SW-846 analytical batches

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

9 posts Page 1 of 1
Those of you who use SW846 methods - how do you define the "Batch" time window for QC purposes? In a low volume situation can you get away with extending it over multiple days as long as your instrument QC is good?


The glossary gives this definition:

A group of samples, including quality control samples, which are
processed together using the same method, the same lots of reagents,
and at the same time or in continuous, sequential time periods.
Samples in each batch should be of similar composition and share
common internal quality control standards. For QC purposes, if the
number of samples in a batch is limited to 20; laboratory QC samples
are not included in the batch count.
Each batch should be uniquely identified within the laboratory for
tracking purposes. Samples collected from the same site would
normally be grouped together for batching purposes within the
constraints imposed by the method holding times and batch size.
Samples prepared in the same batch would normally be analyzed
together on a single instrument. However, laboratories may find it
necessary to group multiple clients’ samples into a single batch. Under
these circumstances, additional matrix QC samples (i.e., duplicates,
matrix spikes) may be needed to evaluate the effect of the matrix from
each site on method performance.
I'm not an authority on this subject, but it has always been my understanding that a batch can run for several days as long as the instrument QC stays in spec. Of course, the batch ends after 20 samples.
Don Shelly
LGC Standards
The batch definition covers a group of samples and can be either preparation, analysis or both. There is no time frame imposed except that they have to be processed as a group.
it has been my experience that the analyst's interpretation of the method and the data reviewer/auditor's interpretation can be widely divergent... when in doubt, I just start a new batch, even if there are only 2 or 3 samples.
Hm, ok. I typically only have to run 8270 on a single sample monday, wednesday, and friday. Basically the same matrix with slight variations. It seems a little disheartening to have to do so many QC samples for so few analytical samples. Problem is we can't group them because we need quick turnaround (16 hours if they are clean, but if they are above LDR limits we want to know asap), and unfortunately the samples show up ~11 pm when we only have one guy on staff.

Not to mention... I'm afraid of the 3 am phone calls that this could lead to... :P
A single batch over multiple days defies logic- are the conditions going to be exactly the same for the whole week? But you're right, the EPA methods do not define a time frame. However, I doubt an auditor is going to let that fly. For example, in PA
Batch, preparation—A batch composed of 1 to 20 environmental samples of
the same matrix with a maximum time between the start of processing of the
first and last sample in the batch to be 24 hours.

NELAC also defines a batch as 24 hours- just the nature of the business to produce defensible data.
The confusing "batch" definition is a holdover from old 625 days, when you ran QA on a "batch" basis of once every 20 samples. Since each sample contained surrogate standards and 625 was quite matrix specific (wastewater) the EPA used to feel that matrix spikes, etc. could be run once every 20 samples or once a month. This unfortunately carried over into SW-846 since the SW-846 methods really aren't new methods but just re-writes of the old 625 methods.

NELAC is quite specific; you define batches based on the extractions performed in a 24 hour period. Note that the analysis can be comprised of multiple batches, as long as you meet the 12 hour tuning and continuing calibration criteria.
Mark Krause
Laboratory Director
Krause Analytical
Austin, TX USA
I don't recall SW-846 using the term batch. I recall most QC and validation requirements having to be repeated for either specific time intervals, or between a specified number of analytical runs.
The new versions of 8270E and 8260D (coming this summer to a website near you) have the term "batch" used more in line with TNI standards and include both analytical and preparation batches.
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