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Instrument Operation
A suitable barcode scanner is available from Advanced Instruments. To
interface with the 4250, the barcode scanner must be programmed as
follows, referring to the scanner users guide.
1200 bps
CR suffix
disable beep after good decode
triggerless trigger mode (optional)
Sample preparation
No special sample preparation is required. If whole milk is to be tested
and has separated, sampling from the low-fat portion gives more repeat-
able results; congealed liquids can randomly cause premature crystal-
lization of the sample, also referred to as a “Sample Pre-Freeze”.
If premature crystallization is occurring because of congealed liquids in
the sample, the problem may be alleviated by pre-warming the samples
to 40°C for 5 minutes, but note that, for calibration accuracy, the stan-
dards should be pre-warmed as well.
Particulate matter can also cause premature crystallization. Both particu-
late matter and congealed liquids may be removed by filtration through
an inert filter, or by centrifugation of the sample.
Sample handling
Different sample tube styles and sample sizes should not be intermixed
because each may require a different instrument adjustment and/or cali-
bration. Sample tubes should be as uniform as possible in composition,
shape and size.
Samples should always be pipetted or measured; 2.5-mL or 2.0-mL
samples may be used in Advanced Instruments sample tubes. To
achieve the specified performance, we recommend that you use 2.5-mL
samples; 2.0-mL samples require somewhat more critical probe and
stir/freeze wire adjustments for similar precision in results. The 4250
should be calibrated with the same sample size used for testing.
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