This document extends the work concerning the HPLC systems presented in (2016). We refer to the original manuscript for a description of the theory behind applications.
msqc1 1.34.0
This vignette file is thought to demonstrate the retention time stability of the msqc1_8rep
and msqc1_dil
data contained in the msqc1 R package.
Retention Time (RT) form different LC-MS platforms are often not comparable (duration, offset).
The iRT concept [proposed in pmid22577012 for the RT normalization is used. Instead of using the iRT-peptides MSQC1-peptides are used as reference peptides between the different chromatographic settings and systems.
The normalization is done by applying the following steps:
stats::lm
function) which maps the RT space of the corresponding platform into reference platform RT space (by using the stats::predict.lm
method)The code below shows the used R functions for the applied RT normalization.
msqc1:::.normalize_rt
## function (S, S.training, reference_instrument = "Retention.Time.QTRQP")
## {
## S.normalized <- S
## for (instrument in unique(S.normalized$instrument)) {
## i <- paste("Retention.Time", instrument, sep = ".")
## rt.out <- S.training[, reference_instrument]
## rt.in <- S.training[, i]
## S.fit <- lm(rt.out ~ rt.in)
## S.normalized[S.normalized$instrument == instrument, "Retention.Time"] <- predict(S.fit,
## data.frame(rt.in = S.normalized[S.normalized$instrument ==
## instrument, "Retention.Time"]))
## }
## S.normalized.min <- min(S.normalized$Retention.Time, na.rm = TRUE)
## S.normalized.delta <- max(S.normalized$Retention.Time, na.rm = TRUE) -
## S.normalized.min
## S.normalized$Retention.Time <- (S.normalized$Retention.Time -
## S.normalized.min)/S.normalized.delta
## return(S.normalized)
## }
## <bytecode: 0x6545daefbf80>
## <environment: namespace:msqc1>
The reshape_rt
method is used for reshaping the data from long to wide format which ease the the model building in the msqc1:::.normalize_rt
method above.
msqc1:::.reshape_rt
## function (S, peptides = peptides, plot = TRUE, ...)
## {
## S <- S[grep("[by]", S$Fragment.Ion), ]
## S <- S[S$Peptide.Sequence %in% peptides$Peptide.Sequence,
## ]
## S <- aggregate(Retention.Time ~ Peptide.Sequence * instrument,
## FUN = mean, data = S)
## S <- droplevels(S)
## S.training <- reshape(S, direction = "wide", v.names = "Retention.Time",
## timevar = c("instrument"), idvar = "Peptide.Sequence")
## if (plot == TRUE) {
## pairs(S.training[, 2:6], pch = as.integer(S.training$Peptide.Sequence),
## col = as.integer(S.training$Peptide.Sequence), lower.panel = NULL,
## ...)
## }
## return(S.training)
## }
## <bytecode: 0x6545da98fa60>
## <environment: namespace:msqc1>
The following R code listings displays some helper functions designed to ease the visualization of the msqc1_8rep
and msqc1_dil
RT values.
msqc1:::.plot_rt_8rep
## function (S, peptides, ...)
## {
## .figure_setup()
## S <- S[grep("[by]", S$Fragment.Ion), ]
## S <- S[S$Peptide.Sequence %in% peptides$Peptide.Sequence,
## ]
## S <- aggregate(Retention.Time ~ Peptide.Sequence * File.Name.Id *
## instrument * relative.amount * Isotope.Label.Type, FUN = mean,
## data = S)
## S <- droplevels(S)
## xyplot(Retention.Time ~ File.Name.Id | Isotope.Label.Type *
## instrument, data = S, layout = c(10, 1), group = S$Peptide.Sequence,
## auto.key = list(space = "right", points = TRUE, lines = FALSE,
## cex = 1), ...)
## }
## <bytecode: 0x6545dac145a0>
## <environment: namespace:msqc1>
msqc1:::.plot_rt_dil
## function (S, peptides, ...)
## {
## .figure_setup()
## S <- S[grep("[by]", S$Fragment.Ion), ]
## S <- S[S$Peptide.Sequence %in% peptides$Peptide.Sequence,
## ]
## S <- aggregate(Retention.Time ~ Peptide.Sequence * File.Name *
## instrument * relative.amount * Isotope.Label.Type, FUN = mean,
## data = S)
## S <- droplevels(S)
## xyplot(Retention.Time ~ relative.amount | Isotope.Label.Type *
## instrument, data = S, layout = c(10, 1), group = S$Peptide.Sequence,
## scales = list(x = list(rot = 45, log = TRUE, at = sort(unique(S$relative.amount)))),
## auto.key = list(space = "right", points = TRUE, lines = FALSE,
## cex = 1), ...)
## }
## <bytecode: 0x6545dac88430>
## <environment: namespace:msqc1>
Prepare the training data for the linear model.
S.training.8rep <- msqc1:::.reshape_rt(msqc1_8rep, peptides=peptides, cex=2)