| AT Std No. 571 | Lab Analysis Aldehyde(s) | Edition: 07/27/98 |
| Approved by: CRM | by HPLC (based on EPA Method TO-11 |
STANDARD PREPARATION
Accurately weigh the 2,4-dinitrophenylhydrazone (2,4-DNP) derivative of the aldehyde to be analyzed into a measured volume of HPLC grade acetonitrile to make a Stock Standard Solution equivalent to 1.0 mg of derivative per ml in acetonitrile. Store the Stock Standard under refrigeration and make fresh monthly. Dilute Stock Standard Solution in acetonitrile weekly to make 3-5 Working Standards in the range of interest. Store Working Standards in a closed container under refrigeration when not in use. Prior to injection, dilute solution 1:1 with mobile phase, and filter using a 0.45 µm filter.
SAMPLE PREPARATION
Remove each Monitor to be tested from the Return Container. Using forceps or a spatula as a pry, un-snap the Sampling Grid exposing the Sampling Wafer (a single yellow filter disc ¾" in diameter).
Place the Sampling Wafer in a clean 5 ml glass vial or inert filtration vial (e.g., Whatman Uniprep® Filter Vial, 0.45µm PVDF, Item No UN513UAQU). Accurately pipet 1.0 ml of acetonitrile into the vial, close, and seal. Agitate the vial for one minute. Allow to stand 15 minutes, then add 1.0 ml of mobile phase solution, agitate again, and filter the solution through a 0.45 µm filter (or Uniprep). Reserve for analysis.
BLANK PREPARATION
Remove the Wafer (yellow filter disc) from an unexposed Monitor and process this "BLANK" in exactly the same fashion as the Sample Preparation (above).
HIGH PERFORMANCE LIQUID CHROMATOGRAPHY(HPLC) ANALYSIS
Inject an aliquot of the Sample Preparation from each Monitor to be analyzed into a HPLC System using the following conditions.
HPLC Column - Reversed Phase C-18a (15 cm x 3 mm id)
Mobile Phase - 50% acetonitrile / 50% Acetate Bufferb
(adjust 0.05M HOAc to pH5 with KOH in HPLC grade water)
Flow Rate - 1 ml per min (nominal)
Injection Volume - 10-50 microliter (nominal)
Detector Wavelength - 345-365 nm
Concomitantly, inject measured aliquots of a BLANK Preparation and three Standard Preparations in the range of interest (i.e. which bracket the concentrations of the Sample Preparations)
CALCULATION
Determine the Analyte Peak Area as follows.
PEAK AR (Analyte) = [ PEAK AR (Sample Preparation) ] - [ PEAK AR(Blank) ]
Determine the Analyte Concentration (C) graphically from the PEAK AR versus the Standard Curve prepared by linear regression analysis (least squares).
Calculate Exposure Level from Analyte Concentration as follows.
EXPOSURE LEVEL (ppm) = 1000(C)(V)(F)(R)
(M)(SR)(T)
Where
C = Analyte Concentration Found
µg/ml Formaldehyde DNP Derivative)V = Volume of Solvent (1.0 ml)
F = Fraction of Aldehyde in DNP Derivative
(HCHO = 0.143)
R = Molar Volume @ 22oC (24.1 l/mole)
M = Analyte Molecular Wt (HCHO = 30.03 g/mole)
SR = Monitor Sampling Rate (ml/min)
T = Sampling Time (min)
EXPOSURE LEVEL (ppm aldehyde) = 1000(C)(V)(F)(R)
(M)(SR)(T)