The working solution was then diluted 1∶10 in a chloroform/methanol mixture (2∶1, v/v) for same-day use to the final concentration used for internal standard addition.
A mixture of internal standards prepared by dilution of individual stock solutions in methanol was used for internal standard calibration.
High-purity Al2O3 (0.25 g; AX-5HM, Hinomoto Kenmazai Co., Ltd., Tokyo, Japan) was used for the internal standard, which was well mixed with 1 g of the powdered sample using 4 ml of ethanol and a shaker.
The selected ion monitoring of p, p′-DDE was performed at m/ z 318, whereas m/ z 330 was used for the internal standard.
They were used as internal standards for quantification and to test for cross reactivity of antibodies (Gentest Corporation, Woburn, MA, USA).
We prepared in vitro transcribed RNAs to be used as internal standards for template preparation of GATC-PCR and standards for quantification by real-time PCR.
Eight deuterated analogues were used as internal standards for quantification.
Heptane and decane were used as internal standards for GC analysis.
13C-labelled PCB congeners were used as internal standards for non-ortho-PCBs.
18O-PFHxS and later 13C-PFHxS were used as internal standards for PFBS and PFHxS.
