Analysis of Caffeine by Immunoassay - Caffeine: Chemistry, Analysis, Function and Effects - page 225

Intra-day and inter-day precision was assessed, as displayed in Table 12.4,
by assaying the sample dilutions five times on the same day (intra-day) and
repeating them over 3 days in triplicate analysis (inter-day). Variations below a
10% threshold were typically obtained.
The accuracy and precision figures obtained, oaths the immunoassay a bright
perspective in industrial plants as process control and for quality control of the
final product. Its low-cost and high-throughput are matchless within available
analytical methods for assessing caffeine concentrations in liquid samples.
Within a few hours batches of 66 samples can be analyzed in a single microtitre
plate and, several plates can be run simultaneously. Furthermore, the cross-
bordering application of the immunoassay allows for the quantitation of
caffeine in several matrices other than beverages and consumer products.

d n 0 t 2 n g | 3

12.3 Final Considerations
Caffeine is produced by nature, consumed by humans and sent back to nature
through our home toilets. All along this cycle, caffeine concentration can be
measured using a single analytical tool, the proposed immunoassay, after some
adjustment regarding the calibration range selection and an appropriate
sample pre-treatment. Concerning beverages, a pre-treatment is required only
if samples contain CO 2 , which can be easily removed by bubbling an inert gas
like argon, for example. Having a calibration range adapted to the mgL 21
range, the immunoassay can ensure a caffeine-free status to some beverages, at
least below 1 mgL 21 caffeine.
The high-throughput of the assay associated with the low volumes of sample
required for testing (below 50 mL)—without compromising accuracy and
precision—constitute a major improvement in cost-saving for process quality
control in industrial plants and analytical laboratories.

Summary Points

N

This chapter focuses on immunoassay technique to quantify caffeine in
several aqueous sample types.

N

Caffeine concentrations as low as 1 microgram per liter can be determined.

N

The assay is robust, reliable, precise and accurate to verify caffeine content
in several beverages and other consumer products such as caffeine tablets
and shampoos.

N

No sample pre-treatment is required besides degasification (with carbon
dioxide containing beverages) and dilution in ultrapure water.

N

The assay is based on a commercially available monoclonal antibody.

N

A step-by-step description of the method is provided and it can be easily
performed in analytical labs possessing conventional immunoassay equip-
ment: 96-well microtitre plates, microtitre plate photometer (''reader''),
microtitre plate shaker and microtitre plate washer.