The most of time we can get certified reference materials (CRMs) in order to demostrate the method is accurate, but there isnt exists one for biogenic silica. may be a intercalibration excercise? someone have samples of known concentrations?
yes, it is the silicon which can be incorporated in the frustules and it can be extracted by alkaline treatment.
After struggling with the reproducubility of the method for several months, we discovered that one of the critical factors was matching the matrix for the spectrophotometric analysis of the dissolved silicate, i.e., make sure the sodium concentration in your silicate standards (calibration curve) is the same as in your samples.
You can use Sodium fluorosilicate (Na2SiF6) as a primary standard to create a standard curve with your spectrophotometer. See below. Given the accuracy of this method this is adequate. If you have material you have run in the past when you used a CRM run it as an in-house standard if you have enough of it and it is reproducible. If you only have a small amount of material purchase some diatomite and calibrate against something you know and then you will have a larger stock on in-house standard. Not perfect, but at least from batch to batch you know if you are going astray.
Primary silica standard: dissolve 0.5642 g in a Nalgene 1 liter volumetric flask fill to 1 liter with Nanopure/Milli-Q water. Dissolution is slow, so allow at least 30 minutes. This cannot be rushed. The concentration of this standard is 3000 µmoles Si/liter. Store in a 1000 ml Nalgene bottle. Standard is stable indefinitely. The below concentrations should cover your range.
a. Dilution from primary standard: when making a dilution, use Nanopure/Milli-Q water and store in Nalgene bottles. Using a 50 ml Nalgene volumetric flask, add the following amounts of primary silica standard and then bring the volume to 50 ml total.
30 µM Si - 0.5 ml of primary Si std.
60 µM Si - 1.0 ml of primary Si std.
120 µM Si - 2.0 ml of primary Si std.
240 µM Si - 4.0 ml of primary Si std.
360 µM Si - 6.0 ml of primary Si std.
480 µM Si - 8.0 ml of primary Si std.
600 µM Si - 10.0 ml of primary Si std.
900 µM Si - 15.0 ml of primary Si std.
1200 µM Si - 20.0 ml of primary Si std.
Hello everybody, thanks for your comments
For cuantitative determination we are using flame ionization atomic apsortion spectrophomotometry , and we use the calibration curve prepared from a certified solution of sodium silicate (merck). ( it means the curve is prepared as dissolved silicon, not as biogenic silica)
we extract the biogenic silica using alkaline treatment ( biogenic silica become dissolved silicon) and then we analyze the extract ( dissolved silicon) .
The problem is to ensure a good recuperation percentage (in alkaline extraction) from a known value of BIOGENIC silica , NOT TOTAL SILICON or DISOLVED SILICON Neither, because we are no interested about inorganic sources. There is CRM for Total Silicon, but theres not for biogenic silica : this is the problem.
maybe somebody has samples which have been analyzed several times, whose value of concentration (biogenic silica) can be considered as a reference,
.
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