| Author | Message | ||
     Dr Neil J. Dominy (neil) Junior Member Username: neil Post Number: 7 Registered: 7-2003 |
Dr Balmurugan, Your check cell values are referenced against all others that have been measured since the check cell was set up. It is important then to know is it an outlier according to GH or T statistic. If it is GH then this should disappear within a couple of runs unless this part of your database has been contaminated with other samples (delete the contamination). If it is a T statistic then maybe your check cell needs to be replaced. It is much more important to run your diagnostic analysis on a daily basis. All instruments in my network have a time point at which no scans can be run until a full diagnostic analysis has been run and "passed". Hope this helps. | ||
| BALAMURUGAN RAMASAMY (suguna) New member Username: suguna Post Number: 2 Registered: 4-2006 |
Dr. Dave, It would be helpful for us to know what software you are using for the analysis? - The software we use is WINISI II. What does the red color you mention signify, according to your software manual? It mentions the outliers. How stable are your check samples? Only one is out from the expected value. Regards, Balamurugan Ramasamy | ||
| David W. Hopkins (dhopkins) New member Username: dhopkins Post Number: 84 Registered: 10-2002 |
Dr. Balamurugan, It would be helpful for us to know what software you are using for the analysis? What does the red color you mention signify, according to your software manual? Is it a particular number of standard deviations out from the expected value? How stable are your check samples? Perhaps if one is out from the expected value, it is okay, as long as the trend shows that the value is essentially the same as the last time you measured it. We can say more after we hear more details from you. Regards, Dave | ||
| balamurugan ramasamy (suguna) New member Username: suguna Post Number: 1 Registered: 4-2006 |
It would be really helpful to me when the following details are given. I am in the very begining stage of starting NIR analysis on poultry feed. I have FossNIR system 5000 with own equations developed for poultry feed. 1. Should the scaned check cell values always match with the values mentioned over the check cell given for reference? 2. While checking the Check cell value, if red colour value appear, can we proceed for routine analysis or not? 3. After routine analysis, we like to have a print out of all datas which is shown on the system like Sample Number, Product, ID line 1,2,3 and the columns like constituents, As received, Dry matter, Global H, Neighbour H, and T values. Currently, in the print out, we get only the constituents, As received data only. Expecting your help to make my NIR analysis succesful. Regards Dr.R.Balamurugan Suguna poultry Farm Ltd., India. [email protected] | ||
| Howard Mark (hlmark) Senior Member Username: hlmark Post Number: 17 Registered: 9-2001 |
Jack - the two techniques are so different that it's even difficult to compare them, so it's best just to consider the characteristics of each one. ATR - Attentuated Total Reflectance is the characteristic by which light, upon encountering an interface between materials of high and low index of refraction (from the high-index side of the interface) is completely (100%) reflected back into the high-index material, as long as there is no absorbance by either material. In the reflection process, a small electric field due to the light penetrates the interface, into the low-index material; this is called the evanescent wave in the low-index material. If the low-index material has some absorbance at the wavelength of the light, then energy can be absorbed from the evanescent wave, and the reflectance at the interface is reduced. This phenomenon has been used for a long time in the mid-IR spectral region as a way of measuring liquids and other materials that can be put into intimate contact with a high-index material, commonly prepared in a suitable form for such measurements, and called an ATR plate. Since the pathlength of the evanescent wave in the low-index material is very short, on the order of 1/4 to 1/2 wavelength of the light, the samples have to be highly absorbing; this is the reason the technique has been largely used in the mid-IR region. Attempts have been made to apply the technique to the NIR spectral region by enabling hundreds or thousands of reflections, but this has not enjoyed much usage. More recently, some instruments have been developed using diamond for the ATR plate, which is useful for solids since they can be pressed hard against the plate to create the intimate contact. For obvious reasons, the diamond "plates" are small, and therefore only very small samples can be measured this way. This is not necessarily a disadvantage, since oftentimes only very small samples are available, so the diamond ATR is a match to the small sample. On the other hand, it makes it difficult or impossible to get a representative sampling of inhomogeneous materials. Diffuse reflection, on the other hand, is eminently suited to measurement of inhomogeneous samples. Coupling the diffuse reflection measurement to the use of the near-infrared portion of the EM spectrum where the absorbtivity of most materials is small allows relatively deep penetration of almost any sample, when then automatically creates an effect of optically averaging the inhomogeneity of the samples. This technique is therefore eminently suited to measurements of inhomogeneous samples, when large amounts of sample are available and forms the basis for modern NIR analysis. NIR has other beneficial characteristics but to avoid making this message into a whole book, I will forebear a general discussion of NIR analysis. So to sumamrize, ATR is preferred when: Measurements are made in the mid-IR Samples are homogeneous Samples are small and diffuse reflectance is preferred when: Measurement are made in the near-IR Samples are inhomogeneous Large amounts of sample (or large samples) is available. Implementation of NIR/diffuse reflection is almost always done in conjunction with applying chemometrics to extract the useful information from the data. Chemometrics can also be applied to mid-IR/ATR measurements, but the data can also be analyzed via the classical "manual" methods. Howard \o/ /_\ | ||
| Jack (jack2006) New member Username: jack2006 Post Number: 1 Registered: 5-2006 |
What are the advantages of ATR over diffuse reflectance? Thanks. |