Common Operations and Wet Chemical Methods in Environmental Laboratories - Fundamentals of Environmental Sampling and Analysis - page 129

Immediately after each use, soak dirty glassware in a 2% hot detergent
solution. Do not use household detergent, but use commercially available
laboratory detergents such as Alconox or Liquinox for a detergent wash.
Brush thoroughly to clean-up obvious residuals but avoid scratch. A
detergent wash should not be used if a surfactant is the analyte of interest.
For metal anlaysis, prepare an acid bath using 10-15% HNO 3 (except for N
analysis), or 10-15% HCl for labwares. An acid rinse should not be applied
to metallic items such as caps, spatulas, and brushes with metal parts.
For trace organic analysis, use wash bottles filled with pesticide-grade
isopropanol, acetone, or methanol to thoroughly rinse the glassware. Acetone
is the most commonly used.
In between detergent wash and acid or acetone wash, use running hot tap
water to allow the water to run into and over the labware for a short time, and
then fill each item with water, thoroughly shaking and emptying at least three
times. After acid or acetone wash, use reagent water (Section 6.1.2) to rinse
at least three times.
Once labware is properly cleaned, dried, and stored in a location that
prevents contamination from airborne dust or other particles, air-dry test
tubes, culture tubes, and flasks are hanged in a basket with their mouths
facing downward over folded paper towels. If oven drying is used, do not
exceed over 140 C for glassware or 60 C for plasticware. Never oven dry
burets, pipets, or volumetric flasks as their measuring accuracies will be
affected.
In biological work, glassware (serology tubes, Petri dishes) contaminated
with blood clots or bacteria must be sterilized with 2% disinfectant solution
or boiling water prior to cleaning. If virus or spore-bearing bacteria are
present, autoclaving is absolutely necessary.
For special types of precipitates, aqua regia (concentrated HCl: HNO 3 at 3:1
ratio) is the preferred approach. This is a very corrosive substance and should
be used only when required. For extremely dirty glassware and those with
coagulated organic residuals, a chromic acid wash is very effective, but it has
been deprecated in many countries. The chromic acid cleaning solution can
be prepared by adding 20 g of technical grade powder sodium dichromate
into 300-mL concentrated H 2 SO 4 . This solution is now replaced with other
non-chromium-based solutions, such as Nochromix 1 .
6.1.2 Chemical Reagent Purity, Standard,
and Reference Materials
1. Reagent water
Water is the most widely used analytical solvent for the preparation of analytical
blanks, samples and standard solutions. Poor water quality is one of the easiest