequency table with the data readings which will give approximately a Gauss normal distribution centered at media and with a spread at 95% of its values of 2.6 SD (standard deviation). To this you call noise. A value outside of the 2.6 x ( +- 3) relatively to the medium value is not noise - is a signal. The factor of 10 for LOQ is to ensure a clear signal from noise, with a good safe margin for things like drifts.
Your instrument software should have a tool to calculate the signal to noise ratio. For GLP analyses, the suggested minimum value is 10, although you can opt for another value in your SOP. The LOQ is the lowest point on your calibration curve which meets the specified S/N ratio. Notably, concentrations below the low calibrator should not be reported regardless of what the S/N ratio is. The LOD is of little practical use anymore in regulated work.
LOD (limit of detection)
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 reliably detected.
Based on Signal-to-Noise Approach: Determination of the signal-to-noise ratio is performed by comparing measured signals from samples with known low concentrations of analyte with those of blank samples and by establishing the minimum concentration at which the analyte can be reliably detected. A signal-to-noise ratio between 3 or 2:1 is generally considered acceptable for estimating the detection limit.
Based on the Standard Deviation of the Response and the Slope: The detection limit (DL) may be expressed as:=3X STANDRD DEVIATION OF LOW CONCEN/ SLOPE OF THE CALIBRATION LINE
LOQ (limit of quantification)
The quantification limit of an individual analytical procedure is the lowest amount of analyte in a sample which can be quantitatively determined with suitable precision and accuracy. The quantification limit is a parameter of quantitative assays for low levels of compounds in sample matrices, and is used particularly for the determination of impurities and/or degradation products.
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.
Based on Signal-to-Noise Approach: Determination of the signal-to-noise ratio is performed by comparing measured signals from samples with known low concentrations of analyte with those of blank samples and by establishing the minimum concentration at which the analyte can be reliably quantified. A typical signal-to-noise ratio is 10:1.
Based on the Standard Deviation of the Response and the Slope: The quantitation limit (QL) may be expressed as: 10XSTANDRD DEVIATION OF LOW CONCEN/ SLOPE OF THE CALIBRATION LINE
Dear Praveen,
Colleagues had written before me the meaning of LOD and LOQ. There are three ways of determining these parameters 1) based on visual evaluation, 2) based on signal to noise ratio, 3) based on standard deviation of the response and slope.
ICH gives detailed procedures to obtain these parameters, you can download the free PDF at
http://www.ich.org/products/guidelines/quality/article/quality-guidelines.html
(Analitical Validation Q2)
Good luck!
Bedigama Kankanamge Kolita Kamal Jinadasa
sir can you say what is the mean blank value
respected All please tell me if our concentration range is 2-10 mM than how LOD
is coming in micromolar range
The real answer is to be found in reference:
Clinical and Laboratory Standards Institute. Protocols for Determination of Limits of detection and Limit of Quantitation, Approved Guideline. CLSI document EP17. Wayne, PA USA: CLSI; 2004.
Dear Praveen Dhyani,
I think that this file can help you for understanding.
Best Wishes,
What I understood is that the concentration of analyte which has S/N = 3:1 or 2:1 is concentration of Limit of Detection. Am I correct? If so, should I gradually lower the concentration until S/N reach 3:1?
OK Here is my curve and data .... LOD=3*STEYX/Slope .... but what are the units?
Detection and Quantitation Limits (LOD and LOQ)
There are several terms that have been used to define LOD and LOQ. In general, the LOD is taken as the lowest concentration of an analyte in a sample that can be detected, but not necessarily quantified, under the stated conditions of the test. The LOQ is the lowest concentration of an analyte in a sample that can be determined with acceptable precision and accuracy under the stated conditions of test. [9]
Although reagent package inserts may state that an assay has a dynamic range that extends from zero concentration to some upper limit, typically an assay is simply not capable of accurately measuring analyte concentrations down to zero. Sufficient analyte concentration must be present to produce an analytical signal that can reliably be distinguished from "analytical noise," the signal produced in the absence of analyte. [10]
However, some common methods [11] for the estimation of detection and quantitation limit are
Visual definition
Calculation from the signal-to-noise ratio (DL and QL correspond to 3 or 2 and 10 times the noise level, respectively)
Calculation from the standard deviation of the blank
Calculation from the calibration line at low concentrations
Where
F: Factor of 3.3 and 10 for DL and QL, respectively
SD: Standard deviation of the blank, standard deviation of the ordinate intercept, or residual standard deviation of the linear regression
b: Slope of the regression line
The estimated limits should be verified by analyzing a suitable number of samples containing the analyte at the corresponding concentrations. The DL or QL and the procedure used for determination, as well as relevant chromatograms, should be reported.
Signal- to-noise
By using the signal-to-noise method, the peak-to-peak noise around the analyte retention time is measured, and subsequently, the concentration of the analyte that would yield a signal equal to certain value of noise to signal ratio is estimated. The noise magnitude can be measured either manually on the chromatogram printout or by auto-integrator of the instrument. A signal-to-noise ratio (S/N) of three is generally accepted for estimating LOD and signal-to-noise ratio of ten is used for estimating LOQ. This method is commonly applied to analytical methods that exhibit baseline noise. [11]
For chromatography a test sample with the analyte at the level at which detection is required or determined is chromatographed over a period of time equivalent to 20 times the peak width at half-height [Figure 1]. The signal-to-noise ratio is calculated from Equation (1).
Figure 1: Signal-to-noise examples of 10:1 (top) and 3:1 (bottom), using the method of the EP
Click here to view
where H is the height of the peak, corresponding to the component concerned, in the chromatogram obtained with the prescribed reference solution, and measured from the maximum of the peak to the extrapolated baseline of the signal observed over a distance equal to 20 times the width at half-height h is the peak-to-peak background noise in a chromatogram obtained after injection or application of a blank, observed over a distance equal to 20 times the width at half-height of the peak in the chromatogram obtained.
This approach is specified in the European Pharmacopoeia. [5] It is important that the system is free from significant baseline drift and/or shifts during this determination.
[Figure 1] shows examples of S/N ratios of 10:1 and 3:1 which approximate the requirements for the QL and DL, respectively. This approach works only for peak height measurements.
Blank determination
It is assumed that they both have the same variance and are normally distributed. As the curves overlap there is a probability that we could conclude that we have detected the analyte when this is in fact due to the blank signal (false positive, α error or type 1 error). Alternatively, we can conclude that the analyte is not detected when it is in fact present (false negative, β error or type 2 error). When addressing the issue about when an analyte has been detected it is always a matter of risk. [11]
The blank determination is applied when the blank analysis gives results with a nonzero standard deviation. LOD is expressed as the analyte concentration corresponding to the sample blank value plus three standard deviation and LOQ is the analyte concentration corresponding to the sample blank value plus ten standard deviations as shown in the following equations:
LOD=Xb1 +3Sb1 ,
LOQ=Xb1 +10Sb1 ,
where Xb1 is the mean concentration of the blank and Sb1 is the standard deviation of the blank. This is a simple and quick method. The weakness is that there is no objective evidence to prove that a low concentration of analyte will indeed produce a signal distinguishable from a blank (zero concentration) sample. [9]
Linear regression
For a linear calibration curve, it is assumed that the instrument response y is linearly related to the standard concentration x for a limited range of concentration. [9] It can be expressed in a model such as
y=a+bx.
This model is used to compute the sensitivity b and the LOD and LOQ. Therefore, the LOD and LOQ can be expressed as
LOD=3S a/b,
LOQ=10S a/b,
where S a is the standard deviation of the response and b is the slope of the calibration curve. The standard deviation of the response can be estimated by the standard deviation of either y-residuals, or y-intercepts, of regression lines. This method can be applied in all cases, and it is most applicable when the analysis method does not involve background noise. It uses a range of low values close to zero for calibration curve, and with a more homogeneous distribution will result in a more relevant assessment.
Limit of blank
LoB as the highest apparent analyte concentration expected to be found when replicates of a sample containing no analyte are tested. Note that although the samples tested to define LoB are devoid of analyte, a blank (zero) sample can produce an analytical signal that might otherwise be consistent with a low concentration of analyte. LoB is estimated by measuring replicates of a blank sample and calculating the mean result and the standard deviation (SD). [2]
LoB=mean blank +1.645(SD blank )
After calculating this value LOD can be calculated according to LOD=LOB+1.645(SD low concentration sample ).
Precision-based approaches
The quantitation limit can also be obtained from precision studies. [10],[11] For this approach, decreasing analyte concentrations are analyzed repeatedly and the relative standard deviation is plotted against the corresponding concentration (precision function). If a predefined limit is exceeded (such as 10% or 20%), the corresponding concentration is established as the quantitation limit However, in practice, due to the high variability of standard deviations the true precision function is much more difficult to draw unless a large number of concentrations is included.
The QL can be specifically calculated [11] using the actual precision of the analytical procedure at this concentration. The calculation is based on the compatibility between analytical variability and specification acceptance limits. QL can be regarded as the maximum true impurity content of the manufactured batch, i.e., as the basic limit
AL Acceptance limit of the specification for the impurity.
s Precision standard deviation at QL, preferably under intermediate or reproducibility conditions. AL and s must have the same unit (e.g., percentage with respect to active, mg, mg/ml, etc.).
Nassay Number of repeated, independent determinations in routine analyses, as far as the mean is the reportable result, i.e., is compared with the acceptance limits. If each individual determination is defined as the reportable result, n=1 has to be used.
tdf Student t-factor for the degrees of freedom during determination of the precision, usually at 95% level of statistical confidence.
How do you calculate the uncertainty of LoD and LoQ?
ex. LOD=0.31+/- 0.16
LOQ=1.05+/-0.16
I only know how to compute for 0.31=3.3 s/slope and 1.05=10s/slope.
Does anyone here knows the formula for added uncertainty in the equation?
Thank you.
http://www.ema.europa.eu/docs/en_GB/document_library/Scientific_guideline/2009/09/WC500002662.pdf
How to calculate limit of detection, limit of quantification, standard deviation of the intercept and the standard deviation of the response for spectrophotometric analysis? Thank you very much.
I would like to express my opinion. I think that an important high-recovery analysis in HPLC-photometric detection is only performable by using the gradient elution method (please see files; Lysozyme by RP-HPLC, Insulin RP-HPLC and PTH Roma RP-HPLC).
Peak height may change in response to gradient time and gradient method. Then, parameters for use in notorious isocratic elution (limit of detection, limit of quantification and signal to noise ratio) are not so important issues. Most important issue is to measure the recovery value from the column to obtain the reliable and reproducible high-recovery analysis.
I was amassed by all the answers and YES, every single one was contributing to the its perfection . Thank you very much to all.
I think this video is helpful..
https://www.youtube.com/watch?v=F2Pvt6HHZs4
Dharam, You haven't given enough information to possibly answer if you did the calculations correctly. However, as has been said multiple times in the thread, LOD is of marginal interest at this point and as a practical matter LOQ is your lowest passing calibrator that has been validated.
Excellent OECD guidance docs are available in case of pesticide residue estimation to define LOD and LOQ.
You can follow the ICH guidelines on this matter (see attached). It is very straight-forward.
Your LOD is the lowest amount of your analyte that can be statistically discriminated from zero concentration. S/N can approximate this but a S:N of 2 may allow blank injections to quantitate noise. see the following reference:
A. Hubaux, G.Voss, "Decision and detection limits for linear calibration curves" Anal.Chem. 42 (1970) 849-855. Noise can be calculated in many ways and most of us are doomed to use what ever calculation is in our software. The best method I have used is the ASTM E685. Take the noise of five areas of baseline (usually 1 minute each) and average them. Agilent Chemstation used this method.
There are three ways of determining these parameters 1) based on visual evaluation, 2) based on signal to noise ratio, 3) based on standard deviation of the response and slope.
More info pls visit the following link:
http://www.ich.org/products/guidelines/quality/article/quality-guidelines.html
Dear All,
You all have done good discussion on reporting analytical limits. I feel that you can report method detection limit (MDL) for your method (instead of LOD and LOQ). Then you can conveniently report your results. Also you can apply this method for any analytical method. Please go through EPA method.
Also you can fiend some applications in text given below:
Data hPLC doc
Article Determination of Pesticide Residues in Water by Solid Phase ...
Regards
Piyal
Hi. how to get LOD if i have a linear graph of wavelength shift vs concentration?
LOD is equal to 3 SIGMA IS ESTIMATE OF DETECTION LIMIT DO = 3× sigms/ M where Sigma = y intercept from calibration curve M = slope of the calibration curve for example DL= 3× 20712.54/ 29475.00 LOD = 0.0002% hope you are understand Good luck
We just published a paper in Sensors about this interesting topic. We hope that our work will help some of the people who raise doubts in this forum.
We attach some links to the paper.
www.mdpi.com/1424-8220/18/7/2038/pdf
Article On the Determination of Uncertainty and Limit of Detection i...
Hello J.M. Campiña,
I'm going to try to answer your second question "How will you connect XL with its corresponding CL (as CL is the LOD)? "
Let's begin supposing you know exactly (without uncertainty) the calibration curve X=f(C) where X is the signal provided by the measuring device and C is the concentration being measured.
If you know, without uncertainty, the function X=f(C) you will know, also without uncertainty, b=f(C=0) and a=f'(C=0) where f'(C=0)=df/dC at C=0. Please note that b would be XL,ab. Around C=0 you could approximate X=f(C) using the linear function X=b+a*C which implies C=(X-b)/a.
So, you would estimate CL using the following expression:
CL = (XL-b)/a = [ (XL,ab+k*SDb) - XL,ab ] / a = k*SDb/a
But things are actually more complicated: you know the calibration curve WITH UNCERTAINTY, so this uncertainty affects the LOD. If you takes into account the uncertainty of the calibration curve then LOD becomes higher.
We have published recently a review paper about that:
Article On the Determination of Uncertainty and Limit of Detection i...
In page 9 of that paper (equation 32) you can find an expression that permits to estimate LOD taken into account the uncertainty of the calibration curve and the resolution of the measuring device.
Best Regards
In the attached file you can find a Review article which provides information relating to the calculation of the limit of detection and limit of quantitation, as well as brief information about differences in various regulatory agencies about these parameters.
LOD is 3 times Signal to Noise ratio (S/N) and LOQ is 10 times S/N.
Could you please explain me what is this"standard deviation of response" means? Can it be" standard deviation of target concentration"
I recommend you to read this paper: Article On the Determination of Uncertainty and Limit of Detection i...
Best
I think following are the expression and definition for your query:
The limit of detection (LOD) is a measure of how sensitive the analytical method is. LOD = the smallest quantity of analyte that is “significantly different” from the blank.
A variety of methods exist to measure LOD:
LOD = 3 x Signal/Noise
The limit of quantitation (LOQ) is the smallest quantity of analyte that can be measured with ‘acceptable’ accuracy and precision.
A variety of definitions exist for LOQ:
LOQ = 10 x Signal/Noise
There are many methods for determining a limit of detection. IUPAC specifies three times the standard deviation of the baseline above the baseline. However, no matter which method you choose, you should validate your LOD by preparing a standard at that concentration or mass and ensuring that you can RELIABLY detect it, i.e., in more than one trial or sample.
Dear Drs all i have analysed sample as per ICH Guideline of the plant raw mar trail.
Detection Limit: (LOD) is equal to 3σ is a good estimate. The equation of Detection Limit (DL) can be expressed as
DL = 3 σ
M
Where σ= y-intercepts from calibration curve
M= slope of the calibration curve
DL = 3x20712.54
29475.000
LOD for picroside I is = 2.1 ppm
= 0.0021 mg/ml
= 0.0002 %
LOD for picroside II = DL = 3x31150
30845.16
= 3.02 ppm
= 0.003 mg/ml
= 0.0003%
Quantitation Limit: (LOQ) is equal to 10σ is a good estimate. The equation of Quantitation Limit (QL) can be expressed as
QL= 10σ
M
Where σ= y-intercepts from calibration curve
M= slope of the calibration curve
QL= 10 x 20712.54
29475.00
LOQ for Picroside I is = 7.0 ppm
= 0.007mg/ml
= 0.0007.0%
QL= 10 x 31150
30845.16
LOQ for Picroside II is = 10 ppm
= 0.01 mg/ml
= 0.001%
To calculate signal to noise ratio you need to calulate the height of the noise signal of your baseline (h) and height of your peak (H) when you add your analyte. The height here means substructing min value from max value of your signal.
Then you calculate S/N as:
S/N=2H/h
This works if you have a peak in your method.
Every method of analysis has inbuilt characteristics that allow the signal of an analyte of interest to be picked-up by the method, only above a minimal level that is 3 times the noise level of the method. This is LOD of the method for the specific analyte. Similarly, LOQ is 10 times that of the noise. All modern instruments have the capability to calculate these automatically.
lod is :LOD = 3.3 σ/S
σ = Standard deviation of Intercepts of calibration curves
S = Mean of slopes of the calibration curves
It is the lowest concentration of the analytics that the device can measure
It is the lowest concentration that the method can detect or quantify. There is no standard way to calculate.
http://www.cysonline.org/article.asp?issn=2229-5186;year=2011;volume=2;issue=1;spage=21;epage=25;aulast=Shrivastava
Article Limit of detection and limit of quantification development p...
Limit of detection is three times of standard deviation, while the limit of quantification is 10 times of standard deviation.
Dear Dr. Dhyani numbers of Reserchers give very simple answares with examples. i also already attached file.
Detection Limit: (LOD) is equal to 3σ is a good estimate. The equation of Detection Limit (DL) can be expressed as
DL = 3 σ
M
Where σ= y-intercepts from calibration curve
M= slope of the calibration curve
DL = 3x20712.54
29475.000
LOD for picroside I is = 2.1 ppm
= 0.0021 mg/ml
= 0.0002 %
LOD for picroside II = DL = 3x31150
30845.16
= 3.02 ppm
= 0.003 mg/ml
= 0.0003%
Quantitation Limit: (LOQ) is equal to 10σ is a good estimate. The equation of Quantitation Limit (QL) can be expressed as
QL= 10σ
M
Where σ= y-intercepts from calibration curve
M= slope of the calibration curve
QL= 10 x 20712.54
29475.00
LOQ for Picroside I is = 7.0 ppm
= 0.007mg/ml
= 0.0007.0%
QL= 10 x 31150
30845.16
LOQ for Picroside II is = 10 ppm
= 0.01 mg/ml
= 0.001% this just example
Limit of Detection is equal to 3 times of standard deviation and limit of Quantification is equal to ten times of standard deviation.
Limit of detection (LOD) is the lowest concentration of analyte that can be detected by an instrument. The signal (peak) for LOD should have a signal-to-noise ratio (S/N) of 3. On the other hand, limit of quantification (LOQ) is the lowest quantifiable concentration of your analyte and should have a S/N of 10.
Use the following formulae
LOD = 3 σ/S
σ = Standard deviation of Intercepts of calibration curves
S = Mean of slopes of the calibration curves
LOQ = 10 σ/S
σ = Standard deviation of Intercepts of calibration curves
S = Mean of slopes of the calibration curves
Limit of detection (LOD) and limit of quantification (LOQ) are two important performance characteristics in method validation. LOD and LOQ are terms used to describe the smallest concentration of an analyte that can be reliably measured by an analytical procedure
Sample answers along with examples already send me 26 April of this years you can used if any problem send my mail id
Dr Panikumar Durga Anumolu completely answered your question
I agree with Dr P. D. Anumolu for his detailed answers, To me it is enoughthank you sir for your wise explanations.
The LOD was calculated as𝐿𝑂𝐷=10(𝑌+3𝑆𝐷)―𝐴/𝐵
Y= Y blank + 3SD
what are the basis for this equation to calculate the LOD?
In general the others have answered most applied are the curve or S/N ratio based LOQ/LOD calculations.
However pay attention since some specific fields may have special method validation and evaluation criterias. Especially important areas, for example regarding pesticide residue analysis there may very well be special rules in effect, since accredited or GLP environment measurements can cause legal and safety issues. I decided for fun to ellaborate on through an example since as a person who works now in research I frequently apply QC techniques I learned at other areas for my research oriented measurements to ensure scientific accuracy and method quality control and good data quality. I'm personally feel attached to pesticides from my past, so in my post I'm going to look at this issue from the angle of pesticide residue analysis for fun and for your consideration as a food for thought.
There is a general guideline (concerning GLP experiments there are separate more extensive, strict specific guidelines) method validation and quality control good practice proposal called SANTE/11813/2017 in the European Union. (https://ec.europa.eu/food/sites/food/files/plant/docs/pesticides_mrl_guidelines_wrkdoc_2017-11813.pdf ) for calibratons, ion ratios in MS, and also for LOD-LOQ considerations! It is a good idea to read this document I advise it for all analyst as a food for thought. I have found it to be very handy for method assessment regarding other analytical fields in relation to compelx matrices and LC/GC-MS tecniques relatad to other fields, such as targeted quantitative metabolomics for example.
More specificly, in the case of pest residues general LOQ calculations does not apply. Regarding pesticides LOQ of a method has to be estabilished by recovery from at least / representative matrix commodity at the desired LOQ level (5times) and 2-10X of the LOQ (also 5 times). Preferrably a previously measured blank commodity sample has to be used for recovery experiments where no more than 20-30% of the tartget LOQ can be found. The recovery has to be between a certain range and RSD even during QC-s after expanding the uncertainty of the initial and day to day and re-validations continously collected, registered and evaluated at the analyte control chart of a lab where every year at least one recovery test at LOQ and 2-10X LOQ / representative commodity has to be tested in the lab during routine work distributed in a rolling program to continuosly produce evidence of that the necessary LOQ can be roboustly maintained regularly. (And of course we won't say anything regarding lab ring tests so called prficiency tests, that is another topic, but connects here and it's important!)
So i you want to have a low LOQ of lets say 1ppb then, you have to get a "blank" commodity lets say a batch of avocados would be a high fat content plant matrix, a lemon would be high water and acid type matrix, an apple could be high water content, and a liver sample can be animal origin. In pestresidue analysis there are many more matrices and representative commodites. Spo once again stating for at least each representative commodity group you have to make a spike level at desired LOQ and at 2-10x LOQ also to demonstrate linearity of recovery. That will be the official LOQ of your method. Its also important that no method on this field can be acceptable where LOQ is not as low at least as the corresponding allowed maximum residue limit regarding an analyte and a commodity. So if MRL is 10ppb your LOQ has to be at least 10ppb preferably at least 5. There are many more detailed rules, especially for compounds that have metabolites, MRL could be that the residue definition will say: Analyte X and all related metabolites, isomers, etc experessed as compund X. That would mean if you have a compound with 3 metabolites that have a conversion factor of 1 for original compund X where compound X's residue definition woud say X+metabolites expressed as X where MRL=10ppb, than individually for X and for metabolites you would need an LOQ of 2.5ppb to maintain the required LOQ as sum expressed based on the residue definiton. Tricky on since some compounds can have +6-8 metabolites forcing the analyst to go down one order of magnitude in required LOQ, which can be an issue especially with older instruments. And lets not forget to state measurement uncertainty also, when giving our finaly result report. There are someitmes multiple approaches for calculating or estimating MU, even in pest residue analysis. Anyone took time to read this "short" example, please have my gratitude and thanks for letting me sharing the basics and my curiosity for this field's speciality and complexity.
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