The VST syringe filters are expensive. I was wondering if anyone has figured out what the VST syringe filters specs are. Biomedical sells all types of filters for half the price.

As I recall they are 0.22um but also multistage, with a coarser filter material up front.

An alternative which apparently works well is a centrifuge.

I hadn't thought about that. It looks like a cheap centrifuge costs $50!

Just got my Atago. According to Socratic Coffee, syringe filters are overrated...

socraticcoffee.com/2015/07/measuring-total-dissolved-solids-a-refractometer-comparison-part-iii-espresso-filters/

So don't use them then.

But I'd be careful about coming to that conclusion from their limited tests. They didn't even say they were overated exactly. Rather, they suggested that you might "reconsider whether or not you really need to filter".

Take a look at their raw data. There weren't really enough samples to say with certainty but they look a bit noisier. And they are very obviously different in absolute value, although the trueness of the measured value may not matter to you.

Go buy some lab grade milipore filters and filter as you want. You can buy them in multiple sizes and porosity.

Do you have a link? These look even more expensive that VST filters.

jpender wrote:So don't use them then.

But I'd be careful about coming to that conclusion from their limited tests. They didn't even say they were overated exactly. Rather, they suggested that you might "reconsider whether or not you really need to filter".

Take a look at their raw data. There weren't really enough samples to say with certainty but they look a bit noisier. And they are very obviously different in absolute value, although the trueness of the measured value may not matter to you.

I didn't look at the raw data yet, but if I remember correctly, the Atago behaved better than the VST refractometer without filters. Since I have an Atago, I might skip the filters.

Milipore is the source for many different lab grade filters and filter paper. What is available and at what cost I have not looked into. Once you get a part number then googling that number usually finds the bargain price if ther is one. Filter syringes will be expensive while filter paper and a funnel are much lower cost.

felyko wrote:I didn't look at the raw data yet, but if I remember correctly, the Atago behaved better than the VST refractometer without filters.

It behaved better in the sense that repeated measurements of a particular sample produced less variation in the results. But both the VST and Atago devices reported values that were very different than the filtered values. And the differences were not consistent from sample to sample. That is, sometimes they read a lot higher than the filtered value, sometimes a lot lower. So while you may not care about the absolute value of the reading it should concern you if you aren't getting consistent values from shot to shot. That's kind of the point, isn't it?

For example, the unfiltered sample 1 measured about 0.3% TDS lower than sample 4. But when filtered, sample 1 measured 1.3% higher than sample 4.

The filtered method is what has been validated by VST against dehyration. Unfiltered is an unknown. If you're going to go that route, or try something else like a centrifuge or filter papers, it makes sense to spend the time and validate that approach yourself.