# Limit of Detection

For a gc method for limit of impurities, how to do a limit of detection experiment

what are the steps required

[quote=amithg3]For a gc method for limit of impurities, how to do a limit of detection experiment

what are the steps required[/quote]

I’d spike placebo at series of levels below your target level. There is no pass or fail at limit of detection. One would desire that the LOD and LOQ would be significantly lower than the typical level, ideally.

Dear Amith,

For GC Method validation determination of Limit of detection and Limit of quantitation based on 2 methods as per ICH and USP.

1. Signal to Noise Method: For this method Inject impurities at lower conc. and calculate the impurities signal to noise . Tipically for LOD S/N is 3:1 and for LOQ S/N is 10:1.
2. Standard deviation of the response and slope Method: For this method we have to prepare a minium of six different levels at lower concentrations.
Determine the slope and Residual standard deviation for the each impurity by using the peak area and concentration (ppm). Calculate the LOD and LOQ values by using the below formula.

LOD = 3.3 x Residual standard deviation(STEYX) / slope
LOQ = 10 x Residual standard deviation (STEYX) / Slope.

Regards,
srinivas.
8140780409.

Hi, now I performing analytic method validation including HPLC method.Can someone help me to calculate LOD and LOQ.When I calculate slope it always equal to 0. 3.3 x SD/0 is nonsense.What to do?

Dear arzakan,

I think you are wrong because it is not possible to slope value is 0.
Please try to calculate by using above formula and you will get LOD, LOQ values.
If not, Please share the values you have to found during the study.

Regards,
Srinivas.

[quote=srini1koduru]Dear arzakan,

I think you are wrong because it is not possible to slope value is 0.
Please try to calculate by using above formula and you will get LOD, LOQ values.
If not, Please share the values you have to found during the study.

Regards,
Srinivas.[/QUOTE

Slope can not be zero.

Usually steyx may become zero, this is possible only when lower levels you injected got the correlation 1, your standard error(steyx) becomes zero.
Therefore , you get LOD and LOQ Zero.

conc area
0.01 1000
0.02 2000
0.03 3000
0.04 4000
0.05 5000
slope 100000
Steyx 0
LOD 0
LOQ 0

you may type these values in excel and check slope and steyx

Regards,
Bujji Reddy Kanchi
9676749937

Dear Mr. bujji,
Practically it is imposible to obtained exact values. we are using the same method for many years. we don`t face this type of problem.

Regards,
Srinivas.

[quote=srini1koduru]Dear Mr. bujji,
Practically it is imposible to obtained exact values. we are using the same method for many years. we don`t face this type of problem.

Regards,
Srinivas.[/quote]

Dear srinivas,

You are right.

Practically steyx and slope never becomes zero.

I have given an example what are the possibilities of steyx becoming zero.

secondly,

If slope becomes zero, there is no absorbance, i.e the absorbance against a concentration should be zero. this is also not possible.

Hence slope and steyx practically can not be zero.

Hi, if slope never can not be zero, why when I process the integration slope shows zero.Our software is Empower for Waters HPLC.

Can you give the example for that.

Dear bujjikanchi can you write you email address so I can attach results with slope.You can see results in the attachment.

Summary by Linearity in Esmolol.pdf (67.3 KB)

System Suitability Summary1 in .pdf (65.6 KB)

Hi, who knows how to attach files here?

When you use the Quick Reply button, then click Go Advanced and then click the Manage Attachments button:

I edited my previous message here and now you can see results in the attachment.

from the chromatograms…when i plot the conc vs area…
conc area
0.13 214994.9
0.16 263586.4
0.19 317368.5
0.22 365880.3
0.25 421461.1
0.28 461535.6

here’s what excel gives the equation…
y = 2E+06x - 1807
R² = 0.9987
here in the slope = 2000000.

is this right>? approach to calculate the slope?

0.13 214994.9
0.16 263586.4
0.19 317368.5
0.22 365880.3
0.25 421461.1
0.28 461535.6

Here the excel gives. Please check once again.

y=50138x+16532
correl:0.999342

Regards,
Bujji Reddy. K
9676749937

where did you find the numbers 50138 and 16532.Today I tried to calculate slope by excel formula and nothing.

correlation of linearity in our result is 0,998685 it isn’t = to 0.999342

here’s the excel sheet which i worked out for the given data set…
now i have another basic query…why is there a difference between the trend line drawn using scatter plot and line chart?

book01.docx (13.0 KB)